Construction method for large-section rectangular pipe jacking in cemented conglomerate stratum

Abstract

The present application discloses a construction method for large-section rectangular pipe jacking in a cemented conglomerate stratum, comprising the following construction steps: arranging a pipe shed (1) on the outer contour of the top of an excavation cross-section to achieve support of the top of the excavation cross-section; dividing the excavation cross-section into a rock stratum region (2) and a soft soil region (3), arranging positioning drilling holes (4) in the rock stratum region, and arranging positioning grouting reinforcement holes (5) in the soft soil region; performing horizontal drilling in the rock stratum region on the basis of positioning points of the drilling holes, and after drilling of the drilling holes is completed, injecting a bentonite-slaked lime mixed slurry into the drilling holes to fill the drilling holes; performing horizontal high-pressure jet grouting pile construction at the grouting reinforcement holes in the soft soil region to achieve reinforcement of the soft soil stratum; and after treatment of the soft soil region and the rock stratum region is completed, using a pipe jacking machine to perform jacking along a jacking route. The present application enables smooth jacking construction in complex strata having abrupt stratum changes.

Description

Construction method of large-section rectangular pipe jacking in cemented conglomerate strata Technical Field

[0001] This application belongs to the technical field of pipe jacking construction, and particularly relates to a method for constructing large-section rectangular pipe jacking in cemented conglomerate strata. Background Technology

[0002] Pipe jacking is a trenchless pipeline laying technology for underground engineering, similar to shield tunneling. It uses a pipe jacking machine to create a hole, and then pushes a pre-formed pipe into the jacking shaft to form a continuous lining structure.

[0003] With the development of construction equipment manufacturing in my country, rectangular pipe jacking construction is widely used in underground pedestrian crossings attached to subway stations, which reduces ground excavation and thus reduces the impact of subway construction on surrounding road traffic and underground pipelines.

[0004] During pipe jacking construction, the geological conditions have a significant impact on the smooth advancement of the pipe. Currently, there are geological conditions with abrupt changes in the strata. Due to these abrupt changes, the geological structure is complex, the strata are not clearly defined, and other strata are interspersed within the strata, making pipe jacking difficult. In particular, when encountering high-strength rock strata such as large-diameter boulders and cemented conglomerate layers, the rock-breaking capacity of conventional pipe jacking machines does not exceed 5MPa. In such strata, pipe jacking machines face difficulties in jacking, their posture is difficult to control, ground settlement is uncontrollable, and it is difficult to remove boulders after they enter the soil chamber. Large boulders can easily jam the auger disc. Summary of the Invention

[0005] This application provides a method for constructing large-section rectangular pipe jacking in cemented conglomerate strata, which solves the problem of difficulty in tunneling through hard rock strata during rectangular pipe jacking construction.

[0006] This application provides a method for constructing large-section rectangular pipe jacking in cemented conglomerate strata, including the following construction steps:

[0007] Pipe sheds are constructed on the top outer contour of the tunneling cross section to provide support for the top of the tunneling cross section;

[0008] The tunneling cross section is divided into a rock stratum zone and a soft soil zone. Positioning drilling holes are arranged in the rock stratum zone, and grouting reinforcement holes are positioned in the soft soil zone to replace the rock stratum.

[0009] In the rock strata area, horizontal drilling is carried out according to the positioning point of the drilling hole. After the drilling is completed, bentonite-lime mixture slurry is injected into the drilling hole to fill it.

[0010] Horizontal high-pressure jet grouting piles were constructed at each grouting reinforcement hole in the soft soil area to reinforce the soft soil strata.

[0011] After the strata treatment in the soft soil and rock strata areas is completed, the pipe jacking machine is used to excavate along the tunneling route.

[0012] Furthermore, the drilling and grouting of the borehole, as well as the construction of horizontal high-pressure jet grouting piles from the grouting reinforcement hole into the stratum, can all be carried out according to the principle of approaching the middle from both ends of the tunneling route.

[0013] Furthermore, if the formation changes during drilling, drilling should be stopped and the end of the borehole should be sealed by grouting.

[0014] Furthermore, during the drilling process, if the water output from a single hole is less than 30 L / min, drilling can continue; if the water output from a single hole is greater than 30 L / min, drilling should be stopped immediately and grouting should be performed to seal the hole.

