A method for constructing retaining piles for subway lines

Abstract

This invention relates to the field of pile foundation construction, specifically to a method for constructing subway retaining piles. The method includes surveying and setting out, excavating guide wall trenches, tying reinforcing bars and pouring concrete for the guide wall trenches to form two opposing guide walls, with the top surface of the guide walls exceeding the top surface of the pile hole. The method involves marking the pile location, excavating the first section of exploratory borehole soil between the two guide walls, tying the first section of retaining wall reinforcing bars, and pouring the first section of retaining wall concrete. This process is repeated for the second section of exploratory borehole soil, tying the second section of retaining wall reinforcing bars, and pouring the second section of retaining wall concrete, continuing this cycle until all pile hole segments are excavated. The pile holes are formed using a rotary drilling rig, and drilling mud is injected into the holes and stored within the two guide walls for recycling. A reinforcing cage is placed into the pile hole, and underwater concrete is poured. By setting up guide walls, the method solves the problems of borehole collapse and inaccurate pile foundation positioning. The guide walls fix the left and right positions of the retaining piles, reduce pile position deviation, and collect drilling mud to reduce mud pollution.

Description

Technical Field

[0001] This invention relates to the field of pile foundation construction, and in particular to a method for constructing retaining piles for subways. Background Technology

[0002] In the construction of deep foundation pits for subway stations in rail transit projects, retaining piles serve as a crucial support structure, and their construction quality directly impacts the safety of the foundation pit and its surrounding environment. However, existing retaining pile construction techniques still present numerous technical challenges that urgently need to be addressed. First, when drilling pile holes in complex geological conditions such as water-rich soft soil or sandy strata, the stability of the borehole wall is difficult to control effectively, easily leading to borehole collapse or even large-scale ground subsidence accidents, seriously threatening the safety of construction personnel and increasing handling costs. Second, due to factors such as underground obstacles, drilling deviation, and measurement and positioning errors, the planar position of the retaining pile foundation often deviates significantly, resulting in insufficient verticality of the pile body or pile misalignment, thereby weakening the overall load-bearing capacity of the retaining structure and even causing the risk of subsequent foundation pit leakage. In addition, existing construction methods mostly employ mud slurry wall protection or dry rotary drilling, which generate large amounts of waste mud, dust, and noise during the excavation process, causing serious pollution to the urban construction site and the living environment of surrounding residents, failing to meet the requirements of green construction and environmental protection. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for constructing subway retaining piles.

[0004] A method for constructing retaining piles for subway lines includes the following steps:

[0005] S1: Survey and set out, excavate guide wall trench, tie steel bars and pour guide wall trench concrete to form two guide walls set opposite each other, with the top surface of the guide wall higher than the top surface of the pile hole. S2: Locate the pile position, excavate the first section of test hole soil between the two guide walls, tie the first section of retaining wall reinforcement, pour the first section of retaining wall concrete, excavate the second section of test hole soil between the two guide walls, tie the second section of retaining wall reinforcement, pour the second section of retaining wall concrete, and repeat this cycle until all pile hole excavation segments are completed. The pile holes are formed using a rotary drilling rig, and mud is injected into the holes. The mud is stored in two guide walls for recycling. S3: Place the steel cage into the pile hole and pour underwater concrete.

[0006] Preferably, in S1, the guide wall includes a vertical section and a horizontal section, the horizontal section is located outside the vertical section, and the elevation of the horizontal section is lower than the road surface elevation.

[0007] Preferably, step S2 further includes stopping drilling after the design depth is reached, measuring the hole depth, and using the horizontal section of the guide wall as the reference surface for measuring the hole depth.

[0008] Preferably, step S2 further includes, after drilling reaches the designed depth, checking and confirming that the hole diameter, hole depth, and verticality are qualified, and then using a slurry pumping method to clean the hole.

[0009] Preferably, in step S3, when the reinforcing cage is lowered to the borehole position, sleepers are set on the horizontal section of the guide wall, and suspension steel pipes are installed to suspend and support the reinforcing cage on the sleepers.

[0010] Preferably, the concrete is poured continuously using the tremie pipe method.

