Method suitable for analyzing drivability of outer core of cement-soil mixing pile of stiff composite pile
By employing differentiated pretreatment of sand layers and precise implantation of core pipe piles, the construction challenges of medium-strength composite piles in deep sand layers in the southwestern mountainous region were solved, improving the quality and bearing capacity of the pile foundation project and achieving the dual goals of cost savings and construction quality improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA MCC5 GROUP CORP LTD
- Filing Date
- 2026-03-27
- Publication Date
- 2026-05-26
AI Technical Summary
In the deep sand layers of the southwestern mountainous region, the construction of rigid composite piles faces challenges such as poor pretreatment, difficulty in implanting core pipe piles, poor adaptability to vertically differentiated sand layers, and difficulty in pile quality testing, which affect the quality and bearing capacity of the pile body.
Differential pretreatment construction of sand layers is adopted, including detailed survey, layered mixing pretreatment and flexible pile quality pre-control, combined with the precise implantation construction of equal core inner core pipe piles. Through guiding devices, layered implantation and resistance control and real-time correction, the coaxiality and verticality of flexible piles and inner core pipe piles are ensured.
It significantly improves the tightness of the bond between the flexible pile and the sand layer and the implantation quality of the inner core pipe pile, ensuring the bearing capacity and construction integrity of the composite pile, and reducing project costs and construction risks.
Smart Images
Figure CN122082425A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pile foundation or foundation treatment technology, and in particular to a method for analyzing the driveability of the outer core of a reinforced composite cement-soil mixing pile. Background Technology
[0002] The mountainous regions of southwestern my country have well-developed river systems, resulting in widespread river sediments, with some areas even containing thick sand layers reaching tens of meters in thickness. These sand layers are generally loosely structured with well-developed pores, and locally contain interlayers of pebbles and gravels. Due to differences in depositional time and environment, the physical and mechanical properties of the sand layers, such as grain size and density, vary significantly vertically, generally exhibiting a loose upper layer that gradually transitions to a medium-dense state downwards, while the grain size gradually coarsens from top to bottom.
[0003] Under the above special geological conditions, pile foundation engineering faces many technical challenges, which are as follows: (1) The side friction and end resistance of piles in deep sand layers are generally low. In order to meet the bearing requirements, longer piles and larger cross-sectional dimensions are required, which directly leads to increased project costs and extended construction period; (2) Pile formation in deep sand layers is difficult. Taking bored cast-in-place piles as an example, hole collapse and diameter reduction are prone to occur during the hole formation stage, making it difficult to effectively guarantee the construction quality of the pile body; (3) If high-strength prestressed pipe piles are used alone, due to the poor matching of pile-soil strength, the pile body often reaches the ultimate bearing state due to excessive settlement or shear failure of the surrounding soil before the strength of the pile body material is fully utilized, resulting in a large waste of the strength of the pile body material. Based on this, stiffened composite piles, which are widely used in soft soil areas, have become the best choice to solve the above problems, and can achieve the dual goals of saving project costs and improving the construction quality of pile foundations.
[0004] The construction process of rigid-flexible composite piles involves first pretreating the sand layer using a cement-soil mixing method to form a flexible pile body. Then, high-strength prestressed concrete pipe piles are inserted into the flexible pile, ultimately forming a new type of rigid-flexible composite pile where the high-strength concrete pipe pile and cement-soil work together to bear the load. However, during the insertion of inner-core pipe piles into deep sand layers, the difficulty of the pipe pile insertion operation increases significantly with increasing insertion depth, coarser sand particle size, and hardening of the cement-soil. If targeted control measures are not taken for the characteristics of sand layers at different depths, construction quality problems such as uncontrollable pile body deviation, difficulty in sinking, pile body cracking, pile head damage, and outer core cracking are likely to occur, seriously affecting the integrity and bearing capacity of the pile body, and consequently causing significant economic losses. Therefore, exploring a construction method suitable for deep and complex sand layers in the southwestern mountainous areas that can achieve efficient and reliable pile formation has become a pressing technical bottleneck in this field. Considering the geological characteristics of deep sand layers in mountainous areas (loose, with large differences in vertical particle size and density, and local inclusions of pebbles and gravel), and the core requirement of "rigid-flexible synergistic bearing capacity" for equal-core stiffness composite piles, the core technical problems that need to be solved in the current construction process are as follows: 1. Poor sand layer pretreatment effect and weak bond between flexible pile and sand layer: The deep sand layer in mountainous areas has well-developed pores and local gravel. Traditional cement-soil mixing pretreatment method is prone to uneven mixing and weak bonding between cement-soil and sand layer, resulting in insufficient bearing capacity of flexible pile and failure to fully exert the "rigid-flexible synergy" effect, which in turn affects the overall bearing performance of composite pile.
