CFG pile foundation construction method

Abstract

The CFG pile foundation construction method comprises the following steps that S1, construction preparation is conducted, the pile position of a CFG pile is measured and lofted, a drilling machine is placed on one side of the pile position, and the perpendicularity, the size of a drill bit and the position of a drill tip are checked; s2, a drilling machine drills and forms a hole to the designed elevation, after the hole is drilled to the designed elevation, drilling is stopped, concrete is poured into a pile hole in a pressing mode, a drilling tool is lifted at the same time till the concrete reaches the designed pile top elevation, after pouring and pile forming are completed, the pile top is sealed with wet clay, the drilling machine is moved, and CFG piles are constructed one by one according to the set sequence; s3, concrete of the CFG piles is cured, soil between the piles is cleaned, and concrete pile heads are chiseled; and S4, the CFG piles are detected, and a mattress layer is laid. According to the method, the prevention measures are mainly used for preventing broken piles, each operation link needs to be carefully checked before pouring, the effective prevention measures are designated, the pouring operation is continuous and compact, the lifting speed is controlled to reduce the pile breaking rate, and the pile breaking rate is reduced by 60% or above compared with the pile breaking rate implemented in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of foundation construction, and particularly relates to a construction method for CFG pile foundation. Background Art

[0002] During the construction process of foundation treatment, according to the requirements of the foundation bearing capacity of each functional area and different settlement control standards, the foundation treatment is divided into different areas, and then a suitable foundation treatment method for this area is selected, such as CFG pile composite foundation treatment. CFG pile is a kind of low-strength concrete pile, which can make full use of the bearing capacity of the soil between piles to act together, and can transfer the load to the deep foundation.

[0003] In the related technology, after the soil between piles is excavated and removed, when cutting the pile head, usually the pile head is cut horizontally by manually pushing a pile cutter. After cutting, three steel nails are inserted at the same horizontal plane at the cutting seam of the pile head, and the pile head is cut off by hitting with tools such as hammers, and then the pile top is manually leveled to realize the cutting of the pile head.

[0004] Reasons for pile breakage: A. During the construction process of the pile foundation, local mud is mixed, forming local pile body defects, which are shown as broken piles in the detection; B. During the excavation of the soil between piles, the pile body is accidentally touched by the machine during operation, resulting in pile breakage. There are two types of fracture parts of such broken piles, above and below the design elevation.

[0005] C. During the pile cutting process, excessive force causes local damage to the pile head. Content of the Invention In view of this, the present invention aims to propose a construction method for CFG pile foundation to solve at least one technical problem in the background art.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows: A construction method for CFG pile foundation includes the following steps: S1: Carry out construction preparation, measure and set out the pile positions of CFG piles, place the drill on one side of the pile position, and check the verticality, drill bit size and drill tip position; S2: The drill is drilled to the design elevation. After the drilling reaches the design elevation, stop drilling, while pumping concrete into the pile hole and lifting the drill tool until the concrete reaches the design pile top elevation. After the pouring of the pile is completed, the pile top is sealed with wet clay, and the drill is shifted, and the CFG piles are constructed one by one according to the set order; S3: Cure the concrete of the CFG piles, clean the soil between piles and chisel the concrete pile head; S4: Detect the CFG piles and lay the cushion layer.

[0007] Furthermore, remove the surface vegetation and dig out the extremely loose topsoil for planting. According to the comparison result between the measured original ground elevation and the designed pile top elevation, when leveling the drilling site, the original ground elevation is 50 cm higher than the pile top of the designed pile. And / or, measuring and lofting the pile positions of the CFG piles includes measuring and lofting the positions of the CFG piles according to the CFG pile position layout diagram, and drawing grid lines with lime. And / or, preliminarily level the original ground where the CFG pile foundation is located. Place the drilling rig along the east-west direction and align it with the center of a row of piles. During construction, skip-pile construction is carried out from the southeast corner side. After the drilling rig is in place, check whether the drilling rig is operating normally.

[0008] Furthermore, the inspection of the verticality, bit size, and drill tip position in step S1 includes moving the drilling rig to align with the hole position, and the hole position deviation shall not be greater than 50 mm. The verticality error of the main shaft of the drilling rig shall not be greater than 1%. Precisely measure the length of the drill tool and make significant marks to determine the drilling depth. Check the diameter of the drill pipe, and its diameter error < 20 mm. Otherwise, immediately replace the drill pipe.

[0009] Furthermore, in step S2, start pumping concrete with a ground pump. When the drill pipe is filled with the mixture, start pulling out the pipe. It is strictly prohibited to pull out the pipe first and then pump the material. The pulling speed of the formed pile is controlled at 1 - 2 m / min, and the pile forming process is continuous. It should be avoided to stop waiting for materials due to slow feeding. After the pouring and pile forming are completed, the pile top is sealed with wet clay for protection. The feeding volume of each pile during construction shall not be less than the designed pouring volume. And / or, the concrete strength grade is C25 or C20, the concrete slump is 180 - 220 mm, and a 500 mm concrete pile head is reserved when the cast-in-place pile is formed. And / or, polycarboxylic acid powder water reducer and fly ash are added to the concrete. And / or, the slump of the concrete shall be controlled at 180 - 220 mm. When it is confirmed that drilling reaches the bottom of the hole, it should rotate in place for 1 - 2 minutes, lift the drill pipe by 20 cm, and then start the concrete delivery pump to pump the concrete under pressure. Wait until the mixture is pumped into the drill pipe and the material returns from the exhaust hole, and then lift the drill tool. The lifting speed must be coordinated with the pump volume to ensure that the drill tip is always buried in the mixture and keep the pump operation and drill lifting coordinated.

