A rapid testing method for bidirectional controlled load cell and pile foundation bearing capacity

Abstract

This application provides a bidirectional controlled load cell and a rapid testing method for pile foundation bearing capacity, relating to the field of pile foundation testing technology. The load cell includes: two fixed plates for connection to the pile or reinforcing cage; multiple opposing-moving loading jacks located between the two fixed plates, distributed along the axis of the fixed plates, with the cylinder and piston rod of each jack fixedly connected to one of the two fixed plates; a first U-shaped commutator and a second U-shaped commutator located between the two fixed plates, arranged in a circumferential array at equal intervals along the axis of the fixed plates, with the openings of the first and second U-shaped commutators in the same group interlocking and their open ends detachably connected to the corresponding fixed plates; and opposing-moving loading jacks connected between the closed ends of the first and second U-shaped commutators in the same group. This application achieves all the testing effects of a reverse self-balancing experimental device and uses only one load cell, exhibiting high equipment integration.

Description

Technical Field

[0001] This application relates to the field of pile foundation testing technology, and in particular to a bidirectional controlled load cell and a rapid testing method for pile foundation bearing capacity. Background Technology

[0002] The bearing capacity of pile foundations is a key aspect of pile foundation engineering design. Commonly used methods for determining this capacity include static load testing (direct loading, anchor pile beam reaction method, surcharge method), dynamic testing (high strain and low strain dynamic testing), in-situ testing (standard penetration test, static cone penetration test), theoretical calculation (load transfer method, empirical formula method), and code-recommended methods.

[0003] The self-balancing method is one approach for determining the bearing capacity of pile foundations. The principle of the self-balancing method involves placing one or more load cells inside the pile. By applying pressure within the load cells, the pile undergoes upward displacement, while the soil around the pile generates a downward reaction force, thus balancing the applied load. This method reduces the impact of the test on the site and construction progress, and is suitable for various geological conditions and construction environments. While the self-balancing method eliminates the need for external reaction devices, reducing site influence, it has drawbacks including limitations in theoretical assumptions, load cell installation issues, complex interpretation of test results, the influence of soil layer differences, limitations on pile displacement, high cost, and low accuracy due to the conversion between positive and negative skin friction. These factors can lead to errors in the test results and hinder the widespread adoption of the method.

[0004] To this end, Chinese patent application CN2016102219915 proposes an improved reverse self-balancing method and test device for testing the vertical bearing capacity of pile foundations, such as... Figure 1 As shown, (a) represents the movement of two pile segments in opposite directions, and (b) represents the movement of two pile segments in opposite directions; among them, For downward displacement, For upward displacement, This represents the negative bearing capacity of the upper section of the pile. This represents the positive bearing capacity of the lower pile section. This represents the positive bearing capacity of the upper pile section. This refers to the negative bearing capacity of the lower pile segment. Its core principle is to add a vertical loading device at the pile top to the traditional self-balancing test, solving the technical challenge of converting negative skin friction to positive skin friction in the upper pile segment during self-balancing pile testing, and also testing the pile's tensile bearing capacity. The effectiveness of this method has been verified through theoretical analysis and numerical simulation, which helps promote its application in practical engineering and further improves the evaluation method for the vertical bearing capacity of a single pile.

[0005] However, the existing reverse self-balancing method still requires the installation of pile top load cells and pile body load cells during operation, and also requires the reservation of a through-loading rod pipe in the upper pile section. The operation is relatively cumbersome and the equipment integration is not high. Therefore, it needs to be optimized and improved. Summary of the Invention

[0006] To address the cumbersome operation caused by the requirement of setting up at least two load cells that move in opposite directions during the existing reverse self-balancing method, this application provides a rapid testing method for bidirectional controlled load cells and pile foundation bearing capacity.

[0007] Firstly, this application provides a bidirectional control load cell, which adopts the following technical solution:

[0008] A bidirectional control load cell, comprising:

[0009] Two fixing plates are provided and are used to connect to the pile or the reinforcing cage;

[0010] Opposite moving loading jacks are located between the two fixed plates, and multiple jacks are distributed in a circular array with equal spacing around the axis of the fixed plates. The cylinder and piston rod of the opposite moving loading jacks are fixedly connected to the two fixed plates respectively.

