A method for testing the vertical compressive bearing capacity of expanded pile foundation

Abstract

The present invention relates to the field of building technology, and discloses a method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation, comprising: obtaining basic information of an in-situ pile foundation; the basic information includes pile bottom burial depth, foundation, pile diameter, bottom-enlarged size, and concrete material number; setting an equivalent pile foundation within a preset distance of the in-situ pile foundation according to the basic information of the in-situ pile foundation; performing a compressive bearing test on the equivalent pile foundation; wherein the test method includes a heap loading method or a self-balancing method; judging whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements according to the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test. The present invention proposes a method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation, which can realize the vertical compressive bearing capacity detection of a bottom-enlarged pile foundation with a shorter pile length, and can also prevent the columns of the bottom-enlarged pile foundation from being damaged due to loading.

Description

Technical Field

[0001] The invention relates to the technical field of construction, and in particular to a method for detecting the vertical compressive bearing capacity of an expanded base pile foundation. Background Art

[0002] In semi-excavation subway construction, pile foundations are often set up under the cover slab columns. Considering factors such as the cover slab span, column spacing, cover slab load, foundation conditions, and cost control, a shorter pile length and expanded bottom pile foundation is a good choice.

[0003] According to the Technical Specifications for Building Foundation Pile Testing (JGJ 106-2014), there are two methods for testing the vertical bearing capacity of a single pile, namely, the single pile vertical compressive static load test and the high strain method. Since the high strain method is not suitable for testing the vertical compressive bearing capacity of large-diameter expanded piles, the compressive static load test method is considered for testing; the static load test method includes the heap load method, the self-balancing method, etc.

[0004] The pile loading method has disadvantages such as large site requirements, time-consuming and labor-intensive. In addition, during the pile loading test, the specification requires that the pile top load be loaded to twice the design load, and there is a risk of compressive damage to the column. Therefore, the pile loading method for in-situ pile testing is not applicable to this project.

[0005] The self-balancing method has the advantages of saving time, labor, safety, no pollution, and is not limited by site conditions and loading tonnage. It is currently used by most pile foundation engineering inspections. According to the "Self-balancing Method for Static Load Test of Pile Foundation" (JT / T 738-2009), the self-balancing method requires the load box to be placed at the balance point of the pile body (the sum of the effective deadweight of the upper pile body and the ultimate friction resistance of the pile side is basically equal to the sum of the ultimate friction resistance of the lower pile side and the ultimate pile end resistance). By applying hydraulic pressure to the load box and combining the pile deformation data, it is judged whether the pile foundation bearing capacity meets the design requirements. For short pile length and expanded bottom pile foundation, there is no condition for burying the load box. Therefore, the self-balancing method is not applicable for in-situ pile testing.

[0006] Therefore, there is an urgent need for a method for testing the vertical compressive bearing capacity of an expanded base pile foundation, which can be suitable for testing the vertical bearing capacity of an expanded base pile foundation with a shorter pile length, and can also prevent the columns of the expanded base pile foundation from being damaged due to loading. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for detecting the vertical compressive bearing capacity of an expanded base pile foundation, which can be applied to the vertical bearing capacity detection of an expanded base pile foundation with a shorter pile length, and can also prevent the columns of the expanded base pile foundation from being damaged due to loading.

[0008] The present invention provides a method for detecting the vertical compressive bearing capacity of a base-enlarged pile foundation, comprising the following steps:

[0009] S1. Obtain basic information of the in-situ pile foundation; the basic information includes pile bottom burial depth, foundation, pile diameter, bottom expansion size, and concrete material grade used;

[0010] S2. Within a preset distance of the in-situ pile foundation, an equivalent pile foundation is set according to the basic information of the in-situ pile foundation;

[0011] S3. Conduct a compressive bearing test on the equivalent pile foundation; the test method includes a heap loading method or a self-balancing method;

[0012] S4. Determine whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements based on the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test.

[0013] Furthermore, in S1, the in-situ pile foundation is composed of an expanded bottom pile foundation and a column whose lower end is embedded in the expanded bottom pile foundation, and the pile top of the in-situ pile foundation is buried underground; wherein, the pile top refers to the top of the expanded bottom pile foundation.

[0014] Furthermore, in S2, the equivalent pile foundation as a whole is composed of an expanded bottom pile foundation, and the buried depth of the pile top of the equivalent pile foundation is located at a preset height above the ground; wherein, the pile top refers to the top of the expanded bottom pile foundation.

