Preparation method of mud cake penetration test sample of pile foundation structure

Abstract

The invention relates to the technical field of mud cake penetration tests, and discloses a preparation method of a mud cake penetration test sample of a pile foundation structure, which comprises the following preparation steps: 1) measuring the radius and height of the mud cake penetration test sample in advance; (2) the mud over-filling height is obtained and calculated; (3) a cylindrical mold is prepared; a coiled material is used as a peripheral cylinder of the mold, a plurality of through holes are formed in the coiled material, and the coiled material forms the peripheral cylinder of the mold; the peripheral cylinder surrounds to form a die cavity and is provided with a bottom opening and a top opening; the inner side wall of the peripheral cylinder is covered with rectangular geotechnical cloth, and a bottom opening is covered with circular geotechnical cloth; (4) slurry of the pile foundation structure is obtained; (5) the slurry is placed in the mold cavity through the top opening; (6) water in the slurry in the mold cavity is circumferentially lost through the multiple through holes, the water content of the slurry is measured, the mold is disengaged until the water content of the slurry reaches the set water content, and the slurry in the mold is formed into a cylindrical mud cake penetration test sample.

Description

Technical Field

[0001] The invention relates to the technical field of mud skin penetration test, specifically, to a method for preparing mud skin penetration test specimens for pile foundation structures. Background Art

[0002] In recent years, the demand for infrastructure such as high-rise buildings, highways and railway bridges has continued to increase. Cast-in-place piles have become the most commonly used pile foundation structure for these facilities due to their high bearing capacity and small deformation. Ground-anchored walls, due to their higher bearing capacity and smaller deformation, are mostly found in buildings with higher protection requirements around construction sites, as well as projects with high requirements for deformation and waterproofing of the foundation pit itself.

[0003] Pile foundation structures (such as bored piles or ground-anchored walls) usually use a mud wall protection process. The particles in the mud are adsorbed and deposited on the wall of the pile hole. After mixing with the water, they gradually accumulate to form a layer of mud skin with low permeability. This mud skin can prevent the hole wall from collapsing, while isolating the water flow inside the pile hole and maintaining the stability of the hole wall.

[0004] As drilling progresses, the mud swirls inside the pile hole and mixes fully with the soil, further promoting the formation of mud skin. However, the mud skin is a weak interlayer, and its existence reduces the lateral friction resistance, thereby having a greater impact on the bearing capacity of the pile foundation structure.

[0005] The process of mud forming mud skin will produce water loss. The less water loss, the smaller the hydration of the soil layer and the more stable the pore wall. As the mud gradually loses water, the mud skin at different times shows different permeability. The study of mud skin permeability directly affects the calculation of consolidation time. The consolidation time can be used to estimate the moisture content and strength of the mud skin at different periods.

[0006] The permeability coefficient of mud skin is a key factor affecting its consolidation rate. A lower permeability coefficient means that the consolidation process will be slower, and the migration rate of water in the mud skin will slow down, thereby affecting the dehydration and consolidation effect of the mud skin. Therefore, in order to determine the permeability coefficient of mud at different water content states during the process of mud loss and becoming mud skin, it is necessary to make mud skin permeability test samples for mud skin permeability test.

[0007] In the prior art, conventional mud skin penetration test specimens are made by layering and compacting solid soil samples. However, the mud skin of the pile foundation structure is formed by the gradual transformation of the mud due to continuous water loss and evaporation. Therefore, the initial preparation of the mud skin penetration test specimen is relatively complicated. If the mud skin after excavation of the pile foundation structure is directly taken, it is often impossible to form a larger mud skin on site because the standard mud skin penetration test specimen for the laboratory penetration test is too large. Therefore, the method of directly taking the mud skin on site is also not advisable. Summary of the Invention

[0008] The object of the present invention is to provide a method for preparing a mud cake penetration test specimen of a pile foundation structure, aiming to solve the problem that it is difficult to prepare a mud cake penetration test specimen of a pile foundation structure in the prior art.

