A method for constructing a gravel pile composite foundation by using a combined squeezing and water replacement technology

Abstract

The present application relates to the technical field of complex soft foundation treatment, and particularly relates to a method for constructing a gravel pile composite foundation by using an extrusion and silt displacement combined water displacement technology, which comprises the following steps: S1, construction preparation and investigation; S2, typical pile site construction and elevation measurement; S3, extrusion and silt displacement, and pipe sinking and row-by-row setting; S4, vibration water displacement and dredging; S5, pile quality inspection; and S6, preloading by heaping. The present application effectively solves the problem that it is difficult to penetrate the upper hard layer of stone under the basin-shaped geological condition, and at the same time, the lower silt is centrally and uniformly treated by using the fluidity of the silt, so that the ground is prevented from being uplifted, and the purpose of overall replacement is achieved. Meanwhile, by combining the change value of the ground elevation, the specific implementation quantity of the two methods, the discharge quantity of the silt and the like, the site flatness is accurately controlled, and the subsequent preloading process is ensured to be smoothly implemented.

Description

Technical Field

[0001] This invention relates to the field of complex soft soil foundation treatment technology, and in particular to a method for constructing a composite foundation of crushed stone piles using a combination of silt removal and water flushing replacement technology. Background Technology

[0002] Artificial land reclamation projects involve creating two seawalls by blasting and squeezing out marine silt from the original sea area. Stone is then directly backfilled between the two seawalls, forming a basin-shaped geological condition with a hard stone layer on the upper and sides and a soft marine silt layer at the bottom. This is referred to as the transition zone between the seawalls. Figure 1 The upper and side hard stone layers reach 5-15m, while the lower soft silt layer is 15-5m deep. Due to the presence of silt in the lower transition zone between cofferdams, the bearing capacity is low. Generally, crushed stone piles are used to replace the lower silt layer, reducing the risk of uneven settlement caused by the lower silt. Conventional crushed stone pile techniques, such as vibratory compaction and vibratory driven crushed stone pile methods, are difficult to penetrate the upper hard stone layer and form piles in the silt layer. If rotary drilling is used to assist in crushed stone pile construction, the cost of rotary drilling is extremely high, making it suitable only for local use and not conducive to large-scale project construction.

[0003] Currently, when crushed stone piles are constructed using the impact method, they are generally used for backfilling geological conditions. When encountering a thick layer of silt, the silt is difficult to compress directly during construction. Due to the impact pile construction, the silt flows and spreads to the surrounding weak areas. As the crushed stone pile construction continues, the area where the silt can spread gradually becomes limited, and the silt flows upward, causing a large area of ​​ground heave, which greatly affects the quality of the project. Summary of the Invention

[0004] To address the challenge of penetrating the hard upper layer of stone in basin-shaped geological conditions, and to utilize the fluidity of silt to centrally treat the lower silt and prevent ground uplift, thus achieving overall replacement, this invention proposes a method for constructing a composite foundation using a combination of silt-squeezing and water-flushing replacement technology. The upper stone layer serves as the working platform, and the transition zone between cofferdams is divided into two construction zones (or proportionally divided into multiple construction areas) for separate construction. Taking two construction zones as an example, one zone with a thicker upper stone layer (where the upper stone has greater weight, preventing silt uplift) is selected. Piles are then driven row by row using hammer-driven pipes, squeezing the silt into the adjacent construction zone with a thinner upper stone layer (where the upper stone has less weight, making silt uplift easier). In the already raised construction area, a bottom-discharge vibratory compaction device is used, employing a vibratory water jetting method to remove the concentrated silt from the bottom. By calculating the number of piles for different processes, the amount of silt discharged is controlled, achieving dynamic adjustment and control of the ground elevation. Ultimately, this creates a large, flat area for crushed stone piles, facilitating the implementation of the unified loading process above. This method reduces the cost of rotary drilling and improves overall construction efficiency, while also avoiding ground "uplift" and reducing the risk of uneven settlement.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for constructing a gravel pile composite foundation using a combination of silt removal and water flushing replacement technology, comprising the following steps: S1. Construction preparation and survey: Before construction, based on the design requirements, key indicators such as pile location, pile diameter, and pile length are determined, and construction parameters such as the diameter of the silt-squeezing and settling pipe, compaction current, and material-carrying reverse insertion height are determined; construction parameters such as the power of the vibratory compaction equipment, compaction current, vibration time, and water pressure are determined.

