A method for constructing a composite foundation of crushed stone variable diameter piles using geosensing technology

Abstract

This invention relates to the field of complex soft soil foundation treatment technology, and particularly to a method for constructing a composite foundation of crushed stone variable diameter piles using geosensing technology. The method includes: S1, construction preparation and investigation; S2, drilling and sampling at typical pile locations; S3, driving the driven pipe with a tip and collecting penetration data; S4, analyzing the penetration data of the driven pipe; S5, removing the tip of the driven pipe; S6, segmented filling of the lower silt layer and multiple hammer blows; S7, segmented filling of the upper backfill layer and fewer hammer blows; S8, pile diameter and bearing capacity testing. This invention reduces pile diameter waste in the stone layer by approximately 56%, shortens the overall construction period by approximately 40% through a rapid drilling method, ensuring both the effectiveness of the large-diameter crushed stone pile composite foundation in the silt layer and reducing material waste in the crushed stone pile body in the stone layer, thus guaranteeing overall construction quality.

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 variable diameter piles using geological sensing technology. Background Technology

[0002] Artificial land reclamation projects involve directly backfilling stones onto the existing marine silt layer, creating a large-scale, wave-shaped geological condition with a hard upper layer of stone and a soft lower layer of marine silt (hereinafter referred to as "stone-silt" geological condition, with the hard upper stone layer reaching 10-20m). During the backfilling process, the stone and silt mix, forming irregular "stone interlayers" at the boundary between them. Conventional crushed stone pile techniques, such as vibratory compaction and vibratory driven stone pile methods, struggle to penetrate the hard upper stone layer and form piles in the silt layer. Furthermore, conventional crushed stone pile techniques cannot identify the "geological condition change points" between the stone and silt layers, requiring the use of fixed construction parameters for the silt layer for overall pile construction. However, the high bearing capacity of the stone layer eliminates the need for treatment, leading to a waste of resources through "ineffective treatment" of the stone layer and significantly increasing the amount of crushed stone used in the pile construction.

[0003] Currently, when pile foundations are formed using impact drilling, it is generally used for backfill soil geological conditions. However, when encountering soft base layers such as silt, the shrinkage of the silt makes drilling difficult. Furthermore, existing pile-forming techniques do not utilize sensing technology during the drilling process, especially in large-area pile group construction. This makes it impossible to quickly determine layered geological conditions and to effectively treat weak geological layers through the loose-pile effect of crushed stone piles. Summary of the Invention

[0004] To address the challenge of penetrating the hard upper layer of stone in "stone above, mud below" geological conditions, and to solve the problem of small-diameter crushed stone piles in stone layers and large-diameter crushed stone piles in mud layers, this invention proposes a method for constructing a composite foundation of crushed stone variable-diameter piles using geosensing technology. The upper stone layer serves as the working platform, and a pile hammer is used to drive a pipe with a pointed tip to the designed pile bottom position. During the penetration process, a digital system collects the penetration depth of each driven pipe, generating an in-situ "time-depth" penetration velocity curve for judging geological conditions at different depths. When the driven pipe reaches the designed bottom elevation, the separate pointed tip at the bottom is removed, forming a hollow filling channel inside the pipe. Based on the geological conditions at different depths determined during the driven pipe process, piles of different diameters are formed using the number of hammer blows inside the pipe. The silt layer is formed into a large-diameter pile through "multiple hammering inside the pipe", while the hard layer, including the upper stone covering layer, stone interlayer, and clay layer, is formed into a small-diameter pile through "few hammering inside the pipe". In the end, a "variable diameter" crushed stone pile composite foundation is formed, which greatly reduces the amount of crushed stone used in the pile body of the backfill layer.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for constructing a composite foundation of crushed stone variable diameter piles using geosensing technology, comprising the following steps:

[0006] S1. Construction preparation and investigation;

[0007] S2. Sampling and analysis of typical pile locations;

[0008] S3. Drilling and penetration data acquisition of the pipe tip;

[0009] S301. Determine the construction parameters. The diameter of the driven pipe should be 600–800 mm to ensure the diameter of the construction pile. To ensure the driven pipe is quickly driven into the upper stone backfill layer, a detachable pipe tip should be installed at the bottom of the driven pipe to reduce resistance during the driving process. The spacing between the crushed stone piles should be 1.0–3.0 m, the pile diameter in the backfill layer should be 600–800 mm, the pile diameter in the silt layer should be 1000–1200 mm, and the pile length should be 15–25 m.