[0009] The present invention is implemented as follows. The method for preparing a mud cake penetration test specimen of a pile foundation structure includes the following preparation steps:

[0010] 1), Measure the radius and height of the instrument used for the penetration test to accommodate the mud cake penetration test specimen in advance;

[0011] 2), Calculate and obtain the calculated mud overpour height;

[0012] 3), Prepare a cylindrical mold; use a rectangular-shaped coil as the outer peripheral cylinder of the mold. The length of the coil is 105%-115% of the circumference of the mud cake penetration test specimen, and the width of the coil is 110%-120% of the mud overpour height; form a plurality of through holes on the coil; along the length direction of the coil, roll the coil into a cylindrical shape, and the coil forms the outer peripheral cylinder of the mold;

[0013] The outer peripheral cylinder surrounds to form a mold cavity. The bottom of the outer peripheral cylinder forms a bottom opening, and the top of the outer peripheral cylinder forms a top opening; cover a rectangular geotextile on the inner side wall of the outer peripheral cylinder, and the rectangular geotextile seals the plurality of through holes; cover a circular geotextile on the bottom opening of the outer peripheral cylinder;

[0014] 4), Obtain the mud of the pile foundation structure;

[0015] 5), Place the mold longitudinally, with the top opening facing upwards and the circular geotextile facing downwards; place the mud into the mold cavity through the top opening, and the height of the mud is the initial mud pouring height. The initial mud pouring height is the sum of the height of the mud cake penetration test specimen and the mud overpour height;

[0016] 6), The moisture of the mud in the mold cavity leaks circumferentially through the plurality of through holes. Measure the moisture content of the mud until the moisture content of the mud reaches the set moisture content, and then disengage the mold. The mud in the mold is formed into a cylindrical mud cake penetration test specimen.

[0017] Further, in the preparation step 2),

[0018] Measure the initial moisture content ω0 of the mud and the moisture content ω1 of the mud cake required for the penetration test;

[0019]

[0020] Wherein, the mass of water in the initial mud is m 水 ; the mass of water in the mud after water loss is m 水';The mass of solid in the mud is m 土 ;

[0021] The radius of the mud skin penetration test specimen is set to r0, the height is h0, the mud specific gravity is γ, the mud overfilling height is h, and the mud initial pouring height h1 is:

[0022] h1=h+h0 (3)

[0023] The total mass m of the slurry poured is:

[0024]

[0025] The mud water loss mass m1 is:

[0026] m1=m 水 -m 水 ' (5)

[0027] The density of water is ρ0 = 1 g / cm 3 , the mud water loss volume v1 is:

[0028]

[0029] Combining formulas (2) to (6), we can obtain the mud overfilling height h as follows:

[0030]

[0031] Furthermore, in the preparation step 3), the coiled material is a PVC coiled material.

[0032] Furthermore, in the construction step 3), the plurality of through holes are arranged at intervals along the length direction of the coil and at intervals along the width direction of the coil.

[0033] Furthermore, in the construction step 3), along the length direction of the coil, the two ends of the coil respectively have overlapping parts, and the overlapping parts are extended along the width direction of the coil; after the coil is rolled into an outer tube, the two overlapping parts of the coil are overlapped and fixedly connected to form an overlapping position, so that the coil forms a fixed outer tube.

[0034] Furthermore, in the construction step 3), adhesive tape is used to connect the two overlapping parts. The adhesive tape fixes the two overlapping parts together.

[0035] Furthermore, in the construction step 3), after the coil forms an outer peripheral tube, multiple circles of outer peripheral wire are arranged on the outer periphery of the outer peripheral tube. The multiple circles of outer peripheral wire are arranged at intervals along the axial direction of the outer peripheral tube, and the outer peripheral wire is arranged around the circumference of the outer peripheral tube.

[0036] Further, in the preparation step 3), multiple layers of the circular geotextiles are capped at the bottom opening, and the multiple layers of circular geotextiles are arranged in a stacked manner. An outer peripheral ring portion is formed on the outer periphery of the circular geotextile. The outer peripheral ring portions of the multiple layers of circular geotextiles enclose an outer peripheral cylinder, and the outer peripheral ring portions of the multiple layers of circular geotextiles are fixed to the outer peripheral cylinder by bottom tie wires.

[0037] Further, in the preparation step 3), the circular geotextile includes a central portion, and the outer peripheral ring portion is formed on the outer periphery of the central portion. The central portions of the multiple layers of circular geotextiles are capped at the bottom opening in a stacked manner; an elastic water filter plate is provided between adjacent central portions. Multiple water filter holes are provided in the water filter plate. The water filter plate is clamped and relatively fixed by two central portions, and the water filter plate is fixedly connected to the two central portions through multiple points.

[0038] In the preparation step 6), after the slurry is placed in the mold cavity, the slurry presses against the water filter plate and the multiple central portions to elastically deform. The water in the slurry is lost through the multiple central portions and the bottom of the water filter plate, and the water filter plate restricts the rate of water loss from the bottom of the slurry.