[0015] Furthermore, when the pile loading method is selected for the compressive bearing test, in S3, the compressive bearing test of the equivalent pile foundation includes:

[0016] S3a1. Calculate the maximum vertical load of the equivalent pile foundation under the pile loading method;

[0017] S3a2. The maximum vertical load is graded, and the vertical load is applied to the pile top of the equivalent pile foundation step by step according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load is recorded until the last level of vertical load is reached.

[0018] Furthermore, in S3a1, the maximum vertical load of the equivalent pile foundation under the pile loading method is calculated using the following formula:

[0019] F k1max =2×F k +2×G kc -G kfz +q sk ×u×L;

[0020] Among them, F k1max It represents the maximum vertical load on the top of the equivalent pile foundation under the pile loading method, F k G represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects. kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, qsk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the elevation of the top of the in-situ pile foundation.

[0021] Furthermore, when the self-balancing method is selected to perform the compressive bearing test, in S3, the compressive bearing test of the equivalent pile foundation includes:

[0022] S3b1. Calculate the maximum vertical load of the equivalent pile foundation under the self-balancing method;

[0023] S3b2. Calculate the maximum loading capacity of the load box of the equivalent pile foundation under the self-balancing method;

[0024] S3b3. The maximum vertical load and the maximum load of the load box load are graded respectively, and the vertical load and the load box load are applied to the pile top of the equivalent pile foundation step by step according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load and load box load is recorded until the last level of vertical load and load box load is reached.

[0025] Furthermore, in S3b1, the maximum vertical load of the equivalent pile foundation under the self-balancing method is calculated using the following formula:

[0026] F k2max =2×F k +2×G kc -G kfz -q sk ×u×L;

[0027] Among them, F k2max F represents the maximum vertical load on the top of the equivalent pile foundation under the self-balancing method. k G represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects. kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, q sk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the elevation of the top of the in-situ pile foundation.

[0028] Furthermore, in S3b2, the maximum load of the load box of the equivalent pile foundation under the self-balancing method is calculated using the following formula:

[0029] Q umax =Q Lmax =2×(F k +G kc );

[0030] Among them, Q umax Indicates the maximum upward load of the load box, Q Lmax Indicates the maximum downward load of the load box.

[0031] Further, in S4, judging whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements according to the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test includes:

[0032] If the vertical displacement of the pile top of the equivalent pile foundation does not exceed 40mm, and the vertical displacement of the pile top of the equivalent pile foundation caused by the application of the last level of load does not exceed 5 times the vertical displacement of the pile top of the equivalent pile foundation caused by the previous level of load, the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements.

[0033] The embodiments of the present invention have the following technical effects:

[0034] The present invention adopts an equivalent pile foundation to replace the in-situ pile foundation for vertical pressure bearing test for the expanded base pile foundation with a shorter pile length, so as to avoid the damage of the column due to loading; comprehensively considering the site conditions and economy, the stacking method or the self-balancing method is selected to carry out the compressive bearing test on the equivalent pile foundation, and the formula derived by the present application is used to convert the maximum vertical load at the pile top and the maximum load of the load box load, so as to provide the conditions for the vertical pressure bearing test of the equivalent pile foundation, thereby obtaining the vertical compressive bearing capacity test result of the in-situ pile foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a flow chart of a method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation provided by an embodiment of the present invention;

[0037] Figure 2 It is a structural schematic diagram of an in-situ pile foundation of an expanded bottom pile foundation provided by an embodiment of the present invention;

[0038] Figure 3 It is a structural schematic diagram of a compressive bearing test of an equivalent pile foundation by a heap loading method provided by an embodiment of the present invention;

[0039] Figure 4 It is a structural schematic diagram of a compressive bearing test of an equivalent pile foundation by a self-balancing method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0041] The present invention proposes a method for detecting the vertical compressive bearing capacity of a base-enlarged pile foundation. Figure 1 is a flow chart of a method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation provided by an embodiment of the present invention, see Figure 1 , including:

[0042] S1. Obtain basic information of in-situ pile foundation.

[0043] In some embodiments, Figure 2 is a schematic structural diagram of an in-situ pile foundation of an expanded bottom pile foundation provided by an embodiment of the present invention, see Figure 2 The in-situ pile foundation consists of an expanded bottom pile foundation and a column with the lower end embedded in the expanded bottom pile foundation. The pile top of the in-situ pile foundation is buried underground; the pile top refers to the top of the expanded bottom pile foundation. The basic information of the in-situ pile foundation includes the pile bottom burial depth, foundation, pile diameter, expanded bottom size, concrete material grade, etc.

