4.1 ADDITIONAL WATER RECLAMATION (NETWORK) DEPARTMENT, PUB’S REQUIREMENTS FOR SEWERS AND MANHOLES
Use approved flexible joints thickwall concrete pipes and vitrified clay pipes with flexible joints in accordance with the current Standard Specification and tests of the Water Reclamation (Network) Department, PUB.
Comply with the clauses laid down in the current "Standard Specification for Sewerage Works" published by Water Reclamation (Network) Department, PUB. The Standard specification may be obtained from the Water Reclamation (Network) Department, PUB.
4.2 EXCAVATION AND REFILLING
Carry out the excavation in accordance with Clauses 2.5 to 2.14 (inclusive) of the Specifications.
Carefully excavate and install timbering in accordance with the Drawings in such a manner that the toes of the runners are always at least 150mm below the bottom of the excavation.
Where necessary in order to keep the road open to vehicular and foot traffic, cart away excavated material from the trench as may be necessary so to keep the road open.
Should any of the sewer trenches be excavated to a greater depth than is necessary for the proper execution of the Works, fill in the part over-excavated with Grade 15 concrete or other approved hard material.
4.3 TIMBERING OF EXCAVATION
Brace all excavation adequately and securely with suitable timber using the methods indicated in the Drawings where necessary or otherwise approved by the SO Rep.
Notwithstanding the approval given, the SO Rep shall, where necessary, instruct the Contractor to improve, alter or strengthen the timbering from time to time. The Contractor shall be responsible for any injury to the Works and any consequential damages caused and any permission given by the SO Rep shall not relieve the Contractor from this responsibility.
In the particular case of timber to be left in trenches the class of timbering shall be approved by the SO Rep and this timber shall be cut off only after backfilling is completed, as indicated in the Drawings.
Take every precaution against slips and falls or other disturbances to both the temporary and permanent work in the excavations. If however any slips, falls etc should occur, at once make good the same including all surface restoration all to the satisfaction of the SO Rep. If any slip or fall disturbs or weakens any foundation or support of the Works or to existing structures mains etc or cause a space to be left outside the new work itself or causes excessive surface cracks to appear in the ground surrounding the excavation, execute such additional works or take such additional precautions as the SO Rep may require in consequence thereof and fill up the space so caused with concrete if necessary, as the SO Rep may direct. The Contractor shall be fully responsible for the reinstatement or repair to the disturbances or damages caused.
4.4 PILING OF FOUNDATIONS
Where bakau piles are indicated in the Drawings, they shall be of approved lengths and driven straight and in approved positions and to the full length of the piles or to the required set as determined by the SO Rep and any pile not correctly driven shall be duplicated. Where other types of piles are indicated in the Drawings, they shall be installed in the approved manner.
Where horizontal bakau rollers are specified they shall be laid horizontally in the bottom of the excavations to correct gradients in approved positions.
4.5 SEWER FOUNDATION
Lay pipes and concrete in every instance on an even and solid foundation. The pipes shall be laid evenly on the barrel at the required level. Hollows, voids or foreign material under the pipe shall not be allowed.
Complete the bedding to the correct profile as shown in the Drawings.
Provide all sections of the sewer with either hard filling, concrete base with/without piling as specified.
However, should the SO Rep decide to change the type of foundation after the close of the Tender, such change shall constitute a variation to the contract and shall be valued in accordance with the Contract provisions.
4.6 SEALING COAT
Where indicated in the Drawings and immediately after a sufficient length of trench has been bakau piled and/or passed by the SO Rep, lay a seal coat of Grade 15 concrete, 75mm thick across the complete width of the trench, including filling with concrete to the temporary drainage channel. Finish the seal coat neatly such that the bakau pile heads, if any, are left projecting 25mm.
4.7 CONCRETE BED FOUNDATION
The concrete bed formation for the sewer pipes shall consist of a concrete foundation using Grade 30 concrete as shown in the Drawings according to the different Type Sections.
4.8 GRANOLITHIC CONCRETE
Granolithic concrete shall consist of one part of Portland Cement, two parts of fine aggregate and three parts of 10mm granite chippings free from dust. In all other respects it shall comply with the remainder of the Specifications for concrete.
