阅读说明：本技术 后注浆钻孔灌注桩施工方法 (Post-grouting cast-in-situ bored pile construction method ) 是由 郭俊义 杜锦强 李达疆 汪洋 连丽 于 2019-10-12 设计创作，主要内容包括：本发明公开了一种后注浆钻孔灌注桩施工方法,包括如下步骤：成孔：先测量桩位,再将钢护筒的中心对准桩孔中心垂直埋设,最后钻进成孔,钻孔达到达到设计深度后,用清孔钻头进行一次清孔；将制作好的钢筋笼制通过运笼车运到现场,并下方到位；下放导管后进行二次清孔,二次清孔半小时内对桩深进行浇筑混凝土,灌注接近桩顶时,及时用重锤或测杆测量桩顶标高；最后进行后注浆施工,后注浆施工应先向桩侧注浆,待浆液初凝后,再向桩底注浆。利用该工法施工,对邻近建筑物及周围环境的有害影响小,桩长和直径可按设计要求变化自如,桩端可进入持力层或嵌入岩层,单桩承载力大。(The invention discloses a post-grouting cast-in-situ bored pile construction method, which comprises the following steps: forming holes: firstly, measuring the pile position, then aligning the center of the steel casing to the center of a pile hole for vertical embedding, finally drilling to form a hole, and after the drilled hole reaches the designed depth, carrying out primary hole cleaning by using a hole cleaning drill bit; transporting the manufactured reinforcement cage to the site through a cage transporting vehicle, and placing the lower part of the reinforcement cage in place; placing the guide pipe, then carrying out secondary hole cleaning, pouring concrete for the depth of the pile within half an hour, and measuring the elevation of the pile top by using a heavy hammer or a measuring rod in time when the pile top is close to the pile top in pouring; and finally, performing post-grouting construction, wherein the post-grouting construction is to perform grouting to the pile side firstly and perform grouting to the pile bottom after the grout is initially set. The construction method has the advantages that the construction method has small harmful influence on adjacent buildings and surrounding environment, the length and the diameter of the pile can be freely changed according to design requirements, the pile end can enter a bearing layer or be embedded into a rock stratum, and the bearing capacity of a single pile is large.)

1. A post-grouting cast-in-situ bored pile construction method is characterized by comprising the following steps:

construction preparation:

1) selecting proper mechanical equipment such as a drilling machine, a drill bit, a protective arm sleeve and the like according to the physical characteristics of the soil layer of the construction land;

2) the concrete adopts compact sandstone materials, the cement adopted by post-grouting is PC32.5 ordinary portland cement, and the water cement ratio is 1: 2;

3) selecting reinforcing steel bars and welding rods, wherein the reinforcing steel bars are selected from phi-HPB 300, phi-HRB 335 and phi-HRB 400 grades; wherein: e43 type welding rods are adopted for the HPB300 steel bars, and E50 type welding rods are adopted for the HRB335 steel bars and the HRB400 steel bars;

the construction method comprises the following specific steps:

A. forming holes

1) Positioning: measuring and placing an axis by using a total station by adopting a wire guiding method to position a pile, drilling a hole on the measured pile position by using a steel bar, inserting a short steel bar as a mark, and curing the periphery by using concrete for 300 m;

2) manufacturing and sinking a protective cylinder: the welding seam is adopted, the inner diameter of the steel casing is 100mm larger than the pile diameter, the wall thickness is 4mm, and the height is 1.5 m; embedding the steel pile casing vertically, allowing the steel pile casing to enter undisturbed soil for 300mm, filling clay around the steel pile casing, and ensuring that the error between the center of the steel pile casing and the center of a pile hole is less than or equal to 20 mm;

3) preparing slurry: adopting high-plasticity clay or bentonite as the rotary-drilled slurry, and making slurry by using a stirrer;

4) positioning a drilling machine: the error of the drill bit aiming at the center of the pile is controlled within 50mm, the verticality of the drill rod is controlled within 0.3 percent, and the plane error and the verticality of the pile hole are ensured;

