A method and structure for detecting vertical compressive bearing capacity of a single pile with an enlarged head pile

Abstract

The present invention belongs to the technical field of pile foundation bearing capacity detection, and specifically relates to a single pile vertical compressive bearing capacity detection method and detection structure of an enlarged head pile, including a load box, the load box including an upper plate, a hydraulic device and a lower plate, the upper plate, the hydraulic device and the lower plate are stacked and connected layer by layer, and the lower plate is a double-layer hollow structure; the double-layer hollow structure is two layers of hollow steel plates, and the two layers of hollow steel plates are connected by an annular hollow vertical wall in the middle, there are several hydraulic devices, and the oil storage tanks of several of the hydraulic devices are interconnected, and also include an upper displacement pipe, a lower displacement pipe and a sleeve, the upper displacement pipe and the lower displacement pipe are respectively connected to the upper plate and the lower plate, the sleeve is sleeved on the outside of the upper displacement pipe and the lower displacement pipe, the upper plate is provided with a mounting plate, the mounting plate is used for the installation and positioning of the steel cage, the load box is arranged at the bottom of the enlarged head pile, and the above structure is improved during the self-balancing static load test of the enlarged head pile. The structural strength of the pile body and the installation effect of the load box are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation bearing capacity detection, and in particular relates to a method and a detection structure for detecting the vertical compressive bearing capacity of a single pile of an enlarged head pile. Background Art

[0002] With the construction of high-rise buildings and large bridges, the loads on buildings are getting heavier, and the requirements for the bearing capacity of building foundation piles are getting higher and higher. The traditional static load test method of foundation piles is increasingly unable to cope with the task of static load test of large-tonnage foundation piles due to its own limitations. Therefore, the self-balancing method came into being. The core device of the self-balancing method is a load box composed of upper and lower connecting plates of a hydraulic device and a displacement device. Before the experiment, the load box is installed at the balance point of the pile body reinforcement cage, welded to the reinforcement cage as a whole, and displacement tubes are installed on the upper and lower plates of the load box respectively. After the reinforcement cage is placed in the pile hole and concrete is poured, the load box is pressurized by a pressurizing device and the stress and displacement of the pile body are recorded by sensors.

[0003] In addition to the existing foundation piles with equal cross-section, there are also expanded head piles. Expanded head piles are a pile foundation treatment technology that increases the bearing capacity of the pile and reduces the number of piles by adding an expanded head at the bottom or side of the pile, thereby saving engineering costs. The expanded head pile includes a uniform cross-section section and a variable cross-section section. When a pile with an expanded head is subjected to a self-balancing static load test to measure its single pile vertical compressive bearing capacity, it is necessary to determine the balance point of the pile body through calculation and experience. The balance point of the pile body is the resistance of the lower pile end to the soil plus the friction of the soil on the side of the lower pile The conventional practice in the prior art is to bury the load box at the junction between the equal-section section and the variable-section section to measure the vertical bearing capacity of the equal-section section of the pile body and the vertical bearing capacity of the enlarged head part. However, in power line projects, the equal-section section with enlarged-head piles is generally less than 10 meters. When the load box is placed at the variable section, the shear and bending bearing capacity may be insufficient at this section. Therefore, the load box cannot be buried at the variable section but can only be buried at the bottom of the pile.

[0004] When the load box is buried at the bottom of the pile, new problems will arise. That is, the structure of the existing load box is composed of a plurality of hydraulic devices, an upper plate and a lower plate. The plurality of hydraulic devices are located between the upper plate and the lower plate, and the upper plate and the lower plate are circular. The plurality of hydraulic devices form a ring array between the upper plate and the lower plate. When the pressure on the plurality of hydraulic devices is increased, the oil pressure is provided to each hydraulic device individually through a plurality of hydraulic oil pipes, resulting in a slight difference in the oil pressure of the plurality of hydraulic devices, resulting in an unbalanced force provided to the bottom of the pile body during a static load test. In addition, the existing load box is fixedly connected to the balance point of the pile body, so the upper plate and the lower plate are respectively connected to the upper and lower sections of the steel cage, so the lower plate of the load box is a plane. However, if the existing load box is buried at the bottom of the pile, a small gap will be generated between the lower plate and the bottom of the pile. Then, after pouring the concrete, the concrete will not completely enter the gap between the lower plate and the bottom of the pile, and the load box will not form a good combination with the bottom of the pile, resulting in errors in the data during the static load test and safety hazards to the subsequent use of the pile body.

[0005] Based on this, it is necessary to design a new detection method and detection structure for enlarging the head pile in the self-balancing static load test. Summary of the invention

[0006] In order to solve the problem in the prior art that when the load box is placed at the junction of the equal-section section and the variable-section section of the pile body, the cross-section may cause insufficient shear and bending bearing capacity, the present invention provides a method and a detection structure for the vertical compressive bearing capacity of a single pile with an enlarged head pile.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for testing the vertical compressive bearing capacity of a single pile of an enlarged head pile, characterized in that the pile body is first divided into a uniform cross-section pile body and a variable cross-section pile body, the bottom of the uniform cross-section pile body is coaxially fixedly connected to the top of the variable cross-section pile body, and then a load box is set at the bottom of the variable cross-section pile body and fixedly connected to the bottom steel bars of the pile body steel cage before pouring concrete, and the load box is used to pressurize and test the vertical compressive bearing capacity of the single pile after the pile body concrete is solidified.

