tl foundations fleet strategy

TL FOUNDATIONS FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved.

TL FOUNDATIONS

Fleet Strategy

Document TP. FL 01.02

16/10/2013

TL Foundations Fleet Strategy

TP.FL 01.02 Issue 1 October 2013

TL FOUNDATIONS © Transpower New Zealand Limited 2013. All rights reserved.

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TL Foundations Fleet Strategy TP.FL 01.02

Issue 1 October 2013

TL FOUNDATIONS © Transpower New Zealand Limited 2013. All rights reserved.

Table of Contents

EXECUTIVE SUMMARY ...................................................................................................................... 1

SUMMARY OF STRATEGIES .............................................................................................................. 3

1 INTRODUCTION ....................................................................................................................... 5

1.1 Purpose ................................................................................................................................. 5

1.2 Scope .................................................................................................................................... 5

1.3 Stakeholders ......................................................................................................................... 5

1.4 Strategic Alignment ............................................................................................................... 6

1.5 Document Structure .............................................................................................................. 6

2 ASSET FLEET .......................................................................................................................... 7

2.1 Asset Statistics ...................................................................................................................... 7

2.2 Asset Characteristics .......................................................................................................... 10

2.3 Asset Performance .............................................................................................................. 17

3 OBJECTIVES .......................................................................................................................... 20

3.1 Safety .................................................................................................................................. 20

3.2 Service Performance ........................................................................................................... 20

3.3 Cost Performance ............................................................................................................... 21

3.4 New Zealand Communities ................................................................................................. 21

3.5 Asset Management Capability ............................................................................................ 21

4 STRATEGIES.......................................................................................................................... 24

4.1 Planning .............................................................................................................................. 24

4.2 Delivery ............................................................................................................................... 34

4.3 Operations ........................................................................................................................... 35

4.4 Maintenance ........................................................................................................................ 37

4.5 Disposal and Divestment .................................................................................................... 42

4.6 Capability ............................................................................................................................. 42

4.7 Summary of RCP2 Fleet Strategies .................................................................................... 45

APPENDICES ..................................................................................................................................... 47

A GRILLAGE EXAMPLES .......................................................................................................... 48

B FOUNDATION CONDITION CODES ..................................................................................... 50

C GRILLAGE ENCASEMENT MODELLING .............................................................................. 53

TL Foundations Fleet Strategy TP.FL 01.02 Issue 1 October 2013

TL FOUNDATIONS FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved. Page 1 of 58

EXECUTIVE SUMMARY

Introduction

The condition and performance of tower and pole foundations is essential to the structural integrity of transmission lines, and to ensuring reliability of supply to customers, and maintaining public safety.

Our asset management approach for foundations seeks to maintain them in perpetuity, at least lifecycle cost, and ensure the integrity and reliability of tower structures and the conductors they support. We have long term programmes of work in progress to encase deteriorated grillage foundations and maintain the asset health of foundation components.

Asset Fleet and Condition Assessment

The transmission line network includes approximately 25,000 structures that are supported by foundations.

Most of our foundation fleet is used to support steel lattice towers, but we also have a small number of monopole foundations and special types of foundations used in riverbeds. The two main types of foundations supporting steel lattice towers are steel grillage and concrete plug.

Our foundations are designed to withstand severe climatic loading conditions, and we monitor and maintain them to ensure satisfactory performance. Structural failures of foundations are rare, with only 12 recorded since 1963. These failures are usually associated with extreme weather events.

Our condition assessment programme monitors and records the condition of foundations. We forecast the future condition of each foundation based on its current condition and our knowledge of the expected rate of degradation at each location. The forecast of future condition provides the basis for asset management decision making.

Our condition assessment programme is risk-based, and the intervals between inspections are adjusted based on the condition of the foundation and its criticality. Assessments are performed more frequently as the foundation condition approaches the replacement criteria. Foundations located in unusually aggressive environments, or deemed to be highly critical, either to the Grid or for safety reasons, are also assessed more frequently.

Foundations include grillage types, consisting of steel buried in the ground, to which tower footings are attached. Grillage foundations were widely used until the late 1960s, and support about one half of our steel lattice towers. Buried steel grillage foundations are subject to below-ground corrosion, leading to risk of foundation failure and subsequent tower failure with consequent safety, environment and network performance impacts.

Overall, our foundation assets are in reasonable condition, reflecting recent work to encase our ageing fleet of steel grillage foundations. The average age of the fleet of steel grillage foundations is 57 years, while the average age of the entire foundation fleet is 44 years.

Foundation Strategies

The main strategy for the foundations asset fleet is the condition-based encasement of deteriorated steel grillage foundations. Inspections carried out to date show that some of our grillage foundations have deteriorated to the point where refurbishment is needed to



keep them in satisfactory condition, and to avoid them declining to a point where tower propping and major steel work replacement is required.

Since the mid-2000s, 1,700 grillages have been ‘converted’ to concrete over grillage foundations by encasing them in concrete. A long-term programme of grillage encasement work is now in place. We intend to refurbish foundations at 400 towers each year throughout RCP2. Most expenditure identified in this strategy is for this refurbishment work.

The rest of the expenditure planned during the RCP2 period relates to repair of tower baseplates and below-ground stubs that have corroded to the point where remedial work is required. The plan involves refurbishing corroding foundation components at 630 sites each year over RCP2.

A smaller amount of expenditure is allocated to the strengthening of existing undersized foundations. The plan involves investigating foundations at 40 towers each year and strengthening 8 each year over the RCP2 period.

Improvements

In our planning for the RCP2 period, we have made a number of improvements to the asset management of foundations, including:

improved modelling of condition degradation

introduction of Asset Health Indices (AHI) to allow better comparison of asset condition across fleets

using asset criticality as an important factor in planning foundation asset works – in particular refurbishments

planning decisions that consider the whole-of-life cost of foundation assets, covering Planning, Delivery, Operations, Maintenance and Disposal, as well as their impacts on other assets, such as towers and poles

using updated and more detailed building blocks for cost estimates.

For the grillage fleet, our approach remains unchanged from the RCP1 period.

Further improvements will include:

refinement of condition assessment techniques and asset health models

refinement of the asset criticality framework.



SUMMARY OF STRATEGIES

The following summaries include the main strategies and their respective costs during the RCP2 period (2015/16–2019/20).

Capital Expenditure

Grillage Refurbishments RCP2 Cost $51m

A large number of grillages are deteriorating due to their age and environment. Grillage refurbishments extend the life of grillages and reduce the chance of foundation failure, tower structure collapses and conductor drops.

The strategy is to refurbish, generally by concrete encasement, all grillages that currently have a condition assessment of less than 30 by 2020, and ensure no grillage foundation has a condition assessment of less than 40 by 2033 (in 20 years). Ideally, grillages should be encased in concrete before the condition gets too poor (condition assessment less than 40) and it becomes necessary to prop the tower and replace steelwork at significant cost.

The plans will involve refurbishing approximately 400 grillages each year at an annual cost of $10.2m, or $51m over RCP2.

Bridge Replacements RCP2 Cost $6.1m

A number of bridge replacements are required on access corridors to maintain access to the transmission lines and structure foundations. Well maintained access tracks are essential to allow safe access to transmission line assets when responding to faults or performing routine inspections and maintenance.

The strategy is to replace bridges to ensure continuing safe and efficient access to transmission lines for maintenance and project works.

The plan involves 64 bridge replacements over RCP2.

Undersized Foundation Strengthening RCP2 Cost $4.4m

Poor design process used for foundations constructed before 1983 has led to the occasional installation of undersized bored concrete foundations. Strengthening undersized foundations reduces the chance of tower structure collapse (with significant implications for safety and reliability).

The strategy is to strengthen undersized foundations in all critical locations to minimise the risk of tower failure due to overloading.

The plan involves investigating foundations at 40 towers each year and strengthening 8 each year over RCP2.



Operating Expenditure

Component Refurbishments RCP2 Cost $17.5m

A large number of ageing foundation components are deteriorating. Component refurbishments reduce the chance of foundation failure and tower structure collapse (with significant implications for safety and reliability).

The strategy is to refurbish corroding baseplates, anchor bolts and cast-in stubs prior to onset of significant rusting. This refurbishment is based on the minimum condition assessment score of the four leg-based codes collected at each site. The typical threshold is condition assessment 50 before any significant rusting or loss of section is apparent.

The plan involves refurbishing corroding foundation components at 630 sites each year over RCP2 at an overall cost of $17.5m.

Further detail on the above RCP2 strategies and discussion of the remaining strategies can be found in chapter 4.



1 INTRODUCTION

Chapter 1 introduces the purpose, scope, stakeholders, and strategic alignment of the foundations fleet strategy.

1.1 Purpose

We plan, build, maintain and operate New Zealand’s high-voltage electricity transmission network (‘Grid’) including the foundations that support conductor-bearing structures (towers and poles).

The purpose of this strategy is to describe our approach to lifecycle management of our transmission tower and large pole foundation assets on the Grid. This includes objectives for future performance and strategies being adopted to achieve these objectives. The strategy sets the high-level direction for fleet asset management activities across the lifecycle of the fleet. These activities include Planning, Delivery, Operations, and Maintenance.

This document has been developed based on good practice guidance from internationally recognised sources, including BSI PAS 55:2008.

1.2 Scope

The scope of the strategy includes the foundations of towers and non-direct buried poles, and limited to:

grillage foundations (direct buried grid of steel)

concrete foundations with cast-in tower legs

concrete foundations with cast-in anchor bolts and tower/pole baseplates

large piled foundation structures (typically at river crossings and estuaries)

driven piles and wailings used for mounting poles in riverbeds.

1.3 Stakeholders

Correct operation and maintenance of foundations is essential for the safe and reliable transport of electricity from generators to customers and distribution networks across public and private land. Key stakeholders include:

landowners

relevant Transpower Groups (Grid Development, Performance and Projects)

regulatory bodies: Commerce Commission, Electricity Authority, local and regional Councils, and the Environmental Protection Authority

Department of Conservation

service providers

customers, including distribution network businesses and generators.



1.4 Strategic Alignment

A good asset management system shows clear hierarchical connectivity or ‘line of sight’ between the high-level organisation policy and strategic plan, and the daily activities of managing the assets.

This document forms part of that line of sight by setting out our strategy on the foundations asset fleet. The strategy directly informs the portfolio asset management plans.

This hierarchical connectivity is represented graphically in Figure 1. It indicates where this fleet strategy and plan fit within the asset management system.

Figure 1: Position of this Strategy within the Transpower Asset Management Hierarchy

1.5 Document Structure

The rest of this document is structured as follows.

Chapter 2 provides an overview of transmission line foundations including fleet statistics, characteristics and their performance.

Chapter 3 sets out asset management related objectives for the assets. These objectives have been aligned with the corporate and asset management policies, and higher-level asset management objectives and targets.

Chapter 4 sets out the fleet specific strategies for managing the assets. These strategies provide medium-term to long-term guidance and direction for asset management decisions and will support the achievement of the objectives in chapter 3.

Appendices are included that provide further detailed information to supplement the fleet strategy.

