Technical scheme of pipe jacking construction

Technical scheme of pipe jacking construction

Pipe jacking construction is a trenchless construction method, and it is a pipeline burying construction technology with no excavation or less excavation. Let me share with you the technical scheme of pipe jacking construction. Welcome to read and browse.

First, the working principle and process selection of pipe jacking

Working principle of pipe jacking: the pipe jacking construction starts from the pipe jacking working well, and the main jack system is installed in the working well to provide horizontal thrust. Firstly, the pipe jacking machine head installed on the guide rail is pushed into the soil through the broken door of the outlet hole reserved in the front wall, guided by the machine head, and then the reinforced concrete pipe is pushed forward section by section with the machine head. At the same time, the soil dug by the nose is continuously discharged, transported horizontally to the working well, and then transported vertically to the ground to transport waste soil. Adopt 24-hour continuous construction until the nose enters the receiving well for recovery and pipe jacking is completed.

Selection of pipe jacking technology: There are many kinds of pipe jacking construction methods, such as earth pressure balance method, mud-water balance method and air pressure balance method, which are determined by the functional classification of pipe jacking tools (heads). The suitable pipe jacking machine head should be selected according to the soil properties and groundwater conditions through which the machine head passes. The pipe jacking machine head is installed at the front end of the pipeline, which has the functions of controlling the direction of pipe jacking, digging and preventing collapse, and its shape and size are similar to those of pipe joints. Mud water balance head is proposed for this project.

Second, the equipment configuration and installation

(1) underground jack-up equipment

1. main jack: each jack station is equipped with three 300t hydraulic jacks, of which 1 is standby.

2. Combined bracket: the main jack is fixed on the combined bracket and symmetrically arranged left and right according to the cross section of the pipeline.

3. Oil pump: In order to ensure the stroke synchronization and joint action of the hydraulic jack, 1 electric high-pressure oil pump is used to form a parallel oil circuit to provide oil pressure for the jack. Each jack is equipped with an independent control valve.

4. Backseat load-bearing wall: the main jacking oil cylinder provides horizontal thrust to push the pipeline forward in the soil layer, and its reverse thrust acts on the steel member of the back seat and spreads to the back wall of the working well. The rear seat structure consists of 50mm thick steel plate (weighing about 2t) and 50cm thick concrete wall. A layer of 5cm thick wooden board is placed between the back seat and the back wall of the working well, so that the concentrated jacking force of the two cylinders can be transmitted and diffused to the working well wall.

5. Top iron and pressure dividing ring: The outer diameter and inner diameter of the pressure dividing ring are the same as those of the reinforced concrete pipe, and the length is 50cm. The jacking force of the two main jacking cylinders acts on the pressure dividing ring, and then the pressure dividing ring is uniformly diffused and transmitted to the rear end face of the concrete pipe. The structure of the annular top iron is the same as that of the pressure dividing ring. Its function is that one stroke of the oil cylinder is not enough to push a section of concrete pipe into place. After the oil cylinder is retracted, the jacking structure should be put between the pressure dividing ring and the oil cylinder, and then the oil cylinder is pushed again in the second stroke, so that a section of concrete pipe which greatly exceeds the stroke length of the oil cylinder can be pushed into place repeatedly. The length of the two jacking irons in this project is 1.0m, and they are made of 20cm thick steel plates and weigh about1t.

6. Setting and location of relay room

Answer: The 800 relay station consists of 10 sets of 30T hydraulic jacks, with a total jacking force of 300t and a telescopic amount of 30cm. The sectional placement position of the relay room on the pipeline can be determined by calculating the jacking resistance.

B, in general, because there are too many uncertain factors such as head-on resistance in front of the nose and pipeline outer wall resistance, in order to maintain a large safe jacking force reserve, the relay room 1 should be set as close as possible to the nose, generally 20 meters away from the nose (the relay room at the back should be arranged according to a certain length. Only one relay room is needed for each section of pipe jacking in this project, namely 1# relay station.

Three, pipe jacking tool pipe installation

After the head of the pipe jacking machine is repaired and debugged, it is transported to the site and hung on the guide rail in the working well. Check whether the nose and the track are balanced, and the central direction and relative height difference between the front and rear ends of the nose are less than 2mm, and then connect the oil circuit, mud and control system of the nose one by one. All components are connected firmly, without leakage, installed correctly, and the system is carefully inspected and tested.