[0006] S2. Typical pile location construction and elevation measurement: In the basin-shaped transverse section, a typical construction area was selected. Ground elevation measurements were conducted before construction and re-measured after construction. Due to differences in the compaction effect of vibrating soil during construction, the settlement values ​​of the silt-squeezing pipe method and the vibratory water jetting method are different. The theoretical settlement value 'a' for the silt-squeezing pipe method and the theoretical settlement value 'b' for the vibratory water jetting method were obtained (based on on-site construction experience of the two methods, the settlement value 'b' is generally greater than the settlement value 'a'). This value was used for matching analysis between the silt-squeezing volume of the pipe and the change in ground elevation during subsequent large-scale construction, thereby determining the number and scope of construction piles for the silt-squeezing pipe method and the vibratory water jetting method.

[0007] S3. Silt-squeezing and submerging pipes are installed row by row, and silt is squeezed out: S301. Determine the construction equipment parameters. To facilitate construction, use silt-draining pipes with the same diameter as the piles. The pipe diameter can be 800-1000mm, and the pipe-driving equipment is a 10-15t diesel pile driver.

[0008] S302. Analysis and calculation of the construction quantity of the silt-dispatch and pipe-sinking method: Based on the designed pile location map, the total construction area of ​​the pile formation area is S. 总 The total number of piles under construction is n 总 The average area occupied by a single pile is S 单 =S 总 / n 总 The volume of the silt section of a single pile, V0, is equal to the volume of silt replaced by the single pile. The estimated construction area using the silt-displacement and pipe-sinking method is S1, and the construction area using the vibratory water jetting method is S2, for a total construction area of ​​S... 总 =S1+S2. To eliminate the settlement difference between the two processes and ensure a uniform elevation, the additional uplift in zone S2 is equal to the amount of mud discharged from zone S1 due to the driving of the hammer-driven pipe and silt-squeezing piles, i.e., S2×(ba)=n1V0, where S2=S 总 -S1=S 总 -S 单 n1, the merging formula is (S 总 -S 单 n1)×(ba)=n1V0, where: S 总 S represents the total construction area (known). 单 Let n1 be the average footprint of a single pile (known), n1 be the number of crushed stone piles constructed (unknown), a be the theoretical settlement value of the hammer-driven pipe method (obtained from typical construction), b be the theoretical settlement value of the vibratory water jetting method (obtained from typical construction), and V0 be the volume of silt replaced by a single pile (known). Substituting these values ​​into the calculation, we obtain the number of hammer-driven pipe crushed stone piles n1 and the number of vibratory water jetting stone piles n2 = n 总 -n1. Determine the pile locations for different processes based on the calculation results, organize on-site construction, and measure the changes in site elevation in real time during construction. In case of abnormalities, the construction sequence and number of pile locations can be adjusted appropriately based on on-site experience.

[0009] S303. On-site surveying and setting out, according to the planned construction sequence, determine the center point of each row of piles to ensure that subsequent construction is carried out row by row. That is, after the outermost row of piles is driven, the adjacent row of piles will be driven to ensure that the bottom silt is squeezed and flowed to the unconstructed area.

[0010] S304. During construction, a diesel pile driver is used to move the pipe to the center point of the arranged pile position, slowly lower the pipe, place the pipe at the center point and fix it, and the diesel pile driver will drive the pipe with the pile tip to the design depth.

[0011] S305. Use a crane to lift the hopper, fill the filling material at the inlet of the sinking pipe, fill the sinking pipe with crushed stone, pull the sinking pipe out 1-2m, and insert it back into the pipe once with material inside to achieve the purpose of compaction of the pile body. Repeat the above steps until the pile body is completed. Repeat the pile construction steps until the entire area is constructed. During the construction process, measure the changes in ground elevation and make timely adjustments if problems occur.