5) drilling to form a hole:

a. measuring the diameter of a drill bit, the total length of a drilling tool, the drilling hole depth and the exposed length of a drill rod;

b. during drilling, a vertical control instrument is observed to ensure the verticality of a drilled hole, the drilling is not interrupted and stopped without any reason during the hole forming, the drilling speed is paid attention to before the final hole to prevent hole collapse, the pile body is positioned below the underground water level, slurry is required to be used, the liquid level of the slurry in the hole is ensured to be not lower than the natural ground in the drilling process, for a soil layer of the hole easy to collapse, a low-speed footage is adopted, when the distance from the soil layer is 1 ~ 0.5.5 m, the footage speed is controlled to be 0.2 ~ 0.5.5 m/h, and the drilling in a decompression state is ensured;

c. cleaning the hole by using a hole cleaning drill after the hole is drilled to reach the preset depth;

b. Manufacturing, transporting and placing of reinforcement cage

1) Manufacturing a steel reinforcement cage:

a. main reinforcement: the main ribs are welded by flash welding;

b. and (3) processing the stiffening hoops and the reinforcement cage framework: winding the reinforcing steel bars into stiffening hoops with the inner diameter of a specified size by using a die, wherein the spacing of the stiffening hoops is 2m, the hooping parts are lapped and welded together by adopting a single surface, and the width of a welding seam is 0.7 d;

c. coiling and welding the centralizer: before winding, straightening the disc, winding the disc into a disc with the diameter corresponding to that of the reinforcement cage by using a mold, and winding the disc on the manufactured reinforcement cage framework according to requirements;

d. and (3) mounting a rear grouting pipe: the rear grouting pipe is a seamless steel pipe with the size of 1 inch, and is connected with the steel reinforcement cage by adopting a pipe hoop or a coupling;

B. and (3) transporting and placing the reinforcement cage:

the steel reinforcement cage is transported by a cage transporting vehicle, and cedar poles are bound in the steel reinforcement cage, so that the steel reinforcement cage is prevented from deforming in the transportation process; before the steel reinforcement cage is placed, the elevation of the steel tapping protecting cylinder is measured by a level gauge, and the length of a hanging rib or a pressing rod is calculated; when the steel reinforcement cage is placed, the steel reinforcement cage does not touch the wall of the hole and keeps vertical centering, and the cross arm of the hanging bar or the pressure lever is placed on the sleeper and cannot be pressed on the protective cylinder; calculating the ground elevation according to the same elevation, fixing the pressure rod on the orifice cross arm after the reinforcement cage is put down in place, and preventing the reinforcement cage from floating upwards or moving downwards during pouring;

C. down-placing guide pipe and secondary hole cleaning

a. Adopting phi 219 guide pipes which are connected by screw threads or flange plates and sealed by rubber rings or rubber plates; the guide pipe is placed in the middle of the lower inlet hole, and the cleaned screw thread is fastened when the guide pipe is connected;

b. after the guide pipe is placed into the hole, secondary hole cleaning is carried out, and the slurry performance is kept during hole cleaning; removing sediments at the bottom of the hole, and simultaneously avoiding reducing the silty clay; the density of the mud returned by secondary hole cleaning is less than or equal to 1.15, and the sediment at the bottom of the hole is less than or equal to 100 mm;

D. pouring of concrete

a. During primary concrete pouring, the lower end of the guide pipe is 0.3 ~ 0.5.5 m away from the bottom of the hole, a waterproof bolt is added before pouring, the depth of the bottom of the guide pipe embedded in the concrete after primary pouring is ensured to be 2m ~ 5m, the slump of the primary poured concrete is 140-160 mm, and the slump of the concrete is 160-220 mm at other times;

b. during pouring, the concrete in the pipe is observed to descend and the water return condition of the orifice is observed, the ascending height of the concrete surface in the hole is measured in time, and the upper guide pipe is lifted and dismantled in sections in time; the guide pipe is embedded in the concrete, and the depth of the guide pipe is 2-6 m; when the pile top is poured, measuring the elevation of the pile top, wherein the elevation of the pile top of the poured pile is more than or equal to 0.8m, and slowly moving the guide pipe up and down after the concrete surface reaches the elevation of the over-poured length to slowly close the opening of the concrete surface;

E. post grouting construction

1) And (3) processing and mounting a rear grouting pipe:

a. the bottom grouting pipe is a 1 'seamless steel pipe, the bottom nozzle is processed into a ring shape by a plastic pipe with the pipe diameter of 1.2', and the nozzle is arranged at the bottom; the grouting pipe and the reinforcement cage are fixed by welding or binding; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

b. the annular pipe of the side grouting pipe nozzle is a plastic pipe with the pipe diameter of 1.2 ″, the annular pipe is arranged 15.0m away from the pile end, the flexible nozzle pipe is connected with the grouting pipe through a tee joint, and the grouting pipe is fixedly connected with the reinforcement cage in a welding or binding mode; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

2) grouting: the grouting sequence adopts slow grouting, firstly grouting to the pile side, and then grouting to the pile bottom after the grout is initially set, wherein the time interval between the grouting to the pile side and the grouting to the pile bottom is not less than 2 hours; and (4) when the grouting amount reaches 4/5 of a design value, the grouting pressure exceeds 3-4 MPa, and the grouting can be stopped after the grouting amount is stabilized for 3-10 minutes.

