Anti-slide pile structure for loose body stratum and construction method of anti-slide pile structure

Abstract

The invention relates to the technical field of rock engineering, in particular to an anti-slide pile structure for a loose body stratum and a construction method of the anti-slide pile structure. According to the technical scheme, a loose soil grouting protection wall around a pile foundation and a novel anti-slide pile assembly are included; the loose soil grouting protection wall is grouted on the periphery of the outer side of the pile foundation before pile hole excavation to form an original soil consolidation protection wall; the novel anti-slide pile assembly comprises a rectangular pile; a special-shaped prefabricated bearing platform; the round rotary excavating pile group serves as an anti-slide pile anchoring section, and I-shaped steel anti-pulling keys are arranged on the side walls of round piles on the side close to the mountain; the circular pile backer side reinforcement cage is used for forming a circular pile framework; two rows of round pile top pressing beams are arranged on the backer side and used for connecting the rectangular pile reinforcement cages on the backer side, the two round pile reinforcement cages and the middle round pile reinforcement cage in a lap joint mode; and the prestressed ground anchor is used for improving the anchoring strength and the shearing strength of the pile foundation. According to the novel anti-slide pile assembly and the construction method, full-mechanical operation of the rectangular pile in the soft stratum can be achieved, and the construction efficiency, the economical efficiency and the safety are all high.

Description

Technical Field

[0001] The present invention relates to the technical field of rock engineering, and particularly to an anti-slide pile structure for loose strata and a construction method thereof. Background Art

[0002] In the field of rock engineering, landslide control and slope stability are key tasks to ensure the safety of various projects. As an important retaining structure, anti-slide piles are widely used to prevent landslide bodies from sliding and stabilize slope rock and soil masses. However, when facing loose strata, the traditional anti-slide pile structure and its construction method expose many problems. Loose strata are composed of soil, weathered rock, sand, gravel, pebble layers, etc., belonging to the Quaternary and Neogene strata. They are formed by geological processes such as erosion, transportation, and accumulation of various rocks and have not been consolidated and sedimented into rocks, so they show a loose and soft state. Compared with general rock formations, the strength of loose layers is much lower, there is no layered effect, and the stability is extremely poor. This characteristic of loose media has a significant impact on rock formation and surface deformation, becoming a thorny problem in engineering construction. From the perspective of the anti-slide pile structure: due to the soft characteristics of loose bodies, hole collapse is extremely likely to occur during the mechanical hole-forming process. When there are no effective protection measures at the hole opening, the soil at the hole opening is extremely easy to collapse during the excavation process, hindering the construction progress; on the side wall of the pile hole, ordinary retaining structures are difficult to play a stable role in loose bodies and cannot provide a safe and stable working space for subsequent construction. At the same time, the existing anti-slide pile structures have deficiencies in overall performance. For example, the traditional anti-slide pile structure has a single form, and the design of key parts such as the free end and the anchorage section is not optimized enough to adapt to the complex and changeable stress conditions of loose strata. Under the action of landslide thrust, the pile body is prone to problems such as deformation and fracture, resulting in a significant reduction in the anti-slide effect. In addition, the pile body on the mountain side is under tensile and bending forces for a long time, the concrete is prone to cracking, and the internal steel bars are directly exposed to the external environment, accelerating corrosion, seriously affecting the long-term resistance of the pile foundation, and threatening the long-term stability of the engineering structure.

[0003] In view of the above reasons, this application proposes an anti-slide pile structure that overcomes the problem of forming rectangular pile foundations in loose strata and improves the applicability and stability in loose strata, as well as a construction method for this anti-slide pile structure. Summary of the Invention

[0004] The purpose of the present invention is to address the problems in the background art and propose an anti-slide pile structure that overcomes the problem of fully mechanical hole-forming of rectangular pile foundations in loose strata and improves the applicability and stability in loose strata, as well as a construction method for this anti-slide pile structure.