[0012] S4. Vibratory water flushing and sludge removal: After the completion of the S401 area of ​​the silt-squeezing and sinking crushed stone pile construction, the silt has been squeezed to the adjacent vibratory water jetting crushed stone pile area. The ground elevation of the vibratory water jetting construction area has increased, resulting in a bulging state. Based on field experience, the average elevation of the vibratory water jetting area is 0.5 to 1.5 meters higher than the average elevation of the silt-squeezing and sinking area. The elevation of the construction site will be measured again to check the difference in construction elevation for subsequent construction status analysis.

[0013] S402. Due to the basin-shaped geological conditions, it is difficult to penetrate the hard layer of upper stone. A rotary drilling rig is used to drill the hole, and a steel casing with a diameter of 800-1000m is used to protect the wall to prevent the hole from collapsing during the drilling process. The drilling is continued until the backfilling of the cover layer is completed. The steel casing is retained until the crushed stone pile is constructed to the bottom elevation of the cover layer. Then the steel casing is removed and the pile construction is carried out until the top of the pile is reached.

[0014] S403. The crane slowly places the vibrator at the bottom of the casing, starts the water supply pump with a water pressure of 200-700 kPa, and slowly sinks the vibratory compactor into the silt layer. During the vibratory compaction process, water is kept flowing out of the nozzle. The silt at the bottom is squeezed into the vibratory compaction hole by the pressure of the surrounding soil and carried out of the pile hole by the upward flow of water in the hole. The silt is discharged into the surrounding silt pond for sedimentation by a water pump. As the pile construction continues to discharge silt, the "ground uplift" state gradually disappears and forms a unified elevation with the surrounding area.

[0015] S404, Fill with crushed stone and compact it into piles. Use a loader to transfer the stones to the hopper, then use a crawler crane to lift the hopper and fill the bottom of the hole with crushed stone through the hopper's discharge pipe. The thickness of each fill should not exceed 0.5-1.0m. Use a bottom-discharge vibratory compactor to sink into the fill for compaction and pile making. The compaction current value should not be less than 130-150A, and the vibration time should be 8-15s. The length of each compaction section should be 0.5-1.0m. After compaction, lift the vibratory compactor 0.5-1.0m. When compaction reaches the bottom of the steel casing pilot hole, the steel casing needs to be pulled out section by section. Repeat the above operation to make the pile body section by section from bottom to top until the pile is completed.

[0016] S5. Pile completion quality inspection; After construction is completed, the pile bodies in each block are tested according to the pile forming process and parameters. The density and diameter of the crushed stone piles are tested through dynamic penetration and drilling tests.

[0017] S6. Surcharge preloading; S601. After the construction is completed, on the basis of the crushed stone construction area, the foundation treatment area is subjected to graded loading. The siltation and pipe sinking area and the vibration water flushing area are simultaneously loaded in grades. The loading height is 4.5-6m, and it is divided into 3 levels. The time interval between the graded loading is 30-45 days. The loading height of each level is 1.5-2m. The slope ratio is 1:1.5. The layers are compacted. S602. During the graded loading process, the ground elevation is measured in a timely manner to analyze the loading effect. The loading height is determined by the on-site settlement stability and design calculations to eliminate uneven settlement in different pile construction areas.

[0018] This invention effectively solves the problem of difficulty in penetrating the hard upper layer of stone under basin-shaped geological conditions. Simultaneously, it utilizes the fluidity of silt to centrally and uniformly treat the lower silt, preventing ground heave and achieving overall replacement. By combining calculations of ground elevation changes, the specific implementation quantities of the two methods, and the amount of silt discharged, the site flatness is accurately controlled, ensuring the smooth implementation of subsequent surcharge procedures. During implementation, the silt-squeezing and pipe-driving method is first used to quickly penetrate the pile positions, with piles being constructed row by row towards the designated location to squeeze out silt, greatly improving construction efficiency. Then, the vibratory water jet replacement method is used to uniformly remove the bottom silt from both methods, preventing ground heave and ensuring construction quality. This maximizes the benefits of integrated construction. This invention shortens the overall construction period by approximately 40% and reduces the cost of rotary drilling by approximately 40% through rapid pre-drilling. Theoretical calculations adjust the ground flatness to avoid silt over-discharge, saving approximately 20% of the replacement crushed stone. This invention improves construction efficiency, prevents ground heave, facilitates the implementation of the unified surcharge procedure, and ensures overall construction quality. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of basin-shaped geological conditions.