2. The method for constructing a post-grouting bored pile according to claim 1, wherein: after drilling to form a hole, the drill bit is lifted out, the slurry with higher density is replaced by the slurry with lower relative density by a slurry replacement method, and the original water head height in the hole is kept during hole cleaning.

One, the technical field

The invention relates to a construction method of a pile foundation, in particular to a post-grouting bored pile construction method, and belongs to the technical field of building construction.

Secondly, background art:

in pile foundation construction, a method of grouting after filling a pile is often adopted to improve the bearing capacity and the uplift resistance of the pile, and for main buildings (structures) of a power plant, a natural foundation cannot meet the requirements of strength and deformation, and an artificial foundation is needed; the foundation of the main power plant of the general power plant is buried between-5.00 m and-7.50 m, the main bearing layer of the foundation is a layer I and a layer II, and the part of the foundation is a layer II or a layer III, when the site is met and is distributed with hard silty clay with larger thickness and contains a large amount of calcium nodules, the concrete precast pile is difficult to penetrate through the hard silty clay layer.

Thirdly, the invention content:

the technical problem to be solved by the invention is as follows: the defects of the prior art are overcome, the construction method of the post-grouting bored pile is provided, the problem that the concrete precast pile is difficult to penetrate through a hard powdery clay layer is solved, and the effect of strong bearing capacity is achieved.

The technical scheme adopted by the invention for solving the technical problem is as follows:

the invention relates to a post-grouting cast-in-situ bored pile construction method, which comprises the following steps:

construction preparation:

1) selecting proper mechanical equipment such as a drilling machine, a drill bit, a protective arm sleeve and the like according to the physical characteristics of the soil layer of the construction land;

2) the concrete adopts compact sandstone materials, the cement adopted by post-grouting is PC32.5 ordinary portland cement, and the water cement ratio is 1: 2;

3) selecting reinforcing steel bars and welding rods, wherein the reinforcing steel bars are selected from phi-HPB 300, phi-HRB 335 and phi-HRB 400 grades; wherein: e43 type welding rods are adopted for the HPB300 steel bars, and E50 type welding rods are adopted for the HRB335 steel bars and the HRB400 steel bars;

the construction method comprises the following specific steps:

A. forming holes

1) Positioning and lofting: measuring and placing an axis by using a total station by adopting a wire guiding method to position a pile, drilling a hole on the measured pile position by using a steel bar, inserting a short steel bar as a mark, and curing the periphery by using concrete for 300 m;

2) manufacturing and sinking a protective cylinder: the welding seam is adopted, the inner diameter of the steel casing is 100mm larger than the pile diameter, the wall thickness is 4mm, and the height is 1.5 m; embedding the steel pile casing vertically, allowing the steel pile casing to enter undisturbed soil for 300mm, filling clay around the steel pile casing, and ensuring that the error between the center of the steel pile casing and the center of a pile hole is less than or equal to 20 mm;

3) preparing slurry: adopting high-plasticity clay or bentonite as the rotary-drilled slurry, and making slurry by using a stirrer;

4) positioning a drilling machine: the error of the drill bit aiming at the center of the pile is controlled within 50mm, the verticality of the drill rod is controlled within 0.3 percent, and the plane error and the verticality of the pile hole are ensured;