Foundations Plan

Foundations Strategy

Corporate Objectives & Strategy

Asset Management Policy

Asset Management Strategy

Lifecycle Strategies

DeliveryPlanning Operations DisposalMaintenance



2 ASSET FLEET

Chapter 2 describes the asset fleet with a focus on:

asset statistics – including population, diversity, age profile, and spares

asset characteristics – including safety and environmental considerations, asset criticality, asset condition, asset health, maintenance requirements and interaction with other assets

asset performance – including reliability, safety and environmental and identification of risks and issues.

Foundations play an important role on the Grid by supporting transmission line towers and poles, which in turn support conductors.

More than half of all tower foundations are original buried steel grillage foundations that are subject to corrosion. This results in an increased risk of foundation and subsequent tower failure. It is important to maintain these in an appropriate condition through timely maintenance and refurbishment.

2.1 Asset Statistics

This section outlines the foundations asset fleet population, along with the diversity and age profiles of the physical assets.

2.1.1 Asset Population

The Grid is made up of approximately 12,000 route km of transmission line, supported by approximately 41,000 transmission line support structures (such as towers and direct buried poles). As at 30 June 2012, there are approximately 25,000 foundation-supported structures on the network (such as towers).

2.1.2 Fleet Diversity

Asset fleet diversity is an important asset management consideration. Foundations vary in size and type depending on the design loads, soil type and the preferred construction practices of the day. The quantities of each type (along with descriptions) are shown in Table 1.



Foundation Type Description Population

Towers

Steel Grillage Grillages that have not yet been refurbished 12,350

Concrete over Steel Grillage Refurbished grillage foundations (by encasement in concrete) 1,667

Concrete Plug (bored dug) Currently preferred foundation type 9,971

Other

Includes foundation types such as:

Driven Pile with Pile Cap – generally only used at river crossings or sites with very poor soils

Pad and Chimney – occasionally used at sites with poor soils

Raft and screw pile type foundations

653

Poles

Driven Pile and Wailings For mounting poles in riverbeds 272

Total 24,913

Table 1: Foundation Types and Populations as at 30 June 2013

The type of foundation used has varied with time. Buried steel grillage foundations are the oldest type of tower foundation on the Grid and comprise more than half of all tower foundations. They were the preferred foundation type until the late 1960s when concrete foundations were introduced.

Of the concrete foundations, some 6,500 towers have baseplate and anchor bolt connections. This type of foundation and connection was installed between the mid-1960s and the late 1970s. Since then, essentially all foundations have been constructed with a concrete pile/plug and cast-in stub leg. The proportion of concrete foundations will increase over time as new lines are constructed, lines are divested or decommissioned and grillages are encased with concrete. Figure 2 depicts the diversity of the asset fleet.

Figure 2: Foundations – Diversity

2.1.3 Age Profile

Foundation assets have been installed progressively since the 1930s. There are a large number of buried steel grillages in service that were installed up until the late 1960s which are deteriorating due to their age and environments. Over 600 grillage foundations were refurbished by re-galvanising between 1992 and 2008 and are treated as being new from that date; yet the bulk of the population are aged between 45 and 90.

GRILLAGE (50%)

CONCRETE OVER GRILLAGE (7%)

CONCRETE PLUG, BORED OR DUG (40%)

OTHER TOWER FOUNDATIONS (3%)

POLE FOUNDATION (1%)

FOUNDATIONS- DIVERSITY



The age profile of the foundation fleet is shown in Figure 3.

Figure 3: Foundations - Age Profile

Foundation life expectancy

The life expectancy for each type of foundation is shown in Table 2. It is based on observed life and typical condition degradation rates for each foundation type. Life expectancy should be interpreted as the period after which the risk of failure is deemed unacceptable. The actual life will depend on the specific site, weather exposure, and construction quality. While age is of interest for predicting future needs, works are always planned based on actual condition, not age (see subsection 2.2.3).

One of the fleet’s main strategies relates to the effective replacement of grillage foundations through concrete encasement. This achieves, on average, an expected 120-year life extension with correct maintenance in place.

Foundation Type Average Age Life Expectancy Comment

Grillage 57 70 Varies from 50 to over 100 years

Concrete over grillage 3 120 As for concrete plug

Concrete plug, bored or dug

36 120 Assumes concrete/steel interface is maintained periodically

Other – Driven pile with concrete pile cap

37 120 Generally in more aggressive environment than standard concrete plug

Other – Pad and chimney

28 120 As for concrete plug

Other - Other foundations

27 50 Timber or steel piles driven into riverbeds

Table 2: Foundation Life Expectancy

0

500

1,000

1,500

0 10 20 30 40 50 60 70 ≥80

AGE (YEARS)

GRILLAGE

CONCRETE OVER GRILLAGE

CONCRETE PLUG, BORED OR DUG

OTHER

POLE FOUNDATION

FOUNDATIONS - AGE PROFILE



2.2 Asset Characteristics

The foundations asset fleet can be characterised according to:

safety and environmental considerations

asset criticality

asset condition

asset health

maintenance requirements

interaction with other assets.

These characteristics and the associated risks are discussed in the following subsections.

2.2.1 Safety and Environmental Considerations

We are committed to ensuring that safety and environmental risks are minimised at all times. The most significant safety and environmental consideration for the foundations asset fleet is the prevention of a transmission structure failure.

Prevention of tower failure

Foundation failure leading to a tower failure and conductor drop is a significant safety consideration with risk of electrocution, fire and physical impact damage. The risk is clearly dependant on land use, and is higher in urban environments and over busy roads than in back country rural environments. Regular condition assessments and a robust design process are essential to minimise the risk of foundation failures.

Environmental

There is potential for significant environmental impacts when constructing or removing foundations, particularly when working in sensitive areas such as riverbeds.

Environmental issues are mitigated by working closely with the relevant regulatory bodies and landowners and by ensuring compliance with the Resource Management Act 1991 (RMA 1991).

2.2.2 Asset Criticality

Our approach to asset management has been adapted to recognise the differing levels of asset criticality. Highly critical assets will be designed and maintained to provide a higher level of reliability than less critical assets.

A framework has been developed for transmission line assets. The methodology considers various aspects that would be impacted by a failure such as load carried, the level of reliability required by the customers, constraints that would be placed on the rest of the Grid, and the level of redundancy. Further information on the asset criticality approach is provided in the document ‘Asset Risk Management – Criticality Framework’.



Figure 4 shows the proportion of foundations in each criticality category.

Figure 4: Foundations – Criticality

Approximately half of the foundation asset fleet are classified as medium impact or high impact with respect to network criticality. The reliability and performance of these assets need to be managed carefully to minimise failure risks.

We are still at a relatively early stage in the development and application of safety criticality, and will continue to refine and develop this throughout RCP2.

Subsections 2.2.4 and 4.1.2 discuss how criticality is taken into account, in combination with asset health to determine prioritised replacement programmes.

2.2.3 Asset Condition

Regular condition assessments on foundations are carried out to assess their condition. These assessments produce a condition assessment score, where a score between 91 and 100 is considered as new and 0 is seriously degraded to a point where failure could occur under everyday loading conditions.

New foundation assets are first assessed just prior to the expiration of any defect liability period. Thereafter, tower line assets are generally assessed every 8 years. If the condition assessments score is less than 50, the assessment period is reduced to 4 years. Sites with a high consequence of failure may be assessed more frequently.

During regular condition assessments the two locations assessed are:

1. the foundation connection

2. the foundation.

A separate condition assessment score is recorded for each. At a condition assessment score of 20, the foundation is incapable of carrying its full design loads.

Grillage foundations

Many towers with buried steel grillage foundations are now showing corrosion on tower legs and bracing near the ground line. Having severely rusting foundations on the network is a major risk that is compounded by the fact that they cannot be readily assessed for condition.

Despite numerous national and international trials, no reliable non-intrusive method has been found to accurately predict which towers have corroded grillages. Age, original galvanising quality, soil type and moisture content are all known to influence the grillage condition.

The only reliable method of determining the condition of the buried part of the foundation condition is to dig and visually inspect. Excavation and inspection (see Figure 5) is relatively

LOW (45%)

MEDIUM (39%)

HIGH (16%)

FOUNDATIONS -NETWORK CRITICALITY



expensive and also leads to accelerated corrosion, as oxygen will enter into what was a largely oxygen-starved system. Excavations undertaken on some 1,000 towers have revealed that the extent of corrosion further underground, at the grillage level, varies from light to severe.

For grillage-type foundations the connection is deemed to be the steel from 100mm above ground level to 300mm below. For concrete foundations with bolted connections or cast-in stubs, the connection relates to the steel/concrete interface. Assessment guidelines for foundations are included in Appendix B.

Figure 5: Excavated Grillage

The bottom of a grillage foundation is typically 2.5 to 3m below ground level. As discussed above, assessing the steel at this depth is disruptive and expensive. Consequently grillage condition assessment has been carried out on a sampling basis. Less than 1,000 towers have had their grillage foundations condition assessed to the base of the grillage. Analysis of the results shows that in 80% of cases the condition of the grillage is within 10 condition assessment points of the ground-line interface condition, and is within 20 condition assessment points 93% of the time. Of the 7% outside 20 condition assessment points, in half the cases the grillage was in better condition than the ground interface. Given the high cost and landowner disruption associated with accurately assessing the condition of the buried part of the foundation, we now use the ground-line interface condition as a proxy for the lower grillage condition.



Figure 6: Foundations – Asset Condition1

Figure 6 shows the distribution of condition assessment codes for foundations. The majority of the fleet has a condition assessment score of above 40 although approximately 1,400 (or 11%) of grillage foundations are at or below condition assessment 30.

Foundation connection components

For concrete foundations with bolted connections or cast-in stubs, the connection relates to the steel/concrete interface. Assessment guidelines for foundations are included in Appendix B. As for grillages, a large number of foundation connection components are deteriorating due to their age and environment. Poor quality dry-pack mortar originally used under baseplate- type foundations is porous and has led to mortar crumbling. Moisture ingress under the baseplate has subsequently led to corrosion of the anchor bolts and baseplate (which is not visible until the grout is removed).

Concrete foundations with cast-in stub legs are generally in good condition, but an increasing number are starting to corrode at the concrete and steel interface. Typically, the rust does not extend very far into the concrete (<20mm). Refurbishment by blasting and painting has proven highly successful. In extreme cases a small area of concrete is broken out, the steel cleaned, and the area repaired by grouting. Note that once a grillage foundation is refurbished by concrete encasement, the foundation connection becomes a cast-in stub-type arrangement.

1 Using ground-line condition as a proxy for grillage foundations.

0

1,000

2,000

3,000

4,000

5,000

6,000

0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

CONDITION ASSESSMENT (CA) SCORE

GRILLAGE CONCRETE OVER GRILLAGE

CONCRETE PLUG, BORED OR DUG OTHER

FOUNDATIONS - CONDITION



Figure 7: Components – Asset Condition

Figure 7 shows the condition of foundation components. Foundation component refurbishment is based on the minimum condition assessment score of the four leg-based codes collected at each site. The typical threshold is condition assessment 50 before any significant rusting or loss of section is visible.

