Annular multi-stage well point dewatering reserved core soil excavation construction method

Abstract

The invention relates to the technical field of bearing platform construction, in particular to an annular multi-stage well point dewatering reserved core soil excavation construction method which comprises the steps that S1, construction preparation is conducted; s2, the site is leveled, side line lofting is conducted, outward expansion is conducted according to the side line of the bearing platform, and the slope making projection width and the operation space are reserved; s3, the annular foundation trench is excavated; s4, a precipitation system is arranged, installed and debugged; s5, well point pipe spacing and depth calculation and installation arrangement are carried out, the well point pipes are buried deeply to penetrate through the permeable layer, and the precipitation effect is ensured; s6, running the precipitation system; s7, performing multi-stage excavation to reach the designed elevation of the ditch bottom; s8, core soil in the middle of the foundation pit is excavated; s9, re-checking and adjusting the monitoring measurement data; s10, the precipitation system is dismantled and blocked; the annular multi-stage well point dewatering reserved core soil excavation method is adopted, layered excavation is easy to control, the construction difficulty is small, the progress is fast, the production efficiency is improved, procedure conversion is easy, and rapid dewatering can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the construction technology field of bearing platform, and particularly relates to a method for excavating reserved core soil by ring multi-stage well point dewatering. BACKGROUND

[0002] With the rapid development of national infrastructure construction, the construction technology of bearing platform in bridge engineering is increasingly mature and widely used. In the construction area with poor geological conditions such as soft soil layer, the excavation of foundation pit easily causes construction safety problems, and the insertion and driving of steel sheet pile cofferdam technology is often used to ensure the stability of the foundation pit.

[0003] When the engineering construction involves plain fill, miscellaneous fill, silt and silty sand layer, the underground water level of such soil layer is high, and the stratum is mainly saturated fine sand. When the foundation pit is excavated, there are risks of pit wall collapse, water gushing, sand flow and slope instability. For the excavation of the foundation pit under such geological conditions, dewatering and drainage work need to be considered, and construction safety needs to be ensured. The traditional construction of steel sheet pile and support has a large amount of use, high cost, deep excavation, high risk in the construction process, great construction difficulty and limited production efficiency. SUMMARY

[0004] The purpose of the present application is to solve the problems in the prior art and provide a method for excavating reserved core soil by ring multi-stage well point dewatering.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme: A method for excavating reserved core soil by ring multi-stage well point dewatering, comprising the following steps: S1, construction preparation, including core soil planning, advanced support, material and equipment inspection and technical briefing; S2, leveling the site, laying out the boundary line, expanding the boundary line of the bearing platform, and reserving the projection width of the slope and the operation space; S3, ring base trench excavation, using segmented and layered excavation, dividing the ring base trench into 4-6 symmetrical segments to avoid uneven stress on the slope caused by unilateral excavation, and the length of each segment is less than or equal to 10m; S4, dewatering system arrangement, installation and debugging; S5, well point pipe spacing and depth calculation, installation and arrangement, the well point pipe is buried to penetrate the water permeable layer to ensure the dewatering effect; S6, dewatering system operation, ensuring that the dewatering curve is smooth, without sudden changes or local water accumulation; S7, multi-stage excavation to the design elevation of the trench bottom; S8, core soil excavation in the middle of the foundation pit, before excavation, it is confirmed that the ring base trench has been excavated to the design elevation of the bearing platform trench bottom, and the water level of the last stage well point dewatering is stable and lower than the trench bottom by 0.5m; S9, review and adjustment of monitoring and measurement data; S10, dewatering system dismantling and plugging, preventing ground subsidence or groundwater seepage.

[0006] Preferably, in step S1: Core soil planning, determine the size, location and reserved height of core soil, ensure its stability; Advanced support, implement advanced small catheter grouting, pipe shed and other support measures in poor surrounding rock area to enhance the self-stability of surrounding rock; Material and equipment access inspection, well point pipe inspection wall thickness, pipe diameter, filter pipe hole; medium-coarse sand needs to be sieved for particle size and measured for silt content; Before construction, technical briefing is carried out, and the personnel participating in the construction are briefed on the construction steps, operation methods, equipment use, personnel allocation and other aspects in detail and comprehensively.