[0011] Preferably, step S3 includes placing the reinforcing cage into the pile hole, installing a guide pipe, performing secondary hole cleaning, and pouring underwater concrete.

[0012] Preferably, step S3 further includes measuring the burial depth of the catheter, using the horizontal section of the guide wall as the reference surface for measuring the burial depth of the catheter.

[0013] Preferably, step S3 further includes setting a guide pipe support frame in the horizontal section of the guide wall, and measuring and adjusting the height of the guide pipe embedded in the concrete using the guide pipe support frame.

[0014] Preferably, the retaining piles are constructed using a skip-pile method, with each pile being constructed every two holes.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a construction method for subway retaining piles. By setting up a guide wall, it solves the problems of collapse of the construction hole and inaccurate positioning of the pile foundation plane. The guide wall can fix the left and right positions of the retaining piles, reduce pile position deviation, and collect mud to reduce mud pollution.

[0016] In some implementations, the guide wall can also serve as a reference surface for measuring the depth of the hole and the burial depth of the guide pipe, as well as a support structure for the hoisting of the reinforcing cage into the hole and for the guide pipe. Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of the excavation of the guide wall trench described in this invention.

[0018] Figure 2 This is a vertical cross-sectional view of the guide wall described in this invention.

[0019] Figure 3 This is a horizontal cross-sectional view of the relative positions of the guide wall, foundation pit, and pile hole described in this invention.

[0020] Figure 4 This is a vertical cross-sectional view of the protective wall described in this invention.

[0021] Figure 5This is a schematic diagram (front view) of the steel cage suspended and supported on sleepers according to the present invention.

[0022] Figure 6 This is a schematic diagram (top view) of the sleepers and suspension steel pipes described in this invention.

[0023] Figure 7 This is a schematic diagram (front view) of the catheter support frame described in this invention.

[0024] Marked in the image: 1-Guide wall trench, 2-Guide wall, 21-Vertical section, 22-Horizontal section, 3-Road surface, 4-Retaining wall, 5-Pile hole, 6-Foundation pit, 7-Reinforcing cage, 8-Casing, 9-Sleeper, 10-Suspension steel pipe, 11-Hanging rod, 12-Conduit, 13-Conduit support frame, 14-Plumb bob. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0026] Unless otherwise specified, the terms "upper," "lower," "left," "right," "center," "inner," and "outer," etc., used in the description of specific embodiments of the present invention to indicate orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is usually placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, and for enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0027] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," "parallel," and "coaxial" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, parallel, or coaxial. Slight tilt or deviation is permissible, as long as it does not affect the normal function of the relevant component. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," not that the structure must be perfectly horizontal; a slight tilt is acceptable. "Coaxial" means that two components are arranged as coaxially as possible, allowing them to move coaxially or approximately coaxially when their relative positions change. Alternatively, it can be simplified to mean that the corresponding device / component / element, when arranged in "horizontal," "vertical," "suspended," "parallel," or "coaxial" directions, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. For example, the deviation in the "coaxial" direction is controlled within 0.2-1mm, preferably within 0.2-0.5mm. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the solution of the present invention.

[0028] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0029] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as two, three, four, five, six, seven, eight, or nine, and can even exceed nine.

[0030] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to connection methods commonly used in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0031] Example This embodiment provides a construction method for subway retaining piles. This method solves the technical problems of borehole collapse and inaccurate pile foundation positioning during subway retaining pile construction by setting up a guide wall 2. The guide wall 2 has multiple functions, including fixing the left and right positions of the retaining piles, reducing pile position deviation, collecting mud to reduce mud pollution, serving as a reference surface for measuring borehole depth and guide pipe burial depth, and serving as a support structure for hoisting the reinforcing cage 7 and the guide pipe 12. The specific implementation steps of this construction method are described in detail below.

[0032] I. Construction Preparation Remove all obstacles at the pile location, including large rocks, tree roots, and production waste; clear debris from the site, backfill low-lying areas with cohesive soil, compact it, and ensure proper drainage to place the drilling rig base on a solid surface to guarantee borehole quality; and determine the location of the mud pit. To ensure the width of the foundation pit meets design requirements, and considering construction errors, the retaining pile positions should be 15-20cm beyond the designed pile positions.