[0005] 2. The implantation of inner core pipe piles is difficult and the quality of the pile body is hard to control: As the implantation depth increases, the sand layer becomes coarser and denser, and the strength of the cement soil gradually increases during the hardening process, which leads to a sharp increase in the resistance of pipe pile implantation. Problems such as pile body deviation, difficulty in sinking, pile head damage, and cracking of the outer core cement soil are likely to occur. At the same time, it is difficult to ensure the coaxiality (equal core requirement) of the inner core pipe pile and the flexible pile, which affects the uniformity of the pile body stress.
[0006] 3. Poor adaptability to vertically differentiated sand layers: The sand layer is loose at the top and medium-dense at the bottom, with the particle size gradually increasing from fine to coarse. Traditional construction methods do not adjust construction parameters according to the characteristics of sand layers at different depths, resulting in uneven pretreatment effects and the quality of pipe pile implantation. Problems such as insufficient mixing and obstruction of pipe pile sinking are prone to occur in the coarse-grained sand layer at the bottom.
[0007] 4. Difficulty in pile quality inspection: The geology of deep sand layers in mountainous areas is complex. After the construction of composite piles, it is difficult to accurately inspect the bonding quality of flexible piles and inner core pipe piles, the integrity of the pile body and coaxiality. It is also difficult to detect hidden quality defects such as pile body cracking and outer core tearing in time, which can easily leave safety hazards. Summary of the Invention
[0008] The purpose of this invention is to provide a method for analyzing the driveability of the outer core of a rigid composite cement-soil mixing pile, thereby addressing the above-mentioned shortcomings and solving many technical problems in carrying out pile foundation engineering in loose sand layers.
[0009] This invention is achieved through the following scheme: A method for analyzing the driveability of the outer core of reinforced composite cement-soil mixing piles includes the following steps: Step S1, differentiated pretreatment construction of sand layers, includes pre-construction survey and parameter design, layered mixing pretreatment, and flexible pile quality pre-control steps: Step S2 involves the precise implantation of the equal-core inner core pipe pile, which includes steps such as implantation timing control, equal-core positioning and guidance, layered implantation and resistance control, and real-time correction of pile body deviation.
[0010] In step S1, the pre-construction survey and parameter design specifically involves: firstly, conducting a detailed survey of the sand layer in the construction area to clarify the particle size, density, distribution range and content of gravel and pebbles in sand layers at different depths, dividing the area into three regions: "upper loose fine sand layer", "middle transition sand layer" and "lower medium-dense coarse sand layer", and designing cement-soil mixing parameters accordingly.
[0011] In step S1, the layered mixing pretreatment is specifically as follows: a deep mixing pile machine is used to mix cement and soil according to the principle of "from top to bottom and layered adaptation" to form a flexible pile body; the upper loose fine sand layer adopts the "slow mixing and slow lifting" mode; the middle transition sand layer adopts the "medium speed mixing and uniform speed lifting" mode; the lower medium-dense coarse sand layer adopts the "high pressure mixing + crushing mixing" combined mode, equipped with special alloy crushing teeth, to first crush the gravel and then perform high pressure mixing of cement and soil.
[0012] In step S1, the quality pre-control of flexible piles is specifically as follows: after mixing, the diameter, verticality and cement-soil consistency of the flexible piles are promptly tested to ensure that the uniformity error of the flexible pile diameter is ≤50mm and the verticality deviation is ≤1%.