[0007] Preferably, in step S4: Dewatering system arrangement, according to the geological conditions, design annular multi-stage well points, including well point pipe, water collection main pipe, vacuum pump or submersible pump, well point spacing and depth are determined by calculation to ensure that the dewatering effect covers the excavation area; Dewatering system installation and debugging, drill well point holes, install well point pipes and filter pipes, fill filter material, connect water collection main pipes and vacuum pumps or submersible pumps, conduct test pumping, check system tightness and dewatering effect; monitor the change of underground water level, adjust dewatering parameters such as pumping intensity and well point spacing until the excavation requirements are met.

[0008] Preferably, in step S5, the well point pipe spacing is 0.8-1.2m, the small value is taken for sand layer and the large value is taken for clay layer; the filter pipe needs to be completely buried in the permeable layer, the length is 1.2-1.5m, and the bottom is 0.3-0.5m higher than the trench bottom to prevent clogging.

[0009] Preferably, in step S5, the well point pipe installation and arrangement are as follows: a1, use water flushing method, including two processes of punching and pipe burying, when punching, first use lifting equipment to lift the flushing pipe and insert it at the well point position, then start the high-pressure water pump to flush the soil, the flushing pipe is vertically inserted into the soil during punching, and is swung up and down to intensify soil loosening, and is sunk while flushing to ensure a certain amount of sand filter layer around the well pipe, the punching depth should be deeper than the filter pipe bottom to prevent the flushing pipe from being pulled out and part of the soil particles from sinking to the filter pipe bottom; a2, after the well hole is punched, the flushing pipe is immediately pulled out, the well point pipe is inserted, and the sand filter layer is quickly filled between the well point pipe and the hole wall to prevent the hole wall from collapsing, and the filling is 1-1.5m above the filter pipe top to ensure smooth water flow, after the well point is filled with sand, the well point pipe upper opening is sealed with clay to prevent air leakage; a3, rubber sealing ring connects the well point pipe and the annular main pipe, the main pipe is laid along the slope of the foundation trench, and each joint is sealed with adhesive tape; a4, the main pipe is connected with the pumping equipment.

[0010] Preferably, in step S6, the operation process of the dewatering system is: b1, after the well pipe is buried, the power is turned on, the single pipe is tested, the water yield is checked, and whether there is air leakage and siltation is checked; the single pipe water yield is ≥1.5m³ / h, and the vacuum degree is ≥70kPa; after no abnormality is found, all well point pipes are opened for linkage test pumping, and the water level drop rate is monitored; b2, after the test pumping is qualified, formal dewatering is carried out, and two conditions need to be met before the next layer is excavated: the water level is stable and lower than the current trench bottom by 0.5-1.0m; and the slope has no obvious water seepage; b3, before excavating the next layer of annular foundation trench inward, the well point system of this layer is started in advance, the depth of the inner side foundation trench well point pipe needs to be 1.0-1.5m deeper than the outer side, and the deep water level is controlled; in order to avoid mutual interference, the spacing between the upper and lower well point pipes is ≥2.0m, and after each layer of dewatering is completed, the upper well point pipe needs to be closed to prevent excessive dewatering from causing ground subsidence; b4, during the operation of the well point pumping equipment, the operator monitors the equipment operation to ensure that the pumping equipment works normally; the dewatering system records the daily single well water yield and water level observation hole data; it is checked whether the water level is stable and lower than the excavation surface by 0.5-1.0m; if an abnormality is found, such as a sudden drop in vacuum degree or a sharp decrease in water yield, the equipment needs to be repaired immediately.

[0011] Preferably, in step S7, multi-stage excavation is carried out to the design elevation of the trench bottom: the excavation depth of each layer is 1.5m, and the next layer of foundation trench can be excavated only after the current layer of dewatering is stable and the slope is stable; when excavating, the machinery needs to advance from the already excavated section to the unexcavated section to avoid damaging the installed well point pipe; when excavating to 0.3m from the design elevation of the support trench bottom, manual excavation is carried out, the final trench bottom elevation error is ≤50mm, and overexcavation is avoided; after excavating to the design elevation, it is checked whether the soil quality of the foundation bottom is consistent with the design survey report and whether the flatness meets ≤50mm / 2m.

