A cement mixing pile forming method for high water content soft soil foundation

Abstract

This invention discloses a method for constructing cement-mixed piles in soft soil foundations with high water content, belonging to the field of soft soil foundation treatment technology. This process targets fluid-plastic silt layers with a natural water content ≥55% and a liquidity index ≥1.0. The drilling and lifting speed of the pile driver is controlled at 0.7–0.9 m / min, and the construction proceeds in the following sequence: “first sinking pre-mixing (without grouting) → first lifting grouting and mixing → second sinking grouting and mixing → forced in-situ re-mixing at the pile bottom → second lifting mixing (without grouting) → forced in-situ re-mixing at the pile top.” Combined with the synergistic effect of enhanced re-mixing at the pile bottom and top, this method solves the technical problems of easy dilution and loss of cement slurry, easy necking and breakage of piles, and insufficient strength in soft soils with high water content. It significantly improves the integrity and strength of the pile body, increasing the first-pass yield rate from approximately 80% to over 94%. It is particularly suitable for the reinforcement of fluid-plastic silt layer foundations in coastal and lacustrine facies areas.

Description

Technical Field

[0001] This invention relates to the field of soft soil foundation treatment technology, specifically to a method for forming cement mixing piles in soft soil foundations with high water content. Background Technology

[0002] Cement mixing piles are a common method for reinforcing soft soil foundations. A mixing pile machine forcibly mixes cement slurry with in-situ soft soil to form cement-soil piles with a certain strength and stability, thereby improving the bearing capacity of the foundation and controlling settlement. This method has advantages such as fast construction speed, relatively low cost, and minimal impact on the surrounding environment, and is widely used in soft soil treatment in highway, railway, building, and port engineering projects.

[0003] However, in coastal sedimentary and lacustrine facies areas with high water content in soft soil, the natural water content of this type of soil is as high as 60% or more, with a liquidity index greater than 1.0, exhibiting a fluid plastic state and characteristics such as high compressibility, low strength, and high sensitivity. Under these extreme soft soil conditions, cement mixing pile construction faces two major technical challenges: First, frequent pile necking and breakage occur. Due to the extremely poor self-supporting properties of the high-water-content fluid plastic silt, during the lifting process of the mixing pile drill bit, the surrounding soft soil is prone to collapse and squeeze into the pile hole, leading to a local reduction in the diameter of the pile (necking) or even complete interruption (pile breakage), seriously affecting the integrity and bearing capacity of the pile. Second, the pile strength is difficult to meet design requirements. The presence of high water content causes excessive dilution of the cement paste, resulting in an uncontrolled water-cement ratio and a deterioration of the cement hydration reaction environment; at the same time, the organic matter and soluble salts in the fluid plastic soil may inhibit cement solidification, leading to slow strength growth in the later stages of the pile and difficulty in reaching the strength indicators at the design age.

[0004] Existing conventional "two-mixing-two-spraying" or "four-mixing-two-spraying" processes, such as the "Preliminary Study on Cement Mixing Pile Reinforcement Technology in the Haihe River Confluence Area" published by Yang Wenjun et al., mostly focus only on the impact of modified curing agent admixture on pile formation. Research on optimizing construction process parameters and controlling the quality of key pile components remains significantly insufficient, especially for the special condition of high-water-content fluid soft soil. Specifically, conventional processes, in pursuit of construction efficiency, typically set the drilling and lifting speed to around 1.0 m / min. Excessive speed can lead to rapid dilution and loss of cement slurry in high-water-content soft soil, failing to ensure uniform mixing of the slurry and soil, further exacerbating pile defects. It is worth noting that even appropriately reducing the drilling and lifting speed still makes it difficult to guarantee a high pile formation rate.

[0005] Therefore, for the special soft soil conditions of high water content fluid silt, there is an urgent need to develop a cement mixing pile construction method that can effectively control the construction speed, strengthen end treatment, and ensure uniform mixing of slurry and soil, so as to solve the technical problems of frequent pile defects and substandard strength in the existing process. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for forming cement mixing piles in soft soil foundations with high water content, in order to solve the problems of frequent pile defects and substandard strength in the existing process.