[0009] A single pile vertical compressive bearing capacity detection structure of an enlarged head pile, the load box comprising an upper plate, a hydraulic device and a lower plate, the upper plate, the hydraulic device and the lower plate are stacked and connected layer by layer, and the lower plate is a double-layer hollow structure;

[0010] The double-layer hollow structure is two layers of hollow steel plates, and the two layers of hollow structures are connected by an annular hollow vertical wall in the middle.

[0011] Furthermore, there are a plurality of hydraulic devices, and the plurality of hydraulic devices form a ring array between the upper plate and the lower plate based on the axis of the upper plate and the lower plate, and the oil storage tanks of the plurality of hydraulic devices are interconnected.

[0012] Furthermore, one of the hydraulic devices is provided with an oil receiving port, a circular hole is provided on the upper plate at a position corresponding to the oil receiving port, and the oil receiving port is connected to the loading device through a hydraulic oil pipe.

[0013] Furthermore, it also includes an upper displacement tube, a lower displacement tube and two sleeves, one end of the upper displacement tube is detachably connected to the upper plate, one end of the lower displacement tube passes through the upper plate and is detachably connected to the lower plate, the other ends of the upper displacement tube and the lower displacement tube are detachably connected to the displacement sensor, the two sleeves are coaxially sleeved on the outside of the upper displacement tube and the lower displacement tube, and the two sleeves are detachably connected to the upper plate and the lower plate, respectively.

[0014] Furthermore, there are a plurality of upper displacement tubes and lower displacement tubes, and the plurality of upper displacement tubes and lower displacement tubes are arranged at different positions of the upper plate and the lower plate.

[0015] Furthermore, a mounting plate is provided on the upper plate. The mounting plate is formed by enclosing an annular vertical wall on the upper plate. The mounting plate is used for mounting and positioning the pile body.

[0016] Furthermore, the hydraulic device includes a movable end and a fixed end, the movable end is fixed to the lower plate, and the fixed end is fixed to the upper plate, and the hydraulic device is used to control the distance between the upper plate and the lower plate.

[0017] Furthermore, the upper plate and the lower plate are annular structures with a hollow center, and the two ends of the annular hollow vertical wall are respectively connected to the inner ring edges of the upper plate and the lower plate, and protrude upward from the plane of the upper plate.

[0018] The beneficial effects of the present invention are:

[0019] (1) By making the lower plate of the load box a double-layer hollow steel plate, and connecting the two layers of hollow steel plates through the middle annular hollow vertical wall, it can effectively avoid the problem of insufficient structural strength of the pile body caused by the load box being buried at the bottom of the pile hole and the bottom or side of the load box forming a cavity with the bottom and side of the pile hole during concrete pouring, and can effectively ensure the quality of the pile body after pouring.

[0020] (2) By arranging a mounting plate on the upper plate of the load box, the vertical steel bars at the bottom of the steel cage can be abutted against the side and bottom of the mounting plate when connected to the load box, and the vertical steel bars at the bottom of the steel cage are welded to the mounting plate of the upper plate of the load box, thereby improving the connection strength between the steel cage and the load box and ensuring the parallel state of the load box and the steel cage when connected.

[0021] (3) By burying the load box at the bottom of the pile hole, the problem of insufficient shear and bending bearing capacity at the cross-section when the load box is placed at the variable cross-section can be avoided, and the shear and bending bearing capacity of the pile body can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0023] Figure 1 It is a schematic diagram of the side structure of the load box of the present invention;

[0024] Figure 2 It is a schematic diagram of a cross-sectional structure of a load box of the present invention from a top view;

[0025] Figure 3 It is a schematic diagram of the structure of the load box of the present invention from a top view;

[0026] Figure 4 It is a position relationship diagram of the pile body and the load box of the present invention;

[0027] Figure 5 It is a schematic diagram of the variable cross-section cone structure of the pile body of the present invention;

[0028] Figure 6 The force analysis diagram of the pile body and the load box of the present invention is

[0029] Explanation of the reference numerals in the accompanying drawings: 1. upper plate; 2. hydraulic device; 3. lower plate; 4. mounting plate; 5. oil storage tank; 6. vertical wall; 7. lower displacement pipe; 8. upper displacement pipe; 9. oil receiving port; 10. through hole; 11. load box; 12. variable cross-section section; 13. uniform cross-section section; 14. soil in area 1; 15. soil in area 2. DETAILED DESCRIPTION

