3.2.1 fatal flaw phase investigations -...

SECTION 3 Geotechnical Investigations

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3 Geotechnical Investigations

3.1 Introduction

This section of the report provides details of the geotechnical/geological conditions of each of the harbour crossing options including previous and current phases of geotechnical investigations undertaken, geotechnical assessment for each of the options and ongoing risks during the pipeline’s design life. The options being considered are described in Section 2 of this report.

3.2 Geotechnical Investigations for Harbour Crossings

This section covers previous and current geotechnical investigations undertaken within the harbour and shoreline fringe zones to assess geotechnical subsurface conditions for the options being considered.

3.2.1 Fatal Flaw Phase Investigations

Preliminary broad-brush geotechnical investigations of the listed harbour crossing options were undertaken as part of the ‘fatal flaw assessment’ of the pipeline routes in December 2005. The initial harbour investigation programme comprised Heavy Dynamic Cone Penetrometer (HDCP) testing .The testing was done off a floating barge and all levels were measured from the top of the barge. The levels obtained thus had a limited accuracy of ± 1m, being approximately the tidal variation during testing. The test procedure mimics the standard penetration test (SPT) method. The penetration resistance of the soils is measured by counting the number of blows (fixed mass falling through a fixed distance) to drive a steel coned rod through a 300mm soil column. Unlike the SPT, the cone is solid steel and the test is a continuous process, with the driving of the rods being the only mechanism for advancing the probe. With increasing depth, there is a likelihood of shaft friction affecting the resistance measured (the blow count). The results are converted to a standard SPT (N) blows per 300mm using available empirical correlations. The results are indicative only as the empirical correlations are not based on New Zealand Volcanic soils. The tests enable consistency variations to be readily identified and for layers of different strengths to be interpreted.

No core samples were obtained and therefore no detailed borehole descriptions were made. In this preliminary early phase, soil type interpretation was thus based on existing information within the upper harbour (for example Maungatapu Bridge crossing and from the Tauranga Water Front).

The HDCP test locations and the geological cross sections are shown on drawings appended in Volume 3 of this report.



3.2.2 Detailed Investigations

Subsequent to the preliminary fatal flaw investigations, Route E (western route) was identified as the preferred route by TCC. The subsurface data available was, however, insufficient for a realistic selection to be made of a preferred harbour crossing option so greater clarity of subsurface ground conditions was required. Increased certainty of the geology present, the associated soil strength, grain size and other key geotechnical parameters was essential for preliminary design and for the associated constructability assessment (submarine and HDD options), so further geotechnical investigations were undertaken

Investigations and Testing Schedule

The detailed harbour investigations comprised a total of 16 boreholes and covered the following crossing options (shown in detail on drawing 12300-G-601-012, page 2-4):

1. Horizontal Directional Drilling (HDD) from First Avenue to the end of Matapihi Road – boreholes BH1 to BH6, with drilling up to 75m below seabed to cater for the geometric and constructability constraints and issues associated with the HDD method.

2. A purpose-built bridge from The Strand to the existing eastern rail embankment (to be widened) – boreholes BH7 to BH9 for the bridge, drilled up to 40m below seabed, and BH15 and BH16, drilled to 10m for the embankment widening.

3. Submarine pipeline options

a. Across the harbour from First Avenue to Matapihi, generally parallel to the existing railway crossing

b. Along the City harbour-side from Memorial Park to the Strand – boreholes BH10 to BH14, drilled up to 10m below seabed.

The drilling contract was awarded to Perry Drilling of Tauranga following a competitive tender process. Drilling commenced on 6th July 2006 and practical completion was achieved by 2nd August 2006 (refer Appendix I Volume 3 for photos). Drilling of boreholes BH3 to BH11 was undertaken off a jack-up barge. Boreholes BH1 and BH2 were undertaken by driving across the inter-tidal mud flats. Some of the boreholes more removed from the city were drilled around the clock (namely, a 24-hour, 7-day operation), in order to control costs and programming. Boreholes along the city shoreline were only drilled during daylight only to manage noise levels.

Boreholes BH12 to BH16 were drilled by overland access using a separate mini-rig during low tide periods, by a separate contractor, Soil Engineering Ltd.

Insitu testing within the boreholes included standard penetration testing (SPT) at 1.5metre intervals, measuring water temperatures every 10metres depth (to determine any thermal activity within the harbour indicating possible presence of faults) and collecting push tube soil samples for laboratory testing.



Soil samples from the top 3metres of BH7 to BH9 (drilled for the bridge) were taken for laboratory testing (for example, grain size distribution and settlement velocities) to obtain data for the hydro-dynamic sediment transport modelling (refer ASR report).

The recovered core from the drilling programme has been stored locally in a storage shed until the end of construction for future reference, as required.

The following laboratory tests were carried out on collected soil core samples (from Push Tube and triple coring):

1. Multi-specimen Consolidated Drained Triaxial Tests

2. Grading curves, including wet sieve and hydrometer

3. Atterberg Limits (for fine grained cohesive soils, if any)

4. Bulk Density, Solid Density and water content

5. Dispersivity (pin hole tests and jar-slake tests)

6. Allophane content testing

The testing contract was awarded to Geotechnics Ltd in Tauranga. Samples were delivered to Geotechnics on a daily basis with appropriate instructions.

Borelogs, core photographs and laboratory test results are appended to this report in Appendix J and K, Volume 3.

3.3 Geology/Sub-Surface Ground Conditions

3.3.1 Geology

The geology across the Tauranga Harbour comprises the following sequence from the surface down (refer Preliminary Geotechnical Report 11, dated January 2006 for detailed physical geography and geological information):

• Recent sand and mud deposited with rising sea levels since the Ice Age ( 0 to 10,000 years ago) Period.

• Reworked (fluviatile) volcanic deposits of the Matua Subgroup. These are essentially pyroclastic (from hot volcanic ash clouds) and volcanic sediments deposited during the Ice Age (10,000 to 2 million years ago) over the Tauranga region. Following deposition, these soils have been transported into the Tauranga Harbour by existing river flows.

• Papamoa/Waiteariki Ignimbrite from the Pliocene period (2 to 5 million years ago). The Ignimbrite is buff brown, partially welded crystal and pumice rich; the lower unit contains andesitic (dark grey) to rhyolitic (whitish grey) pumice; the upper unit is rhyolitic.



3.3.2 Sub-Surface Geotechnical Conditions

The following is a brief summary of key geotechnical conditions of the Tauranga Harbour (refer Drawings 12300-D-607-001 and 002 on pages 3-6 and 3-7 for geological/geotechnical cross sections):

Recent Sediments

• Recent marine sand deposits were encountered to 3 metres depth on the western (city) side, and to about 22metres in borehole BH2.

• These sand deposits typically comprise medium to coarse sands with abundant shells and are generally loose (SPT ‘N’ of less than 10) to medium dense (SPT ‘N’ less than 30) in consistency.

• The upper sand deposits are generally mobile namely, the top metre of sediments are subject to movement during tidal movements. More information regarding the specifics of sediment movement and transport can be found in ASR report in Volume 2.

• Borehole BH3 encountered a 15metre thick estuarine mud deposit from a depth of 18metres below seabed. The material comprised organic rich clayey silts of soft to firm consistency. However, these deposits were not encountered in any other boreholes (BH1, BH2, BH4 to BH6) along this long section. It is inferred from this information that the main channel/river may have been draining through this area in the recent geological past (last 3,000 years).

• Estuarine mud was also encountered in boreholes BH7 and BH8, in the vicinity of the eastern abutment of the railway bridge.

Reworked Volcanic Sediments

• Reworked volcanic sediments are fluviatile (stream/river deposits) sediments deposited within the harbour during a period of low sea levels. The sediments are inferred to have been deposited typically in near horizontal layers of alternating sand and silts.