2.2.4 Asset Health

The AHI reflects the forecast remaining life for any given asset – in effect, it is an assessment of current and future asset ‘fitness for purpose’. The AHI forecast of remaining useful life is based on modelling deterioration or risk that cannot be addressed by normal maintenance (where maintenance to address the deterioration or risk is not possible/practical, or is uneconomic). For transmission line foundations, this is when the foundation can no longer be relied upon to carry its design loads. At this point, major intervention is required, such as total replacement of the asset or refurbishment that significantly extends the original design life.

Asset health indicators provide a proxy for the probability of failure in asset risk management analysis.

The AHI is calculated using:

the current condition of the asset

the age of the asset

the typical degradation path of that type of asset

any external factors that affect the rate of degradation, such as proximity to the coast, and so affect the rate of corrosion of steel towers.

Assessing asset health is particularly important as it is used to understand the deterioration profile of asset fleets and to forecast and prioritise replacement and refurbishment activities. Asset health information is used in combination with asset criticality data to assign an overall priority to each asset, which is used to optimise the level of investment in the fleet.

We are still at a relatively early stage in developing and applying asset health indicators. More details on our asset health methodology are set out in the document ‘Asset Risk Management – Asset Health Framework’.

0

1,000

2,000

3,000

0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100

CA SCORE

BASEPLATE / ANCHOR BOLT CAST IN SITU STUB LEG

FOUNDATION COMPONENTS - CONDITION



The association of asset health to the probability of failure is not strongly formed until a condition assessment score of 20 or below is recorded. Between a score of 100 and 30, the failure risk changes very little. Below a score of 30, there is a slight increase in the risk of failure. As the condition assessment score reduces below 20, the risk of failure increases markedly.

Asset health information is used in combination with asset criticality data to assign an overall priority to each asset, which is used to optimise the level of investment in the fleet. Figure 8: shows that prioritisation is based on a combination of condition (remaining life) and criticality. As an example, ‘Now Due’ grillages with a condition assessment score under 30 are a higher priority than a high criticality site just reaching 40, due to the heightened risk of them failing.

Figure 8: Prioritisation Approach

Asset health for the foundation fleet has been calculated assuming replacement criteria at a condition assessment score of 20 for all foundations except grillages where replacement is modelled at CA 30. CA 30 has been selected for grillages to account for the uncertainty regarding their below-ground condition. A linear degradation rate from the original installation date to the most recent condition assessment score is assumed.2

For grillages, ground-line interface condition has been used as a proxy for grillage condition as discussed in subsection 2.2.3 above. Note: maintenance works such as refurbishment of baseplates and anchor bolts must be carried out periodically to achieve these predicted lives (as noted in Figure 9).

Figure 9: Foundations – Asset Health Indices

The greatest asset management challenge for the ageing fleet of foundations is managing the corrosion of buried steel grillages. While the overall health of the tower foundations is generally good, a number of ageing foundations have a relatively poor condition. The manner in which asset health is taken into account in the management of the assets is described further in chapter 4.

2 Literature on in-ground corrosion of galvanised steel suggests the corrosion rate is roughly linear while galvanising is

still there, but may actually decrease once corrosion starts. The more replacements we do, the better our understanding in this area will be.

Increasing Criticality

Decre

asin

g

AssetH

ealth

12+ YRS (90%)

7-12 YRS (4%)

2-7 YRS (3%)

0-2 YRS (0%)

NOW DUE (6%)

FOUNDATIONS- ASSET HEALTH (12/13)



2.2.5 Maintenance Requirements

This subsection describes the maintenance requirements of the foundation fleet. These requirements have informed the maintenance strategies discussed in section 4.4. The most common types of maintenance carried out on lines assets are:

preventive maintenance, including:

- condition assessments

- servicing

corrective maintenance, including:

- fault response

- repairs

Maintenance Projects.

The Maintenance Lifecycle Strategy provides further details on our approach to the above maintenance works. Detailed maintenance requirements are included in the relevant service specification documents.

In addition, we periodically undertake maintenance projects, which are programmes of works (essentially made up of small projects) used to address repetitive issues identified through preventive maintenance or fault responses.

Preventive maintenance

Line patrols are generally performed once a year on every transmission line asset. The main purpose of the patrols is to identify defects and sites with very high safety criticality that may then be patrolled more frequently. A ground-based patrol visits each structure/span and walks the conductor line, if possible, to visually identify any defects. A patrol report identifies defects required to be rectified. Repair jobs are raised in the Maintenance Management System and the maintenance contractors are responsible for carrying out this work.

As discussed in 2.2.3, condition assessments are carried out on a cyclic basis and entail a detailed inspection of the structure and span. The assessment produces a condition assessment score for various components and a defect list.

Corrective maintenance

Typical maintenance activities for foundations include removing soil and vegetation from the top of concrete foundations and installing protection works such as rip rap in rivers.

The most common fault response and repair work required for foundations relate to foundation failures due to land subsidence or rapid soil erosion. Contributing factors include:

severely damaged foundations

geotechnical risks due to slips, scouring and subsidence

third party excavation or construction around tower foundations.

Each year a number of sites require stabilising work and repairs to avoid failure. In extreme cases a structure may be relocated.



Maintenance projects

Maintenance projects typically consist of relatively high-value planned repairs or replacements of components of larger assets. Maintenance projects would not be expected to increase the original design life of the larger assets. Maintenance jobs are typically run as a project where there are operational and financial efficiencies from doing so. The drivers for maintenance projects include asset condition, mitigating safety and environmental risks, and to improve performance. Examples of past maintenance projects are set out below.

Connection component refurbishments

Foundation connection components comprise two types, those with baseplates and anchor bolts and those with cast-in stubs. All are subject to corrosion. The refurbishment of corroded steel and the replacement of mortar prior to significant degradation in baseplate and anchor bolt foundations are carried out to ensure that structural integrity is maintained. Similarly, the steel at the concrete interface of cast-in in situ foundation legs is painted prior to significant rusting. This constitutes a RCP2 strategy and is discussed in more detail in subsection 4.4.3.

Historic spend – maintenance projects

Table 3 provides an overview of historic maintenance project expenditure. Future maintenance projects are discussed in subsection 4.4.3.

Project 2009/10 2010/11 2011/12 Total

Various $2.0m $2.8m $2.1m $6.9m

Table 3: RCP1 Spend on Maintenance Projects

2.2.6 Interaction with other Assets

The foundations programme is closely aligned with conductor and tower works, as any new tower work requires foundation work. Towers supporting a line being supplied with a new (or refurbished) conductor may require foundation strengthening due to heavier conductors and higher tension being used. These integration processes are managed through the Integrated Works Planning (IWP) processes discussed in subsection 4.1.3.

2.3 Asset Performance

This section describes the historic performance of foundation assets and any associated risks and issues.

2.3.1 Reliability

Achieving an appropriate level of reliability for our asset fleets is a key objective as it directly affects the experience of our customers. Reliability is measured primarily by the frequency and length of outages.

While foundation failures due to extreme climatic loading, land movement and washout do occur, with established modern design practices the probability of foundation failure is low.

Since 1963 there have been 12 foundation failures. Five failures were caused by land movement or river scour; the remaining seven were due to high wind events pulling the foundations from the ground. Since 2005, only one tower foundation failure has occurred and was due to river washout. In this instance, conductors were transferred to a temporary structure prior to the foundation (and tower) failure.



In many instances, condition assessments and line patrols identify foundation issues before towers fail. We maintain a register of problematic areas and at-risk structures are monitored after major weather events.

2.3.2 Safety and Environmental Performance

No people have been harmed by any foundation failure on our network. Our environmental record is considered to be very good, as we work closely with authorities and landowners to mitigate any adverse effects associated with our works.

2.3.3 Performance Benchmarking

International Transmission Operations & Maintenance Study (ITOMS) involves performance comparisons (including reliability) between 27 utilities. ITOMS considers overall transmission line performance (not on an asset type basis, such as tower foundations). This overall performance is considered in the Conductors and Insulators fleet strategy.3

2.3.4 Risks and Issues

This subsection briefly discusses risks and the identified issues relating to the foundation asset fleet.

Limited effectiveness of near-surface visual inspections

Severely rusting foundations on the network present a major risk, compounded by the fact that foundations buried at depth cannot be readily condition assessed. Some below-ground sampling has been carried out to inform the asset management approach, however there is a risk that the condition of any buried grillage is worse than predicted. A slight conservative approach is therefore warranted.

Age profiles

Grillage foundations are the oldest type of foundation, with the bulk of the fleet now aged between 45 and 90. Approximately 10% of grillages and foundation components are now corroded to the point of requiring replacement or refurbishment. Age-based deterioration is the major driver of the work programme related to this asset fleet. The risks associated with foundation corrosion include rapidly increasing costs to maintain if left too late and reduced structural strength that could lead to foundation and tower failure.

Undersized foundations

Studies have revealed that concrete foundations built before 1983 were usually designed based on very limited soil testing and with assumptions made about soil properties, leading to undersized foundations occasionally being installed. Recent studies, including full-scale foundation testing, suggest that under-strength foundations still exist in some cases. Structures with concrete pile foundations built before 1983 continue to be investigated, with priority given to sites whose failure would pose significant risk to people, property or the Grid.

3 Details can be found in the Conductors and Insulators fleet strategy.



Foundation failure

Foundation failures can result in tower collapses and conductor drops. These events can cause fire on public or private land, fatalities and injuries from electrocution or impact of falling objects, property damage and loss of power supply.

Washouts and landslides

Poor slope stability and/or river scouring have been significant causes of foundation failures. We maintain a register of problematic areas. Maintenance managers and contractors monitor at-risk structures after major weather events.



3 OBJECTIVES

Chapter 3 sets out asset management objectives for transmission line foundations. As described in section 1.4, these objectives have been aligned with the corporate objectives, and higher-level asset management objectives and targets as set out in the Asset Management Strategy.

Our overarching vision for our foundations fleet is to maintain them in perpetuity, at least lifecycle cost, and to ensure the integrity and reliability of tower structures and the conductors they support. Further objectives in the following areas have been defined:

Safety

Service performance

Cost performance

New Zealand communities

Asset management capability.

These objectives are set out below. Chapter 4 discusses the strategies to achieve them.

3.1 Safety

We are committed to becoming a leader in safety by achieving injury-free workplaces for our employees and to mitigate risks to the general public. Safety is a fundamental organisational value and we consider that all incidents are preventable.

Safety Objectives for Foundations

- Zero injuries caused by foundation failures.

- No major failure of foundation assets with high or very high safety criticality.

Recognising the reduced level of control we have in relation to public safety, we will take all practicable steps to ensure transmission line assets do not present a risk of serious harm to any member of the public or significant damage to property.

3.2 Service Performance

Ensuring appropriate levels of network performance is a key underlying objective. We have specified our network performance in terms of Grid Performance (reliability) and Asset Performance (availability) in our Asset Management Strategy.

Grid Performance objectives state that a set of measures are to be met for GXPs based on the criticality of the connected load. In addition Asset Performance objectives linked to system availability have also been defined. These high-level objectives are supported by a number of fleet specific objectives, and we will work towards these being formally linked in the future.

Service Performance Objectives for Foundations

- Less than 1 foundation failure every 5 years. The current rate is 1.2 every 5 years.



3.3 Cost Performance Effective asset management requires optimising lifecycle asset costs while managing risks and maintaining performance. We are committed to implementing systems and decision-making processes that allow us to effectively manage the full lifecycle costs of our assets.