[0030] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0031] A method for testing the vertical compressive bearing capacity of a single pile of an enlarged head pile. When performing a self-balancing static load test on an enlarged head pile to measure the vertical compressive bearing capacity of the single pile, it is necessary to determine the balance point position of the pile body through calculation and experience. The balance point of the pile body is the position where the resistance of the lower pile end to the soil plus the friction of the soil on the side of the lower pile is equal to the gravity of the upper pile plus the friction between the upper pile and the soil. On the enlarged head pile, its balance point is at the junction of the uniform cross-section section 13 and the variable cross-section section 12 or close to the junction. A load box 11 is buried between the uniform cross-section section 13 and the variable cross-section section 12. The intersection between the two sections may cause insufficient shear and bending bearing capacity, so the load box 11 cannot be buried at the variable section. Therefore, in one embodiment, the pile body is first divided into a pile body of a uniform cross-section section 13 and a pile body of a variable cross-section section 12. The bottom of the pile body of the uniform cross-section section 13 is coaxially fixedly connected to the top of the pile body of the variable cross-section section 12. Then, the load box 11 is set at the bottom of the pile body of the variable cross-section section 12, and is fixedly connected to the bottom steel bars of the pile body steel cage before pouring concrete. After the pile body is poured with concrete and solidified, the load box 11 is used to pressurize and test the vertical compressive bearing capacity of the single pile of the pile body.

[0032] Therefore, Figure 4 As shown, unlike the prior art in which the load box 11 is set at the junction of the equal-section section 13 and the variable-section section 12 of the pile body during the self-balancing static load test, the load box 11 is set at the bottom of the enlarged head pile in the present solution, which can effectively improve the structural strength of the pile body, avoid the pile body being broken due to the horizontal stress in the area where the load box 11 is placed during the self-balancing static load test, or the upper and lower parts of the pile body load box 11 being bent, so that the integrity of the pile body is stronger, safer and more reliable.

[0033] When the load box 11 is buried at the bottom of the pile and loaded to the limit value N, the bearing capacity of the soil at the bottom of the pile can be obtained by multiplying the measured unit stress P1 = N / A (A is the bottom area of ​​the load box 11) by A' to obtain the bearing capacity Qud of the soil at the bottom of the pile. At this time, the force N on the pile body includes the deadweight W of the pile body, the friction resistance N2 of the pile section, the normal stress P2 of the soil body on the pile enlarged head perpendicular to its inclined surface, and the friction resistance μP2 of the soil body on the inclined surface of the enlarged head (μ is the friction coefficient between the soil and the pile surface). It is easy to know that the deadweight W is a known item. If the bearing capacity N3 of the pile body of the equal cross-section section 13 is required, it is necessary to analyze and obtain the influence of P2 and μP2 on the pile enlarged head.

[0034] Depend on Figure 6 As shown, the soil in area 1 where the enlarged head pile is located is the same layer as the soil in area 2. When the self-balanced static load test reaches the limit value, the load value of the load box 11 is N, and the force perpendicular to the inclined surface of the pile enlarged head is N. 1 The frictional resistance parallel to the inclined surface at the enlarged head is N 2 , the force on the pile above the pile section is N3 , the unit soil resistance at the enlarged head slope is P 2 (direction perpendicular to the slope downward), unit friction parallel to the surface (direction is parallel to the enlarged head inclined surface downward), the diameter of the pile body with equal cross section is d, and the angle between the enlarged head inclined surface and the plane is .in, is the friction coefficient between soil and concrete on the surface of the enlarged head, In order to expand the area of ​​the bottom of the head, the deadweight of the pile is W.

[0035] like Figure 5 As shown in the figure, the soil resistance is perpendicular to the force acting on the slope of the enlarged pile head. As shown in formula (1):

[0036] (1

[0037] in To expand the side surface area of ​​the cone at the head.

[0038] The vertical downward force on the pile is As shown in formula (2):

[0039] (2

[0040] Frictional resistance of soil on the enlarged pile parallel to its slope N 2 As shown in formula (3):

[0041] (3

[0042] The vertical downward force on the pile is As shown in formula (4):

[0043] (4

[0044] The vertical force of soil on the enlarged pile is Formula (5):

[0045] (5

[0046] Depend on Figure 6As shown, since the soil 14 in area 1 and the soil 15 in area 2 are of the same type and have the same properties, and the soil 14 in area 1 is subjected to three-dimensional forces, and the soil 15 in area 2 has no lateral restraint above its pile top, when the load box 11 is set at the pile bottom and pressurized, the load box 11 applies pressure to the pile bottom and the enlarged head pile at the same time. At this time, the unit stress required to produce the same unit displacement by pressing downward at the pile bottom of the soil 14 in area 1 for a flat plate load test is greater than that required to produce the same unit displacement by pressing upward along the inclined surface of the enlarged head of the soil 15 in area 2 for a flat plate load test, that is, when the soil at the pile bottom and perpendicular to the inclined surface produce the same displacement, the following relationship (6) is obtained:

[0047] (6

[0048] Because of the relationship in equation (6), the soil mass 14 in area 1 at the bottom of the pile can be measured. The curve replaces the area 2 soil 15 curve, and the result is conservative.

