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Introduction To Construction Technology And Process Of Trenchless Pipe Jacking Technology

January 12, 2023

Pipe jacking construction technology has become an indispensable part of the current municipal engineering with a series of advantages such as small impact on the environment and saving manpower. However, due to the pipe jacking construction technology, additional stress field is generated in the surrounding soil, resulting in changes in mechanical properties such as loading and unloading, causing soil disturbance. Although the disturbance is inevitable, it can be reduced by some means.

1. Construction preparation

1. Data include construction design drawings, contracts, various data of personnel, and review records of materials
2. Enclosed enclosure on site (set enclosure according to the traffic guidance scheme approved by the traffic management department to guide temporary traffic;
3. Before the commencement of technical safety disclosure, the technical director of the construction project shall carry out technical safety disclosure to the construction personnel according to the approved construction scheme, emphasizing the engineering difficulties, technical points and safety measures, and sign after the disclosure.
4. The setting out survey shall close and densify the known survey control points and establish a survey control network.
5. Make some tests on the mix ratio of concrete and mud.

2. Excavation of working pit

The excavation, support and dewatering of the working pit shall be 3 meters as a special plan, and 5 meters shall be demonstrated by experts. If there are special requirements, do not comply with the size requirements.
The excavation method includes the combination of short-arm excavator and long-arm excavator. The small excavator is used to transport the excavated earth to the side of the retaining wall, and the crane is used to lift the earth.
The support methods of working pit are row pile support, soil nailing wall support, 13+1 * 1-9-10+2 * 97+3 anchor rod support, combined support of retaining cast-in-place pile and soil anchor rod, steel sheet pile support, underground continuous wall support, retaining wall plus internal support.
The dewatering methods of foundation pit include open ditch plus water collecting well, light well point dewatering, jet well point dewatering and tube well point dewatering.

3. Equipment installation

1. Guide rail
The working well foundation generally adopts concrete foundation, and the foundation concrete strength is C20. The steel plate is embedded in the concrete with a thickness of 20 cm. The two rails should be parallel, of equal height, and the longitudinal slope should be consistent with the design slope of the pipe. The guide rail and the embedded steel plate in the concrete foundation should be welded.
2. Back
The back is a measure to resist the jacking force, mainly to provide sufficient support for the back when the jack is pushed out.
3. Water stop ring
The function of the pipe jacking opening sealing structure is to prevent muddy water from flowing into the working shaft from the gap between the pipe joint and the opening during pipe jacking.

4. Jacking

1. Mud circulating system
Main equipment of muddy water sludge discharge system: including inlet and outlet mud pump, mud pipe, muddy water treatment device, mud water tank, etc.
The sludge discharge system has two functions: one is to discharge soil, the other is to balance groundwater.
2. Measurement system
The main equipment of the measuring system is composed of laser theodolite, measuring target and monitor.
The function of the measuring system is to monitor the axis deviation of the pipe jacking machine during the pipe jacking construction.
The pipe jacking machine is placed on the track in the working shaft, and the center of the measurement target is adjusted to be basically consistent with the pipeline centerline and perpendicular to the pipeline centerline. Adjust the height of the laser theodolite base so that the height of the laser beam of the laser theodolite is basically consistent with the elevation of the pipeline centerline. Adjust the laser beam according to the measurement positioning point so that the laser beam basically coincides with the pipeline axis. Adjust the size of the laser beam point of the measurement target, and adjust the position of the measurement target according to the position of the laser spot of the measurement target, so that the laser point coincides with the center point of the target.
3. Deviation correction system
Main equipment of deviation correction system: deviation correction jack, oil pump station, displacement sensor and inclinometer.
The function of the deviation correction system is to control the pushing direction of the pipe jacking machine during the pipe jacking construction. The action control of the deviation correction system is remotely controlled on the operation console in the ground operation room. The deviation correction amount is controlled by the displacement sensor placed on the deviation correction jack. The deviation correction action is realized by a combined action of the deviation correction jack.
4. Relay system in relay room
Main equipment of relay ring relay system: small jack, hydraulic pump station, shell body
The role of the relay ring relay system is to push the whole pipeline section by section to reduce the main pushing force.

5. Exit the hole

The range from the jacking ring of the pipe jacking machine to the cutting of the pipe jacking machine is 6m from the working shaft. The outer layer of the receiving shaft of the pipe jacking machine shall be reinforced to improve the soil mass, usually deep mixing, high-pressure rotary jet grouting and deep grouting. Before going out of the tunnel, a double-layer rubber water stop device is installed at the portal to prevent water and soil from flowing into the working well at the front of the pipe jacking machine when going out of the tunnel. The other function is to prevent the loss of the drag reduction mud pressed in during the jacking construction and ensure that a complete and effective mud sleeve can be formed.

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