[0011] A first U-shaped commutator and a second U-shaped commutator are located between two fixed disks, and multiple sets are distributed in a circumferential array at equal intervals along the axis of the fixed disks. The openings of the first and second U-shaped commutators in the same set are relatively fitted together, and their opening ends are detachably connected to the corresponding fixed disks.

[0012] The opposing moving loading jacks are connected between the closed ends of the first and second U-shaped commutators in the same group.

[0013] Furthermore, the outer contour shape of the fixing plate is the same as that of the target pile, and the outer diameter of the fixing plate is less than or equal to the outer diameter or inner diameter of the target pile.

[0014] Furthermore, a working hole is provided through the center of the fixed plate.

[0015] Furthermore, each of the two fixed plates has anchoring steel bars on its opposite side for connection with the pile segment or the reinforcing cage.

[0016] Secondly, this application provides a rapid testing method for pile foundation bearing capacity, based on the aforementioned bidirectional controlled load cell, comprising the following steps:

[0017] S1. Determine the rated bearing capacity of the bidirectional control load box and the outer contour dimensions of the fixed plate based on the design bearing capacity of the target pile;

[0018] S2. Based on the geological environment parameters of the target pile, determine the equilibrium point of the target pile and define it as the installation location of the loading section and the bidirectional control load box;

[0019] S3. Based on the equilibrium point position, the target pile is divided into an upper pile section and a lower pile section. The upper pile section and the lower pile section are connected by two fixing plates, or the upper pile section reinforcement cage and the lower pile section reinforcement cage are connected by two fixing plates. The final target pile is formed by pile construction according to the traditional method.

[0020] S4. Connect the oil pipe of the bidirectional control load box to the oil pump and perform equipment debugging and balance point;

[0021] S5. First, start the opposing moving loading jacks, record the output axial force and piston rod elongation of the opposing moving loading jacks, and record the axial force displacement curves of the upper and lower pile sections respectively. Determine the compressive bearing capacity and tensile bearing capacity according to the pile foundation design code. Then, control the oil return of the opposing moving loading jacks, start the opposing moving loading jacks, record the output axial force and piston rod elongation of the opposing moving loading jacks, and record the axial force displacement curves of the upper and lower pile sections respectively. Determine the tensile bearing capacity and compressive bearing capacity according to the pile foundation design code.

[0022] S6. Based on the principle of calculating the bearing capacity of reverse self-balancing pile foundations, the compressive bearing capacity of the upper pile segment and the compressive bearing capacity of the lower pile segment are taken as the target pile compressive bearing capacity; similarly, the tensile bearing capacity of the upper pile segment and the tensile bearing capacity of the lower pile segment are taken as the target pile tensile bearing capacity.

[0023] S7. Reinforce the loading section between the upper and lower pile sections;

[0024] S8. On-site response at the test site, test completed.

[0025] Furthermore, in step S6, the two fixed plates are moved in opposite directions by the opposing-moving loading jacks to measure the negative bearing capacity of the upper pile section. and the positive bearing capacity of the lower pile section ;

[0026] By applying load using the opposing moving jacks, the two fixed discs move towards each other, allowing the positive bearing capacity of the upper pile section to be measured. and the negative bearing capacity of the lower pile body ;

[0027] The ultimate vertical compressive bearing capacity of the target pile is the sum of the positive bearing capacity of the upper and lower pile sections, plus the self-weight of the target pile. ;

[0028] The ultimate vertical uplift bearing capacity of the target pile is the sum of the negative bearing capacity of the upper pile segment and the negative bearing capacity of the lower pile segment, minus the self-weight of the target pile. ;

[0029] Where W is the self-weight of the target pile.

[0030] Furthermore, if the target pile is a permanent cast-in-place concrete pile, the loading section is reinforced by grouting through pre-embedded grouting pipes, and the pile foundation quality is certified to form an integral permanent pile body.

[0031] Furthermore, before reinforcing the loading section in step S7, the bidirectional control load box is first removed and recycled. Then, a steel reinforcement section is set in the loading section to connect the upper pile reinforcement cage and the lower pile reinforcement cage. Finally, concrete is poured.