• The reworked volcanic sediments were encountered from depths of 5 metre to 22 metre below seabed level, down to 55metres. These sediments were found to be typically sensitive during field investigations, namely, the residual soil shear strength is considerably less than the peak shear strength, so the soils may lose strength if worked by machinery. However, allophane content testing of recovered soil indicated most samples to have less than 5%, which suggests that the soils are not particularly sensitive.

• In general, the top layer of the sediments comprised white/light grey pumiceous, sensitive silts of firm to stiff consistency. This layer is typically 2 metres to 3 metres thick, moderately dense and is generally underlain by medium to coarse sands.



• The underlying sediments comprised fine to medium grained sands with inter-fingered silt layers. These deposits were generally of medium dense (SPT ‘N’ value between 10 to 30) consistency, with the silt layers being firm to stiff.

• Dense to very dense (SPT ‘N’ value greater than 50), fine to medium grained, uniformly graded sands were encountered between 25 metres to 55 metres below seabed.

• It was noted that whilst sands were tested insitu to be dense to very dense, there was no apparent ‘core cohesion’ observed within the recovered soil core, namely, core could be indented by finger pressure with ease, when unconfined.

Undifferentiated Ignimbrite

• The reworked volcanic deposits are underlain by undifferentiated Ignimbrite at a depth of 50 metres to 55metres below current seabed level. The top surface of this Ignimbrite represents an unconformity and has been eroded to form an inferred ‘paleo-valley’.

• Within the extent of the boreholes drilled (down to 75 metres maximum), two distinct Ignimbrite layers were encountered; an upper layer comprised of dark green/ brown welded dense to very dense, fine to medium grained sands and the bottom layer comprised brown/buff brown silts of hard soil to extremely weak rock consistency.

• The soil (undifferentiated Ignimbrite) core recovered has shown signs of apparent cohesion (welding), as most of the core was hard to break with finger pressure and difficult to indent with fingernails.



3.3.3 Laboratory Testing

As mentioned earlier, extensive laboratory testing was undertaken as part of the detailed geotechnical investigations. Refer to Appendix L of Volume 3 for a summary of laboratory data and test results.

3.3.4 Geothermal Activity

As part of the geotechnical investigations, groundwater temperatures were measured at 10metre depth intervals to check for any geothermal activity along the harbour crossing routes being investigated. Maximum water temperature levels measured were 17.3o Celsius (C) at 75m below seabed level.

As part of geothermal activity analysis within the harbour, URS has carried out a search of borehole database within Environmental Bay of Plenty (EBoP) database (refer Appendix M Volume 3 for summary details). The data obtained indicates that temperature recorded at 75metres depth (in Well No .4569, at the end of Asher Road in Welcome Bay) was 22o Celsius, and the maximum temperature in this borehole was 42oC at 300 metres below ground level.

Based on all available data to date, it is therefore concluded that the likelihood of geothermal activity within the design depth of 75 metres for the HDD option below current seabed level is very small.

3.3.5 Earthquake Hazards

Earthquake hazard is one of the key geotechnical risks for all the harbour crossing options. All of the harbour crossing will be subject to this hazard, however, relative risks are lower (namely, residual risk following design) for some options than others. Option-specific assessment is as follows.

The recognised earthquake hazards are: -

• Ground shaking - resulting from either a local earthquake event or a larger event some distance from Tauranga. The inertia from ground shaking exerts additional dynamic loads during an earthquake

• Liquefaction - is a process where soil looses its inherent shear strength due to a significant increase in pore pressures due to ground motions (namely the soils behave as a liquid)

• Ground deformation – end effect following ground shaking and/or liquefaction process for example, settlement and lateral movement or spreading.

Liquefaction can lead to the following effects, which can cause damage:

• Ground damage being subsidence, lateral spreading and causing soils to flow leading to failures;

• Foundation failure due to reduction / loss of bearing capacity and loss of lateral restraint to piles;

• Settlement of structures on liquefied materials;



Of particular note to buried structures is the increased risk of buoyancy, foundation failures, loss of bearing pressures and settlements. Areas of “localised liquefaction” can expect ground subsidence varying from none to small namely less than 100 mm. The areas of “extensive liquefaction” will generate ground subsidence greater than 300 mm and possibly over 1000 mm in places (Brabhaharan et al, 2003).

Lateral spreading can occur along river / stream banks and coastal areas, where the liquefied ground could move upwards towards the free surface. Any embankments or bridge abutments built on liquefiable ground are also likely to be affected.

Where the pipeline traverses through non-liquefiable to liquefiable soils (for example through Ignimbrite soils to areas of estuarine deposit), differential movement of the pipe is likely and may even result in pipe breaking during a strong ground shake.

Design Requirements

The Australian/New Zealand Structural Design Actions Code AS/NZS 1170:2002-2004 (the Code), written for Structures, states that a structure shall be designed and constructed in such a way that it will, during its design working life, with appropriate degrees of reliability, sustain all actions and environmental influences likely to occur. The design requirements for the structures take into consideration various static and dynamic loads from the environment that it is built in, to ensure the design meets some minimum performance requirements.

The design requirements include consideration of the importance level of the structure, thus driving the Annual Probability of Exceedance for various external forces, such as earthquakes. Table 3-1 depicts important levels for building types (AS/NZS 1170:2002-2004).

Table 3-1 Structure Importance Levels for Earthquake Assessments

Importance Level

Comment Examples Consequence of Failure

1

Structures presenting a low degree of hazard to life

Farm buildings and isolated structures

Low consequence for human life

2 Normal structures Single family dwellings and car parks

Medium consequence for human life or considerable economic, social or environmental consequence

3 Structures as a whole may contain people in crowds

Buildings with more than 300 people and public facilities NOT designated as post-disaster

Wastewater treatment and other public utilities not designated as “post-disaster” (namely not a “lifeline” asset)



Importance Level

Comment Examples Consequence of Failure

4 Structures with special post-disaster functions

Facilities designated as essential facilities and with special post-disaster function

High consequence for loss of human life or very great economic, social or environmental consequences. Utilities required as a backup for buildings and facilities of Importance Level 4. Facilities containing hazardous materials capable of causing hazardous conditions that extend beyond the property boundary.

5 Special structures (outside scope of standard)

Structures that have special functions or whose failure poses catastrophic risk to a large area or a large number of people (100,000) e.g. dam failure

Exceptional consequence of failure

The importance level of the Southern Pipeline and its associated structures was determined to be Level 4, as the infrastructure has a 1:100 year design life and would be designated post-disaster of having consequences of failure being “very great economic, social or environmental.”

Based on this importance level the Code requires the structures for the Southern Pipeline to be designed for an earthquake event with an annual probability of exceedance (APE) of 1/2500 (or 0.04%) for the Ultimate Limit State (namely, avoidance of structural collapse). A return period of 25 years is required for a Serviceability Limit State (SLS1) requiring avoidance of damage that prevents a structure from being used as originally intended without repair. For Importance Level 4 there is an additional more onerous Serviceability limit State (SLS2) requiring critical facilities to remain operational following a 1/500 (or 0.2%) earthquake event.

The difference between the SLS and ULS is that the structure is still operational after the SLS event but more serious damaged is acceptable after the ULS. The Southern Pipeline will be designed to both SLS and ULS requirements.



Peak Ground Acceleration

There are no known active faults within the pipeline route corridors. The closest active faults are some 20 to 30 kilometres distant (Kerepehi Fault to the west and offshore faulting, such as Mayor Island Fault). Thus the seismic hazard is governed by ground shaking from crustal faults some distance from Tauranga and from deeper subduction event earthquakes. The Tauranga region is located within Seismic Zone 2 (GNS 2000).