[0013] In step S2, the timing of implantation is controlled as follows: the inner core pipe pile is implanted within 4 hours after the cement-soil mixing flexible pile is constructed.
[0014] In step S2, the core positioning and guidance are specifically as follows: a guiding device is set at the top of the flexible pile, and the center of the guiding device coincides with the center of the flexible pile to ensure the coaxiality of the inner core pipe pile during implantation; at the same time, a cross-shaped pile tip is installed at the bottom of the pipe pile.
[0015] In step S2, the layered implantation and resistance control are specifically as follows: according to the characteristics of sand layers at different depths, the "layered pressure application and uniform speed implantation" mode is adopted; for the upper loose fine sand layer, the static pile driving method is adopted; for the middle transition sand layer, the "static pile driving + vibration assistance" mode is adopted; and for the lower medium-dense coarse sand layer, the "low-speed static pile driving" mode is adopted.
[0016] In step S2, the pile body deviation is corrected in real time. Specifically, during the implantation process, a total station is used to monitor the verticality of the pipe pile in real time. The verticality is checked every 1m of sinking. If deviation occurs, the implantation is stopped immediately. The pile body verticality and core equipotentiality are corrected by adjusting the guide device and applying reverse pressure to ensure that they meet the design requirements.
[0017] In step S1, specifically, a "slow stirring and slow lifting" mode is adopted, with no less than 3 stirring times, cement content controlled at 18%-22%, stirring speed of 0.8-1.0 m / min, and stirring time of no less than 1.2 min per meter; For the intermediate transition sand layer, a "medium-speed mixing and uniform lifting" mode is adopted, with three mixing cycles, cement content controlled at 16%-18%, mixing speed of 1.0-1.2 m / min, and mixing time of 1.0-1.2 min per meter.
[0018] In step S1, specifically, the lower medium-dense coarse sand layer adopts a combination of "high-pressure mixing + crushing mixing" mode, equipped with special alloy crushing teeth. First, the gravel is crushed and broken down to a particle size ≤20mm by the crushing teeth. Then, cement-soil high-pressure mixing is carried out at a mixing pressure of 1.5-2.0MPa, the cement content is increased to 22%-25%, the number of mixing times is not less than 4, the mixing speed is slowed down to 0.6-0.8m / min, and the mixing time per meter is not less than 1.5min. At the same time, 0.08% to 0.10% of retarder is added to slow down the hardening rate of cement-soil, reduce the resistance when the core pile is implanted, and improve penetration.
[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of this solution are: 1. This invention effectively solves problems such as uneven sand layer pretreatment and weak bonding between flexible piles and sand layers by implementing precise sand layer stratification, differentiated mixing pretreatment and filler matching technology, significantly improving the quality of flexible piles, laying a solid foundation for rigid-flexible co-bearing, and ensuring the construction quality and integrity of the pile body.
[0020] 2. This invention effectively reduces the implantation resistance of inner core pipe piles by implementing flexible pile maintenance control, layered pile planting, and real-time monitoring and correction technology, avoiding various pile quality problems, ensuring equal core requirements, and achieving low carbon emissions.
[0021] 3. This solution can fully leverage the rigid-flexible synergistic bearing advantages of equal-core stiffness composite piles, effectively improve the bearing capacity of composite piles, reduce the incidence of pile quality defects, successfully solve the technical bottleneck of pile foundation engineering in deep sandy layers in mountainous areas, ensure the long-term stability of the project, and has significant engineering application value and promotion prospects. Attached Figure Description
[0022] Figure 1 A schematic diagram of a typical sand layer structure in a mountainous area; Figure 2 Flowchart for the construction of equal-core stiffness composite piles in deep sandy areas; Attached diagram labels: 1. First sand layer; 2. Second sand layer; 3. Third sand layer; 4. Pipe pile; 5. Cement-soil mixing pile. Detailed Implementation
[0023] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.
[0024] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.
[0025] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a predetermined orientation, or be constructed and operated in a predetermined orientation. Therefore, they should not be construed as limitations on this invention.