[0010] S302. Before construction, a depth sensor is installed on the upper part of the immersed tube. During the process of driving the immersed tube with a diesel pile hammer, the time and depth of each tube penetration are collected for subsequent analysis of the penetration depth data of immersed tubes in different strata.

[0011] S303. Before driving the pipe, the center point of the pile position is determined by measurement and layout. A crane is used to place the split pipe tip at the bottom of the pipe onto the pile point and fix it with the surrounding soil. A diesel pile driver is used to move the pipe above the pipe tip and slowly lower the pipe to combine the pipe and the pipe tip.

[0012] S304. Start the diesel pile driver and drive the pipe with the pile tip to the designed pile depth. During the driving process, pay attention to the penetration of each drive. When the penetration changes suddenly, it means that the pipe has entered a different geological layer. When the design pile position bottom elevation is reached, stop driving and move the pile driver away.

[0013] S4. Analysis of immersed tube penetration data;

[0014] S401. Through sensors and a digital platform, data on the time, depth, and number of times each tunnel boring is collected, forming a statistical table of time-number-depth data for in-situ tunnel boring of the pile body. The statistical data is plotted as a time-depth curve of the tunnel boring process, and the vertical change of the strata can be displayed through the curve.

[0015] S402, including the upper backfill stone layer, stone interlayer, and clay layer, is a hard layer where each pipe run has a smaller penetration depth and slower penetration speed, resulting in a gentler curve. The lower silt layer has a larger penetration depth and faster penetration speed, resulting in a steeper curve. The inflection point between these two curves indicates a change in geological conditions. By combining the drilling and sampling results from typical pile locations in the early stages, a matching relationship between penetration depth and soil type is established. This allows for the assessment of different geological conditions during formal construction, facilitating the selection of specific construction parameters under varying geological conditions.

[0016] S5. Remove the tip of the submerged tube;

[0017] S6. The lower silt layer is filled in sections and hammered multiple times;

[0018] S601. Use a crane to lift the hopper and fill the filling at the pipe opening. Each filling height is 2-4m, and the pipe is pulled out 1-2m.

[0019] S602. As the pipe is pulled out, the stones inside the pipe fall into the silt layer. The bottom stones are then tamped with a columnar hammer inside the pipe to expand the diameter of the pile in the silt layer. The number of tamping blows is 4 to 6. The tamping depth is measured. The diameter of the expanded pile is calculated according to the volume method. The number of tamping blows is adjusted appropriately based on the calculated pile diameter. The specific method is as follows: The volume of the filling material is calculated using formula (1):

[0020] (1)

[0021] Where: V is the volume of primary filler, d0 is the diameter of the submerged pipe, and h0 is the height of the stone material inside the pipe;

[0022] The pile diameter is calculated using formula (2):

[0023] (2)

[0024] Where: V is the volume of primary filling material, d1 is the pile diameter, and h1 is the height of the stone material after compaction;

[0025] When the pile diameter does not meet the requirements, the stone material inside the pipe is further tamped by using a cylindrical hammer inside the pipe to make it sink. Each tamping blow will sink the stone material by 8-20cm. After tamping, the pile diameter is recalculated based on the height of the stone material after sinking, until the requirements are met.

[0026] Repeat the above steps until the silt section of the pile body is completed; the selected column hammer parameters include: pile body diameter 1.0-1.2m, column hammer weight 3-7t, drop height 10-20m, and number of tamping blows 4-6.

[0027] S7. The upper backfill layer is filled in sections with fewer hammer blows;

[0028] S701. Based on the judgment curve at the point of geological condition change, when the pipe extraction height reaches the hard layer including the upper stone layer, stone interlayer, and clay, filler is introduced into the pipe through the hopper, and the bottom crushed stone is tamped with a column hammer inside the pipe, with 1 to 2 tamping times to increase the density of the pile body and form a small diameter pile body until the pile is completed, and the driven pipe is extracted; the selected column hammer parameters include: column hammer weight 3 to 7t, drop height 10 to 20m, segmented pipe extraction height 2 to 4m, and 1 to 2 tamping times.