[0012] Preferably, in step S8, the core soil in the middle of the foundation pit is excavated: c1, before the core soil is excavated, it is confirmed that the annular foundation trench has been excavated to the design elevation of the support trench bottom; the last stage of well point dewatering is stable and lower than the trench bottom by 0.5m; the foundation pit slope has no displacement, no settlement, and no abnormal deformation; c2, the core soil is excavated by using an excavator to dig and load the soil, and a dump truck to transport the soil; one-time excavation to the bottom in a single area is prohibited; if the core soil height is ≤3m, it can be excavated in two layers; if the height is >3m, it is excavated in three or more layers, and manual excavation is switched at 0.2m from the trench bottom surface during mechanical excavation; the core soil slope is preserved during excavation, and vertical excavation is prohibited.

[0013] Preferably, in step S9: the monitoring points of horizontal convergence, vault subsidence and the like are arranged, the deformation of the surrounding rock is mastered in real time, the horizontal convergence and vault subsidence amount need to be within the allowable range of design, and the deformation rate gradually tends to be stable; the precipitation intensity, excavation footage or support parameters are adjusted according to the monitoring data, the construction safety is ensured, and the excavation is immediately suspended when the data is abnormal, the causes are analyzed and reinforcement measures are taken.

[0014] Compared with the prior art, the present application has the following beneficial effects: 1、The annular multi-stage well point precipitation reserved core soil excavation construction method has the advantages of easy control of stratified excavation, small construction difficulty, fast progress, greatly improved production efficiency, easy process conversion, realization of rapid precipitation, reduction of the number of steel sheet piles and supports, great reduction of mechanical and labor costs and steel sheet pile materials, and low construction cost. 2、The reserved core soil technology can enhance the embedded stability, keep the excavation surface stable, has small safety hazards, optimizes the precipitation layout, reduces the water gushing risk, improves the construction safety and economic benefits, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A work flow chart of an annular multi-stage well point precipitation reserved core soil excavation construction method is provided. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0017] REFERENCE Figure 1 An annular multi-stage well point precipitation reserved core soil excavation construction method, comprising the following steps: S1, construction preparation, including core soil planning, advanced support, material and equipment inspection and technical briefing; Core soil planning, determining the size (area not less than 50% of the excavation section), position and reserved height of the core soil to ensure its stability; Advanced support, implementing advanced small pipe grouting, pipe shed and other support measures in the poor surrounding rock area to enhance the self-stability of the surrounding rock; Material and equipment access inspection, well point pipe inspection wall thickness, pipe diameter, filter pipe hole; medium and coarse sand need to be sieved for particle size and mud content; for unqualified raw materials, remove them according to relevant regulations. Before starting, send the total station to a third-party measurement agency for calibration, and the calibration report must be qualified.

[0018] Before construction, technical disclosure is carried out to the personnel involved in the construction, and detailed and comprehensive technical disclosure is carried out on construction steps, operation methods, equipment use, personnel allocation, etc. to ensure clear responsibilities and requirements during construction, close coordination and order in each link, and high-quality and efficient completion of construction tasks.

[0019] S2, level the site and lay out the sidelines, expand the pile cap sidelines, and reserve the slope projection width and operation space; (the slope coefficient is 1:1.05, when the depth is 1.5 m, the horizontal projection width of the slope is 1.5*1.05=1.575 m), pop out the outer edge line and inner edge line of the ring-shaped foundation trench with lime; if there is a slope change in the foundation pit (such as local soil layer is sand layer), the adjusted slope coefficient needs to be marked at the sidelines, the sand layer can be adjusted to 1:1.1, and the clay layer remains 1:1.05; mark the 1.5-3m trench bottom width and 1.5m excavation depth (allowable deviation ±50mm) beside the sidelines with wooden stakes.

[0020] S3, ring-shaped foundation trench excavation, adopt segmented and layered excavation, divide the ring-shaped foundation trench into 4-6 symmetrical sections to avoid uneven stress on the side slope caused by unilateral excavation, and the length of each section is ≤10m; use the total station to monitor the excavation depth in real time, switch to manual excavation when the mechanical excavation reaches 200-300mm from the design depth to prevent mechanical over-excavation; reserve a 100mm thick protective soil layer at the bottom of the trench, and manually clean it to the design elevation before installing the well point pipe.

