Foundation pit supporting pile structure and supporting construction method

Abstract

The invention provides a foundation pit supporting pile structure and a supporting construction method. The supporting construction method comprises the steps of supporting pile construction, crown beam construction and pre-stressed anchor cable construction. The construction of the support pile comprises the following steps: S11, measuring and positioning; s12, a pile casing is embedded; s13, slurry preparation; s14, drilling construction is carried out; s15, hole cleaning is conducted; s16, a reinforcement cage is manufactured and hoisted; s17, a guide pipe is installed; s18, concrete pouring is conducted; top beam construction; s21, top beam earth excavation is carried out; s22, a virtual pile head is chiseled away; s23, steel bars are manufactured and installed; s24, a formwork is installed; s25, concrete pouring is conducted; pre-stressed anchor cable construction; s31, drilling construction is carried out; s32, manufacturing and placing an anchor cable; s33, grouting is conducted; s34, mounting I-shaped steel; s35, pre-stressed anchor cable tensioning and locking anchor cable tensioning construction are carried out; and S36, hole sealing, grouting and external protection are conducted. The supporting piles provide deep support, and the anchor rods are anchored in a soil body to form an integral supporting system, so that the integral stability of the foundation pit is enhanced, and collapse is prevented.

Description

Technical Field

[0001] The invention belongs to the field of foundation pit construction, and in particular relates to a foundation pit supporting pile structure and a supporting construction method. Background Art

[0002] Urban foundation pit excavation projects have a deep excavation depth (5.78-11.82m), and the surrounding environment is complex and close to existing buildings. According to geological surveys, the soil and groundwater levels in the construction area are complex, and preparations should be made to deal with the lateral pressure and water pressure of the soil. Since there are many buildings around the construction site in the city, the need to effectively prevent the sedimentation of the buildings is also an urgent problem to be solved. Summary of the invention

[0003] In view of this, the present invention aims to propose a foundation pit support pile structure and a support construction method, wherein the support piles provide deep support, and the anchor rods are anchored in the soil to form an overall support system, thereby enhancing the overall stability of the foundation pit and preventing collapse.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows: The foundation pit support pile structure and support construction method are composed of a support system combining support piles and anchor rods, including support pile construction, cap beam construction and prestressed anchor cable construction; The construction of supporting piles includes the following steps: S11, measurement and positioning; S12, casing burial; S13, mud preparation; S14, drilling construction; S15, hole cleaning; S16, steel cage production and hoisting; S17, conduit installation; S18, concrete pouring; The crown beam construction includes the following steps; S21, excavation of crown beam; S22, removal of virtual pile heads; S23, production and installation of steel bars; S24, installation of formwork; S25, pouring of concrete; The construction of prestressed anchor cables includes the following steps: S31. Drilling construction; S32. Anchor cable production and placement; S33. Grouting; S34. Installation of I-beams; S35. Prestressed anchor cable tensioning and locking anchor cable tensioning construction; S36. Sealing hole grouting and external protection.

[0005] Further, the support pile is constructed, wherein in step S12, the steel casing is made of a 5 mm thick steel plate, the inner diameter is 20 to 40 cm larger than the pile diameter, the casing is 1.5 m long, a 0.4 m high and 0.2 m wide slurry outlet is left at the top of the casing, and a blade foot is provided at the lower end of the bottom casing; When burying the steel casing, first place the pile position, draw a cross line through the center of the pile position, set a control pile 80-100cm outside the casing, and dig a circular pit at the pile position; when burying the steel casing, first place the pile position, and align the center of the steel casing with the pile position; Fill the bottom of the steel casing with clay about 30cm-50cm thick, compact it layer by layer, then install the casing and fill it with clay around it. The burial depth should not be less than 1.5m.

[0006] Further, in step S16, arc welding is used for welding the steel cage with a double-sided overlap length of 5d and a single-sided welding of 10d; the positioning reinforcement 10@2000mm is welded with the longitudinal reinforcement, the steel cage is processed in sections according to the total length, hoisted in batches, the hole is in place, and overlap welding is performed at the hole; The main reinforcement spacing of the steel cage is controlled within ±10mm, and the length is controlled within ±50mm; the stirrup spacing is ±20mm, the diameter is ±10mm, the steel cage installation depth is controlled within ±100mm, and the protective layer thickness is controlled within ±20mm.

[0007] Furthermore, in step S17, the conduit is subjected to a watertightness test before installation; the specific method is as follows: a. Check whether there are obvious holes in each section of the catheter, and check the sealing ring of each section of the catheter; b. Select a site so that the conduits can be docked evenly on the ground; when docking, number each tube in sequence; c. Install closing devices at both ends of the conduit, using existing pressure test sleeves; install water inlet holes at both ends of the pressure test seal; when installing, make sure the two holes are located directly above the pipe so that air can overflow from the holes when water is injected; d. Install a water pipe to inject water into the conduit. Stop when water comes out from the other end of the pipe. Make sure the conduit is filled with more than 70% of water before stopping. e. Seal the water injection hole at one end and connect the other end to the air compressor. Check the installation of the closed end of the conduit connection. After the inspection is qualified, pressurize the air compressor to 0.6MPa and maintain the pressure for 15 minutes; check the water overflow at the conduit joint and make a record of the overflow. During the pressure test, roll the conduit 180°, pressurize it again, maintain the pressure for 15 minutes, and make a record of the inspection situation; f. Before installing the conduit, check the smoothness of its inner wall and record it by number; no flange is installed at the lower end of the last section, and the length is generally 4-6m, so that the concrete will not be moved when the pipe is pulled out, and then 2.5m pipe sections are installed in sequence; after considering that the bottom of the hole is suspended 30-50cm, calculate the height to the top surface of the chuck so that the length of the conduit can be adjusted with 1.5m pipe sections for the top few sections; the flange surface of the conduit interface must be flat, and a rubber pad must be placed between the two flanges, and a layer of butter should be evenly applied on both sides of the pad to facilitate sealing; the conduit should be placed in the center of the hole; the storage hopper is connected to the upper end of the conduit, and the storage hopper is wetted with water before use, and the upper end of the jack rope for pulling the plug is tied to the top of the storage hopper; an operating bracket is set up next to the storage hopper, and a working platform is set up on it; the position relationship between the upper hopper, storage hopper, concrete transport vehicle and crane is arranged to facilitate operation and free advance and retreat; the preparation work should be shortened as much as possible to reduce the sedimentation at the bottom of the hole; Furthermore, in step S18, before pouring, the thickness of the sediment at the bottom of the hole is controlled, and if it does not meet the requirements, a second hole cleaning is performed, but the hole wall must be stabilized to prevent hole collapse.