Seismic resistance design of structures is typically based on an annual probability of exceedance of a 1/500 (or 0.2%) and a 1/2500 (or 0.04%) event required by the Code. The site-specific ground motions (namely, peak ground acceleration) is calculated using a probabilistic hazard assessment techniques where a variety of earthquake sources, their recurrence intervals and maximum fault earthquake motions are considered, in combination with underlying soil types. In NZ there are commonly three or four potential earthquake sources:-

i) Distributed seismicity for the upper crust (lower magnitude, but much more frequent earthquakes);

ii) A discrete fault rupture source;

iii) The subduction boundary interface; and

iv) The subducted crust.

Thus, the resultant ground shaking (ground response spectra) results are estimated from the probabilistic hazard assessment. A site-specific assessment would be ideal for determining peak ground acceleration for the respective annual probability of exceedance (return period). In the absence of site-specific ground motion response spectra, the design code could be utilised, which is generally conservative. At this stage no separate site specific assessment has been done for the Southern Pipeline.

The subsurface ground conditions are one of the key parameters driving the probabilistic hazard assessment, as the ground conditions can either amplify or dampen the transmitted energy from the epicenter of the earthquake. The Code thus refers to various soil classes to determine the likely peak ground acceleration for a given return period. The ground conditions underlying the Tauranga harbour are interpreted to be soil class D (deep soil conditions, as defined by the Code)

In absence of a site-specific study, URS have reviewed the following information to date to determine the likely peak ground accelerations for this project:

i) NZS 1170.5:2004 – New Zealand earthquake structural design actions

ii) Western Bay of Plenty Lifelines Study (Brabhaharan et al, 2003) providing an area-specific assessment of earthquake hazard for the Tauranga region.

iii) Site-specific studies undertaken for the Tauranga Hospital by Institute of Geological and Nuclear Sciences in 2005; and

iv) Site-specific assessment undertaken by Beca for the Tauranga Harbour Link Project in 2006.



Table 3-2 depicts the peak ground accelerations recommended by various sources.

Table 3-2 Summary of Peak Ground Accelerations

Source Soil Class (NZS1170.5

:2004)

Peak Ground Acceleration (PGA) (1/500 or 0.2% APE

event, SLS2)

Peak Ground Acceleration

(1/2500 or 0.04% APE event, ULS)

NZS 1170.5: 2004 D (deep soil) 0.22g 0.40g

Brabharan et al (2003)

C (shallow soil) – uses old code

0.35g 0.40g

IGNS (2005)* D (deep soil) 0.20g* 0.30g*

Beca (2006) D (deep soil) Not quoted 0.345g

* Used in this report

Table 3-3 shows that the site-specific studies generally prove that the Code (NZS 1170.5: 2004) peak ground acceleration is conservative. The Code allows usage of the lower value between the Code and site-specific seismic assessment.

The IGNS 2005 site-specific analysis undertaken for the Tauranga Hospital was chosen for the Southern Pipeline analysis at this stage of the project. The site-specific studies undertaken for the Tauranga Harbour Link project would be more relevant for the harbour crossing. URS are awaiting additional information to review this assessment. The present assessment will thus be reviewed during the detailed design stage for the Southern Pipeline.

Liquefaction Assessment

Liquefaction is defined as the transformation of a granular material from a solid to a liquefied state as a consequence of increased pore water pressures and reduced effective soil stress (Marcuson, 1978). Increased pore water pressure is induced by the tendency of granular materials to compact when subjected to cyclic shear deformations from an earthquake. The change of state occurs most readily in loose to moderately dense granular soils with poor drainage such as silty sands, or sands and gravels capped by or containing seams of impermeable sediment.

There is currently no New Zealand design code specifically for liquefaction. In the absence of a liquefaction code it is common practise in NZ to use AS/NZS 1170:2002 to 2004. The bridge design however IS covered by the Code and therefore consideration of earthquake (including liquefaction) effects is implicit in the design.

A liquefaction assessment is chiefly based on empirical correlations with observations made to date by various authors in various countries. The likelihood of liquefaction is generally assessed based on shear strength (consistency) of soils and grain size analysis. It is known that uniformly graded loose sands are



highly susceptible to liquefaction where as stiff clay deposits (namely, cohesive soils) are unlikely to liquefy. In other words, an increase in percentage content of silt and clay sized particles reduces the likelihood of potential liquefaction.

The liquefaction assessment is based on both soil strengths and grain size (namely the engineering behaviour) of the soils. The assessment was undertaken for both 1/500 (or 0.2%) and 1/2500 (or 0.04%) APE events with peak ground accelerations shown in Table 3-2.

1. Assessment based on grain size distribution

– As part of extensive laboratory testing carried out during our geotechnical investigations, URS have undertaken several particle size distribution tests of recovered soils.

– Based on grain size distribution alone and using published information (Tsuchida et al), it was found that 90% of soil samples tested for all boreholes fall within ‘most liquefiable’ soils and 95% of soil samples fall within ‘potentially liquefiable’ soils. Refer Appendix J, Volume 3 for the assessment charts of boreholes BH1 to BH6.

– Therefore for the assessment based on the grain size distribution alone, most of the soils (even at depth) underlying the Tauranga Harbour are ‘potentially liquefiable’ soils.

– It should however be noted that the soil strengths play a key role in liquefaction process as dense sands are already in a well-consolidated stage and hence do not allow pore pressure increase and also do not self-compact due to their higher relative density.

2. Assessment based on soil strengths and grain size

– In this method the cyclic stress ratio (CSR, demand) is calculated using the peak ground acceleration due to an event, and the cyclic resistance ratio (CRR, capacity) is calculated using the available strength of soils. Based on observations made during past earthquakes, an assessment can then be made to verify whether liquefaction is likely to occur. A factor of safety is calculated by dividing (CSR, demand) by (CRR, capacity). A factor of safety of less than 1 is indicative that liquefaction is likely to occur (NCEER, 1997).

– Assessment was carried out for both 1/500 (0.2%) (PGA of 0.20g, where “g” is the acceleration due to gravitational force) and 1 /2500 (0.04%) (PGA of 0.30g) annual probability of exceedance events. Assessment was not undertaken for the 25year return period earthquake (PGA of 0.078g) as it would not generate enough load cycles for the liquefaction to occur.

– Assessment was undertaken for each borehole (BH1 to BH6) by correcting SPT ‘N’ values for overburden pressures and percentage silt/clay sized particles.

– Analyses indicated that depth of liquefiable soil varies from 6metres to up to 30metres below seabed level 1/500 (0.2%) and 1 /2500 (0.04%) annual probability of exceedance events.



– Analyses of boreholes BH4 to BH6 within the main channel indicate relatively shallower depth (6metre to 10metre) of liquefiable soils where as BH1 to BH3 over the mudflats indicate 15m to 30m of liquefiable soils.

– Settlement estimates based on published data (NCEER, 1997) indicated settlements in the order of 200mm to greater than 1000mm, following an earthquake event.

– It is important to note that due to highly variable soils (grain size and shear strength), settlement and/or floatation of the seabed following an earthquake will not be uniform across the harbour.

A 100 year design life asset such as the Southern Pipeline needs to be designed to be capable of withstanding an earthquake event of equivalent magnitude to the 1987 Edgecumbe earthquake.

3.4 Geotechnical Assessment of Proposed Options

This section provides a geotechnical assessment for the proposed harbour crossing options.

3.4.1 Option 1: Bridge and Embankment

Bridge

The conceptual design for the proposed pipe bridge is based on a single pier founded on a pile cap resting on smaller (namely, 600mm) diameter piles. The pier cap is proposed to be constructed above mean high water mark for navigational safety reasons.

The piles would be founded at least 4 to 8 pile diameters within the dense (SPT ‘N’ greater than 50), non-liquefiable sands at a varying depth between 15 metres and 40 metres across the main channel. This is to ensure that the bridge foundations and hence super-structure are not compromised during the design earthquake event. The piles would be designed based on skin friction and end bearing capacities, taking into account possible reduction in support during and after an earthquake event.