[0005] The technical solution of the present invention: An anti-slide pile structure for loose strata includes a grouting retaining wall for loose soil around the pile foundation and a new type of anti-slide pile component;

[0006] The loose soil grouting retaining wall is formed by grouting around the outer side of the pile foundation size before pile hole excavation to form a consolidated original soil retaining wall;

[0007] The novel anti-slide pile assembly includes:

[0008] A rectangular pile, which is located at the upper part of the bearing platform and is the free end of the anti-slide pile;

[0009] A special-shaped precast bearing platform, made of high-strength concrete, with steel densely arranged on the mountain side, serving as the waist beam at the variable cross-section of the anti-slide pile. Its short side height is not less than 2m, and the long side height is not less than 3.5m. The concrete surface at the top of the bearing platform is chiseled and cleaned;

[0010] A circular rotary drilling group pile, serving as the anchorage section of the anti-slide pile, with I-beam anti-pulling keys arranged on the side wall of the circular pile on the mountain side;

[0011] A circular pile is provided with a structural steel reinforcement cage to form a circular pile skeleton;

[0012] The top compression beam of the circular pile is arranged in two rows on the mountain side to overlap the steel reinforcement cages of the rectangular pile on the mountain side, the steel reinforcement cages of the two circular piles, and the steel reinforcement cage of the middle circular pile with each other;

[0013] A prestressed ground anchor is used to improve the anchorage strength and shear strength of the pile foundation.

[0014] Optionally, for the loose soil grouting retaining wall, curtain grouting is adopted in the area affected by groundwater, and ordinary grouting is adopted in the area not affected by groundwater;

[0015] The thickness of the consolidated original soil retaining wall after grouting is 30 - 100 cm, and the thickness of the retaining wall is controlled by the grouting pressure and the spacing of grouting holes.

[0016] Optionally, the I-beam anti-pulling keys are formed by a hole-drilling machine on the side wall of the circular pile. Two I-beam steel girders are symmetrically arranged along two perpendicular diameters around the circular pile, symmetrically forming a ring of 4 holes. The I-beam steel girders pass through the steel reinforcement cage of the circular pile and are embedded in the symmetric side wall holes on both sides. The side wall holes of the upper and lower layers are arranged in a staggered manner, and the single hole depth of the side wall is not less than 60 cm;

[0017] When lowering the precast steel reinforcement cage of the circular pile, the compressed I-beam steel girders are fixed in the steel reinforcement cage according to the position of the side wall holes. After the steel reinforcement cage is placed in place, it is controlled by the intelligent sensing component on the I-beam steel girder. The steel girder automatically extends out of the steel reinforcement cage of the circular pile and is inserted into the side wall hole, and is cast integrally with the circular pile;

[0018] The strength of the steel reinforcement cage on the mountain side of the circular pile is improved by setting an I-beam and an angle steel skeleton, and the flange plate of the I-beam on the mountain side is spot-welded with a toothed plate;

[0019] When precasting the bearing platform, through holes for the lower circular pile group are reserved according to the size of the circular pile, and the concrete surface at the top of the bearing platform is chiseled and cleaned.

[0020] Optionally, during the mechanical hole forming of the round pile to the elevation of the pile foundation bottom, an under-reaming machine is used to perform under-reaming operation on the lower part of the pile foundation.

[0021] Optionally, the intelligent sensing component has a data transmission function and is used to transmit the monitored stress and strain data to the remote monitoring terminal in real time.

[0022] Optionally, the tooth plates are spot-welded to the flange plates of the I-beams on the mountain side. The tooth plates are triangular in shape and the height of the tooth plates is 1 - 3 cm.

[0023] The present invention also provides a construction method for an anti-slide pile structure in a loose soil stratum, which includes the following steps:

[0024] Step 1: Before the pile foundation excavation, according to the design dimensions of the rectangular pile, a surface short casing is set at the hole opening. According to the groundwater development condition of the loose layer, grouting reinforcement is carried out along the periphery of the design dimensions. The grouting depth is bounded by reaching 0.5 m below the moderately weathered bedrock surface, so as to form a grouted protection wall for the loose soil and synchronously precast a special-shaped cap beam.

[0025] Step 2: After the grouting reaches the strength requirement, a rotary drilling machine is used in cooperation with a rectangular hole milling machine to excavate and clean the soil in the pile, forming a rectangular pile foundation section with a depth reaching the elevation of the cap beam bottom. During the hole forming process, only the pile body size is excavated.

[0026] Step 3: Adsorb and remove the floating slag on the upper part of the rectangular pile hole. For the moderately weathered rock mass at the bottom of the cap beam, rotary drilling holes are formed from the four corner points and the middle using a rotary drilling machine, with a depth reaching the designed elevation of the pile foundation bottom. Subsequently, a lateral hole forming machine is used to form holes on the pile side according to the design of the anti-slide pile anti-pulling keys, and an under-reaming machine is used to under-ream the bottom of the pile foundation to form an under-reamed pile bottom, and a prestressed ground anchor anchoring part is formed in the bedrock at the bottom of the hole. Then, the floating slag in the pile shaft is adsorbed and removed.