[0008] Furthermore, in step S21, the excavation of the crown beam is carried out by a small excavator, and the excavation is carried out in sections. The length of each section is controlled according to the on-site geological conditions. The stability of the slope must be ensured during the excavation process; the remaining soil is removed by manual excavation, and the elevation is controlled to 500mm below the crown beam.

[0009] Further, in step S22, since the concrete at the top of the pile contains slurry during the pouring of concrete, the pile head within the height range of 500-600mm at the top of the supporting pile needs to be chiseled out, and the pile head steel bars are first stripped out. When stripping the steel bars from the concrete, the concrete is broken along the pile body to ensure that the stripped steel bars are straight and avoid the steel bars from being bent. When the pile head slurry and excess concrete are chiseled out with a pneumatic machine, at least 20-30cm is reserved for manual chiseling along the pile body horizontally with a drill or cutting along the pile body with a cutting machine, and the drill cooperates with the chiseling to ensure that the pile top after chiseling is a complete plane; The chiseling is carried out with electric shovels, pneumatic guns, steel chisels, and drills. Before chiseling, an elevation line is placed on the outer supporting pile to control the elevation of the top of the supporting pile. The top surface of the chiseled supporting pile must be flat, and the local height difference should not exceed 20mm. After the chiseling of the top of the supporting pile is completed, it must be cleaned and washed with water; In step S23, the stressed steel bars are connected by binding lap joints. The binding lap joints arranged in the same component are staggered with each other. The staggered distance is 35d of the steel bar diameter and should not be less than 500mm. The cross-sectional area of ​​the stressed steel bars with joints in this section accounts for no more than 50% of the stressed surface area.

[0010] Further, in step S31, the drilling construction includes anchor hole positioning, drilling equipment preparation, anchor hole drilling construction by drilling rig, waterless dry drilling should be used for anchor hole drilling, the formation changes of each hole should be recorded during the drilling process, the actual drill bit diameter used for the hole diameter and hole depth should not be less than the designed hole diameter, anchor hole cleaning, and anchor hole inspection; In step S32, the steel strands are cut strictly according to the design size, and the length error of each strand is no more than 50 mm; the steel strands are arranged straight, and a wire ring is set every 1.5 m along the axis of the rod body at the anchoring section of the rod, and the grouting pipe should be firmly tied to the rod body; Before installation, ensure that each steel strand is straight, not twisted or forked, evenly arranged, and derusted and degreased. Remove any dead bends, mechanical damage, and rust pits. Apply butter to the free section of the steel strand and cover it with a Ø20PVC corrugated pipe for corrosion protection, ensuring that the thickness of the protective layer of the anchor cable is not less than 20mm.

[0011] Furthermore, in step S35, the construction process of prestressed anchor cable tensioning and locking anchor cable tensioning is as follows: Install dynamometer → install working anchor and clip → use small jack to tension and straighten the steel-ammonium wires one by one → install limit plate → tension → lock → grouting and sealing holes for permanent rust prevention → cut off the extra long part of the steel-ammonium wire above the working anchor → pour the second phase concrete.

[0012] Furthermore, in step S36, after compensating for tensioning, sealing grouting is immediately performed; for downward-inclined anchor cables, the grouting pipe is inserted from the reserved hole until the pipe mouth is about 50 cm from the top surface of the anchoring section; for upward-inclined and horizontal anchor cables, grouting is performed through the reserved grouting pipe; the air in the hole is discharged through the exhaust pipe provided at the positioning stop ring.

[0013] Compared with the prior art, the foundation pit support pile structure and support construction method described in the present invention have the following advantages: (1) The foundation pit support pile structure and support construction method of the present invention, the combination of support piles and anchor rods effectively resists the lateral pressure of the soil, prevents the collapse of the soil during the foundation pit excavation process, and ensures construction safety.

[0014] (2) The foundation pit support pile structure and support construction method of the present invention can reduce the impact on surrounding buildings by providing strong support and prevent settlement or cracks caused by foundation pit excavation.

[0015] (3) The foundation pit support pile structure and support construction method of the present invention, combined with anchor rod construction, can effectively control the water level in the foundation pit, ensure dry operation of the foundation pit, and avoid the influence of water on the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 It is a schematic diagram of the construction coordination of support piles and anchor rods in a foundation pit according to an embodiment of the present invention.

[0017] Description of reference numerals: 1. Support piles; 2. Anchor rods. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0019] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention 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 cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0021] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0022] The foundation pit support pile structure and support construction method are characterized by: a support system composed of support piles and anchor rods, including support pile construction, crown beam construction and prestressed anchor cable construction; The construction of supporting piles includes the following steps: S11. Measurement and positioning; (1) To identify and record the construction process, the bored piles are uniformly numbered; a measurement control network is established to locate the bored piles, and the center position of the bored piles is marked and numbered using the cross positioning method; (2) The pile position measurement uses the main structure axis position, and adopts total station and level to measure and locate, and the hole position error is less than 1 cm; (3) At the same time, various construction error reserves (pile position offset and verticality deviation) and the thickness of the pile mesh sprayed without chiseling the pile skin and the outer waterproofing should be considered. During construction, the pile position coordinates should be considered to have a construction error reserve of 150mm outside; the retest and acceptance are qualified.