[0010] Furthermore, the curing of the concrete of the CFG piles in step S3 includes: 3 to 7 days after the pile is formed, the pile excavation and the cleaning of the soil between piles can be carried out. Use a cutting device to cut around the concrete pile head; the cutting depth is 10 cm to 15 cm, then move the cutting device away, and then the operator uses a chisel to strike around the pile at the same time until the pile head breaks. Finally, manually chisel the uneven pile head. The elevation control requirement of the pile head is to enter the cushion layer by ±50 mm; The elevation of the cushion layer laying should be controlled by a level, and the ramming degree should not be greater than 0.9; Before laying the cushion layer, manually clean the composite foundation to the design elevation, and check the foundation trench to ensure that there is no disturbance in the foundation soil. The cushion layer uses crushed stone with a particle size of 10 mm - 20 mm. The laying thickness of the cushion layer should be uniform, and the allowable deviation of the thickness is ±10 mm. The laying range of the cushion layer is 200 mm outward from the outer edge of the foundation cushion treatment; The cushion layer is rammed by a frog rammer, keeping the drop height at 400 - 500 mm, and the ramming times are not less than 3 times.

[0011] Furthermore, the cutting device includes a base, a first support plate, a first connecting rod, a workbench, a cutting assembly, and a first cylinder; The first support plate is arranged on the base through a first connecting block. A first connecting rod is vertically arranged on one side of the first support plate, and a first cylinder is installed at the end of the first connecting rod; The output end of the first cylinder is connected to the workbench, and several cutting assemblies are arranged along the circumference under the workbench.

[0012] Furthermore, a first guide rod is arranged on the first connecting block, a first guide block is arranged on the output end of the first cylinder, and the first guide block is slidably connected to the first guide rod through a second connecting rod; And / or, the cutting assembly includes a second support plate and a second cylinder. The upper end of the second support plate is fixedly arranged at the bottom of the workbench. The installation end of the second cylinder is arranged on one side of the second support plate, and the output end of the second cylinder is connected to the installation end of the output motor; The output end of the output motor is connected to the annular saw blade; And / or, a second guide rod is arranged inside the second support plate, a second guide block is arranged on the output end of the second cylinder, and the second guide block is slidably connected to the second guide rod through a third connecting rod.

[0013] Furthermore, the base is an annular base, and several uniformly arranged support legs are provided along the circumference at the bottom of the base. Lockable universal wheels are provided at the bottom of the support legs.

[0014] Furthermore, the detection of the CFG pile in step S4 includes the detection of the pile body integrity. The pile body integrity of the CFG pile is detected by the low-strain dynamic test. The pile body integrity is judged according to the detection results, and the detection quantity is 20% of the total number of piles; The number of inspections of composite foundation bearing capacity in composite foundation static load test and single pile static load test shall not be less than 1% of the total number of piles and shall not be less than 3 points; Furthermore, it also includes the treatment of broken piles. According to the pile foundation test results, shallow broken piles with a height of less than or equal to 100mm are directly laid with a cushion layer, and those with a height greater than 100mm are connected according to the design requirements. The broken pile treatment includes the following steps: A1: Find the broken pile, clean up the surrounding soil, and continue to cut the pile to the designed elevation if the broken part is above the base. If the broken part is below the base, manually expand the pile body by 100mm on each side, and the depth is 100mm deeper than the broken part. A2: Cut off the pile head above the fractured part and hoist it out of the foundation pit to check the condition of the fractured part to see if the surface is flat and intact. A3: Clean and level the broken parts, and use a wire brush to clean the soil around the pile body; A4: Bend the iron sheet into a cylinder with a diameter 200mm larger than the pile diameter, put it on the pile head on the fracture surface, and connect it to the designed pile top elevation with concrete one grade higher than the pile body concrete. Pay attention to protecting the soil between the piles during the process of connecting the pile heads; S4: After pouring is completed, when the concrete has finally set and reached a strength of more than 1.2MPa, remove the iron sheet wrapped around the newly poured pile head, and backfill the surrounding gaps in a timely and relatively even manner, and compact them layer by layer.

[0015] In this application, the preventive measures for broken piles should be mainly preventive. Before pouring, each operation link should be carefully checked and effective preventive measures should be specified. During pouring, strictly abide by the operating procedures to ensure that the pouring operation is continuous and compact. After the hole is drilled to the designed depth, concrete should be pumped first and then the drill should be lifted. It is strictly forbidden to lift the drill first and then pump. During construction, the drill rod should be lifted at a uniform speed, and the lifting speed should not exceed 1.2-1.5m / minute. If the broken pile is shallow, the pile head above the broken pile can be manually dug out, and the soil and loose concrete particles on the surface of the pile head can be cleaned. Use graded gravel to backfill to the designed pile top elevation. The graded gravel particle size, proportion and construction quality requirements are the same as the cushion layer of this project, that is, the cushion layer is partially thickened. If the broken pile is deep, the foundation pit is manually excavated to 100mm below the fracture surface, the broken pile is removed, and the fracture surface is leveled and cleaned. Use concrete with a grade higher than the designed pile body concrete to cast the pile, and vibrate and compact it. The concrete is poured to the designed pile top elevation.

