Pipe jacking construction is an important method of trenchless construction. Each pipe jacking construction method has its own advantages and disadvantages. In the actual construction, the appropriate pipe jacking construction method should be selected according to the engineering practice. In the same project, different pipe jacking construction methods can be selected according to the changing characteristics of construction strata. Let me share with you the application methods and skills of pipe jacking construction. Welcome to read and browse.
1, pipe jacking method
Brief introduction of 1 and 1 pipe jacking method
Pipe jacking construction is mainly used for soil layers below Grade III. In pipe jacking construction, a large-tonnage pipe jacking machine is usually used to directly jack into the pipeline or to jack into the pipeline while discharging soil. In order to reduce the resistance, the front end of the first section of pipeline is generally wedge-shaped. For large-diameter pipeline construction, people can directly enter the front to dump soil, and the wedge surface is at the upper part, which is beneficial to prevent stratum collapse and protect workers' safety. As shown in figure 1. When abandoning soil, according to the stability of soil layer, a certain degree of overbreak can be carried out to reduce jacking resistance and speed up pipe jacking. For small diameter pipe jacking, auger and hydraulic method can be used to assist soil discharge. This method is difficult to control the accuracy of pipeline laying, especially when the pipeline is heavy.
Classification and comparison of 1 and 2 pipe jacking methods
According to the jacking process, the traditional pipe jacking methods can be divided into the following categories:
(1) hydrostatic jacking pipe, that is, simply push and pull the casing by using the feed cylinder;
(2) Hydraulic sprint hydrostatic jacking pipe, that is, using high-pressure hydraulic sprint to break ground, the oil cylinder pushes the casing and discharges a small amount of muck out of the pipe;
(3) Rotary pipe jacking, that is, the drill bit cuts the soil layer, the casing is synchronously followed, and the slag is discharged from the pipe. It can be divided into two types: diamond and non-diamond, and can also be divided into two types: rotating and non-rotating casing.
The static pressure jacking method is the simplest, and the equipment needs a certain jacking force and tension. The jacking depth of hydrostatic jacking pipe is generally 50 m ~ 70 m, and multistage jacking can also be carried out. The calculation formula of pipe jacking force is:
Where: f pipe jacking resistance (kn); T0 Initial resistance of pipe jacking end (kn); D outside diameter of pipe jacking (m); Uniformly distributed load around the Q tube (kPa); ? Friction coefficient between pipeline and soil layer; Adhesion between C pipe and soil layer (kPa); L pipe jacking length (m); As can be seen from the above formula, the greater the diameter and length of pipe jacking, the greater the resistance of pipe jacking; The deeper the horizontal pipe is buried, the greater the resistance of pipe jacking. In addition, it is found in engineering practice that there is also a direct ratio between pipe jacking speed and pipe jacking resistance. For example, the pipe diameter 127mm, depth 20m, pipe jacking length 20m, and pipe jacking resistance up to 720KN. It can be seen that the static jacking pipe does not discharge slag, which has a compaction effect on the soil layer and has a large jacking resistance.
Hydraulic sprint hydrostatic jacking pipe construction means that high-pressure water is used to cut the soil layer at the drill bit, and the oil cylinder is used to push the soil into the casing, and some soil cuttings cut by hydraulic thrust flow into the well from outside the pipe to keep the casing clean. The construction equipment of hydraulic sprint hydrostatic jacking pipe is more complicated than hydrostatic jacking pipe. The key is the machining of drill bit and hydraulic feed. The drill bit is larger than the casing, and the soil cut by reaming and plugging will enter the casing. The front end of the drill bit is equipped with a water supply nozzle with a centripetal angle of 3 mm ~ 4 mm and 8 ~ 10 of 30? ~45? Nozzle, high-pressure water pump injects water into the soil through the drill pipe, and the high-pressure water pressure is generally 0.5 MPa ~ 3.0 MPa. High pressure water has two functions: (1) scouring the soil layer, temporarily disturbing and liquefying the soil layer to reduce the resistance; (2) High-pressure water can drive the tailings around the pipeline to flow, and play the role of slag discharge and drag reduction. The water quantity and water pressure should be adjusted according to the jacking depth. Generally, the water pressure within 0 m ~ 5 m is 0.5Mpa5m ~ 15m, and the water pressure is1.0 MPa ~ 2.0 MPa ~ 2.0 MPa; The water pressure above 15m is 2.0 MPa ~ 3.0 MPa. The water quantity is about 25l/min ~ 100l/min.