[0026] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.
[0027] Example 1 like Figure 1 As shown: This invention provides a technical solution: A method for analyzing the driveability of the outer core of reinforced composite cement-soil mixing piles includes the following steps: Step S1, differentiated pretreatment construction of sand layers, includes pre-construction survey and parameter design, layered mixing pretreatment, and flexible pile quality pre-control steps: Step S2, precise implantation of the equal-core inner core pipe pile, includes implantation timing control, equal-core positioning and guidance, layered implantation and resistance control, and real-time correction of pile body deviation. In step S1, the pre-construction survey and parameter design specifically involves: firstly, conducting a detailed survey of the sand layer in the construction area to clarify the particle size, density, distribution range and content of gravel and pebbles in sand layers at different depths, dividing the area into three regions: "upper loose fine sand layer", "middle transition sand layer" and "lower medium-dense coarse sand (containing gravel and pebbles) layer", and designing cement-soil mixing parameters accordingly.
[0028] In step S1, the layered mixing pretreatment is specifically as follows: a deep mixing pile machine is used to mix cement and soil according to the principle of "from top to bottom, layered adaptation" to form a flexible pile body. For the upper loose fine sand layer, a "slow mixing and slow lifting" mode is adopted, with no less than 3 mixing cycles, cement content controlled at 18%-22%, mixing speed 0.8-1.0 m / min, and mixing time per meter no less than 1.2 min; for the middle transition sand layer, a "medium-speed mixing, uniform lifting" mode is adopted, with 3 mixing cycles, cement content controlled at 16%-18%, mixing speed 1.0-1.2 m / min, and mixing time per meter 1.0-1.2 min; for the lower medium-dense coarse sand (including gravel) layer, a "high-pressure mixing + crushing mixing" combined mode is adopted, equipped with a special alloy... The crushing teeth (tooth width 8-10cm, tooth height 5-6cm) are used to crush the gravel and pebbles, breaking them down to a particle size ≤20mm. Then, the cement-soil mixture is subjected to high-pressure mixing (mixing pressure 1.5-2.0MPa), with the cement content increased to 22%-25%. The mixing is repeated at least 4 times, with the mixing speed slowed to 0.6-0.8m / min and the mixing time per meter not less than 1.5min. At the same time, 0.08% to 0.10% of a retarder is added to slow down the hardening rate of the cement-soil mixture, reduce the resistance during the implantation of the core pile, and improve penetration.
[0029] In step S1, the quality pre-control of flexible piles is specifically as follows: after mixing, the diameter, verticality and cement-soil consistency of the flexible piles are promptly tested to ensure that the diameter of the flexible piles is uniform (error ≤ 50 mm) and the verticality deviation is ≤ 1%, so as to avoid the deformation of the flexible piles affecting the subsequent core-equal core implantation of the inner core pipe piles.
[0030] In step S2, the timing of implantation is controlled as follows: the inner core pipe pile is implanted within 4 hours after the cement-soil mixing flexible pile is constructed. At this time, the cement-soil is not completely hardened and has low strength, which can reduce the implantation resistance and avoid the outer core from cracking.
[0031] In step S2, the core positioning and guidance are specifically as follows: a special guiding device is set at the top of the flexible pile, and the center of the guiding device coincides with the center of the flexible pile to ensure the coaxiality of the inner core pipe pile during implantation (core deviation ≤ 30mm); at the same time, a cross-shaped pile tip is installed at the bottom of the pipe pile to reduce the sand layer resistance during implantation and avoid damage to the pile head.
[0032] In step S2, layered implantation and resistance control are specifically implemented as follows: Based on the characteristics of sand layers at different depths, a "layered pressure application, uniform speed implantation" mode is adopted. For the upper loose fine sand layer, static pile driving is used, with the pressure application speed controlled at 1-1.5 m / min to avoid excessive speed causing pile deviation. For the middle transition sand layer, a "static pile driving + vibration-assisted" mode is adopted, with appropriate low-frequency vibration (frequency 20-30 Hz) applied to reduce sand layer resistance. For the lower medium-dense coarse sand (including gravel) layer, a "low-speed static pile driving" mode is adopted, with the pressure application speed controlled at 0.5-1 m / min to ensure the pipe pile sinks smoothly to the design depth.