[0032] Furthermore, if the target pile is a segmental assembled steel pipe pile, the target pile is divided into the upper pile body, the loading pile body and the lower pile body according to the position of the balance point, and the outer diameter of the fixing plate is less than or equal to the inner diameter of the target pile;

[0033] The upper and lower pile sections are fixed to the inner walls of the pile body with mounting rings. Two fixing discs are connected to the upper and lower pile sections respectively through the mounting rings. The loading section is sleeved outside the bidirectional control load box and is not connected to the upper and lower pile sections.

[0034] Furthermore, in step S7, if the target pile is used as a permanent pile for the engineering load and the working space inside the steel pipe pile meets the work needs of the construction personnel, the bidirectional control load box is first removed and taken out, and then the construction personnel weld the upper pile body, the lower pile body and the loading section pile body to form an integral permanent pile body.

[0035] If the target pile is not intended to be a permanent load-bearing pile for the project, it can be removed by vibratory pile extraction or rotary sleeve extraction, and then used for the next test after maintenance.

[0036] In summary, this application includes at least one of the following beneficial technical effects:

[0037] 1. The bidirectional control load cell of this application can achieve all the testing effects of the reverse self-balancing experimental device, and only one load cell is used, which is simpler and easier to operate. The equipment has a high degree of integration, mature technology, low R&D difficulty, and the simplified equipment is easy to test pile foundation under complex operating conditions, which has great market potential.

[0038] 2. Compared with existing pile foundation vertical bearing capacity test methods such as surcharge method and anchor pile method, the rapid testing method of this application gives full play to the advantages of the self-balancing method, without the need for conventional surcharge or anchor pile test, and is particularly suitable for field operations and pile foundations with large bearing capacity;

[0039] 3. Compared with the self-balancing method, the rapid testing method of this application overcomes the shortcomings of the traditional self-balancing method, such as the upper section of the pile having negative skin friction, the test results being different from the positive skin friction of the engineering pile, the test results being conservative, the load cell requiring a certain cost, and the inability to be recycled. It can directly obtain the vertical compressive bearing capacity and tensile bearing capacity of the pile foundation. The test device is simple and easy to operate, some equipment can be recycled and reused, it has good economic benefits, and is highly practical and widely applicable.

[0040] 4. The rapid testing method of this application optimizes and improves the existing reverse self-balancing pile testing method, which uses two sets of equipment, namely the pile top load cell and the pile body load cell, to perform load testing by moving them in opposite directions. Instead, it uses a single load cell to perform load testing by moving it in opposite directions. By simplifying the loading equipment and improving the equipment level, the pile foundation testing method is simplified. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the traditional reverse self-balancing pile foundation bearing capacity test principle;

[0043] Figure 2 This is a schematic diagram of the overall structure of the bidirectional control load cell according to an embodiment of this application;

[0044] Figure 3 This is an exploded structural diagram of the opposing moving loading jack, the first U-shaped commutator, and the second U-shaped commutator according to an embodiment of this application;

[0045] Figure 4 This is an implementation diagram of the operation of a cast-in-place concrete pile as an example in the embodiments of this application;

[0046] Figure 5 This is an implementation diagram of the operation of segmental steel pipe piles as an example in the embodiments of this application.

[0047] Figure label:

[0048] 1. Fixed plate;

[0049] 21. Moving loading jacks in opposite directions; 22. Moving loading jacks towards each other;

[0050] 31. First U-shaped commutator; 32. Second U-shaped commutator;

[0051] 4. Target pile; 41. Upper pile section; 42. Loaded pile section; 43. Lower pile section. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] Reference Figure 2 and Figure 3 This application discloses a bidirectional control load cell, which includes:

[0054] Two fixing plates 1 are provided, made of steel and used to connect to the pile body or the reinforcing cage. Specifically, the outer contour shape of the fixing plate 1 is the same as that of the target pile 4. A working hole is opened through the middle of the fixing plate 1, and the outer diameter of the fixing plate 1 is less than or equal to the outer or inner diameter of the target pile 4. Anchoring steel bars (not shown in the figure) are provided on the opposite sides of the two fixing plates 1 for connecting to the pile body or the reinforcing cage.