[0033] II. Guide Wall Construction First, surveying and setting out are conducted to determine the center pile position of a section of retaining piles. Then, the guide wall trench 1 is excavated, as follows: Figure 1 As shown, for example, two gray lines are drawn on both sides of the center line of the pile, 85cm and 105cm away from the center. The vertical trench is dug to a depth of 80cm from 0cm to 85cm and to a depth of 35cm from 85cm to 105cm. The guide wall trench 1 is 1.4 meters wide and 0.8 meters high.

[0034] Next, the reinforcing bars are tied. HRB300 (8mm) round steel bars are placed at 30cm intervals along the cross-section of the guide wall, and HRB300 (8mm) round steel bars are also placed at 30cm intervals longitudinally to form a reinforcing mesh. After the reinforcing bars are tied, the formwork is closed, and concrete is poured into the guide wall trench 1 to form two opposing guide walls 2.

[0035] like Figure 2 As shown, the guide wall 2 includes a vertical section 21 and a horizontal section 22. The horizontal section 22 is located outside the vertical section 21, and its elevation is lower than that of the road surface 3. The top surface of the guide wall 2 is higher than the top surface of the pile hole 5. The vertical section 21 has a height of 0.6m, and the horizontal section 22 has a thickness of 0.2m. The guide wall 2 is constructed of C20 reinforced concrete and is cured until the concrete strength meets the design requirements after construction.

[0036] The guide wall 2 effectively solves the problem of borehole collapse. When drilling pile holes 5 in water-rich soft soil or sandy strata, the vertical section 21 of the guide wall 2 can restrain the soil around the borehole opening, preventing borehole wall instability and collapse accidents, thus significantly improving construction safety. At the same time, the guide wall 2 can fix the left and right positions of the retaining piles, significantly reducing pile position deviation, ensuring accurate positioning of the retaining pile foundation plane, and improving the overall load-bearing performance of the retaining structure.

[0037] The horizontal section 22 of the guide wall 2 is lower than the road surface 3, forming a closed mud collection pool. This allows the mud generated during rotary drilling to be stored within the two guide walls 2 for recycling, avoiding environmental pollution caused by mud spillage. Compared to traditional construction methods, this invention significantly reduces the amount of waste mud generated, meeting the requirements of green construction and environmental protection, and is particularly suitable for urban construction sites.

[0038] III. Hole Exploration After the construction of guide wall 2 is completed, the pile positions will be marked out using the cross-shaped method. Before excavation of the retaining pile holes, manual excavation should be used for detection, with the assistance of detection instruments. The depth of manual excavation should not be less than 3 meters to determine whether there are underground pipelines at the hole location.

[0039] like Figure 3 As shown, exploratory boreholes are excavated between the two guide walls 2. The borehole diameter is the design pile diameter plus 0.4m, the retaining wall 4 thickness is 0.15m, and the borehole diameter after the retaining wall 4 is completed is the design pile diameter plus 0.1m. The specific construction steps are as follows: (1) Surveying and setting out: After the site is cleared and leveled, the hole positions are determined according to the valid design drawings, and the center point of the hole position is determined. After the check is correct, the work team will install cross-shaped protective piles. The cross-shaped protective piles must be reinforced and protected with mortar or concrete. The protective piles are installed using the cross method. A12mm steel bars with a cross shape are set around the hole opening and driven into the ground. The steel bars are 40cm long and driven into the ground to a depth of 30cm. After the hole locking construction is completed, cement nails are used to drive the protective piles into the well opening wall 4. The protective piles should be firm and secure.

[0040] (2) Road surface demolition: Excavators (rockers) and air compressors and pneumatic picks are used to demolish the original asphalt surface and concrete road surface within the pipeline area. When the original road surface is soil, manual excavation is carried out directly.