[0049] Foundation bearing capacity curve ( The curve refers to the relationship between the foundation bearing capacity and foundation settlement in a certain area. Usually, when a certain pressure load is applied to the foundation, the foundation will settle and the bearing capacity will increase accordingly. A curve can describe this relationship. The curve usually presents a nonlinear relationship, that is, when the pressure load increases, the rate of increase of the foundation bearing capacity gradually decreases. This is because during the compaction and deformation process of the foundation material in the initial stage, as the settlement increases, the particles of the soil are rearranged, compacted and deformed. In this process, the structure of the soil, the friction between particles and the shear strength of the soil will change, so the bearing capacity of the foundation will also change.

[0050] Through the above content, the vertical downward force of the soil on the enlarged head when the load box 11 loads the pile at the bottom of the pile can be obtained: The conservative value of is the following equation (7): (7

[0051] In formula (7), According to the soil 14 in area 1 The curve obtains the stress value corresponding to the displacement on the load box 11.

[0052] but Figure 6 As shown in the figure, when the load box 11 is loaded to the ultimate bearing capacity N of the pile, the force N above the variable cross-section of the pile body 3 It is the ultimate bearing capacity of the pile minus the sum of the soil resistance and friction of the variable cross-section section 12, as shown in the following formula (8): (8

[0053] The vertical bearing capacity of soil 14 in area 1 on piles is given by the following formula (9):

[0054] (9

[0055] In summary, the vertical bearing capacity of the above pile is as follows (10):

[0056] (10

[0057] in, is the pull-out coefficient, It refers to the ratio of the foundation resistance caused by horizontal load to the foundation soil pullout resistance. r is half of the difference between the bottom diameter of the variable cross-section pile and the diameter of the uniform cross-section pile. The soil 14 in area 1 is the soil under the enlarged head pile.

[0058] In summary, through the analysis of the bearing capacity of the self-balancing static load test pile, the calculation method of the vertical bearing capacity of the enlarged head pile can be obtained.

[0059] Since the load box 11 in the present invention is arranged at the bottom of the enlarged head pile, when the load box 11 is at the bottom of the pile body, the contact surface between the bottom of the load box 11 and the bottom of the pile hole is large. When the concrete is poured into the pile hole, the fluidity of the concrete is insufficient and the concrete cannot completely flow into the gap between the contact surface between the bottom of the load box 11 and the bottom of the pile hole. As a result, after the pouring of the pile body is completed, during the pressurization process of the self-balancing static load test, the bottom of the load box 11 is not filled with concrete and cannot provide sufficient supporting force. As a result, the load box 11 will tilt or deviate when pressurized, resulting in inaccurate data collected in the experiment and insufficient stability of the pile body. Figure 1-3 As shown, a single pile vertical compressive bearing capacity detection structure of an enlarged head pile of the present invention comprises a load box 11, wherein the load box 11 comprises an upper plate 1, a hydraulic device 2 and a lower plate 3, wherein the upper plate 1, the hydraulic device 2 and the lower plate 3 are stacked and connected layer by layer, and the lower plate 3 is a double-layer hollow structure;

[0060] The double-layer hollow structure is two layers of hollow steel plates, and the two layers of hollow steel plates are connected by a middle annular hollow vertical wall 6;

[0061] Since the present invention is mainly used to expand the detection of the vertical compressive bearing capacity of a single pile of the head pile, the load box 11 is used to detect the vertical compressive bearing capacity of the single pile. In order to prevent the load box 11 from being placed at a variable cross-section, which may cause insufficient shear and bending bearing capacity at the cross-section, the load box 11 cannot be buried at the variable cross-section but can only be buried at the bottom of the pile. Since the load box 11 needs to be buried at the bottom of the pile, a small gap will be generated between the bottom of the load box 11 and the bottom of the pile hole when pouring in the pile hole. Since the poured concrete has a certain viscosity, it cannot flow into each gap like water. Therefore, a cavity will be formed in the gap between the bottom of the load box 11 and the bottom of the pile hole, resulting in the pile body after pouring not being completely in contact with the bottom of the pile hole. When doing a static load test, the bottom of the pile hole will be subjected to a large pressure. Therefore, when there is a cavity between the bottom of the pile hole and the bottom of the load box 11, the reaction force received by the load box 11 during the experiment will be uneven, which will cause errors in the experimental data.

[0062] Therefore, in order to bury the load box 11 at the bottom of the pile hole and enable the concrete to be poured into every corner of the pile hole during concrete pouring, the lower plate 3 is made into a hollow structure, and in order to enable the lower plate 3 to provide a stable foundation for the entire pile body and the load box 11 during the static load test after pouring the concrete, so as to ensure the accuracy of the static load test data, the lower plate 3 is made into a double-layer hollow structure. When the pile body is poured, the concrete will enter the double-layer hollow structure of the lower plate 3, and a stable foundation can be provided for the pile body and the load box 11 after the concrete solidifies. When the load box 11 is pressurized, the soil layer under the pile body and the load box 11 can be evenly stressed, thereby improving the accuracy of the experimental data.