[0015] Furthermore, the spacing of the drill holes at the outer edge of the rock stratum is more dense than that in the middle of the rock stratum.

[0016] Furthermore, after drilling is completed, all drilled holes are pressure tested with clean water. After the pressure test, grouting is slowly injected under pressure. After grouting is completed, re-pressure is applied until the grout is fully diffused and penetrated before sealing the holes.

[0017] Furthermore, the drilling area of ​​the borehole covers the interface between the rock strata and the soft soil.

[0018] Furthermore, before carrying out soil modification construction in the rock and soft soil areas, a construction step is included to arrange settlement monitoring points on the ground above the tunneling route, with the settlement monitoring points being densified at the pipeline.

[0019] Furthermore, when using a pipe jacking machine to excavate forward, the machine employs a composite cutterhead, which combines tearing cutters, shell cutters, and fishtail cutters.

[0020] Furthermore, the composite cutterhead is configured as a 6-spoke type, with a reinforcing ring on the outer edge and middle of each spoke, tearing blades on both sides of the spokes, heavy-duty tearing blades at the ends, a shell blade made of large alloy in the middle, a fishtail blade in the middle of the cutterhead, and a shovel blade with wear-resistant welding on the casing of the pipe jacking machine.

[0021] In summary, this application includes at least one of the following beneficial effects:

[0022] 1. Before the rectangular pipe jacking construction, the construction method of this application first pre-treats the hard rock layer, that is, drilling holes in the hard rock layer and refilling the holes with grout, thereby reducing the structural strength of the rock layer area at the tunnel face; on the other hand, grouting is used to reinforce the silty clay layer to improve the soil strength of the soft soil area, thereby balancing the jacking resistance of the rectangular pipe jacking machine in each area during the jacking process, so that the pipe jacking construction in complex strata with abrupt changes can be smoother.

[0023] 2. The construction method of this application involves simultaneously approaching the drilling hole from both the starting portal and the receiving portal in both directions, which can reduce the drilling depth of the drilling hole on one side, thereby reducing the construction difficulty and improving the drilling efficiency of the drilling hole. At the same time, grouting reinforcement of soft soil strata in both directions can shorten the grouting interval, improve construction efficiency, and allow for real-time adjustment of grouting construction according to the strata conditions.

[0024] 3. Based on the geological conditions after stratum treatment, the cutterhead structure is adaptively adjusted. By combining multiple cutterheads, the cutting kinetic energy of the pipe jacking equipment can be enhanced, thereby achieving smoother tunneling. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the strata at a certain tunneling section of the strata being tunneled in this application;

[0026] Figure 2 is a schematic diagram of the tunneling section after the formation treatment is completed in this application;

[0027] Figure 3 is a geological profile diagram used in this application to illustrate the pipe jacking tunneling route;

[0028] Figure 4 is a schematic diagram of the rectangular composite cutter head of this application;

[0029] Figure 5 is a schematic diagram of the MM cross-section in Figure 4;

[0030] Figure 6 is a cross-sectional schematic diagram of NN in Figure 4.

[0031] The components represented by each number in the attached diagram are listed below: 1. Pipe roof; 2. Rock strata area; 3. Soft soil area; 4. Drill hole; 5. Grouting reinforcement hole. Detailed Implementation

[0032] The present application will be further described in detail below with reference to Figures 1-6.

[0033] This application discloses a method for constructing large-section rectangular pipe jacking in cemented conglomerate strata. It addresses geological conditions where the cemented conglomerate abruptly transitions into a silty clay layer, and where some sections of the tunneling route also include a gravel layer, as shown in Figure 1. On the jacking cross section, cemented conglomerate and silty clay layers coexist. This results in significant resistance and difficulty in jacking the pipe when it passes through the cemented conglomerate layer, while jacking is smooth in the silty clay layer. This leads to inconsistent forward resistance on both sides of the pipe jacking machine, further complicating the jacking process.

[0034] The construction method for large-section rectangular pipe jacking in cemented conglomerate strata includes the following steps, as shown in Figures 2 and 3:

[0035] Step 1: Construct pipe roof 1 along the top outer contour of the tunneling route. Pipe roof 1 provides support above the tunneling route, reducing the occurrence of soil collapse or surface subsidence during the jacking process.