[0023] S12, burying casing; (1) The steel casing is made of 5mm thick steel plate, with an inner diameter 20~40cm larger than the pile diameter. The casing is 1.5m long overall. A 0.4m high and 0.2m wide grouting outlet is left at the top of the casing, and a blade foot is set at the bottom of the bottom section of the casing; (2) When burying the steel casing, first place the pile position, draw a cross line through the center of the pile position, set the control pile 80-100cm outside the casing, and dig a circular pit at the pile position; when burying the steel casing, first place the pile position, and align the center of the steel casing with the pile position; (3) Fill the bottom of the steel casing with clay about 30cm-50cm thick, compact it layer by layer, then install the casing and fill the surrounding area with clay. The burial depth should not be less than 1.5m.

[0024] S13, mud preparation; Under the premise of not affecting the drilling construction, according to the pile foundation construction plan, a mud slurry station is set up in the middle of every two caps, and slurry mixing equipment, water tank, slurry tank and sedimentation tank are set up in the station. The slurry tank and sedimentation tank are arranged in a connected manner. In order to reduce pollution, steel boxes are used as slurry tanks and sedimentation tanks. There are 4 14.4m³ steel boxes in total; the size of the steel box is 3×2.4×2=14.4m³, and each drilling rig is equipped with 2 steel boxes. The steel box is processed with a steel plate thickness of 8mm, and L75 angle steel is used for edging, 10# channel steel is used for back rib reinforcement, p32 steel bars are used as lifting ears, qp48×3.5mm steel pipes are used for temporary support, and the mud is pumped into the hole with a 4-inch mud pump; During drilling, mud can prevent hole wall collapse and suppress groundwater, so mud is an important factor in ensuring hole wall stability. Due to the presence of silt sand layers in the foundation soil and the high ground water level, the performance indicators of the prepared mud are particularly important.

[0025] According to the characteristics of rotary drilling rigs with fast drilling speed, the raw materials of mud are made of high-quality bentonite. Commonly used mud materials are generally made of high-quality bentonite plus soda ash, polyacrylamide, water, etc. The mud is designed according to the construction machinery, process and the conditions of the soil layer to be crossed. Two ZL400 type pulping machines are selected, and the machine body is installed firmly and stably. The mixer should be equipped with a rainproof operating shed, and all kinds of clutches, brakes, wire ropes, and protective covers must be safe, reliable and effective. The mixer must have a good separate grounding. The mud is prepared according to the specified mix ratio. The mixing time for each plate of bentonite is 3 minutes, and the amount of various materials added shall not exceed 5%; Mud treatment agents such as soda ash, CMC and polyacrylamide should be prepared into aqueous solutions of a certain concentration before use to improve their effect. The concentration of soda ash aqueous solution is 20%, and that of CMC and polyacrylamide aqueous solution is 1.5%.

[0026] After the mud is stirred in the mud pool with a mud mixer, the newly made mud needs to be stored for 12 hours. It can be used after it is fully swollen, and then pumped into the hole and the rotary drill drills evenly and slowly. This not only drills but also plays the role of mud wall protection. When drilling, master the footage speed, pay attention to the situation in the hole at any time, and add mud in time to maintain the liquid level. The mud preparation index requirements of the "Technical Specification for Bored and Cast-in-Place Piles" (GB-20121126M) are: specific gravity 1.03~1.1, viscosity greater than 20-35pa.s, colloid rate greater than 95%, and sand rate not more than 4%; according to different geological structures, configure the corresponding mud according to the above requirements.

[0027] During construction, the mud surface in the casing should be more than 1.5m higher than the bottom of the casing to ensure the water head height in the hole and prevent the hole from collapsing. During the hole cleaning process, the mud should be replaced continuously until the mud index in the hole meets the requirements and then pour underwater concrete.

[0028] During the bored pile construction process, the sediment in the sedimentation tank and the waste mud overflowed during concrete pouring should be cleaned at any time to prevent mud overflow. The mud should be transported to the designated location for dumping by mud trucks. It is prohibited to discard the slag on the spot and pollute the surrounding environment.

[0029] Mud testing and control requirements: Take samples in the mixer and measure the specific gravity and funnel viscosity after hydration and swelling for 12 hours: Take samples in the newly built slurry storage tank and test the mud specific gravity and viscosity: When the main hole is drilled normally, the circulating slurry is tested for specific gravity, viscosity and sand content.

[0030] During construction, the mud conveying equipment uses a 22kw centrifugal mud pump with a 5-inch steel pipe or rubber hose. The fresh mud (mud stored in the mud pool for more than 12 hours) is transported from the mud pool to the drilling site. Each mud pool is divided into a circulation pool and a storage pool, with a mud channel in the middle. Unqualified mud during construction can be transported to the abandoned mud pool and then to the waste dump.

[0031] S14, drilling construction; (1) The drilling rig is positioned accurately, horizontally and stably, and the center of the drill tool and the center of the casing coincide. After the drilling rig is positioned, the upper end of the casing is hung on the chassis of the drilling rig with a wire rope. During the drilling process, the pulley block, the rotator and the drill bit at the head of the drilling rig tower are always kept on the same plumb line to ensure that the drill bit drills in a tightened state. The diameter of the hole must reach the designed pile diameter, and a pot body with an outer diameter 50mm smaller than the pile body diameter is selected, and the pot body ensures roundness.

[0032] (2) The drilling tool’s guiding device is in good condition to ensure the verticality of the hole, and a total station is used to calibrate the verticality of the drill rod.

[0033] (3) In order to prevent the collapse of bored piles due to the close distance between two adjacent piles or the short interval between them, the construction of bored piles should be carried out in batches. During the construction of bored piles, one hole should be constructed at each interval. The construction of adjacent piles should be carried out after the initial setting of the concrete. That is, the odd-numbered piles "1, 3, 5..." should be constructed first, and then the even-numbered piles "2, 4, 6..." should be constructed. It is ensured that the 2m range around the pile body will not be disturbed within 24 hours after the concrete pouring of the pile body. At the same time, mud suitable for geological conditions should be selected during construction. When drilling in sandy soil and thick sand-interlayer, the mud specific gravity should be controlled at 1.0-1.2. When drilling in soil layers prone to collapse, the mud specific gravity should be controlled at 1.1-1.3. The mud specific gravity, viscosity and sand content should be measured frequently during construction, and the mud should be adjusted according to different soil layers. The mud carrying slag flows into the sedimentation tank through the ditch. After sedimentation, part of the mud is reused and part is discarded. The mud density is adjusted in time according to the stratum to ensure the stability of the sand layer. The water head height can also be raised or powdered materials can be added to rotate and mix in the drilling hole.