[0007] To achieve the above and other related objectives, the present invention provides a method for forming cement-mixed piles in soft soil foundations with high water content, comprising the following steps:

[0008] Step 1, Geological Confirmation and Parameter Setting: Based on the geological survey report, the soft soil layer in the area to be constructed is determined to be a high water content fluid plastic silt layer, and the design parameters for cement mixing piles are set.

[0009] Step 2, Drilling and Lifting Speed ​​Control: Control the sinking and lifting speed of the mixing pile machine drill bit when it passes through the silt layer at 0.7 to 0.9 m / min;

[0010] Step 3: Position the piling machine and perform the mixing and spraying and forced re-mixing operations in sequence according to the sub-steps (1) to (6) below:

[0011] (1) First sinking and pre-mixing: The drill bit is rotated forward and sinks to the design elevation of the pile bottom. No grouting is sprayed during this process;

[0012] (2) First lifting and grouting: reverse the drill bit at the bottom of the pile and simultaneously spray cement grout until the pile top is raised to the design elevation;

[0013] (3) Second sinking and grouting: immediately turn the drill bit forward at the top of the pile and continue grouting during the sinking process until the design elevation of the pile bottom is reached;

[0014] (4) Forced in-situ re-mixing at the bottom of the pile: After the drill bit reaches the bottom of the pile, rotate and mix in place at the bottom elevation for at least 60 seconds;

[0015] (5) Second lifting and mixing: After the pile bottom re-mixing is completed, reverse the drill bit and lift it. No grout is sprayed during this process until the ground surface is reached;

[0016] (6) Forced in-situ re-mixing at the top of the pile: After the drill bit reaches the top of the pile, it is lowered again to a predetermined depth below the top of the pile and mixed in place for at least 60 seconds, and cement slurry is selectively added according to the fullness of the slurry at the top of the pile.

[0017] Step 4, Pile Curing: Move the pile driver to the next pile foundation positioning point and repeat Step 3 until all cement mixing piles are constructed, and cure the constructed piles to the design age.

[0018] As a preferred embodiment of this application, in step 1, the design parameters include pile diameter, pile length, cement content and / or water-cement ratio.

[0019] As a preferred embodiment of this application, in step 1, the cement slurry is drinking water and ordinary Portland cement with a strength grade of 42.5 or higher.

[0020] As a preferred embodiment of this application, in step 1, the water-cement ratio of the cement slurry is set to 0.5.

[0021] As a preferred embodiment of this application, in step 1, the cement content is set to 15% to 20% of the original soil weight.

[0022] As a preferred embodiment of this application, the pressure of pumping cement slurry is 0.4~0.6MPa.

[0023] As a preferred embodiment of this application, in step 2, the maximum construction speed at any depth within the entire pile length is ≤0.9 m / min.

[0024] As a preferred embodiment of this application, in step 2, the maximum lifting speed or maximum drilling speed is 0.9 m / min.

[0025] As a preferred embodiment of this application, in step 3 (6), the predetermined depth range is 0.01 to 1.0 m below the pile top, and the in-situ mixing time is 60 to 90 seconds.

[0026] As a preferred embodiment of this application, the high water content fluid plastic silt layer is a fluid plastic silt soil with a natural water content ≥55%, a liquidity index ≥1.0, and a saturation degree ≥95%.

[0027] As a preferred embodiment of this application, the maintenance described in step 4 is natural maintenance.

[0028] The present invention also provides a cement mixing pile prepared according to the cement mixing pile formation method for soft soil foundation with high water content.

[0029] The present invention also provides an application of a method for forming cement mixing piles on soft soil foundations with high water content in the preparation of cement mixing piles for treating fluid silt layers of coastal facies deposits.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. Significantly reduce the necking and pile breakage rate: By strictly controlling the sinking / lifting speed to 0.7-0.9 m / min, combined with the "one-stirring, two-spraying, one-stirring" and forced re-stirring process, the cement slurry has sufficient time to mix with the soil in the soft soil with high water content, reducing slurry loss and soil disturbance. The measured pile necking / pile breakage rate is reduced by more than 80%.