[0041] (3) Erecting the derrick, installing the winch and lighting equipment: Before the exploratory borehole excavation, the derrick must be erected according to the actual site conditions. The derrick should be covered with plastic sheeting to prevent rainwater from entering the borehole. Install the winch and the slag-carrying bucket, and at the same time install a sturdy and reliable safety ladder for personnel to enter and exit the pile hole 5. Install pulley blocks and electric hoists or wire ropes for the winch on the vertical transport derrick, and select an appropriate location to install the winch. Rubber-insulated cables should be used for lighting inside the borehole, and no joints are allowed.

[0042] (4) Excavation of the first test borehole: The test borehole should be filled with interlocking concrete, and then excavated layer by layer from top to bottom. First, excavate the soil in the middle part, and then expand the excavation to the periphery to effectively control the cross-sectional dimensions of the pile hole 5. The excavation height should be determined according to the soil quality and design. The interlocking joint should be made of C20 reinforced concrete and extend 0.2m above the ground. During the excavation process, dig gently and slowly, and closely observe whether there are pipelines in the soil to avoid damaging the pipelines by excessive force.

[0043] (5) Tie the first section of retaining wall reinforcement and pour the first section of retaining wall concrete: such as Figure 4 As shown, retaining wall 4 is constructed using C20 reinforced concrete, surrounded by A12@200×200 steel mesh. Longitudinal reinforcement is extended 0.1m into the lower retaining wall 4 to ensure connection between upper and lower sections. After the formwork of retaining wall 4 is securely supported, 0.15m thick concrete should be poured immediately, manually poured and compacted. Formwork can be removed once the concrete strength reaches 2.5MPa. Depending on weather conditions, formwork for retaining wall 4 can generally be removed 24 hours after pouring.

[0044] (6) Excavation of the second section of the test hole: Starting from the second section, use the lifting equipment to transport soil. Personnel inside the pile hole 5 should wear safety helmets. When the bucket is 1.5 meters away from the top of the hole, push the movable safety cover to cover the hole opening to prevent soil, stones and other debris from falling into the hole and injuring people. After the bucket is unloaded, open the movable cover and lower the bucket to load soil. After the pile hole 5 is excavated to the specified depth, use a ruler to check the diameter of the pile hole 5 and the arc of the well wall. Trim the hole wall to make it vertical and smooth.

[0045] (7) Tie the second section of retaining wall reinforcement and pour the second section of retaining wall concrete: The second section of vertical reinforcement is lapped with the first section of vertical reinforcement, with a lap length of not less than 0.2m, and is hooked with the circumferential reinforcement. The retaining wall formwork is reused by dismantling the upper section and supporting the lower section in sequence. A concrete pouring opening with a height of 100mm is left at the top of the formwork. The concrete is transported by bucket, poured manually, and compacted manually.

[0046] (8) Continue the operation in a cyclical manner until all segments of the pile hole 5 are excavated: During the excavation of the exploratory borehole, ventilation should be provided to the well to enhance air convection. If necessary, oxygen should be supplied to prevent the hazards of toxic gases. Personnel on the exploratory borehole should closely observe the situation of personnel below the borehole and coordinate with each other. A movable cover plate that can be pushed horizontally should be installed at the pile opening. When someone is digging soil in pile hole 5, the safety cover plate should be covered to prevent debris from falling and injuring people. The safety cover plate should be opened only when the soil is being hoisted.

[0047] (9) Final Hole Excavation and Inspection: After the exploratory borehole reaches the designed depth (2.2m in this example), a comprehensive inspection of the borehole depth, borehole diameter, borehole centerline, and inclination shall be conducted. If no underground pipelines are found during construction, the excavation shall be stopped only after joint confirmation with the supervising engineer. If underground pipelines are found, construction shall be carried out in accordance with the pipeline relocation and protection plan, or the relevant property owner shall be contacted for handling.

[0048] At this point, the vertical section 21 of the guide wall 2 and the retaining wall 4 effectively prevent the orifice from collapsing and improve construction efficiency.

[0049] IV. Hole Formation by Rotary Drilling Rig After the exploratory drilling was completed and passed inspection, rotary drilling rigs were used to form the final boreholes. The retaining piles were constructed using a skip-piling method, with piles installed every two holes to minimize mutual interference between adjacent pile holes and ensure the quality of the borehole formation.