[0044] S2. Within a preset distance of the in-situ pile foundation, an equivalent pile foundation is set according to the basic information of the in-situ pile foundation.

[0045] In some embodiments, the preset distance can be set according to actual conditions. The equivalent pile foundation is composed of an expanded bottom pile foundation as a whole, and the pile top of the equivalent pile foundation is located at a preset height above the ground; wherein the pile top refers to the top of the expanded bottom pile foundation. The pile bottom burial depth, foundation, pile diameter, expanded bottom size, concrete material grade, etc. of the equivalent pile foundation are consistent with those of the in-situ pile foundation.

[0046] S3. Carry out compressive bearing test on equivalent pile foundation.

[0047] In some embodiments, since the equivalent pile foundation is relatively long and provides conditions for the burial of the load box, the test method can adopt a stacking method to avoid the risk of crushing the columns under the in-situ cover plate. A self-balancing method can also be used to reduce the limitations of site factors.

[0048] In some embodiments, Figure 3 is a schematic diagram of a structure for carrying out a compressive bearing test on an equivalent pile foundation by a heap loading method provided by an embodiment of the present invention, see Figure 3When the pile loading method is selected for the compressive bearing test, reference beams and brackets are arranged on both sides of the pile top of the equivalent pile foundation, and the reference beam is fixedly connected to the pile top of the equivalent pile foundation through a magnetic base; wherein, the magnetic base is also called a universal base, one end of which can be fixed on the iron reference beam by magnetic force, and the other end can clamp a dial indicator for measuring the vertical displacement of the pile top; the bracket is used to support the weight of the heavy object; a jack (not shown in the figure) is arranged between the heavy object and the pile top of the equivalent pile foundation, and the jack is used to apply vertical load to the pile top step by step; the reference beam often adopts steel components such as scaffolding steel pipes, I-beams, triangular trusses, and channel steels to ensure the stability of the magnetic base.

[0049] When the pile loading method is selected for the compressive bearing test, the compressive bearing test of the equivalent pile foundation includes:

[0050] S3a1. Calculate the maximum vertical load of the equivalent pile foundation under the pile loading method.

[0051] The calculation formula is as follows:

[0052] F k1max =2×F k +2×G kc -G kfz +q sk ×u×L;

[0053] Among them, F k1max It represents the maximum vertical load on the top of the equivalent pile foundation under the pile loading method, F k G represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects. kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, q sk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the elevation of the top of the in-situ pile foundation.

[0054] For example, take the semi-covered excavation column pile foundation of a subway station as an example:

[0055] F k =6696.5KN; G kc =559KN; G kfz =1735.23KN;q sk =53.34kpa; u=5.65m; L=26.29m;

[0056] Then F k1max =2×6696.5KN+2×559KN-1735.23KN+53.34kpa×5.65m×26.29m

[0057] =20698.81KN.

[0058] S3a2. The maximum vertical load is graded, and the vertical load is applied to the pile top of the equivalent pile foundation step by step according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load is recorded until the last level of vertical load is reached.

[0059] Among them, the maximum vertical load can be graded with reference to the "Technical Specifications for Testing of Building Foundation Piles" (JGJ 106-2014). For example, it can be divided into 10 levels, and each level applies a vertical load of 10% of the maximum vertical load to the top of the equivalent pile foundation, among which the first level load can be twice the graded load.

[0060] In some embodiments, Figure 4 is a structural schematic diagram of a compressive bearing test of an equivalent pile foundation by a self-balancing method provided by an embodiment of the present invention, see Figure 4 When the self-balancing method is selected for the compressive bearing test, a loading system is set up near the equivalent pile foundation. The loading system is mostly a high-pressure oil pump, which is set on the ground and is used to fill the load box with oil; brackets are set on both sides of the pile top of the equivalent pile foundation, and the brackets are used to support the weight of the heavy object; a jack (not shown in the figure) is set between the heavy object and the pile top of the equivalent pile foundation, and the jack is used to apply vertical load to the pile top step by step; a displacement rod and an oil pipe are set inside the equivalent pile foundation, and the ends of the displacement rod and the oil pipe are located at the pile top line of the original pile foundation; a load box and a guide body are also set inside the equivalent pile foundation; the load box is a special loading device in the self-balancing method test, and it is at the balance point of the pile body. The same load is loaded upward and downward at the same time; the guide body is a conical guide body arranged at the lower part of the load box. When the concrete is poured for the second time within the range of the load box, it guides the concrete smoothly to avoid the formation of voids; wherein, the displacement rod is used to transfer the displacement at the load box to the ground and should have a certain rigidity. For example, when the pile length of the equivalent pile foundation is less than or equal to 40m, a steel pipe with a diameter of 25mm~30mm can be used as the displacement rod; when the pile length of the equivalent pile foundation is greater than 40m, a displacement steel wire should be used instead of the displacement rod; the oil pipe is a pipeline used to connect the high-pressure oil pump and the load box, and is used to input oil into the load box to realize the step-by-step application of the load loading of the load box.