[0039] Further, in the preparation step 3), multiple elastic rings are provided on the outer periphery of the rectangular geotextile. After the rectangular geotextile is attached and fixed to the inner side wall of the outer peripheral cylinder, the elastic rings are fixedly attached to the inner side wall of the outer peripheral cylinder and surround the outer periphery of the through hole; in the preparation step 6), after the slurry is placed in the mold cavity, the slurry presses against the rectangular geotextile in the circumferential direction, the elastic rings are squeezed and compressed and deformed, and an elastic gap is formed between the rectangular geotextile and the through hole. As the water in the slurry is lost, the elastic rings elastically recover and the elastic gap increases.

[0040] Compared with the prior art, the method for preparing a mud skin penetration test specimen of the pile foundation structure provided by the present invention has the following advantages:

[0041] 1) Obtain mud skin penetration test specimens in different moisture content states during the process of mud loss to mud skin, ensuring the accuracy of the mud skin penetration test;

[0042] 2) Use a coil as the outer peripheral cylinder of the mold. Multiple through holes are provided on the coil, facilitating the circumferential loss of water flow in the slurry and accelerating the consolidation speed of the mud skin penetration test specimen;

[0043] 3) Determine the overpour height of the slurry according to the calculation, reserve the later mud loss settlement height, and there is no need to replenish the slurry again during the curing process, which is convenient and fast;

[0044] 4) The diameter of the mold is slightly larger than that of the mud skin penetration test sample. After obtaining the mud skin penetration test sample, it can be further trimmed to prevent damage to the outer surface of the mud skin penetration test sample caused by unexpected situations during the test;

[0045] 5) The preparation of the mud skin penetration test sample is simple and easy to operate, so that the test results are close to the actual situation. Description of the Drawings

[0046] Figure 1 is a schematic flow chart of the method for preparing a mud skin penetration test sample of the pile foundation structure provided by the present invention;

[0047] Figure 2 is a front view schematic diagram of the mold provided by the present invention;

[0048] Figure 3 is a partial sectional view schematic diagram of the cooperation between the outer peripheral cylinder and the circular geotextile provided by the present invention;

[0049] Figure 4 is a partial sectional view schematic diagram of the cooperation between the outer peripheral cylinder and the rectangular geotextile provided by the present invention. Detailed Embodiment

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

[0051] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0052] In the drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0053] Referring to Figures 1-4 as shown, it is a preferred embodiment provided by the present invention.

[0054] A method for preparing a mud skin penetration test sample of a pile foundation structure, characterized in that it includes the following preparation steps:

[0055] 1) Measure in advance the radius r0 and height h0 of the instrument used for the seepage test to accommodate the mud cake seepage test specimen;

[0056] 2) Calculate to obtain the calculated overpour height h of the slurry;

[0057] 3) Prepare a cylindrical mold; use a rectangular coil as the outer peripheral cylinder 100 of the mold. The length of the coil is 105%-115% of the circumference of the mud cake seepage test specimen, and the width of the coil is 110%-120% of the overpour height of the slurry; form a plurality of through holes 103 on the coil; along the length direction of the coil, roll the coil into a cylindrical shape, and the coil forms the outer peripheral cylinder 100 of the mold;

[0058] The outer peripheral cylinder 100 encloses to form a mold cavity 105. The bottom of the outer peripheral cylinder 100 forms a bottom opening, and the top of the outer peripheral cylinder 100 forms a top opening; cover a rectangular geotextile 104 on the inner side wall of the outer peripheral cylinder 100, and the rectangular geotextile 104 seals the plurality of through holes 103; seal a circular geotextile 200 at the bottom opening of the outer peripheral cylinder 100;

[0059] 4) Obtain the slurry of the pile foundation structure;

[0060] 5) Place the mold longitudinally with the top opening facing up and the circular geotextile 200 facing down; place the slurry into the mold cavity 105 through the top opening, and the height of the slurry is the initial pouring height of the slurry;

[0061] 6) The moisture of the slurry in the mold cavity 105 leaks circumferentially through the plurality of through holes 103. Measure the moisture content of the slurry until the moisture content of the slurry reaches the set moisture content, then separate the mold, and the slurry in the mold forms a cylindrical mud cake seepage test specimen.