[0034] (4) When drilling underwater with a rotary drill, stop for 1-3 minutes and then slowly lift the drill to prevent negative pressure from sucking the hole wall out. After lifting the soil, inject water or slurry in time to change the water head to prevent the hole wall from collapsing.

[0035] (5) After drilling is completed, the hole depth must be checked. The design requires a hole depth deviation of +500mm.

[0036] (6) The drilling technology should be reasonably selected based on the engineering geological conditions, design requirements, project characteristics and trial drilling conditions.

[0037] S15, hole cleaning; (1) The bored pile is bored to the designed elevation, and the drill rod is fully utilized to carry out the first hole cleaning in situ. The slurry replacement, slurry extraction and slag removal methods are adopted, and the thickness of the sediment at the bottom of the hole is measured to be less than 100 mm; (2) When cleaning the hole, care must be taken to maintain the water head in the hole to prevent the hole from collapsing; (3) It is prohibited to increase the drilling depth instead of cleaning the hole.

[0038] S16, steel cage production and hoisting; The steel cage is welded by arc welding with a double-sided overlap length of 5d and a single-sided welding of 10d: the positioning reinforcement 10@2000mm is welded with the longitudinal reinforcement. The steel cage is processed in sections according to the total length, hoisted in batches, the hole is in place, and overlap welding is performed at the hole; The welds at the overlapped joints of the steel cage must be full, smooth and free of welding slag. Before welding the steel cage, adjust the flow of the electric welder to ensure that the steel bars are not burned or the welding strength is insufficient; The spacing between main reinforcement bars of the steel cage is controlled within ±10mm, and the length is controlled within ±50mm; the spacing between stirrups is ±20mm, the diameter is ±10mm, the installation depth of the steel cage is controlled within ±100mm, and the thickness of the protective layer is controlled within ±20mm; It is strictly forbidden to drag the steel cage during transportation. The steel cage should be clean and tidy before being put into the hole without soil corrosion. After drilling to the design elevation, check that the hole depth, hole diameter, verticality meet the requirements and the sediment at the bottom of the hole meets the requirements, and then prepare to put the steel cage. The steel cage is hoisted in sections using a car crane, and the hole mouth is overlapped and welded. Measures are taken to prevent deformation of the steel cage during lifting, transportation and installation. The lifting point is set at the location of the reinforced stirrups. After lifting, it is firmly fixed to prevent the steel cage from floating during concrete pouring.

[0039] S17, catheter installation; Before installing the conduit, the conduit must be tested for water tightness; the specific method is as follows: a. Check whether there are obvious holes in each section of the catheter, and check the sealing ring of each section of the catheter; b. Select a site so that the conduits can be docked evenly on the ground; when docking, number each tube in sequence; c. Install closing devices at both ends of the conduit, using existing pressure test sleeves; install water inlet holes at both ends of the pressure test seal; when installing, make sure the two holes are located directly above the pipe so that air can overflow from the holes when water is injected; d. Install a water pipe to inject water into the conduit. Stop when water comes out from the other end of the pipe. Make sure the conduit is filled with more than 70% of water before stopping. e. Seal the water injection hole at one end and connect the other end to the air compressor. Check the installation of the closed end of the conduit connection. After the inspection is qualified, pressurize the air compressor to 0.6MPa and maintain the pressure for 15 minutes; check the water overflow at the conduit joint and make a record of the overflow. During the pressure test, roll the conduit 180°, pressurize it again, maintain the pressure for 15 minutes, and make a record of the inspection situation; f. Before installing the conduit, check the smoothness of its inner wall and record it by number; no flange is installed at the lower end of the last section, and the length is generally 4-6m, so that the concrete will not be moved when the pipe is pulled out, and then 2.5m pipe sections are installed in sequence; after considering that the bottom of the hole is suspended 30-50cm, calculate the height to the top surface of the chuck so that the length of the conduit can be adjusted with 1.5m pipe sections for the top few sections; the flange surface of the conduit interface must be flat, and a rubber pad must be placed between the two flanges, and a layer of butter should be evenly applied on both sides of the pad to facilitate sealing; the conduit should be placed in the center of the hole; the storage hopper is connected to the upper end of the conduit, and the storage hopper is wetted with water before use, and the upper end of the jack rope for pulling the plug is tied to the top of the storage hopper; an operating bracket is set up next to the storage hopper, and a working platform is set up on it; the position relationship between the upper hopper, storage hopper, concrete transport vehicle and crane is arranged to facilitate operation and free advance and retreat; the preparation work should be shortened as much as possible to reduce the sedimentation at the bottom of the hole; S18, concrete pouring; (1) Before pouring, the thickness of the sediment at the bottom of the hole should be controlled. If it does not meet the requirements, the hole must be cleaned for the second time, but attention should be paid to stabilizing the hole wall to prevent the hole from collapsing. When the concrete is transported to the pouring site, the workability and slump should be checked. If it does not meet the requirements, it shall not be used. After the storage hopper is installed and other preparations are in place, after the storage hopper is filled with concrete (concrete reserves for continuous pouring should also be prepared), the first batch of concrete can be poured. After cleaning the hole and lowering the steel cage, pour the concrete immediately. When pouring concrete, a conduit should be used for pouring. The conduit should be inserted into the concrete for no less than 1.5m, and the lifting speed of the conduit should meet the construction requirements and specifications. The slump of concrete pouring is 180mm-220mm. The initial setting time of the first batch of concrete pouring shall not be earlier than the completion time of all concrete pouring of the bored pile. The pouring time should be shortened as much as possible and the operation should be continuous.