[0029] S702. After the crushed stone piles are completed, use a column hammer to compact the pile location 1-2 times. Continue to fill the settlement area after compaction. After filling, level and compact the pile 1-2 times.

[0030] S8. Pile diameter and bearing capacity testing.

[0031] 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, and determining construction parameters such as the diameter of the driven pipe, the type of columnar hammer inside the pipe, and the hammering height inside the pipe.

[0032] The drilling sampling and analysis of the typical pile locations of S2 include:

[0033] According to the geological survey report, typical pile locations were selected for drilling and sampling. The drilling and sampling depth was greater than the designed pile length. Geotechnical tests were conducted to determine the soil type at different depths, which was used for the matching analysis of the penetration depth and soil type in the subsequent tunneling process.

[0034] The step S5 involves removing the tip of the submerged tube, including:

[0035] S501. The vibratory pipe puller with a lifting hook is aligned with the installed pipe. The vibratory pipe puller connects to the pipe wall and pulls the pipe out by 0.5 to 1.0m, reducing the tightness between the pipe and the tip.

[0036] S502. The reserved steel wire rope connecting the pipe tip is lifted by the lifting hook. The assembled pipe tip is separated from the whole circle into a semi-circle under the force. The valve pile tip is taken out inside the immersed pipe to form a hollow immersed pipe material unloading channel.

[0037] The testing of the S8 pile diameter and bearing capacity includes:

[0038] After construction is completed, each segment is tested based on the number of pile segments and the settlement status. Through dynamic penetration and drilling tests, the density and diameter of the crushed stone piles are tested. The matching relationship between the hammer impact energy in the hole and the diameter expansion capacity of the crushed stone pile is further analyzed to provide technical parameters for subsequent hammer-driven diameter expansion pile construction.

[0039] This invention effectively solves the problem of difficulty in penetrating the hard upper layer of stone under "stone above, mud below" geological conditions. It also addresses the challenge of varying pile diameters, where the crushed stone piles in the stone layer have small diameters while those in the silt layer have large diameters. This reduces the amount of crushed stone used in pile construction. Furthermore, by combining digital penetration depth acquisition technology, the location of each pile at the "geological condition change point" is identified, ensuring the quality of the variable-diameter crushed stone piles. During implementation, a hammer-driven pipe is used to quickly penetrate the pile location, and the "pipe tip" is flexibly removed to create a channel for filling the crushed stone piles in the lower silt layer. The silt layer is filled with this material and undergoes multiple hammer blows within the pipe to form a large-diameter pile. The stone and clay layers are filled with material through fewer hammer blows within the pipe to form a small-diameter pile, thus achieving the required diameter variation for the crushed stone piles. This method reduces pile diameter waste in the stone layer by approximately 56% and shortens the overall construction period by approximately 40% through rapid drilling. It ensures both the effectiveness of the large-diameter crushed stone pile composite foundation in the silt layer and reduces material waste in the stone layer, guaranteeing overall construction quality. Attached Figure Description

[0040] Figure 1 This is a diagram illustrating the process of compacting and expanding gravel piles in a silt layer.

[0041] Figure 2 This is a schematic diagram of the pile layout.

[0042] Figure 3 This is a schematic diagram of the cross-sectional form of a composite foundation.

[0043] Figure 4 This is a time-depth curve of the tunnel immersion process.

[0044] In the diagram: 1. Upper backfill stone layer, 2. Silt interlayer, 3. Stone interlayer, 4. Lower silt layer, 5. Clay layer, 6. Separated pipe tip, 7. Sinking pipe, 9. Expanded diameter crushed stone pile, 10. Unexpanded diameter crushed stone pile. Detailed Implementation

[0045] 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.

[0046] Example 1

[0047] In this embodiment, the construction area was directly backfilled with quarry rock without dredging. By directly backfilling the "marine silt layer" in the original sea area, a special geological condition was formed, with a large-scale hard rock layer on top and a soft marine silt layer below, hereinafter referred to as the "rock-silt-top" geological condition. The upper hard rock layer reached 10-20m in thickness. The thickness of the lower soft silt layer was mainly between 5-15m, forming an irregular "rock interlayer" at the junction of the rock and silt.