[0016] Compared with the prior art, the CFG pile foundation construction method created by the present invention has the following advantages: 1. The preventive measures in this application should focus on prevention of broken piles. Each operation link should be carefully checked before pouring, and effective preventive measures should be specified. The pouring operation is continuous and compact, and the lifting speed is controlled to reduce the broken pile rate. The broken pile rate is reduced by more than 60% compared with the broken pile rate implemented in the prior art.

[0017] During the construction of this application, when encountering a silt stratum, the lifting speed of the drill pipe and the pumping speed of the pumped concrete should be appropriately slowed down. When necessary, the drill pipe can be paused for 2 - 3 seconds every 2 meters during the pumping process and then the drill pipe can be lifted, which can reduce the diameter reduction.

[0018] This application is equipped with a cutting device, which avoids manual cutting by operators in the prior art, increases the safety of the device, and the cutting device is equipped with universal wheels, which can facilitate the movement of the cutting device. Moreover, this application uses a cutting assembly for cutting, and the cutting is performed in a circular shape, with high cutting efficiency. Description of the Drawings

[0019] The drawings constituting a part of this invention are used to provide a further understanding of this invention. The schematic embodiments of this invention and their descriptions are used to explain this invention and do not constitute an improper limitation to this invention. In the drawings: Figure 1 It is a schematic flow chart of the CFG pile foundation construction method described in the embodiment of this invention; Figure 2 It is a schematic diagram of pile splicing described in the embodiment of this invention; Figure 3 It is a schematic diagram of the cutting device described in the embodiment of this invention; Figure 4 It is a schematic diagram of the cutting assembly described in the embodiment of this invention.

[0020] Description of the reference numerals in the drawings: 1. Base; 2. First support plate; 3. First connecting rod; 4. Workbench; 5. Cutting assembly; 501. Second support plate; 502. Second cylinder; 503. Circular saw blade; 504. Second guide rod; 505. Second guide block; 506. Third connecting rod; 507. Output motor; 6. First cylinder; 7. First guide rod; 8. First guide block; 9. First connecting block; 10. Second connecting rod; 11. Support leg; 12. Universal wheel. Detailed Description of the Invention

[0021] It should be noted that, without conflict, the embodiments in this invention and the features in the embodiments can be combined with each other.

[0022] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is 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 should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0023] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0024] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0025] Embodiment 1 Construction preparation (1) Remove the surface vegetation and dig out the extremely loose surface planting soil.

[0026] (2) According to the comparison result of the measured original ground elevation and the designed pile top elevation, when leveling the drilling site, make its elevation 50 cm higher than the pile top.

[0027] (3) Familiarize with the drawings and relevant materials, conduct on-site verification, and promptly feedback relevant problems.

[0028] (4) Make a corresponding construction plan for the CFG pile construction, and reasonably arrange the construction period, progress, personnel, and mechanical equipment.

[0029] (5) The CFG pile equipment and personnel enter the site. Select the mechanical equipment and relevant construction personnel according to the requirements of the construction technology.

[0030] (6) Initially level the original ground where the CFG pile foundation is located. Place the drill rig along the east-west direction opposite to the center of a row of piles. During construction, jump-pile construction is carried out from the southeast corner side. After the drill rig is in place, check whether the drill rig is operating normally.

[0031] (7) Measurement and setting out: Measure and set out the positions of CFG piles according to the CFG pile layout plan, and draw grid lines with lime. Also, measure the elevation of the levelled ground (especially the elevation at the pile positions), and make records to determine the depth of the pile bottom relative to the ground.

[0032] (8) Number each CFG pile in each building separately to facilitate recording the construction situation and preparing materials.

[0033] (9) Before construction, the project department management personnel should conduct safety and technical disclosure to the subcontracting construction personnel, and retain image data and disclosure records.

[0034] Construction method: Positioning and setting out Transfer the control points set in the site to the foundation pit. The full-time surveyors set the pile positions according to the drawings. The center point of the pile is driven into the ground by 20 cm with a steel bar and filled with lime for marking.

[0035] (2) Drill rig positioning and commissioning The signalman and the drill rig operator cooperate to align the drill rig with the pile position, and adjust the level of the drill rig and the verticality of the drill tool according to the pendulum needle: 1) Move the drill rig to align with the hole position, and the hole position deviation shall not be greater than 50 mm; 2) Use the outrigger cylinder to level the drill rig, and the verticality error of the drill rig spindle shall not be greater than 1%; 3) Accurately measure the length of the drill tool and make significant marks to determine the drilling depth; 4) Check the diameter of the drill pipe, and its diameter error < 20 mm, otherwise the drill pipe should be replaced immediately.

[0036] (3) Drilling 1) After the pile position is accepted, the drill rig is positioned and the fuselage is adjusted. Use the front and rear vertical poles of the drill rig tower to check the guide rod and correct the area to make the drill pipe vertically align with the center of the pile position to ensure that the verticality deviation of the pile body shall not be greater than the allowable deviation.

[0037] 2) Before drilling, first moisten the hopper and pipeline of the concrete pump with clean water (lubricate the pipeline to prevent pipe blockage), then stir a certain amount of cement mortar for pumping, and pump out all the mortar outside the pipe.

[0038] 3) The signalman and the drill rig operator cooperate to align the drill rig with the pile position, and adjust the level of the drill rig and the verticality of the drill tool according to the pendulum needle. Seal the drill bit valve. When the drill pipe moves downward until the drill bit touches the ground, start the drill rig and rotate the drill bit. Generally, it should be slow first and then fast. During the hole forming process, if it is found that the drill pipe shakes or is difficult to drill, stop the machine or slow down the feed. Stop drilling when encountering obstacles, analyze the reasons, and prohibit forced drilling.