Four, working well ground facilities

1, expansion grouting system: including bentonite mixing tank, grouting pump, pipeline, etc. For long-distance pipe jacking, the pumping capacity of mud pump is high, and the pressure should not be lower than 3Mpa.

2. Abandoned soil mud pit: mud and water are balanced, and the abandoned soil mud pit is set on the ground above the well. The spoil mud is pumped to the mud truck by the mud pump and transported to the place designated by the government for discharge. The sedimentation tank is provided with two circulating filtration tanks connected together. The open space of a single mud pit is 10m long, 5m wide and 2m high. The walls around the mud pit are made of 750mm bricks, of which the brick is Mu 100, and the cement mortar is M 10, and the inside and outside are plastered with 20mm thick cement mortar. C 15 concrete foundation slab with a thickness of 30cm is used at the bottom of the well.

3. Reservoir: Mud-water balance is adopted, and high-pressure water in front of the nose needs a lot of water to break ground. The reservoir needs to be built on the ground. The empty size of the reservoir is 5m long, 5m wide and 2m high. The walls around it are made of 750mm bricks, and the bricks are Mu 100 and M 10 cement mortar, and the inside and outside are plastered with 20mm thick cement mortar. The bottom hole adopts 20cm thick C 15 concrete foundation slab.

4. High-pressure oil pump station: including high-pressure oil pump, oil pipe, oil tank, pressure limiting valve, overflow valve and pressure gauge. Select 1 50Mpa high-pressure oil pump. After the hydraulic system equipment is installed, it should be put into trial operation, and regular maintenance should be carried out during use, so as to eliminate faults in time.

5. Air compressor station: supply air to the pipeline and the nose to ensure the breathing safety of the workers in the pipeline and the pressurization conditions in the gas cabin. The compressed air generated by the air compressor is purified and then input into the pipeline. Adopt 1 3m3 air compressor.

6. Mud station: including grouting pump, mixer, mud pit, pipeline, pressure gauge and valve, etc. Used to supply drag-reducing mud into the pipeline. Equipped with 1 grouting pump (0.8Mpa).

7. Lifting equipment: 25t truck crane is selected.

Five, pipe jacking out of the hole

When all the preparations inside and outside the well are completed, the nose can be hung on the guide rail in the well, the direction can be adjusted, and the pipe jacking drilling can be started. The front wall of the working well wall is reserved with organic head holes and pipe holes. Because of the rich groundwater level, in order to prevent water and soil outside the well from flowing into the working well from the gap between the reserved hole and the outer wall of the nose, the conventional sealing device between the reserved hole and the pipeline is replaced by the passive sealing device.

1, hole sealing structure: The function of hole sealing structure is to prevent mud from flowing into the well from the gap between the pipe joint and the hole during pipe jacking. Due to the high groundwater level, the general sealing structure has been changed.

According to the center line of the pipeline and the position of the reserved hole in the shaft wall, the inner coupling of double-layer steel structure is made. The inner ring of the collar is provided with a plurality of rubber waterstops, and butter is filled between the waterstops. The collar is installed between the reserved hole and the pipe joint, its periphery is welded on the embedded steel plate of the hole, and the inner ring rubber is close to the pipe joint.

2. Hole through the wall: When the front end of the machine head enters the hole sealing ring, it can be broken through the wall. The reserved hole of the working well has been temporarily blocked by the steel sealing door. Before jacking, cut off the sealing door horizontally bit by bit by gas cutting, and then push the nose forward and cut it into the soil, so that normal pipe jacking construction can be carried out. In order to ensure the safety of the jacking head, in addition to the large-diameter well point, the soil around the hole should be compacted by double-liquid grouting in advance to prevent water and soil from entering the working well more effectively. The compaction range of double liquid grouting is: 2m long? 4m wide? Six meters deep.

3. Direction monitoring: Only by controlling the direction of the pipe jacking hole can the whole pipe be jacked, but if the pipe jacking hole is not good, it is difficult to jack the whole pipe. Therefore, we must strictly control the accuracy of the pipe jacking hole, adopt tracking measurement, and adjust the direction and elevation deviation of the nostril at any time.

