Construction method of layered cement mixing pile for road soft foundation treatment

Abstract

The invention relates to the technical field of cement mixing piles, in particular to a road soft foundation treatment layered cement mixing pile construction method which comprises the following steps that S1, the surface of a foundation to be constructed is cleaned, and pile positions are marked; s2, a test pile position is selected, sampling detection is conducted after a pile is formed through a pile machine, and technological parameters are adjusted; s3, on the basis of the adjusted process parameters, the pile machine is adopted for conducting pile forming on the remaining pile positions so as to form the cement mixing pile; and S4, the quality of the cement mixing pile is judged after sampling detection is conducted on the cement mixing pile. The construction method solves the problems that cement paste on the lower portion of a pile body is reversed, and mixing of the cement paste and soil is not uniform.

Description

Technical Field

[0001] This invention relates to the field of cement mixing pile technology, and in particular to a construction method for layered cement mixing piles for road soft soil treatment. Background Technology

[0002] In road construction, the stability of weak subgrades has a significant impact on project quality and service life. Cement mixing piles, as a foundation reinforcement technology, have become a commonly used solution for treating soft subgrades due to their strong adaptability, high construction efficiency, and significant reinforcement effects. Cement mixing piles can significantly improve the bearing capacity and deformation resistance of the subgrade, thereby reducing the risks caused by foundation settlement and uneven settlement, and ensuring the smoothness and durability of the road. However, if the quality of cement mixing pile construction is poor, it may lead to insufficient pile bearing capacity and poor pile-soil interface bonding, resulting in foundation instability, pavement cracking, and other engineering defects. Therefore, ensuring the construction quality of cement mixing piles is crucial in the treatment of weak subgrades. Existing cement mixing pile technologies suffer from problems such as low raw material utilization, high slurry return rate, and failure to meet design strength requirements. Summary of the Invention

[0003] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a construction method for layered cement mixing piles for road soft soil treatment, so as to improve the quality of cement mixing piles in the prior art.

[0004] This invention provides a construction method for layered cement mixing piles for road soft soil treatment, the construction method comprising the following steps:

[0005] S1: Clean the surface of the foundation to be constructed and mark the pile positions;

[0006] S2: Select test pile locations, use a pile driver to construct piles, take samples for testing, and adjust process parameters;

[0007] S3: Based on the adjusted process parameters, the pile driver is used to pile the remaining pile positions to form the cement mixing piles;

[0008] S4: After sampling and testing the cement mixing piles, determine the quality of the cement mixing piles.

[0009] In some embodiments, the grout used for pile formation includes silicate cement, gypsum, sodium sulfate, and a water-reducing agent, and the water-cement ratio of the grout is 0.4 to 0.6.

[0010] In some embodiments, the cement content of the pile segment from the top of the cement mixing pile to 75% to 85% of the pile height is 15%, and the cement content of the remaining pile segment is 17%.

[0011] In some embodiments, the piling machine includes a drill bit, the drill bit includes a main shaft, and at least two secondary shafts are arranged around the main shaft. At both ends of the at least two secondary shafts are provided with soil-turning blades, and the soil-turning blades are provided with breaking teeth.

[0012] In some embodiments, the secondary rotating shaft is two secondary rotating shafts, and the soil turning blades include an upper soil turning blade and a lower soil turning blade respectively connected to both ends of the two secondary rotating shafts.

[0013] In some embodiments, the drill bit includes a radial grouting pipe, one end of which is connected to a longitudinal grouting pipe within the spindle, and the other end of which is connected to a jetting head.

[0014] In some embodiments, the longitudinal grout delivery pipe includes a first longitudinal grout delivery pipe and a second longitudinal grout delivery pipe, the first longitudinal grout delivery pipe and the second longitudinal grout delivery pipe are connected to one end of a solenoid valve, and the other end of the solenoid valve is connected to the radial grout delivery pipe.

[0015] In some embodiments, the pile formation includes the steps of drilling, first lifting, sinking, and second lifting;

[0016] The drilling speed is 0.8~1.2m / min;

[0017] The first lifting speed is 0.5~0.8 m / min, and the shotcrete pressure is 0.5~0.6 MPa;

[0018] The sinking speed is 0.4~0.6 m / min, and the shotcrete pressure is 0.4 MPa;

[0019] The second lifting speed is 0.4~0.6 m / min, and the grouting pressure is 0.4 MPa.