Seabed scouring effects of the proposed new bridge piers on the existing railway bridge piers are covered in ASR’s report in detail and in the Bridge Option section of this report. It was noted that provided new piles are constructed at least 50 metres away from the existing bridge, scouring effects are negligible. However, should the bridge be constructed 30 metres to 40 metres from the existing, some scour effects on the existing railway bridge are likely, but manageable by providing some scour protection to the existing railway bridge piles.

The current available technology allows the design of the bridge to sustain the design earthquake event such that the lifeline asset would still be operational post-earthquake.



Embankment

The conceptual design of the proposed embankment widening is currently to simply ‘place and compact’ selected granular material. This is to ensure minimal disturbance to the existing railway embankment so that it will remain fully operational during construction.

The subsoil conditions underlying the proposed alignment indicate that the construction methodology is viable. However, settlement of the new embankment is likely to occur owing to the presence of loose to medium dense sands. It is also noted that 90% of the likely magnitude of the settlement will occur immediately following construction. Therefore it is recommended that the embankment should be constructed during the earlier stages of harbour crossing construction phase to ensure settlements would occur prior to commissioning of the pipeline.

Liquefaction analyses carried out indicates that liquefaction of the ground under the seabed to a depth of 15 metres to 30metres is likely to occur along the proposed embankment alignment. Any mitigation design for the embankment would be cost-prohibitive. This means that the embankment is likely to settle 200 mm to 1000 mm along its entire length following an earthquake event. There is also a possibility of lateral spreading of the embankment due to the underlying liquefiable soils. It is therefore assessed that the pipeline could be damaged within the embankment and/or where the pipe lands on the embankment from the pipe bridge, dependant upon the magnitude of the differential settlements.

Overall Assessment of the Bridge/Embankment Option

1. The proposed separate bridge could be designed to withstand the design earthquake event to a high degree of certainty, based on currently available understanding and technology for design and construction. This will ensure that the bridge would be operational following the design earthquake event.

2. The construction equipment and experience for the bridge construction is largely available locally, within New Zealand.

3. The embankment construction is viable using the available technology with minimal disturbance to the existing railway embankment.

4. Static settlement of the embankment upon construction is likely and the majority of the settlement would occur during and immediately after construction.

5. Liquefaction of the underlying soils is likely to occur with a consequence of settlement and/or lateral spreading of the embankment. Any mitigation design would be cost-prohibitive. Damage to the pipeline could occur within the embankment and/or where the pipe lands on the embankment from the pipe bridge, dependant upon the magnitude of differential settlements caused by an earthquake.

6. The overall geotechnical risks for this harbour crossing option are considered to be ‘relatively’ low compared to the submarine and HDD options, as any damage repair works could be carried out quickly and economically.



3.4.2 Options 2, 4 and 5: Submarine Pipeline Options

Constructability

The submarine pipeline construction methodology is detailed in the Submarine Option section 8 of this report. The proposed construction methodology was verified by a Contractor and was deemed viable.

The pipeline construction methodology within the main channel comprises ‘bottom pulling’ the pipeline after assembly of the pipe string on the widened railway embankment before lowering on to the seabed. The pipe would be progressively lowered into the seabed by either trenching or “jetting” the soils under the pipe. The resultant trench is expected to self-cover (and the surface “self-heals”) due to ongoing sediment transportation occurring at the seabed level.

The geotechnical aspects of the three submarine pipeline options are summarised below:

Option 2: Submarine and Embankment – The depth of loose to medium dense recent sand sediments along this route varies from 3 metres to 6 metres. There is soft estuarine mud underlying the sand layer. Should this soft layer be exposed during construction of the pipeline seating of the pipeline at the final level could become difficult.

The pipeline at the eastern end (Matapihi) would be constructed within a widened embankment adjacent to the existing railway embankment. This widened embankment would be used for pipe assembly during installation of the pipeline in the main channel.

Option 4: Submarine Direct – The depth of loose to medium dense sand sediments along this route varies from 3 metres to 16 metres below the seabed. The pipeline along the main channel would be constructed using the methodology discussed above for Option 2.

The inter-tidal mudflats from BH3 location to the end of Matapihi do not allow for any barge for the pipe placement access due to shallow depth of water. This means that the construction methodology along this section would need to be two, 300 to 400 metre long temporary trestles (like a pier of wharf) or embankments. Embankments are considered not desirable due to potential environmental effects. The trench for the twin pipes in the inter-tidal areas would then be excavated from the trestles. This excavation may need to be sheet piled to limit the excavation width and to stop running sands/sand boiling. The pipeline would be buried beneath the seabed and the temporary trestles and sheet piles would be removed after construction.

The buried Telecom line from the Memorial Park to Matapihi will need to be crossed at the Matapihi end of the route. Locating the cable during construction would be difficult as the Telecom were not able to locate the cable within the harbour during geotechnical investigations. Should this option be chosen, locating the cable and protecting it during construction could be a major issue.



Option 5: Submarine Memorial to Matapihi – The subsurface investigation along this route was carried out during our previous geotechnical investigations using HDCP testing. The ground conditions along a third of this route (from Memorial Park end) are inferred to have a crest of sand sediments of 0.5 metres up to 1 metre thick underlain by very soft to soft estuarine mud sediments. The rest of the pipeline route is inferred to have similar ground conditions as for other submarine options.

The section of the pipeline along the main channel would be constructed using the jetting technique discussed in Option 2. However the presence of soft mud beneath the sand could pose some difficulties and is likely to result in plumes of mud/sediment in the harbour during construction, which may form preferential sediment transport plumes.

The both ends of the pipeline within the intertidal mudflats (both at Matapihi and at Memorial Park ends) would need to be constructed using the trestle technique discussed for Option 4 above. However, presence of soft sediments could result in delays and could result in an increase in cost and risk.

The Telecom cable within the harbour could pose difficulties during construction as discussed for Option 4 above.

On-going settlement/Floatation Risks

Any one of the submarine pipeline options would be subject to ongoing settlement and floatation risks following construction. Settlement risks originate from the following scenarios:

• The construction methodology proposed within the harbour has an inherent risk of non-uniform seating of pipeline. Should this occur, there could be ‘long spans’ of pipeline not being supported resting, thus resulting in extra pipe pressures and likely differential settlement. This risk would be able to be minimised by design and careful on site construction supervision.

• The Tauranga Harbour is an aggressive environment with mobile sands. Settlement from the ongoing material build up of the harbour (assumed to be 1 metre over the pipeline life) due to rising sea levels, is estimated to be in the order of 300mm to 600mm. It should be noted that settlement is likely to be differential owing to variable subsurface ground conditions.

• Settlement following liquefaction is likely as the loose sediments along the proposed route alignments compact following the release of excess pore pressures. The settlement following liquefaction is often difficult to estimate with any certainty owing to variable ground conditions and empirical relationships available to date.

Floatation risks originate from the following scenarios:

• Floatation during normal operations when the pipeline is empty. The pipeline would be designed to provide adequate protection against floatation during empty conditions. The concrete cover weight will need to be balanced such that it does not cause any settlement during normal flow conditions.



• Floatation risks can occur during the liquefaction process in the event of an earthquake. The floatation risk is not ‘uniform’ along the pipeline route owing to various subsurface (grain size and shear strength) ground conditions. This matter is discussed in the next section.

Liquefaction damage

It was determined during the liquefaction assessment that even a 1 /500 (0.2%) APE event earthquake could cause liquefaction of underlying soil within the harbour. The liquefaction process could result in floatation and/or settlement of the pipeline during and post-earthquake causing pipeline damage, possibly in several locations. The repair of such damage would be expected to take several weeks due to access difficulties. For option 2, the embankment could settle due to settlement/lateral spreading.

