顶管法施工方案

Method Statement for Pipe Jacking

1.Construction of Pits

The jacking pit with a dimension of 6mx5 clear opening with depth of 250mm below invert level of the steel pipe.

The floor will be leveled by 100mm thick concrete blinding fixing tow I beams in the center of the pit for fixing jacking frame.

2.Installation of Jacking Frame

After the construction of drive, the jacking rig will be lowered into the pit and adjust to the control line and level.

The rig will be used on this contract consist of two number of hydraulic cylinders with a capacity of 150 ton each to give a total jacking force of 300 tons. The rig will have guided rails, pushing plate and base plate to hydraulic power back with control unit. The hydraulic system will run through

a diesel engine installed the top of the pit.

The rig will installed to the correct line and level and check by the consultant in respect to level and alignment.

3.Thrust Wall

Constructing a concrete block behind the base plate of the rig to a dimension of will be provided to take and distribute the jacking load.

4.Pipe Jacking Operation

A steel shield is used at the front of the pipe to accommodate

the miner and to allow for steering of the pipe jack. The soil within the shield is manually excavated and loaded into

a wheel skip for transport to the pit bottom. The miner does

not dig outside the shield (both in front and radically) and the front, or cutting edge, of the shield is always kept buried in the face, so stability is maintained. The shield is thus used to trim the excavation to the size of the pipe thus minimizing the potential for settlement of the ground above the pipe jack.

In the pit bottom, the skip is hoisted to the surface, emptied and returned to the used to loosen it prior to digging. The exact diameter of shield will be selected to suit the pushing pipes.

As excavation continues, the shield is jacking forward using two hydraulic jacks thrusting from the back wall. When the shield is buried, the jacks are retracted and the first sleeve pipe lowered on to the rails. This in then pushed up to the shield and excavation can then continue.

When the sleeve pipe is pushed home, the hydraulic jacks are retracted and the services (lighting& ventilation)

disconnected. The next sleeve pipe is lowered on to the rails and the services reconnected and the cycle repeated until the shield is pushed into the receiving pit and the pipeline pushed into final position.

5.Maintaining Line and Level

In order to maintain the correct line and level, a graduated target plate is located within the shield. The site engineer notes the position of the visible sport on the target, this initial position is used as reference value to locate the relative position of the shield at all times during the drive.

At each push, the site engineer monitors the position reference value with the help of level instrument and theodalite, thus giving a shield position (high or low, right or left) relative to the design position. Based on this information, the operator manipulates a correct course.

Extending or retracting a combination of steering rams causing the front of the shield to articulate in the required direction carries out the steering. As the pipe follows the shield, the correct line and level will be maintained. At all times, the amount steering applied is kept to minimum.

6.Fixing Carrier Pipes

After completion of the pipe jacking , we check the line and

level for the steel pipe and we take the exact line and level for the carrier pipe with the help of survey instruments.

A 3’ steel angle b ar fixed by welding in the correct bottom

level of the carrier pipe, then 3mm thick flat bar half moon claps will fixed through wielding in the correct line after that we put neoprene rubber 3mm thick in the clamp to avoid the scratches of the carrier pipes.

Then we start laying the carrier pipe one by one and fix the clamps through nuts and bolts. After fixing the nuts and bolts we make angle support in between the top of the clamp and top of the pipe. Then we fix the other pipe in the same manner. The same procedure will continues up to the requirement.

7.Grouting

Upon completion of pipe jacking we make 4’ 2 holes like ventilation in every meter, it helps the concrete fill the gap between the steel pipe and ground. Then we fixed six inch grouting pipe vertically one meter height in the top of the pipe both end jacking and receiving. One side will keep ventilation and the other side for connection and the concrete pump.

After that we lay the carrier pipe in the correct line and

level then check with the consultant and make the test required from the consultant then we close the both end between steel and carrier pipe by m/s plate welding or masonry, the gap between steel sleeve and ground in the both end we close by cement.

During grouting the grout will push through the down string end.

Pumping process will continue till the grout reaches the up string end ventilation pipe. When the grout will overflow from the ventilation pipe, grouting process is completed.