[0036] Because the pipe jacking construction is carried out in urban areas with shallow overburden and proximity to existing municipal pipelines, the pipelines are prone to settlement or even damage during construction. To protect the pipelines, when the pipelines are located within 1.5 meters outside the structure's outline, a Φ159@300 pipe roof (1) is used for protection between the pipelines and the structure, reducing disturbance to the pipelines during construction. The pipe roof (1) also provides support for the smooth progress of the pipe jacking construction, minimizing the risk of overburden collapse and interruption of the construction.

[0037] In the design of pipe roof 1, hot-rolled seamless steel pipes of Φ159 diameter with a wall thickness of 8mm and a section length of 3m were used. The horizontal and vertical spacing of the steel pipes was 300mm. The design length of pipe roof 1 was determined based on the location of the pipeline and the tunnel portal, and the end of pipe roof 1 extended beyond the pipeline by no less than 2m. The steel pipes were driven into the ground at an elevation angle of 1°, parallel to the centerline of the tunnel. Cement grout was used for grouting with a water-cement ratio of 1:1. Grouting of pipe roof 1 was mainly of the filling type, and the grouting pressure was strictly controlled.

[0038] Due to abrupt geological changes, the geological conditions at each drilling cross-section along the drilling route differ. In areas where cemented conglomerate abrupt strata exist at the edge of the excavation zone, the top support can be directly achieved through the cemented conglomerate. However, some drilling cross-sections may not include cemented conglomerate abrupt strata. By designing pipe roof 1, top support can be achieved for the entire excavation section, making the entire construction process safer.

[0039] The construction operation of pipe shed 1 specifically includes the following procedures: erecting a drilling platform, installing a drilling machine, drilling, cleaning the hole, inspecting the hole, installing the steel pipes of pipe shed 1, grouting, and dismantling the platform.

[0040] During the drilling process, a Φ200mm drill bit is used to facilitate the installation of the steel pipe. The drilling depth should be greater than the designed 0.5m to facilitate pipe insertion. The drilling sequence proceeds from the highest hole to the lowest. When the first drill rod penetrates the soil and 20-30cm remains at the end, drilling is stopped. Two pipe wrenches are used manually to clamp the drill rod, and the drilling rig is reversed at low speed to disengage it. The drilling rig returns to its original position along the guide rail. The second drill rod is then manually inserted, and a connecting sleeve is installed at the front end. The drilling rig is then fed at low speed to the end of the first drill rod, and after alignment, they are connected as one unit. After drilling to the required depth, the drill rods are disassembled using the same method.

[0041] In the hole cleaning and inspection process, the drill bit is used to sweep the hole back and forth to remove floating slag to the bottom of the hole, ensuring that the hole diameter and depth meet the requirements and preventing the hole from being blocked; then, high-pressure air is used to clean the drill slag from the bottom of the hole to the hole opening; finally, the hole depth is checked with a drill rod and the inclination angle is checked with a total station.

[0042] During the installation of the steel pipes for pipe shed 1, Φ6-8mm grouting holes are drilled around the perimeter of the steel pipes. A guide drill bit is welded to the front end. Φ6-8mm overflow holes are drilled in the middle of pipe shed 1, arranged in a quincunx pattern to prevent dead zones during grouting. The spacing between the overflow holes is 200mm. No holes are drilled within 150cm of the tail end of the steel pipe to prevent grout leakage. The steel pipe joints use threaded connections, with each thread being 150mm long.

[0043] After the steel pipes of pipe shed 1 are installed, cement grout is used for grouting with a water-cement ratio of 1:1 and the grouting pressure is controlled between 0.5 and 1.0 MPa.

[0044] Step 2: Set up settlement monitoring points on the ground above the tunneling route. Before proceeding with subsequent drilling operations, settlement monitoring points must be established to monitor surface settlement, underground pipeline settlement, surrounding road settlement, and building settlement during the pipe jacking construction process. Specifically, the monitoring method employs precise leveling, using an electronic level to obtain the initial elevation by connecting the settlement monitoring points with nearby benchmarks. Throughout the entire construction cycle, ground settlement changes at the settlement monitoring points are monitored.