It is often difficult to estimate likely settlement/floatation with certainty due to variable ground conditions and empirical correlations used.

Overall Assessment

1. The construction of the pipeline along the main channel would be easy to construct compared to the mudflats.

2. The presence of soft estuarine mud below the sand crust layer is problematic as if the pipeline trench breaks into this layer during construction, there are potential project delays and cost escalation risks. This principally applies to Options 4 and 5.

3. A high level of construction supervision will be required during pipeline installation to ensure that no long unsupported pipeline spans occur which could subsequently cause operational problems.

4. Settlement and floatation risks are apparent during and post-earthquake. It is often difficult to estimate settlement/floatation due to variable ground conditions and empirical correlations being used.

5. The liquefaction process could result in floatation and/or settlement of the pipeline during and post-earthquake causing pipeline damage, possibly in several locations. The repair of such damage would be expected to take several weeks due to access difficulties.

6. The overall geotechnical risks for the submarine pipeline options are higher than those for the HDD and bridge options, in that order.

7. Exposed pipe can be subject to flow induced oscillations, resulting in pipe failure.



3.4.3 Option 3: Horizontal Directional Drilling Option

Constructability and Associated Geotechnical Risks

The HDD pipeline would be drilled from the western end of Matapihi Road, exiting at the intersection of Devonport Road with First Avenue (refer the Drawing on page 8-2 for schematic HDD long section details). Based on data provided by a specialist HDD contracting firm the pipeline would be installed at 10o to horizontal at the entry, straightening once reaching the target depth, and exiting at 15o at the City end.

The construction methodology is somewhat similar to drilling a vertical borehole. It is proposed to commence drilling with a smaller diameter pilot hole, followed by several (5 to 7 times) reams of larger diameter. Upon drilling to the target drillhole diameter, the pipe (already assembled in 250 metre to 300 metre long sections) would then be welded into one length and pulled through, preferably within a 24 hour period.

The main risk during construction would be during drilling where an unsupported hole might collapse during either one of the reams or during the time when the assembled pipe is being pulled, thus resulting in project delay and possible cost escalation.

The current phase of detailed geotechnical investigations were undertaken to determine ground conditions for the proposed HDD option. Based on the subsurface ground conditions, it is our opinion that the undifferentiated Ignimbrite layer founded between 52metres and 75metres below current seabed level would be suitable for an HDD hole during drilling. This was based on the fact that the sands and silts within this layer are partially, to fully welded, thus exhibiting apparent core cohesion upon soil recovery. In addition, the recovered soil core did not have any bedding and/or fractures which, if present, would accentuate the possibility of drillhole collapse.

The loose to medium dense and dense sands above this layer within the recent sediments and reworked volcanic sediments are considered unsuitable to self-support a horizontal drillhole. This opinion is based on the recovered soil core which did not have any core cohesion when unconfined within the corebox, namely the core could be broken with finger pressure. The drill hole would need support where the water pressure is equal to or less than soil shear strength. It is therefore recommended to case both ends of the HDD option drillhole to minimise the risk of hole collapse.

The geotechnical information was reviewed by a specialist HDD contractor who confirmed that the pipeline construction using HDD technique is viable. Due to the specialist nature of the HDD work, installing the pipeline using HDD will need to be done under a design/build procurement process.



Liquefaction Damage

The depth to liquefiable soils underlying the harbour is assessed to be varying between 6 metres to 30metres below seabed. Based on the liquefaction assessment undertaken, pipeline damage would occur where the pipeline traverses through different geological layers particularly at the Matapihi end of the harbour. The risk chiefly depends upon the ‘relative’ movement of liquefied and non-liquefied soils along the length of the pipeline. Should the differential movement between these layers be significant and beyond the allowable ultimate pipe stress, pipeline damage is likely. The estimated total movement is between 200 millimetres to 1000 millimetres (the higher figure being in the mudflat areas).

The required excess soil pore pressure for significant movement to occur at depth is directly proportional to the available strength of the soil and effective stress. Thus, the potential for significant movement increases with shallower depth. Based on preliminary analysis, it is thus considered that there is a higher risk of pipeline damage within the top 10metres of the buried pipe and the risk of pipeline damage at the boundaries between liquefiable and non-liquefiable soils is considered low.

Liquefaction damage over the remainder of the HDD pipeline length at depth (over 30 metres) is considered unlikely.

Any mitigation design against liquefaction for HDD option is cost-prohibitive. However, consideration could be given to allow for any differential movement at target depths following detailed assessment during detailed design.

Any post-earthquake repair works to the damage would however be expensive if not impractical owing to the access depths required in the most likely area. Repair options could include re-lining the inside of the pipe dependant upon the level of damage. A new hole may have to be drilled if the pipeline cannot be lined or repaired from the surface.

Pipe floatation could also occur at the Matapihi end where the pipeline has minimal ground cover during liquefaction process. The risk could be minimised with adequate engineering.

Overall Assessment

1. The likelihood of settlement/floatation during static conditions is low and adequate engineering would minimise the risk.

2. The majority of risk would be during construction, due to a possible drillhole collapse prior to pulling the pipe. There is a risk of possible project delay and cost over-run should this event occur.

3. Liquefaction damage could occur at points where the pipeline passes through liquefiable and non-liquefiable soil boundaries when the differential ground movement exceeds ultimate pipe pressures.



4. Allowance could be made for some differential movement during detailed design. Damage repair works could include re-lining the inside of the pipe provided the damage was not severe. In the event of significant damage, post-disaster repair work would be very difficult if not impractical and a new hole may have to be drilled.

5. Pipe floatation could also occur at the Matapihi end where the pipeline has minimal ground cover during liquefaction process. Engineering design can minimise this risk.

6. The overall geotechnical risks are higher than the bridge option, but lower than that for the submarine option.



3.5 Summary of Geotechnical Assessment for Various Options

Table 3-3 summarises the geotechnical assessment for each option.

Table 3-3 Summary of Geotechnical Assessment

Harbour Crossing Option

Key Benefits Key Risks

Option 1 Bridge and Embankment

• The bridge can be designed to withstand the design earthquake event to a higher degree of certainty, based on currently available understanding and technology for design and construction

• Damage repairs post-earthquake could be undertaken relatively quickly and economically.

• Static settlement of the new embankment following construction is likely, but will occur quickly after construction.

• Liquefaction of the underlying soils is likely to occur with a consequence of settlement and /or lateral spreading of the embankment. Damage could occur at some points along the pipeline where differential movement is maximum (for example at the bridge/embankment interface).

Options 2 Submarine and Embankment

• Damage repairs post-earthquake are ‘relatively’ quick and easier, when compared to HDD option due to relative ease of access.

• Should the pipeline trench cut into the lower level of soft estuarine mud this could result in possible project delay, cost escalation and risk of pipeline settlement.

• Ongoing risk of settlement and floatation during static condition always exist (even after design) due to variable ground conditions and construction methodology.

• Liquefaction of underlying soil is likely, resulting in settlement and/or floatation of the submarine pipeline and embankment. The possible damage could occur at several points due to differential settlement and floatation risks across the harbour.

• The combined risk of liquefaction damage for the submarine and embankment is higher than for the bridge and embankment or HDD option

Option 3 Horizontal Directional Drilling

• The likelihood of settlement/floatation during static conditions is low.

• Should the drillhole collapse during construction, this would result in possible project delays and/or cost escalation

• Liquefaction damage could occur in the top 10 metres of soil at the Matapihi end.

• Damage repair works post-earthquake is likely to be time consuming and expensive. Installation of a new pipe maybe required.

