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Pipe Jacking , Method Statement
The following are the steps to be adopted:
No objection certificates shall be obtained from all authorities prior to commencement of any excavation and pipe lying.
Road Surface Levels
Road surface level shall be taken along the pipe jacking route 10mm each side every 2m jointly with consultant surveyor before during and after the operation of pipe jacking.
The thrust pit will be constructed with normal trench sheet excavation if necessary. Two steel rails will be positioned within the Thrust pit parallel to the line and gradient. The rails will ensure correct entry of pipe. A steel plate will be placed at the rear of the Thrust Pit and a concrete wall to be poured behind if necessary to distribute the point load from the jacking force. The steel plate will be positioned normal to both line and gradient.
Jacking Set Up And procedure
Hydraulic jacks will be positioned on a support frame against the Thrust wall to line and gradient. This will be powered by diesel hydraulic power pack operated by the banks man on instruction from the pit bottom. The steel jacking pipe will be placed over the rails and thrust ring (pushing ring) placed between it and the jacks to distribute the jacking force onto the pipe.
Excavation And Removal of Soil
The soil will be hand-excavated at the face using pneumatic tools if necessary or manually using experienced personnel. The excavated soil will then to be loaded into a muck skip place on wheel bogey which is pushing into the pipe manually and pulled out to the pit bottom by air which or other machine. The leading edge of the first pipe will be profiled to be suit the soil conditions i.e. un soft ground a hood will be used. Pipe will be jacked forward as the excavation proceeds. When the pipe has been pushed to the limit of the jack’s stroke the jack will be retractedand a spacer block will be placed between the jacks and thrust ring and jacking will proceed. The operation will be repeated until the pipe is fully buried. At this time the next pipe will be placed at the pit bottom welded in place and the whole process will be repeated until the drive has reached the reception end. Surveyor shall check line and level regularly during the pipe jacking process.
Ventilation And Lighting
Lighting to the face will be provided using a mobile generator fitted with a 110 volt transformer Forced Air Ventilation will be provided.
Carrier Pipe Installation and Annulus Filling
Subsequent to the satisfactory installation of the steel sleeve, the installation of the pipe through the steel sleeve will commence. The carrier pipes will be laid to line and level supported on flat bars welded across the steel sleeve. When first pipe is placed inside the steel sleeve completely, the next pipe is joined with the first pipe with coupling and sliding thepipe into the steel sleeves is continued until the pipes are fully laid. Laid pipe will be primary tested by an air test to ensure that the laying of the pipe in the Sleeve is satisfactory.
A) External Grouting between the sleeve and the soil. B) Fixing of main carrier pipe and Annulus Filling. C) Internal Grouting between GRP Pipe and the Sleeve. After the drive has been completed, a grout will be done between Sleeve and the ground to avoid any settlement and carrier pipe will belaid to the line and level supported on steel flat bar welded across the jacking pipe (supporting detail will vary according to the pipe dia and material), pipes are to be wrapped with 6mm thick neoprene rubber at the support place only. Once all pipes are in position and securely fixed and checked, a breather pipe will be placed at the soffit and head walls of block work will be built at the ends of the steel pipe.
Filling of annulus by dune/cement grout with super plasticizer added to aid flow by means of a sandpiper pump or pressure head. The filling operation will be continued until the Sleeve is completely filled.