[0045] The principle for arranging settlement monitoring points is as follows: Settlement monitoring points are laid out according to the monitoring design drawings, with one point every 3.5m along the cross-section and one every 5m along the longitudinal section, with denser placement at pipeline locations. The construction method for settlement monitoring points includes the following steps: Drilling observation holes downwards into the unobstructed ground surface using a water drill or truck drill (taking a 22cm diameter observation hole as an example); driving a detection rod into the observation hole, the diameter of which is smaller than the diameter of the observation hole. In this embodiment, it can be a threaded steel bar with a diameter of 18cm, and a length of 0.8m to 1.2m, with a stainless steel elliptical head welded to the top; after driving the detection rod into the ground, filling the area around the rod with fine sand and compacting it. In one embodiment, if the surface is concrete or asphalt concrete pavement, the bottom of the detection rod should penetrate at least 20cm into the subgrade below the pavement and be isolated from the pavement.

[0046] To minimize the impact of road surface settlement on settlement monitoring data at settlement monitoring points, the monitoring rods must not be fixed inside the observation holes with concrete or cement. Finally, ABS engineering plastic protective covers should be placed on top of the settlement monitoring points for protection. All settlement monitoring points should be marked with red paint and uniformly numbered for easy location and monitoring by construction personnel.

[0047] Step 3: Drill holes 4 are arranged and drilled at intervals in the cemented conglomerate area of ​​the excavation face, and grouting reinforcement holes 5 are positioned at intervals in the silty clay layer area of ​​the excavation face.

[0048] For ease of description, the cemented conglomerate layer area at the excavation face is referred to as rock layer area 2, and the silty clay layer area is referred to as soft soil area 3. It should be noted that as the excavation route advances, the area occupied by rock layer area 2 and soft soil area 3 on each excavation section is dynamically changing, and some sections of the excavation section also contain gravel layers. When arranging the drill holes 4, the density of drill holes 4 on the periphery of the excavation section is greater than the density of drill holes 4 in the central area of ​​the excavation end face, thereby forming a more interconnected drill hole area on the periphery of the excavation section. This makes it less likely for the pipe jacking rig to deviate, head up, or get stuck during the drilling process.

[0049] During the actual construction, firstly, at both ends of the route to be excavated, the starting portal and receiving portal are formed by excavating downwards from the ground surface. The construction personnel determine the drilling points of drilling hole 4 and grouting reinforcement hole 5 at the stratum cross section at the starting portal and receiving portal, based on the geological survey report and the actual rock stratum distribution during the excavation of the station and auxiliary foundation pit.

[0050] The geological treatment of rock strata zone 2 and soft soil zone 3 can be carried out simultaneously to shorten the construction period. During construction in rock strata zone 2, horizontal drilling equipment, such as a auger, is used to drill into the rock strata. During construction in the soft soil zone, grouting pipes are directly driven into the grouting reinforcement hole at point 5.

[0051] In the preferred embodiment, drilling of the entry hole 4 is carried out simultaneously from both the starting portal and the receiving portal ends. Drilling of the entry hole 4 follows the principle of approaching the middle from both ends to improve construction efficiency and accelerate the drilling progress. During the drilling of the entry hole 4, if the water output from a single hole is less than 30 L / min, drilling can continue; if the water output from a single hole is greater than 30 L / min, drilling should be stopped immediately and grouting should be performed for sealing.

[0052] Additionally, if the formation changes from cemented conglomerate to silty clay or gravel during drilling of borehole 4, drilling must be stopped immediately. Grouting should then be performed at the end of borehole 4 to reinforce the formation at that end, reducing disturbance to the gravel layer, or to reinforce the silty clay layer.

[0053] Step 4: After drilling hole 4 is completed, a bentonite-lime mixture grout is injected into hole 4 to fill it. Simultaneously, a jet grouting hole is drilled at the location of the grouting reinforcement hole 5 in soft soil zone 3 using a horizontal drilling jet grouting machine. High-pressure grout is sprayed during the drilling process, ultimately forming a horizontal high-pressure jet grouting pile within the soft soil zone 3 stratum, thus reinforcing the soft soil zone 3 stratum.