[0050] (1) Drilling Rig Positioning: The drilling rig is installed after the center pile position marked by the surveyor is checked and confirmed by the supervising engineer. Before positioning the drilling rig, check for power lines and obstacles above and around the rig. Only after confirming that everything is in order can the next construction procedure be carried out. Before positioning the drilling rig, check all the preparatory work before drilling, including the inspection and maintenance of the main machinery and equipment. The base and top should be stable and should not be displaced or subsided.

[0051] (2) Drilling: A rotary drilling rig is used for drilling. When starting drilling, the pressure should be light and the advance should be slow, and the drilling time should be appropriately extended. High-quality mud should be injected into the hole in a timely manner to balance the formation pressure. The soil is cut by rotary drilling with the drill bit, and the drill bit is pulled out of the hole. The bottom cover of the drill bit is opened to dump the soil. During the drilling process, the advance speed should be controlled, and the drill bit should be lifted and lowered slowly, with each stroke not exceeding 0.5m. The mud is stored in the two guide walls 2 for recycling. After the mud is used up and settled, the clear water at the top is pumped into the water storage tank, and the settled mud at the bottom is transported by mud tanker truck to the designated spoil disposal site for treatment.

[0052] Rotary drilling rigs were used for hole formation. Verticality was controlled by the rig's own verticality detection device, supplemented by manual correction in two directions simultaneously. During drilling, the hole depth was monitored using a measuring rope. As the hole approached its designated depth, the drilling depth was precisely controlled. Drill cuttings were collected promptly during drilling, and any problems were addressed immediately. Drilling was continuous, and drilling records were filled out regularly. Cuttings samples were collected at points of soil strata change to identify the soil layers, and a geological columnar section of the pile hole was drawn for comparison with the geological profile. Any discrepancies with the design geological profile were promptly reported to the supervising engineer, and the engineer's instructions were followed.

[0053] (3) Final Drilling: After drilling reaches the designed depth, stop drilling, measure the hole depth, and use the horizontal section 22 of the guide wall 2 as the reference surface for measuring the hole depth. Verify the top elevation. Use a measuring rope to measure the hole depth. Before using the measuring rope, it should be wetted and verified with a steel ruler. Report to the supervising engineer for hole inspection, measuring the hole depth, hole bottom, sediment thickness, hole diameter, hole position deviation, and verticality, etc. After passing the inspection, begin cleaning the hole. Hole inclination and hole diameter are checked by lowering a steel reinforcement inspection tool into the hole. The outer diameter of the inspection tool is the diameter of the steel reinforcement cage 7 plus 100mm (not greater than the drill bit diameter), and the length is 4 to 6 times the outer diameter.

[0054] The horizontal section 22 of the guide wall 2 serves as a reference surface for measuring hole depth, providing a stable and reliable measurement benchmark. This ensures the accuracy of hole depth measurement and avoids measurement errors caused by the lack of a unified reference surface in traditional construction. Simultaneously, the skip-pile construction method effectively reduces the mutual influence between adjacent pile holes 5, preventing quality problems such as cross-hole drilling and hole collapse.

[0055] V. Cleaning the Hole After drilling to the design elevation, the borehole diameter, depth, and verticality are checked and confirmed to be within acceptable limits. Then, the borehole is cleaned using a slurry pumping method. When cleaning and removing slag, the water head in the borehole must be maintained to prevent borehole collapse. After cleaning, the thickness of the sediment at the bottom of the borehole should not exceed 50mm. The mud parameters after cleaning should meet the following requirements: relative density: 1.03~1.10; sand content <2%.

[0056] VI. Reinforcing Cage Hoisting After the borehole cleaning is completed, the reinforcing cage 7 is hoisted. For this project, the reinforcing cage 7 for the bored piles is fabricated at the steel reinforcement factory, transported to the construction site by truck, and then hoisted using a 25T truck crane. For reinforcing cages 7 longer than 24m, they are fabricated in sections at the steel reinforcement factory and spliced ​​at the pile foundation location. Since the reinforcing bars are generally 12m long, the standard section length of the reinforcing cage 7 is 24m, with each section measuring [length in meters].