[0039] 4) Determine the drilling depth according to the designed pile length and make prominent markings in the corresponding area of the drill rig tower as the basis for controlling the pile length during construction. When the bottom surface of the power head reaches the mark, the pile length meets the design requirements.

[0040] 5) Drill the drill pipe to the predetermined depth. The on-site construction technicians shall analyze based on the geological exploration report and the actual observation of the soil excavated from the borehole to determine whether the soil layer meets the design requirements. In case of special geological conditions, construction shall be immediately stopped, and the supervisor and the owner unit shall be reported. The exploration and design units shall be organized to conduct on-site exploration to determine the specific implementation plan.

[0041] 6) Determine the driving sequence and the walking route of the drill rig according to the site conditions (to avoid the drill rig rolling over the formed piles): For the overall single-building staircase area, construct from north to south and from west to east. If restricted by the site, for individual piles that cannot be avoided, wooden squares must be padded for the drill rig to walk.

[0042] 7) Take effective measures to prevent missing driving and missing grouting, that is: after each pile is constructed, mark it on the drawing while making records.

[0043] (4) Forming piles by pumping concrete Commercially produced concrete with strength grades C25 and C20 shall be uniformly used. Pump the concrete in the ground pump pipe. Make 2 groups of standard cube specimens of the mixture. After 7-day / 28-day standard curing, conduct compressive strength tests on the specimens.

[0044] 1) After the CFG pile is drilled to the design elevation, stop drilling and start pumping concrete with the ground pump. When the drill pipe core is filled with the mixture, start pulling out the pipe. It is strictly prohibited to pull out the pipe first and then pump the material. The pulling speed of forming the pile shall be controlled at 1 - 2 m / min. The process of forming the pile shall be continuous, and it shall be avoided to stop waiting for materials due to slow feeding. After the pouring and forming of the pile are completed, the pile top shall be capped with wet clay for protection. The feeding volume of each pile during construction shall not be less than the designed pouring volume.

[0045] 2) The concrete strength grades are C25 and C20, and the concrete slump is 180 - 220 mm. To ensure its workability and slump, pay attention to adjusting the sand ratio and adding water-reducing agents, fly ash, etc. The pile body concrete shall be 500 mm higher than the pile top elevation from the pile bottom to the pile top. Before constructing the bearing platform, chisel off the excess concrete part and saw it to the designed pile top elevation.

[0046] 3) When pouring the concrete, select experienced machine operators and use hammers to strike to determine the amount of concrete poured. It shall be appropriately higher than the designed pile top elevation to ensure that after chiseling off the floating slurry, the pile top elevation meets the design requirements.

[0047] 4) According to the on-site conditions, to ensure the construction quality of the pile body concrete, the following technical measures shall be taken during pumping concrete to guarantee the quality of the formed piles.

[0048] a) To ensure the quality of concrete, its slump should be controlled at about 180-220mm to ensure that the concrete has good workability; b) When it is confirmed that the drill has reached the bottom of the hole, it should be rotated in situ for 1 to 2 minutes, the drill rod should be pre-lifted 20 cm, and then the concrete delivery pump should be turned on to start pumping concrete; c) After the mixed material is pumped into the drill pipe and returned to the exhaust hole, slowly lift the drill. The lifting speed must match the pump volume to ensure that the drill tip is always buried in the mixed material; d) An effective communication method should be established between ground pump feeding and drilling rig operation to ensure coordination between pumping and drilling; e) Each pile must be poured continuously. If an unexpected situation occurs during the pile construction process and continuous pouring is not possible, appropriate treatment measures must be taken to eliminate the fault and resume pouring in the shortest possible time. If the interruption time is too long, timely communication with the designer is required. In principle, the remedial measure is to re-pile near the original pile position; f) Control the pressure difference between the concrete pumping pressure and the pipeline pressure. The pressure difference should not be too large, but also not too small to prevent pipe blockage; g) During the process of pumping concrete, the drilling rig operator shall check the concrete filling in the drill rod at any time to control the amount of concrete pumped in; h) When the drill is lifted to 0.5m from the hole, stop pumping concrete, use the concrete retained in the pipe to fill the top of the pile, and then proceed with the construction of the next pile according to the above steps and requirements; i) Measure the elevation of the pile top. If it does not meet the design requirements, high-grade concrete should be used to connect the piles according to the method of connecting the broken piles in the drawing.

[0049] (5) Displacement When the construction of the previous pile is completed, the drilling rig is moved to the next pile. During construction, due to the large amount of soil on the CFG pile, the adjacent pile positions are often covered. Sometimes, the originally calibrated pile position is moved because the supporting feet of the drilling rig are pressed next to the pile position. Therefore, when constructing the next pile, the pile position to be constructed should also be checked according to the position of the axis or surrounding piles to ensure the accuracy of the pile position. After the machine is moved, the excavated soil from the drill hole is cleared out of the site as needed.

[0050] (6) Clearing the soil between piles, excavating piles and chiseling pile heads 3 to 7 days after the piles are formed, the excavation of the piles and the cleaning of the soil between the piles can be carried out. In order to ensure the progress of the project, the soil cleaning and pile forming are carried out alternately. The soil cleaning adopts small excavators combined with manual methods to prevent the mechanical construction from disturbing the pile body and the soil between the piles.