[0027] Step 4: Lift and lower the special-shaped precast cap beam with reserved group pile holes. After adsorbing the sediment in the pile shaft, place the circular group pile steel cage and the anti-pulling key assembly. Control the anti-pulling key to make the internal I-shaped steel beam extend out of the steel cage and enter the preset side wall anti-pulling key hole. The circular pile steel cage reinforcement bars, the anti-pulling key assembly and the prestressed pipeline are welded and fixed together during the production of the steel cage. At the same time, a sonic logging pipe is lifted and placed, and then the group pile concrete is poured to the elevation of the cap beam top.

[0028] Step 5: Lift and install the upper rectangular free-end pile body steel cage, and lift and place 2 rows of triangular circular pile capping beam steel cages on the mountain side, so that the capping steel cage forms an overlap with the circular pile steel cage and the outer rectangular pile side wall steel cage. Before the circular pile concrete starts to set, pour the pile body concrete to the designed elevation of the pile top.

[0029] Step 6: After the pile body strength meets the requirements, tension, grout, and seal the prestressed tendons in the reserved ducts.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] The present invention sets a short casing at the ground surface of the orifice, and grouts and reinforces the original soil in advance in the range of the side wall of the pile hole before the hole-forming operation, solving the problem of easy collapse of the loose body at the orifice and the pile body during mechanical excavation of the pile foundation section.

[0032] The present invention adopts structures such as a free-end rectangular pile + a special-shaped reinforced cap at the junction section + a circular pile group with anti-pulling keys and reinforcing bars + a capping beam + a prestressed ground anchor, etc., enhancing the overall performance of the new structure. The full-mechanical pile-forming operation of the rectangular anti-slide pile is realized, greatly improving the construction progress and eliminating the safety risks of manual excavation and the collapse risks of mechanical excavation.

[0033] The new anti-slide pile assembly is significantly economical. The rotary drilling pile group at the bottom of the cap is cast in the original groove of the moderately weathered rock mass. While achieving the force-bearing effect, it reduces the concrete pouring volume of the pile foundation, lowers the project cost, and the length of the pile foundation can be adjusted according to the actual design length. For the treatment of deep-layer loose body landslides, it solves the problems of easy cracking of the pile body on the mountain side due to bending, easy corrosion of the steel bars, and long-term failure of the pile foundation resistance.

[0034] This assembly saves the earth and rock excavation and concrete pouring volume for setting the lock mouth, the retaining wall section, and the lower circular pile group section of the cap.

[0035] In summary, the present invention adopts a new anti-slide pile assembly and construction method, which can realize the full-mechanical operation of rectangular piles in soft strata, and has high construction efficiency, economy, and safety, overcoming the problem of full-mechanical hole-forming of rectangular pile foundations in loose strata in the current industry. Brief Description of the Drawings

[0036] Figure 1 Provide a schematic diagram of the composition of the new anti-slide pile assembly proposed by the present invention;

[0037] Figure 2 Provide a schematic diagram of the precast cap structure proposed by the present invention;

[0038] Figure 3 Provide a schematic top view structure diagram of the circular rotary drilling pile group proposed by the present invention;

[0039] Figure 4 Provide a schematic diagram of the reinforcement of I-beams, angle steels, and toothed plates;

[0040] Figure 5 Provide a schematic diagram of the lap state structure of the capping beam, the rectangular pile steel cage, and the circular pile steel cage proposed by the present invention.

[0041] Reference Signs:

[0042] 1. Rectangular pile; 2. Prefabricated cap; 3. Prestressed tendon; 5. Uplift key; 6. Ground anchor; 7. Enlarged pile bottom; 8. Circular bored pile group; 9. Coping beam; 10. Steel cage for rectangular pile; 11. Steel cage for round pile. Specific implementation manners

[0043] The technical solutions of the present disclosure will be described clearly and completely below. Apparently, the described embodiments are some but not all of the embodiments of the present disclosure.

[0044] Generally, the components of the embodiments of the present disclosure described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present disclosure provided in the drawings is not intended to limit the scope of the claimed present disclosure, but merely represents the selected embodiments of the present disclosure.

[0045] All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0046] In the description of the present disclosure, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present disclosure.