[0032] 2. Ensure the pile body strength meets the standard: The pile bottom and pile top are forcibly re-mixed in place for at least 60 seconds, which solves the common problem of insufficient strength of cement soil at the pile end and pile head in high water content soil layers due to grout dilution. The 28-day unconfined compressive strength of the sampled core samples meets the design requirement of ≥1.0MPa in 100% of cases.

[0033] 3. Improve the first-pass yield rate: In soft soil with a water content as high as 61.8%, the first-pass yield rate of construction quality is increased from the conventional 80% to over 94%, which greatly reduces rework and saves costs. Attached Figure Description

[0034] Figure 1 This is a flowchart of the pile-forming method of the present invention.

[0035] Figure 2 This is a schematic diagram of "one stirring, two sprayings, one stirring, and re-stirring at the top and bottom of the pile". Detailed Implementation

[0036] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application.

[0037] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0038] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0039] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0040] Example 1

[0041] This embodiment provides a method for constructing cement-mixed piles in soft soil foundations with high water content, used to treat fluid-plastic silt layers deposited in coastal facies. The method includes the following steps:

[0042] S1 Geological Confirmation and Parameter Setting

[0043] According to the geological survey report, the soft soil layer to be constructed was determined to be a high-water-content, fluid-plastic silt layer. In this embodiment, the average natural water content of the silt in the soft soil layer was 61.8%, the liquid limit was 55.2%, the liquidity index was 1.24, and the saturation was 98.0%, exhibiting a fluid-plastic state. The cement mixing piles were designed with a diameter of 500mm, a length of 10-15m (using 10m as an example), and a pile spacing of 1.2m. The design requirement was a 28-day pile strength ≥ 1.0MPa. The cement content was set at 15% of the original soil weight, and the cement slurry water-cement ratio was set at 0.5.

[0044] S2 Drilling and Hoisting Speed ​​Control:

[0045] The control systems of all 10 piling machines were debugged, and the maximum drilling speed and lifting speed of the drill bit were locked at 0.9 m / min through hardware locking. The grouting pipeline and mixing system were checked to ensure normal operation.

[0046] The S3 piling machine was positioned, and the mixing and spraying and forced re-mixing operations were carried out sequentially according to the sub-steps (1) to (6) below:

[0047] S31 First settling and pre-mixing (without spraying)

[0048] The drill bit rotates clockwise and descends to the designed elevation of the pile bottom. The descent speed is controlled at 0.85 m / min, and the actual controlled speed in this example is 0.85 m / min. No grouting is used during this process; only the soil is pre-mixed and broken up.

[0049] S32 First Lifting of Shotcrete Mixing

[0050] The drill bit is reversed and lifted at the bottom of the pile while cement grout is continuously and evenly injected. The lifting speed is controlled at 0.85 m / min until the top elevation of the pile is reached.

[0051] S33 Second Submersion Spraying and Mixing

[0052] Immediately rotate the drill bit clockwise at the top of the pile and continue grouting during the descent. The descent speed is controlled at 0.85 m / min until the designed elevation of the pile bottom is reached.

[0053] S34 In-situ mixing at the bottom of the pile (mandatory)

[0054] After reaching the bottom of the pile in step S33, the drill bit is not lifted immediately. Instead, it is rotated and stirred in place at the bottom elevation of the pile for at least 60 seconds to ensure that the cement and soil at the pile tip are fully mixed. Figure 2 The details of the pile bottom mixing process are clearly shown in the image.

[0055] S35 Second stirring (without spraying)

[0056] After completing the bottom mixing, reverse the drill bit and lift it. During this process, no grout is sprayed; only mixing is performed. The lifting speed is controlled at 0.85 m / min until the ground is reached.

[0057] S36 Pile top in-situ re-mixing (mandatory)

[0058] After reaching the pile top elevation in step S35, the drill bit is not immediately moved. For example... Figure 2 As shown, the drill bit is lowered to within 1.0 meter below the pile top and rotated and stirred in place for at least 60 seconds. During the in-place re-stirring process, selective grouting is added according to the saturation of the grout to ensure that the grout at the pile head is full and meets the strength requirements.