5) drilling to form a hole:

a. measuring the diameter of a drill bit, the total length of a drilling tool, the drilling hole depth and the exposed length of a drill rod;

b. during drilling, a vertical control instrument is observed to ensure the verticality of a drilled hole, the drilling is not interrupted and stopped without any reason during the hole forming, the drilling speed is paid attention to before the final hole to prevent hole collapse, the pile body is positioned below the underground water level, slurry is required to be used, the liquid level of the slurry in the hole is ensured to be not lower than the natural ground in the drilling process, for a soil layer of the hole easy to collapse, a low-speed footage is adopted, when the distance from the soil layer is 1 ~ 0.5.5 m, the footage speed is controlled to be 0.2 ~ 0.5.5 m/h, and the drilling in a decompression state is ensured;

c. cleaning the hole by using a hole cleaning drill after the hole is drilled to reach the preset depth;

b. Manufacturing, transporting and placing of reinforcement cage

1) Manufacturing a steel reinforcement cage:

a. main reinforcement: the main ribs are welded by flash welding;

b. and (3) processing the stiffening hoops and the reinforcement cage framework: winding the reinforcing steel bars into stiffening hoops with the inner diameter of a specified size by using a die, wherein the spacing of the stiffening hoops is 2m, the hooping parts are lapped and welded together by adopting a single surface, and the width of a welding seam is 0.7 d;

c. coiling and welding the centralizer: before winding, straightening the disc, winding the disc into a disc with the diameter corresponding to that of the reinforcement cage by using a mold, and winding the disc on the manufactured reinforcement cage framework according to requirements;

d. and (3) mounting a rear grouting pipe: the rear grouting pipe is a seamless steel pipe with the size of 1 inch, and is connected with the steel reinforcement cage by adopting a pipe hoop or a coupling;

2) and (3) transporting and placing the reinforcement cage:

the steel reinforcement cage is transported by a cage transporting vehicle, and cedar poles are bound in the steel reinforcement cage, so that the steel reinforcement cage is prevented from deforming in the transportation process; before the steel reinforcement cage is placed, the elevation of the steel tapping protecting cylinder is measured by a level gauge, and the length of a hanging rib or a pressing rod is calculated; when the steel reinforcement cage is placed, the steel reinforcement cage does not touch the wall of the hole and keeps vertical centering, and the cross arm of the hanging bar or the pressure lever is placed on the sleeper and cannot be pressed on the protective cylinder; calculating the ground elevation according to the same elevation, fixing the pressure rod on the orifice cross arm after the reinforcement cage is put down in place, and preventing the reinforcement cage from floating upwards or moving downwards during pouring;

C. down-placing guide pipe and secondary hole cleaning

a. Adopting phi 219 guide pipes which are connected by screw threads or flange plates and sealed by rubber rings or rubber plates; the guide pipe is placed in the middle of the lower inlet hole, and the cleaned screw thread is fastened when the guide pipe is connected;

b. after the guide pipe is placed into the hole, secondary hole cleaning is carried out, and the slurry performance is kept during hole cleaning; removing sediments at the bottom of the hole, and simultaneously avoiding reducing the silty clay; the density of the mud returned by secondary hole cleaning is less than or equal to 1.15, and the sediment at the bottom of the hole is less than or equal to 100 mm;

D. pouring of concrete

a. During primary concrete pouring, the lower end of the guide pipe is 0.3 ~ 0.5.5 m away from the bottom of the hole, a waterproof bolt is added before pouring, the depth of the bottom of the guide pipe embedded in the concrete after primary pouring is ensured to be 2m ~ 5m, the slump of the primary poured concrete is 140-160 mm of soil, and the slump of the concrete is 160-220 mm in other times;

b. during pouring, the concrete in the pipe is observed to descend and the water return condition of the orifice is observed, the ascending height of the concrete surface in the hole is measured in time, and the upper guide pipe is lifted and dismantled in sections in time; the guide pipe is embedded in the concrete, and the depth of the guide pipe is 2-6 m; when the pile top is poured, measuring the elevation of the pile top, wherein the elevation of the pile top of the poured pile is more than or equal to 0.8m, and slowly moving the guide pipe up and down after the concrete surface reaches the elevation of the over-poured length to slowly close the opening of the concrete surface;

E. post grouting construction

1) And (3) processing and mounting a rear grouting pipe:

a. the bottom grouting pipe is a 1 'seamless steel pipe, the bottom nozzle is processed into a ring shape by a plastic pipe with the pipe diameter of 1.2', and the nozzle is arranged at the bottom; the grouting pipe and the reinforcement cage are fixed by welding or binding; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

b. the annular pipe of the side grouting pipe nozzle is a plastic pipe with the pipe diameter of 1.2 ″, the annular pipe is arranged 15.0m away from the pile end, the flexible nozzle pipe is connected with the grouting pipe through a tee joint, and the grouting pipe is fixedly connected with the reinforcement cage in a welding or binding mode; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

2) grouting: the grouting sequence adopts slow grouting, firstly grouting to the pile side, and then grouting to the pile bottom after the grout is initially set, wherein the time interval between the grouting to the pile side and the grouting to the pile bottom is not less than 2 hours; and (4) when the grouting amount reaches 4/5 of a design value, the grouting pressure exceeds 3-4 MPa, and the grouting can be stopped after the grouting amount is stabilized for 3-10 minutes.