[0055] The opposing moving loading jacks 21 are located between two fixed disks 1, and multiple jacks are distributed in a circumferential array with equal spacing around the axis of the fixed disks 1. The cylinder and piston rod of the opposing moving loading jacks 21 are fixedly connected to the two fixed disks 1 respectively.

[0056] The first U-shaped commutator 31 and the second U-shaped commutator 32 are located between two fixed disks 1, and multiple sets are distributed in a circumferential array with equal spacing around the axis of the fixed disks 1. The openings of the first U-shaped commutator 31 and the second U-shaped commutator 32 in the same set are fitted together and the opening ends are detachably connected to the corresponding fixed disks 1; and

[0057] The opposing loading jacks 22 are connected between the closed ends of the first U-shaped commutator 31 and the second U-shaped commutator 32 in the same group.

[0058] In operation, the opposing-moving loading jack 21 applies load, causing the two fixed plates 1 to move in opposite directions, which in turn moves the piles at both ends in opposite directions. Conversely, the opposing-moving loading jack 22 applies load, causing the two fixed plates 1 to move in opposite directions, which in turn moves the piles at both ends in opposite directions. When the opposing-moving loading jack 21 applies load, the opposing-moving loading jack 22 returns oil. The reverse is also true.

[0059] Furthermore, based on the design bearing capacity of target pile 4, the rated bearing capacity of the bidirectional control load cell in this application is determined, and the model and quantity of loading jacks are determined based on the rated bearing capacity of the load cell. Generally, the rated bearing capacity of the bidirectional control load cell is required to be no less than 2 to 2.5 times the design bearing capacity of target pile 4. The pile foundation design bearing capacity is divided into compressive bearing capacity and tensile bearing capacity.

[0060] Therefore, the bidirectional control load cell of this application optimizes and improves the existing reverse self-balancing pile testing method, which uses two sets of equipment, namely the pile top load cell and the pile body load cell, to move in opposite directions to conduct load testing, into a single load cell that operates in opposite directions to conduct load testing. By simplifying the loading equipment, improving the equipment level, and thus simplifying the pile foundation testing method.

[0061] Moreover, the bidirectional control load cell of this application can achieve all the testing effects of the reverse self-balancing experimental device, and only one load cell is used, which is simpler and easier to operate. The equipment has a high degree of integration, mature technology, low R&D difficulty, and the simplified equipment is easy to test pile foundation under complex operating conditions, which has great market potential.

[0062] This application also discloses a rapid testing method for pile foundation bearing capacity, based on the aforementioned bidirectional controlled load cell, employing the following technical solution:

[0063] A rapid testing method for pile foundation bearing capacity, referring to Figure 2 , Figure 4 and Figure 5 This includes the following steps:

[0064] S1. Based on the design bearing capacity of the target pile 4, determine the rated bearing capacity of the bidirectional control load box and the outer contour dimensions of the fixed plate 1;

[0065] S2. Based on the geological environment parameters of the target pile 4, determine the equilibrium point of the test pile and set it as the installation position of the loading section and the bidirectional control load box;

[0066] S3. Based on the equilibrium point position, the target pile 4 is divided into an upper pile body 41 and a lower pile body 43. The upper pile body 41 and the lower pile body 43 are connected by two fixing plates 1, or the upper pile body 41 reinforcement cage and the lower pile body 43 reinforcement cage are connected by two fixing plates 1 respectively. The final target pile 4 is formed by pile construction according to the traditional method.

[0067] S4. Connect the bidirectional control load box oil pipe to the oil pump and perform equipment debugging;

[0068] S5. First, start the opposing moving loading jack 22, record the output axial force and piston rod elongation of the opposing moving loading jack 22, and record the axial force displacement curves of the upper pile 41 and the lower pile 43 respectively. Determine the compressive bearing capacity and tensile bearing capacity according to the pile foundation design code. Then, control the oil return of the opposing moving loading jack 22, start the opposing moving loading jack 21, record the output axial force and piston rod elongation of the opposing moving loading jack 21, and record the axial force displacement curves of the upper pile 41 and the lower pile 43 respectively. Determine the tensile bearing capacity and compressive bearing capacity according to the pile foundation design code.