[0063] Since the cross-sectional area of ​​the bottom of the pile body is relatively large, in order to enable the load box 11 at the bottom of the pile to exert sufficient force on the pile body, and also to balance the force exerted by the load box 11 on the pile body, in one embodiment, there are a plurality of hydraulic devices 2, and the plurality of hydraulic devices 2 form a ring array between the upper plate 1 and the lower plate 3 based on the axis of the upper plate 1 and the lower plate 3, and the oil storage tanks 5 of the plurality of hydraulic devices 2 are connected to each other;

[0064] Since the load box 11 is composed of a plurality of hydraulic devices 2, and the hydraulic device 2 has an oil storage tank 5 for storing hydraulic oil, and the oil storage tank 5 is connected to an external pressurizing device to adjust the pressure, the external pressurizing device needs to be connected to the oil storage tank 5 through a plurality of pressurized oil pipes, and each oil storage tank 5 is pressurized separately through the plurality of pressurized oil pipes, and pressurizing each oil storage tank 5 separately will lead to uneven pressurization, which will cause slight differences in the forces applied by the load box 11 to different positions of the pile body, and the static load test has high requirements on the accuracy of the displacement data of each part of the pile body, so in order to keep the forces output by each hydraulic device 2 synchronized and the output pressure the same, by making the load box 11 The oil storage tanks 5 of all the hydraulic devices 2 on 1 are interconnected, which ensures that the output pressure of each hydraulic device 2 is the same and synchronous. In addition, by connecting the oil storage tanks 5 of multiple hydraulic devices 2, the problem of using an adapter to connect a main pressurized oil pipe into multiple small pressurized oil pipes in the prior art can be avoided. In addition, since the concrete solidifies after the pile body is poured with concrete, the pressurized oil pipe adapter will be squeezed or deformed. Therefore, the use of an adapter to connect may cause the adapter and the pressurized oil pipe to loosen and cause hydraulic oil leakage. Therefore, by connecting the oil storage tanks 5 of multiple hydraulic devices 2, the equipment failure rate can be effectively reduced, and the stability of the load box 11 during operation can be improved.

[0065] Since the oil storage tanks 5 of multiple hydraulic devices 2 in the load box 11 in the above embodiment are connected, it is not necessary to provide hydraulic oil and apply pressure to each hydraulic device 2 separately. Therefore, in one embodiment, an oil receiving port 9 is provided on one of the hydraulic devices 2, and a circular hole is provided on the upper plate 1 at a position corresponding to the oil receiving port 9, and the oil receiving port 9 is connected to the loading device through a hydraulic oil pipe; the oil receiving port 9 is used to connect with the pressurized oil pipe. Since the oil storage tanks 5 of multiple hydraulic devices 2 on the load box 11 are interconnected, only one hydraulic device 2 needs to be provided with an oil receiving port 9 to provide force to all hydraulic devices 2. This not only reduces the adapter in the above embodiment, but also reduces the oil receiving port 9 that needs to be provided for each hydraulic device 2. Only one oil receiving port 9 needs to be retained. When the adapter and the oil receiving port 9 are reduced, the failure rate of the equipment can be effectively reduced, and the stability and balance of the force applied by the load box 11 to different positions of the pile body are improved, thereby improving the accuracy of the static load test detection of the pile body.

[0066] In the above embodiment, after the hydraulic device 2 in the load box 11 applies pressure to cause the pile body to move in the vertical direction, it is necessary to detect the displacement data of the pile body. Therefore, in one embodiment, it also includes an upper displacement tube 8, a lower displacement tube 7 and two sleeves, one end of the upper displacement tube 8 is detachably connected to the upper plate 1, one end of the lower displacement tube 7 passes through the upper plate 1 and is detachably connected to the lower plate 3, the other ends of the upper displacement tube 8 and the lower displacement tube 7 are detachably connected to the displacement sensor, the two sleeves are coaxially sleeved on the outside of the upper displacement tube 8 and the lower displacement tube 7, and the two sleeves are detachably connected to the upper plate 1 and the lower plate 3 respectively;

[0067] After the load box 11 applies pressure to the pile body, not only will the pile body move upward under the action of the load box 11, but also because the pile body itself has a heavy deadweight and under the friction between the side of the pile body and the side of the soil layer, the load box 11 itself will also move downward toward the soil layer below under the reaction force. Therefore, it is necessary not only to detect the upward movement data of the pile body, but also to detect the downward movement data of the load box 11. Therefore, it is necessary to detect through the upper displacement tube 8 and the lower displacement tube 7. The upper displacement tube 8 is connected to the upper plate 1 of the load box 11, and the upper plate 1 of the load box 11 is connected to the pile body reinforcement cage. Therefore, by detecting the upper displacement tube 8 of the load box 11, the upper displacement tube 8 and the lower displacement tube 7 are connected. The displacement data of the plate 1 can be used to obtain the displacement data of the pile body, and the lower displacement tube 7 is connected to the lower plate 3 of the load box 11. Since the lower plate 3 is below the upper plate 1, the lower displacement tube 7 needs to pass through the through hole 10 opened on the upper plate 1 and is connected to the lower plate 3 through the through hole 10. When the load box 11 is working, the pile body of the part where the load box 11 is located will be broken under the action of pressure, and the distance between the upper plate 1 and the lower plate 3 of the load box 11 will also increase. At this time, the displacement data of the upper displacement tube 8 and the lower displacement tube 7 are detected, and the displacement data are collected and analyzed through an external displacement sensor;