[0062] The method for preparing the mud cake seepage test specimen of the pile foundation structure provided above has the following advantages:

[0063] 1) Obtain mud cake seepage test specimens in different moisture content states during the process of slurry water loss to form mud cakes, ensuring the accuracy of the mud cake seepage test;

[0064] 2) Use a coil as the outer peripheral cylinder 100 of the mold. The coil is provided with a plurality of through holes 103, which is convenient for the water flow in the slurry to leak circumferentially and speeds up the consolidation speed of the mud cake seepage test specimen;

[0065] 3) Determine the overpour height of the slurry according to the calculation, reserve the later slurry water loss settlement height, and there is no need to replenish the slurry again during the curing process, which is convenient and fast;

[0066] 4) The diameter of the mold is slightly larger than the diameter of the mud skin penetration test sample. After obtaining the mud skin penetration test sample, it can be further sheared to prevent damage to the outer surface of the mud skin penetration test sample due to unexpected circumstances during the test;

[0067] 5) The mud skin penetration test specimen is simple to make and easy to operate, so that the test results are close to reality.

[0068] In this embodiment, in the preparation step 2),

[0069] Measure the initial moisture content of the mud ω0 and the moisture content of the mud skin required for the penetration test ω1;

[0070]

[0071] Among them, the mass of water in the initial mud is m 水 ; The mass of water in the mud after dehydration is m 水 ';The mass of solid in the mud is m 土 ;

[0072] The radius of the mud skin penetration test specimen is set to r0, the height is h0, the mud specific gravity is γ, the mud overfilling height is h, and the mud initial pouring height h1 is:

[0073] h1=h+h0 (3)

[0074] The total mass m of the slurry poured is:

[0075]

[0076] The mud water loss mass m1 is:

[0077] m1=m 水 -m 水 ' (5)

[0078] The density of water is ρ0 = 1 g / cm 3 , the mud water loss volume v1 is:

[0079]

[0080] Combining formulas (2) to (6), we can obtain the mud overfilling height h as follows:

[0081]

[0082] In this embodiment, in the preparation step 3), the coiled material is a PVC coiled material, which facilitates the bending and deformation of the coiled material, and after the outer peripheral tube 100 is formed by bending and deformation, the shape of the outer peripheral tube 100 can be maintained.

[0083] In this embodiment, in construction step 3), a plurality of through holes 103 are arranged at intervals along the length direction of the coil material and also at intervals along the width direction of the coil material. In this way, after the slurry is placed in the mold cavity 105, it is convenient for the moisture in the slurry to drain from a multi-faceted circumferential range, and a mud skin penetration test specimen is quickly formed.

[0084] In this embodiment, in construction step 3), along the length direction of the coil material, both ends of the coil material respectively have overlapping portions, and the overlapping portions extend along the width direction of the coil material; after the coil material is wound into the outer peripheral cylinder 100, the two overlapping portions of the coil material are overlapped and fixedly connected to form an overlapping position, so that the coil material forms a fixed outer peripheral cylinder 100.

[0085] In this way, after the coil material is wound into the outer peripheral cylinder 100, the two overlapping portions overlap each other to form an overlapping position, thereby realizing the stability of the structure of the outer peripheral cylinder 100.

[0086] In this embodiment, in construction step 3), adhesive tape is used to connect to the overlapping position, and the adhesive tape fixedly connects the two overlapping portions. In this way, it is convenient to fixedly connect the two overlapping portions directly.

[0087] In this embodiment, in construction step 3), after the coil material forms the outer peripheral cylinder 100, multiple circles of outer peripheral binding wires are arranged on the outer periphery of the outer peripheral cylinder 100. The multiple circles of outer peripheral binding wires are arranged at intervals along the axial direction of the outer peripheral cylinder 100, and the outer peripheral binding wires are arranged in a circumferential direction around the outer peripheral cylinder 100. By arranging a plurality of outer peripheral binding wires, the structure of the outer peripheral cylinder 100 can be kept stable in the entire circumferential direction and the entire axial direction.

[0088] In this embodiment, in preparation step 3), multiple layers of the circular geotextile 200 are covered at the bottom opening. The multiple layers of circular geotextiles 200 are arranged in a stacked manner. An outer peripheral ring portion 201 is formed on the outer periphery of the circular geotextile 200. The outer peripheral ring portions 201 of the multiple layers of circular geotextiles 200 enclose the outer peripheral cylinder 100, and the outer peripheral ring portions 201 of the multiple layers of circular geotextiles 200 are fixed to the outer peripheral cylinder 100 by using the bottom binding wires 202.