[0021] S4, arrangement, installation and debugging of the dewatering system; Dewatering system arrangement: design a ring-shaped multi-stage well point according to the geological conditions, including well point pipe, water collection main pipe, vacuum pump or submersible pump, well point spacing and depth are determined through calculation to ensure that the dewatering effect covers the excavation area; Dewatering system installation and debugging: drill well point holes, install well point pipes and filters, fill filter material (such as coarse sand, gravel), connect the water collection main pipe and the vacuum pump or submersible pump, and conduct a test pumping to check the system's sealing performance and dewatering effect; Monitor the change of underground water level and adjust the dewatering parameters (such as pumping intensity, well point spacing) until the excavation requirements are met.

[0022] S5, well point pipe spacing and depth calculation, installation and arrangement, well point pipe buried depth penetrates through the water permeable layer to ensure the dewatering effect; Well point pipe installation arrangement parameters: well point pipe spacing is 0.8-1.2 m, small value for sand layer, large value for clay layer; filter pipe needs to be completely buried in permeable layer, length is 1.2-1.5 m, bottom is 0.3-0.5 m higher than ditch bottom, to prevent clogging; Well point burial depth H calculation formula (not including filter pipe): H≥H1+△h+iL(m); In the formula, H1 represents the distance from well pipe burial surface to foundation pit bottom; △h represents the distance from bottom surface at foundation pit center to lowered underground water level; i represents underground water drawdown slope, 1 / 10 of ring well point; L represents horizontal distance from well point pipe center to foundation pit center.

[0023] Well point pipe installation arrangement: a1, water flushing method is adopted, including two processes of hole flushing and pipe burying, when flushing hole, first, hoist the diameter 50 mm flushing pipe with hoisting equipment and insert it at well point position, then start high pressure water pump, flush soil, when flushing hole, flush pipe is vertically inserted into soil and swings up and down, to intensify soil loosening, flush while sink, flushing hole diameter should not be less than 450 mm, to ensure that there is a certain amount of sand filter layer around well pipe, flushing hole depth should be about 500 mm deeper than filter pipe bottom, to prevent part of soil particles from sinking to pit bottom and touching filter pipe bottom when flushing pipe is pulled out; a2, after well hole is flushed, flush pipe is immediately pulled out, well point pipe is inserted, and sand filter layer is quickly filled between well point pipe and hole wall, to prevent hole wall from collapsing, sand filter layer filling quality is the key to ensure smooth work of light well point, generally, clean coarse sand should be used, filling should be uniform, filling should be 1-1.5 m above filter pipe top, to ensure water flow is smooth, after well point is filled with sand, well point pipe upper opening should be sealed with clay, to prevent air leakage; a3, rubber sealing ring connects well point pipe and ring main pipe (well point pipe diameter is 400 mm, main pipe diameter is 500 mm), main pipe is laid along foundation trench slope, each joint is wrapped with adhesive tape for sealing 3 layers; a4, main pipe is connected with water pumping equipment, to ensure joint is tight.

[0024] S6, ensure that the operation of the dewatering system is smooth, without sudden changes or local water accumulation; Dewatering system operation process: b1, after well pipe burial is completed, power is connected, single pipe is tested for pumping, to check water yield, check whether there is air leakage or clogging; single pipe water yield is ≥1.5 m³ / h, vacuum degree is ≥70 kPa; after no abnormality is found, all well point pipes are started for pumping, to monitor water level drawdown rate; b2, after test pumping is qualified, formal dewatering is started, 2 conditions need to be met before next layer excavation is performed: water level is stable and is 0.5-1.0 m lower than current ditch bottom; there is no obvious seepage in slope, if there is seepage point, well point pipe or pressure grouting sealing needs to be added at the seepage point; b3. Before excavating the next layer of annular trench inward, the well point system of that layer must be started 24 hours in advance. The depth of the well point pipes in the inner trench must be 1.0 to 1.5 m deeper than that in the outer trench to control the deep water level. To avoid mutual interference, the distance between the upper and lower well point pipes must be ≥2.0 m. After each layer of dewatering is completed, the upper well point pipe must be closed to prevent excessive dewatering from causing ground subsidence. b4. Wellpoint drainage is discharged through drainage ditches into a water pool ≥20m away from the foundation pit; b5. Arrange for dedicated personnel to clean the silt and debris at the bottom of the drainage ditch, and regularly clean the well point pipes to prevent filter media from clogging and maintain precipitation efficiency; b6. During the operation of the wellpoint pumping equipment, the operators shall monitor the operation of the equipment to ensure that the pumping equipment is working properly; the daily monitoring of the dewatering system shall record the vacuum degree ≥70kPa, the water output of a single well and the data of the water level observation well; check whether the water level is stably 0.5 to 1.0m below the excavation face; if any abnormality is found, such as a sudden drop in vacuum degree or a sharp decrease in water output, repair shall be carried out immediately.