Six, jacking construction

A, after the tool pipe is jacked into the soil outside the front wall of the open caisson, leave its tail on the guide rail for about 30cm, recover the jack piston rod, remove the jacking iron, install the pipe joint and pressure dividing ring, and start the pipe jacking construction.

B, in order to achieve a jacking distance of 80m at a time, the following two technical measures are planned to be taken in this project: first, thixotropic mud is injected outside the pipe wall to form a mud sleeve with a certain thickness, and the jacking resistance is reduced by the lubrication of thixotropic mud; Secondly, the relay indirect force jacking technology is adopted to jacking step by step.

C, drag reduction by grouting: injecting thixotropic mud under pressure to fill the gap around the pipeline is an important measure to reduce formation loss, control ground subsidence and reduce jacking resistance to realize long-distance pipe jacking. For the grouting at the end of the pipe jacking machine head, it is necessary to follow the pipe jacking synchronously. In order to make the mud formed on the periphery of the pipeline always play the role of supporting the stratum and reducing the resistance, it is necessary to track and supplement the mud at the appropriate point of the subsequent pipeline to supplement the mud loss during jacking. The grouting equipment includes: ① grouting pump (screw pump, displacement 1000L/min, pressure 3 MPa); ② Agitator; Grouting pipe (supervisor? 50mm steel pipe, branch pipe? 25mm)； ④ Pipeline valves and pressure gauges. The thixotropic mud used consists of bentonite, water and additives in a certain proportion. The weight ratio of thixotropic mud in the construction site is: water: bentonite =8: 1, bentonite: CMC=30: 1. In this project, it is planned to purchase bagged bentonite composite materials and add water to stir them at the construction site. The grouting quantity is 1.5 times the annular gap around the pipeline, and the grouting pressure depends on the water pressure at the top of the pipeline.

Seven, measurement and rectification

① Pipe jacking survey control

Establishment of survey control network and underground survey platform: Before construction, according to the design drawings and survey control points provided by the owner, high-precision survey control network will be laid around the working well, and temporary leveling points will be set. According to the design requirements, the center line of the pipeline is determined on the ground, and the center line piles are set at both ends of the working well. According to the set center line of the pipeline and the well location of the working well, the ground and underground measurement control systems are established. The control pile is located in a place where it is not easy to be disturbed, the line of sight is clear, and it is easy to check.

On the jacking axis of jacking working well, near the back backrest, a measuring platform is set, and a temporary leveling point introduced by the ground leveling point is set on the platform, so as to proofread and adjust the height of the instrument during shift change. The jacking axis is introduced into the well by the design pipeline center through theodolite or hanging vertical line, 2? 3 rear viewpoints, check each other. The underground measuring platform must be stable, not in contact with pipes, equipment and backrest, and not affected by pipe jacking operation.

(2) Pipe jacking axis and elevation measurement

Using laser theodolite to determine the deviation between the pipe jacking direction and the pipe axis, and control the centering and centering of the roadheader. The measuring method is to align the starting point of the laser theodolite equipment in the underground measuring platform with the laser target plate set at the measuring point in the pipeline. The distance between the laser beam emitted by the laser theodolite and the center of the light target is the deviation value of the pipe jacking axis, but the direction is opposite. The elevation of pipe jacking is determined by the level.

③ Ground survey control of pipe jacking.

Ground subsidence will occur more or less in pipe jacking construction. The key is to observe the subsidence at any time and take effective measures. Generally, a set of settlement observation points are set up every 10 meter on the axis of pipe jacking for fixed-point and regular observation. If there is a large settlement, it must be treated. The treatment method is ground grouting, and the treatment area is determined according to the measurement.

④ Rectification of pipe jacking

Check whether the pipeline is jacked along the design pipe axis by measuring method, check the deviation of the pipeline axis position by theodolite, and measure the elevation of the pipeline inner bottom by level.

The deviation in the process of pipe jacking is completed by adjusting the direction of the nose by manipulating the correction jack group in the nose.

When rectifying deviation, it should be rectified in jacking, and gradually rectified at a small angle, so as to measure and rectify deviation frequently.

⑤ Axis and elevation control standards

Implement the standards of relevant specifications.

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