[0020] In some embodiments, in step S4, determining the quality of the cement mixing pile includes taking cement mixing piles at different depths to measure the cement content, drawing a curve of cement content change with depth based on the cement content results, analyzing the cement content and mixing uniformity at each depth, and determining the quality of the cement mixing pile.

[0021] In some embodiments, the cement mixing piles at different depths are sampled by multiple sections of soil sampling pipe connected in series, with each section of soil sampling pipe having a length of 20cm and a movable door on it.

[0022] This invention provides a construction method for layered cement mixing piles for soft soil treatment in roads. This method can quickly determine the cement content ratio of the mixing pile, control the construction quality in real time, reduce subsequent rework, solve the problems of cement slurry backflow in the lower part of the pile and uneven mixing of cement slurry and soil, ensure that the pile length and strength meet the relevant requirements, and also take into account the large differences in vertical soil quality. By adopting layered cement mixing piles, the quality is ensured while reducing the amount of materials used, making it low-carbon and environmentally friendly. Attached Figure Description

[0023] Figure 1 The diagram shown is a process flow chart of the construction method of this invention.

[0024] Figure 2 The diagram shown illustrates the principle of using cement mixing piles to reinforce soft soil foundations according to the present invention.

[0025] Figure 3 The diagram shows the location layout of the pile positions according to the present invention.

[0026] Figure 4 The diagram shows a schematic of the longitudinal grout delivery pipe inside the drill bit of this invention.

[0027] Figure 5 The image shown is a top sectional view of the drill bit of this invention.

[0028] Figure 6 The diagram shown is a schematic diagram of the soil sampling device of the present invention. Detailed Implementation

[0029] Please see Figures 1 to 6 This invention provides a construction method for layered cement mixing piles for road soft soil foundation treatment. The construction method is applicable to treating normally consolidated soil layers such as silt, silty soil, plain fill, cohesive soil (soft plastic, plastic), peat soil, silt (slightly dense, medium dense), fine sand (loose, medium dense), medium coarse sand, and saturated loess, so that the soft soil hardens into a composite foundation with integrity, water stability, and high bearing capacity.

[0030] like Figure 2As shown, cement mixing piles 100 use a mixture of cement and water as the main curing agent in soft soil treatment and reinforcement. A mixture of various curing materials can also be used, along with admixtures such as water-reducing agents and early-strength agents, depending on project requirements and soil conditions. Using cement mixing pile construction machinery, pre-mixed cement slurry is sprayed into the soft soil foundation 200 and forcibly mixed, allowing a thorough physicochemical reaction to occur between the foundation soil and the cement slurry and other curing agents. This alters the original soil structure, reduces the compressibility and plasticity of the soft soil foundation 200, and bonds to form high-strength columnar cement-reinforced soil. This soil, together with the soil between the piles 300, bears the superstructure load, transforming the soft soil foundation 200 into a composite foundation with integrity, water stability, and a certain strength. This achieves the purpose of improving the foundation bearing capacity, reducing foundation settlement, or preventing lateral soil sliding.

[0031] The construction method includes the following steps:

[0032] 1. Construction Preparation

[0033] Remove stones, tree roots, and other debris from the foundation surface. Harden and level the foundation. If low-lying areas exist, backfill and compact a layer of cohesive soil or sand cushion to improve the bearing capacity of the pile foundation. Drain surface water to allow the foundation surface to gradually harden, thus ensuring working space. If the surface soft soil has a high and varied organic matter content, it is advisable to use an excavator to directly remove that portion of the surface soft soil.

[0034] 2. Pile location layout

[0035] The pile numbers are arranged in horizontal and vertical columns, with the vertical column following the direction of road travel and the horizontal column from left to right. After the site is leveled, the starting point, ending point, left side line, right side line, and center pile position are marked for each construction section. Combining the boundaries determined during surveying and setting out, and considering the pile layout diagram, equipment such as a total station is used to determine the pile axis and pile center position. After the positioning work is completed, markers are made using lime and wooden stakes. Based on the leveled ground elevation and the pile top elevation on the drawings, the pile numbers from the pile layout diagram are marked on bamboo stakes using bookmarks.