4.9 PIPE LAYING
Lay pipes for sewers true to line and grade as shown in the Drawings and all in accordance with Clause 2.70 "Pipe Laying".
4.10 CLEARING PIPELINES OF OBSTRUCTION
After testing the pipelines as specified and at a time to be directed by the SO Rep, inspect the interior of the pipelines to ascertain that the pipes are entirely clear of obstruction and that the invert is smooth.
The outside diameter of the ends of the plug shall not be smaller than the diameter of the pipe through which it is to be passed by 25mm and its length shall not be less than its diameter.
The SO Rep may not instruct for this test until he is satisfied that the lengths concerned are complete and ready for operation.
Remove any obstruction in the pipelines and make good any unevenness of the invert.
If, as a result of the removal of any obstruction, the SO Rep considers that any damage may have been caused to the pipelines, the Contractor shall be required to re-test again the length of such pipelines.
Should such re-test prove unsatisfactory, amend the work and carry out such further tests as required by the SO Rep.
4.11 TESTING OF GRAVITY SEWERS
(i) General
(a) All gravity sewers of 600 mm or less in diameter shall be tested by filling with water to an internal pressure of 1.5 metre head of water above the invert of the pipe at the highest end of the pipeline.
(b) Testing shall be carried out for the whole length of the pipeline between manholes and before the pipeline is concreted and covered. The Contractor shall bear the cost and expense for the testing of gravity sewers to comply with the requirements of PUB.
(ii) Testing Procedure
(a) Ensure that the following equipment is available :
(i) A plug of appropriate size to be fitted at the downstream end of the pipeline.
(ii) A measuring cylinder to measure the actual loss of water.
(iii) A 90 degree elbow bend and vertical pipe of equal diameter to be fitted at the highest end of the pipeline. For minor sewers, the elbow bend and the vertical pipe shall be of the same diameter of the sewer. For main sewers, the minimum diameter of the elbow bend and vertical pipe shall be 225mm although the same diameter as that of the pipeline is always preferable.
(b) Ensure that the pipeline is properly anchored.
(c) Fit the plug at the downstream end of the pipeline and the elbow bend with the vertical pipe at the highest end of the pipeline.
(d) Fill the pipeline with water through the vertical pipe up to its brim making sure that there are no pocket of trapped air.
(e) Ensure that the pipeline is completely filled with water by allowing the water to drain away at the downstream end and topping up with water again to the brim of the vertical pipe.
(f) Allow the pipeline to stand for a minimum of 2 hours for absorption and topping up as necessary before carrying out the water test.
(g) Test the pipeline at the required head of 1.5 metres head of water. Top up the vertical pipe using the measuring cylinder at intervals of 5 minutes and noting the quantity of water needed to maintain the test head over a period of 30 min.
(h) On completion of the test, remove the plug at the end of the pipeline and observe the water level at the vertical pipe to ensure that the level drops freely and the water in the pipeline drains away.
(iii) Acceptance Criteria
(a) The pipeline shall not be accepted until they have withstood the required pressure head of 1.5 metres head of water for 30 minutes without loss of water in excess of 1.5 litres for 100m length of pipe for each 300mm in diameter.
(b) Formula to calculate permissible loss of water for 30 minutes is as follows :
Permissible Loss (ml) = Diameter of Pipe (mm) X Effective Length of Pipeline (m) X 1500ml
300 (mm) 100 (m)
Gravity sewer of 600 mm and above in diameter need not be hydraulically tested. They shall be inspected by Closed-Circuit Television (CCTV) inspection or for man-entry sewers, manual inspection shall be carried out. The Contractor shall make appropriate arrangements to install the CCTV and keep proper records of the sewer inspection. The Contractor shall bear the cost and expense for the CCTV and man-entry inspection in accordance with the requirements of PUB.
Do not cover the pipes until they have been inspected and passed.
4.12 BUILT-IN PIPES
At all points where pipes are built into concrete walls or floors, take great care that the joint is watertight. If found to be otherwise, cut away and replace the concrete to make a watertight joint to the satisfaction of the SO Rep.