[0020] Figure 2 A schematic diagram of the planar layout of different pile bodies.

[0021] Figure 3 This is a schematic diagram of the ground uplift process.

[0022] Figure 4 This is a schematic diagram of the surface sludge removal process.

[0023] In the diagram: 1. Blasting and silt-squeezing cofferdam on both sides; 2. Soft silt layer; 3. Hard stone layer; 4. Design mud-rock boundary line; 5. Design ground backfill line; 6. Silt-squeezing pipe-driven crushed stone pile; 7. Vibratory water jetting crushed stone pile; 8. Boundary line between different pile positions; 9. Silt-squeezing pipe; 10. Schematic diagram of pile arrangement sequence; 11. Schematic diagram of ground bulge; 12. Schematic diagram of silt flow direction; 13. Steel casing of upper backfill layer; 14. Vibratory water jetting hole trajectory line. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited to the specific embodiments.

[0025] Example

[0026] In this embodiment, the construction area was directly backfilled with quarried rock without dredging. Two sea-reclamation dikes were formed by blasting and squeezing the soft marine silt layer in the original sea area. Stone was directly backfilled between the two dikes, creating a basin-shaped geological condition with a hard stone layer on the upper part and sides, and a soft marine silt layer at the bottom. The hard stone layer reached a thickness of 10-15m, and the soft marine silt layer was between 10-15m thick.

[0027] A method for constructing a gravel pile composite foundation using a combined silt-displacement and water-flushing technique includes the following steps: S1. Construction preparation and investigation; Before construction, based on the design requirements, key indicators such as pile location, pile diameter, and pile length are determined, and construction parameters such as the diameter of the silt-squeezing and settling pipe, compaction current, and material-carrying reverse insertion height are determined; construction parameters such as the power of the vibratory compaction equipment, compaction current, vibration time, and water pressure are determined.

[0028] S2. Typical pile location construction and elevation measurement; In the "basin-shaped" transverse section direction, a typical construction area was selected. Ground elevation was measured before construction and remeasured after construction. Due to the compaction effect of vibrating soil during construction, the average elevation reduction difference of the silt-squeezing and pipe-sinking method was measured to be 0.4m, and the average elevation reduction difference of the vibratory water jetting method was 0.5m. The obtained data were used for matching analysis between the silt-squeezing volume of the pipe-sinking and pipe-squeezing method and the ground elevation change value during subsequent large-scale construction, thereby determining the construction scope of the silt-squeezing and pipe-sinking method and the vibratory water jetting method.

[0029] S3. The silt-squeezing and submerging pipes are installed row by row and silt is squeezed out S301. Determine the construction equipment parameters. To facilitate construction, use silt-draining pipes with the same diameter as the piles. The pipe diameter can be 800mm, and a 10t diesel pile driver will be used for the pipe driving equipment.

[0030] S302. Analysis and calculation of the number of piles to be constructed using the silt-squeezing and pipe-sinking method: According to the design pile location map, the total construction area of ​​the pile-forming area is 30,000㎡, the total number of piles is 5,555, the average area occupied by a single pile is 5.4㎡, the length of the silt section of a single pile is 10m, the pile diameter is 1.2m, and the volume of the silt section is 11.3m³ (equal to the volume of silt replaced by a single pile). The theoretical settlement value of the typical construction measured hammer-driven pipe-sinking method is 0.3m, and the theoretical settlement value of the vibratory water jetting method is 0.6m. The number of silt-dissipating crushed stone piles to be constructed was calculated using the formula (30000-5.4×n1)×(0.6-0.3)=n1×11.3. The calculated number of silt-dissipating crushed stone piles (n1) was 697, with a construction area of ​​697×5.4≈3760㎡. The number of vibratory water-jetting crushed stone piles to be constructed was 5555-697=4858, with a construction area of ​​4858×5.4≈26240㎡. Based on the calculation results, pile location diagrams for different construction methods were drawn, and on-site construction was organized.