[0051] According to the design and construction specifications, when the cast-in-place piles are formed, the concrete density of the top 500mm of the pile may not meet the requirements, so a 500mm concrete pile head must be reserved. When the concrete strength reaches more than 80%, it is cut by machinery and the cut concrete is transported to the designated location on site at a distance from the design elevation.

[0052] After manually clearing the soil to the design elevation, use the cutting device to first cut into the area around the pile, with a cutting depth of 10 cm to 15 cm. Then, three people simultaneously use chisels to strike around the pile until the pile head breaks. Finally, manually chisel the uneven pile head. The elevation control requirement for the pile head is to enter the cushion layer by ±50 mm.

[0053] The cutting device includes a base 1, a first support plate 2, a first connecting rod 3, a workbench 4, a cutting assembly 5, and a first cylinder 6. The first support plate 2 is arranged on the base 1 through a first connecting block 9. A first connecting rod 3 is vertically provided on one side of the first support plate 2, and a first cylinder 6 is installed at the end of the first connecting rod 3. The output end of the first cylinder 6 is connected to the workbench 4, and several cutting assemblies 5 are arranged along the circumference below the workbench 4.

[0054] A first guide rod 7 is provided on the first connecting block 9, and a first guide block 8 is provided on the output end of the first cylinder 6. The first guide block 8 is slidably connected to the first guide rod 7 through a second connecting rod 10. The cutting assembly 5 includes a second support plate 501 and a second cylinder 502. The upper end of the second support plate 501 is fixedly arranged at the bottom of the workbench 4, the installation end of the second cylinder 502 is arranged on one side of the second support plate 501, and the output end of the second cylinder 502 is connected to the installation end of an output motor 507. The output end of the output motor 507 is connected to an annular saw blade 503. A second guide rod 504 is arranged inside the second support plate 501, a second guide block 505 is provided on the output end of the second cylinder 502, and the second guide block 505 is slidably connected to the second guide rod 504 through a third connecting rod 506. The base 1 is an annular base 1, and several uniformly arranged support legs 11 are provided along the circumference at the bottom of the base 1. A lockable universal wheel 12 is provided at the bottom of the support leg 11, and the universal wheel 12 adopts the prior art.

[0055] During specific use, the operator moves the universal wheel 12 to the CFG pile, locks the universal wheel 12 with the car locking function, makes the center of the workbench 4 correspond to the center of the CFG pile, the first cylinder 6 drives the workbench 4 to move downward, the workbench 4 drives the cutting assembly 5 to move to the outer wall of the CFG pile to be cut. At this time, the second cylinder 502 and the output motor 507 start to move, and multiple cutting assemblies 5 along the circumference move simultaneously, with a cutting depth of 10 cm to 15 cm. Then, three people simultaneously use chisels to strike around the pile until the pile head breaks. Finally, manually chisel the uneven pile head. The elevation control requirement for the pile head is to enter the cushion layer by ±50 mm, with good cutting effect and high cutting efficiency.

[0056] (7)Laying of cushion layer 1) Process flow Locate the laying range line of the cushion layer → Clear the soil to the design elevation → The sand and gravel for the cushion layer enter the site → The thickness of the loose gravel → Compact to 200mm with a plate vibrator.

[0057] 2) The laying thickness, material particle size, and ramming degree of the cushion layer shall meet the design requirements. It is strictly prohibited to use unqualified materials.

[0058] 3) The elevation of the cushion layer laying shall be controlled by a level, and the ramming degree shall not be greater than 0.9 (the ramming degree is the ratio of the compacted thickness to the loose laying thickness).

[0059] 4) Before laying the cushion layer, manually clean the composite foundation to the design elevation, and inspect the foundation trench to ensure that there is no disturbance in the foundation soil.

[0060] 5) The cushion layer uses crushed stones with a particle size of 10mm - 20mm.

[0061] 6) The laying thickness of the cushion layer shall be uniform, and the allowable deviation of the thickness is ±10mm.

[0062] 7) The laying range of the cushion layer: Expand 200mm outside the edge of the treatment of the outer skin of the foundation cushion.

[0063] 8) The cushion layer shall be fully compacted, compacted with a frog rammer, keep the drop height at 400 - 500mm, and compact comprehensively, generally not less than 3 times. The edges and corners are compacted manually or with a frog rammer.

[0064] (8) Quality inspection 1) Detection of pile body integrity The integrity of the CFG pile body is detected by low-strain dynamic testing. The integrity of the pile body is judged according to the test results. The number of tests is 20% of the total number of piles. In this project, at least 85 piles are randomly selected for low-strain testing and pile body integrity testing.

[0065] 2) The static load test of the composite foundation and the static load test of a single pile are entrusted to a third party by the owner. The number of inspections for the bearing capacity of the composite foundation shall not be less than 1% of the total number of piles and shall not be less than 3 points; the number of inspections for the bearing capacity of a single pile shall not be less than 1% of the total number of piles and shall not be less than 3 points. The specific quantity and pile numbers are specified by the supervision unit. The project department shall cooperate with the construction as required.

[0066] 3) CFG pile concrete strength Two groups of standard cube specimens of the mixture are made. After 7d / 28d standard curing, the compressive strength of the specimens is detected. The quality situation is judged according to the test results. Each group of test blocks is marked with its representative pile number according to the construction records to ensure the traceability of the project tests.