Options 4 and 5 Submarine Direct and Memorial Park to Matapihi

• Same as for option 2 • All of the above for Option 2 and; • Method of construction within the inter-tidal

mudflats have high risk of project delays and cost escalation due to variable ground conditions

• There is an increased risk of settlement following construction for Option 5 on the Memorial Park side due to possible formation of a preferential flow path/plume for sediment transport.

• The buried Telecom cable crossing within the harbour could poses issues during construction.

SECTION 4 Hydrodynamic Investigations


4 Hydrodynamic Investigations

4.1 Introduction

A field investigation and numerical modelling study was undertaken by ASR Limited (ASR), a specialist marine consulting and research company, to determine the potential hydrodynamic effects associated with construction of a harbour crossing. The harbour crossing options assessed in detail by ASR were:-

(i) Option 1 – Pipeline bridge built adjacent to the existing Ontrack railway bridge (~500m long); and

(ii) Options 2 and 5 – Two submarine pipeline options at different distances south of the existing bridge.

Option 3: HDD did not need to be investigated due to its depth below the seabed. Option 4: Submarine Direct was introduced after the completion of ASR’s report.

The following is a synopsis of the full report, a copy of which is in Appendix F in Volume 2.

4.2 Existing Conditions

Numerical modelling showed that the currents at the study location near the rail bridge exceed 0.9 metres per second. The existing causeway and the bridge piers create flow constriction and increased current velocity across the channel. The estimated net sediment transport through southern Tauranga Harbour near the rail bridge is a maximum of 20,000 cubic metres per year. The sediment transport and hydrodynamic model results, as well as field observations, indicate that the estuary in the study region is relatively stable and presently close to being in “dynamic equilibrium”. The estuary’s known tendency to be relatively stable, relates not only to the equilibrium morphology but also to the low net transport rates, particularly in the presence of shell lags (areas of shells on the seabed). As the grain sizes and current velocities determine the sediment fluxes, subtle variations in grain size can lead to equilibrium conditions, where changing grain sizes can balance out the effect of changing currents. In the presence of new man-made structures, a slightly changed dynamic equilibrium would be anticipated to occur.

On the inter-tidal zone south of the causeway, flood currents are blocked by the presence of the causeway, while the stronger ebb currents result in net sediment transport to the north. In the channel offshore, flood dominance completes a sediment re-circulation loop, which exists south of the rail bridge on the eastern side of the channel. In terms of construction impacts, any interruption to sediment transport within this loop is likely to be felt over the full span of the loop, and so the study considered the potential effects on sediment dynamics in detail.



4.3 Assessment of Option 1: Bridge

Examination of the seabed near the existing rail bridge piers shows that the bridge has caused localised scour which appears to have reached equilibrium, but has not affected the overall sediment dynamics of the region. The modelling and data analysis has described the nature of the scour holes and the likely spatial influence of the bridge piers. The mean maximum scour depth observed is 2.15 metres and the average total length of the scour holes is 53 metres. With similar sized piers, it can be assumed that the proposed bridge piers for the Southern Pipeline pipe bridge are likely to create scour depths similar to the observed scour holes at the railway bridge.

To add a degree of caution, it is ASR’s opinion that either:

a) The separation between the bridges be increased to 50-60 metres from the proposed distance of 40 metres; or

b) An allowance is made to mitigate any unforseen impacts by placement of scour protection at the existing rail bridge piers, if monitoring shows that such placement is warranted. The results in this study indicate that scour protection would be highly effective.

At 40 metres, minor interaction between the scour holes would be anticipated. However, while this interaction may deepen the edges of the existing holes, the new scour hole is not predicted to penetrate all the way back to the existing railway bridge piers. Therefore a 40 metre spacing is achievable.

In terms of the hydrodynamic effects, the construction of the new pipe bridge is not expected to cause any unforseen problems.

The existing causeway has caused some changes to the inter-tidal flats. However, a minor widening of the existing causeway by approximately 12 metres (as proposed) is not expected to have additional physical impacts. Notably, no lengthening of the causeway, into the channel is proposed, which would be of more concern.

The study has shown that the proposed pipe bridge is unlikely to have any substantial effects on the physical environment. The existing railway bridge has caused localised scour which appears to have reached equilibrium and has not affected the overall sediment dynamics of the region. The same outcome is anticipated for the proposed pipeline bridge.

4.4 Assessment of Options 2 and 5: Submarine

The two submarine pipeline options considered in this report (Options 2 and 5) are predicted to alter the hydrodynamics and sediment transport in the main channel, but only at a very local scale. The impact of the pipe by trapping sand and current flows will be negligible, except locally at the pipe where currents passing over the pipe temporarily accelerate. It should be noted that if the pipe self-buried then the effects will be even smaller. No effects on the existing railway bridge are anticipated.



The northern submarine option near the railway bridge (Option 2) is found to be superior in relation to flow alterations, sedimentary impacts, visual appearance and boating safety. One negative influence of a surface placed southern submarine option (Option 5) is the identified potential for muds to build up in the zone between the pipe and railway causeway. These muds may degrade the inter-tidal zone, change the biota and potentially lead to higher pollutant contamination. From a hydrodynamic viewpoint the northern option (Option 2) is preferred for these reasons and because negligible effects are anticipated along this route.

Figure E1: Shaded relief map of the sea bed near the existing rail bridge across Tauranga Central to Matapihi peninsula and locations of the proposed pipeline bridge and submarine pipeline routes (Options 2 and 5)

Subsequent discussions with ASR identified the following additional matters:-

i. If route Option 5 (Memorial to Matapihi) were adopted then sediment plumes may result during the process of burying the pipeline, particularly if jetting were used.

ii. The route Option 5 had the potential to introduce a longer term weakness along the trench line far in the intertidal mud flat areas. Back filling with sand, of a particular designed grain size, would be required to minimise this effect but permanent “soft spots” along the pipe trench (and possibly at the trestle leg positions) may still exist. In addition there is a risk of the pipeline trenches forming a permanent preferential drainage pathway for incoming and outgoing tides.

2789600 2789800 2790000 2790200 2790400 2790600 2790800Easting (m)

638480 0

638500 0

638520 0

638540 0

638560 0

N or thi ng ( m )

abcdefghIj k lm

Pt. B B2 B3 B4 B5 B6 Pt. A

Pt. DC2

C3C4

C5C6

C7C8

C9C10

C11C12

C13C14

Pt. C

0 100 200 300 400 500

Scale (m)

Bridge Option

Submarine Pipeline Option 2

Submarine Pipeline Option 5



iii. The sand bank in the centre of the estuary that cuts across the proposed alignment moves over time and therefore there remains a potential for variable loads on a submarine pipeline in this area and a risk of exposing the pipeline.

SECTION 5 Environmental Investigations


5 Environmental Investigations

5.1 Introduction

Several environmental field investigations and desktop assessments were conducted as part of the assessment of harbour crossing options. These studies focused on the hydrodynamic (refer Section 4) and ecological aspects of areas of the harbour that will be of potentially critical importance in final option selection and pipeline design. The main studies conducted in this phase of the harbour crossings investigations were as follows:

• Harbour Hydrodynamic Modelling Study – conducted by ASR Limited, which is separately reported on in Section 4; and

• Intertidal Ecological Survey – conducted by the Cawthron Institute.

Key points from the Cawthron Institute Study are summarised below. The full reports generated by the studies are contained in Appendices F and G in Volume 2.

Further environmental investigations have been deferred until one of the harbour crossing options has been selected.

