1.12 Complex Shield Tunneling Construction Technology
The trenchless pipe-laying construction technologies most widely used mainly include pipe jacking, directional drilling crossing technology, and large-section rectangular channel boring technology.
1.12.1 Technical Content
The trenchless pipe-laying construction technologies most widely used mainly include pipe jacking, directional drilling crossing technology, and large-section rectangular channel boring technology.
(1) Pipe Jacking Method
Pipe jacking is a construction method for laying pipelines in soft soil layers or water-rich soft strata. With the continuous development and maturity of pipe jacking technology, a large number of ultra-large-diameter and ultra-long-distance pipe jacking projects have emerged. The maximum diameter of concrete jacking pipes has reached 4000 mm, and the longest single jacking distance has reached 2080 m. With the emergence of a large number of ultra-long-distance and ultra-large-diameter pipe jacking projects, corresponding new pipe jacking construction technologies have also been developed.
1) To maintain earth pressure balance during ultra-long-distance jacking, an intelligent screw conveyor soil discharge and speed regulation construction technology under constant jacking speed and multi-stage jacking conditions is adopted; this new technology, combined with the reasonably determined parameters of the earth pressure fluctuation range, enables the pipe jacking machine to intelligently adapt to earth pressure changes and avoid large vibrations.
2) To address the problem of excessive jacking force during ultra-large-diameter and ultra-long-distance jacking, a fully automatic grouting system has been developed, which intelligently distributes the grouting volume and effectively performs local resistance reduction.
3) The automatic measurement and deviation prediction technology for ultra-long-distance and multi-curve pipe jacking is by far the most suitable measurement system for ultra-long-distance and curved pipe jacking. This measurement system uses networked tracking measurement technology with multiple measuring robots and, combined with historical data, predicts the direction and magnitude of the tool pipe guidance, greatly improving jacking efficiency and the quality of jacked pipelines.
4) The splicing technology for prestressed concrete cylinder pipe jacking (JPCCP) uses auxiliary rails, auxiliary jacks, and main jacks for all-round three-dimensional adjustment of the pipe joint interface posture, effectively solving the splicing difficulty of high-precision interfaces for this new type of composite pipe material.
(2) Directional Drilling Crossing
A crossing curve is designed according to the entry point and exit point. Then, according to the crossing curve, a crossing drilling rig is used to first drill a guide hole and then perform reaming. After the pipeline is pulled back, the prefabricated and pressure-tested pipe sections are pulled back using the wall-protection and lubrication effects of mud to complete pipeline laying construction. Its new technologies include:
1) A measurement-while-drilling system for measuring the drill bit position. The key technologies of the measurement-while-drilling system are the sealing of the drill pipe body and the sealing of the permanent cable connection inside the drill pipe while ensuring drill pipe strength.
2) A new rotary steerable drilling system with a downhole motor. This system effectively solves the service life problems of the stator and bearings and can perform rotary drilling according to the set guidance.
(3) Large-Section Rectangular Underground Channel Boring Construction Technology
This is a trenchless construction technology that uses a rectangular tunnel boring machine to excavate ahead, and then jacks and assembles prefabricated concrete structural sections in the soil layer to form an underground channel structure.
During the jacking process of the rectangular tunnel boring machine, by adjusting the propulsion speed of the rear main jacking cylinders or adjusting the rotation speed of the screw conveyor, the pressure of the mixing chamber is controlled to keep it balanced with the earth pressure of the stratum where the boring machine is located, ensuring smooth jacking of the boring machine and achieving low disturbance to the overlying soil; under the continuous rotation of the cutterhead, the soil cut from the excavation face enters the mixing chamber and is stirred into soft-plastic disturbed soil; for natural soil that cannot be softened, water, clay, or other materials are added to plasticize it and stir it into mixed soil with certain plasticity and fluidity, which is discharged from the mixing chamber by the screw conveyor and then discharged by special conveying equipment; when the tunnel boring machine has advanced to the specified stroke, the main thrust cylinders are retracted, the prefabricated concrete pipe sections are lifted in and assembled, and then jacking continues until the entire underground channel structure is formed.
The large-section rectangular underground channel boring construction technology has a high degree of construction mechanization, fast boring speed, and high utilization rate of the rectangular section. The trenchless construction of underground channel structures has little impact on ground operating facilities and can meet the construction needs of underground channels with various section sizes.
1.12.2 Technical Indicators
(1) Pipe Jacking Method
1) According to the actual project, analyze the changing trend of the screw conveyor's soil discharge capacity under different pressures and soil conditions, and design and set a screw conveyor intelligent speed regulation function suitable for the project to cope with the influence of different soil layers on the soil discharge mechanism;
2) Using grouting devices with ball valves and automatic opening and closing, combined with an intelligent control platform, each grouting hole is included in the automatic control range, with remote control and setting of grouting parameters and reasonable distribution of grouting volume. In relatively hard pebble soil layers, a larger grouting volume should be allocated; in relatively soft and water-rich soil layers, less or no grouting may be performed, achieving targeted results;
3) For prestressed concrete cylinder pipe jacking construction of pressure pipelines, a specially made intermediate ring system is adopted. The socket and spigot of the intermediate ring should be manufactured according to the precision requirements of the prestressed concrete cylinder pipe socket and spigot to ensure good sealing performance with the interfaces of other pipe sections;
4) For the interface splicing construction of prestressed concrete cylinder jacking pipe sections, when using the three-dimensional splicing system, when the socket and spigot are close, the jacking speed should be controlled at 0.001 m/s, and it is better to be slow than fast.
(2) Directional Drilling Crossing
1) Use wireless transmission instruments for measurement while drilling, eliminating the distance limitation caused by wired transmission. Install signal receiving instruments at the borehole position to promptly feed back trajectory monitoring data and grasp drilling direction dynamics.
2) Set the directional parameters of the rotary drill bit and the power parameters of the downhole motor according to the soil layer conditions, and combine with a remote control platform for intelligent drilling crossing construction.
(3) Large-Section Rectangular Underground Channel Boring Construction Technology
The maximum width of the underground channel is 6.9 m; the maximum height of the underground channel is 4.3 m.
1.12.3 Scope of Application
(1) Pipe Jacking Method
1) It is particularly suitable for construction in cohesive soil, silty soil, and sandy soil layers, and is also suitable for construction in soil layers with pebbles, gravel, and weathered residual soil.
2) It is suitable for the construction of interception pipes for urban water pollution control, for the construction of liquefied gas and natural gas transmission pipes, oil pipes, and pipeline construction for power cables, broadband networks, optical fiber networks, and other cable projects.
3) It is suitable for the construction of comprehensive channels crossing under highways, railways, and buildings in urban municipal underground engineering, as well as subway pedestrian passages.
(2) Directional Drilling Crossing
1) The stratum conditions suitable for the directional drilling crossing method are sand, silt, cohesive soil, pebbles, and other ground conditions.
2) Without excavating the ground surface, it can be widely used in pipeline laying construction for water supply, gas, electric power, telecommunications, natural gas, petroleum, and other pipelines.
(3) Large-Section Rectangular Underground Channel Boring Construction Technology
It can adapt to various cohesive soils, sandy soils, silty soils, and quicksand strata with N values below 10; it has good waterproof performance, with a maximum overburden depth of 15 m; through the cross-section module combination of the tunnel boring machine, it can meet the construction needs of underground channels of various cross-section sizes.