[0067] It also includes the treatment of broken piles. According to the pile foundation test results, small excavators are used in combination with manual methods to clean the soil between piles to prevent mechanical construction from disturbing the pile body and the soil between piles. When an accident occurs and the upper pile head is damaged or broken, the shallow broken pile with a height of less than or equal to 100mm is directly laid with a cushion layer, and the pile with a height greater than 100mm is connected according to the design requirements. The specific pile connection method is as follows: Construction method: a. According to the pile foundation inspection report, find out the location of the broken pile; if the broken pile is caused by mechanical excavation collision, the lower pile body is intact after inspection and is marked; from the appearance, it can be determined that the lower pile body is broken and the pile head is obviously tilted; b. After finding the broken pile, arrange workers to clean up the surrounding soil. If the broken position is above the base, continue to cut the pile to the designed elevation; if the broken position is below the base, manually expand the pile body by 100mm on each side, and the depth is 100mm deeper than the broken position; c. Cut off the pile head above the fractured part and hoist it out of the foundation pit, check the condition of the fractured part, whether the surface is flat and whether there is any defect; d. Clean and level the broken parts, and clean the soil around the pile with a wire brush; e. Use iron sheet to bend into a cylinder with a diameter 200mm larger than the pile diameter, put it on the pile head on the fracture surface, and connect it to the designed pile top elevation with concrete one grade higher than the pile body concrete. Pay attention to protecting the soil between the piles during the process of connecting the pile heads. See the attached figure for specific methods: f. After pouring is completed, wait until the concrete has finally set and reaches a strength of more than 1.2MPa, remove the iron sheet wrapped around the newly poured pile head, and backfill the surrounding gaps in a timely and relatively even manner, and compact them layer by layer.

[0068] (9) Quality standards and requirements: 1) Excavation between piles should avoid disturbing the foundation bearing layer, and the elevation after excavation must be within the range specified in the design and specification. 2) During the excavation process, strictly control the excavation size to avoid over-excavation or secondary excavation.

[0069] 3) Horizontal heavy hammer pile driving is not allowed, and the allowable deviation of pile head clearance must comply with design and specification requirements.

[0070] (10) Finished product protection measures: 1) After the piles are cleaned, prevent heavy machinery from moving or disturbing them to prevent the pile heads from being loosened, causing the concrete on the pile top to be deformed or the pile to break.

[0071] 2) Soil is cleared and leveled manually to avoid breaking piles and disturbing the foundation soil.

[0072] 3) The pile head insulation measure is to use a layer of quilt and a layer of plastic film 4) For details on the soil clearing boundaries between CFG piles, please refer to the construction drawings and construct according to the drawings.

[0073] (1) Broken pile Broken piles are mainly caused by the drill rod lifting speed being too fast while the rising speed of the pumped concrete is lower than the drill rod lifting speed.

[0074] Preventive measures: Prevention should be the priority for broken piles. Before pouring, each operation link should be carefully checked and effective preventive measures should be specified. During pouring, strictly abide by the operating procedures to ensure continuous and compact pouring operations. After drilling to the designed depth, concrete should be pumped first and then the drill should be lifted. It is strictly forbidden to lift the drill first and then pump. During construction, the drill rod should be lifted at a uniform speed, and the lifting speed should not exceed 1.2-1.5m / minute.

[0075] Treatment measures: If the broken pile is shallow, the pile head above the broken pile can be manually excavated, and the soil and loose concrete particles on the pile head surface can be cleaned. Use graded gravel to backfill to the designed pile top elevation. The graded gravel particle size, mix ratio and construction quality requirements are the same as the cushion layer of this project, that is, the cushion layer is partially thickened. If the broken pile is deep, manually excavate the foundation pit to 100mm below the fracture surface, remove the broken pile, and level and clean the fracture surface. Use concrete with a grade higher than the designed pile body concrete to cast the pile, and vibrate to compact it. The concrete is poured to the designed pile top elevation.

[0076] (2) Reduction The shrinkage is generally caused by the presence of a silt layer in the stratum. When pumping concrete in this stratum during construction, the drill rod is lifted at a faster speed, forming a negative pressure in the hole. The silt around the hole rebounds under the action of the negative pressure, shrinking the hole diameter and causing shrinkage. This is generally more likely to occur in locations with higher groundwater levels.

[0077] Precautionary measures: When encountering silt formations during construction, the drilling rod lifting speed and the concrete pumping speed should be appropriately slowed down when pumping concrete. If necessary, the drilling rod can be lifted after pausing for 2 to 3 seconds after every 2 meters of lifting during the pumping process; Treatment measures: Generally, piles need to be drilled and then piled up. Special cases can be handled according to design requirements.

[0078] (3) Honeycomb piles Precautionary measures: During on-site construction, the maximum particle size of the gravel in the concrete should not exceed the above regulations. When designing the concrete mix ratio, the influence of admixtures such as water reducer, lubricant, and early strength agent should be considered. 10%-15% fly ash can be added to increase the lubricity and workability of the concrete in the pipe.

[0079] Treatment measures: If the honeycomb is not too serious and only appears on the outer skin, chisel away the loose concrete and pour with a higher grade of expansive concrete. If the honeycomb is large, communicate with the designer and ask experts to verify it before construction.

[0080] (4) Pile position deviation Preventive measures: Set out the lines strictly according to the construction drawings, and only start construction after the supervision unit and the construction party have rechecked and confirmed that they are correct.