Cost Performance Objectives for Foundations

- Improved efficiency through extension of the planning horizon.

- Design, construct and maintain foundations to minimise lifecycle costs while meeting required levels of performance.

- Minimise cost of capital projects through long-term resource planning of service providers.

- Minimise cost of works by packaging work into blocks of consecutive structures wherever possible.

3.4 New Zealand Communities Asset management activities associated with the foundation asset fleet have the potential to impact on the environment and on the daily lives of various stakeholders. Relationships with landowners and communities are of great importance to us and we are committed to using asset management approaches that protect the natural environment.

New Zealand Communities Objectives for Foundations

- Compliance with RMA 1991 requirements, such as erosion and sediment control during site works.

- Disestablished site foundations should be re-instated to their former natural forms to allow the land to recover.

- No damage to third party property due to foundation failures.

- Minimise stakeholder disruption by packaging work into blocks of consecutive spans wherever possible.

- Maintain effective relationship with stakeholders affected by foundation works.

3.5 Asset Management Capability We aim to be recognised as a leading asset management company. To achieve this, we have set out a number of maturity and capability related objectives. These objectives have been grouped under a number of processes and disciplines that include:

Risk Management

Asset Knowledge

Training and Competency

Continual Improvement and Innovation.

The rest of this section discusses objectives in these areas relevant to the foundation asset fleet.



3.5.1 Risk Management

Understanding and managing asset-related risk is essential to successful asset management. We currently use asset criticality and asset health as proxies for a fully modelled asset risk approach.

Asset criticality is a key element of many asset management systems. We are currently at an early stage of implementing the framework as we work towards formal and consistent integration of asset criticality into the asset management system. We have commenced this by prioritising fleet replacement expenditure programmes, based on the criticality framework.

Risk Management Objectives for Foundations

- Finalise and implement the safety and network criticality categorisation systems for foundation applications.

- Continuously improve the asset health modelling of foundations.

- Formalise and implement an asset management approach that is differentiated by network and safety criticality.

- Develop a risk-based model for assessing the trade-offs between different work methods (such as live line techniques), including the risk-weighted cost of circuit unavailability (such as the cost of an outage or the increased chance of outage due to reduced redundancy).

3.5.2 Asset Knowledge

We are committed to ensuring that our asset knowledge standards are well defined to ensure good asset management decisions. Relevant asset knowledge comes from a variety of sources, including experience from assets on our network and condition information. This asset knowledge must be captured and recorded so that it can be conveniently accessed.

Asset Knowledge Objectives for Foundations

- Expand knowledge of foundation condition through scheduled condition assessment and analysis of as-found condition during the foundation replacement and refurbishment programme.

- Improve the condition assessment consistency through improved guidelines (such as photographic examples).

- Enhance the failure and incident records system to improve consistency and usefulness of data, including root cause analysis.



3.5.3 Training and Competency

We are committed to developing and retaining the right mix of talented, competent and motivated staff to improve our asset management capability.

Training and Competency Objectives for Foundations

- All foundation works to be carried out by service providers that are suitably qualified and competent for the specific tasks required.

- Increase and then maintain the in-house skill base with regard to asset management principles and application.

3.5.4 Continual Improvement and Innovation

Continual improvement and innovation are important aspects of asset management. A large source of continual improvement initiatives will be ongoing learning from our asset management experience.

Continuous Improvement and Innovation Objective for Foundations

- Continue to monitor new and emerging foundation technologies and designs.



4 STRATEGIES

Chapter 4 sets out the fleet specific strategies used to manage the foundations asset fleet. These strategies provide medium-term to long-term guidance and direction for asset management decisions and will support the achievement of the objectives in chapter 3. The strategies are aligned with our lifecycle strategies below and the chapter has been drafted to be read in conjunction with them.

Planning Lifecycle Strategy

Delivery Lifecycle Strategy

Operations Lifecycle Strategy

Maintenance Lifecycle Strategy

Disposal Lifecycle Strategy

This chapter also discusses capability related strategies which cover asset knowledge, training and competence.

Scope of strategies

The strategies focus on expenditure that is planned to occur over the RCP2 period (2015–2020), but also include expenditure from 1 July 2013 to the beginning of the RCP2 period and some expenditure after the RCP2 period where relevant. Capital expenditure planned for the period is covered by the strategies in section 4.1, while operating expenditure is mainly covered by section 4.4. The majority of capital expenditure consists of grillage refurbishment, which is described in subsection 4.1.2.

4.1 Planning

This section describes our strategies relating to the planning lifecycle phase of the foundations fleet and identifies where and how these strategies support the objectives for the overall fleet.

Planning activities

Planning activities are primarily concerned with identifying the need to make capital investments in the asset fleet. The main types of investment considered in this strategy are enhancement and development, and replacement and refurbishment works.

We support our planning activities through a number of processes, including:

IWP

cost estimation.

The planning lifecycle strategies for these processes are described in the subsections below.

Capital investment drivers

Categories of capital investment generally have specific drivers or triggers that are derived from the condition of the overall system or from individual assets. These drivers include demand growth, compliance with Grid reliability standards, technology changes and failure



risk (indicated by asset criticality and health measures). Specific examples that drive capital investment in foundation assets include:

new line developments or uprating of existing circuits, which is driven by demand

condition of grillages and other foundation components

foundation strengthening and replacements, which is driven by failure risk.

4.1.1 Enhancement and Development

The most important driver for new foundation investments is the facilitation of new or strengthened towers. The tower investments are undertaken to meet expected system growth and to ensure appropriate reliability for customers.

Facilitate line projects

Modify existing foundations, including strengthening and relocation, to

support new structures or to enable upgrading of conductors.

System growth projects principally include new greenfield lines or the uprating of existing lines, which may require stronger structures and foundations. As part of uprating projects, foundations that do not comply with current design standards are strengthened, to increase reliability. These projects drive the need to invest in foundations. The timing and cost of works will be driven by the relevant conductor works.

In the next few years, we will install a number of new tower structures and their associated foundations, and strengthen other foundations as part of specific enhancement projects. From a planning perspective, the cost for such foundation work is currently included in the relevant conductor projects. Following completion of the project, the costs will be allocated out to the relevant foundation asset. Any asset management related costs following their initial installation will be managed through the foundations portfolio.4

4.1.2 Replacement and Refurbishment

This subsection describes replacement and refurbishment strategies for the foundations fleet. Replacement is expenditure to replace substantially all of an asset. Refurbishment is expenditure on an asset that creates a material extension to the end of life of the asset. It does not improve its attributes. This is distinct from maintenance work, which is carried out to ensure that an asset is able to perform its designated function for its normal life expectancy.

Condition driven projects

Foundation replacement and refurbishment works are primarily triggered by asset condition represented by condition assessment score. We use condition assessment data gathered during refurbishment programmes to model the condition of grillages that have not yet been refurbished, enabling better works prioritisation. Specific interventions have been defined for foundations based on their condition and informed by their relative criticality. Prioritisation is undertaken on the basis of asset health and asset criticality, where the priority is higher for assets where the consequence of failure is higher.

4 For more details, see the Conductors and Insulators fleet strategy.



Refurbished foundations will be designed to carry the anticipated design loads of likely future upgrades on the line. These interventions and their rationale are set out below.

Grillage refurbishments – approach

Use concrete encasement designs as the preferred refurbishment option

wherever they can be installed in a cost effective manner.

Between 1992 and 2008, over 600 grillage foundations were refurbished by removing, re-galvanising and replacing them. Since then, concrete encasement of the tower legs has become the preferred refurbishment option. Concrete encasement designs have many advantages over buried steel, including lower cost, less risk to the structure during installation, increased performance and reduced requirements for future condition assessment. Most significantly, they bring the steel interface above ground, simplifying maintenance and condition assessment requirements, and so reducing risk.

In some locations it may be impractical to transport concrete to site. In these instances, the existing grillage should be refurbished or a new grillage installed. The proportion of grillage replacements is predicted to be small (under 10%) compared to the number of concrete encasements.

Alternative approaches for grillage refurbishments have been assessed. Specifically, those options that have been discounted include

Excavate and remove grillages for re-galvanising, and put back in the ground (in another location to allow a rolling programme). Cost is approximately 1.4 times that of encasement,5 there is no scope for strengthening, and we will still be left with buried steel.

Replace with a new grillage designed specifically for the given location – the cost is approximately 1.6 times the cost of encasement and we will still be left with buried steel.

5 For more details on encasement costs, see the cost section of the Grillage Refurbishments Programme strategy.



The flowchart (in Figure 10) outlines the decision process used to decide on concrete encasement or like-for-like replacement.

Figure 10: Decision process for grillage encasement versus replacement

Grillage Refurbishments Programme

By the end of the RCP2 period, refurbish, preferably by concrete encasement,

all grillages that currently have a condition assessment score less than 30.

Ensure no grillage foundation has a condition assessment score less than 40

by 2033 (in 20 years).

Background

Grillage foundations are simply galvanised steel members buried underground. Over 12,000 towers on the network still have grillage foundations — 50% of the foundation fleet. The average grillage age is 57 years, with some now almost aged 90. Investigations have found that many of these buried steel members are severely corroded. Yet grillages cannot be readily condition assessed because they are buried up to 3m below ground. The actual condition of the grillage fleet for the majority of towers is therefore unknown. This poses a significant risk to the network. Since the mid-2000s, 1,700 grillages have been ‘converted’ to concrete over grillage foundations by encasing them in concrete.

- Grillage selected if worst leg condition is

CA 40 or below.

- Grillage may be prioritised again if there

is only 1 low coded leg with the other 3

significantly better coded.

Concrete encasement

or replacement

Grillage Condition

reaches CA 40

Like-for-Like Replacement Concrete Encasement

- Preference is to complete concrete

encasement wherever possible to bring

interface issues above ground where they

can be managed by non-intrusive

inspections and remedial work. In some

locations this is not practical due to the cost

of getting concrete to the site.

- Where costs of concrete encasement

exceed like-for-like replacement by greater

than 30%, complete like-for-like

replacement.



Assessing condition

The ground-line steel condition can be used as a proxy for the grillage condition provided a somewhat conservative approach is taken with regard to refurbishment or replacement timing. We have good ground-line condition data for every foundation. As discussed in subsection 2.2.3, investigations carried out on close to 1,000 towers have revealed that the condition of the steel near ground-line (100mm above to 300mm below ground) is generally quite similar to that of the more deeply buried steel. In 80% of cases it is within 10 condition assessment points, and in 93% of cases it is within 20 condition assessment points. Generally, half the grillages were in better condition than the ground-line steel, with the other half being worse. This means there is a 6.5% chance that a tower with a ground-line interface condition assessment score of 40 may have a grillage condition assessment score between 20 and 30, and a 3.5% chance that its condition assessment score is 20 or less.

Optimum replacement time

Foundation members with a condition assessment score of 20 have lost over 10% cross section and cannot be relied upon to carry their design loads. Foundations with such members have reached replacement criteria and should be targeted for replacement as soon as possible.