[0040] (2) First install the conduit. Use a 25t truck crane to hoist the conduit (with a diameter of not less than 250mm) into the hole. Keep the position centered and keep about 300-500mm between the lower end of the conduit and the bottom of the hole. Before using the conduit and after pouring 4-6 piles, check the tightness of the conduit and its joints to ensure good sealing. Before pouring the first batch of concrete, hang a water stopper in the funnel, and then pour the first batch of concrete. After confirming that the storage volume is sufficient, you can cut the wire and use the weight of the concrete to remove the water in the conduit, leaving the water stopper at the bottom of the hole. After the first batch of concrete is poured normally, pour continuously. During the pouring process, use a hammer to measure the height of the concrete surface, calculate the depth of the lower end of the conduit buried in the concrete, and keep records to correctly guide the lifting and removal of the conduit. When lifting the conduit, the buried pipe should be controlled at 2-6m. It is strictly forbidden to lift the bottom of the conduit out of the concrete surface. Concrete pouring should be continuous and not interrupted. After pouring, the top of the bored pile should be 750mm higher than the design elevation so as to ensure good quality of concrete in the cross section after removing the floating slurry concrete from the pile head.

[0041] (3) The preparation of concrete should meet the requirements of design and specifications, with a slump of 160-220mm and a cement dosage of not less than 360kg / m'. Before formally mixing concrete, select the appropriate mix ratio based on the adaptation results. Use commercial concrete and transport it by concrete tanker. The diameter of the conduit should be 250mm. The conduit should be placed in the center of the hole. The height of the bottom of the conduit from the bottom of the hole should be controlled at 30-50cm, and the length of the first section of the conduit should be not less than 4m. The upper end of the conduit is connected to a concrete funnel with a capacity of not less than 2.2m³. When pouring begins, a water stopper is installed at the lower end of the funnel. After the initial pouring of concrete is sufficient, cut off the wire connecting the water stopper to make the concrete fall suddenly, quickly fall to the bottom of the hole and wrap the conduit, seal the bottom concrete, and make the depth of the conduit buried in the concrete not less than 1.0m.

[0042] (4) The amount of material poured in the first batch must ensure that the conduit is buried more than 1m.

[0043] (5) The underwater concrete pouring work of each pile shall be carried out compactly and continuously, and it is strictly forbidden to stop work in the middle. It is required to provide the concrete use plan to the commercial concrete mixing station one day before the bored pile concrete pouring, and verify the planned concrete supply to ensure the continuity of the pile concrete pouring. At the same time, pay attention to the drop of concrete in the conduit and the rise and fall of water level in the hole, and measure the height of the concrete surface in the hole in time to ensure that the depth of the conduit buried in the concrete during the pouring process is within the range of 2-6m. The conduit should always be buried in the concrete during the concrete pouring process, and it is strictly forbidden to lift the conduit out of the concrete surface. For the first two piles, a designated person should fill in the construction records in order to summarize the experience and guide the subsequent bored pile construction. The top elevation of the bored pile pouring should be at least 0.5m higher than the designed elevation of the pile top to remove the floating slurry and ensure the quality of the pile body.

[0044] Quality inspection and acceptance: (1) After drilling, use a hole tester (a steel cage with a diameter equal to the designed diameter of the pile and a height six times the hole diameter) to test the hole. The hole diameter should not be less than the designed diameter.

[0045] (2) A centralizer should be added to the drilling tool of the drilling rig to adjust the drilling direction and angle of the drilling rig in time according to the measured verticality data to ensure the verticality of the drilled hole. The verticality of the hole is tested by a hole inspection device.

[0046] The key to prevent the steel cage from floating up is to carefully and carefully lay the steel cage and firmly tie or spot weld it under the hole. When placing the conduit, the conduit should be placed along the center of the pile hole. During the pouring process, when the concrete is close to the upper part of the steel cage, the concrete should be poured slowly. Generally, the pouring speed is controlled at about 15m / h to reduce the upward impact of the concrete on the steel cage. Pay special attention to the conduit outlet and the bottom of the steel cage. Generally, the conduit outlet should be higher than the bottom of the steel cage by not less than 1.0m. Concrete should be strictly prepared according to the mix ratio, and the pouring should be carried out continuously to ensure that all the pouring work of the entire pile is completed within the initial setting time of the first batch.

[0047] The crown beam construction includes the following steps; S21, excavation of crown beam; The excavation of the crown beam is carried out by a small excavator. The excavation is carried out in sections. The length of each section is controlled according to the geological conditions on site. The stability of the slope must be ensured during the excavation process. The remaining soil is removed by manual excavation, and the elevation is controlled at 500mm below the crown beam.

[0048] S22, chiseling away the empty pile heads; Since the concrete at the top of the pile contains floating slurry during the pouring of concrete, according to the technical specifications, the pile head within the height range of 500-600mm at the top of the supporting pile needs to be chiseled out. First, the pile head steel bars should be stripped out. When stripping the steel bars from the concrete, try to break the concrete along the pile body to ensure that the stripped steel bars are straight and avoid dead bends. Pneumatic machinery is not allowed to damage the steel bar surface: When using pneumatic machinery to chisel out the floating slurry and excess concrete at the pile head, at least 20 to 30cm should be reserved for manual chiseling along the pile body horizontally with a drill or cutting along the pile body with a cutting machine. The drill cooperates with the chiseling to ensure that the pile top after chiseling is a complete plane. The chiseling is carried out with electric shovels, pneumatic guns, steel drills, and drills. Before chiseling, an elevation line is placed on the outer supporting pile to control the elevation of the supporting pile top. The top surface of the chiseled supporting pile must be flat, and the local height difference should not exceed 20mm. After the chiseling of the supporting pile head is completed, it must be cleaned and washed with water.

[0049] S23, steel bar production and installation; According to the center line of the support pile, the steel bars are manufactured and installed according to the design requirements. The steel bars are manufactured and installed to meet the following technical requirements: (1) The quality certification materials of the selected steel bars are complete, and the inspection and testing work has been carried out as required, and the results meet the use requirements.

[0050] (2) The binding of steel bars shall be carried out in accordance with the design and technical specifications. During the processing and binding process, the steel bars shall be straight without local bends; the surface shall be clean, free of damage, paint and rust; the bending of steel bars shall be carried out at room temperature. Hot bending, hammering or sharp-angle bending are not allowed.