[0081] Treatment measures: When the deviation of the pile position is within one pile diameter, if it is a pile at the column pier position, it is preferred to contact the design unit to increase the size of the column pier; if it is at the raft foundation position, cut the pile length by one pile diameter downward and increase the pile diameter to connect the length. When the deviation of the pile position is greater than one pile diameter, it is necessary to supplement the pile in the opposite direction.

[0082] (5) The pile top elevation is too low Preventive measures: Control the height of the poured concrete surface. When pouring to the end, ensure that the overpouring is more than 0.5 m above the designed pile top elevation. Check the pile top height of the completed piles at any time and adjust the overpouring height in time to avoid the occurrence of negative piles.

[0083] Treatment measures: Treat it as a broken pile and carry out pile connection treatment.

[0084] (6) Shallow broken piles Preventive measures: Shallow broken piles are mainly caused by accidentally breaking the upper part of the pile body when using a small excavator to clean the soil between piles, or by improper operation when using a steel drill and a sledgehammer to chisel the pile head. When using a small excavator to clean the soil between piles, the bucket should not be too close to the pile body. When cleaning to about 10 cm from the pile top elevation, use manual cleaning to the designed pile top elevation; when chiseling the pile head, try to use the sawing method to saw off the protective pile head, and at the same time, heavy vehicles and equipment should be prohibited from rolling over the pile body.

[0085] Treatment measures: Treat it as a broken pile and carry out pile connection treatment.

[0086] (7) String holes Preventive measures: String holes are mainly caused by the existence of collapsible sand layers in the stratum and small pile spacing during construction. When pumping concrete in the sand layer, the speed should be appropriately slowed down, and the construction should adopt the technology of alternate pile driving.

[0087] (8) Pile head protection 1) The foundation of the building in this application is treated with cement fly ash gravel piles (CFG). The concrete strength of the pile body is C25, the pile diameter is 400 mm, and the pile spacing is arranged in a square with a spacing of 1.5 m × 1.5 m. It is required that the characteristic value of the composite foundation bearing capacity is not less than 350 Kpa.

[0088] 2) The designed height of the pile foundation is 50 cm above the foundation bottom surface. The actual on-site situation is that it is about 3 - 5 m above the foundation bottom surface on average, which has a certain impact on the excavation of foundation pit soil and soil between piles, and pile cutting, etc., so that pile cutting occurs 3 - 5 times during the soil excavation process, seriously affecting the construction progress.

[0089] 3) Mark the pile top elevation position on the pile body, and the pile top elevation is flush with the foundation bottom elevation; 4) Fix a special large-diameter steel saw blade on the pile body. The cutting position is at the elevation mark of the pile top. Cut around the pile body in a circumferential direction, with the cutting depth into the pile body being 50 mm. Then, place 2 - 4 steel drills at different angles at the elevation position of the pile top and strike the steel drills simultaneously with a sledgehammer. The force should be moderate and not too strong to avoid damaging the pile body. When the upper and lower pile bodies are separated, the pile head is truncated. 5) Do not use a heavy hammer or heavy object to strike the pile body horizontally to avoid causing a horizontal fracture of the pile body below the pile top elevation. 6) After the pile head is truncated, use a steel drill and a hand hammer to level the pile top from the periphery to the middle to the designed elevation of the pile top (the allowable deviation of the pile top elevation is 0 - +20 mm).

[0090] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. The construction method of CFG pile foundation is characterized in that: It includes the following steps: S1: Conduct construction preparation, measure and set out the positions of CFG piles, place the drill rig on one side of the pile position, and check the verticality, bit size and drill tip position; S2: The drill rig drills to the design elevation. After drilling to the design elevation, stop drilling. While pumping concrete into the pile hole, lift the drill tool until the concrete reaches the design pile top elevation. After the pouring of the pile is completed, the pile top is sealed with wet clay, and the drill rig is moved. The CFG piles are constructed one by one in the set order; S3: Cure the concrete of the CFG piles, clean the soil between the piles and chisel the concrete pile heads; S4: Detect the CFG piles and lay the cushion layer.

2. The CFG pile foundation construction method according to claim 1, characterized in that: The construction preparation in step S1 includes: removing the surface vegetation, excavating the extremely loose surface planted soil. According to the comparison result of the measured original ground elevation and the design pile top elevation, when leveling the drilling site, the original ground elevation is 50 cm higher than the pile top of the design pile; And / or, measuring and setting out the positions of CFG piles includes measuring and setting out the positions of CFG piles according to the CFG pile position layout drawing and drawing grid lines with lime; And / or, preliminarily level the original ground where the CFG pile foundation is located. The drill rig is aligned with the center of a row of piles in the east-west direction. During construction, skip pile construction is carried out from the southeast corner side. After the drill rig is in place, check whether the drill rig is operating normally.

3. The CFG pile foundation construction method according to claim 1, characterized in that: The inspection of the verticality, bit size and drill tip position in step S1 includes that when moving the drill rig, it needs to be aligned with the hole position, and the hole position deviation shall not be greater than 50 mm; The verticality error of the drill rig main shaft shall not be greater than 1%; Precisely measure the length of the drill tool and make obvious marks to determine the drilling depth; Check the drill pipe diameter, and its diameter error < 20 mm, otherwise replace the drill pipe immediately.