[0031] S303. On-site surveying and setting out, according to the planned construction sequence, determine the center point of each row of piles to ensure that subsequent construction is carried out row by row. That is, after the outermost row of piles is driven, the adjacent row of piles will be driven to ensure that the bottom silt is squeezed and flowed to the unconstructed area.

[0032] S304. During construction, a diesel pile driver is used to move the pipe to the center point of the arranged pile position, slowly lower the pipe, place the pipe at the center point and fix it, and drive the pipe (with the pile tip) to the designed depth.

[0033] S305. Use a crane to lift the hopper, fill the filling material at the pipe opening, fill the pipe with crushed stone, pull the pipe out 2m, and then "reverse insert" it once with material inside to achieve the purpose of compacting the pile body. Repeat the above steps until the pile body is completed. Repeat the pile construction steps until the entire area is completed. During the construction process, measure the changes in ground elevation and make timely adjustments if problems occur.

[0034] S4. Vibratory water flushing and sludge removal; After the completion of the S401 area of ​​the silt-squeezing and sinking crushed stone pile construction, the silt has been squeezed to the adjacent vibratory water-jetting crushed stone pile area. The ground elevation of the vibratory water-jetting crushed stone pile construction area has increased, resulting in a "bulging" state. According to theoretical calculation results, the average elevation of the vibratory water-jetting area is 0.5m higher than the average elevation of the silt-squeezing and sinking area. The elevation of the construction site will be measured again to check the difference in construction elevation for subsequent construction status analysis.

[0035] S402. Due to the "basin-shaped" geological conditions, it is difficult to penetrate the hard layer of upper stone. A rotary drilling rig is used to drill the hole, and an 800m diameter steel casing is used to protect the wall to prevent the hole from collapsing during the drilling process. The drilling is continued until the backfilling of the cover layer is completed. The steel casing is retained until the crushed stone piles are constructed to the bottom elevation of the cover layer. Then the steel casing is removed and the pile construction is carried out until the top of the pile is reached.

[0036] S403. The crane slowly places the vibrator at the bottom of the casing, starts the water supply pump with a water pressure of 700 kPa, and slowly sinks the vibratory compactor into the silt layer. During the vibratory compaction process, water is kept flowing out of the nozzle. The silt at the bottom is squeezed into the vibratory compaction hole by the pressure of the surrounding soil and carried out of the pile hole by the upward flow of water in the hole. The silt is discharged into the surrounding silt pond for sedimentation by the water pump. As the pile construction continues to discharge silt, the "bulging" state of the ground gradually disappears and forms a unified elevation with the surrounding area.

[0037] S404, Fill with crushed stone and compact it into piles. The stones are transported to the hopper using a loader, and then the hopper is lifted by a crawler crane. The crushed stone is then filled into the bottom of the hole through the hopper's discharge pipe, with each filling layer being 0.5m thick. A bottom-discharge vibratory compactor is then used to compact the filling material and form the pile. The compaction current is 130A, and the vibration time is 8 seconds. Each compaction section is 0.5m long. After compaction, the vibratory compactor is raised by 0.5m. When compaction reaches the bottom of the steel casing pilot hole, the steel casing needs to be pulled out section by section. The above operation is repeated to form the pile body section by section from bottom to top until the pile is completed.

[0038] S5. Pile completion quality inspection; After construction is completed, the pile bodies in each block are tested according to the pile forming process and parameters. The density and diameter of the crushed stone piles are tested through dynamic penetration and drilling tests.