[0059] S4 Pile Maintenance

[0060] After completing all the above steps, move the machine to the next pile location and repeat S3 until all cement mixing pile construction is completed, and allow the constructed piles to cure naturally to the design age (28 days, 90 days).

[0061] To verify the effectiveness of this embodiment, after the pile formation method of the present invention was completed in the soft soil layer of the construction area, 300 piles were randomly selected for testing. The test items included the pile necking / pile breakage rate, the core sample strength failure rate, and the 28-day unconfined compressive strength of the core sample. The test results are shown in Table 1.

[0062] Example 2

[0063] The difference between this embodiment and Embodiment 1 is that the drilling speed and lifting speed are adjusted to 0.70 m / min. All other process conditions remain the same. After construction, 300 piles were randomly selected for testing. The results showed that the pile bodies were continuous and intact, the core samples showed no necking or broken piles, and the average unconfined compressive strength of the core samples after 28 days reached 1.4 MPa, with a pass rate of 95.33%.

[0064] Example 3

[0065] The difference between this embodiment and Embodiment 1 is that the drilling speed and lifting speed are adjusted to 0.90 m / min. All other process conditions remain the same. After construction, 300 piles were randomly selected for testing. The results showed that the pile bodies were continuous and intact, the core samples showed no necking or broken piles, and the average 28-day unconfined compressive strength of the core samples reached 1.3 MPa, with a pass rate of 94.00%.

[0066] Example 4

[0067] The difference between this embodiment and Embodiment 1 is that the treatment object is a soft soil subgrade project with a higher water content in the silt layer, reaching 68%, and a liquidity index of 1.52. To address these more severe geological conditions, this embodiment adjusts the drilling / lifting speed to 0.75 m / min and extends the in-situ re-mixing time at the pile bottom and top to 70 seconds. After construction, 300 piles were randomly selected for testing. The tests showed that the pile bodies were continuous and intact, and the core samples showed no necking or breakage. The average 28-day unconfined compressive strength of the core samples reached 1.8 MPa, with a pass rate of 96%, further demonstrating the effectiveness and adaptability of the invention's process in extremely high water content soil layers.

[0068] Example 5

[0069] The difference between this embodiment and Embodiment 1 is that the cement content is 20%. All other process conditions are the same. After construction, 300 piles were randomly selected for testing. The results showed that the pile bodies were continuous and intact, the core samples showed no necking or broken piles, and the average 28-day unconfined compressive strength of the core samples reached 1.7 MPa, with a pass rate of 95.67%.

[0070] Comparative Example 1

[0071] Construction was carried out using conventional techniques in a fluid-plastic silt layer of coastal facies sediments, with a drilling / lifting speed of 1.0 m / min. A two-jetting, four-stirring method was employed, without in-situ re-stirring at the pile bottom and top. After the completion of this comparative construction, 300 piles were randomly selected for testing. The tests included the incidence of pile necking / breakage, the rate of unqualified core sample strength, and the 28-day unconfined compressive strength of the core samples. The test results are shown in Table 1.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that forced in-situ re-mixing at the pile bottom and top is not performed. All other process conditions are the same as in Example 1. After construction, 300 piles were randomly selected for testing. The results showed that the pile bodies were continuous and intact, the core samples showed no necking or broken piles, and the average 28-day unconfined compressive strength of the core samples reached 1.1 MPa, with a pass rate of 82.0%.

[0074] Comparative Example 3

[0075] Construction was carried out using conventional techniques in a fluid-plastic silt layer of coastal facies sediments, with a drilling / lifting speed of 0.85 m / min. After the completion of this comparative project, 300 piles were randomly selected for testing. The testing items included the incidence of pile necking / breakage, the incidence of core sample strength failure, and the 28-day unconfined compressive strength of core samples. The test results are shown in Table 1.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 1 is that forced in-situ re-mixing (60 seconds each) is added at the pile bottom and pile top, but the drilling / lifting speed remains at 1.0 m / min. All other process conditions are the same as in Example 1. After construction, 300 piles were randomly selected for testing. The results showed that the pile bodies were continuous and intact, the core samples showed no necking or breakage, and the average 28-day unconfined compressive strength of the core samples reached 1.2 MPa, with a pass rate of 88.00%.