The construction method of the post-grouting bored pile comprises the steps of after drilling to form a hole, lifting a drill bit, replacing mud with higher density by mud with lower relative density by a mud replacement method, and keeping the original water head height in the hole during hole cleaning.

The technology of the invention has the following beneficial effects:

1. the slurry dug by the rotary drilling method is stirred and prepared by adopting high-plasticity clay or bentonite, the slurry parameters are strictly controlled in the drilling process, the collapse and the hole shrinkage of the hole wall are avoided, and the filling quality of the pile is ensured; in the drilling process, a driller can pay attention to the perpendicularity of the vertical control instrument at any time, and pay attention to the drilling speed before final hole drilling, so that the hole collapse condition is prevented.

2. The pile body of the invention is below the underground water level, the mud must be used, and the mud is supplemented into the hole in the drilling process, so that the liquid level of the mud in the hole is ensured not to be lower than the natural ground. The sediment in the mud ditch and the tank is cleaned frequently, the mud ditch and the tank are kept smooth, and the mud quality is ensured.

3. The centralizer is arranged on the reinforcement cage, so that the thickness of a protective layer can be ensured, and the hole wall is prevented from being damaged in the process of descending the reinforcement cage; in the transportation process of the reinforcement cage, fir poles are tied in the reinforcement cage, so that the reinforcement cage is prevented from being extruded and deformed in the transportation process; when the reinforcement cage is lowered to the place, the pressure lever is fixed on the orifice cross arm to prevent the reinforcement cage from floating upwards or moving downwards during pouring.

4. After the concrete surface of the invention reaches the elevation of the over-grouting length, the guide pipe should be moved up and down slowly without pulling out the pipe quickly, so that the concrete surface opening is closed slowly, and the quality defects of slurry mixing, formation of a concrete core or water seepage of a pile head and the like caused by the fact that the pipe is pulled out too quickly are prevented.

5. By utilizing the construction method for construction, the harmful influence on adjacent buildings and the surrounding environment is small, the length and the diameter of the pile can be freely changed according to the design requirement, and the pile end can enter a bearing stratum or be embedded into a rock stratum; the single pile has large bearing capacity.

Fourthly, the specific implementation mode:

the post-grouting cast-in-situ bored pile construction method comprises the following steps:

a post-grouting cast-in-situ bored pile construction method is characterized by comprising the following steps:

construction preparation:

1) selecting proper mechanical equipment such as a drilling machine, a drill bit, a protective arm sleeve and the like according to the physical characteristics of the soil layer of the construction land;

2) the concrete adopts compact sandstone materials, the cement adopted by post-grouting is PC32.5 ordinary portland cement, and the water cement ratio is 1: 2;

3) selecting reinforcing steel bars and welding rods, wherein the reinforcing steel bars are selected from phi-HPB 300, phi-HRB 335 and phi-HRB 400 grades; wherein: e43 type welding rods are adopted for the HPB300 steel bars, and E50 type welding rods are adopted for the HRB335 steel bars and the HRB400 steel bars;

the construction method comprises the following specific steps:

A. forming holes

1) Positioning and lofting: measuring and placing an axis by using a total station by adopting a wire guiding method to position a pile, drilling a hole on the measured pile position by using a steel bar, inserting a short steel bar as a mark, and curing the periphery by using concrete for 300 m;

2) manufacturing and sinking a protective cylinder: the welding seam is adopted, the inner diameter of the steel casing is 100mm larger than the pile diameter, the wall thickness is 4mm, and the height is 1.5 m; embedding the steel pile casing vertically, allowing the steel pile casing to enter undisturbed soil for 300mm, filling clay around the steel pile casing, and ensuring that the error between the center of the steel pile casing and the center of a pile hole is less than or equal to 20 mm;

3) preparing slurry: adopting high-plasticity clay or bentonite as the rotary-drilled slurry, and making slurry by using a stirrer;

4) positioning a drilling machine: the error of the drill bit aiming at the center of the pile is controlled within 50mm, the verticality of the drill rod is controlled within 0.3 percent, and the plane error and the verticality of the pile hole are ensured;