[0061] When the self-balancing method is selected for the compressive bearing test, in S3, the compressive bearing test of the equivalent pile foundation includes:

[0062] S3b1. Calculate the maximum vertical load of the equivalent pile foundation under the self-balancing method.

[0063] The calculation formula is as follows:

[0064] F k2max=2×F k +2×G kc -G kfz -q sk ×u×L;

[0065] Among them, F k2max F represents the maximum vertical load on the top of the equivalent pile foundation under the self-balancing method. k G represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects. kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, q sk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the elevation of the top of the in-situ pile foundation.

[0066] S3b2. Calculate the maximum load of the load box of the equivalent pile foundation under the self-balancing method.

[0067] The calculation formula is as follows:

[0068] Q umax =Q Lmax =2×(F k +G kc );

[0069] Among them, Q umax Indicates the maximum upward load of the load box, Q Lmax Indicates the maximum downward load of the load box.

[0070] For example, take the semi-covered excavation column pile foundation of a subway station as an example

[0071] F k =6696.5KN; G kc =559KN;G kfz =1735.23KN;q sk =53.34kpa; u=5.65m; L=26.29m;

[0072] Q umax =Q Lmax =2×(6696.5KN+559KN)=14511KN, which is the maximum load capacity of the load box.

[0073] F k2max =2×6696.5KN+2×559KN-1735.23KN-53.34kpa×5.65m×26.29m

[0074] =4852.73KN, which is approximately 20%~25% of the maximum vertical load on the pile top of the equivalent pile foundation under the heap loading method.

[0075] It can be seen from this that the maximum vertical load on the top of the equivalent pile foundation required by the pile loading method is large, and a larger site is needed to place the heavy objects. When site conditions do not allow, the pile loading method can be used for compressive bearing tests.

[0076] S3b3. The maximum vertical load and the maximum load of the load box load are graded respectively, and the vertical load and the load box load are applied to the pile top of the equivalent pile foundation step by step according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load and load box load is recorded until the last level of vertical load and load box load is reached.

[0077] Among them, the maximum vertical load and the maximum load of the load box load can be graded with reference to the Technical Specifications for Testing of Building Foundation Pile (JGJ 106-2014), and the grading of the maximum vertical load and the maximum load of the load box load should be the same. For example, the maximum vertical load and the maximum load of the load box load can be divided into 10 levels, and each level applies a vertical load of 10% of the maximum vertical load and a load box load of 10% of the maximum load of the load box load to the top of the equivalent pile foundation. When the pile end is coarse-grained soil, coarse-grained soil or hard clay, the first level can be loaded at 2 times the graded load.

[0078] S4. Determine whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements based on the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test.

[0079] In some embodiments, if the vertical displacement of the pile top of the equivalent pile foundation does not exceed 40 mm, and the vertical displacement of the pile top of the equivalent pile foundation caused by applying the last level of load does not exceed 5 times the vertical displacement of the pile top of the equivalent pile foundation caused by the previous level of load, then the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements.

[0080] In addition, after the vertical compressive bearing test of the pile foundation is completed, the equivalent pile foundation can be connected to the bottom plate of the main structure of the station and serve as anti-floating piles as an anti-floating safety reserve, which can also reduce material waste.

[0081] It should be noted that the terms used in the present invention are only for describing specific embodiments, rather than limiting the scope of the present application. As shown in the present specification, unless the context clearly indicates an exception, the words "one", "a", "a kind of" and / or "the" do not specifically refer to the singular, but may also include the plural. The terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or device. In the absence of more restrictions, the elements defined by the sentence "include one..." do not exclude the presence of other identical elements in the process, method or device including the elements.