[0057] (1) Selection of lifting points for steel cage 7: The center of gravity of steel cage 7 is approximately located in the middle of the structure, i.e., at 0.5L, where L is the pile length. When lifting steel cage 7, the main hook of the crane should be used to lift it horizontally off the ground first, and then the auxiliary hook of the crane should be used to lift it vertically in the air before lowering it. When lifting steel cage 7 horizontally off the ground, a three-point balance method is used, with one lifting point in the center and the other two 0.13L from the ends (Note: Lifting points for fiberglass reinforced piles must be set on hot-rolled steel bars; lifting points are not set on fiberglass reinforced sections). When vertically lifting steel cage 7 in the air, the lifting points are set at 0.3L from the lifting end. Round steel bars with the same diameter as the main reinforcement are placed at the lifting point positions as reinforcing bars to ensure that steel cage 7 is not deformed and is lifted safely.

[0058] (2) Lifting steps for rebar cage 7: Before lifting, prepare all necessary work, direct the crane to move to the lifting position, and have the slinger install wire ropes and shackles at the lifting points of rebar cage 7. After checking the installation of the crane wire ropes and the center of gravity, begin simultaneous horizontal lifting. After the rebar cage 7 is lifted to 0.3m to 0.5m above the ground, check whether the rebar cage 7 is stable. Then, the main crane slowly lifts the hook, and depending on the distance between the tail of the rebar cage 7 and the ground, direct the auxiliary crane to cooperate in lifting the hook. After the rebar cage 7 is lifted, the main hook slowly lifts and raises, with the auxiliary crane cooperating to maintain the distance between the rebar cage 7 and the ground, until the rebar cage 7 is perpendicular to the ground. Direct the slinger to remove the hook from the auxiliary lifting point of the rebar cage 7, and then move away from the lifting operation area.

[0059] The crane operator directs the cage to enter and position itself in the hole, ensuring smooth crane rotation. A traction rope is then pulled onto the reinforcing cage 7. If the reinforcing cage 7 gets stuck in the hole during lowering, it must be lifted out to check the hole position before being lowered again; it must not be forced into the hole. When lowering the reinforcing cage 7, first remove the internal support and simultaneously install protective layer pads. When the reinforcing cage 7 reaches the lowest lifting point, pause lowering and remove the wire rope and shackles from the lifting point. As the reinforcing cage 7 continues to be inserted, pause lowering when it reaches the highest lifting point, insert the steel pipe, and secure the reinforcing cage 7 to the top of the casing 8. Then, remove the wire rope and shackles from the lifting point, install and weld symmetrical lifting rods 11, insert them into the steel pipe, and weld the lifting rods 11 to the steel pipe. Install shackles and wire ropes on top of the lifting rods 11, lift the reinforcing cage 7, remove the steel pipe, and lower the reinforcing cage 7. For sectionally installed reinforcing cages 7, splicing is performed at this stage.

[0060] (3) Suspension and fixing of the steel cage 7: such as Figure 5 and Figure 6 As shown, when the reinforcing cage 7 reaches the borehole position, sleepers 9 are set on the horizontal section 22 of the guide wall 2, and suspension steel pipes 10 are installed to suspend and support the reinforcing cage 7 on the sleepers 9. The elevation of the top of the casing 8 is measured with a level instrument at this time. Based on the elevation of the top of the reinforcing cage 7, the length of the suspension rod 11 is calculated. The suspension rod 11 is welded to the main reinforcement of the reinforcing cage 7. Then, the hook is hung on the suspension rod 11, and the cage is slowly lowered to the design position. Two parallel suspension steel pipes 10 are inserted into the top suspension ring of the reinforcing cage 7. The suspension steel pipes 10 are placed horizontally on the sleepers 9, and the entire cage is suspended on the sleepers 9 on both sides of the top of the casing 8 to ensure the accuracy of the position, height, and verticality of the reinforcing cage 7.

[0061] By utilizing the horizontal section 22 of the guide wall 2 to install sleepers 9 and suspension steel pipes 10, a stable and reliable support structure is provided for the reinforcing cage 7, effectively preventing displacement or tilting of the reinforcing cage 7 during hoisting and ensuring the accuracy of the position, height, and verticality of the reinforcing cage 7. Compared with the method of temporarily erecting support structures in traditional construction, the support structure of this invention is more stable, has higher construction efficiency, and better safety.

