07-dg-section 7 works affecting sewers-version 0.0

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ADSSC/DG Design Guidelines Section 7 Works Affecting Sewers Rev: 00 Sep. 2010 Page 1 of 10

ABU DHABI SEWERAGE SERVICES COMPANY

(ADSSC)

DESIGN GUIDELINES

SECTION 7

WORKS AFFECTING SEWERS


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Abu Dhabi Sewerage Serv ices Company

(ADSSC)


DOCUMENT CONTROL SHEET

Revision No. Date Revision Description / Purpose of Issue

01September

2010First Issue

02

03

04

05

06

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08

09

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TABLE OF CONTENTS

1.0 INTRODUCTION ................................................................................................41.1 APPLICATION .............................................................................................4

2.0 PRELIMINARY SITE INVESTIGATIONS ...........................................................42.1 DETAILED INVESTIGATION ......................................................................42.2MITIGATION OPTIONS ...............................................................................5

3.0 REMEDIAL WORKS ...........................................................................................53.1 PIPE REPAIRS............................................................................................5

4.0 PERMANENT BUILDING WORKS .....................................................................54.1 WORKS ADJACENT TO SEWERS ............................................................54.2

WORKS OVER A SEWER ..........................................................................7

4.3 WORKS OVER MANHOLES/ACCESS CHAMBERS .................................74.4 VEGETATION AND PLANTING ADJACENT TO SEWERS .......................74.5 PERMANENT ACCESS ..............................................................................7

5.0 CONSTRUCTION WORKS ADJACENT TO SEWERS ......................................85.1 EXCAVATION, DRILLING AND COMPACTION .........................................85.2 TEMPORARY ACCESS/CROSSING POINTS ...........................................8

6.0 CHANGES TO FINISHED GROUND LEVELS ...................................................97.0 CLEARANCES FROM OTHER SERVICES .......................................................98.0 FINAL INSPECTIONS AND PERMANENT MONITORING ..............................10

8.1 CCTV ON COMPLETION ..........................................................................108.2 PERMANENT MONITORING.................................................................... 10

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1.0 INTRODUCTION

1.1 APPLICATION

This document, the Design Guidelines for Works Affecting Sewers, is for useby design consultants and contractors when carrying out the design andconstruction of projects, which may affect ADSSC public sewers. It presentsguidelines for the design, but it does not include design theories andmethods of calculation but instead describes local practices and criteria to beadopted.

Where any deviation from these criteria is considered necessary by thedesigner, ADSSC should be consulted and prior approval obtained.

The guidelines shall be used only by competent practitioner(s) / consultants,with due diligence and utmost care shall be taken. The design consultants /contractors shall be responsible for any damage to ADSSC s Asset(s).

2.0 PRELIMINARY SITE INVESTIGATIONS

2.1 DETAILED INVESTIGATION

A detailed investigation is required to determine and verify the location,material, depth, size and levels of existing sewers and pipelines and toenable the design for any protective measures to be undertaken. Theinvestigation should include but not be limited to the following:-

Liaison with other utilities to obtain as-constructed drawings and otheravailable information.

Examination of all records to determine the location of any existingutilities or services within the limit of the site.

Survey and setting out the locations and alignments of all existingservices.

The excavation of trial pits to determine the exact depth, materialcondition, size and levels of existing pipelines. A detailed methodstatement for the excavation of trial pits shall be submitted by the

contractor for approval by the ADSSC.

A CCTV (closed circuit television) inspection of the existing asset may berequired to determine the condition and location of the pipeline. This willdepend on the specific circumstances of the site and the requirement will beassessed on a case by case basis.


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2.2 MITIGATION OPTIONS

If works are proposed over an existing ADSSC sewer there are a number ofoptions to consider.

a) Avoidance of the sewer and the zone of influence by modifying the

building or structure plans.

b) Diversion of the sewer around the proposed structure such that the

foundations are not within the sewers zone of influence;

Proposal for the works shall be submitted for review and approval by ADSSC

prior to commencement of any work.

If the sewer is to be diverted, the cost of diverting the sewer must be borne

by the Contractor.

For any construction near an ADSSC Asset, a permission must be sought

from ADSSC and the planned works must conform to Sections 4.2 of this

document.

3.0 REMEDIAL WORKS

3.1 PIPE REPAIRS

If the pipe is not in good condition, as determined by joint inspection betweenADSSC and the Designer/Contractor, repairs must be carried out prior to anybuilding activities commencing on site. All costs for any remedial works shallbe borne by the contractor at agreed price.

4.0 PERMANENT BUILDING WORKS

4.1 WORKS ADJACENT TO SEWERS

Buildings or structures (and their foundations) constructed adjacent tosewers shall avoid the zone of influence of the pipeline. The zone of

influence is the area around an asset that is likely to be influenced bybuilding loads. The angle of the zone of influence line depends on the soilconditions. Reference should be made to Figure 4.1 for further details.

This rule would also apply to new sewers constructed adjacent to existingstructures where similar distances from the building should be maintained.


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Figure 4.1: Sewer Zone of Influence Line

If the sewer is located within the zone of influence the foundations shall betaken 1000mm below the influence line, as shown in Figure 4.2, or until arock stratum is reached, whichever is the shallower.

Figure 4.2: Piles Located with in the Zone of Influence


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Alternatively a concrete surround could be provided to the pipe and thestructure footing deepened to intercept the zone of influence line.

4.2 WORKS OVER A SEWER

Building constructed directly over a sewer are not generally permitted. Inexceptional circumstances proposal should be submitted for consideration.

