Seeking advice on jacking construction techniques

The choice of pipe jacking method is determined through technical and economic comparison, taking into account factors such as the properties of the soil layer in which the pipe is to be installed, the pipe diameter, the groundwater level, as well as nearby above-ground and underground buildings, structures, and various facilities. The conventional jacking method is a manually or mechanically excavated jacking technique used in cohesive or sandy soil layers, where there is no influence from groundwater. 　　(1) Working pit 　　① The location of the jacking pipe working pit should be chosen to facilitate drainage, soil removal, and transportation, and to allow for easy implementation of protective measures as well as ensure safe operations in relation to above-ground and below-ground buildings and structures. 　　②The prefabricated back wall is assembled from square timber, shaped steel, or steel plates, etc., and the resulting back wall for athletes possesses sufficient strength and stiffness. 　　③The support for the work pit should form a closed formwork frame, with diagonal braces added at the four corners of the rectangular work pit. 　　(2) Equipment installation 　　① Guides: Made of steel, the two guides are installed firmly, straightly, parallel to each other and at the same height; their longitudinal slope is consistent with the designed slope of the pipeline. During use, regularly check and verify the guide rails to prevent displacement. 　　②Jack: It is fixed to the bracket during installation and is symmetrical with respect to the vertical line through the center of the pipe; the point of action of its combined force lies on the vertical line through the center of the pipe. 　　③Oil pump: It should match the jack, and a spare oil pump should be used ； Conduct a trial run after installation is complete. If the oil pressure suddenly increases during the jacking process, jacking must be stopped immediately; the cause should be investigated and resolved before continuing with the jacking. 　　④Ejector pins: The modularly assembled ejector pins must have sufficient stiffness, and the adjacent surfaces of the ejector pins should be perpendicular to each other. 　　After installation, the axis of the ejector iron should be parallel and symmetrical to the axis of the pipeline, and there should be no dirt or oil on the contact surface between the ejector iron and the guide rail. 　　When replacing the top iron, first observe it in use to check for any abnormalities. 　　A cushioning material is used as a pad between the jacking iron and the pipe end; when the jacking force approaches the allowable compressive strength of the pipe segment material, U-shaped or ring-shaped jacking irons should be added at the pipe end. 　　Lifting equipment: Before starting formal operations, it should be tested by lifting to check the bundling of the load and its braking performance ； Overloading during lifting is strictly prohibited. 　　(3) Jacking 　　① Adopt manual jacking methods, lower the groundwater level to at least 0.5 M below the bottom of the pipe, and take measures to prevent other water sources from entering the jacking pipe. 　　②All equipment can be used for jacking forward after being inspected and passing trial operation. The jacking procedure is as follows: install the jacking iron, start the oil pump; after the piston of the jacking hammer moves one stroke forward, turn off the oil pump and the jacking hammer stops working while the piston retracts. Then a jacking iron is placed in the gap, and the oil pump is started again, and this process is repeated over and over. 　　③The tool pipe is pushed forward within a range of 5–10 m; the allowable deviations are: 3 mm for the axis position, and 0–+3 mm for the elevation. If these deviations are exceeded, measures must be taken to correct them. 　　④When manual tunneling and jacking is used, the following requirements shall be complied with: After the tool tube comes into contact with or penetrates the soil layer, excavation shall be carried out layer by layer from top to bottom. 　　When normal loading is applied in stable soil layers where over-excavation is permitted, over-excavation is not allowed within a 135-degree range below the pipe ； The over-excavation above the top of the pipe shall not exceed 15 mm ； The over-excavation in front of the pipe is determined based on specific circumstances, and safety protection measures are established. 　　⑤After the jacking process is completed, the internal gap at the joint of the pipe segments shall be treated in accordance with the design specifications; if no such specifications exist, asbestos cement, elastic sealant, or cement slurry can be used for sealing. The filler should be smoothed out and must not protrude into the tube. 　　⑥Measure the center and elevation of the tool pipe during jacking. When manual excavation is used, as the tool pipe moves into the soil layer, measurements should be taken at least once every 0.3 meters of advancement ； When the pipe is pushed forward normally after entering the soil layer, measurements are taken every 1.0 meter; the frequency of measurements is increased during alignment correction. 　　After the entire section is completed, measure the axial position and elevation at each joint between pipe segments ； When there is a misalignment, the relative height difference is measured. 　　⑦Correction: A small angle is used, with correction being made gradually as the pipe moves forward.