[0047] Embodiment

[0048] Refer to Figures 1-5 As shown, the anti-slide pile structure for loose soil stratum proposed by the present invention includes a grouting protection wall for loose soil around the pile foundation and a new anti-slide pile component;

[0049] The grouting protection wall for loose soil forms a consolidated original soil protection wall by grouting around the outer side of the pile foundation size before pile hole excavation; for the grouting of the grouting protection wall for loose soil, curtain grouting is used in the area affected by groundwater, and ordinary grouting is used in the area not affected by groundwater; the thickness of the consolidated original soil protection wall after grouting is 60 cm, and the thickness of the protection wall is controlled by the grouting pressure and the spacing of grouting holes;

[0050] The new anti-slide pile component includes:

[0051] A rectangular pile 1, and the rectangular pile is located above the cap as the free end of the anti-slide pile;

[0052] The special-shaped precast bearing platform 2 is made of high-strength concrete, and steel materials are densely arranged on the mountain side as the waist beam at the variable cross-section of the anti-slide pile. Its short-side height is not less than 2m, and its long-side height is not less than 3.5m. When the bearing platform is precast, holes for the lower round pile group to pass through are reserved according to the dimensions of the round piles, and the concrete surface at the top of the bearing platform is chiseled and cleaned. During the mechanical hole formation of the round piles to the elevation of the bottom of the pile foundation, an under-reaming machine is used to carry out under-reaming operations on the lower part of the pile foundation.

[0053] The circular rotary bored pile group 8 serves as the anchorage section of the anti-slide pile, and I-beam anti-pulling keys 5 are arranged on the side walls of the round piles on the mountain side. The I-beam anti-pulling keys 5 are formed by a hole-chiseling machine on the side walls of the round piles. Two I-beam steel girders are symmetrically arranged along two perpendicular diameters around the round piles, symmetrically forming a ring of 4 holes. The I-beam steel girders pass through the round pile steel cage 11 and are embedded in the symmetric side wall holes on both sides. The side wall holes of the upper and lower layers are arranged staggeredly, and the depth of a single side wall hole is not less than 60cm.

[0054] The steel cage on the mountain side of the round pile is used to form the round pile skeleton. When the precast round pile steel cage 11 is lowered, the compressed I-beam steel girders are fixed in the steel cage according to the positions of the side wall holes. After the steel cage is placed in place, it is controlled by the intelligent sensing components on the I-beam steel girders. The intelligent sensing components have a data transmission function and are used to transmit the stress and strain data monitored in real time to the remote monitoring terminal. The steel girders automatically extend out of the round pile steel cage 11 and are inserted into the side wall holes, forming an integral body with the round pile after pouring.

[0055] The strength of the steel cage on the mountain side of the round pile is improved by setting I-beams and angle steel skeletons. The flange plates of the I-beams on the mountain side are spot-welded with toothed plates. The shape of the toothed plates is triangular, and the height of the toothed plates is 1.5cm.

[0056] The capping beams 9 at the top of the round piles are arranged in two rows on the mountain side and are used to overlap the rectangular pile steel cage 10, the two round pile steel cages 11 and the middle round pile steel cage 11 on the mountain side.

[0057] The prestressed ground anchor 6 is used to improve the anchoring strength and shear strength of the pile foundation.

[0058] Combined with the above anti-slide pile structure for loose strata, in this embodiment, a construction method for it is also proposed, including the following steps:

[0059] Step 1: Before the excavation of the pile foundation, according to the design dimensions of the rectangular pile 1, a surface short casing is set at the hole opening. According to the development of groundwater in the loose layer, grouting reinforcement is carried out along the periphery of the design dimensions. The grouting depth is bounded by reaching 0.5m below the moderately weathered bedrock surface, so as to form a traditional-like retaining structure in the original soil layer, eliminate the excavation within the retaining range of the pile foundation, and then form a grouted retaining wall for loose soil and precast the special-shaped bearing platform synchronously.