[0048] A method for constructing a composite foundation for gravel piles with varying diameters using geosensing technology includes the following steps:

[0049] S1. Construction preparation and investigation;

[0050] Before construction, based on the design requirements, the key indicators of pile location, pile diameter, and pile length are clarified, and the construction parameters of pipe diameter, internal cylindrical hammer type, and internal hammering height are determined.

[0051] S2. Sampling and analysis of typical pile locations;

[0052] According to the geological survey report, typical pile locations were selected for drilling and sampling. The drilling and sampling depth was greater than the designed pile length. Geotechnical tests were conducted to determine the soil type at different depths, which was used for the matching analysis of the penetration depth in the subsequent pipe sinking process. The soil samples from top to bottom were: upper stone backfill layer, silt interlayer, stone interlayer, lower silt layer, and clay layer.

[0053] S3. Drilling and data acquisition of the submerged tube with the pipe tip;

[0054] S301. Determine the construction parameters. The diameter of the driven pipe is selected to be 800mm to ensure the diameter of the construction pile. To ensure the driven pipe is quickly driven into the upper stone backfill layer, a detachable pipe tip is installed at the bottom of the driven pipe to reduce resistance during the driving process. The spacing between the crushed stone piles is 2.5m, the pile diameter is 800mm in the backfill layer and 1200mm in the silt layer, and the pile length is 25m.

[0055] S302. Before construction, depth sensors are installed on the upper part of the immersed tube. During the driving of the immersed tube with a diesel pile hammer, the time and depth of each penetration are collected in real time. For the first driving, typical pile locations are selected for sampling to establish a matching relationship between penetration depth and soil type; the penetration depth is smaller in backfill layers and larger in silt layers. Subsequent construction at normal pile locations will use this matching relationship between the penetration depth of the typical pile location and the soil type to facilitate the judgment of different geological conditions during the driving process.

[0056] S303. Before driving the immersed tube, the center point of the pile position is determined by measurement and layout. A crane is used to place the split pipe tip at the bottom of the immersed tube onto the pile point and fix it with the surrounding soil. A diesel pile driver is used to move the immersed tube above the pipe tip and slowly lower the immersed tube to combine the immersed tube and the pipe tip.

[0057] S304. Start the diesel pile driver to drive the pipe (with pile tip) to the designed pile depth. During the driving process, pay attention to the penetration depth of each drive. When the penetration depth suddenly increases, it indicates that the pipe has entered the silt layer. Stop driving when the bottom elevation of the designed pile position is reached and move the pile driver away.

[0058] S4. Immersed tube penetration induction data analysis includes:

[0059] S401. Using sensors and a digital platform, collect data on the time, depth, and number of insertions for each tunnel section, generating a statistical table of in-situ tunnel section insertion time-number-depth data as shown in Table 1. This statistical data will then be used to create a time-depth curve for the tunnel section insertion process. Figure 4 As shown, this is used to determine the vertical geological conditions of each pile.

[0060] Table 1. Statistical Table of In-situ Piling "Sinking Time - Number of Times - Depth"

[0061]

[0062] S402. Because the upper backfill layer, including the stone interlayer and the hard clay layer, has a smaller penetration depth and slower penetration speed each time the tube is driven, the curve is relatively gentle. The lower silt layer has a larger penetration depth and faster penetration speed each time the tube is driven, the curve is relatively steep. Therefore, the inflection point of the two curves is the "location of geological condition change". Combined with the soil drilling and sampling situation before the tube is driven, the geological conditions of each segment are judged.

[0063] S5. Removing the tip of the immersed tube includes:

[0064] S501. The vibratory pipe puller with a lifting hook is aligned with the installed pipe. The vibratory pipe puller connects to the pipe wall and pulls the pipe out 0.5m to reduce the tightness between the pipe and the tip.