[0051] (3) The stress-bearing steel bars shall be connected by tied lap joints. The tied lap joints in the same component shall be staggered with a staggered distance of 35d of the steel bar diameter and shall not be less than 500mm. The cross-sectional area of ​​the stress-bearing steel bars with joints in this section shall not exceed 50% of the stress-bearing surface area.

[0052] (4) The intersections of the steel bars should be tied securely with iron wire in a plum blossom shape.

[0053] S24, template installation; Since the cross section of the crown beam is small, the template installation is relatively simple. The template control line is laid out through the center line of the supporting pile. The template installation must meet the following technical requirements: (1) The formwork support must have sufficient bearing capacity, rigidity and stability to reliably withstand the lateral pressure of the newly poured concrete and the loads generated during construction.

[0054] (2) To ensure that the template joints do not leak, the gaps between the templates must be sealed tightly during support. Before installing the template, the template surface should be carefully cleaned and the release agent should be evenly and fully applied.

[0055] S25, concrete pouring; The crown beam adopts C25 commercial concrete. Subsequent construction can be carried out only after the first concrete support reaches the required strength time and strength.

[0056] (1) Before pouring concrete, check whether the formwork and steel bars are installed correctly and keep records. Clean the garbage and dirt in the formwork and the oil stains on the steel bars, and sprinkle water on the wooden formwork to moisten it.

[0057] (2) When pouring concrete, use a vibrator to vibrate. Avoid touching the steel bars during the vibrating process, and vibrate fully to ensure that the concrete is dense. Keep test pieces according to the specifications, mark the date on the test pieces, and send them to the laboratory for standard curing the next day.

[0058] (3) After pouring concrete, cover the exposed surface with a layer of plastic sheeting, then cover it with black cotton and maintain it in time. Water the concrete within 12 hours after pouring. In the early stage of maintenance and when the temperature is high, water it several times to ensure that the concrete is sufficiently moist.

[0059] (4) The concrete at the crown beam construction joint should be treated by roughening the concrete surface, cleaning it, and removing the weak concrete layer. The concrete should be carefully compacted to ensure a tight connection between the new and old concrete.

[0060] The construction of prestressed anchor cables includes the following steps: S31, drilling construction; (1) Anchor hole positioning: According to the requirements of the construction design drawing of the anchoring project at the specific work site, the anchor hole position should be accurately measured and placed on the slope surface. The vertical and horizontal errors of the hole position on the slope surface shall not exceed 50mm.

[0061] (2) Drilling equipment: The selection of drilling equipment should be based on the type of anchoring stratum, the diameter of the anchor hole, the depth of the anchor hole, and the conditions of the construction site. The anchor hole should be drilled using a down-the-hole drill or an anchor cable drill. In strata that are prone to hole collapse and drill bit burial, such as broken or soft saturated rock, the following pipe drilling technology should be used.

[0062] (3) Drilling rig positioning: During anchor hole drilling construction, a scaffolding that meets the corresponding bearing capacity and stability conditions should be set up. The drilling rig should be accurately installed and fixed according to the hole position measured on the slope, and the machine position should be strictly and carefully adjusted to ensure that the longitudinal and transverse errors of the anchor hole drilling position do not exceed 50mm, and the elevation error does not exceed ±100mm. The inclination angle and direction of the drilling hole should meet the design requirements, and the allowable inclination error is 3.0.

[0063] (4) Drilling method: Anchor hole drilling should be done by dry drilling without water, and water drilling is prohibited to ensure that the anchoring construction will not deteriorate the geological conditions of the slope geotechnical engineering and ensure the bonding performance of the hole wall. The drilling speed should be strictly controlled according to the performance of the drilling rig and the anchoring stratum to prevent the borehole from twisting and changing in diameter, causing difficulties in anchoring or other accidents.

[0064] (5) Drilling process: During the drilling process, the changes in the formation of each hole, the drilling status (drilling pressure, drilling speed), groundwater and some special situations should be recorded on site. If there are unfavorable drilling phenomena such as hole collapse and shrinkage, the drilling should be stopped immediately and the wall should be grouting in time. The grouting pressure should not be less than 1.5MPa. After the cement mortar is initially set, the hole should be re-drilled.

[0065] (6) Hole diameter and depth: The borehole diameter and depth must not be less than the designed value. To ensure the anchor hole diameter, the actual drill bit diameter must not be less than the designed hole diameter. To ensure the anchor hole depth, the actual drilling depth must be greater than the designed depth by 0.5m.

[0066] (7) Anchor hole cleaning: After drilling reaches the designed depth, drilling cannot be stopped immediately. Steady drilling is required for 1 to 2 minutes to prevent the bottom of the hole from pinching out and failing to reach the designed hole diameter. The borehole wall must not have sediment and sticky water. It must be cleaned. After drilling is completed, high-pressure air (wind pressure 0.2~0.4MPa) is required to be used in principle to remove all rock powder and water in the hole to avoid reducing the bonding strength between the cement mortar and the rock and soil on the hole wall. Except for anchoring relatively hard and intact rock mass, high-pressure water flushing should not be used. If pressurized water flows out of the anchor hole, the anchor cable and grouting can be installed only after the water pressure and water volume decrease. If necessary, drainage holes can be set at appropriate locations around. If the design requires the treatment of water accumulation inside the anchor hole, grouting and secondary drilling are generally used.

[0067] (8) Anchor hole inspection: The hole diameter and hole depth inspection generally uses the designed hole diameter drill bit and standard drill rod to inspect the hole. During the inspection, the drill bit is required to advance smoothly without impact or shaking. The drill tool inspection length meets the designed anchor hole depth. The drill withdrawal is required to be smooth. High-pressure wind blowing is used to check that there is no obvious flying dust and water. At the same time, it is required to recheck the anchor hole position, inclination and orientation. After all the anchor hole construction sub-items are qualified, the anchor hole drilling inspection can be considered qualified.