[0068] Since the upper displacement tube 8 and the lower displacement tube 7 are respectively connected to the upper plate 1 and the lower plate 3 of the load box 11, after completing the installation of the load box 11, the pressurized oil pipe, the upper displacement tube 8 and the lower displacement tube 7, it is necessary to pour concrete in the pile hole so that the concrete is combined with the load box 11 and the steel cage to form a complete pile structure. Therefore, after the poured concrete solidifies, the upper displacement tube 8 and the lower displacement tube 7 will be fixed by the concrete solidification and cannot produce effective displacement during the static load test. Therefore, in order to enable the upper displacement tube 8 and the lower displacement tube 7 to still be able to move up and down after the concrete solidifies, it is necessary to sleeve the outer part of the upper displacement tube 8 and the lower displacement tube 7 so that the upper displacement tube 8 and the lower displacement tube 7 can slide inside the sleeve, and one end of the sleeve is also detachably connected to the upper plate 1 and the lower plate 3 of the load box 11, so that it can be ensured that the concrete will not enter the sleeve when pouring concrete, and thus it can also be ensured that the upper displacement tube 8 and the lower displacement tube 7 can slide inside the sleeve.

[0069] In the above embodiment, only one upper displacement tube 8 and one lower displacement tube 7 are provided. However, in actual detection, since the cross-sectional area of ​​the load box 11 is relatively large and there is a probability that the load box 11 is tilted to one side at the bottom of the pile hole, when there is only one upper displacement tube 8 and one lower displacement tube 7, if the load box 11 is tilted just based on the position of the upper displacement tube 8 or the lower displacement tube 7 as the center of the circle, the upper displacement tube 8 and the lower displacement tube 7 cannot detect that the load box 11 is in a tilted state, resulting in deformation at the bottom of the pile body, so that erroneous experimental data are obtained. Therefore, in one embodiment, there are a plurality of upper displacement tubes 8 and lower displacement tubes 7, and the plurality of upper displacement tubes 8 and lower displacement tubes 7 are arranged at different positions of the upper plate 1 and the lower plate 3;

[0070] By arranging a plurality of upper displacement tubes 8 and lower displacement tubes 7 at different positions of the upper plate 1 and the lower plate 3 of the load box 11 and performing detection at the same time, when one side of the load box 11 is tilted, it can be discovered in time, which can effectively improve the detection of the state of the load box 11 and the detection of the upper and lower displacement data of the pile body and the load box 11 during the self-balancing static load test, thereby improving the safety of the experiment and the accuracy of the experimental data.

[0071] Since the load box 11 needs to be connected to the steel cage, the steel cage and the load box 11 are formed into a whole by welding the inner side of the vertical steel bars at the bottom of the steel cage to the side of the upper plate 1 of the load box 11. However, there are a large number of vertical steel bars extending from the steel cage and the length of each steel bar is not exactly the same. Therefore, it cannot be guaranteed during welding that the vertical steel bars on the steel cage and the upper plate 1 of the load box 11 can be welded to make the load box 11 in a horizontal state. Therefore, in one embodiment, a mounting plate 4 is provided on the upper plate 1, and the mounting plate 4 is formed by enclosing the annular vertical wall 6 on the upper plate 1. The mounting plate 4 is used for the installation and positioning of the steel cage.

[0072] By arranging the mounting plate 4 on the upper plate 1 of the load box 11, when the steel cage is connected to the upper plate 1, the side of the vertical steel bar at the bottom of the steel cage abuts against the mounting plate 4, and the bottom of the vertical steel bar abuts against the top of the upper plate 1. On the one hand, the side position of the steel bar can be positioned. Since the steel cage is manually fixed and welded by workers, the shape of the steel cage is not completely circular, and the vertical steel bars extending from the bottom of the steel cage are not annular. Therefore, when welded to the upper plate 1 of the load box 11, some of the vertical steel bars will not abut against the upper plate 1, resulting in some parts not being welded or being poorly welded, resulting in the steel cage and the load box 11 being in a state of being out of alignment. The connection strength of the load box 11 is insufficient, so by adding a mounting plate 4 on the upper plate 1, when the steel cage is connected to the load box 11, the outer side of the vertical steel bars at the bottom of the steel cage are abutted against the mounting plate 4 and then welded, so that each steel bar can be connected and fixed to the upper plate 1 of the load box 11, and the original welding of the vertical steel bars to the side of the upper plate 1 is changed to the abutment welding of the bottom of the vertical steel bars to the bottom and side of the mounting plate 4 of the upper plate 1, thereby increasing the welding area, providing vertical support force for the steel cage, making the connection between the steel cage and the load box 11 more reliable, and the support force provided by the load box 11 can also make the pile body more stable.