[0054] During the grouting construction of borehole 4, the grouting pipe and pressure relief pipe were installed immediately after borehole 4 was drilled. After effective sealing, the borehole 4 was filled with a mixture of bentonite and hydrated lime. The grouting pipe can be a 50mm diameter PVC pipe, and the pressure relief pipe can be a 25mm diameter PVC elbow. The sealing of the grouting pipeline was checked by water pressure, and at the same time, the rock fissures were flushed to expand the grout passage and increase the compactness of the grout filling.

[0055] Specifically, after drilling is completed, all drilled holes 4 are pressure tested with clean water. This serves two purposes: firstly, to clean the holes and increase the diffusion area of ​​the dual-liquid slurry; and secondly, to check which holes can be pressured with clean water and to mark the holes that can be pressured with clean water.

[0056] During grouting, apply pressure slowly and evenly. Generally, when the pressure reaches the specified value of 1-1.5 MPa, maintain the pressure until a continuous and full flow of cement grout overflows from the overflow hole. Then, plug the overflow hole with a wooden plug and maintain the pressure for at least 3-5 minutes to allow the grout to fully diffuse and penetrate the bottom of the slab, achieving a compaction and filling effect. If any pressure loss is observed during the pressure holding process, replenish it promptly. After the required pressure holding time is met, open the unloading switch and slowly reduce the pressure until it returns to zero.

[0057] Re-pressurization: Re-pressurization should be completed within 0.5-2 hours. Pressurization should be applied slowly and evenly. Generally, when the pressure reaches the specified value of 1.5-2 MPa, maintain the pressure for at least 3-5 minutes to allow the grout to fully diffuse and penetrate the bottom of the slab, achieving a compaction and filling effect. If pressure loss is observed during the holding period, it should be replenished promptly. After the required holding time is met, open the unloading switch and slowly reduce the pressure until it returns to zero.

[0058] Sealing the hole: When the grouting is finished, the grouting plug should be pulled out immediately and a wooden plug should be inserted immediately to allow enough time for the two-component grout to fully solidify. After ensuring that the two-component grout will not be squeezed out of the hole, the wooden plug can be pulled out after 8-10 minutes. The hole opening should be permanently sealed with quick-setting cement mortar. When sealing the hole opening, it should be tamped down with a chisel first and then smoothed.

[0059] When constructing horizontal high-pressure jet grouting piles in soft soil area 3, a horizontal drilling jet grouting machine is used to drill jet grouting holes horizontally or inclined in the loose and weak strata. High-pressure grout of over 20 MPa is sprayed from small nozzles at the rear and sides of the drill bit. The nozzles spray from the bottom of the hole while rotating and retracting; the sprayed high-pressure grout quickly solidifies with the soil and rock cut and broken off within a certain range to form a columnar solidified body, whose strength is significantly higher than that of the original strata, thus reinforcing the surrounding strata.

[0060] When reinforcing the soft soil zone 3, both horizontal MJS piles and horizontal WSS grouting methods can be used. However, with WSS grouting, the grout diffuses primarily through grouting pressure within the soil, resulting in an uncertain diffusion range and lower controllability compared to horizontal MJS and jet grouting piles. This is particularly problematic in areas with shallow overburden and large voids in the soft soil. Improper grouting pressure control can lead to grout diffusion into rock zone 2, reconsolidating the fractured hard rock and reducing the effectiveness of pre-fracture construction in rock zone 2. While horizontal MJS piles are more expensive, and although their effectiveness is slightly less than that of horizontal MJS piles, the reinforced soil can still meet the site's requirements for soft soil reinforcement.

[0061] Step 5: After the bentonite-lime mixture in the drilling hole 4 in the rock stratum 2 has solidified and the horizontal high-pressure jet grouting pile in the soft soil 3 has been formed, the soil pretreatment is completed, and a tunneling face with small strength difference is formed along the tunneling end face. At this time, the pipe jacking machine is used to tunnel from the starting face of the tunneling route along the tunneling route.