4. The construction method of CFG pile foundation according to claim 1, characterized in that: In step S2, start pumping concrete with a ground pump. When the drill pipe core is filled with the mixture, start pulling out the pipe. It is strictly prohibited to lift the pipe first and then pump the material; the pulling speed of the formed pile is controlled at 1 - 2 m / min, and the pile forming process is continuous. It is necessary to avoid stopping for material due to slow feeding; after the pouring of the pile is completed, the pile top is sealed with wet clay for protection; the feeding amount of each pile during construction shall not be less than the designed pouring amount; And / or, the concrete strength grade is C25 or C20, the concrete slump is 180 - 220 mm, and a 500 mm concrete pile head is reserved when the cast-in-place pile is formed; And / or, polycarboxylic acid powder water reducer and fly ash are added to the concrete; And / or, the slump of the concrete shall be controlled at 180 - 220 mm; When it is confirmed that the drilling reaches the bottom of the hole, it should rotate in place for 1 - 2 minutes, lift the drill pipe 20 cm, and then start the concrete delivery pump to pump the concrete; wait until the mixture is pumped into the drill pipe until the material returns from the exhaust hole, and then lift the drill tool. The lifting speed must cooperate with the pump volume to ensure that the drill tip is always buried in the mixture and keep the pumping and lifting of the drill coordinated.

5. The construction method of CFG pile foundation according to claim 1, characterized in that: The curing of the concrete of the CFG piles in step S3 includes: After 3 to 7 days of pile formation, the pile excavation and the cleaning of the soil between piles can be carried out. A cutting device is used to cut around the concrete pile head; the cutting depth is 10 cm to 15 cm. Then, the cutting device is moved away, and then the operator uses chisels to strike around the pile simultaneously until the pile head breaks. Finally, the uneven pile head is manually chiseled. The elevation control requirement for the pile head is to enter the cushion layer by ±50 mm; The elevation of the cushion layer laying should be controlled by a level, and the ramming degree should not be greater than 0.9; Before laying the cushion layer, the composite foundation is manually cleaned to the design elevation. The foundation pit inspection ensures that there is no disturbance in the foundation soil. The cushion layer uses gravel with a particle size of 10 mm - 20 mm. The laying thickness of the cushion layer should be uniform, and the allowable deviation of the thickness is ±10 mm. The laying range of the cushion layer is 200 mm outside the edge of the outer skin treatment of the foundation cushion; The cushion layer is compacted by a frog rammer, keeping the drop distance at 400 - 500 mm, and the compaction times are not less than 3 times.

6. The CFG pile foundation construction method according to claim 5, characterized in that: The cutting device includes a base, a first support plate, a first connecting rod, a workbench, a cutting assembly, and a first cylinder; The first support plate is arranged on the base through a first connecting block. A first connecting rod is vertically arranged on one side of the first support plate, and a first cylinder is installed at the end of the first connecting rod; The output end of the first cylinder is connected to the workbench, and several cutting assemblies are arranged along the circumference under the workbench.

7. The CFG pile foundation construction method according to claim 6, wherein: A first guiding rod is arranged on the first connecting block, and a first guiding block is arranged on the output end of the first cylinder. The first guiding block is slidably connected to the first guiding rod through a second connecting rod; And / or, the cutting assembly includes a second support plate and a second cylinder. The upper end of the second support plate is fixedly arranged at the bottom of the workbench. The installation end of the second cylinder is arranged on one side of the second support plate, and the output end of the second cylinder is connected to the installation end of the output motor; The output end of the output motor is connected to the annular saw blade; And / or, a second guiding rod is arranged inside the second support plate, and a second guiding block is arranged on the output end of the second cylinder. The second guiding block is slidably connected to the second guiding rod through a third connecting rod.

8. The CFG pile foundation construction method according to claim 6, characterized in that: The base is an annular base. A number of uniformly arranged support legs are provided along the circumference at the bottom of the base, and universal wheels that can be locked are provided at the bottom of the support legs.

9. The CFG pile foundation construction method according to claim 1, characterized in that: In step S4, the detection of CFG piles includes the detection of pile body integrity. The pile body integrity of CFG piles is detected by low-strain dynamic tests. The pile body integrity is judged according to the test results, and the detection quantity is 20% of the total number of piles; In the composite foundation static load test and the single-pile static load test, the inspection quantity of the composite foundation bearing capacity should not be less than 1% of the total number of piles, and should not be less than 3 points.

10. The CFG pile foundation construction method according to claim 9, characterized in that: It also includes the treatment of broken piles. According to the pile foundation test results, for shallow broken piles with a height less than or equal to 100 mm, the cushion layer is directly laid, and for those with a height greater than 100 mm, pile splicing treatment is carried out according to the design requirements. The treatment of broken piles includes the following steps: A1: Locate the broken pile, clean the surrounding soil. If the fracture position is above the foundation base, continue to cut the pile to the design elevation. If the fracture position is below the foundation base, the pile body is manually enlarged by 100 mm on each side, and the depth is 100 mm deeper than the fracture position; A2: Cut off the pile head above the fracture part and hoist it out of the foundation pit. Check the condition of the fracture part, whether the surface is flat and whether there are any defects; A3: Clean and level the fractured part, and use a wire brush to clean the soil around the pile body; A4: Bend the iron sheet into a cylinder with a diameter greater than 200 mm larger than the pile diameter, put it on the pile head at the fracture surface, and use concrete with a strength grade one higher than that of the pile body concrete to pour up to the designed pile top elevation. Pay attention to protecting the soil between piles during the process of connecting the pile heads; S4: After the pouring is completed, wait until the concrete has undergone final setting and reached a strength of more than 1.2 MPa, then remove the iron sheet wrapped around the newly poured pile head, and promptly backfill the surrounding voids relatively evenly, and tamp them layer by layer.

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