[0089] By covering multiple layers of circular geotextiles 200 at the bottom opening, the bottom opening can be blocked, and the formation of multiple layers of circular geotextiles 200 can realize the support of the bottom of the mold, ensure that the slurry is stably placed in the mold cavity 105, and limit the rate of moisture loss from the multiple layers of circular geotextiles 200 in the slurry.

[0090] In this embodiment, in preparation step 3), the circular geotextile 200 includes a central portion 203, and an outer peripheral ring portion 201 is formed on the outer periphery of the central portion 203. The central portions 203 of multiple layers of circular geotextiles 200 are stacked and sealed at the bottom opening; an elastic water filter plate 300 is provided between adjacent central portions 203. The water filter plate 300 is provided with a plurality of water filter holes 301. The water filter plate 300 is clamped and relatively fixed by two central portions 203, and the water filter plate 300 is fixedly connected to the two central portions 203 through a plurality of points.

[0091] In preparation step 6), after the slurry is placed in the mold cavity 105, the slurry presses against the water filter plate 300 and the central portions 203 of multiple layers to elastically deform. The water in the slurry flows out through the bottom of the central portions 203 of multiple layers and the water filter plate 300, and the water filter plate 300 restricts the rate of water loss at the bottom of the slurry.

[0092] By surrounding the outer peripheral ring portion 201 around the outer periphery of the outer peripheral cylinder 100 and fixing it with the bottom tie wire 202, it can be ensured that the central portion 203 blocks the bottom opening. An elastic water filter plate 300 is arranged between two central portions 203, and the supporting strength of multiple central portions 203 can be supported by the water filter plate 300. When the slurry is placed in the mold cavity 105, it is avoided that the central portion 203 is sunken or protruded downward, which affects the formation of the specimen for the mud cake permeability test; in addition, by arranging the water filter plate 300 and the water filter plate 300 is provided with a plurality of water filter holes 301, the water loss at the bottom can be restricted on the premise of not affecting the water loss at the bottom, so as to ensure the actual situation of mud cake formation in actual situations, so that the formed specimen for the mud cake permeability test is more in line with the actual situation and ensures the accuracy of the mud cake permeability test.

[0093] In this embodiment, in preparation step 3), a plurality of elastic rings 106 are provided on the outer periphery of the rectangular geotextile 104. After the rectangular geotextile 104 is attached and fixed to the inner side wall of the outer peripheral cylinder 100, the elastic rings 106 are fixedly attached to the inner side wall of the outer peripheral cylinder 100 and surround the outer periphery of the through hole 103; in preparation step 6), after the slurry is placed in the mold cavity 105, the slurry presses against the rectangular geotextile 104 in the circumferential direction, the elastic rings 106 are compressed and deformed, and there is an elastic gap 107 between the rectangular geotextile 104 and the through hole 103. As the water in the slurry flows out, the elastic rings 106 elastically recover and the elastic gap 107 increases.

[0094] By arranging the elastic rings 106, an elastic gap 107 can be maintained between the rectangular geotextile 104 and the through hole 103, which is convenient for the water in the slurry to flow out through a plurality of through holes 103, and as the water flows out, the elastic gap 107 changes to adjust the rate of water flow.

[0095] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a sample for the mud cake penetration test of a pile foundation structure, characterized in that, The method comprises the following preparation steps: 1) Measure in advance the radius and height of the instrument used for the penetration test to accommodate the mud skin penetration test sample; 2) Calculate and obtain the mud overfilling height; 3) Prepare a cylindrical mold; use a rectangular coil as the outer tube of the mold, wherein the length of the coil is 105%-115% of the circumference of the mud skin penetration test specimen, and the width of the coil is 110%-120% of the mud overfill height; form a plurality of through holes in the coil; and roll the coil into a cylindrical shape along the length direction of the coil, so that the coil forms the outer tube of the mold; The outer tube surrounds and forms a mold cavity, the bottom of the outer tube forms a bottom opening, and the top of the outer tube forms a top opening; a rectangular geotextile is covered on the inner side wall of the outer tube, and the rectangular geotextile covers a plurality of through holes; a circular geotextile is covered on the bottom opening of the outer tube; 4) Obtaining slurry for pile foundation structure; 5) Place the mold in a longitudinal direction with the top opening facing upward and the circular geotextile facing downward; place the mud into the mold cavity through the top opening. The height of the mud is the initial mud pouring height, which is the sum of the height of the mud skin penetration test specimen and the mud over-pouring height; 6) The moisture of the mud in the mold cavity is lost circumferentially through multiple through holes, and the moisture content of the mud is measured. After the moisture content of the mud reaches the set moisture content, the mold is disengaged and the mud in the mold is formed into a cylindrical mud skin penetration test specimen.