[0036] like Figure 2 As shown, the pile diameter d and pile spacing L of cement mixing piles can be set according to design requirements. d can be 60cm and pile spacing L=150cm.

[0037] like Figure 3 As shown, in this embodiment, the pile positions are arranged in an equilateral triangle.

[0038] 3. Piling machine in place

[0039] Place the mixing pile machine at the first pile location, verifying its position. Ensure the center points of the pile machine and the pile hole coincide, with a deviation not exceeding 10cm. The pile machine guide frame must be perpendicular to the ground, with an inclination rate not exceeding 1%. Draw prominent depth markings (with reflective effect) on the frame, increasing sequentially from top to bottom, with a spacing of 1m. Use sleepers to level and stabilize the pile machine, ensuring it is properly positioned. Debug and check key components such as the measuring instrument and drill bit blades. Repeat the above steps after the previous pile location is completed, then move the mixing pile machine to the next pile location.

[0040] 4. Test pile construction

[0041] (1) According to the construction drawings, the design requirements for cement mixing piles are: cement content of more than 12%, cement content of not less than 55kg per meter of pile length, water-cement ratio of 0.4-0.6, ordinary Portland cement of grade 32.5 or above, and pile length of 10-16m (to reach the bearing layer).

[0042] Soil samples were taken on-site and tested by a third-party soil laboratory. The results showed that the soil was relatively uniform in the site but varied greatly in vertical soil conditions. Slurry was prepared for each elevation section according to the soil conditions.

[0043] (2) Considering strength and workability, the admixture ratio of 32.5 grade cement should reach more than 18% and the water-cement ratio should be 0.5-0.7. The admixture ratio of 42.5 grade cement should reach more than 12% and the water-cement ratio should be 0.4-0.6. The admixture ratio of 52.5 grade cement should reach more than 10% and the water-cement ratio should be 0.3-0.5.

[0044] (3) To coordinate with the design, ordinary Portland cement of grade 42.5 was selected. Through specific laboratory tests, the mix proportion of the test pile grout was determined as follows: cement content ratio of 15%. Considering that it is impossible to achieve compaction during actual construction, the pile height is 12~13m. In some embodiments, the pile height is 12m. The cement content from the top of the pile to a depth of 10m is 15%, and the cement content from 10m to the bottom of the pile is 17%. The cement content per meter of pile length is greater than 55kg, and the water-cement ratio is 0.45 (workability is relatively ideal). 2% cement-based gypsum, 1% cement-based sodium sulfate, and 0.2% cement-based water-reducing agent are also added to achieve rapid setting and early strength. The use of inferior materials such as damp and lumpy cement is prohibited. The grout is prepared in batches according to the construction progress of the cement mixing pile, and the grout placement time is strictly controlled.

[0045] (4) Shotcrete system

[0046] A 15% cement grout is used for the pile section from the top to a depth of 10m, and a 17% cement grout is used for the pile section from 10m to the bottom. The grout is transported, pressurized, sprayed, and shut down by an independent shotcrete system, thus achieving layered mixing piles to better adapt to soil conditions.

[0047] The soil conditions of the two pile sections differ significantly, primarily in the soil at the pile bottom area, which has high water content and high plasticity, making it difficult to inject cement grout and ensuring pile length and strength. Therefore, a cement grout with a higher admixture ratio is used. A layered shotcrete system is employed: from 10m depth upwards, the 15% cement mortar system is activated and the 17% cement mortar system is deactivated; from 10m depth downwards, the 17% cement mortar system is activated and the 15% cement mortar system is deactivated.

[0048] (5) Test pile testing

[0049] 1) Divide the cement mixing pile treatment area into zones based on the distribution and depth of soft soil. During test piles, at least three test piles should be selected in each zone, with the test pile points evenly distributed across all zones. Calculate the average test pile length for each zone using the test piles. This average length will serve as the control pile length for subsequent large-scale construction and can be used as a reference to control the construction pile length during actual construction. If the actual pile length deviates from the average test pile length in a localized area, the actual pile length should be used for control, and the range of pile length variation and the actual construction pile length should be recorded in detail.