[0082] It should also be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are 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, and therefore cannot be understood as a limitation on the present invention. Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the vertical compressive bearing capacity of an expanded bottom pile foundation, which is suitable for testing the vertical bearing capacity of an expanded bottom pile foundation with a shorter pile length, and can also prevent the columns of the expanded bottom pile foundation from being damaged due to loading, and is characterized in that: The steps include: S1. Obtain basic information of the in-situ pile foundation; the basic information includes pile bottom burial depth, foundation, pile diameter, expanded bottom size, and concrete material number; the in-situ pile foundation is composed of an expanded bottom pile foundation and a column whose lower end is embedded in the expanded bottom pile foundation, and the pile top burial depth of the in-situ pile foundation is located underground; wherein the pile top refers to the top of the expanded bottom pile foundation; S2. Setting an equivalent pile foundation within a preset distance of the in-situ pile foundation according to basic information of the in-situ pile foundation; The equivalent pile foundation is composed of an expanded bottom pile foundation as a whole, and the pile top of the equivalent pile foundation is buried at a preset height above the ground; wherein the pile top refers to the top of the expanded bottom pile foundation; S3, performing a compressive bearing test on the equivalent pile foundation; wherein the test method includes a heap loading method or a self-balancing method; S4. Judging whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements according to the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test.

2. A method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation according to claim 1, characterized in that: When the pile loading method is selected to perform the compressive bearing test, in S3, performing the compressive bearing test on the equivalent pile foundation includes: S3a1. Calculate the maximum vertical load of the equivalent pile foundation under the heap loading method; S3a2, the maximum vertical load is graded, and the vertical load is applied to the pile top of the equivalent pile foundation step by step according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load is recorded until the last level of vertical load is reached.

3. A method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation according to claim 2, characterized in that: In S3a1, the maximum vertical load of the equivalent pile foundation under the heap loading method is calculated using the following formula: F k1max =2×F k +2×G kc -G kfz +q sk ×u×L; Among them, F k1max It represents the maximum vertical load on the top of the equivalent pile foundation under the pile loading method, F k It represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects, G kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, q sk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the top elevation of the in-situ pile foundation.

4. A method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation according to claim 1, characterized in that: When the self-balancing method is selected to perform the compressive bearing test, in S3, performing the compressive bearing test on the equivalent pile foundation includes: S3b1. Calculate the maximum vertical load of the equivalent pile foundation under the self-balancing method; S3b2, calculating the maximum loading capacity of the load box load of the equivalent pile foundation under the self-balancing method; S3b3, the maximum vertical load and the maximum load of the load box load are graded respectively, and the vertical load and the load box load are applied step by step to the pile top of the equivalent pile foundation according to the grades, and the vertical displacement of the pile top of the equivalent pile foundation caused by each level of vertical load and load box load is recorded until the last level of vertical load and load box load is reached.

5. A method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation according to claim 4, characterized in that: In S3b1, the maximum vertical load of the equivalent pile foundation under the self-balancing method is calculated using the following formula: F k2max =2×F k +2×G kc -G kfz -q sk ×u×L; Among them, F k2max F represents the maximum vertical load on the top of the equivalent pile foundation under the self-balancing method. k It represents the vertical force acting on the top surface of the in-situ pile foundation column under the standard combination of load effects, G kc Indicates the standard value of the deadweight of the column above the top of the in-situ pile foundation, G kfz It represents the standard value of the deadweight of the equivalent pile above the top of the original pile foundation, q sk It represents the standard value of the ultimate lateral resistance of the soil on the pile side, u represents the circumference of the pile body of the equivalent pile foundation, and L represents the vertical distance from the ground elevation of the equivalent pile foundation to the top elevation of the in-situ pile foundation.

6. A method for detecting the vertical compressive bearing capacity of a base-enlarged pile foundation according to claim 5, characterized in that: In S3b2, the maximum loading capacity of the load box of the equivalent pile foundation under the self-balancing method is calculated, and the calculation formula is as follows: Q umax =Q Lmax =2×(F k +G kc ); Among them, Q umax Indicates the maximum upward load of the load box, Q Lmax Indicates the maximum downward load of the load box.

7. A method for detecting the vertical compressive bearing capacity of a bottom-enlarged pile foundation according to claim 1, characterized in that: In S4, judging whether the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements according to the vertical displacement of the pile top of the equivalent pile foundation caused during the compressive bearing test includes: If the vertical displacement of the pile top of the equivalent pile foundation does not exceed 40 mm, and the vertical displacement of the pile top of the equivalent pile foundation caused by the application of the last level of load does not exceed 5 times the vertical displacement of the pile top of the equivalent pile foundation caused by the previous level of load, then the vertical compressive bearing capacity of the in-situ pile foundation meets the requirements.

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