2. The method for preparing a specimen for the mud skin penetration test of the pile foundation structure according to claim 1, wherein, In the preparation step 2), Measure the initial moisture content of the mud ω0 and the moisture content of the mud skin required for the penetration test ω1; Among them, the mass of water in the initial mud is m 水 ; The mass of water in the mud after dehydration is m 水 ';The mass of solid in the mud is m 土 ; The radius of the mud skin penetration test specimen is set to r0, the height is h0, the mud specific gravity is γ, the mud overfilling height is h, and the mud initial pouring height h1 is: h1=h+h0 (3) The total mass m of the pouring slurry is: The mud water loss mass m1 is: m1 = m 水 -m 水 ' (5) The density of water is ρ0 = 1 g / cm 3 , and the mud filtration loss volume v1 is as follows: Combining formulas (2) to (6), we can obtain the mud overfilling height h as follows:

3. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 1, characterized in that, In the preparation step 3), the coiled material is a PVC coiled material.

4. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 1, characterized in that, In the construction step 3), the plurality of through holes are arranged at intervals along the length direction of the coil and at intervals along the width direction of the coil.

5. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 1, characterized in that, In the construction step 3), along the length direction of the coil, the two ends of the coil respectively have overlapping parts, and the overlapping parts are extended along the width direction of the coil; after the coil is rolled into an outer peripheral tube, the two overlapping parts of the coil are overlapped and fixedly connected to form an overlapping position, so that the coil forms an outer peripheral tube in a fixed state.

6. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 5, characterized in that, In the construction step 3), adhesive tape is used to connect the two overlapping parts. The adhesive tape fixes the two overlapping parts.

7. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 1, characterized in that, In the construction step 3), after the coil forms an outer peripheral tube, multiple circles of outer peripheral wire are arranged on the outer periphery of the outer peripheral tube. The multiple circles of outer peripheral wire are arranged at intervals along the axial direction of the outer peripheral tube and are arranged around the circumference of the outer peripheral tube.

8. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to claim 1, characterized in that, In the preparation step 3), multiple layers of the circular geotextiles are covered on the bottom opening, and the multiple layers of the circular geotextiles are arranged in a stacked manner. An outer peripheral ring portion is formed on the outer periphery of the circular geotextile. The outer peripheral ring portions of the multiple layers of the circular geotextiles enclose an outer peripheral cylinder, and the outer peripheral ring portions of the multiple layers of the circular geotextiles are fixed to the outer peripheral cylinder by bottom tying wires.

9. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to any one of claims 1 to 8, characterized in that, In the preparation step 3), the circular geotextile includes a central portion, and the outer peripheral ring portion is formed on the outer periphery of the central portion. The central portions of the multiple layers of the circular geotextiles are covered on the bottom opening in a stacked manner; an elastic water filter plate is provided between adjacent central portions. A plurality of water filter holes are provided in the water filter plate. The water filter plate is clamped and relatively fixed by two central portions, and the water filter plate is fixedly connected to the two central portions through a plurality of points. In the preparation step 6), after the slurry is placed in the mold cavity, the slurry presses against the water filter plate and the multiple central portions to elastically deform. The water in the slurry flows out through the multiple central portions and the bottom of the water filter plate. The water filter plate restricts the rate of water loss from the bottom of the slurry.

10. The method for preparing a mud skin penetration test specimen of the pile foundation structure according to any one of claims 1 to 8, characterized in that, In the preparation step 3), a plurality of elastic rings are provided on the outer periphery of the rectangular geotextile. After the rectangular geotextile is attached and fixed to the inner side wall of the outer peripheral cylinder, the elastic rings are fixedly attached to the inner side wall of the outer peripheral cylinder and surround the outer periphery of the through hole; in the preparation step 6), after the slurry is placed in the mold cavity, the slurry presses against the rectangular geotextile in the circumferential direction. The elastic rings are squeezed and compressed and deformed, and an elastic interval is formed between the rectangular geotextile and the through hole. As the water in the slurry is lost, the elastic rings elastically recover and the elastic interval increases.

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