Ideally, grillages should be encased in concrete before the condition gets too poor; otherwise it will be necessary to replace significant steelwork. At a condition assessment score of 40 the galvanising is gone and there are initial signs of metal loss. At a condition assessment score of 30, metal loss has certainly occurred, but the members have not yet reached replacement criteria. Foundations with a condition assessment score of 30 can be concrete encased without the need for member replacements. Condition assessment scores less that 30 would require some replacements and more extensive preparation works. Propping a tower and removing members increases cost significantly. It also increases safety risk to workers and the potential risk of tower failure during the works.

On balance, a condition assessment score of 30 to 35 is the optimal time to encase a grillage in concrete. However, because definitive condition information cannot be readily observed, a conservative approach will be adopted, as such a condition assessment score of 40 is deemed the most appropriate condition to target for encasement.

Modelling grillage condition

As discussed in subsection 2.2.4, we have created a model to predict current and future grillage condition. It assumes a linear degradation rate from the original installation date (at condition assessment 100) to the most recent ground-line condition recording, then continues linearly to forecast future condition.

The model also includes grillage foundations that have had their ground-line interfaces refurbished. In the late 1990s and early 2000s approximately 2,200 structures had their ground-line interfaces refurbished by blasting and applying thermal zinc spray. Their ground-line condition is therefore no longer a good proxy for grillage condition. Foundation inspection records for these structures were interrogated to determine the pre-refurbishment condition and inspection date and used to derive the degradation rates for these structures in the model.



The following assumptions are used within the grillage condition model.

Grillage condition assessment score is taken as the worst of the leg interface condition codes.

Degradation rate is linear.

Life expectancy of an encased grillage is 120 years from the encasement date.

As of June 2013, approximately 3,000 grillages are predicted as having condition assessment score below 40. Of these 1,400 have a condition assessment score less than 30. There is a small number predicted to have a condition assessment score less than 20: these are all at sites where interface refurbishments were carried out. The data for these is somewhat less robust than for non-refurbished sites; however they do pose a risk. They will be targeted for refurbishment before the end of RCP1 period. Over the next 20 years the condition assessment score of an additional 4,000 grillages will fall below 40. By 2020 the condition of 880 grillages will fall below condition assessment 30.

Grillage refurbishment objectives and plan

Based on available condition information and reflecting the optimum replacement timings, the following condition-based objectives have been developed:

1. Plan to have no grillages with a condition assessment score under 30 by end of RCP2 (2019/20)

2. Plan to have no grillages with a condition assessment score under 40 within 20 years (2032/33)

3. Beyond 2033, refurbish grillages when they reach a condition assessment score of 40.

Modelling (see Appendix C) has determined that 350 grillage encasements each year is the optimum volume for the programme to achieve the above objectives. Refurbishment volumes of 200 and 300 failed to achieve the grillage refurbishment objectives.6

It should be noted that 350 grillage encasements each year represents an ideal result, as deliverability constraints and needs for scale efficiency will lead to foundations being addressed differently to that modelled. As an example, one key objective is to minimise disruption to stakeholders. To achieve this, it is desirable to refurbish all grillages on a single property at one time. This inevitably means that some works are carried out slightly earlier than they would be if based solely on condition. However, in general, it can be expected that the original installation date, soil conditions and construction are effectively equivalent at each property. It is estimated that for every 350 foundations refurbished based solely on condition, a further 50 will be refurbished somewhat early.

The plan is therefore to refurbish foundations at 400 towers each year throughout RCP2.

Condition assessment data of the excavated steel will be collected while refurbishing the grillage foundations. At the end of RCP2, based on condition data gathered from the previous 10 years, we will re-evaluate the appropriateness of the chosen plan. If the programme continues at 400 grillages each year, all grillages will have been refurbished by 2045. By that time, the youngest original grillage will be almost 80.

6 For the first objective the minimum required numbers are (1400 + 880)/7 years = 326/year, while for the second

objective the minimum required numbers are (3000 + 4000)/20 year = 350/year



Grillage prioritisation

Prioritisation will be based on the priority matrix (see Figure 8), which balances condition and criticality. Grillages with a condition assessment score under 30 are a higher priority than a high-impact grillage just reaching 40, due to the heightened risk of them failing.

Impact of refurbishment programme

Figure 11 shows the predicted impact of the encasement programme on the number of at-risk grillage foundations.

Figure 11: Grillage Asset Health Forecast7

Figure 12 shows the effect of the programme on foundation asset health contrasted with the situation if the grillage encasement programme is not undertaken.

Figure 12: Foundation Asset Health Forecast

Programme cost

Cost and scope estimation for grillage refurbishment works is an example of volumetric forecasting (see Planning Lifecycle and subsection 4.1.4 for further details). To date, the average unit cost of a grillage encasement is $25,000. To complete approximately 400 grillages each year will cost an estimated $10.2m.

The assumptions made in estimating unit costs include:

impact of historic project risks are captured by out-turn unit costs

7 This shows the effect of refurbishing 350 grillages each year of the worst-condition grillages.

0

500

1,000

1,500

2,000

2,500

3,000

3,500

12/13 13/14 14/15 15/16 16/17 17/18 18/19 19/20

GRILLAGES AT OR BELOW CA 40

CA 31-40 CA 0-30

12+ YRS (91%)

7-12 YRS (5%)

2-7 YRS (4%)

0-2 YRS (0%)

NOW DUE (0%)

FOUNDATIONS - ASSET HEALTH (19/20 - PLAN)

12+ YRS (79%)

7-12 YRS (5%)

2-7 YRS (4%)

0-2 YRS (2%)

NOW DUE (10%)

FOUNDATIONS - ASSET HEALTH (19/20 - DO NOTHING)



the building blocks used are sufficiently detailed to reflect typical projects

the proportion of sites with difficult soil conditions will tend toward a constant proportion

the proportion of cost incurred due to access and site topography will tend toward a constant proportion.

Undersized foundation strengthening

Strengthen undersized foundations in all critical locations to minimise the risk

of tower failure due to overloading.

Studies have revealed that concrete foundations built before 1983 were usually designed based on very limited soil testing and often assumed soil properties, leading to occasional installation of undersize foundations. In the 1990s several hundred safety critical sites were investigated, with some 20% later being strengthened. Similar investigations have been carried out in recent years, again resulting in approximately 20% being strengthened. Urban developments and changing land use continue to increase the safety criticality of numerous sites each year.

We will continue to investigate the capacity of existing foundations at critical sites and will strengthen those found to be understrength. The plan is to annually investigate foundations at 40 towers and strengthen an average of 8 each year over the RCP2 period.

The cost of pile foundation strengthening has been derived using our approach to volumetric forecasting, which is discussed in subsection 4.1.4. Costs to strengthen concrete foundations vary considerably, from $25,000 to $170,000 at each site, with an average cost of $105,000 (including design). An annual cost of $880,000 has been allowed for each year from 2015 to 2020 for strengthening undersized pile foundations.

Replace/Refurbish Pile Foundations

Replace or refurbish pile foundations based on condition.

Pile foundation replacement generally focuses on sites susceptible to erosion (where the land is unstable), and those in rivers which have degraded to a point where replacement is warranted. This work is required to support safety and reliability by preventing structure collapses due to foundation failures.

Over the past 10 years, an average of five pile foundations each year have required replacement, with the number each year being somewhat dependent on natural environmental events. Pile foundation replacements for RCP2 are forecast at approximately 9 structures per year addressing condition based replacements and new installations in flood prone river locations.

The cost of pile foundations are derived using our volumetric forecasting methodology, which is discussed in subsection 4.1.4. The average out-turn cost for each foundation replacement is $47,000. Based on 47 pile foundation replacements over RCP2, this equates to a total cost of $2.2m.



Bridge replacements

Replace access corridor bridges based on condition.

The main purpose of this strategy is to ensure continuing safe and efficient access to transmission lines for maintenance and project works.

Well maintained access tracks and bridges are essential to allow safe access to transmission line assets when responding to faults or performing routine inspections and maintenance. Access routes must be maintained so that, as a minimum, the access tracks and bridges can safely support access using conventional 4WD vehicles. The landowners requirements for access and load-bearing capability may be significantly less than ours, and existing bridges may need to be upgraded or replaced to meet our requirements. This is particularly the case where the capacity of an existing bridge is a potential constraint on project works such as grillage replacements or conductor stringing. Our technical standards for bridges rely on the Transit NZ Bridge Manual.

The average annual expenditure on access track bridge replacements over the last five years is approximately $1.0m and this is predicted to continue through RCP2.

Based on a forecast of 64 bridge replacements over RCP2, we estimate a total expenditure of $6.0m.

Prioritise foundation works

Prioritise the refurbishment and strengthening of foundations taking into

account existing condition, asset criticality and other factors.

We have adopted a risk-based prioritisation approach that takes into account four factors to prioritise foundation works:

condition (taking due account of any known discrepancies between grillage and interface condition)

asset criticality (in respect to Grid reliability and safety)

existing foundation capacity and whether the foundation should be strengthened

whether other works are required on the same property (minimise landowner disruption).

4.1.3 Integrated Works Planning

Our capital governance process –IWP – includes the creation of business cases that track capital projects through three approval gates, with the scope and cost estimates becoming more accurate as the project becomes more refined.

The IWP process integrates capex across a moving window of up to 10 years in the future. This optimisation approach seeks to ensure that works are deliverable and undertaken in an efficient and timely manner. Planning of all foundation works takes into consideration relevant site strategies, minimisation of required outages and resources, and any potential synergies with other projects.



Re-assess foundation requirements before re-conductoring or uprating

Ensure any work that changes loadings on structures includes a robust design

assessment of the foundation strength to ensure compliance with current

standards.

This strategy supports delivery of enhancement and development projects discussed in subsection 4.1.1. It ensures that all re-conductored lines and structure foundations on uprated lines where loads are increased comply with current loading and capacity requirements. This enhances safety and reliability.

4.1.4 Cost Estimation

Cost estimation is a key stage of the capital investment process and forms a critical input into projects at various stages in the planning process. Historically, cost estimates for foundation works were developed using proprietary systems. This has now transitioned to the central cost estimation team, which uses the cost estimation tool Transpower Enterprise Estimation System (TEES). Further details on our cost estimation approach can be found in the Planning Lifecycle Strategy document.

Ensure foundation works are scoped to achieve P50

Ensure foundation project estimates are developed and scoped to achieve

P50 cost value. P50 is an estimate of the project cost based on a 50%

probability that the cost will not be exceeded.

Most foundation works are repetitive with similar scopes. They are categorised as volumetric works for estimation purposes. Cost estimates for volumetric capital projects are developed on the basis of tailored ‘building blocks’ informed by actual cost of completed, equivalent historic projects. This feedback-based process is used to derive average unit costs for future works. See subsection 4.1.2 for further details on how this is applied to replacement projects.

The P50 cost value is an estimate of the project cost based on a 50% probability that the cost will not be exceeded; that is, the P50 estimate is based upon an equal chance of project overruns or under runs up to the finalisation of the project scope. In a general sense, the expected cost of a programme of similar projects is of more interest than the costs of projects that are estimated separately. Assumptions made in using a volumetric costs methodology to achieve P50 include:

the sample size of historic works is sufficiently large to provide a symmetric distribution for the cost

a large number of equivalent projects will be undertaken in future

cost building blocks based on historic out-turn costs capture the impact of past risks

volumetric estimates are to be determined using the Transpower Enterprise Estimation System (TEES) (US Cost) system

scope is reasonably well defined and reflects a predetermined list of ‘standard building blocks applied to all estimates.