[0069] S6. Based on the principle of calculating the bearing capacity of reverse self-balancing pile foundations, the compressive bearing capacity of the upper pile 41 and the compressive bearing capacity of the lower pile 43 are taken as the compressive bearing capacity of the target pile 4; similarly, the tensile bearing capacity of the upper pile 41 and the tensile bearing capacity of the lower pile 43 are taken as the tensile bearing capacity of the target pile 4.

[0070] S7. Reinforce the loading section between the upper pile 41 and the lower pile 43;

[0071] S8. On-site response at the test site, test completed.

[0072] In step S6, the two fixed plates 1 are moved in opposite directions by the loading jack 21 to measure the negative bearing capacity of the upper pile 41. and the positive bearing capacity of the lower pile 43 ;

[0073] By applying load using the opposing-moving loading jack 22, the two fixed plates 1 are moved towards each other, and the positive bearing capacity of the upper pile 41 is measured. and the bearing capacity of the lower pile 43 ;

[0074] The ultimate vertical compressive bearing capacity of target pile 4 is the sum of the positive bearing capacity of the upper pile section 41 and the positive bearing capacity of the lower pile section 43, plus the self-weight of target pile 4. ;

[0075] The ultimate vertical uplift bearing capacity of target pile 4 is the sum of the negative bearing capacity of the upper pile segment and the negative bearing capacity of the lower pile segment, minus the self-weight of target pile 4. ;

[0076] Where W is the self-weight of the target pile 4.

[0077] Specifically, in one embodiment, taking a cast-in-place concrete pile as an example, referring to... Figure 4 The specific testing steps are as follows:

[0078] Step 1: Design and fabrication of the bidirectional control load cell. Based on the design bearing capacity of the target pile 4, determine the rated bearing capacity of the bidirectional control load cell in this application. Based on the rated bearing capacity of the load cell, determine the model and quantity of the jacks. Based on the cross-sectional profile of the target pile 4, determine the outline dimensions of the fixing plates 1 at both ends of the bidirectional control load cell.

[0079] Step 2: Locating the equilibrium point of target pile 4. Based on the geological environment parameters of target pile 4 (soil bearing capacity, soil layer thickness, compression modulus, and skin friction), and in accordance with the principles of equal bearing capacity provided by the upper and lower pile segments and the principle of fully utilizing the ultimate bearing capacity of the upper and lower pile segments simultaneously, the equilibrium point is determined to be the location of the load cell.

[0080] Step 3: Construction of Target Pile 4. Based on the equilibrium point location, the pile body is divided into an upper pile section 41 and a lower pile section 43. The reinforcing cages for both sections are fabricated and then connected via a bidirectional control load cell to form a complete reinforcing cage. Following traditional methods, the pile hole is constructed, monitoring sensors are pre-embedded, the reinforcing cage is hoisted into the hole, concrete is poured, and after curing, the target pile 4 is finally formed.

[0081] Step 4: Test Equipment Debugging. Connect the oil pipe of the bidirectional control load cell to the oil pump with automatic and intelligent control functions, connect the control equipment to the pile foundation bearing capacity test control system, start the equipment for trial operation, and ensure that the load cell, oil pump, controller, and control system are working properly.

[0082] Step 5: Pile Foundation Bearing Capacity Test. When initiating the bearing capacity test, first activate the opposing moving loading jack 22, recording the output axial force and cylinder extension of the opposing moving loading jack 22. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the compressive and tensile bearing capacities according to the pile foundation design specifications. Then, return the oil from the opposing moving loading jack 22, activate the opposing moving loading jack 21, recording the output axial force and cylinder extension of the opposing moving loading jack 21. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the tensile and compressive bearing capacities according to the pile foundation design specifications.