[0025] S7. Multi-stage excavation to the design elevation of the trench bottom; Each layer must be excavated to a depth of 1.5m. The next layer of foundation trench can only be excavated after the current layer has been dewatered and the slope has been stabilized. During excavation, machinery must be advanced from the excavated section to the unexcavated section to avoid damaging the installed well point pipes. When excavating to 0.3m from the design elevation of the bottom of the trench, manual excavation should be carried out, and the final bottom elevation error should be ≤50mm to avoid over-excavation; after excavating to the design elevation, check whether the foundation soil quality is consistent with the design survey report and whether the flatness meets ≤50mm / 2m. After each layer of the annular foundation trench is excavated, the elevation, slope, and bottom width are re-measured; during manual cleaning, the foundation soil is checked for disturbance. Excavate in layers and blocks, and check the thickness of each layer and the slope of the slope. When manually repairing the slope, ensure that the slope surface is smooth, without steep slopes or over-excavation. If there is over-excavation, backfill with graded crushed stone to the design base elevation and compact it.

[0026] S8. Excavation of the core soil in the middle of the foundation pit, with core soil size deviation ≤ ±5% and position deviation ≤ ±10cm; c1. Before the core soil excavation, confirm that the annular foundation trench has been excavated to the design elevation of the bottom of the foundation trench; the water level of the last stage well point dewatering is stably 0.5m below the bottom of the trench; and there is no displacement, settlement, or abnormal deformation of the foundation pit slope. C2, core soil excavation, the core soil in the middle of the foundation pit is excavated by a excavator, loaded into a truck, and transported by a dump truck, the core soil is divided into four symmetrical areas in the order of "upper left→lower right→upper right→lower left", and single area excavation to the bottom at one time is prohibited; if the core soil height is less than or equal to 3m, the core soil can be excavated in two layers; if the core soil height is greater than 3m, the core soil is excavated in three layers or more, and manual excavation is switched at a distance of 0.2m from the bottom surface of the trench during mechanical excavation; the core soil slope (1:1.05) is reserved during the excavation process, and vertical excavation is prohibited. Core soil stability control, the core soil size needs to meet the support requirements, and instability caused by being too small is avoided, the core soil surface is flat, and interference on the excavation equipment is reduced.

[0027] S9, monitoring and measuring data review and adjustment; Arrange monitoring points such as horizontal convergence and vault subsidence, and real-time master the deformation of surrounding rock, the horizontal convergence and vault subsidence need to be within the allowable range of design, and the deformation rate gradually tends to be stable; According to the monitoring data, the dewatering intensity, excavation footage or support parameters are adjusted to ensure construction safety, and when the data is abnormal, excavation is immediately suspended, the cause is analyzed and reinforcement measures are taken.

[0028] S10, dewatering system removal and plugging, after excavation is completed, the well point pipe and dewatering equipment are gradually removed, the well hole is backfilled and plugged to prevent ground subsidence or underground water seepage.

[0029] In the embodiment: The first step is to measure personnel to release the pile cap boundary line, excavate a ring-shaped foundation trench along the boundary line around the foundation pit, the depth is 1.5m, the slope coefficient is selected to be 1:1.05, and the bottom width can be selected to be 1.5-3m according to the situation; The second step is to install well point pipes in the foundation trench range, which can realize regional rapid dewatering, reduce lateral displacement and settlement of the slope soil body, stabilize the slope, eliminate quicksand, reduce the uplift of the foundation soil, and provide suitable humidity for construction conditions; after completion, the ring-shaped foundation trench is continuously excavated inward, and the drainage well is installed until the pile cap trench bottom design elevation is reached; The third step is to excavate the core soil in the middle of the foundation pit.