The working principle of rotary pipe jacking has many similarities with the following pipe drilling method. The equipment generally includes the working head of the roadheader, control system, mud and water output system and rear jacking system. The advancing pipeline is connected to the working head of the roadheader, and the jacking system is generally a group of 4-6 hydraulic jacks arranged regularly, which requires reaction wall. Its suitable pipe diameter is 250 ~ 3000 mm
This construction method has the following characteristics: (1) the front end of the pipe jacking machine adopts the eccentric rotation of the banner cutter head, which breaks the rock, so that it can be used for construction in clay, silt, gravel and other strata; (2) The pipe jacking machine has the function of rectifying deviation, and the operator can predict the deviation value of the pipe jacking machine relative to the jacking plan line through the positioning system, so as to correct the direction. The deviation is within 30 mm; (3) The primary jacking distance can reach more than 100m, and the jacking speed is 70 ~ 200 mm/min.
In pipe jacking construction technology, jacking force is an important basis for selecting construction method, determining rear wall reinforcement scheme and determining construction progress. According to construction practice, hydrostatic jacking pipe has the largest resistance and jacking force, followed by hydrostatic jacking and rotary jacking. The rotary construction method has the highest requirements for machines and tools, and the static pressure jacking pipe method has the simplest requirements for machines and tools. Therefore, when selecting the pipe jacking construction, the appropriate construction method should be selected according to the jacking force and equipment capacity required for jacking.
2. Engineering application
In order to reduce the influence of groundwater in the ash field of the ash dam on the initial earth dam, four radial wells with an inner diameter of 3m and a spacing of 60m were arranged in parallel at a distance of 93 m from the initial earth dam. 127 diversion steel pipes are connected into radial docking wells. Pipe jacking construction method is adopted in this project. At first, static pressure jacking pipe was used, but the diversion steel pipe was difficult to squeeze soil, slag discharge, pipe diameter friction and construction. Therefore, the construction of hydrostatic jacking pipe is changed to hydraulic sprint, but hydraulic erosion leads to stratum construction? Ash? Seriously. Finally, the construction method of combining drilling rig and pipe jacking machine is adopted to complete the docking well construction.
2. 1 Pipe jacking technology and process
(1) for the first time. According to the design drawings and site layout, determine the opening position of well 1, and then use an air compressor to open the hole; Determine the installation position and direction of the pipe jacking machine, and install and fix the pipe jacking machine; Install the pipe jacking in place. Pay special attention to the fact that the first pipe is a tool pipe, and whether its jacking direction and elevation are accurate is the key to ensure the quality of the whole pipe jacking; When jacking, the control pressure is 8- 12MPa. When jacking is difficult, a section of pipe jacking should be withdrawn before jacking. Repeated jacking of 25 ~ 35m is required during construction.
(2) Switch drilling rigs and drill evenly for 25 ~ 35m at a speed lower than 40r/min. The pressure is controlled at 7 ~ 8 MPa. Uniform feed should be ensured during drilling. Once the footage slows down, it may lead to well deviation.
(3) Lift the drilling rig, lower the pipe jacking machine to the working well for positioning, and then jack it into the No.2 well along the drill pipe. What needs to be laid in the reducing joint of No.2 well? 127 the water diversion pipe is connected with the pipe jacking, and the water diversion pipe is slowly dragged back to complete the laying.
2, 2 matters needing attention
In actual construction, attention should be paid to prevent jacking. Ash? , fixed to the wall with steel plates. The central opening of the steel plate ensures the pipe jacking to pass through; When encountering groundwater, you can choose to raise the opening position appropriately to avoid the groundwater level. Because of the great resistance of horizontal well construction, it is necessary to pull out the casing after jacking, and the casing is connected by thread, and the torsional, compressive and tensile strength of the threaded part is much smaller. Therefore, the pipe should be selected according to the maximum jacking force and pull-out force, including material, pipe diameter, wall thickness, thread type, specification and size. In the actual construction, thick-walled high-quality geological steel pipe is selected.
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