5) drilling to form a hole:

a. measuring the diameter of a drill bit, the total length of a drilling tool, the drilling hole depth and the exposed length of a drill rod;

b. during drilling, a vertical control instrument is observed to ensure the verticality of a drilled hole, the drilling is not interrupted and stopped without any reason during the hole forming, the drilling speed is paid attention to before the final hole to prevent hole collapse, the pile body is positioned below the underground water level, slurry is required to be used, the liquid level of the slurry in the hole is ensured to be not lower than the natural ground in the drilling process, for a soil layer of the hole easy to collapse, a low-speed footage is adopted, when the distance from the soil layer is 1 ~ 0.5.5 m, the footage speed is controlled to be 0.2 ~ 0.5.5 m/h, and the drilling in a decompression state is ensured;

c. cleaning the hole by using a hole cleaning drill after the hole is drilled to reach the preset depth;

b. Manufacturing, transporting and placing of reinforcement cage

1) Manufacturing a steel reinforcement cage:

a. main reinforcement: the main ribs are welded by flash welding;

b. and (3) processing the stiffening hoops and the reinforcement cage framework: winding the reinforcing steel bars into stiffening hoops with the inner diameter of a specified size by using a die, wherein the spacing of the stiffening hoops is 2m, the hooping parts are lapped and welded together by adopting a single surface, and the width of a welding seam is 0.7 d;

c. coiling and welding the centralizer: before winding, straightening the disc, winding the disc into a disc with the diameter corresponding to that of the reinforcement cage by using a mold, and winding the disc on the manufactured reinforcement cage framework according to requirements;

d. and (3) mounting a rear grouting pipe: the rear grouting pipe is a seamless steel pipe with the size of 1 inch, and is connected with the steel reinforcement cage by adopting a pipe hoop or a coupling;

B. and (3) transporting and placing the reinforcement cage:

the steel reinforcement cage is transported by a cage transporting vehicle, and cedar poles are bound in the steel reinforcement cage, so that the steel reinforcement cage is prevented from deforming in the transportation process; before the steel reinforcement cage is placed, the elevation of the steel tapping protecting cylinder is measured by a level gauge, and the length of a hanging rib or a pressing rod is calculated; when the steel reinforcement cage is placed, the steel reinforcement cage does not touch the wall of the hole and keeps vertical centering, and the cross arm of the hanging bar or the pressure lever is placed on the sleeper and cannot be pressed on the protective cylinder; calculating the ground elevation according to the same elevation, fixing the pressure rod on the orifice cross arm after the reinforcement cage is put down in place, and preventing the reinforcement cage from floating upwards or moving downwards during pouring;

C. down-placing guide pipe and secondary hole cleaning

a. Adopting phi 219 guide pipes which are connected by screw threads or flange plates and sealed by rubber rings or rubber plates; the guide pipe is placed in the middle of the lower inlet hole, and the cleaned screw thread is fastened when the guide pipe is connected;

b. after the guide pipe is placed into the hole, secondary hole cleaning is carried out, and the slurry performance is kept during hole cleaning; removing sediments at the bottom of the hole, and simultaneously avoiding reducing the silty clay; the density of the mud returned by secondary hole cleaning is less than or equal to 1.15, and the sediment at the bottom of the hole is less than or equal to 100 mm;

D. pouring of concrete

a. During primary concrete pouring, the lower end of the guide pipe is 0.3 ~ 0.5.5 m away from the bottom of the hole, a waterproof bolt is added before pouring, the depth of the bottom of the guide pipe embedded in the concrete after primary pouring is ensured to be 2m ~ 5m, the slump of the primary poured concrete is 140-160 mm, and the slump of the concrete is 160-220 mm at other times;

b. during pouring, the concrete in the pipe is observed to descend and the water return condition of the orifice is observed, the ascending height of the concrete surface in the hole is measured in time, and the upper guide pipe is lifted and dismantled in sections in time; the guide pipe is embedded in the concrete, and the depth of the guide pipe is 2-6 m; when the pile top is poured, measuring the elevation of the pile top, wherein the elevation of the pile top of the poured pile is more than or equal to 0.8m, and slowly moving the guide pipe up and down after the concrete surface reaches the elevation of the over-poured length to slowly close the opening of the concrete surface;