[0062] VII. Installation of Conduit and Pouring of Underwater Concrete (1) Installation of Conduit 12: After the reinforcement cage 7 is installed and inspected and approved by the supervising engineer, conduit 12 can be installed. Conduit 12 is a steel conduit with an inner diameter of 300mm. Before installation, conduit 12 is tested on the ground for water tightness, pressure resistance, and joint tensile strength to ensure good sealing performance. The water pressure for the water tightness test should not be less than 1.3 times the water depth in the hole, nor less than 1.3 times the maximum internal pressure that the wall and weld of conduit 12 may withstand when pouring concrete. The installation length of conduit 12 should be accurate. To prevent errors, conduit 12 should be lowered to the bottom of the hole and then raised 25-40cm. The tightness of each connection of conduit 12 should be checked, and the bolts should be tightened symmetrically. The rubber gaskets of conduit 12 connections should not be aged or damaged; otherwise, they should be replaced.

[0063] like Figure 7 As shown, a guide pipe support frame 13 is installed on the horizontal section 22 of the guide wall 2. The height of the guide pipe 12 embedded in the concrete is measured and adjusted by the guide pipe support frame 13 in conjunction with a plumb bob 14. The guide pipe support frame 13 is a steel structure and is stably installed on the horizontal section 22 of the guide wall 2 to ensure the stability of the guide pipe 12 during the grouting process.

[0064] (2) Secondary hole cleaning: After the steel cage 7 and guide pipe 12 are installed, the second hole cleaning is carried out. During the cleaning, attention must be paid to maintaining the water head in the hole to prevent the hole from collapsing. The mud parameters after cleaning should meet the following requirements: relative density: 1.03~1.10; sand content <2%. After checking that the sediment at the bottom of the hole meets the requirements (the sediment thickness at the bottom of the pile shall not exceed 100mm), the underwater concrete is poured after obtaining the approval of the supervising engineer.

[0065] (3) Underwater concrete pouring: After the secondary hole cleaning meets the design and specification requirements, underwater concrete is poured immediately. The concrete is poured continuously using the tremie pipe method. The size of the concrete hopper and the concrete mixer truck are determined according to the pile diameter and the initial embedment height of the tremie pipe 12 into the concrete.

[0066] The horizontal section 22 of the guide wall 2 serves as the reference surface for measuring the burial depth of the guide pipe 12, providing a stable and reliable measurement benchmark. This ensures the accuracy of the burial depth measurement of the guide pipe 12 and effectively controls the burial depth of the guide pipe 12 within a reasonable range of 2–6 m, guaranteeing the quality of underwater concrete pouring. Simultaneously, the guide pipe support frame 13 ensures the stability of the guide pipe 12's position during pouring, avoiding concrete pouring quality problems caused by guide pipe 12 displacement.

[0067] 8. Pile head removal After the concrete pouring is completed and cured to the design strength, the pile head is broken. First, the elevation is determined. According to the requirements of the support structure drawings, the lines are measured and laid out. After finding the pile top elevation, a conspicuous mark is made on the pile body with a red marker. To prevent breaking too deeply, breaking begins 50mm above the design elevation of the pile top. Four marking points are made on each pile, and the four points are connected to form a circle as the control line for breaking the pile head.

[0068] Then break the pile head, first removing the concrete cover above the control line until the main reinforcement is exposed, taking care to avoid damaging the main reinforcement. Then use an air compressor to completely remove the pile body. Note that during the pile head removal process, do not break below the elevation control line, do not bend the main reinforcement more than 30 degrees, and do not start breaking from only one direction; break from all four directions inwards, and only chisel horizontally towards the pile core, not downwards from the pile head, to avoid forming a cone shape.

[0069] Clean up the broken concrete blocks, then manually chisel away and clean the top, ensuring the pile head is flat and smooth. After chiseling, clean away any loose dust with a wire brush and wash with water. Cut the pile head reinforcement according to the design requirements for the required anchorage length.