4.2 Delivery

Once planning activities are completed, Capex projects move into the Delivery Lifecycle. Delivery activities undertaken are described in detail in the Delivery Lifecycle Strategy. The following discussion focuses on delivery issues that are specific to the foundations fleet.

4.2.1 Design

When applied to foundations, the design process8 aims to ensure appropriate site-specific designs are used. As discussed above in subsection 4.1.2, concrete plugs with cast-in tower leg stubs are the preferred method for new foundations. Where concrete is not easily transportable to a particularly remote location, a standard grillage or other foundation type may be considered.

Foundation design

Ensure assets with high safety or Grid criticality are designed and maintained

to be more reliable than less critical assets.

Our transmission line loading standard (TP.DL 12.01) specifies higher-return period weather events for critical assets than for less critical ones (such as higher reliability level for more critical assets). This is in line with standard international practice.

Replacement foundation design

Design replacement foundations to carry the anticipated design loads of likely

future upgrades.

There are significant economies of scale in increasing foundation capacity at the same time as undertaking foundation encasement/replacement. For concrete encasement, the only additional cost is for extra concrete, as little more time is required to dig a bigger hole. For the grillage replacement option, slightly longer grillage members are required, but, again, the installation cost is relatively constant.

Designing replacement foundations taking into account anticipated design loads of likely future upgrades is prudent, sustainable asset management planning and delivers on the objectives relating to network and cost performance.

4.2.2 Procurement

For more details of our general approach to procurement, see The Sourcing, Supply & Contracts Approach (2011) and the Delivery Lifecycle Strategy.

Procurement issues relevant to the foundations fleet during the RCP2 period are set out below.

8 While design activities are undertaken during the Planning Lifecycle, the majority of detailed design takes place as

part of the delivery cycle.



Award contractor work on a sole source ‘yours to lose’ basis.

Award contractor work by geographic locations on a sole source ‘yours to

lose’ basis.

Foundation work is mostly of a volumetric nature. The preferred procurement method is sole source, and second preference, selected tender. This strategy aligns with the objective to control costs by minimising supplier diversity. Performance-based contracting will be used to provide incentives to contractors to align their objectives with ours. Locally based contractors have geographic knowledge of the area and so are more suitable to work in rugged terrain.

Selected projects are put out to tender based on the availability of the expertise required to perform the project. This strategy aligns with the objective to minimise system disruptions and maintain reliability.

4.2.3 Delivery Planning

The plan for delivering new foundations for new transmission lines and upgraded transmission lines are managed under our IWP process as set out in subsection 4.1.3. This subsection sets out how IWP is applied to tower and pole project delivery.

Project deliverability

Ensure planned projects are deliverable within available financial, labour and

material constraints.

Our IWP processes deliver on this strategy. In particular, ensuring deliverability of projects planned in line with the IWP processes is essential to support our objectives of controlling costs and achieving the desired asset management outcomes.

Package work

Package works into blocks of consecutive structures and ensure multiple

works are carried out at one site simultaneously wherever possible.

Where practicable, work is packaged to maximise efficiency and ensure that any travel time, landowner disruption and system outages are minimised. Under the IWP processes, an integrated programme view is taken rather than evaluating the sum of the individual works. This strategy aligns with the objectives in relation to cost optimisation and system performance and reliability.

4.3 Operations

The Operations Lifecycle phase for asset management relates to planning and real time functions. Operational activities undertaken are described in detail in the Operations Lifecycle Strategy. The following discussion focuses on operational issues that are specific to the foundations fleet.



4.3.1 Outage Planning

Power system outages for preventive maintenance, corrective maintenance, and replacements must be planned to minimise disruption to customers. Grid operations identify requirements for outages (including reclose blocks) and manage the planning of outages and reclose blocks. We will follow the strategies set out below when planning outages for foundation assets.

Foundation works outage planning

Plan to minimise disruption to customers for foundation works that require

outages.

Very few foundation works require outages. When works do require an outage, we coordinate with stakeholders to ensure that any unavoidable system disruptions and outages are notified well in advance so that affected parties can prepare. This strategy aligns with the stakeholder and network performance objectives.

4.3.2 Contingency Planning

With thousands of towers on the network, located in many different environments, it is inevitable that foundations and their towers will occasionally fail during extreme events such as high winds, floods and landslides. Planning for failures is essential so that service can be restored relatively quickly when failure occurs.

To ensure rapid network restoration times, we employ the following contingency strategies.

Maintain contingency response resources

Have sufficient plans, skilled manpower and emergency spares in place to

enable rapid restoration of transmission service following single or multiple

structure failure(s) or conductor drop(s).

Resources must be sufficient to manage contingencies using a tiered response where local contractors rectify failures of one or two structures, but may ask others for help following multiple structure failures. We ensure that asset specific emergency plans are developed for critical assets.

Emergency Restoration Team and emergency spares: Maintain readiness of emergency restoration team and structures – ability to temporarily restore a localised failure (up to 5 towers or 2 km) of any one line (double or single circuit) within 10 days where physical Grid redundancy is not available.

Emergency Management Team: Maintain readiness of emergency management team with communications routes to Civil Defence and to site works contractors. Yearly drill for significant outage communications and process. Continue the business continuity plan, including emergency restoration structures.

Business continuity plan: Maintain the business continuity plan, including emergency restoration structures, and put in place as required.

This strategy delivers on the objectives in relation to System Performance and Reliability.



4.4 Maintenance

We and our service providers carry out ongoing works to maintain assets in an appropriate condition and to ensure that they operate as required. Our approach to Maintenance and the activities it undertakes are described in detail in the Maintenance Lifecycle Strategy. Maintenance tasks are classed into three categories:

preventive maintenance

- condition assessments

- servicing

corrective maintenance

- fault response

- repairs

maintenance projects.

The following discussion focuses on maintenance issues that are specific to the foundations fleet, including specific maintenance projects planned for RCP2. These activities and associated strategies are discussed in the following sections.

4.4.1 Preventive Maintenance

Preventive maintenance is work undertaken on a scheduled basis to ensure the continued safety and integrity of assets and to compile condition information for subsequent analysis and planning. Preventive maintenance is generally our most regular asset intervention, so it is important in terms of providing feedback of information into the overall asset management system. Being the most common physical interaction with assets, it is also a potential source of safety incidents and human error. The main activities undertaken are listed below.

Inspections: non-intrusive checks to confirm safety and integrity of assets, assess fitness for service, and identify follow up work.

Condition Assessments: activities performed to monitor asset condition or predict the remaining life of the asset.

Servicing: routine tasks performed on the asset to ensure asset condition is maintained at an acceptable level.

For the foundations fleet, the largest component of preventive maintenance is condition assessment, as little servicing is required, mostly because there are no moving parts. Condition assessments are very important because of their role in planning replacement and refurbishment to prevent foundation failures.

We intend to implement the following two preventive maintenance processes on the foundations fleet in support of our objectives stated in chapter 3.



Perform regular patrols

Carry out regular patrols to allow the planning of work required to mitigate or

avoid any failure risks.

Line patrols are generally performed once a year on every transmission line asset. The frequency of patrols will be assessed based on site or corridor safety criticality. A ground-based patrol visits each structure foundation to identify any defects that could pose a risk to the structure integrity. Such defects include:

severely damaged foundations

geotechnical risks due to slips, scouring and subsidence

third party excavation or construction around tower foundations.

When significant defects are identified a maintenance job is raised to rectify the issue.

This strategy supports the network performance objectives for foundation assets.

Foundation condition assessments

Carry out regular foundation condition assessments.

The condition assessment (CA) programme monitors and records the condition of transmission line structures, foundations, conductors and hardware. The programme provides a basis upon which replacement or maintenance options can be investigated, and enables planning to take into account the impact of varying environmental ageing factors. It also allows extrapolation of the assessed condition into the future. All CA data is currently stored in our maintenance management system MMS, however this is being replaced with a MAXIMO- based asset management information system. By the end of 2013 all CA data will be on the MAXIMO system, which is expected to provide clearer reporting of data and trends.

As discussed in 2.2.3, condition assessments are carried out on a cyclic basis and entail a detailed inspection of the structure and span. The assessment produces a condition assessment score for various components and a defect list. New foundation assets are first assessed just prior to expiration of the defects liability period. Thereafter, tower line assets are generally assessed every 8 years. If the condition assessment score is less than 50, the assessment frequency is reduced to 4 years.

Sites with unusually rapid degradation or those with higher criticality may be assessed more frequently. At June 2013, 5%–10% of individual towers and pole structures are on partial (half cycle) assessments. Condition assessment is carried out in line with TP.SS 02.17B Transmission line condition assessment Part B: Structures.

We will continue to develop and refine the existing condition assessment process to ensure relevant, nationally consistent, high-quality data is collected to inform asset planning and decision making.

4.4.2 Corrective Maintenance

Corrective maintenance includes unforeseen activities to restore an asset to service, make it safe or secure, prevent imminent failure and address defects. It includes the required follow-up action, even if this is scheduled some time after the initial need for action is identified.



These jobs are identified as a result of a fault or in the course of preventive work such as inspections. Corrective works may be urgent and if not completed for a prolonged period, reduced network reliability may result.

Corrective maintenance has historically been categorised as repairs and fault (response) activities. Repairs include the correction of defects identified during preventive maintenance and other additional predictive works driven by known model type issues and investigations.9 Timely repairs reduce the risk of failure, improve redundancy and remove system constraints by maximising the availability of assets. Activities include:

Fault restoration: unscheduled work in response to repair a fault in equipment that has safety, environmental or operational implications, including urgent dispatch to collect more information

Repairs: unforeseen tasks necessary to repair damage, prevent failure or rapid degradation of equipment

Reactive inspections: patrols or inspections used to check for public safety risks or conditions not directly related to the fault in the event of failure

Fault Response

Fault response is required to restore the function of assets as quickly as possible to maintain supply to customers.

Respond to foundation failures in a timely manner

Ensure Lines Maintenance contractors have staff patrolling the asset within

one hour of being notified of a fault and can respond to two faults at the

same time.

The purpose of a fault patrol is to establish if the circuit can be safely re-energised and determine the cause of the fault. For the purposes of system performance and safety, it is critical that this be established as quickly as possible. When the cause is determined, repairs are planned and implemented commensurate with the safety risk and asset criticality. This supports our network performance and safety objectives.

See the strategy Maintain Contingency Response Resources for details on how we will manage the response of contractors to faults.

Repairs

We may repair foundations where a fault has been identified that could potentially result in a failure or when a failure has occurred. In both cases the repairs are carried out to support the safety and network performance objectives.

Slope stability and waterway protection works and minor repairs

Complete slope stability and waterway protection works and minor

foundation repairs at structures where specific defects need repair.

9 Where the number of potential repairs is deemed sufficiently high, a Maintenance Project will be instigated to

undertake the repairs works.



Works covered by this strategy include:

river diversion or bed protection works

checking/repairing splice and anchor bolts

baseplate/ground connection maintenance and repair where scope is sufficiently small that a maintenance project is not raised

re-forming ground where water pooling around tower bases

works associated rectifying ground subsidence or movement

rectifying damage caused by vehicle or farm activity.