4.13 JUNCTIONS AND CONNECTIONS
The junctions where provided shall be securely stoppered, such temporary stopper being secured with cement mortar.
4.14 CONCRETE AROUND PIPES
After each length of pipes has been tested and passed, bed haunch and surround the pipes with concrete as shown in the Drawings.
At approximately every four pipes or 6m whichever is the lesser interval, form a joint in concrete bed or surround by vertically shuttering the bed or surround with 25mm thick fibre board, timber or other approved material. Leave the shuttering material in to form a permanent joint. Where the concrete bed is required to be reinforced, stop all reinforcement on either side of the joint.
The whole of the concrete shall be thoroughly set before any work of refilling is commenced.
4.15 TUMBLING BAYS AND BACKDROPS
Where required, construct tumbling bays and backdrops in accordance with the details of the approved Drawings.
Use special spigot and socket junctions in the junction between the two lines of pipes. For backdrops and tumbling bays above 300mm diameter the junction shall be cast iron to approved dimensions and shape.
Lay the tumbling bays or backdrop pipes on a concrete foundation and completely encase in concrete surround as shown in the Drawings.
Where indicated in the Drawings, build tumbling bay pipes into the walls of the manhole by cutting a neat hole sufficient for building in the pipes and finish flush with the inside of the manhole and neatly splay on the outside to form a watertight joint.
4.16 BRICK MANHOLES
Where detailed, build brick manholes in positions shown and in accordance with details in the Drawings.
Construct the brickwall in accordance with Clauses 2.58 "Bricks" and 2.59 "Brickwork Generally".
Set the reinforced concrete slabs covering the chambers of the manhole and joint in cement mortar as specified to form watertight joints.
Form channels and benching to the concrete floors of the manholes as detailed in Grade 30 concrete as specified and render in cement mortar 20mm thick.
Build ends of pipes into the walls of the manholes and finish off in cement mortar. Set manhole covers and frames in cement mortar and covers left flush with the road surface or the finished ground level.
Flush point internal and external joints of brick manholes in 1:3 cement mortar and finish off to a smooth
4.17 PRECAST CONCRETE MANHOLES
Where indicated, precast reinforced concrete ring manholes shall be built in the positions shown in the Drawings. Submit details of the supply of this item to the SO Rep for approval.
Set the rings forming the chambers of the manholes on a reinforced concrete foundation comprising a base of concrete and a built-up section, sufficient to completely build in the ends of the pipes.
Construct the base, benching and pointing of all precast and in-situ concrete manholes in Ordinary Portland Cement, unless otherwise directed. Form the benching at the soffit level of the out-going sewer pipe rising by 75mm to the manhole walls. Form curves and junction benchings to a radius in the centre line of the channel not less than one and a half times the diameter of this pipe.
Set the reinforced concrete slabs covering the chambers and the shafts of the manholes in 1:3 cement mortar to form watertight joints.
Form channels and benching to the concrete floors of concrete manholes in Ordinary Portland Cement concrete.
Set manhole covers and frames as specified in Clause 2.80 "Manhole Cover And Frame" in cement mortar and surrounded with concrete and covers left flush with the road surface or the finished ground level.
4.18 CLEANING OF SEWERS
Thoroughly clean all sewers to the requirements of Water Reclamation (Network) Department, PUB before final inspection prior to acceptance.
Throughout the Time for Completion and any time period where liquidated damages are imposed under the Contract, when required by the SO Rep, provide without charge one number aluminium ladder, two numbers powerful lamp of at least six cells, two pairs of keys for lifting manhole covers and one number spirit level, two numbers mirrors all to the approval of the SO Rep.