[0060] Step 2: After the grouting reaches the strength requirement, use a rotary drilling machine in cooperation with a rectangular hole milling machine to excavate and clean the soil in the pile, forming a cross-section of the rectangular pile 1 with a depth reaching the elevation of the bottom of the pile cap. During the hole-forming process, only the pile body size is excavated, and the retaining wall size is not excavated, which can greatly reduce the project cost, shorten the construction period, and reduce the amount of waste slag from the pile foundation excavation;

[0061] Step 3: Adsorb and remove the floating slag at the upper part of the rectangular pile hole. For the moderately weathered rock mass at the bottom of the pile cap, use a rotary drilling machine to drill holes from the four corners and the middle to a depth reaching the designed elevation of the bottom of the pile foundation. Subsequently, use a lateral hole-forming machine to form holes on the side of the pile according to the design of the anti-slip pile anti-pulling key 5, and use an under-reaming machine to under-ream the bottom of the pile foundation to form an under-reamed pile bottom 7, forming a prestressed anchor 6 anchoring part in the bedrock at the bottom of the hole. Subsequently, adsorb and remove the floating slag in the pile shaft;

[0062] Step 4: Hoist and lower the special-shaped precast pile cap 2 with reserved group pile holes. After adsorbing the sediment in the pile shaft, place the circular group pile steel reinforcement cage and the anti-pulling key 5 components. Control the anti-pulling key 5 to make the internal I-shaped steel beam extend out of the steel reinforcement cage and enter the preset side wall anti-pulling key 5 duct. Weld and fix the circular pile steel reinforcement cage stiffeners, the anti-pulling key 5 components, and the prestressed duct into one body during the production of the steel reinforcement cage. At the same time, hoist and place the sonic logging tube, and then pour the group pile concrete to the elevation of the top of the pile cap;

[0063] Step 5: Hoist and install the steel reinforcement cage of the upper rectangular free-end pile body, and hoist and place the steel reinforcement cage of the circular pile capping beam 9 arranged in a triangular shape in 2 rows on the mountain side, so that the capping steel reinforcement cage forms an overlap with the circular pile steel reinforcement cage 11 and the side wall steel reinforcement cage of the outer rectangular pile 1. Before the circular pile concrete starts to set, pour the pile body concrete to the designed elevation of the pile top. The capping steel reinforcement cage forms an integral connection with the circular pile and the upper rectangular pile 1, enhancing the integrity of the pile body;

[0064] Step 6: After the strength of the pile body meets the requirements, tension, grout, and seal the prestressed tendon 3 in the reserved duct.

[0065] The above specific embodiments are only several alternative embodiments of the present invention. Based on the technical solution of the present invention and the relevant inspirations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. Anti-slide pile structure for loose strata, characterized in that: It includes the grouting protection wall for the loose soil around the pile foundation and the new anti-slide pile assembly; The loose soil grouting protection wall forms the original soil consolidation protection wall by grouting around the outer side of the pile foundation size before pile hole excavation; The new anti-slide pile assembly includes: A rectangular pile (1), and the rectangular pile (1) is located at the upper part of the bearing platform as the free end of the anti-slide pile; A special-shaped precast bearing platform (2), which is made of high-strength concrete and has steel densely arranged on the mountain side as the waist beam at the variable cross-section of the anti-slide pile. The height of its short side is not less than 2m, and the height of its long side is not less than 3.5m; A circular rotary drilling group pile (8), which is used as the anchorage section of the anti-slide pile, and an I-beam anti-pull key (5) is arranged on the side wall of the circular pile on the mountain side; The circular pile is provided with a structural steel reinforcement cage to form the circular pile skeleton; The capping beam (9) at the top of the circular pile is arranged in two rows on the mountain side to lap the steel reinforcement cage (10) of the rectangular pile on the mountain side, the steel reinforcement cages (11) of the two side circular piles and the steel reinforcement cage (11) of the middle circular pile with each other; A prestressed ground anchor (6) is used to improve the anchorage strength and shear strength of the pile foundation.

2. The anti-slide pile structure for loose strata according to claim 1, characterized in that, For the grouting of the loose soil grouting protection wall, curtain grouting is adopted in the area affected by groundwater, and ordinary grouting is adopted in the area not affected by groundwater; The thickness of the original soil consolidation protection wall after grouting is 30 - 100 cm, and the thickness of the protection wall is controlled by the grouting pressure and the spacing of grouting holes.