[0062] During drilling, a rectangular composite cutterhead is used. Referring to Figures 4 to 6, the earth pressure balance pipe jacking machine cutterhead is configured with a 6-spoke design. Each spoke has a reinforcing ring at its outer edge and center. Tear cutters are installed on both sides of the spokes, with heavy-duty tear cutters at the ends. A large-alloy shell cutter is installed in the center, 37mm higher than the tear cutters. A fishtail cutter, 260mm high, is also installed in the center of the cutterhead to enhance its cutting ability against residual cemented conglomerate. The casing of the pipe jacking machine is equipped with wear-resistant welded blades to ensure the jacking cross-section meets design requirements. The cutterhead configuration is shown in Appendix 3.

[0063] The design principle of the large-section rectangular pipe jacking construction method in cemented conglomerate strata of this application is as follows: For complex strata with abrupt changes in formation, different strata with varying hardness will form at each tunneling cross section during the tunneling process, making it difficult for the pipe jacking machine to tunnel smoothly. The construction method of this application involves setting up drilling holes 4 in the rock strata zone 2 and injecting a bentonite-lime mixture grout into the drilling holes 4 to replace the strata and reduce the hardness of the rock strata zone 2; simultaneously, horizontal high-pressure jet grouting piles are used to grout the soft soil zone 3 to enhance the soil hardness of the soft soil zone 3, thereby making the hardness of each area of ​​the pipe jacking machine's tunneling face more uniform. Combined with the design of the cutterhead structure, this enables the pipe jacking machine to tunnel smoothly along the entire line.

[0064] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for constructing large-section rectangular pipe jacking in cemented conglomerate strata, characterized in that, The construction steps include the following: A pipe shed (1) is constructed on the top outer contour of the tunneling cross section to achieve support at the top of the tunneling cross section; The tunneling cross section is divided into a rock stratum area (2) and a soft soil area (3). Positioning drilling holes (4) are arranged in the rock stratum area (2), and grouting reinforcement holes (5) are positioned in the soft soil area (3). In the rock strata area (2), horizontal drilling is carried out according to the positioning point of the drilling hole (4). After the drilling of the drilling hole (4) is completed, bentonite-lime mixed slurry is injected into the drilling hole (4) to fill the drilling hole (4) and realize the replacement of the strata in the rock strata area (2). Horizontal high-pressure jet grouting piles were constructed at each grouting reinforcement hole (5) in the soft soil area (3) to reinforce the soft soil strata (3); After the strata treatment of the soft soil area (3) and the rock strata area (2) is completed, the pipe jacking machine is used to excavate along the tunneling route.

2. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, The drilling and grouting of the drilling hole (4), as well as the horizontal high-pressure jet grouting pile construction from the grouting reinforcement hole (5) into the stratum, can all be carried out according to the principle of approaching the middle from both ends of the tunneling route.

3. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, If the formation changes during drilling of the borehole (4), drilling should be stopped and grout should be injected at the end of the borehole (4) to seal the end of the borehole (4).

4. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, During the drilling process of hole (4), if the water output of a single hole is less than 30L / min, drilling can continue; if the water output of a single hole is greater than 30L / min, drilling should be stopped immediately and grouting should be performed to seal the hole.

5. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, The spacing of the drill holes (4) at the outer edge of the rock stratum (2) is more dense than that in the middle area of ​​the rock stratum (2).

6. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, After drilling the hole (4), test all the holes (4) with clean water. After the test, slowly pressurize and grout. After grouting, repressurize until the grout is fully diffused and penetrated, and then seal the hole.

7. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, The drilling area of ​​the borehole (4) covers the interface between the rock stratum (2) and the soft soil area (3).

8. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, Before carrying out soil modification construction in the rock strata area (2) and soft soil area (3), a construction step is included to arrange settlement monitoring points on the ground above the tunnel route, with the settlement monitoring points being densified at the pipeline.

9. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 1, characterized in that, When using a pipe jacking machine to excavate forward, the machine employs a composite cutterhead, which combines tearing cutters, shell cutters, and fishtail cutters.

10. The method for constructing large-section rectangular pipe jacking in cemented conglomerate strata according to claim 9, characterized in that, The composite cutter head is configured with 6 spokes, with a reinforcing ring on the outer edge and middle of each spoke. Tear blades are installed on both sides of the spokes, heavy-duty tear blades are installed at the ends, and a shell blade made of large alloy is installed in the middle. A fishtail blade is installed in the middle of the cutter head, and the casing of the pipe jacking machine is equipped with a shovel blade with wear-resistant welding.

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