The purpose of this strategy is to ensure the integrity of the foundation system is maintained and lifecycle costs are minimised.

4.4.3 Maintenance Projects

As discussed in subsection 2.2.5, maintenance projects typically consist of relatively high-value planned repairs or replacements of components of larger assets. Maintenance projects would not be expected to increase the original design life of the larger assets. Maintenance jobs are typically run as a project where there are operational and financial efficiencies from doing so. The drivers for maintenance projects include asset condition, mitigating safety and environmental risks, and to improve performance.

Over the RCP2 period we intend to implement the following maintenance projects on the foundations fleet.

Connection component refurbishments

Refurbish corroding baseplates, anchor bolts and cast-in stubs at a condition

assessment score of 50 prior to onset of significant rusting.

Foundation connection components comprise two types, those with baseplates and anchor bolts and those with cast in stubs. All are subject to corrosion. Foundation components are considered a relatively minor part of the overall foundation and tower structure and, as such, their refurbishment is considered a maintenance project activity. Regardless, their failure has the potential to result in a structure collapse with significant implications for safety and reliability.

We periodically review refurbishment criteria and designs to ensure appropriate practice is being employed.

Baseplate /anchor bolt: Poor-quality dry-pack mortar originally used under baseplate- type foundations is porous and has led to mortar crumbling. Moisture ingress under the baseplate has subsequently led to corrosion of the anchor bolts and baseplate (which is not visible until the grout is removed during refurbishment). Refurbishment selection is based on the minimum condition assessment score of the four leg-based scores collected at each site. The typical threshold score of 50 before any significant rusting or loss of section is visible. Some 1,300 baseplate connections currently have a condition assessment score less than 50 (see subsection 2.2.3).

Cast-in in-situ stub leg: There are often rust issues at the concrete interface (ringbark corrosion), but they typically do not extend far into the concrete (<20mm). Refurbishment by blasting and painting has proven highly successful. In extreme



cases a small area of concrete is broken out, the steel cleaned, and the area repaired by grouting. Refurbishment selection is based on the minimum condition assessment score of the four leg-based codes collected at each site. The typical threshold is condition assessment 50 before any significant rusting or loss of section is visible. Some 670 stub connections currently have a condition assessment score less than 50 (see subsection 2.2.3).

Once refurbished, these connections will require periodic paint maintenance at a repeat cycle of between 12 and 20 years depending on the site environment.

We plan to carry out an ongoing connection refurbishment programme of approximately 630 sites each year throughout RCP2 – 360 baseplates and 270 cast-in in-situ legs. This is based on existing condition assessment information and expected degradation.

The cost of these refurbishments is derived in line with our volumetric forecasting methodology, discussed in subsection 4.1.4. Average out-turn costs for baseplate and anchor bolt refurbishments are $7,900, and are $2,300 for cast-in in-situ leg refurbishments. At 360 and 270 sites respectively, this equates to an annual expenditure of $3.5m.

Marine foundation refurbishment

Refurbish specific foundations in marine environments.

Transmission line tower foundations are occasionally located in marine environments. As a result of this location, they are subject to additional degradation from tidal activity and chloride ingress attacking the reinforcing steel. We have 8 towers in a marine environment on the Tiwai causeway supporting the 2 transmission lines that supply Tiwai point. Foundation works are planned to protect these foundations from chloride ingress during RCP2.

This work has an estimated cost of $600,000 – an average of $75,000 for each tower.

We plan to complete the programme of refurbishing existing foundations at sites where failure would pose significant risk to people, property or the Grid.

During RCP2, we will also complete the marine foundation refurbishment works on the HEN-OTA-A line that began in RCP1. The estimated cost of this work is $700,000.

The total expenditure for this strategy is $1.3m over RCP2. This equates to an annual average expenditure of $260,000.

Waterway protection works

Complete waterway protection work on defective pole foundations in

riverbeds.

We plan to complete river protection work on existing pole foundations where river erosion poses a significant threat to security of supply on the Grid. The work is planned for 38 sites on three South Island assets: AHA-OTI-A, DOB-TEE-A and BLN-KIK-A. Estimated costs over RCP2 are $1.0m, which equates to an annual average expenditure of $200,000.



4.5 Disposal and Divestment

The disposal and divestment phase includes the process from when planning of disposal of an asset begins through to when the asset is no longer owned by us. The approach is set out in detail in the Disposal Lifecycle Strategy. This subsection describes our approach to the disposal of assets within the foundations fleet.

4.5.1 Disposal

The Disposal Lifecycle eventuates when foundations are no longer needed or when a foundation has degraded to an extent where refurbishing is uneconomic. Foundations may be replaced with new ones, yet there are important requirements for the disposal phase.

In the case of a failure, we carry out diagnostic inspection and testing to investigate the cause of the failure. This information is fed into the management of the entire foundation asset fleet.

Site reinstatement

Reinstate decommissioned site foundations to their former natural forms.

Consistent with environmental objectives, we will follow appropriate decommissioning process, including requirements for foundation removal, recovery and recycling/disposal of materials. Decommissioned site foundations should be re-instated to their former natural forms to allow the land to recover. We will monitor rehabilitated areas for a period of time after re-instatement.

4.5.2 Divestment

Implementation of divestment is primarily the change of ownership, although we must also remain cognisant of any safety and environmental issues and technical impacts on the Grid such as a change in constraints and flexibility of Grid operation.

Foundation divestment

Divest foundations as part of transmission line divestments to customers.

We are continuing with the transfer of a number of assets at the fringes of the existing Grid to our distribution business customers. This process and its justification are described fully in the Disposal and Divestment Lifecycle Strategy.

Refer to the Towers and Poles Fleet Strategy for the number of towers and poles likely to be transferred to customers between 2013/14 and 2019/20. This includes all divestments that we believe have a 50% or greater likelihood of occurring during the timeframe.

The total number of assets to be transferred represents 4% of the total tower and 9% of the total pole fleet as at June 2013. All towers will have associated foundations and these will be divested with the tower structure.

4.6 Capability

We require grid assets and equipment to be maintained, tested and operated to high standards of skill, professionalism and safety. Work is to be carried out only by individuals



with competencies that are both appropriate and current (see TP.SS 06.20 Minimum Competencies for Line Maintenance, and TP.SS 06.25 Minimum Requirements for Transpower field Work). This helps to prevent injury to workers and damage to assets, and to protect the public and their property from harm.

This section describes the approach used to ensure that these competencies are present in those undertaking work on the foundation and access assets.

The capability strategies are described under three headings:

Asset Knowledge

Risk Management

Training and Competence.

4.6.1 Asset Knowledge

Robust asset knowledge is critical to good decision making for asset management.

Maintain up-to-date asset records

Maintain up-to-date records of all foundation asset attributes, condition and performance.

Comprehensive records that cover the original installation of a foundation structure and any subsequent modifications are vital to enable quality asset management decisions. Data must include details of exactly what is installed, type test reports, design reports, condition data and investigation reports. Quality condition data is also required.

While good asset attribute and condition data is available for most foundation sites, some fields are currently incomplete. Data quality and completeness will continually be reviewed and amended as required to ensure a high-quality dataset is maintained. The current project to transition to the MAXIMO-based asset management information system will include a review and cleansing of data.

We plan to enhance the failure and incidence records system to improve consistency and usefulness of the data, including root cause analysis.

To improve condition assessment consistency, improved guidelines will be developed including more photographic examples where relevant.

Maintain and develop fleet strategies

Maintain and develop the fleet strategy for the foundation fleet.

Continue the development and refinement of models to predict the asset health of foundations, particularly for grillages. Ensure the modelling includes lessons learned from the refurbishment programme in relation to observed degradation in various soil types, moisture contents, land use etc.

Revise building blocks on an ongoing basis using costs from completed works and forecast innovations and improvements. Use these costs in the economic modelling along with degradation rates and AHI to define least lifecycle cost options for programmes of work.



4.6.2 Risk Management

Our approach to risk management is central to our decision making as we seek to achieve our overall asset management objectives and optimise the timing of major investments.

Knowledge of foundation condition is crucial to the assessment of options for foundation replacement and refurbishment. As outlined in subsection 2.2.3, we apply an adaptive condition assessment approach where the frequency and extent of condition assessment interventions is determined based on the most recent condition assessment and the predicted current state.

Understanding and modelling uncertainty then becomes an increasingly important element in risk management decision making, particularly given the consequences of foundation failure on transmission line performance. In recognition of this, we are developing asset health and criticality frameworks to improve and integrate our risk-based asset management. The strategies below discuss how we plan to progress this in regards to the foundations fleet.

Risk-based options evaluation framework

Develop a risk-based framework and associated tools for evaluating

foundation investments.

We will develop an improved risk management framework and tools that can be used across the foundations fleet to evaluate investment options. The key parts of this framework will be tools for making quantitative estimates of the likely impacts of foundation failures on service performance and safety on a span-by-span basis. The risk model will specifically consider uncertainty in the inputs to risk-based decision making.

We will ensure more robust and detailed development of scope for major replacements to improve the accuracy of cost estimates and the validity of the economic analysis of options. Risk management processes will be made more robust and systematic, and will allow risk assessments to be more readily communicated to internal and external stakeholders.

4.6.3 Training and Competence

We have two service specifications that define the competency requirements for working on transmission line assets, including foundations:

TP.SS 06.20 Minimum competencies for lines maintenance

TP.SS 06.25 Minimum requirements for Transpower field work.

Foundation worker competencies

Adhere to the following service specifications, TP.SS 06.20 (Minimum competencies for lines maintenance) and TP.SS 06.25 (Minimum requirements for Transpower field work).

We maintain a minimum baseline of retained skilled workforce: engineers and site works operators who understand the physical assets. All workers must hold appropriate competencies to work on our assets in line with the service specifications.



Since 2011, much of the training has been provided to service providers at no cost (other than the employee’s time). This has resulted in a considerable increase in service provider training. We plan to continue with this training strategy.

Asset management competency

Increase and then maintain the in-house skill base with regard to Asset Management.

To ensure better long-term asset management outcomes, we plan to increase the emphasis on training in Asset Management principles and application across all relevant parts of the business.

4.7 Summary of RCP2 Fleet Strategies

Our asset management plans for the fleet of foundation assets for each lifecycle stage are summarised in the table below.

Planning

Enhancement

and

Development

Modify existing foundations, including strengthening and relocation, to support new structures or to enable upgrading of conductors.

Replacement

and

Refurbishment

Use concrete encasement designs as the preferred refurbishment option wherever they can be installed in a cost effective manner.

By the end of the RCP2 period, refurbish, preferably by concrete encasement, all grillages that currently have a condition assessment score less than 30. Ensure no grillage foundation has a condition assessment score less than 40 by 2033 (in 20 years).

Strengthen undersized foundations in all critical locations to minimise the risk of tower failure due to overloading.

Replace or refurbish pile foundations based on condition.

Replace access corridor bridges based on condition.

Prioritise the refurbishment and strengthening of foundations taking into account existing condition, asset criticality and other factors.

Integrated

Works Planning Ensure any work that changes loadings on structures includes a robust design assessment of the foundation strength to ensure compliance with current standards.