Correction methods: The excavation correction method involves digging less soil on the side where the pipe is tilted to one side, and digging more soil on the other side, thereby forcing the pipe to shift to the other side as it moves forward. Suitable for deviations of 10-20mm. 　　Wooden bar support method: When the end of the pipe sags or the pipe becomes misaligned, the wooden bar support method can be used for correction; it is suitable for deviations of up to 20 mm. 　　⑧During the jacking process, measures should be taken to address the following emergency situations: An obstacle is encountered in front of the tool pipe; The rear wall deforms severely; The jacking iron becomes twisted; The pipe’s position deviates too much and correction is ineffective; The jacking force exceeds the allowable value for the pipe end; Abnormalities occur in the oil pump or oil circuit; Mud leaks from the joints

6.1.1 The construction design for pipe jacking shall include the following main contents: 6.1.1.1 Layout plan of the construction site； 　6.1.1.2 Selection of jacking method and determination of unit length of jacked pipe section ； 　6.1.1.3 Selection of the location for the work pit and design of its structural type ； 　6.1.1.4 Selection of jacking machine head and specifications, models, and quantities of various equipment ； 　6.1.1.5 Top force calculation and back design ； 　6.1.1.6 Design of door closures for openings ； 　6.1.1.7 Methods of measurement and correction ； 　6.1.1.8 Layout of vertical and horizontal transportation ； Methods for lowering pipes, digging soil, transporting soil, or removing mud and water ； 　 　6.1.1.9 Drag reduction measures ； 　6.1.1.10 Measures to control ground uplift and settlement ； 　6.1.1.11 Groundwater drainage methods ； 　6.1.1.12 Grouting reinforcement measures ； 　6.1.1.13 Safety technical measures. 6.1.2 The selection of the pipe jacking method shall be determined through technical and economic comparison, taking into account factors such as the properties of the soil layer in which the pipe is located, the pipe diameter, the groundwater level, as well as nearby above-ground and underground buildings, structures, and various facilities. It shall also comply with the following provisions: 6.1.2.1 In clay or sandy soil layers, where there is no influence from groundwater, the manual or mechanical excavation jacking method is preferred ； When the soil is gravelly, supportive tool pipes or grouting can be used to reinforce the soil layer ； 　6.1.2.2 In soft soil layers where there are no obstacles and the soil layer above the pipe crown is thick, the extrusion-type or mesh-type pipe jacking method is advisable ； 　6.1.2.3 When it is necessary to control ground subsidence in clay layers, the earth pressure balance jacking method is advisable ； 　6.1.2.4 In silt layers where it is necessary to control ground heave, the slurry-added earth pressure balance or slurry balance jacking method is recommended ； 　6.1.2.5 When pushing metal pipes with a short jacking length and small diameter, the jacking method for compacting soil layers in a single operation is recommended. 6.1.3 When using a manually excavated jacking pipe, the groundwater level should be lowered to at least 0.5 mm below the bottom of the pipe, and measures should be taken to prevent other water sources from entering the jacking pipe. 6.1.4 For surveying during jacking construction, a surface and underground survey control system should be established; control points should be located in areas that are not prone to disturbance, have clear line of sight, are convenient for verification, and are easy to protect. 6.2 Working Pit 6.2.1 The location of the jacking pit shall be selected in accordance with the following conditions: 6.2.1.1 The location of the pipe shaft ； 　6.2.1.2 The pit wall soil can be utilized as a backfill ； 　6.2.1.3 Facilitate drainage, excavation, and transportation ； 　6.2.1.4 Measures to facilitate protection and safe construction for above-ground and underground buildings and structures ； 　6.2.1.5 Proximity to power and water sources, with convenient transportation ； 　6.2.1.6 It is advisable to locate it on the downstream side during one-way jacking. 