[0078] Table 1 Comparison of Mixing Pile Quality Before and After Implementation

[0079] serial number First pass rate Pile necking / pile breakage rate Core sample strength failure rate Range / value of unconfined compressive strength of 28-day core samples (MPa) Example 1 94.67% (284 / 300) 1.33% (4 / 300) 0% (0 / 300) 1.12～1.62 Example 2 95.33% (286 / 300) 1.00% (3 / 300) 0% (0 / 300) 1.30～1.70 Example 3 94.00% (282 / 300) 1.67% (5 / 300) 0% (0 / 300) 1.20～1.55 Example 4 96.00% (288 / 300) 0.67% (2 / 300) 0% (0 / 300) 1.60～1.92 Example 5 95.67% (287 / 300) 1.33% (4 / 300) 0% (0 / 300) 1.52～2.05 Comparative Example 1 80.00% (240 / 300) 7.67% (23 / 300) 6.67% (20 / 300) 0.65~1.2 (Some piles are substandard) Comparative Example 2 82.00% (246 / 300) 6.67% (20 / 300) 5.33% (16 / 300) 0.8~1.3 (Some piles are substandard) Comparative Example 3 85.00% (255 / 300) 5.00% (15 / 300) 3.33% (10 / 300) 0.9–1.4 (Some piles are substandard) Comparative Example 4 88.00% (264 / 300) 3.33% (10 / 300) 2.00% (6 / 300) 0.95~1.1 (Some piles are substandard)

[0080] As shown in Table 1, the process of this invention achieves a core breakthrough in improving the quality of pile formation in soft soil with high water content. This process significantly improves the pile formation quality of soft soil foundations with high water content, fundamentally controlling core quality defects (necking / fractured piles, insufficient strength). Compared with conventional processes, the first-pass yield rate jumps dramatically from 80% to 94.67% or higher, an increase of nearly 15 percentage points. The incidence of pile necking / fractured piles drops sharply by 82.6% (from 7.67% to 1.33%). More importantly, it completely eliminates the incidence of insufficient pile strength (reduced to 0%). After 28 days of curing, the pile strength is significantly improved and all piles meet the standards. The core of this leapfrog improvement lies in the synergistic effect of "speed control + in-situ re-mixing": Comparative Example 4 shows that with only in-situ re-mixing added while the speed remains at 1.0 m / min, the pass rate is only 88%, and 2% still fail to meet strength standards; while Comparative Example 2 shows that with only speed reduction without in-situ re-mixing, the pass rate is only 82%, and the failure rate for strength is as high as 5.33%. Only by combining the two (as in Example 1) can the quality defects be transformed from "widespread" to "fundamentally eliminated," fundamentally solving the technical problem of insufficient strength at the pile tip and pile head in soft soil with high water content. By comparing different drilling speeds (Examples 1-3), it can be seen that the lower the speed (0.70 m / min), the better the pile quality, but considering construction efficiency, a speed of 0.70-0.85 m / min is recommended.

[0081] Example 4 further verifies that the present invention also performs excellently in soft soil with extremely high water content (68%). Even in extremely soft soil with a water content as high as 68%, by appropriately reducing the speed (0.75 m / min) and extending the in-situ re-mixing time (70 seconds), the first-pass yield can still reach 96%, and the strength reaches 1.60-1.92 MPa, even better than Example 1 under conventional geological conditions. This means that the process has extremely strong geological adaptability and can cope with different working conditions without significant adjustments. Comparative analysis shows that simply reducing the speed or simply increasing the in-situ re-mixing cannot achieve the optimal effect; the synergistic effect of both is the key to quality improvement. More importantly, the above advantages do not depend on increasing the cement content—the standard can be achieved at a 15% content (Example 1), while increasing the content to 20% (Example 5) is only an option for strength surplus. Therefore, this invention achieves a fundamental guarantee of pile quality with minimal cost increase (only adding tens of seconds of in-situ re-mixing time), completely solving the long-standing technical problems of "neck shrinkage, pile breakage, pile head rot, and soft pile tip" in mixing piles in fluid plastic soft soil, and has extremely high engineering promotion value.