[0033] In step S2, the pile body deviation is corrected in real time. Specifically, during the implantation process, the verticality of the pipe pile is monitored in real time using a total station. The verticality is checked every 1m of sinking. If deviation occurs (deviation > 1%), the implantation is stopped immediately. The verticality and core equipotentiality of the pile body are corrected by adjusting the guide device and applying reverse pressure to ensure that the verticality and core equipotentiality of the pile body meet the design requirements.
[0034] Example 2 This solution provides a more specific implementation: Step 1: Before construction, conduct a geological survey of the site to determine the composition, thickness, and distribution of the first sand layer 1, the second sand layer 2, and the third sand layer 3.
[0035] Step 2: Construction preparation, placement of the mixer, and preparation of cement slurry.
[0036] Step 3: Measure and mark the center points of each pile.
[0037] Step 4: The mixer is pre-mixed and lowered to the design elevation, and then grouting is injected to raise and mix the mixture.
[0038] Step 5: During the grouting and lifting process to form cement-soil mixing piles 5: For the first sand layer 1, the mixing frequency shall be no less than 3 times, the cement content shall be controlled at 18%-22%, the mixing speed shall be 0.8-1.0 m / min, and the mixing time per meter shall be no less than 1.2 min; for the middle transition second sand layer 2, the mixing frequency shall be 3 times, the cement content shall be controlled at 16%-18%, the mixing speed shall be 1.0-1.2 m / min, and the mixing time per meter shall be 1.0-1.2 min; for the lower medium-dense coarse third sand layer 3, the mixing frequency shall be... Prepare special alloy crushing teeth (tooth width 8-10cm, tooth height 5-6cm) to crush the gravel first, and crush the gravel to a particle size ≤20mm as much as possible. Then, perform high-pressure mixing of cement and soil (mixing pressure 1.5-2.0MPa), increase the cement content to 22%-25%, mix at least 4 times, slow the mixing speed to 0.6-0.8m / min, and mix for at least 1.5min per meter. At the same time, add 0.08% to 0.10% of retarder.
[0039] Step 6: Position the hydraulic pile driver and implant the high-strength prestressed pipe pile 4 within 4 hours after the cement-soil mixing flexible pile 5 is completed.
[0040] Step 7: During the pile driving process, the upper loose fine sand first layer 1 is driven using static pile driving, with the driving speed controlled at 1-1.5 m / min; the middle transition second sand layer 2 is driven using a "static pile driving + vibration-assisted" mode, with appropriate low-frequency vibration (frequency 20-30 Hz); the lower medium-dense coarse sand (containing pebbles and gravel) third sand layer 3 is driven using a "low-speed static pile driving" mode, with the driving speed controlled at 0.5-1 m / min. A total station is used to monitor the verticality of the pipe pile in real time, and verticality correction is performed every 1 m of driving.
[0041] Step 8: During the implantation process, if the length of a single high-strength prestressed concrete pipe pile 4 is insufficient, the piles are spliced together, and the verticality of the piles is corrected using a total station. Repeat step seven until the pipe pile 4 is delivered to the design elevation.
[0042] Step 9: After cutting the piles and filling the core, conduct testing.
[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for analyzing the drivability of an outer core of a cement-soil mixing pile of a stiff composite pile, characterized by, The method comprises the following steps: Step S1, sand layer differentiation pretreatment construction, which comprises the following steps of pre-construction survey and parameter design, layered mixing pretreatment and flexible pile quality pre-control: Step S2, equal core inner core pipe pile precise implantation construction, which comprises the following steps of implantation time control, equal core positioning and guiding, layered implantation and resistance control and pile body deflection real-time correction.