[0073] Since the pile hole needs to be poured with concrete after the steel cage is placed in the pile hole, and a static load test is performed after the concrete solidifies, the distance between the upper plate 1 and the lower plate 3 will increase under the action of the hydraulic device 2 during the static load test, thereby pulling the pile body at the position of the load box 11 horizontally apart. Therefore, in one embodiment, the hydraulic device 2 includes a movable end and a fixed end, the movable end is fixed on the lower plate 3, and the fixed end is fixed on the upper plate 1. The hydraulic device 2 is used to control the distance between the upper plate 1 and the lower plate 3. Therefore, the upper plate 1 and the lower plate 3 are movably connected by the hydraulic device 2. The movable end of the hydraulic device 2 in the load box 11 is fixed on the lower plate 3, and the fixed end is fixed on the upper plate 1. The upper plate 1 and the lower plate 3 of the load box 11 are slid up and down by relative sliding of the movable end and the fixed end of the hydraulic device 2, so that the pressure of the hydraulic device 2 pulls off the pile body of the load box 11, and the displacement of the pile body and the load box 11 is detected.

[0074] After the steel cage is fixedly connected to the load box 11, and then the high-pressure oil pipe, casing, upper displacement tube 8 and lower displacement tube 7 and other devices are installed and fixed, the steel cage and the load box 11 need to be placed in the pile hole together, and the load box 11 is placed at the bottom of the pile hole. After completing the above steps, the pile hole needs to be poured with concrete. When pouring the pile hole, the concrete pouring pump pipe is used to pour from the bottom of the pile hole, so that the concrete gradually fills the bottom of the pile hole and then continues to pour so that the concrete gradually fills the entire pile hole upward. The load box 11 is placed at the bottom of the pile hole, so that the concrete in the part of the bottom area of ​​the pile hole cannot flow to fill the entire load box 11 during pouring, resulting in a cavity in the area of ​​the load box 11, resulting in insufficient structural strength of the bottom of the pile body after the concrete solidifies. Therefore, in one embodiment, the upper plate 1 and the lower plate 3 are annular structures with a hollow center, and the two ends of the annular hollow vertical wall 6 are respectively connected to the inner ring edges of the upper plate 1 and the lower plate 3, and protrude upward from the plane of the upper plate 1;

[0075] Through the annular structure of the upper plate 1 and the lower plate 3, the center of the load box 11 is a hollow structure. When pouring concrete, the pouring pump pipe can extend into the center of the load box 11 and fill the entire load box 11 area with concrete. In addition, through the hollow structure of the upper plate 1 and the lower plate 3 in the above embodiment and the vertical wall 6 in this embodiment, the concrete can flow into the gap between the load box 11 and the pile hole along the holes of the hollow structure. After the concrete solidifies, the load box 11 and the pile hole form a relatively good combination, avoiding the concrete from not being poured into the inner wall of the pile hole and the bottom or side area of ​​the load box 11 due to the obstruction of the upper plate 1 of the load box 11, resulting in the formation of a cavity after the pile body is poured. The structural strength of the bottom of the pile body can be effectively improved, and a relatively good structural foundation can be provided for the load box 11 when performing a self-balancing static load test, thereby avoiding errors in the experimental data.

[0076] In order to better enable the load box 11 to bear the load of the pile body, it is necessary to add guide steel bars on the side of the steel cage when welding the steel cage and the load box 11, and connect the other end of the guide steel bars to the part of the upper plate 1 extending from the upper wall 6 of the load box 11, so that the end of the guide steel bar connected to the load box 11 can be better stressed, thereby improving the stability of the connection between the load box 11 and the steel cage.

[0077] Since the position and method of setting the load box 11 are different when the pile body is subjected to the self-balancing static load test, the data detection and analysis process of the pile body will also be different. This embodiment proposes a method for detecting the vertical compressive bearing capacity of a single pile with an enlarged head pile, and the method comprises the following steps:

[0078] S1, placing the bottom of the pile body steel cage on the inner side of the mounting plate 4 on the upper plate 1, and welding and fixing the steel cage and the mounting plate 4;

[0079] S2, a plurality of guide steel bars are fixedly connected to the steel cage, the vertical wall 6 extends to the upper surface of the upper plate 1, and one end of the plurality of guide steel bars abuts against the vertical wall 6 and is fixedly connected to the vertical wall 6, and the plurality of guide steel bars are connected to the steel cage and the vertical wall 6 to form an inverted cone structure;

[0080] S3, connect one end of the hydraulic oil pipe to the oil receiving port 9, connect the other end of the hydraulic oil pipe to the loading device, connect the upper displacement pipe 8 and the lower displacement pipe 7 to the upper plate 1 and the lower plate 3 respectively, connect the upper displacement pipe 8 and the lower displacement pipe 7 to the displacement sensor, sleeve the sleeve outside the upper displacement pipe 8 and the lower displacement pipe 7 and connect the upper plate 1 and the lower plate 3;

[0081] S4, placing the steel cage in the pile hole, and making the load box 11 at the bottom of the pile hole;

[0082] S5, pouring the pile hole through the hollow part of the steel cage and the annular structure of the upper plate 1, so that the concrete is gradually poured from the bottom to the top of the pile hole;

[0083] S6, after the concrete is initially solidified, the plurality of hydraulic devices 2 are pressurized by the loading device, so that the load box 11 simultaneously produces upward and downward displacements, so that the pile body of the hydraulic device 2 part is transversely fractured, and the required data is measured by the displacement sensor;