[0068] S32, anchor cable production and placement; The steel strands are cut strictly according to the design size, and the length error of each strand is no more than 50mm. The steel strands are arranged straightly according to a certain rule. A wire ring is set every 1.5m along the axis of the rod body in the anchoring section of the rod. The grouting pipe should be firmly tied to the rod body. Before installation, ensure that each steel strand is straight, not twisted or forked, evenly arranged, rusted and degreased, and dead bends, mechanical damage and rust pits are removed; the free section of the steel strand is coated with butter and covered with Ø20PVC corrugated pipe for corrosion protection, ensuring that the thickness of the anchor cable protective layer is not less than 20mm.

[0069] When placing the assembled anchor cable, prevent the rod from twisting, compression and bending, and insert it to the designed depth and ensure that the pull rod is in the center of the drill hole.

[0070] S33, grouting; The grouting pipe's outlet should be inserted less than 300mm from the bottom of the hole. The slurry should be poured continuously from bottom to top, and ensure smooth drainage and exhaust from the hole. After grouting, the rod body should not be knocked or pulled at will, and heavy objects should not be hung on the rod body.

[0071] Grouting precautions: (1) Samples of the poured cement slurry should be taken for indoor compression test to verify its strength index.

[0072] (2) The slurry should be used immediately after stirring and should be used up before initial setting. At the beginning of the grouting operation, circulate the grouting system with dilute cement slurry for 1-2 minutes to ensure smooth flow of slurry during grouting.

[0073] (3) After the slurry hardens, if it is found that the slurry does not fill the anchor hole, add grouting.

[0074] (4) After grouting of a batch of anchor holes is completed, the grouting pipe circulation system must be cleaned.

[0075] S34, install I-beams; The I-beam is a compression member that transfers the concentrated load of the anchor to the sprayed concrete surface. In addition, since the sprayed concrete surface of the hole is generally not perpendicular to the axis of the anchor cable, the I-beam also has the function of adjusting the force direction of the rock surface. In order to make the surface of the I-beam perpendicular to the axis of the anchor cable, a slanted iron pad is added under the channel steel in advance.

[0076] S35, prestressed anchor cable tensioning and locking anchor cable tensioning construction; Install dynamometer → install working anchor and clip → use small jack to tension and straighten steel-ammonium wires one by one → install limit plate → tension → lock → grouting and sealing holes for permanent rust prevention → cut off the extra-long steel-ammonium wire above the working anchor → pour the second phase concrete; The tensioning and prestressing of anchor cables shall comply with the following provisions: (1) Before prestressing the anchor cable, the tensioning equipment should be calibrated.

[0077] (2) Prestressed anchor cables should be tensioned 10 days after the construction of the anchor cables. Tensioning can be carried out when the slurry strength of the anchoring section reaches 80% of the design strength grade. The specific time is determined based on the test (7 days after the secondary grouting if no early strength agent is added).

[0078] (3) The order of tensioning anchor cables is to consider the impact on adjacent anchor rods: tension every other anchor cable.

[0079] (4) Before the anchor cable is formally tensioned, take 20% of the design tension load and pre-tension it 1-2 times to ensure that it is in close contact with the anchor and the steel strand is completely straight.

[0080] S36, sealing grouting and external protection; After compensating the tension, the hole is immediately sealed and grouting is performed. For the downward-inclined anchor cable, the grouting pipe is inserted from the reserved hole until the pipe mouth enters the top surface of the anchoring section by about 50 cm: for the upward-inclined and horizontal anchor cables, grouting is performed through the reserved grouting pipe. The air in the hole is discharged through the exhaust pipe located at the positioning stop ring; After sealing the hole and grouting, retain 50mm of the steel strand from the anchor, cut off the rest, and cover it with a cement mortar protective layer with a thickness of not less than 50mm.

[0081] In order to complete the construction task on time with quality and quantity guaranteed, we insisted on using scientific working methods at every stage from beginning to end, formulated a series of countermeasures and implementation methods, timely improved the anchor cable structure, actively improved the construction technology, adopted advanced network technology to organize construction, tried our best to achieve balanced production, ensured that the drilling, grouting, tensioning, anchor sealing and other processes would not delay each other and were carried out in parallel, and kept construction records in a unified form.

[0082] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The foundation pit support pile structure and support construction method are characterized by: The support system is composed of supporting piles and anchor rods, including supporting pile construction, cap beam construction and prestressed anchor cable construction; The construction of supporting piles includes the following steps: S11, measurement and positioning; S12, casing burial; S13, mud preparation; S14, drilling construction; S15, hole cleaning; S16, steel cage production and hoisting; S17, conduit installation; S18, concrete pouring; The crown beam construction includes the following steps; S21, excavation of crown beam; S22, removal of virtual pile heads; S23, production and installation of steel bars; S24, installation of formwork; S25, pouring of concrete; The construction of prestressed anchor cables includes the following steps: S31. Drilling construction; S32. Anchor cable production and placement; S33. Grouting; S34. Installation of I-beams; S35. Prestressed anchor cable tensioning and locking anchor cable tensioning construction; S36. Sealing hole grouting and external protection.

2. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: Support pile construction, wherein in step S12, the steel casing is made of 5mm thick steel plate, the inner diameter is 20-40cm larger than the pile diameter, the casing is 1.5m long, a 0.4m high and 0.2m wide slurry outlet is left at the top of the casing, and a blade foot is provided at the lower end of the bottom casing; When burying the steel casing, first place the pile position, draw a cross line through the center of the pile position, set a control pile 80-100cm outside the casing, and dig a circular pit at the pile position; when burying the steel casing, first place the pile position, and align the center of the steel casing with the pile position; Fill the bottom of the steel casing with clay about 30cm-50cm thick, compact it layer by layer, then install the casing and fill it with clay around it. The burial depth should not be less than 1.5m.

3. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S16, arc welding is used for welding the steel cage, with a double-sided overlap length of 5d and a single-sided welding length of 10d; the positioning reinforcement 10@2000mm is welded with the longitudinal reinforcement, the steel cage is processed in sections according to the total length, hoisted in batches, the hole is in place, and overlap welding is performed at the hole; The main reinforcement spacing of the steel cage is controlled within ±10mm, and the length is controlled within ±50mm; the stirrup spacing is ±20mm, the diameter is ±10mm, the steel cage installation depth is controlled within ±100mm, and the protective layer thickness is controlled within ±20mm.

4. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S17, the conduit is subjected to a watertightness test before installation; the specific method is as follows: a. Check whether there are obvious holes in each section of the catheter, and check the sealing ring of each section of the catheter; b. Select a site so that the conduits can be docked evenly on the ground; when docking, number each tube in sequence; c. Install closing devices at both ends of the conduit, using existing pressure test sleeves; install water inlet holes at both ends of the pressure test seal; when installing, make sure the two holes are located directly above the pipe so that air can overflow from the holes when water is injected; d. Install a water pipe to inject water into the conduit. Stop when water comes out from the other end of the pipe. Make sure the conduit is filled with more than 70% of water before stopping. e. Seal the water injection hole at one end and connect the other end to the air compressor. Check the installation of the closed end of the conduit connection. After the inspection is qualified, pressurize the air compressor to 0.6MPa and maintain the pressure for 15 minutes; check the water overflow at the conduit joint and make a record of the overflow. During the pressure test, roll the conduit 180°, pressurize it again, maintain the pressure for 15 minutes, and make a record of the inspection situation; f. Before installing the conduit, check the smoothness of its inner wall and record it by number; no flange is installed at the lower end of the last section, which is generally 4-6m long so that the concrete will not be moved when the pipe is pulled out, and then 2.5m pipe sections are installed in sequence; after considering that the bottom of the hole is suspended 30-50cm, calculate the height to the top surface of the chuck so that the length of the conduit can be adjusted with 1.5m pipe sections for the top few sections; the flange surface of the conduit interface must be flat, a rubber pad must be placed between the two flanges, and a layer of butter must be evenly applied on both sides of the pad to facilitate sealing; the conduit should be placed in the center of the hole; a storage hopper is connected to the upper end of the conduit, and the storage hopper is wetted with water before use, and the upper end of the jack rope for pulling the plug is tied to the top of the storage hopper; an operating bracket is set up next to the storage hopper, and a working platform is set up on it; the positional relationship between the upper hopper, storage hopper, concrete transport vehicle and crane is arranged to facilitate operation and free advance and retreat; the preparation work should be shortened as much as possible to reduce sedimentation at the bottom of the hole.

5. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S18, before pouring, the thickness of the sediment at the bottom of the hole is controlled, and if it does not meet the requirements, a second hole cleaning is performed, but the hole wall must be stabilized to prevent hole collapse.

6. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S21, the excavation of the crown beam is carried out by a small excavator. The excavation is carried out in sections. The length of each section is controlled according to the on-site geological conditions. The stability of the slope must be ensured during the excavation process. The remaining soil is removed by manual excavation, and the elevation is controlled at 500mm below the crown beam.

7. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S22, since the concrete at the top of the pile contains slurry during the pouring of concrete, the pile head within the height range of 500-600mm at the top of the supporting pile needs to be chiseled out. First, the pile head steel bars are stripped out. When stripping the steel bars from the concrete, the concrete is broken along the pile body to ensure that the stripped steel bars are straight and avoid the steel bars from being bent. When the pile head slurry and excess concrete are chiseled out with a pneumatic machine, at least 20-30cm is reserved for manual chiseling along the pile body horizontally with a drill or cutting along the pile body with a cutting machine. The drill cooperates with the chiseling to ensure that the pile top after chiseling is a complete plane. The chiseling is carried out with electric shovels, pneumatic guns, steel chisels, and drills. Before chiseling, an elevation line is placed on the outer supporting pile to control the elevation of the top of the supporting pile. The top surface of the chiseled supporting pile must be flat, and the local height difference should not exceed 20mm. After the chiseling of the top of the supporting pile is completed, it must be cleaned and washed with water; In step S23, the stressed steel bars are connected by binding lap joints. The binding lap joints arranged in the same component are staggered with each other. The staggered distance is 35d of the steel bar diameter and should not be less than 500mm. The cross-sectional area of ​​the stressed steel bars with joints in this section accounts for no more than 50% of the stressed surface area.

8. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S31, the drilling construction includes anchor hole positioning, drilling equipment preparation, anchor hole drilling construction by drilling rig, waterless dry drilling should be used for anchor hole drilling, the formation changes of each hole should be recorded during the drilling process, the actual drill bit diameter used for the hole diameter and hole depth should not be less than the designed hole diameter, anchor hole cleaning, and anchor hole inspection; In step S32, the steel strands are cut strictly according to the design size, and the length error of each strand is no more than 50 mm; the steel strands are arranged straight, and a wire ring is set every 1.5 m along the axis of the rod body at the anchoring section of the rod, and the grouting pipe should be firmly tied to the rod body; Before installation, ensure that each steel strand is straight, not twisted or forked, evenly arranged, and derusted and degreased. Remove any dead bends, mechanical damage, and rust pits. Apply butter to the free section of the steel strand and cover it with a Ø20PVC corrugated pipe for corrosion protection, ensuring that the thickness of the protective layer of the anchor cable is not less than 20mm.

9. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S35, the construction process of prestressed anchor cable tensioning and locking anchor cable tensioning is as follows: Install dynamometer → install working anchor and clip → use small jack to tension and straighten the steel-ammonium wires one by one → install limit plate → tension → lock → grouting and sealing holes for permanent rust prevention → cut off the extra long part of the steel-ammonium wire above the working anchor → pour the second phase concrete.

10. The foundation pit support pile structure and support construction method according to claim 1, characterized in that: In step S36, after compensating for tensioning, sealing grouting is immediately carried out; for downward-inclined anchor cables, the grouting pipe is inserted from the reserved hole until the pipe mouth enters the top surface of the anchoring section by about 50 cm; for upward-inclined and horizontal anchor cables, grouting is performed through the reserved grouting pipe; the air in the hole is discharged through the exhaust pipe provided at the positioning stop ring.

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