[0065] S502. The reserved steel wire rope connecting the pipe tip is lifted by the lifting hook. The assembled pipe tip is separated from the whole circle into a semi-circle under the force. The valve pile tip is taken out inside the immersed pipe to form a hollow immersed pipe material unloading channel.

[0066] S6. Segmented filling of silt layer, multiple hammerings;

[0067] S601. Use a crane to lift the hopper and fill the filling at the pipe opening. Each filling height is 2m, and the pipe is pulled out by 1m.

[0068] S602. As the pipe is pulled out, the stones inside the pipe fall into the silt layer. The bottom stones are then tamped with a columnar hammer inside the pipe to expand the diameter of the pile in the silt layer. The number of tamping blows is 4 to 6. The tamping depth is measured. The diameter of the expanded pile is calculated according to the volume method. The number of tamping blows is adjusted appropriately based on the calculated pile diameter. The specific method is as follows: The volume of the filling material is calculated using formula (1):

[0069] (1)

[0070] Where: V is the volume of primary filler, d0 is the diameter of the submerged pipe, and h0 is the height of the stone material inside the pipe;

[0071] The pile diameter is calculated using formula (2):

[0072] (2)

[0073] Where: V is the volume of primary filling material, d1 is the pile diameter, and h1 is the height of the stone material after compaction;

[0074] When the pile diameter does not meet the requirements, the stone material inside the pipe is further tamped by using a cylindrical hammer inside the pipe to make it sink. Each tamping blow will sink the stone material by 8-20cm. After tamping, the pile diameter is recalculated based on the height of the stone material after sinking, until the requirements are met.

[0075] Repeat the above steps until the silt section of the pile is compacted. The parameters of the column hammer used in this process are as follows: pile diameter 1.2m, column hammer weight 3.6t, drop height 10m, and 6 blows.

[0076] S7. Segmented filling of stone layer, with fewer hammer blows:

[0077] S701. Based on the "geological condition change" curve, when the pipe extraction height reaches the stone layer (including the upper stone layer, stone interlayer, and hard clay layer), filler is introduced into the pipe through the hopper. A columnar hammer inside the pipe is used to tamp the bottom gravel once to increase the pile density and form a small-diameter pile. This process continues until the pile is complete, at which point the pipe is removed. The parameters for the columnar hammer used in this process include: a 3.6t weight, a 10m drop height, a 2m segmented pipe extraction height, and one tamping blow.

[0078] S702. After the crushed stone piles are completed, use a columnar hammer to compact the pile location once. Continue filling the settlement area after compaction. After filling, level and compact the pile once.

[0079] The above-mentioned process of compacting and expanding the crushed stone piles in the silt layer is shown in the diagram. Figure 1 As shown in the diagram. A schematic diagram of the pile layout after construction is shown below. Figure 2 .

[0080] S8. Pile diameter and bearing capacity testing:

[0081] S801. After construction is completed, each segment is tested according to the number of pile segments and the settlement status. The density and diameter of the crushed stone pile are tested through dynamic penetration and drilling tests.

[0082] S802. Based on the test results, compare the theoretically calculated pile diameter with the actual pile diameter, further analyze the matching relationship between the tamping energy of the in-hole hammer and the diameter expansion capacity of the crushed stone pile, and form a test report to provide technical parameters for subsequent hammer-driven diameter expansion pile construction.

[0083] Figure 3 This is a schematic diagram of the cross-sectional shape of the composite foundation after using the above construction method.

[0084] Example 2

[0085] In this embodiment, the construction steps of the method for constructing a composite foundation for gravel variable-diameter piles using geosensing technology are the same as in Embodiment 1, except that:

[0086] S301. Determine the construction parameters: the diameter of the sinking pipe is 600mm, the pile spacing of the crushed stone piles is 1.0m, the pile diameter is 600mm in the backfill layer and 1000mm in the silt layer, and the pile length is 15m.

[0087] S601. Use a crane to lift the hopper and fill the filling at the pipe opening. Each filling height is 4m, and the pipe is pulled out 2m.

[0088] S602. The parameters of the column hammer selected in this process include: 1.0m diameter of the tamping pile, 7t weight of the column hammer, 20m drop height, and 4 tamping blows.