[0084] S7. After the experimental data is completed, concrete is poured again on the external section of the load box 11 through the lower displacement tube 7 to repair the section.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for testing the vertical compressive bearing capacity of a single pile with an enlarged head pile, characterized in that: Firstly, the pile body is divided into a pile body of a uniform cross-section section and a pile body of a variable cross-section section, the bottom of the pile body of the uniform cross-section section is coaxially fixedly connected to the top of the pile body of the variable cross-section section, and then a load box is arranged at the bottom of the pile body of the variable cross-section section and fixedly connected to the steel bars at the bottom of the pile body steel cage before pouring concrete, and the vertical compressive bearing capacity of the single pile of the pile body is tested by pressurizing the pile body after the concrete poured into the pile body solidifies; The force of soil resistance perpendicular to the slope of the enlarged pile As shown in formula (1): （1； in In order to expand the side surface area of ​​the cone at the head, is the normal stress of the soil on the pile enlarged head perpendicular to its inclined surface; the diameter of the pile with uniform cross section is d, and the angle between the enlarged head inclined surface and the plane is , r is half of the difference between the bottom diameter of the variable cross-section pile and the diameter of the uniform cross-section pile The vertical downward force on the pile is As shown in formula (2): (2； Frictional resistance of soil to the enlarged head pile parallel to its slope As shown in formula (3): （3； is the friction coefficient between soil and concrete on the surface of the enlarged head; The vertical downward force on the pile is As shown in formula (4): (4； The vertical force of soil on the enlarged pile is Formula (5): (5； When the soil at the bottom of the pile and perpendicular to the slope produces the same displacement, the following relationship (6) is obtained: （6； Through the above content, we can obtain the vertical downward force of the soil on the enlarged head when the load box loads the pile at the bottom of the pile The conservative value of is the following equation (7): (7； in Based on the soil mass in area 1 The curve obtains the stress value corresponding to the displacement on the load box; the soil in area 1 is the soil under the enlarged head pile; when the load box is loaded to the ultimate bearing capacity of the pile When the pile body is subjected to load above the variable cross section It is the ultimate bearing capacity of the pile minus the sum of the soil resistance and friction of the variable cross-section section, as shown in the following formula (8): (8； The vertical bearing capacity of the soil in area 1 on the pile is as follows (9): (9； To expand the head bottom area, In summary, the vertical bearing capacity of the above pile is as follows (10): (10； in, is the pull-out coefficient, It refers to the ratio of the foundation resistance caused by horizontal load to the pull-out resistance of the foundation soil; the deadweight of the pile is W; The load box comprises an upper plate, a hydraulic device and a lower plate, wherein the upper plate, the hydraulic device and the lower plate are stacked and connected layer by layer, and the lower plate is a double-layer hollow structure; The double-layer hollow structure is two layers of hollow steel plates, and the two layers of hollow structures are connected by a middle annular hollow vertical wall; There are a plurality of hydraulic devices, and the plurality of hydraulic devices form a ring array between the upper plate and the lower plate based on the axis of the upper plate and the lower plate, and the oil storage tanks of the plurality of hydraulic devices are interconnected; One of the hydraulic devices is provided with an oil receiving port, and a circular hole is provided on the upper plate at a position corresponding to the oil receiving port, and the oil receiving port is connected to the loading device through a hydraulic oil pipe; It also includes an upper displacement tube, a lower displacement tube and two sleeves, one end of the upper displacement tube is detachably connected to the upper plate, one end of the lower displacement tube passes through the upper plate and is detachably connected to the lower plate, the other ends of the upper displacement tube and the lower displacement tube are detachably connected to the displacement sensor, the two sleeves are coaxially sleeved on the outside of the upper displacement tube and the lower displacement tube, and the two sleeves are detachably connected to the upper plate and the lower plate, respectively.

2. The method for detecting the vertical compressive bearing capacity of a single pile with an enlarged head pile according to claim 1, characterized in that: There are a plurality of upper displacement tubes and a plurality of lower displacement tubes, and the plurality of upper displacement tubes and the plurality of lower displacement tubes are arranged at different positions of the upper plate and the lower plate.

3. The method for detecting the vertical compressive bearing capacity of a single pile with an enlarged head pile according to claim 2, characterized in that: The upper plate is provided with a mounting plate, which is formed by enclosing an annular vertical wall on the upper plate and is used for mounting and positioning the pile body.

4. The method for detecting the vertical compressive bearing capacity of a single pile of an enlarged head pile according to claim 2, characterized in that: The hydraulic device comprises a movable end and a fixed end, wherein the movable end is fixed to the lower plate, and the fixed end is fixed to the upper plate, and the hydraulic device is used to control the distance between the upper plate and the lower plate.

5. The method for detecting the vertical compressive bearing capacity of a single pile with an enlarged head pile according to claim 2, characterized in that: The upper plate and the lower plate are annular structures with a hollow center. The two ends of the annular hollow vertical wall are respectively connected to the inner ring edges of the upper plate and the lower plate, and protrude upward from the plane of the upper plate.

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