|
Annex A - Good Sewer and Pumping Main Laying Practice
(Addendum No. 1 - Feb 2001) |
|
5.1 |
Connection to Existing Manholes |
|
|
(a) |
Every care shall be taken to ensure that the connections of pipelines to existing manholes are watertight and the existing sewers and manholes are not damaged. |
|
|
(b) |
In connecting the pipeline to the existing manhole, a circular hole large enough to accommodate the pipeline shall be made in the wall and the cut end of the pipe neatly rendered to form a smooth bore. |
|
|
(c) |
Every care shall be taken to ensure that there is no interruption to existing flows during connection works. No debris shall be allowed to fall or be discharged into the existing sewers. |
|
5.2 |
Abandoned Sewers, Pumping Mains, Manholes and Chambers |
|
|
(a) |
Ends of the abandoned sewers/pumping mains shall be sealed watertight with 225mm thick brick plugs and rendered with cement mortar. The abandoned sewers/pumping mains of 300mm diameter and above on public roads shall be filled with concrete or cement grout. |
|
|
(b) |
All abandoned manholes/chambers are to be demolished and manhole frames and covers removed. |
|
5.3 |
Connection to Existing Pipes |
|
|
A compatible fit between new and existing pipes shall be ensured whenever connections are to be made to existing pipes. Where such a fit is not possible, specially manufactured piece for the transition will have to be used. |
|
5.4 |
Pipe Jacking |
|
|
(a) |
Prior to pipe jacking, a comprehensive soil investigation along the route of the pipeline shall be carried out. Stable soil conditions at the jacking face shall be maintained at all times to prevent loss of ground above the jacking operation and movement of the surrounding earth. Maintenance of face stability and prevention of ground movement and subsidence shall be by methods where fluid slurry or earth pressure is applied to the tunnel face. Unstable ground ahead of the jacking face may be stabilised by the injection of suitable chemicals. Methods used shall not lead to significant ground loss. |
|
|
(b) |
Methods which require workmen to carry out excavation either manually or semi-mechanically in pipes or tunnels smaller than 1200mm in diameter shall not be used. |
|
|
(c) |
Measures shall also be taken to ensure that there are no voids outside the pipes. |
|
5.5 |
Diversion of Existing Sewers |
|
|
(a) |
Whenever manholes are to be constructed onto existing sewer, precautionary measures are to be taken to ensure that there is no interruption to the flow in the existing sewer. Care shall also be taken to prevent any debris from falling into the sewer and being carried downstream. Any debris falling into the sewer must be removed immediately. No existing sewer shall be sealed off until the new line has been completely inspected and certified fit for use. For such cases, the ends of the newly constructed sewer shall be plugged up until diversion of flow can be implemented. |
|
|
(b) |
No drain-lines/sewers affected by the work shall be sealed off without prior and proper diversion of the affected drain-lines/sewers. |
|
5.6 |
Advanced Sewer Connections |
|
|
The ends of advance sewer connections and Y-junctions for which future connections are provided for are to be satisfactorily sealed with approved material. Where applicable, markers (timber or otherwise) are to be labelled clearly and erected accurately to mark the ends of advance connections and Y-junctions. The markers are to be fixed into the ground in a manner that they will not be easily removed. |
|
5.7 |
Safe Working in Confined Spaces |
|
|
(a) |
All safety requirements for workmen working in sewers, pumping mains, chambers, sumps and other confined spaces, including the provision of adequate ventilation and necessary apparatus, as stipulated by the Ministry of Manpower shall be strictly complied with. |
|
|
(b) |
Approval from Water Reclamation(Network) Department (PUB) shall be obtained prior to carrying out any sewer connection works in the public sewerage system. |
|
5.8 |
Setting Out |
|
|
The sewer shall be properly set out before any work commences. |
|
5.9 |
Pipe Bedding with Granular Material |
|
|
(a) |
The bedding for the pipes shall be thoroughly compacted. The pipes shall be laid evenly on the barrel at the required level. There should be no hollows, voids or foreign materials under the pipe. Any concrete blocks or wedges should be removed on completion of bedding. |
|
|
|
|
|
(b) |
Particular care must be taken to ensure that proper bedding is obtained at and on either side of the pipe joints. Where pipe jointing holes are left in the bedding, particular care must be taken to ensure complete and proper filling of the holes after pipe testing. |
|
5.10 |
Concrete Bed, Haunching and Surround to Pipe |
|
|
(a) |
The concrete used for the concrete bed foundation shall be well rammed or vibrated and worked under and around the pipes. |
|
|
(b) |
At approximately every four pipes or 6 metres whichever is the less interval, a joint shall be formed in the concrete bed or surround by vertically shuttering the bed or surround with 25 mm thick fibreboard, timber or other approved materials. The shuttering material shall be left in to form a permanent joint. Where the concrete bed is required to be reinforced, all reinforcement shall stop on either side of the joint. |
|
5.11 |
Pipe Laying |
|
|
(a) |
All pipes shall be carefully brushed out inside and shall be tested for soundness before being laid. The pipes shall be laid separately to true inverts, straight lines and falls, each pipe being separately boned between sight rails and bearing evenly upon the solid ground or concrete for its full strength. |
|
|
(b) |
Where pipes are laid without a concrete bed, holes shall be cut in the bottom of the trench of such size and depth as to allow the joints to be properly made and the barrel of the pipe to bear evenly on the solid ground for its full length. |
|
|
(c) |