[0039] S6. Surcharge preloading; S601. After the construction is completed, on the basis of the crushed stone construction area, the foundation treatment area is subjected to graded loading. The siltation and pipe sinking area and the vibration water flushing area are simultaneously loaded in graded manner. The loading height is 6m, and it is divided into 3 levels with a 30-day interval between the graded loading. The loading height of each level is 2m, the slope ratio is 1:1.5, and the layers are compacted. S602. During the graded loading process, the ground elevation is measured in a timely manner to analyze the loading effect. The loading height is determined by the on-site settlement stability and design calculations to eliminate uneven settlement in different pile construction areas.

[0040] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for constructing a composite foundation of crushed stone piles using a combination of silt removal and water flushing replacement technology, characterized in that, Includes the following steps: S1. Construction preparation and investigation; S2. Typical pile location construction and elevation measurement; S3. Silt-squeezing and submerged pipes are installed row by row, and silt is squeezed out; specifically including: S301. Determine the construction equipment parameters: To facilitate construction, use silt-squeezing pipes with the same diameter as the piles. The pipe diameter is selected as 800-1000mm, and the pipe-squeezing equipment is a 10-15t diesel pile driver. S302. Analysis and calculation of the construction quantity of the silt-dispatch and pipe-sinking method: Based on the designed pile location map, the total construction area of ​​the pile formation area is S. 总 The total number of piles under construction is n 总 The average area occupied by a single pile is S 单 =S 总 / n 总 The volume of the silt section of a single pile, V0, is equal to the volume of silt replaced by the single pile; the estimated construction area for the silt-squeezing and pipe-sinking method is S1, the construction area for the vibratory water jetting method is S2, and the total construction area is S. 总 =S1+S2; To eliminate the settlement difference between the two processes and ensure a uniform elevation, the additional uplift in zone S2 should be equal to the amount of mud discharged from zone S1 due to the driving of the hammer-driven pipe and silt-squeezing piles, i.e., S2×(ba)=n1V0, where S2=S 总 -S1=S 总 -S 单 n1, the merging formula is (S 总 -S 单 n1)×(ba)=n1V0, where: S 总 S represents the total construction area. 单 Let n1 be the average footprint of a single pile, a be the theoretical settlement value obtained from typical construction using the hammer-driven pipe method, b be the theoretical settlement value obtained from typical construction using the vibratory water jetting method, and V0 be the volume of silt replaced by a single pile. Substituting these values ​​into the calculation, we obtain the number of hammer-driven pipe crushed stone piles n1 and the number of vibratory water jetting stone piles n2 = n 总 -n1; Determine the pile positions for different processes based on the calculation results, organize on-site construction, measure the changes in site elevation in real time during construction, and adjust the construction sequence and number of pile positions appropriately based on on-site experience in case of abnormalities. S303. On-site measurement and layout are carried out, and the center point of each pile position is determined row by row according to the planned construction sequence to ensure that subsequent construction is carried out row by row. That is, after the outermost row of pile positions is completed, the adjacent row of pile positions is then driven to ensure that the bottom silt is squeezed and flowed to the unconstructed area. S304. During construction, a diesel pile driver is used to move the pipe to the center point of the arranged pile position, slowly lower the pipe, place the pipe at the center point and fix it, and the diesel pile driver will drive the pipe with the pile tip to the design depth. S305. Use a crane to lift the hopper, fill the filling at the pipe opening, fill the pipe with crushed stone, pull the pipe out 1-2m, insert the pipe with material inside once to achieve the purpose of compacting the pile body, repeat the above steps until the pile body is completed; repeat the pile construction steps until the entire area is constructed, measure the changes in ground elevation during the construction process, and make timely adjustments if problems occur. S4. Vibratory water flushing and sludge removal; S5. Pile completion quality inspection; S6. Surcharge preloading.

2. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The S1 construction preparation and investigation include: before construction, clarifying key indicators such as pile location, pile diameter, and pile length according to design requirements, determining construction parameters such as the diameter of the silt-squeezing and settling pipe, compaction current, and material-carrying reverse insertion height; and determining construction parameters such as the power of the vibratory compaction equipment, compaction current, vibration time, and water pressure.

3. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The construction and elevation measurement of typical S2 pile locations include: selecting a typical construction area in the basin-shaped transverse section direction, measuring the ground elevation before construction, and re-measuring the ground elevation after construction. Due to the compaction effect of vibrating soil during construction, the theoretical settlement value 'a' of the silt-squeezing pipe method and the theoretical settlement value 'b' of the vibratory water jetting method are obtained. The obtained data are used for the matching analysis between the silt-squeezing volume of the pipe and the change in ground elevation during subsequent large-scale construction, thereby determining the construction scope of the silt-squeezing pipe method and the vibratory water jetting method.

4. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The empirical value c is 0.5 to 1.5 m.

5. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The S4 vibratory water flushing and dredging includes: After the completion of the S401 area of ​​the silt-squeezing and sinking crushed stone pile construction, the silt has been squeezed to the adjacent area of ​​the vibratory water-jetting crushed stone pile construction area. The ground elevation of the vibratory water-jetting crushed stone pile construction area has increased, resulting in a bulging state. According to the theoretical calculation results, the average elevation of the vibratory water-jetting area is 0.5 to 1.5 m higher than the average elevation of the silt-squeezing and sinking area. The elevation of the construction site will be measured again to check the difference in construction elevation for subsequent construction status analysis. S402. Due to the basin-shaped geological conditions, it is difficult to penetrate the hard layer of upper stone. A rotary drilling rig is used to drill the hole, and a steel casing with a diameter of 800-1000m is followed to protect the wall and prevent the hole from collapsing during the drilling process. The drilling is continued until the backfilling of the cover layer is completed. The steel casing is retained and removed when the crushed stone pile is constructed to the bottom elevation of the cover layer. Then the pile construction is carried out until the top of the pile is reached. S403. The crane slowly places the vibrator at the bottom of the casing, starts the water supply pump, and the water pressure is 200-700 kPa. The vibratory compactor is slowly sunk into the silt layer. During the vibratory compaction process, water is kept flowing out of the nozzle. The silt at the bottom is squeezed into the vibratory compaction hole by the pressure of the surrounding soil. It is carried out of the pile hole by the upward flow of water in the hole. The silt is discharged into the surrounding silt pond for sedimentation by the water pump. As the pile construction continues to discharge silt, the ground heave gradually disappears and forms a unified elevation with the surrounding area. S404. Fill with crushed stone and compact it to form piles: The stones are transported to the hopper using a loader, and then the hopper is lifted by a crawler crane. The crushed stone is then filled into the bottom of the hole through the hopper's discharge pipe. The thickness of each filling layer should not exceed 0.5 to 1.0 m. A bottom-discharge vibratory compactor is used to sink into the filling layer for compaction and pile making. The compaction current value should not be less than 130A to 150A, and the vibration time should be 8 to 15 seconds. The length of each compaction section should be 0.5 to 1.0 m. After compaction, the vibratory compactor is raised by 0.5 to 1.0 m. When compaction reaches the bottom of the steel casing pilot hole, the steel casing needs to be pulled out section by section. The above operation is repeated to make the pile body section by section from bottom to top until the pile is completed.

6. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The S5 pile quality inspection includes: after construction is completed, the pile body of each block is tested in combination with the pile forming process and parameters. The density and diameter of the crushed stone pile are tested by dynamic penetration test and drilling test.

7. The method for constructing a composite foundation of crushed stone piles using a combined silt-displacement and water-flushing technique according to claim 1, characterized in that, The S6 surcharge preloading includes: S601. After the construction is completed, on the basis of the crushed stone construction area, the foundation treatment area is subjected to graded loading. The siltation and pipe sinking area and the vibration water flushing area are simultaneously loaded in grades. The loading height is 4.5-6m, and it is divided into 3 levels. The time interval between the graded loading is 30-45 days. The loading height of each level is 1.5-2m. The slope ratio is 1:1.

5. The layers are compacted. S602. During the graded loading process, the ground elevation is measured in a timely manner to analyze the loading effect. The loading height is determined by the on-site settlement stability and design calculations to eliminate uneven settlement in different pile construction areas.

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