4.3 WORKS OVER MANHOLES/ACCESS CHAMBERS

Sewerage manholes or connection chambers cannot be built over in anycircumstance. If the proposed structure cannot be altered, it may be possibleto relocate the access chambers with permission from ADSSC.

A minimum of 1.5 metres clearance is to be maintained from the edge of

manholes.

4.4 VEGETATION AND PLANTING ADJACENT TO SEWERS

In all cases the written approval of ADSSC is required prior to any tree orshrub being planted in the pipe easement.

As a general rule, to minimise root intrusion all vegetation shall be offset fromthe outer edge of the pipeline by minimum of 2.5 times the mature height ofthe tree or shrub. Refer to Figure 4.3 below.

Figure 4.3. Vegetation Offset Requirements

4.5 PERMANENT ACCESS

For permanent access or road diversions across an existing pipeline thedeveloper shall submit a detailed design for approval to ADSSC. The design


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should provide detail of any protective measures required and demonstratethat no additional load is transferred to the pipeline.

Detailed investigation to determine the exact location and condition of allpipelines should be undertaken in accordance with Section 2.1 above. Trialpits will be required to confirm the location and level of the existing sewer.Refer to Appendix A for the methodology for the excavation of trial pits.

5.0 CONSTRUCTION WORKS ADJACENT TO SEWERS

5.1 EXCAVATION, DRILLING AND COMPACTION

In cases where the works are within 50 metres of the pipeline the Designer /

Contractor must be able to demonstrate that ground vibration from suchactivities shall not exceed a peak particle velocity of 25 mm/s in any plane atthe closest point of the pipeline to the works. If the peak particle velocity ispredicted to exceed 25 mm/s the Developer shall include a reportdocumenting any special conditions or proposed adjustments that shall beincorporated into the activities to prevent possible damage to the ADSSCpipeline.

Trenching activities shall be designed to avoid adversely affecting theintegrity of the pipeline and the stability of the pipeline trench. Anyexcavations within 1 m of the pipeline shall be by hand.

No materials including spoil shall be stored on top of the pipeline without prior

consent of ADSSC.

5.2 TEMPORARY ACCESS/CROSSING POINTS

During construction activities, temporary access across existing sewers maybe required for heavy vehicles or equipment. Depending on the depth of thesewer and the anticipated loads, a reinforced concrete raft or equivalent maybe required.

It is the Developers responsibility to provide and maintain a crossing ofsufficient strength to protect the pipeline for the duration of the proposedcrossing activities. Table 5.1 below provides typical requirements for

guidance. Notwithstanding the above an application shall be made in eachcase by the Developer to ADSSC providing details of any protectivemeasures required and demonstrating that no additional load is transferred tothe pipeline.


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Vehicle Gross Weight Typical Crossing Requirement

6-10 tonnesTimber baulks to distribute the vehicle

weight.10-15 tonnes Reinforced concrete slab.

>15 tonnesSuspended crossing to support thepipeline.

Table 5.1. Temporary Access Cross ing Requirements

Detailed investigation to determine the exact location and condition of allpipelines should be undertaken in accordance with Section 2.1 above. Trialpits will be required to confirm the location and level of the existing sewer.Refer to Appendix A for the methodology for the excavation of trial pits.

6.0 CHANGES TO FINISHED GROUND LEVELS

If the construction works will permanently alter the finished ground levelsabove an existing sewer the Designer / Contractor shall ensure that aminimum cover of 1.2 m to the top of the pipeline is maintained. If this covercannot be achieved concrete protection for the affected section of pipelineshall be provided. Reference should be made to section 3.2.5 of the ADSSCSewerage System Design Guidelines (Section 3).

In determining the method of protection to be adopted it will be necessary toconsider the increased loadings on the pipe. It will also be necessary to raisethe level of manhole covers affected by the increase in ground level.

7.0 CLEARANCES FROM OTHER SERVICES

Clearance from other services shall be provided as detailed in Table 7.1below.

Utility Service

Minimumhorizontalclearance

(mm)

Minimumvertical

clearance(mm)

Relevant Standards

Gas mains 250ADNOC Design Guidelines

(June 20060

Telecommunica -tions conduits and

cables

150 50Standard Conditions for

Underground Duct Laying and

Associated Works (Etisalat)

Storm Water Drains 300Roadway Design Manual

Drainage

Electrical LVcables

50Standard Technical

Specifications for ElectricalWorks (ADDC)


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Utility Service

Minimum

horizontalclearance(mm)

Minimum

verticalclearance(mm)

Relevant Standards

Electrical Conduitsand Cables

500Standard Technical

Specifications for ElectricalWorks (ADDC)

Water Mains 2500 300 *Abu Dhabi Water & Electricity

Authority

* - Sewer shall always been constructed under the water mains.

Table 7.1 Clearance Requirements from other Services

8.0 FINAL INSPECTIONS AND PERMANENT MONITORING

8.1 CCTV ON COMPLETION

On completion of the work a CCTV (closed circuit television) inspection of thepipeline may be required to confirm the final condition and that the work hasbeen completed satisfactorily. This will depend on the specific circumstancesof the site and the requirement will be assessed on a case by case basis.

8.2 PERMANENT MONITORING

In order to monitor the condition of the asset in the longer term it may be arequirement to install permanent gauging equipment to monitor settlement ofthe pipeline. This will depend on the specific circumstances of the site andthe requirement will be assessed on a case by case basis.

END OF SECTION

07-dg-section 7 works affecting sewers-version 0.0

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