[0083] Step 6: Calculation of Pile Foundation Bearing Capacity. Based on the principle of calculating the bearing capacity of a self-balancing pile foundation, the compressive bearing capacity of the upper pile segment 41 and the lower pile segment 43 are used as the compressive bearing capacity of the target pile 4; similarly, the tensile bearing capacity of the upper pile segment 41 and the tensile bearing capacity of the lower pile segment 43 are used as the tensile bearing capacity of the target pile 4. Ideally, the bearing capacity of the target pile 4 is compared with the bearing capacity determined by other existing methods such as the self-balancing method to optimize relevant parameters.

[0084] Specifically, the invention principle for calculating the bearing capacity of the aforementioned pile foundation is as follows: Based on the reverse self-balancing method test device, it is improved into a bidirectional loading device. First, loading is achieved by using the opposing moving loading jacks 21 to realize the opposing movement of the two fixed plates 1, which in turn drives the piles at both ends to move in opposite directions, and the negative bearing capacity of the upper pile 41 is measured. and the positive bearing capacity of the lower pile 43 Then, the load box returns to its original position, and the loading jacks 22 are used to move the load in opposite directions, causing the fixed plates 1 at both ends to move in opposite directions. This, in turn, causes the piles at both ends to move in opposite directions, and the positive bearing capacity of the upper pile 41 is measured. and the negative bearing capacity of the lower pile 43 Finally, the total ultimate vertical compressive bearing capacity of target pile 4 is the sum of the positive bearing capacity of the upper pile section 41 and the positive bearing capacity of the lower pile section 43, plus the self-weight of target pile 4, that is... The ultimate vertical uplift bearing capacity of target pile 4 is the sum of the negative bearing capacity of the upper pile section 41 and the negative bearing capacity of the lower pile section 43, minus the self-weight of target pile 4. .

[0085] Step 7: Grouting reinforcement of the loading section. If target pile 4 is used as a permanent pile for the load-bearing structure of the project, the grouting section needs to be reinforced by grouting through pre-embedded grouting pipes. After passing the pile foundation quality certification, an integral permanent pile body is formed.

[0086] Step 8: On-site response at the test site, test completed.

[0087] In another feasible embodiment, taking a cast-in-place concrete pile with a recyclable jack scheme as an example, refer to... Figure 4 The specific testing steps are as follows:

[0088] Step 1: Design and fabrication of the bidirectional control load cell. Based on the design bearing capacity of the target pile 4, determine the rated bearing capacity of the bidirectional control load cell in this application. Based on the rated bearing capacity of the load cell, determine the model and quantity of the jacks. Based on the cross-sectional profile of the target pile 4, determine the outline dimensions of the fixing plates 1 at both ends of the bidirectional control load cell.

[0089] Step 2: Locating the equilibrium point of target pile 4. Based on the geological environment parameters of target pile 4 (soil bearing capacity, soil layer thickness, compression modulus, and skin friction), and in accordance with the principles of equal bearing capacity provided by the upper and lower pile segments and the principle of fully utilizing the ultimate bearing capacity of the upper and lower pile segments simultaneously, the equilibrium point is determined to be the location of the load cell.

[0090] Step 3: Construction of target pile 4. Based on the location of the equilibrium point, the pile body is divided into upper and lower pile sections 43. The upper pile reinforcement cage is fabricated and connected by a two-way control load box to form an integral reinforcement cage. Then, the pile hole is constructed, monitoring sensors are pre-embedded, the reinforcement cage is hoisted into the hole, concrete is poured, and after curing, the target pile 4 is finally formed.

[0091] Step 4: Test Equipment Debugging. Connect the bidirectional control load cell oil pipe to the oil pump with automatic and intelligent control functions, connect the control equipment to the pile foundation bearing capacity test control system, start the equipment for trial operation, and ensure that the load cell, oil pump, controller, and control system are working properly.

[0092] Step 5: Pile Foundation Bearing Capacity Test. When initiating the bearing capacity test, first activate the opposing moving loading jack 22, recording the output axial force and cylinder extension of the opposing moving loading jack 22. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the compressive and tensile bearing capacities according to the pile foundation design specifications. Then, return the oil from the opposing moving loading jack 22, activate the opposing moving loading jack 21, recording the output axial force and cylinder extension of the opposing moving loading jack 21. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the tensile and compressive bearing capacities according to the pile foundation design specifications.