[0082] In summary, this invention, without increasing the cement content (15%–20%), forms a complete and efficient construction process by strictly controlling the drilling / lifting speed within a low-speed range of 0.7–0.9 m / min, combined with an optimized mixing sequence of "one mixing, two sprayings, and one mixing," and particularly by forcibly adding in-situ re-mixing steps at the pile bottom and top. This significantly improves the quality and reliability of pile formation with minimal cost increase. This process is applicable to the treatment of soft soil foundations with high water content in coastal, lacustrine, and fluvial facies soils. It effectively solves the technical problems of necking, breakage, and insufficient strength in cement-mixed piles in high-water-content, fluid-plastic soft soils, significantly improving the first-pass yield rate and possessing high practical value and promotional significance.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. When numerical ranges are given in the embodiments (e.g., drilling / lifting speed 0.7–0.9 m / min, in-situ re-mixing time at least 60 seconds, pile top re-mixing range 0.01–1.0 m, etc.), it should be understood that, unless otherwise specified in the present invention, any of the two endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, based on the mastery of the prior art by those skilled in the art and the description of the present invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of the present invention can be used to implement the present invention. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for forming cement-mixed piles in soft soil foundations with high water content, characterized in that, Includes the following steps: Step 1, Geological Confirmation and Parameter Setting: Based on the geological survey report, the soft soil layer in the area to be constructed is determined to be a high water content fluid plastic silt layer, and the design parameters for cement mixing piles are set. Step 2, Drilling and Lifting Speed ​​Control: Control the sinking and lifting speed of the mixing pile machine drill bit when it passes through the silt layer at 0.7 to 0.9 m / min; Step 3: Position the piling machine and perform the mixing and spraying and forced re-mixing operations in sequence according to the sub-steps (1) to (6) below: (1) First sinking and pre-mixing: The drill bit is rotated forward and sinks to the design elevation of the pile bottom. No grouting is sprayed during this process; (2) First lifting and grouting: reverse the drill bit at the bottom of the pile and simultaneously spray cement grout until the pile top is raised to the design elevation; (3) Second sinking and grouting: immediately turn the drill bit forward at the top of the pile and continue grouting during the sinking process until the design elevation of the pile bottom is reached; (4) Forced in-situ re-mixing at the bottom of the pile: After the drill bit reaches the bottom of the pile, rotate and mix in place at the bottom elevation for at least 60 seconds; (5) Second lifting and mixing: After the pile bottom re-mixing is completed, reverse the drill bit and lift it. No grout is sprayed during this process until the ground surface is reached; (6) Forced in-situ re-mixing at the top of the pile: After the drill bit reaches the top of the pile, it is lowered again to a predetermined depth below the top of the pile and mixed in place for at least 60 seconds, and cement slurry is selectively added according to the fullness of the slurry at the top of the pile. Step 4, Pile Curing: Move the pile driver to the next pile foundation positioning point and repeat Step 3 until all cement mixing piles are constructed, and cure the constructed piles to the design age.

2. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, In step 1, the design parameters include pile diameter, pile length, cement content and / or water-cement ratio.

3. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, In step 2, the maximum construction speed at any depth within the entire pile length is ≤0.9 m / min.

4. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, In step 2, the maximum lifting speed or maximum drilling speed is 0.9 m / min.

5. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, In step 3 (6), the predetermined depth range is 0.01 to 1.0 m below the top of the pile, and the in-situ mixing time is 60 to 90 seconds.

6. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, The high water content fluid plastic silt layer is a fluid plastic silt soil with a natural water content ≥55%, a liquidity index ≥1.0, and a saturation degree ≥95%.

7. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that, The maintenance described in step 4 is natural maintenance.

8. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 2, characterized in that, The water-cement ratio of the cement slurry is set to 0.

5.

9. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 2, characterized in that: In step 1, the cement content is set to 15% to 20% of the original soil weight.

10. The method for forming cement-mixed piles in soft soil foundations with high water content according to claim 1, characterized in that: In step 3, when the natural water content of the soft soil layer is higher than 65%, the sinking drilling speed and lifting speed in each sub-step are controlled at 0.75 m / min, and the in-situ re-mixing time at the pile bottom and pile top is extended to 70 seconds.

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