[0050] 2) The main purpose of test piles is to verify the experimental mix ratio of cement grout and determine process parameters such as the number of mixing times, grouting pressure, grouting flow rate, drill bit lifting speed and sinking speed. For details, please refer to this construction method. During the test pile construction, observe whether there are any abnormal problems such as grout replenishment or interruption of grouting.

[0051] 3) After pile construction is completed, check whether the integrity and strength of the pile body meet the design standards. The inspection method can be to directly excavate after 7 days or take core samples after 14 days, compare the actual construction situation with the expected situation, and refine the optimal values ​​of various process parameters accordingly. Once the construction plan is adjusted and the technical feasibility is met, the cement mixing pile construction activities can be officially carried out.

[0052] Test piles require an infinite compressive strength of not less than 0.5 MPa at 7 days. Mixed piles using 15% uniform shotcrete have a compressive strength between 0.4 and 0.6 MPa, with a grout return rate of 12% to 16%, posing a risk of failing to meet strength standards. Mixed piles using 17% uniform shotcrete achieve a compressive strength of 0.7 to 0.9 MPa, with a grout return rate of 10% to 13%, resulting in high material consumption. Mixed piles using layered shotcrete have a compressive strength of 0.6 to 0.8 MPa, with a grout return rate of less than or equal to 5%.

[0053] 5. Stirring and settling

[0054] (1) Preparation

[0055] Before drilling for cement mixing piles, the entire pipeline should be flushed with water and checked for any blockages. Drilling can only begin after the water has been drained. The pile position and verticality should also be verified. To ensure that the cement content per meter of the pile and the total amount of cement slurry meet the design requirements, the piling machine should be equipped with a computer recorder every day, and a cement slurry specific gravity meter should be available on site.

[0056] (2) Drilling method

[0057] During the initial drilling, to avoid pipe blockage, drilling with grout is permitted, but drilling with water is strictly prohibited. Low-speed operation should be used, and the drilling speed should be controlled between 0.8-1.2 m / min. The mixing method should be rationally selected based on the soil's plasticity: single-axis unidirectional, single-axis bidirectional, or bidirectional bidirectional mixing. Bidirectional mixing is chosen for high plasticity, and unidirectional mixing for lower plasticity. Cement mixing piles should penetrate the weak soil layer to reach the bearing stratum, penetrating at least 50 cm. The depth of the bearing stratum should be determined not only by the geological survey report but also by the ammeter readings during drilling. A significant increase in the reading indicates that the bearing stratum has been reached.

[0058] (3) Drill bit improvement

[0059] To ensure the quality of pile formation in the pile bottom area, the drill bit structure was modified, and the mixing blades were given additional soil cutting and turning functions through self-rotation, thereby improving the mixing intensity and uniformity. Figure 5 This is a three-dimensional cement mixing pile drill bit. The drill bit includes a main shaft 5, which can be driven to rotate by a motor on a pile driver. Two secondary rotating shafts 4 are arranged around the main shaft 5. Soil turning blades are arranged at both ends of the two secondary rotating shafts 4. The soil turning blades are provided with breaking teeth 1. The soil turning blades include upper soil turning blades 2 and lower soil turning blades 3. The drill bit includes a radial grouting pipe 6. One end of the radial grouting pipe 6 is connected to a longitudinal grouting pipe inside the main shaft 5. The other end of the radial grouting pipe 6 is connected to a grouting head 7. The grouting head 7 can be a fan-shaped grouting head. The grouting head 7 and the radial grouting pipe 6 can be connected by a connector 8. The connector 8 can be a rotating structure that can drive the grouting head 7 to rotate at different angles.

[0060] By setting up a secondary rotating shaft 4, it is possible to ensure that the soil-turning blades can rotate on their own while being driven vertically by the main shaft 5, thereby improving the uniformity of mixing after grouting. The secondary rotating shaft 4 can be powered by a separate hydraulic system.

[0061] like Figure 4 As shown, specifically, the longitudinal grouting pipe includes a first longitudinal grouting pipe 401 and a second longitudinal grouting pipe 402. The longitudinal grouting pipe is disposed inside the main shaft 5. The first longitudinal grouting pipe 401 can transport grout with a cement content ratio of 15%, and the second longitudinal grouting pipe 402 can transport grout with a cement content ratio of 17%.