4.19 INSPECTION AND APPROVAL OF SEWERS BY WATER RECLAMATION (NETWORK) DEPARTMENT, PUB
Before their acceptance, thoroughly clean the sewers and made ready for inspections by the SO Rep and by the Water Reclamation (Network) Department, PUB's representative. No sewer or part of a sewer may be put into use until a final inspection has been carried out and the sewers and manholes found to be satisfactory. Provide and install all the necessary plugs to the manholes before the sewers are put into use and remove the plugs when the lines are to be in use all to the requirements and satisfaction of the SO Rep and Water Reclamation (Network) Department, PUB. The Works shall only be certified satisfactory when both the SO Rep and the Water Reclamation (Network) Department, PUB have approved all the sewers and manholes.
4.20 CONNECTION OF HOUSE DRAIN TO SEWER MANHOLE
No final connections may be made from the house drain/s to a sewer manhole until the sewer has been passed as satisfactory, after a final inspection has been carried out.
4.21 CONNECTION OF SEWERS TO EXISTING MANHOLE
All sewer connection to existing manholes shall be included in the Contract, unless otherwise indicated in the Drawings.
4.22 PIPE JACKING
(a) General
(i) Where specified in the Drawings, sections of the sewer shall be laid by pipe jacking.
(ii) Submit details of Construction Equipment, materials and the method of construction to perform and complete the work for approval by the SO Rep before commencing these operations. Approval by the SO Rep shall not relieve the Contractor of his sole responsibility for the efficacy, reliability, soundness of the method employed in completing the work in a satisfactory manner.
(iii) The general soil profile along the route of the sewer shall be given in the borelogs, for the Contractor's information only. The Employer accepts no responsibility for the accuracy, reliability or completeness of this information. The Contractor shall satisfy himself as to the soil conditions along the pipe jacking route and carry out additional soil investigations at his own cost and expense.
(iv) In general, the soil is usually of an unstable nature and the ground water table is usually high. Maintain stable soil conditions at the jacking face to prevent loss of ground above the jacking operation and movement of the surrounding earth. The methods of maintaining face stability and preventing ground movement and subsidence shall be by means of compressed air or other plenum methods where fluid slurry or earth pressure is applied-to the tunnel face. Alternatively, stabilise unstable ground ahead of the jacking face by the injection of suitable chemicals. Methods which require dewatering of the ground and methods which may lead to significant ground loss shall not be accepted. Submit soil stabilization method to the SO Rep for approval.
(v) Monitor movement or settlement of structures, utilities and pavement during the jacking operation and report to the SO Rep. If movement or settlement occurs which, in the opinion of the SO Rep may cause damage, take immediate action to prevent further movement, settlement or damage. Repair any damage and restore structures or pavements to the satisfaction of the SO Rep.
(vi) Inspect the location and familiarise himself with the conditions under which the work shall be performed and with all necessary details as to the orderly execution of the work. The omission of any details shall not relieve the Contractor's full responsibility for the satisfactory installation of the work in its entirety. No monetary or other claims made by the Contractor on the grounds of want of knowledge shall be entertained by the Employer.
(b) Materials
(i) The pipes for jacking operation shall be precast reinforced concrete pipes. The pipes shall be manufactured by a centrifugal or other equivalent process to be approved by the SO Rep.
Design, manufacture and factory testing of the pipes and specials shall be to SS 183 or BS 5911 or AS 1342 or other acceptable standard. The clear cover of concrete over steel reinforcement shall not be less than 50mm.
(ii) All pipes shall be manufactured with two sets of grout holes. Each set shall consist of three grout holes spaced at 120 degrees on centres circumferentially located at the quarter points from either end of the pipe.
(iii) The precast reinforced concrete pipes shall be sufficiently reinforced with steel to withstand all stresses induced by handling, jacking, earth and water pressures and all working loads at the depths at which they are to be used without cracking, spalling or distortion. The pipes shall be of at least strength Class `H'. A load factor of not larger than 1.5 shall be used in the calculations to determine the strength of the pipes required. The strength of the pipes
4.22 PIPE JACKING (CONT'D) (b) Materials (Cont'd)
(v) The pipes shall be sufficiently matured before they are used in the construction of the Works. Handle the pipes with extreme care to prevent the edges of the pipes from chipping.
Repaired pipes shall not be allowed for use in the Contract. The SO Rep may reject any
Repaired pipes shall not be allowed for use in the Contract. The SO Rep may reject any