6.2.2 When using a prefabricated back wall, the following requirements shall be met ； 　6.2.2.1 The prefabricated back wall should be assembled using timber, section steel, or steel plates, etc.; the assembled back wall must possess sufficient strength and stiffness ； 　6.2.2.2 The back soil wall surface shall be smooth and perpendicular to the direction of pipe jacking ； 　6.2.2.3 The bottom end of the prefabricated back wall should be below the bottom of the work pit, and should not be less than 50 cm ； 　6.2.2.4 The backfill soil surface shall be in close contact with the back wall; if there are voids, they shall be filled tightly with sand and gravel ； 　6.2.2.5 The components of the assembled back wall should have consistent specifications within the same floor, and the connections between floors should be tight with each layer being secured properly. 6.2.3 The support for the working pit should form a closed framework, with diagonal braces installed at the four corners of the rectangular working pit. 6.2.4 The walls of the jacking pit and the prefabricated back wall shall be perpendicular to the pipeline axis, and the allowable construction tolerances shall comply with the provisions in Table 6.2.4. 　　　Allowable deviations for the construction of the working pit and the prefabricated back wall (mm)　　　　　　　Table 6.2.4 Item Allowable Deviation Width on each side of the working pit Not less than the value specified in the construction design Length Prefabricated back wall Verticality 0.1%H Horizontal torsion 0.1%L 　Note: 1.H is the height of the prefabricated back wall (mm) ； 　　　　2. L is the length of the prefabricated back wall in mm. 6.2.5 When there is no native soil available for use as a back wall, an artificial back wall with a simple structure, high stability and reliability, materials sourced locally, and easy to remove should be designed. 6.2.6 When the already jacked pipes are used as a backing, the following requirements shall be met: 6.2.6.1 The jacking force required for the pipes yet to be jacked shall be less than the jacking force of the already jacked pipes ； 　6.2.6.2 A cushioning material should be placed between the back steel plate and the pipe opening ； 　6.2.6.3 Take measures to protect the interface already inserted into the pipeline from damage. 6.2.7 When an diaphragm wall is used for the jacking pit, it shall comply with the provisions of the current **standard \"Code for Construction and Acceptance of Foundation Engineering\", and a construction design shall be prepared. The construction design should include the following main contents ； 　6.2.7.1 Layout of the working pit in plan and in elevation ； 　6.2.7.2 Excavation of soil and slurry treatment for trench sections ； 　6.2.7.3 Connection methods for wall concrete and waterproofing measures ； 　6.2.7.4 Design of reserved jacking tunnel openings ； 　6.2.7.5 Reserved pipes, fittings, and measures for their connection to the internal structure ； 　6.2.7.6 Support and bottom sealing measures for the excavation trench ； 　6.2.7.7 Finishing of the inner surface of the wall, lining, and design of the back support after pipe jacking ； 　6.2.7.8 Necessary test and research contents. 6.2.8 The sections of the diaphragm wall should be connected using joint boxes, and the location of these joints should be offset from the points where they meet the internal structure of the shaft. 6.2.9 The allowable deviations for the excavation shape of the trench section shall comply with the provisions in Table 6.2.9. 　　　　　　　Allowable deviation for trench excavation shape (mm)　　　　　　　　　　　Table 6.2.9　 Item Allowable Deviation Axial position 30 Verticality of trench 0.3MPa From the time the steel reinforcement framework is in place until concrete pouring starts 1.00m, 4.00m/h Difference in concrete level between conduits