5.2 Intertidal Survey

Field staff from the Cawthron Institute conducted a sediment quality and ecology survey of intertidal areas of the harbour situated along access routes to be used for subsequent geotechnical investigations. The principal purpose of the survey was to identify whether there were sensitive species that could be significantly damaged by the overland movement of geotechnical investigation equipment. The survey was also designed to gather baseline data that, if required, could be incorporated into later impact assessments for the geotechnical works and for the pipeline installation itself. A summary of the survey’s main findings is provided below:

i) Two dominant habitat classes were identified in the survey area; sea grass (Zostera) beds and open sandy flats. Zostera was the dominant epiflora on the eastern bank of the harbour, but was limited to well defined beds. The western bank was classed as open sandy flat with sparse coverage of macroalgae.

ii) Sediments were uniformly firm, and consisted of medium to coarse sands with a low proportion of silt/mud. Organic content was low at all stations. Indicative metal contaminants were found to be well below ANZECC (2000) sediment quality guideline levels.

iii) No habitats or taxa of special scientific importance or rarity were identified by the survey.

iv) Sea grass beds of the type found in the harbour can be relatively sensitive to mechanical disturbance from which recovery might not be rapid. However, the fact



that only relatively small areas were expected to be impacted by the geotechnical investigations was predicted to aid subsequent regeneration.

v) Density of cockles (Austrovenus stutchburyi) was generally high at all sample stations but individuals in the typically harvestable size range were effectively absent. The species is believed to be widespread in Tauranga Harbour.

vi) Potential disturbance in the intertidal area from geotechnical investigations was expected to be localised to the area of drilling rig movement, and impacts from mechanical disturbance was considered likely to be limited in extent and relatively short term. Recovery of benthic fauna was expected to be fairly rapid considering the high densities of species and limited areas affected.

In response to a specific question raised regarding potential damage to cockles as a result of the movement of geotechnical equipment, URS conducted a limited sampling survey of sediments in the area around the geotechnical investigations. This survey compared numbers of live, undamaged cockles in samples of sediment taken from areas subject to movements of geotechnical equipment, with numbers of live undamaged cockles found in sediment taken from areas not subject to movement of equipment.

The live cockle counts in both were low with only a total of six cockles being found in the disturbed sub samples and two in the undisturbed sub samples. This may have been due to the location of the sampling site in comparison to cockle beds and the limited size of the samples however it does show live cockles were undamaged by the movement of the equipment. There was also no evidence of damage to live cockles in that there were no "cockle parts" in the samples.

Although these intertidal surveys related specifically to the geotechnical investigations (which have since been completed), they demonstrate that there are no areas of significant ecological sensitivity within the locality of the proposed harbour crossing.

5.3 Other Environmental Aspects

Other environmental aspects which have been considered within the assessment of harbour crossing options include:-

• Cultural effects;

• Landscape / visual impacts;

• Residential amenity;

• Property impacts;

• Accessibility; and

• Construction effects eg noise, dust, traffic.



These matters are discussed briefly within the following sections on each of the harbour crossing options, and are also incorporated within the Quadruple Bottom Line Assessment reported on in Section 12 of this report.

SECTION 6 Legal Aspects Relating to Land Access


6 Legal Aspects Relating to Land Access

Preliminary legal advice has been sought from Simpson Grierson on aspects relating to the use of land and seabed for the harbour crossing options. Their preliminary advice is summarised below.

6.1 Overview of Foreshore and Seabed Act

Each of Options 1-5 for the harbour crossing would involve passing either over, along or under areas of foreshore and seabed. Subject to limited exceptions, the foreshore and seabed is vested in the Crown and administered by the Minister of Conservation, under the Foreshore and Seabed Act 2004 (“FSA”).

The definition of “foreshore and seabed” in the FSA is a physical one, that is, the area of land between the line of mean high water springs and the edge of the territorial sea. In effect, it is the “wet” area covered by the ebb and flow of tides. Section 13(1) of the FSA has the effect of vesting the whole of that area in the Crown in fee simple, subject to the limited exception of “specified freehold interests”, which are:

a) any areas of “wet” land that are owned in fee simple in private ownership (namely not Crown or local authority ownership); and

b) Maori freehold land.

Therefore, a significant effect of the Act is to vest all areas of local authority land which lie beneath the line of mean high water springs in the Crown. This includes any parts of local authority titles which may have eroded. An example of this is the area of esplanade reserve immediately to the south of the harbour end of Matapihi Road. By comparison, any such private land which may have been eroded would not be affected, and the “wet” part of such titles would remain in private ownership.

It is not possible for the Crown to alienate any part of the foreshore and seabed now vested in it (which the FSA refers to as the “public foreshore and seabed”) except by way of:

a) a special Act of Parliament ; or

b) an authorised reclamation: however, even in that case, the maximum tenure allowed for under the legislation, even assuming a resource consent can be obtained for the reclamation, is a leasehold term of 50 years, with no right of renewal unless the applicant is a port company.

Therefore, none of Options 1-5, where they pass over or under foreshore or seabed, would be able to obtain “title”, nor could they be the subject of a legal easement, in the absence of special legislation, unless they are the subject of an authorised reclamation. The occupation rights granted by the coastal permit would in effect constitute the “tenure” for the pipeline in this respect.



6.2 Accretion

It is understood that an area of accretion (above the line of mean high water springs) exists immediately to the south of the railway embankment and to the north of the harbour end of Matapihi Road. Accretion occurs where the sea (including tidal water) recedes gradually and imperceptibly from the land. At common law, accretion belongs to the owner of the parcel of land to which it is added, and comes about at the time of accretion. If the area of land in question, which is affected by Options 1 and 2, is in fact accretion, then in effect it could belong to the owner of the adjacent property, which we understand is a Maori Trust. The accretion also adjoins rail land and other private property.

A landowner who is entitled to accreted land may apply to the District Land Registrar to have the accreted land recorded on the Certificate of Title. This is essentially the recognition of an existing ownership right rather than the transfer of ownership.

It therefore follows that the Crown would not have any rights to deal with the accreted land or grant rights over it, regardless of whether the land has been formally added to the adjacent title.

If the change is not slow and imperceptible, the doctrine of accretion does not apply and there is no change in ownership of the land. Therefore any reclamation, whether lawful or unlawful, could not be accretion and does of itself result in an expansion of the owner's entitlement in this case. Further, whether land is legally an accretion or a reclamation is a matter of fact, and requires expert verification.

In order to obtain a grant of suitable tenure, for example in the form of an easement, to enable the pipeline to be constructed and operated on that land, it may be necessary for the Council to assist the landowners in first applying for title to that area, as there is no means of compelling them to do so, and without the title position being resolved in this way it does not appear possible to provide any security of tenure for the pipeline along that route (Options 1 and 2).

While in theory it may be possible to utilise the compulsory purchase powers under the Public Works Act in relation to any land in private ownership, including Maori land, the Environment Court is likely to be reluctant to authorise such a compulsory purchase in the case of Maori land, where other options are available which would not involve such alienation.

6.3 Railway Corridor

In relation to the railway embankment, it is to be expected (although this would need to be checked) that the corridor defined by the embankment was vested in "Her Majesty the Queen for railway purposes", that is, the land in question was administered by the Crown under the railways legislation. Where the railway line is supported by a bridge structure, it is unlikely that the underlying seabed land will have that status, although again that needs to be checked.



Section 28(6) of the FSA states that the vesting of the public foreshore and seabed in Section 13(1) of that Act does not affect the status of land under pre-existing legislation, or any specific public purpose for which an area of the public foreshore and seabed has previously been set aside. This would seem to mean that, if there are any areas of the originally defined railway corridor which now lie below the line of mean high water springs, the status of those areas remains "railway land" and they continue to be administered under the railways legislation.

However this is by no means clear. It is possible that responsibility for those "wet" areas may have transferred to the Minister of Conservation, since:

a) the FSA binds the Crown (Section 6), and

b) Section 28(1) of the FSA states that the Minister of Conservation is entitled to exercise all the functions, duties and powers of the Crown as owner of the public foreshore and seabed.