[0089] S7. Segmented filling of stone layer, with fewer hammer blows:

[0090] S701, 2 tamping blows. The parameters of the column hammer used in this process include: column hammer weight 3t, drop height 20m, segmented pipe pulling height 4m, and 2 tamping blows.

[0091] S702. After the crushed stone piles are completed, use a columnar hammer to compact the pile location twice. Continue filling the settlement area after compaction. After filling, level and compact the pile twice.

[0092] Example 3

[0093] In this embodiment, the construction steps of the method for constructing a composite foundation for gravel variable-diameter piles using geosensing technology are the same as in Embodiment 1, except that:

[0094] S301. Determine the construction parameters: the diameter of the sinking pipe is 700mm, the pile spacing of the crushed stone piles is 3.0m, the pile diameter in the backfill layer is 700mm, the pile diameter in the silt layer is 1100mm, and the pile length is 20m.

[0095] S601. Use a crane to lift the hopper and fill the filling at the inlet of the tube. Each filling height is 3m, and the tube is pulled out 1.5m.

[0096] S602. The parameters of the column hammer used in this process include: 1.1m diameter of the tamping pile, 5.3t weight of the column hammer, 14m drop height, and 5 tamping blows.

[0097] S7. Segmented filling of stone layer, with fewer hammer blows:

[0098] S701. The parameters of the column hammer selected in this process include: weight of 7t, drop height of 15m, and segmented pipe pulling height of 3m.

[0099] 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 gravel variable-diameter pile composite foundation by geological induction technology, characterized in that, The method comprises the following steps: S1, construction preparation and investigation; S2, drilling sampling and analysis at typical pile position; S3, data collection of pipe tip sinking pipe and penetration; S301, construction parameters are determined, the pipe diameter of the sinking pipe is selected as 600-800 mm to ensure the diameter of the construction pile, the detachable pipe tip is installed at the bottom of the sinking pipe to reduce the resistance during the sinking pipe setting process, the pile spacing of the gravel pile is 1.0-3.0 m, the pile diameter in the backfill layer is 600-800 mm, the pile diameter in the silt layer is 1000-1200 mm, and the pile length is 15-25 m; S302, a depth sensor is installed on the upper part of the sinking pipe before construction, the time and depth of each sinking pipe penetration during the sinking pipe setting process by the diesel pile hammer are collected, and the data are used for subsequent analysis of the sinking pipe penetration data in different strata; S303, before the sinking pipe setting, the center point of the pile position is determined by measuring and setting out, the detachable pipe tip at the bottom of the sinking pipe is placed on the pile point by using a crane, the pipe tip is fixed through the surrounding soil, the sinking pipe is moved above the pipe tip by using the diesel pile hammer, the sinking pipe and the pipe tip are combined by slowly lowering the sinking pipe; S304, the sinking pipe with the pipe tip is set to the designed pile depth by starting the diesel pile hammer, the penetration during the setting process is observed, when the penetration suddenly changes, it indicates that the sinking pipe enters different geological layers, the setting is stopped when the sinking pipe is set to the designed pile position bottom elevation, and the pile hammer is removed; S4, sinking pipe penetration data analysis; S401, the time, depth and frequency data of each sinking pipe penetration are collected through the sensor and digital platform, the in-situ sinking pipe time-frequency-depth data table of the pile body is formed, the statistical data are drawn into the sinking pipe process time-depth curve, and the vertical change state of the stratum is displayed through the curve; S402, the penetration of the sinking pipe in the hard layer including the upper backfill stone layer, stone interlayer and clay layer is small, the penetration speed is slow, the curve is slow, the penetration of the sinking pipe in the lower silt layer is large, the penetration speed is fast, the curve is steep, and the turning point of the two curves is the change position of the geological conditions; in combination with the drilling sampling results of the typical construction pile position, the matching relationship between the penetration and the soil type is formed, so that the different geological conditions are judged through the penetration state during the formal construction, and the specific construction parameters are selected under different geological conditions; S5, the sinking pipe tip is taken out; S6, the lower silt layer is filled in sections and hammered for multiple times; S601, a hoist bucket is lifted by using a crane, the material is filled in the upper part of the sinking pipe, the filling height is 2-4 m each time, and the sinking pipe is pulled out by 1-2 m; S602, as the sinking pipe is pulled out, the stone in the pipe falls into the silt layer, the bottom gravel is rammed by using the columnar hammer in the pipe, the purpose of the silt layer pile diameter expansion is achieved, the ramming frequency is 4-6 times, the ramming settlement depth is measured, the pile diameter after the diameter expansion is calculated according to the volume method, the ramming frequency is adjusted in combination with the calculated pile diameter, and the specific method is as follows: the filling volume is calculated through formula (1): （1） in the formula, V is the filling volume, d0 is the sinking pipe diameter, and h0 is the stone height in the pipe; the pile diameter after the pile forming is calculated through formula (2): （2） in the formula, V is the filling volume, d1 is the pile diameter after the pile forming, and h1 is the stone height after the ramming settlement. When the pile diameter does not meet the requirements, further use the in-pipe column hammer to ram the in-pipe stone to sink, each time ramming sinking 8-20 cm, after ramming, calculate the pile diameter again through the height of the stone after sinking, until the requirements are met; Repeat the above steps until the silt section ramming pile body is completed; The selected column hammer parameters include: ramming pile body diameter 1.0-1.2 m, column hammer weight 3-7 t, drop height 10-20 m, and ramming number 4-6 times; S7, the upper backfill layer is filled in sections and hammered a few times; S701, in combination with the judgment curve of the change of the geological conditions, when the pipe pulling height reaches the hard layer including the upper stone layer, the stone interlayer and the clay, fill the material into the pipe through the hopper, use the in-pipe column hammer to ram the bottom gravel, the ramming number is 1-2 times, increase the compactness of the pile body, form a small-diameter pile body, and until the pile forming is completed, the pipe is removed; The selected column hammer parameters include: column hammer weight 3-7 t, drop height 10-20 m, section pipe pulling height 2-4 m, and ramming number 1-2 times; S702, after the gravel pile forming is completed, use the column hammer to supplement the ramming at the pile position, supplement the ramming 1-2 times, continue to fill the material at the settlement position, complete the filling, and then flatten and roll, and the rolling is 1-2 times; S8, pile diameter and bearing capacity detection.