[0062] 6. Shotcrete lifting

[0063] (1) Slurry extraction method

[0064] Before lifting, allow sufficient time for the grout to reach the bottom of the pile to prevent lifting without grouting. To ensure the quality of the pile bottom, top, and body, the drill bit should remain at the bottom of the pile for 30 seconds and continuously spray grout to grind the pile end. Any remaining grout should be sprayed into the pile body during lifting, and lifting should stop at 30cm above the ground while continuing to spray grout for another 30 seconds to grind the pile head. The lifting speed should be controlled at 0.5-0.8 m / min, and the grouting pressure should be 0.5-0.6 MPa. Use a low-speed operation, and the amount of grout sprayed during the first lift should be less than half of the total grout volume.

[0065] (2) Interruption handling

[0066] If an accident (such as power outage, mechanical failure, etc.) causes the shotcreting to be interrupted during the pile driving process, re-shotcreting measures must be taken within 12 hours. The overlap length of the re-shotcreting should preferably be no less than 1.0m. If re-shotcreting 1m is particularly difficult, a significant change in the ammeter reading should be used as a reference. However, before lifting, there should be time to wait for the grout to reach the lower part of the overlap section to prevent pile breakage. Otherwise, the pile should be re-driven, and the distance between the newly installed pile and the scrapped pile should not exceed 15% of the pile spacing.

[0067] 7. Repeated sinking

[0068] The entire process requires repeated mixing. The time for each sinking or lifting of the mixer must be recorded by a designated person, with a time error not exceeding 5 seconds. Compared to the initial drilling, the operation can be increased by one gear. The drilling speed should be controlled at 0.4-0.6 m / min, and the grouting pressure should be 0.4 MPa. Excessive pressure should be avoided to prevent voids in the pile body. After sinking to the pile tip, pause for 30 seconds, then continue mixing and grouting. The drill bits used must be inspected regularly; their diameter wear should not exceed 1 cm, and excessively large diameter drill bits should not be used to avoid poor pile formation. The grout delivery pipes must be frequently inspected for leaks and blockages. The pipes should be kept moist to facilitate grout delivery. If the machine is shut down for 3 hours, the grout delivery pipes should be disassembled and cleaned to prevent grout hardening and blockage.

[0069] 8. Repeated Improvement

[0070] For the second lifting and grouting, the lifting speed should be controlled at 0.4-0.6 m / min, and the grouting pressure should be 0.4 MPa. Compared to the first lifting, the operation can be increased by one gear. The normal pile formation time for each pile should not be less than 40 minutes. The prepared grout should not segregate, should not be left to stand for too long, and grout exceeding 2 hours should not be used. The grout should be filtered when poured into the pump tank to prevent lumps from forming and damaging the pump body. If insufficient grouting volume is found during construction, the entire pile should be re-drived, and the grouting volume of the re-driving should not be less than the design volume. Original records should be kept during the construction process, including pile number, weather, depth, grouting stop elevation, pump pressure, pipeline pressure, drilling rig speed, drilling and lifting speed, cement usage, etc.

[0071] 9. Dosage Detection

[0072] (1) Multi-layer sampling

[0073] Based on the characteristics and requirements of on-site sampling and cement content titration tests for cement mixing piles, a tubular, side-opening / closed-mouth soft soil sampling device was developed. This device can collect samples at 20cm intervals within the target depth range of the cement mixing pile in a single operation. During sampling, a static cone penetrometer is used to press down and lift the sampling device. During the pressing down process, the movable door remains closed; during the lifting process, the movable door opens, allowing the soil sample to enter the sampling device. Each sampling device is isolated from the others to ensure the representativeness of the cement mixing pile core samples. Figure 6 This is a schematic diagram of the soil extraction device.

[0074] The soil sampling device includes multiple soil sampling pipes 400 connected together. Each soil sampling pipe 400 has a movable door 500. The length D of each soil sampling pipe 400 can be 20cm, and the distance between the movable doors 500 can also be 20cm.

[0075] (2) Measurement and conversion

[0076] The Ca in the sample was dissolved using a 10% NH4Cl weak acid. 2+ Then, the free Ca in the aqueous solution was fixed by the complex in the disodium EDTA standard solution. 2+ The consumption of EDTA standard solution in soil samples at different depths was determined by titration. Based on the standard curve, the cement content of the pile core samples at different depths could be determined. Based on the titration results of the pile core cement content, a curve showing the change in cement content with depth was plotted. The cement content and mixing uniformity at each depth were analyzed to assess the quality of the cement-mixed piles and to provide feedback and guidance on whether additional grouting or other measures should be taken.