Therefore, if it is intended to rely upon an area of the original railway corridor lying below the line of mean high water springs for the purposes of securing the route of Options 1 and 2 along a new embankment for the pipeline, it is recommended that this be clarified with the Department of Conservation and possibly also OnTrack. If those areas no longer have the status of railway land, then the land would be administered by the Minster of Conservation in the same manner as other areas of the public foreshore and seabed.

SECTION 7 Option 1: Pipe Bridge


7 Option 1: Pipe Bridge

7.1 Introduction

Two options to attach the proposed pipeline to a bridge have been considered. These are:-

i) To add the Southern Pipeline onto the existing railway bridge across the harbour; or,

ii) To construct a new pipe bridge adjacent, or near to, the existing railway bridge.

Preliminary discussions with Ontrack (New Zealand Railways Corporation) indicated that they were receptive to the pipeline being added to the existing railway bridge. This option was then rigorously investigated.

Investigations conclusively determined that the railway bridge was not suitable for the Southern Pipeline, primarily due to concerns relating to the structural integrity of the existing rail bridge with additional loading and the limited remaining design life for the rail bridge compared with what is required for the Southern Pipeline. The investigations and the principle reasons for not pursuing this option have been detailed to Council previously in several draft reports. A brief summary of findings from these reports is given in Appendix A.

7.2 Proposed Pipe Bridge

For reasons noted above, using the railway bridge to support the Southern Pipeline is deemed to be an unacceptable solution (unless a major bridge upgrade is carried out). As an alternative, the option to construct a new bridge adjacent to the existing bridge has been investigated.

7.2.1 Design Requirements

The design requirements for the new stand alone pipe bridge would be:-

i. The new bridge would need to support a steel pipe of about 1000 mm diameter and use as a pedestrian / cycleway would be included;

ii. The structure would have a minimum design life of 100 years, consistent with the required life for the overall pipeline. The structure is to be designed to resist earthquake and (earthquake related) ground liquefaction consistent with the pipeline design life;

iii. The resulting structure would be an asset of value – financial, social and environmental – to the city of Tauranga.



7.2.2 Pedestrian / Cycleway

In order to enhance the social and environmental value to the community the bridge would be designed to be dual purpose. The topside of the bridge would be designed for pedestrian and cycle use. The underside of the deck would be used to support the Southern Pipeline.

Concrete deck panels are segmented, and could be removed for maintenance of the pipe below. At 4.0 metres wide, the deck width corresponds to international practice for combined use cycle ways and pedestrian bridges as well as aesthetic requirements for users on the bridge. There would also be sufficient width for a lightweight access vehicle to traverse the bridge for maintenance.

7.2.3 Structure and Form

The presently proposed bridge shape and form has been designed by Gordon Moller, of Moller Architects. Copies of the plan and typical bridge section details from Moller Architects are at the end of this section.

Bridge piles would be founded about 30 metres below the sea floor. This would secure the piles in an area of sound volcanic material, and remove the risks from seismic liquefaction.

The foundation pile cap at water level is proposed to be architecturally shaped to conceal the smaller supporting foundation piles. The pile cap would be visible at all tides to minimise the risk of boats striking the pile cap, and to avoid having to use special boat “fender” structures.

The bridge material would be high strength concrete. The deck concrete in particular will be a modified ultra high strength concrete that offers high durability in a marine environment. The underside of the bridge will have the same clearance to the water as the existing rail bridge, under all tidal conditions.

7.2.4 Hydrodynamic (Tidal and Current Effects)

The new bridge will have some effect on the tidal scour of the estuary floor. There may also be some interaction between the existing railway bridge piers and the new bridge piers.

The report by ASR in Appendix F, states that the separation distance between the two bridges is preferably 50 – 60 metres, but that 40 metres could also be made to work. At 40 metres separation there is slight increased risk of estuary bed scour affecting the upstream railway bridge but this is considered to be manageable.

For architectural reasons a bridge separation not exceeding 40 metres is preferred. A larger separation between the rail bridge and the new bridge may cause the new bridge to overshadow the existing houses along The Strand.



The mitigation measures for a 40 metre separation would require further investigation to quantify the risk, or monitoring of the scour of the railway bridge piers. One option to mitigate scour effects is to place appropriately sized rock fill around the existing railway bridge piers during construction of the new bridge. Reducing the separation to less than 40 metres significantly increases the scour risks; unless a more extensive study is undertaken and specific purpose designed scour mitigation measures were provided for each rail bridge and pipe bridge pier.

7.2.5 Durability

The bridge beams and deck will be constructed from a modified ultra high strength concrete. This concrete has excellent durability characteristics in a marine environment. The concrete piles and piers will be constructed from standard concrete and follow current design codes to give a lifespan of at least 100 years.

7.2.6 Bridge Construction

Construction is expected to follow typical bridge construction techniques. Temporary platforms will be established for pile construction and foundation piles will be drilled from a barge mounted rig. Pilecaps and piers will be built in sequence over the piles, working from a barge.

The bridge deck could be placed by lifting from a barge, or sequential erection of beams by passing the beams from the embankment side along the bridge alignment. Lifting from a barge, despite relatively high tidal velocities, is probably the most likely option.

7.2.7 Embankment and Reclamation Construction

The proposed method of embankment construction is discussed in Appendix C. To link the embankment to the Matapihi Road end will require a small reclamation to widen the existing beach in this area (namely to the north of Matapihi Road towards the existing railway embankment). There are some legal issues over land ownership and relationship to the FSA which have been noted earlier in Section 6 and will require further investigation.

The methodology and construction issues outlined above for the embankment associated with Option 1 are also relevant to the embankment associated with Option 2: Submarine and Embankment. The issues associated with the submarine pipeline component of Option 2 are discussed in Section 8 of this report.

A small reclamation where Elizabeth Street meets the harbour may be required subject to detailed design of the proposed bridge / land interface at this point.



7.3 Other Environmental Considerations

The following is a summary of the main environmental considerations for Option 1: Bridge and Embankment.

Information concerning the harbour boating activity was obtained from the Harbour Master on 15 June 2006, the details of which are attached in Appendix B. This information was considered in all options.

Traffic:

• Increased foot and cycle traffic using Matapihi Road and crossing the harbour.

• Temporary effects relate to construction phase of 12 months, when there will be a significant increase in traffic along Matapihi Road to supply construction materials for the embankment and pipeline assembly areas.

• Due to the location of the pipeline bridge there will be traffic effects in Elizabeth Street and Devonport Road from Elizabeth Street to First Avenue which is not the case with the other options.

Visual:

• Long term permanent effects from bridge and embankment.

• Temporary effects relate to construction of bridge and embankment.

Noise:

• No long term permanent effects.

• Temporary noise will be from the construction of bridge. Pile driving is not envisaged. Noise not expected to be an issue as previous noise testing during the geotechnical work showed that the work could comply with the District Plan requirements, even if 24 hour operation was adopted.

Dust and Debris:

• No long term effects are expected.

• Short term construction dust and debris may occur. Debris management to prevent harbour contamination will be required.

Odour:

• No short or long term odour is expected, although an air valve maybe required at the high point on the bridge which may have some minor and very infrequent odour

Dredging and Marine Aspects:

• There are no regular dredging or dumping activities in any of the pipeline crossing areas of interest.

• No dredging as part of the construction is anticipated. There is the embankment construction (Matapihi end) in marine area and possibly a small reclamation at the end of the Strand where Elizabeth Street meets The Strand.



• There is a boat ramp 600m from the bridge, but it is rarely used. Although there are no restrictions for recreational boats to anchor, boats are unlikely to anchor. The bridge traverses an area identified as Moorings Zone in the Regional Coastal Plan.

• There is very little commercial marine traffic in the area where the proposed bridge is located. Boat traffic is limited to recreational boats and kayaks. The speed limit is 5 knots.

3.2.1 fatal flaw phase investigations -...

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