Cost Estimation Ensure foundation project estimates are developed and scoped to achieve P50 cost value. P50 is an estimate of the project cost based on a 50% probability that the cost will not be exceeded.

Delivery

Design

Ensure assets with high safety or Grid criticality are designed and maintained to be more reliable than less critical assets.

Design replacement foundations to carry the anticipated design loads of likely future upgrades.

Procurement Award contractor work by geographic locations on a sole source ‘yours to lose’ basis.

Delivery

Planning

Ensure planned projects are deliverable within available financial, labour and material constraints.

Package works into blocks of consecutive structures and ensure multiple works are carried out at one site simultaneously wherever possible.

Operations

Outage Planning Plan to minimise disruption to customers for foundation works that require outages.

Contingency

Planning

Have sufficient plans, skilled manpower and emergency spares in place to enable rapid restoration of transmission service following single or multiple structure failure(s) or conductor drop(s).



Maintenance

Preventive

Maintenance

Carry out regular patrols to allow the planning of work required to mitigate or avoid any failure risks.

Carry out regular foundation condition assessments.

Corrective

Maintenance

Ensure Lines Maintenance contractors have staff patrolling the asset within one hour of being notified of a fault and can respond to two faults at the same time.

Complete slope stability and waterway protection works and minor foundation repairs at structures where specific defects need repair.

Maintenance

Projects

Refurbish corroding baseplates, anchor bolts and cast-in stubs at a condition assessment score of 50 prior to onset of significant rusting.

Refurbish specific foundations in marine environments.

Complete waterway protection work on defective pole foundations in riverbeds.

Disposal and Divestment

Disposal Reinstate decommissioned site foundations to their former natural forms.

Divestment Divest foundations as part of transmission line divestments to customers.

Capability

Asset

Knowledge

Maintain up-to-date records of all foundation asset attributes, condition and performance.

Maintain and develop the fleet strategy for the foundation fleet.

Risk

Management Develop a risk-based framework and associated tools for evaluating foundation investments.

Training and

Competence

Adhere to the following service specifications, TP.SS 06.20 (Minimum competencies for lines maintenance) and TP.SS 06.25 (Minimum requirements for Transpower field work).

Increase and then maintain the in-house skill base with regard to Asset Management.


TL FOUNDATIONS FLEET STRATEGY © Transpower New Zealand Limited 2013. All rights reserved. Appendices | page 48

A GRILLAGE EXAMPLES

Figure 13 shows a cross section of a grillage foundation.

Figure 13: Cross section of a grillage foundation

The picture above shows a grillage foundation and the areas we assess to determine the condition score (condition assessment score). (CA code). The ground-line interface condition represents the worst of the steel found from 100mm above the ground line to 300mm below the ground line.

The grillage condition score represents the worst of the steel found from 300mm below the ground line to the base of the grillage.

The grillage condition assessment degrades from a score of 100 to 0, where a score of 40 means the galvanising is gone and rust is beginning to pit the steel, and a score of 20 means there has been 10% loss of metal cross section and replacement is required.

Figure 14 shows grillages at a condition assessment score of 20.

Figure 14: Grillages at a condition assessment score of 20

Ground line

interface

Grillage



Figure 15 shows grillages at a condition assessment score of 40.

Figure 15: Grillages at a condition assessment score of 40



B FOUNDATION CONDITION CODES

Table 4 shows the grillage foundation condition assessment guidelines. Table 5 shows grillage foundation connection (buried grillage – soil/main leg interface) condition assessment guidelines.

Condition

Assessment Guidelines

100 New steel grillage fully galvanised, correctly backfilled and compacted as is standard.

90 Surface is dulled to a light grey colouring.

80 Older grillage (now fitted with cathodic protection (C/P)) otherwise in condition score of 50-60.

70 Bolts beginning to rust beneath the surface.

60 Start of steel member surface rusting.

50 Steel surfaces below ground beginning to develop rust spotting.

40 Rust beginning to pit steel below ground line (GL) advancing up main leg member, now visible at the surface. C/P no longer effective and foundation deteriorating.

30 Flaking rust on main leg section of grillage just below GL, and some loss of cross section.

20 (Replacement criteria R/C)

Metal loss on main and/or bracing steel reaches replacement criteria (10% loss of cross section).

10 Metal loss exceeds replacement criteria, but tower not significantly at risk.

0 Metal loss serious, foundation failure probable under ‘everyday conditions’.

Table 4: Grillage Foundation Condition Assessment Guidelines

Condition Assessment

Guidelines

100 New (or refurbished steel members, galvanised and free of damage, with added protective coating in as-new condition).

90 Protective coating 50% of way to failure.

80 New galvanised steel leg without added protective coating.

70 Protective coating failing.

60 Speckled rust.

50 Steel rust stained at ground level and just below the surface. Patches of galvanising gone.

40 Loss of metal, pitting and nodules of rust appearing on steel surfaces at ground line and below.

30 Flaking rust.

20 (R/C) Severe rusting of steel about ground line and below, heavy flaking rust, black underneath with loss of metal cross-sectional area of approximately 10%. Complete breakdown of nuts and bolt heads.

10 Rusting exceeds R/C, but tower not significantly at risk.

0 Serious risk of tower leg tension/compression failure.

Table 5: Grillage Foundation Connection (Buried Grillage – soil/main leg interface) Condition Assessment Guidelines



Table 6 shows the concrete foundation condition assessment guidelines.

Table 7 shows the foundation connection (cast-in in-situ steel stubs/concrete interface) condition assessment guidelines.


Guidelines

100 New foundation, in good condition.

90 Foundation in service at least 10 years, without obvious deterioration.

80 Reinforcing exposed to soil severely corroded. Expansion cracks in cap.

70 Exposed reinforcing, minor rust. Minor spalling off the cap.

60 Embedded reinforcing cage rusting.

50 Spiral reinforcing in some areas corroding, major spalling off the cap.

40 Main vertical reinforcing start corroding.

30 Main reinforcing seriously corroded, with associated underground cracking/spalling.

20 (R/C) Foundation at replacement criteria, and no longer able to reliably sustain ultimate site-specific design loads with reliability, due to crumbling of concrete mass and/or corrosion of the reinforcing, causing serious spalling/cracking etc.

10 Foundation severely cracked unable to sustain design loads, but not at immediate risk of failure.

0 Uplift failure possible under ‘everyday conditions’.

Table 6: Concrete Foundation Condition Assessment Guidelines


Guidelines

100 New foundation. Galvanised leg section is free of damage, is protectively painted 300mm either side of concrete surface level.

90 At least 5 years of service, but no visible deterioration.

80 Galvanising on leg dulled, concrete darkening and surface roughening. Protective paint at concrete level showing signs of peeling or wear.

70 Protective paint depleted.

60 Specks of rust appearing at concrete steel interface.

50 Loss of galvanising from interface/leg surface, increased rust staining.

40 Rust pitting at concrete/steel interface.

30 5% metal loss on leg /concrete interface surface.

20 (R/C) Flaking rust and loss of metal cross section of 10% at concrete level. Minor spalling to concrete as rust penetrates beneath the concrete surface, heavy staining around leg.

10 Metal loss exceeds 20%, but less than 40%.

0 Metal loss exceeds 40%.

Table 7: Foundation Connection (cast-in-situ steel stubs/concrete interface) Condition Assessment Guidelines



Table 8 shows the foundation connection (anchor bolts and baseplate/mortar and concrete

interface) condition assessment guidelines.


Guidelines

100 New or refurbished galvanised steel baseplate onto concrete held anchor bolts. Waterproof mortar packed tightly between baseplate and concrete foundation. New surface protective coating to seal out any water.

90 Surface coating deteriorating, but still effective.

80 Protective coating ineffective, mortar in good condition.

70 Baseplate and anchor bolt galvanising rough, and critical areas discoloured.

60 First sign of rust staining at edge of baseplate.

50 Rust staining appearing as a brown/red rim on bottom of baseplate. First speckled rust appearing on anchor bolt threads.

40 Mortar crumbling, bolts corroding, baseplate surface rust.

30 Significant rusting to bottom of baseplate, but no loss of steel. Rusting of bolt threads and nuts below the baseplate.

20 (R/C) Flaking rust to bottom of baseplate. Chunks of mortar gone exposing significant rusting of inner bolts and baseplate /levelling nuts. 20% metal loss on any one bolt and 10% metal loss over all anchor bolts.

10 Metal loss on anchor bolts which prevents the withstanding of ultimate site-specific design loads.

0 50% or more loss of cross section on anchor bolts overall, or serious risk to tower at a less loss level where structure heavily loaded.

Table 8: Foundation Connection (anchor bolts and baseplate /mortar and concrete Interface) condition assessment Guidelines



C GRILLAGE ENCASEMENT MODELLING

As discussed in sections 2.2.4 and 4.1.2, a model has been created to predict current and future grillage condition and asset health. It assumes a linear degradation rate from the original installation date (at condition assessment 100), to the most recent ground-line condition recording, then continues linearly to forecast future condition. Subsection 4.1.2 shows the impact on condition if the proposed plan to refurbish 350 of the worst condition tower grillages each year is followed (plus an additional 50 each year which are not in such poor condition, but where it is prudent to refurbish them at the same time as the others to minimise landowner disruption). The following two sections show the impact of refurbishing 300 and 200 tower grillages each year.

Encase 300/Year

Key points of alternative plan 300/Year:

Target 300 grillage encasements each year.

Prioritisation as shown in the matrix in Figure 8.

Plan fails to meet the objectives stated in section 4.1.2, that is, no grillages with CA less than 30 by 2020.

Figure 16 shows the effect of the encasement plan on grillage condition.

Figure 16: At-Risk Grillage Forecast (300 encasements/year)

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Jun-2013 13/14 14/15 15/16 16/17 17/18 18/19 19/20

GRILLAGES AT OR BELOW CA 40 (300/YEAR)

CA 31-40 CA 0-30



Figure 17 shows the effect of the programme on foundation asset health/remaining life at the end of RCP2.

Figure 17: Foundation Asset Health Forecast (300 encasements/year)

Encase 200/Year

Key points of alternative plan 200/Year:

Target 200 grillage encasements each year.

Prioritisation as shown in the matrix in Figure 8.

Plan fails to meet the objectives stated in section 4.1.2; that is, no grillages with CA less than 30 by 2020

Figure 18 shows the effect of the encasement plan on grillage condition.

Figure 18: ‘At-Risk’ Grillage Forecast (200 encasements/year)

12+ YRS (88%)

7-12 YRS (5%)

2-7 YRS (4%)

0-2 YRS (2%)

NOW DUE (1%)

FOUNDATIONS - ASSET HEALTH (19/20 - 300/YEAR)

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Jun-2013 13/14 14/15 15/16 16/17 17/18 18/19 19/20

GRILLAGES AT OR BELOW CA 40 (200/YEAR)

CA 31-40 CA 0-30



Figure 19 shows the effect of the programme on foundation asset health/remaining life at the end of RCP2.

Figure 19: Foundation Asset Health Forecast (200 encasements/year)

12+ YRS (85%)

7-12 YRS (5%)

2-7 YRS (4%)

0-2 YRS (2%)

NOW DUE (4%)

FOUNDATIONS - ASSET HEALTH (19/20 - 200/YEAR)

tl foundations fleet strategy

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