E. post grouting construction

1) And (3) processing and mounting a rear grouting pipe:

a. the bottom grouting pipe is a 1 'seamless steel pipe, the bottom nozzle is processed into a ring shape by a plastic pipe with the pipe diameter of 1.2', and the nozzle is arranged at the bottom; the grouting pipe and the reinforcement cage are fixed by welding or binding; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

b. the annular pipe of the side grouting pipe nozzle is a plastic pipe with the pipe diameter of 1.2 ″, the annular pipe is arranged 15.0m away from the pile end, the flexible nozzle pipe is connected with the grouting pipe through a tee joint, and the grouting pipe is fixedly connected with the reinforcement cage in a welding or binding mode; the upper part of the grouting pipe is 0.3m higher than the ground, and the pipe orifice is sealed by a protective cap;

2) grouting: the grouting sequence adopts slow grouting, firstly grouting to the pile side, and then grouting to the pile bottom after the grout is initially set, wherein the time interval between the grouting to the pile side and the grouting to the pile bottom is not less than 2 hours; the grouting amount reaches 4/5 of a design value, the grouting pressure exceeds 3-4 MPa, and the grouting can be stopped after the grouting is stabilized for 3-10 minutes;

after drilling and forming holes, a drill bit is put out, the slurry with higher density is replaced by the slurry with lower relative density by a slurry replacement method, and the original water head height in the holes is kept during hole cleaning;

in the actual construction, also pay attention to:

1. the slurry is changed step by step during hole cleaning, the slurry change gradient is determined according to the geological conditions of the hole wall, and a large amount of clear water cannot be directly injected into the slurry, so that the drilling slag can rapidly sink to the bottom, and hole collapse can be caused to thicken the sediment at the bottom of the hole; the concrete pouring is to be continuously constructed, the speed is properly slowed down at the initial stage of the concrete pouring, and the speed can be properly accelerated later, so that the initial setting time of the first batch of concrete is not exceeded during the final pouring. If the concrete amount is large, the construction temperature is high, and the initial setting time of the concrete is short, a certain amount of retarder can be properly added, but the adding amount of the retarder needs to be determined through strict tests.

2. For a soil layer with easy hole collapse, when the distance between the soil layer and the soil layer is 1-0.5 m, controlling the footage speed to be 0.5m/h, ensuring drilling in a decompression state, observing the change condition of the position of slurry in the casing, and immediately supplementing slurry if slurry leakage occurs, and ensuring the water head pressure difference of the slurry; entering an easily collapsed layer, stopping drilling for 4-8 hours regardless of the slurry leakage phenomenon, and circulating the slurry continuously during the drilling stopping period to ensure that the slurry fully seeps into the well wall and fully protects the wall, thereby avoiding slurry leakage and hole collapse; and (4) adopting low-speed footage on the easily collapsed layer, controlling the speed to be 0.2-0.5 m/h, and ensuring the drilling in a decompression state. The footage is too fast, the mud wall protection time is insufficient, and the mud leakage and hole collapse are easily caused; and controlling the index of the used mud according to different stratums. When backfilling, soft layer and sand layer are drilled, the speed is strictly controlled. When the underground water level is too high, the protective cylinder should be lifted, and the water head is increased. When underground obstacles are treated, residual stones and concrete blocks must be thoroughly removed; when the hole wall is seriously collapsed, the collapse position is required to be detected, sand and clay are mixed and backfilled to the position 1-2 m above the collapse hole section, and the hole is drilled again after tamping.

3. The drill bit with the diameter protection device is selected, the diameter of the drill bit meets the requirement of the diameter of a formed hole, the drill bit is required to be frequently checked and timely repaired, the viscosity of slurry can be properly improved when the hole section easy to reduce is drilled, and the hole diameter can be enlarged by adopting a method of repeatedly sweeping the hole up and down on the part easy to reduce.

4. When the hole is formed, the density of the slurry and the sediment at the bottom of the hole are strictly controlled, and the mud blocks must be thoroughly removed when the hole is cleaned for the first time. The lifting of the guide pipe needs to be slow in the concrete pouring process, particularly when the guide pipe reaches the pile top, the guide pipe is strictly forbidden to be lifted greatly, the buried depth of the guide pipe is strictly controlled, and the material is strictly forbidden to be broken midway when single pile concrete is poured; when the guide pipe is pulled out, the buried depth of the concrete after the guide pipe is pulled out must be accurately calculated and controlled, and the pipe is strictly pulled out by experience.