2. The method for constructing a gravel variable-diameter pile composite foundation by geological induction technology according to claim 1, characterized in that, The S1 construction preparation and investigation includes: before construction, according to the design requirements, clearly the key indicators of the pile position, pile diameter and pile length, determine the pipe sinking diameter, in-pipe column hammer model and in-pipe hammering height construction parameters.

3. The method for constructing the gravel variable-diameter pile composite foundation by the geological induction technique according to claim 1, characterized in that, The S2 typical pile position drilling sampling and analysis includes: According to the geological exploration report, select the typical pile position for drilling sampling, the drilling sampling depth is greater than the design pile length, judge the soil body category at different depths through the soil test, and the matching analysis of the subsequent pipe sinking process penetration depth and soil body category is used.

4. The method for constructing a gravel variable-diameter pile composite foundation by geological induction technology according to claim 1, characterized in that, The S5 taking out the pipe sinking pipe tip includes: S501, the vibration pipe pulling machine with a lifting hook is aligned with the pipe sinking that has been punched, the vibration pipe pulling machine is connected with the pipe sinking wall, the pipe sinking is pulled out 0.5-1.0 m; S502, the reserved steel wire rope connected with the pipe tip is lifted through the lifting hook, the force of the assembled pipe tip is separated from the whole circle into a semicircle, the flap pile tip is taken out in the pipe sinking, and a hollow pipe sinking discharging channel is formed.

5. The method for constructing the gravel variable-diameter pile composite foundation by the geological induction technique according to claim 1, characterized in that, The S8 pile diameter and bearing capacity detection includes: S801, after the construction is completed, in combination with the pile forming section number and ramming situation, each section is detected respectively, the gravel pile compactness and the pile diameter are detected through the dynamic penetration and the drilling test; S802, according to the detection results, compare the theoretical calculation pile diameter, further analyze the matching relationship between the in-hole ramming hammer ramming capacity and the gravel pile expansion capacity, form a detection report, and provide technical parameters for the subsequent hammering expansion pile forming.

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