[0030] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

[0031] It is also important to note that the term "or" as used herein is intended to mean an inclusive "or," such that "A or B" means any or all of the items listed with no options required to be selected with the item. Further, the terms "comprise," "comprising," "include," "including," and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense that may be implied by use of these terms in some instances. As used herein, the terms "program" and "software" are meant to include, but are not limited to, routines, applications, computer programs, computer code, computer instructions, and the like.

[0032] The foregoing description, for purposes of clarity, describes the present application in terms of specific embodiments thereof. However, it is to be understood that the terminology used, and the contents of the description, are not to be interpreted in a limiting sense. Rather, the contents of the description are to be construed in accordance with the principles of the present application. The present application is well suited to achieving the above-described ends. Accordingly, the present application is deemed to cover all modifications of the present application falling within the scope of the hereto appended claims.

Claims

1. A method for excavating core soil for ring-shaped multi-stage wellpoint dewatering, characterized in that, Including the following steps: S1. Construction preparation, including core soil planning, advanced support, material and equipment inspection upon arrival and technical briefing; S2. Level the site and lay out the edge lines, extending outwards along the edge lines of the pier, reserving the width of the slope projection and operating space; S3. For the excavation of the ring-shaped foundation trench, a segmented and layered excavation method is adopted, dividing the ring-shaped foundation trench into 4 to 6 symmetrical segments to avoid uneven stress on the slope caused by unilateral excavation. The length of each segment is ≤10m. S4. Layout, installation and commissioning of the precipitation system; S5. Calculation of wellpoint spacing and depth, installation and layout, and burial depth of wellpoint pipes penetrating the permeable layer to ensure the dewatering effect; S6. The precipitation system is in operation to ensure a smooth precipitation curve without sudden changes or localized water accumulation. S7. Multi-stage excavation to the design elevation of the trench bottom; S8. Excavation of the core soil in the middle of the foundation pit. Before excavation, confirm that the ring trench has been excavated to the design elevation of the bottom of the foundation trench; the water level of the last stage well point dewatering is stable at 0.5m below the bottom of the trench. S9. Review and adjust monitoring and measurement data; S10. Demolition and sealing of the rainwater system to prevent ground subsidence or groundwater seepage.

2. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S1: Core soil planning involves determining the size, location, and reserved height of the core soil to ensure its stability. Advanced support measures, such as advanced small-diameter pipe grouting and pipe roofing, are implemented in areas with poor surrounding rock to enhance the self-stabilizing capacity of the surrounding rock. Materials and equipment are inspected upon arrival; wellpoint pipes are checked for wall thickness, pipe diameter, and filter pipe pore size; medium and coarse sand is screened for particle size and mud content is measured. Before construction, a technical briefing is conducted, providing detailed and comprehensive technical instructions to all personnel involved in the construction, covering aspects such as construction steps, operating methods, equipment usage, and personnel allocation.

3. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S4: The layout of the dewatering system is designed with a ring-shaped multi-stage well point system based on geological conditions. This system includes well point pipes, a main water collection pipe, and a vacuum pump or submersible pump. The spacing and depth of the well points are determined by calculation to ensure that the dewatering effect covers the excavation area. The dewatering system is installed and commissioned, including drilling wellpoint holes, installing wellpoint pipes and filter pipes, filling filter media, connecting the main water collection pipe to the vacuum pump or submersible pump, conducting test pumping, and checking the system's sealing performance and dewatering effect; monitoring changes in groundwater level, and adjusting dewatering parameters such as pumping intensity and wellpoint spacing until the excavation requirements are met.

4. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S5, the well point spacing is 0.8 to 1.2 m, with the smaller value for sand layers and the larger value for clay layers; the filter pipe must be completely buried in the permeable layer, with a length of 1.2 to 1.5 m, and the bottom of the filter pipe is 0.3 to 0.5 m higher than the bottom of the trench to prevent siltation.

5. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 4, characterized in that, In step S5, the wellpoint pipe is installed and arranged: a1. The water flushing method is adopted, which includes two processes: flushing and pipe laying. When flushing, the flushing pipe is first lifted by the lifting equipment and inserted into the well point position. Then, the high-pressure water pump is turned on to loosen the soil. When flushing, the flushing pipe is inserted vertically into the soil and swings up, down and left and right to aggravate the loosening of the soil. It sinks while flushing to ensure that there is a certain amount of sand filter layer around the well pipe. The flushing depth should be deeper than the bottom of the filter pipe to prevent some soil particles from sinking to the bottom of the pit and touching the bottom of the filter pipe when the flushing pipe is pulled out. a2. After the well is punched, immediately pull out the punch pipe, insert the well point pipe, and quickly fill the space between the well point pipe and the borehole wall with sand filter layer to prevent the borehole wall from collapsing. Fill the sand to 1-1.5m above the top of the filter pipe to ensure smooth water flow. After filling the well point with sand, seal the top of the well point pipe with clay to prevent air leakage. a3. Rubber sealing rings connect the well point pipe and the ring main pipe. The main pipe is laid along the slope of the foundation trench, and each joint is sealed with tape. a4. Connect the main pipe to the pumping equipment.

6. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S6, the precipitation system operates as follows: b1. After the well pipe is installed, turn on the power and perform a single-pipe test pumping to check the water output and whether there is any air leakage or blockage. The single-pipe water output should be ≥1.5m³ / h and the vacuum degree should be ≥70kPa. If there are no abnormalities, start all well pipes for a joint test pumping and monitor the rate of water level drop. b2. After the trial pumping passes, formal dewatering can begin. Two conditions must be met before the next layer of excavation can proceed: the water level must be stable and 0.5–1.0 m below the current trench bottom; and there must be no significant seepage on the slope. b3. Before excavating the next layer of annular trench inward, start the well point system of this layer in advance. The depth of the well point pipes in the inner trench should be 1.0 to 1.5m deeper than that in the outer trench to control the deep water level. To avoid mutual interference, the distance between the upper and lower well point pipes should be ≥2.0m. After each layer of dewatering is completed, the upper well point pipe should be closed to prevent excessive dewatering from causing ground subsidence. b4. During the operation of the wellpoint pumping equipment, the operators shall monitor the operation of the equipment to ensure that the pumping equipment is working properly; the operation monitoring of the dewatering system shall record the water output of each well and the data of the water level observation wells daily; check whether the water level is stable and lower than the excavation face by 0.5 to 1.0m; if any abnormality is found, such as a sudden drop in vacuum or a sharp decrease in water output, repair shall be carried out immediately.

7. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S7, multi-stage excavation is carried out to the design elevation of the trench bottom: Each layer must be excavated to a depth of 1.5m. The next layer of foundation trench can only be excavated after the current layer has been dewatered and the slope has been stabilized. During excavation, machinery must be advanced from the excavated section to the unexcavated section to avoid damaging the installed well point pipes. When excavation reaches 0.3m from the design elevation of the bottom of the trench, manual excavation is carried out, and the final bottom elevation error is ≤50mm to avoid over-excavation; After excavation to the design elevation, check whether the foundation soil quality is consistent with the design survey report and whether the flatness meets the requirement of ≤50mm / 2m.

8. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S8, the core soil in the middle of the foundation pit is excavated: c1. Before the core soil excavation, confirm that the annular foundation trench has been excavated to the design elevation of the bottom of the foundation trench; the water level of the last stage well point dewatering is stably 0.5m below the bottom of the trench; and there is no displacement, settlement, or abnormal deformation of the foundation pit slope. c2. Core soil excavation: The core soil in the middle of the foundation pit shall be excavated by excavator and loaded onto trucks, and transported by dump trucks. It is prohibited to excavate a single area to the bottom at one time. If the core soil height is ≤3m, it can be excavated in 2 layers. If the height is >3m, it can be excavated in 3 layers or more. When mechanical excavation is carried out, manual excavation shall be switched at 0.2m from the bottom surface of the trench. The core soil slope shall be preserved during the excavation process, and vertical excavation is prohibited.

9. The method for excavating core soil for annular multi-stage wellpoint dewatering according to claim 1, characterized in that, In step S9: Set up monitoring points for horizontal convergence and crown settlement to monitor the deformation of the surrounding rock in real time. The amount of horizontal convergence and crown settlement must be within the design allowable range, and the deformation rate should gradually stabilize. Adjust rainfall intensity, excavation depth, or support parameters based on monitoring data to ensure construction safety. If data is abnormal, immediately suspend excavation, analyze the cause, and take reinforcement measures.

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