Where pipes are to be laid on rock formation, the excavation shall be taken down to 100mm below bed level and great care shall be taken to ensure that there are no projecting pieces of rock on which the pipe will ride. The bed will then be made up to its true line and level by refilling with either 100 mm of consolidated, selected material from the excavations, well rammed and watered if necessary, or with 100mm of concrete grade 15. |
|
|
(d) |
All blocks and wedges are to be of sufficient size and strength to prevent settlement of the pipes. |
|
5.12 |
Testing of Water-tightness of Sewers |
|
|
(a) |
All gravity pipelines and sewers below 600 mm in diameter before being surrounded and covered shall be tested by filling with water. The pressure shall be measured from the highest point of the pipeline under test and shall be 1.5 metre head of water. Pipelines should not be accepted until they have withstood the required pressure for 30 minutes without a loss in excess of 11/2 litres for 100 m for each 300 mm in diameter. |
|
|
(b) |
Sewers of 600 mm and above in diameter need not be hydraulically tested. They shall be inspected by CCTV inspection or for man-entry sewers, manual inspection shall be carried out. |
|
5.13 |
Testing of Water-tightness Pumping Mains |
|
|
(a) |
All pumping mains of 600 mm or less in diameter shall be tested hydraulically in convenient lengths before being covered up. Water shall be forced into the pipes by means of a force pump, fitted with a pressure gauge to indicate the pressure at the lowest point of the section under test. The test pressure shall be 1.2 N/mm2 for all classes of pipes. |
|
|
(b) |
Before any test commences, the trench if the pipeline is underground, is to be partially backfilled to cover the pipes but leaving the joints exposed for inspection and repairs or remedial work where necessary. Any joints not passing the test shall be refitted, cut out or replaced. No mechanical caulking shall be allowed. Where the pipelines are above ground, anchor blocks and other supports shall be provided prior to testing. |
|
|
(c) |
The method of filling the pipes and arranging the test must ensure that all the air is expelled from the pipeline and joints before any pressure is applied. Air and pressure release cocks shall be provided wherever necessary. |
|
|
(d) |
The testing pressure shall be provided with an isolating valve which, when closed, shall leave the pressure gauge connected to the length of pipeline under test, and at the same time isolate the pump. When the specified pressure has been reached, the isolating valve shall be closed and remain closed for 30 minutes. At the end of that time, if the pressure has dropped the isolating valve shall be opened and the loss of water determined by pumping into the main a measured quantity of water, sufficient to bring that pressure up again to the initial pressure. |
|
|
(e) |
If the loss of water so determined is at a rate less than 10 cc per mm diameter per km of pipeline for 30 minutes, the test shall be considered satisfactory. |
|
5.14 |
Manhole Construction |
|
|
(a) |
Chamber and shaft rings may be supplied in different lengths and each section will be provided with lifting holes. The tapers to be used will be of a fixed length. The joints between the sections shall be of an ogee form. Each section shall be set up accurately in position making the ogee joint with cement mortar to form a watertight joint. Before completion of the manhole, all the lifting holes, ogee and other joints shall be neatly pointed. |
|
|
(b) |
The reinforced concrete slabs covering the chambers and the shafts of the manholes shall be set and pointed in cement mortar to form watertight joints. |
|
|
(c) |
At all points where pipes are built into concrete walls, or floors, great care shall be taken that the joint is watertight. If found to be otherwise, the concrete shall be cut away and replaced with concrete, to make a watertight joint. |
|
|
(d) |
Manhole covers and frames are to be set in cement mortar and surrounded with grade 20A concrete and covers left flush with the surrounding ground or road surface as the case may be and shall be set on two courses of 225mm brickwork. The fine adjustment of cover levels shall be effected by creasing courses of hard burnt tile. Care shall be taken to ensure that the cover is level and sloped to any fall or grade in the surrounding surfaces. |
|
5.15 |
Backdrops and Tumbling Bays |
|
|
Where Backdrops/Tumbling Bays are used, the pipes are to be built in the walls of the manhole by cutting a neat hole in the precast concrete rings sufficient for building in the pipes and pointed in cement mortar. The joint shall be finished flush with the inside of the manhole and neatly splayed on the outside to form a watertight joint. |
|
5.16 |
Inspection of Completed Sewers |
|
|
(a) |
All completed sewers are to be inspected to ascertain that the pipes are entirely clear of obstruction, that the invert is smooth, that the joints are properly constructed, that there are no defects etc. |
|
|
(b) |
In cases where the pipes cannot be inspected from the inside, generally under 600mm in diameter, a loose plug shall be passed through each pipeline to ensure that the pipes are entirely clear of obstruction and that the invert is smooth. The loose plug shall be in the form of a cylinder with solid ends made of timber not less than 25mm in thickness. |
|
|
(c) |
In cases where the sewers are 600mm and above but lesser than 900mm in diameter, CCTV inspection shall be carried out to inspect the completed sewer. Where the sewers are greater than 900mm, visual inspection from the inside of the pipes shall be carried out. |
|
|
|
|
Annex B - Standard Drawing on provision of advance connections to lot Boundaries for Sewer Diversion Work (Drawing No. 5-1)>
(Addendum No. 1 - Feb 2001) |
|
|
Click for drawing in pdf format: |
|
|
(a) pdf format |
|
|
Click here for standard sanitary drawings |