[0070] This embodiment achieves multiple technical effects by setting up a guide wall 2: (1) The vertical section 21 of the guide wall 2 effectively constrains the soil around the borehole, solves the problem of borehole collapse, and improves construction safety; (2) The guide wall 2 fixes the left and right positions of the retaining piles, significantly reduces pile position deviation, and ensures accurate positioning of the pile foundation plane position of the retaining piles; (3) The horizontal section 22 of the guide wall 2 forms a closed mud collection pool, which allows the mud to be recycled in the guide wall 2, greatly reducing the amount of waste mud generated, which meets the requirements of green construction and environmental protection; (4) The horizontal section 22 of the guide wall 2 serves as a unified reference surface for measuring the borehole depth and the burial depth of the guide pipe 12, ensuring the accuracy and consistency of the measurement; (5) The horizontal section 22 of the guide wall 2 provides a stable and reliable support structure for the hoisting of the steel cage 7 and the support of the guide pipe 12, ensuring the accuracy of the position, height and verticality of the steel cage 7 and the guide pipe 12; (6) The use of the skip pile construction method effectively reduces the mutual influence between adjacent pile holes 5 and prevents quality problems such as cross-hole and hole collapse. In summary, the present invention significantly improves the construction quality and efficiency of subway retaining piles, reduces construction costs, and minimizes environmental pollution, demonstrating significant technological advancements and economic benefits.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing retaining piles for subway lines, characterized in that, Includes the following steps: S1: Survey and set out, excavate guide wall trench, tie steel bars and pour guide wall trench concrete to form two guide walls set opposite each other, with the top surface of the guide wall higher than the top surface of the pile hole. S2: Locate the pile position, excavate the first section of test hole soil between the two guide walls, tie the first section of retaining wall reinforcement, pour the first section of retaining wall concrete, excavate the second section of test hole soil between the two guide walls, tie the second section of retaining wall reinforcement, pour the second section of retaining wall concrete, and repeat this cycle until all pile hole excavation segments are completed. The pile holes are formed using a rotary drilling rig, and mud is injected into the holes. The mud is stored in two guide walls for recycling. S3: Place the steel cage into the pile hole and pour underwater concrete.

2. The method for constructing subway retaining piles according to claim 1, characterized in that, In S1, the guide wall includes a vertical section and a horizontal section. The horizontal section is located outside the vertical section, and the elevation of the horizontal section is lower than the road surface elevation.

3. The method for constructing subway retaining piles according to claim 2, characterized in that, S2 also includes stopping drilling after the design depth is reached, measuring the hole depth, and using the horizontal section of the guide wall as the reference surface for measuring the hole depth.

4. The method for constructing subway retaining piles according to claim 3, characterized in that, S2 also includes cleaning the hole by pumping slurry after the hole diameter, hole depth and verticality are checked and confirmed to be qualified after drilling reaches the designed depth.

5. A method for constructing subway retaining piles according to claim 2, characterized in that, In step S3, when the reinforcing cage is lowered to the opening position, sleepers are set on the horizontal section of the guide wall, and suspension steel pipes are installed to suspend and support the reinforcing cage on the sleepers.

6. The method for constructing subway retaining piles according to claim 1, characterized in that, The concrete was poured using the tremie pipe method for continuous pouring.

7. A method for constructing subway retaining piles according to claim 6, characterized in that, S3 includes placing the reinforcing cage into the pile hole, installing the guide pipe, performing secondary hole cleaning, and pouring underwater concrete.

8. A method for constructing subway retaining piles according to claim 7, characterized in that, S3 also includes measuring the burial depth of the conduit, using the horizontal section of the guide wall as the reference surface for measuring the burial depth of the conduit.

9. A method for constructing subway retaining piles according to claim 7, characterized in that, S3 also includes setting a guide pipe support frame in the horizontal section of the guide wall, and measuring and adjusting the height of the guide pipe embedded in the concrete through the guide pipe support frame.

10. A method for constructing subway retaining piles according to any one of claims 1-9, characterized in that, The retaining piles are constructed using a skip-pile method, with each pile being installed every two holes.

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