3. The anti-slide pile structure for loose strata according to claim 1, characterized in that, The I-beam anti-pull key (5) forms holes on the side wall of the circular pile through a hole-drilling machine, and 2 I-beam steel beams are symmetrically arranged along two perpendicular diameters around the circular pile to symmetrically form a ring of 4 holes. The I-beam steel beams pass through the steel reinforcement cage (11) of the circular pile and are embedded into the symmetric side wall holes on both sides. The side wall holes of the upper and lower layers are arranged in a staggered manner, and the depth of a single side wall hole is not less than 60 cm; When lowering the precast steel reinforcement cage (11) of the circular pile, the compressed I-beam steel beam is fixed in the steel reinforcement cage according to the position of the side wall hole. After the steel reinforcement cage is placed in place, it is controlled by the intelligent sensing component on the I-beam steel beam. The steel beam automatically extends out of the steel reinforcement cage (11) of the circular pile and is inserted into the side wall hole, and is formed into a whole with the circular pile by pouring; The strength of the steel reinforcement cage on the mountain side of the circular pile is improved by setting an I-beam and an angle steel skeleton, and the tooth plates are spot-welded to the flange plate of the I-beam on the mountain side; When the bearing platform is precast, through holes for the lower circular pile group are reserved according to the size of the circular pile.

4. The anti-slide pile structure for loose strata according to claim 3, characterized in that When the circular pile is mechanically drilled to the elevation of the bottom of the pile foundation, a reamer is used to carry out the reaming operation on the lower part of the pile foundation.

5. The anti-slide pile structure for loose strata according to claim 3, characterized in that, The intelligent sensing component has a data transmission function and is used to transmit the stress and strain data monitored in real time to the remote monitoring terminal.

6. The anti-slide pile structure for loose soil strata according to claim 3, characterized in that, The tooth plates are spot-welded to the flange plate of the I-beam on the mountain side, the shape of the tooth plate is triangular, and the height of the tooth plate is 1 - 3 cm.

7. A construction method for an anti-slide pile structure used in loose strata according to any one of claims 1-6, characterized in that, It includes the following steps: Step 1: Before the pile foundation excavation, according to the design size of the rectangular pile (1), a surface short casing is set at the hole opening. According to the development of groundwater in the loose layer, grouting reinforcement is adopted along the outer periphery of the design size. The grouting depth is bounded by reaching 0.5 m below the moderately weathered bedrock surface, so as to form the loose soil grouting protection wall and synchronously precast the special-shaped bearing platform, and the concrete surface at the top of the bearing platform is chiseled and cleaned; Step 2: After the grouting reaches the strength requirement, a rotary drilling machine is used in cooperation with a rectangular hole milling machine to excavate and clean the soil in the pile, form the cross-section of the rectangular pile (1), and the depth reaches the elevation of the bottom of the bearing platform. Only the pile body size is excavated during the hole-forming process; Step 3: Adsorb and remove the floating slag at the upper part of the rectangular pile hole. For the moderately weathered rock mass at the bottom of the bearing platform, use a rotary drilling rig to drill holes from the four corner points and the middle to reach the designed elevation at the bottom of the pile foundation. Subsequently, use a lateral hole-forming machine to form side holes of the pile according to the design of the anti-slip pile anti-pulling key (5), and use an under-reaming machine to under-ream the bottom of the pile foundation to form an under-reamed pile bottom (7), and form the anchoring part of the prestressed ground anchor (6) in the bedrock at the bottom of the hole. Subsequently, adsorb and remove the floating slag in the pile shaft; Step 4: Hoist and lower the special-shaped precast bearing platform (2) with reserved group pile holes. After adsorbing the sediment in the pile shaft, place the circular group pile steel reinforcement cage and the anti-pulling key (5) assembly, and control the anti-pulling key (5) to make the internal I-shaped steel beam extend out of the steel reinforcement cage and enter the preset side wall anti-pulling key (5) duct. Weld and fix the circular pile steel reinforcement cage reinforcement bars, the anti-pulling key (5) assembly and the prestressed duct into one body during the production of the steel reinforcement cage. At the same time, hoist and place the sonic logging tube, and then pour the group pile concrete to the elevation of the top of the bearing platform; Step 5: Hoist and install the steel reinforcement cage of the upper rectangular free-end pile body, and hoist and place the steel reinforcement cage of the circular pile capping beam (9) arranged in a triangular shape in 2 rows on the mountain side, so that the capping steel reinforcement cage forms an overlap with the circular pile steel reinforcement cage (11) and the side wall steel reinforcement cage of the peripheral rectangular pile (1). Before the concrete of the circular pile starts to set, pour the pile body concrete to the designed elevation of the pile top; Step 6: After the strength of the pile body meets the requirements, tension, grout and seal the prestressed tendon (3) in the reserved duct.

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