2. The method for analyzing the drivability of the outer core of the cement-soil mixing pile suitable for the stiff composite pile according to claim 1, characterized in that, In step S1, the pre-construction survey and parameter design, specifically: first, the sand layer in the construction area is surveyed in detail, the particle size, density, gravel distribution range and content of the sand layer at different depths are determined, the "upper loose fine sand layer", "middle transition sand layer" and "lower medium dense coarse sand layer" are divided, and the cement-soil mixing parameters are designed accordingly.
3. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 2, wherein In step S1, the layered mixing pretreatment, specifically: a deep mixing pile machine is used, and the cement-soil mixing is carried out according to the principle of "from top to bottom, layered adaptation", to form a flexible pile body; for the upper loose fine sand layer, a "slow mixing and slow lifting" mode is adopted; for the middle transition sand layer, a "medium-speed mixing and uniform lifting and lowering" mode is adopted; for the lower medium dense coarse sand layer, a "high-pressure mixing + broken mixing" combined mode is adopted, a special alloy crushing tooth is provided, the gravel is first crushed, and then the cement-soil high-pressure mixing is carried out.
4. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 3, characterized in that, In step S1, the flexible pile quality pre-control, specifically: after the mixing is completed, the diameter, perpendicularity and cement-soil consistency of the flexible pile are detected in time to ensure that the uniform error of the diameter of the flexible pile is less than or equal to 50 mm, and the perpendicularity deviation is less than or equal to 1%.
5. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 4, wherein In step S2, the implantation time control, specifically: the inner core pipe pile is implanted within 4 hours after the completion of the cement-soil mixing flexible pile construction.
6. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 5, wherein, In step S2, the equal core positioning and guiding, specifically: a guiding device is arranged at the top of the flexible pile, the center of the guiding device coincides with the center of the flexible pile, and the coaxiality of the inner core pipe pile during implantation is ensured; at the same time, a cross pile tip is installed at the bottom of the pipe pile.
7. The method for analyzing the drivability of the outer core of the cement-soil mixing pile of the composite pile according to claim 6, characterized in that, In step S2, the layered implantation and resistance control, specifically: according to the characteristics of the sand layer at different depths, a "layered pressure, uniform speed implantation" mode is adopted; for the upper loose fine sand layer, a static pressure pile method is adopted; for the middle transition sand layer, a "static pressure pile + vibration auxiliary" mode is adopted; for the lower medium dense coarse sand layer, a "low-speed static pressure pile" mode is adopted.
8. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 7, wherein, In step S2, the pile body deflection real-time correction, specifically: during the implantation process, the perpendicularity of the pipe pile is monitored in real time by using a total station, and the detection is carried out once every 1 m of sinking, if deflection occurs, the implantation is stopped immediately, the guiding device is adjusted, and the deflection is corrected by reverse pressure to ensure that the perpendicularity and equal core degree of the pile body meet the design requirements.
9. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 3, wherein, In step S1, specifically, the "slow mixing and slow lifting" mode is adopted, the mixing frequency is not less than 3 times, the cement content is controlled to be 18%-22%, the mixing speed is 0.8-1.0 m / min, and the mixing time per meter is not less than 1.2 min; for the middle transition sand layer, the "medium-speed mixing, uniform lifting and lowering" mode is adopted, the mixing frequency is 3 times, the cement content is controlled to be 16%-18%, the mixing speed is 1.0-1.2 m / min, and the mixing time per meter is 1.0-1.2 min.
10. The method for analyzing the drivability of the outer core of the cement-soil mixing pile according to claim 3, wherein, In step S1, specifically, the lower medium-dense coarse sand layer adopts a combination of "high-pressure mixing + crushing mixing" mode, equipped with special alloy crushing teeth. First, the gravel is crushed and broken down to a particle size ≤20mm by the crushing teeth. Then, cement-soil high-pressure mixing is carried out at a mixing pressure of 1.5-2.0MPa, the cement content is increased to 22%-25%, the number of mixing times is not less than 4, the mixing speed is slowed down to 0.6-0.8m / min, and the mixing time per meter is not less than 1.5min. At the same time, 0.08% to 0.10% of retarder is added to slow down the hardening rate of cement-soil, reduce the resistance when the core pile is implanted, and improve penetration.