[0077] 10. Transfer equipment

[0078] After standing for a period of time, waiting for the grout and soil particles to complete the physicochemical reaction, in order to improve construction efficiency, during the solidification and molding of the first pile, the construction personnel will transport the mixing pile machine to the next pile position, clean the soil clods and residual grout from the mixing blades, grout nozzles and other parts, check the horizontal position and verticality of the pile machine, and after confirming that there are no errors, continue to carry out the mixing, grouting and lifting mixing operations of the subsequent pile bodies.

[0079] The load test was conducted 28 days after pile construction. The test results showed that the single pile bearing capacity of the cement mixing pile was greater than 120 kN, and the bearing capacity of the composite foundation reached 90 kPa.

[0080] 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, it should be understood that, unless otherwise stated in the present invention, both 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, devices, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of the present invention, any prior art methods, devices, 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 construction method of a layered cement mixing pile for soft ground treatment of a road, characterized by: The construction method comprises the following steps: S1: cleaning the surface of the foundation to be constructed and marking the pile position; S2: selecting a test pile position, using a pile machine to form a pile, and then sampling and detecting to adjust the process parameters; S3: based on the adjusted process parameters, using the pile machine to form piles on the remaining pile positions to form the cement mixing pile; S4: sampling and detecting the cement mixing pile to determine the quality of the cement mixing pile.

2. The construction method according to claim 1, characterized in that: The slurry for pile forming comprises Portland cement, gypsum, sodium sulfate and water reducing agent, and the water-cement ratio of the slurry is 0.4-0.

6.

3. The construction method according to claim 2, wherein The cement mixing ratio of the pile section between the top of the cement mixing pile and 75%-85% of the pile height is 15%, and the cement mixing ratio of the remaining pile section is 17%.

4. The construction method according to claim 1, wherein The pile machine comprises a drill bit, the drill bit comprises a main shaft, at least two secondary shafts are arranged on the periphery of the main shaft, and soil turning blades are arranged at the two ends of the at least two secondary shafts, and crushing teeth are arranged on the soil turning blades.

5. The construction method according to claim 4, wherein The secondary shafts are two secondary shafts, and the soil turning blades comprise upper and lower soil turning blades connected to the two ends of the two secondary shafts, respectively.

6. The construction method according to claim 5, wherein The drill bit comprises a radial slurry conveying pipe, one end of the radial slurry conveying pipe is in communication with a longitudinal slurry conveying pipe in the main shaft, and the other end of the radial slurry conveying pipe is in communication with a slurry injection head.

7. The construction method according to claim 6, wherein The longitudinal slurry conveying pipe comprises a first longitudinal slurry conveying pipe and a second longitudinal slurry conveying pipe, one end of the first longitudinal slurry conveying pipe and the second longitudinal slurry conveying pipe is connected to an electromagnetic valve, and the other end of the electromagnetic valve is connected to the radial slurry conveying pipe.

8. The construction method of claim 1, wherein The pile forming comprises the processes of drilling, first lifting, sinking and second lifting; The drilling speed is 0.8-1.2 m / min; The first lifting speed is 0.5-0.8 m / min, and the slurry injection pressure is 0.5-0.6 MPa; The sinking speed is 0.4-0.6 m / min, and the slurry injection pressure is 0.4 MPa; The second lifting speed is 0.4-0.6 m / min, and the slurry injection pressure is 0.4 MPa.

9. The construction method according to claim 1, wherein In step S4, determining the quality of the cement mixing pile comprises measuring the cement content of the cement mixing pile at different depths, drawing a curve of the change of the cement content with the depth according to the results of the cement content, analyzing the cement content and mixing uniformity at each depth, and determining the pile forming quality of the cement mixing pile.

10. The construction method according to claim 9, wherein The cement mixing pile at different depths is sampled by connecting multiple soil sampling pipes in series, and the length of a single soil sampling pipe is 20 cm, and a movable door is arranged on the single soil sampling pipe.

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