[0093] Step 6: Calculation of Pile Foundation Bearing Capacity. Based on the principle of calculating the bearing capacity of a self-balancing pile foundation, the compressive bearing capacity of the upper pile segment 41 and the lower pile segment 43 are used as the compressive bearing capacity of the target pile 4; similarly, the tensile bearing capacity of the upper pile segment 41 and the tensile bearing capacity of the lower pile segment 43 are used as the tensile bearing capacity of the target pile 4. Ideally, the bearing capacity of the target pile 4 is compared with the bearing capacity determined by other existing methods such as the self-balancing method to optimize relevant parameters.

[0094] Step 7: Load box removal. If the diameter of the pile foundation is very large, and the diameter of the post-casting channel reserved in the upper pile section 41 for pouring the lower pile body is greater than 1m to meet the work needs of construction personnel, the load box can be removed and hoisted out through the reserved channel to be recovered.

[0095] Step 8: Reinforcement of the Loading Section of the Loading Box. If target pile 4 is to be used as a permanent pile for the load-bearing structure of the project, the construction personnel need to connect the upper and lower steel cages with steel bars in the loading section space after the load box is removed. Then, concrete is poured using the reserved channel, and the concrete compaction requirements must be met. After passing the pile foundation quality certification, an integral permanent pile body is formed.

[0096] Step 8: Restore the test site and complete the test.

[0097] In another feasible embodiment, taking segmental assembled steel pipe piles as an example, refer to... Figure 5 The specific testing steps are as follows:

[0098] Step 1: Design and fabrication of the bidirectional control load cell. Based on the design bearing capacity of the target pile 4, determine the rated bearing capacity of the bidirectional control load cell in this application. Based on the rated bearing capacity of the load cell, determine the model and quantity of the jacks. Based on the cross-sectional profile of the target pile 4, determine the outline dimensions of the fixing plates 1 at both ends of the bidirectional control load cell.

[0099] Step 2: Locating the equilibrium point of target pile 4. Based on the geological environment parameters of target pile 4 (soil bearing capacity, soil layer thickness, compression modulus, and skin friction), and in accordance with the principles of equal bearing capacity provided by the upper and lower pile segments and the principle of fully utilizing the ultimate bearing capacity of the upper and lower pile segments simultaneously, the equilibrium point is determined to be the location of the load cell.

[0100] Step 3: Construction of Target Pile 4. Based on the equilibrium point location, the pile body is divided into an upper pile section 41, a loading section 42, and a lower pile section 43. A bidirectional control load box is placed inside the loading section 42. The upper pile section 41 and the lower pile section 43 are connected by a bidirectional control load box fixing plate 1. The loading section 42 serves as a protective cover for the bidirectional control load box and is not connected to the upper pile section 41 or the lower pile section 43, forming a movable mechanism. The target pile 4 is driven into the ground to the design elevation using methods such as static pressure, vibratory impact, or pre-drilled static pressure.

[0101] Step 4: Test Equipment Debugging. Connect the bidirectional control load cell oil pipe to the oil pump with automatic and intelligent control functions, connect the control equipment to the pile foundation bearing capacity test control system, start the equipment for trial operation, and ensure that the load cell, oil pump, controller, and control system are working properly.

[0102] Step 5: Pile Foundation Bearing Capacity Test. When initiating the bearing capacity test, first activate the opposing moving loading jack 22, recording the output axial force and cylinder extension of the opposing moving loading jack 22. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the compressive and tensile bearing capacities according to the pile foundation design specifications. Then, return the oil from the opposing moving loading jack 22, activate the opposing moving loading jack 21, recording the output axial force and cylinder extension of the opposing moving loading jack 21. Record the axial force displacement curves of the upper pile section 41 and the lower pile section 43 respectively. Determine the tensile and compressive bearing capacities according to the pile foundation design specifications.

[0103] Step 6: Calculation of Pile Foundation Bearing Capacity. Based on the principle of calculating the bearing capacity of a self-balancing pile foundation, the compressive bearing capacity of the upper pile segment 41 and the lower pile segment 43 are used as the compressive bearing capacity of the target pile 4; similarly, the tensile bearing capacity of the upper pile segment 41 and the tensile bearing capacity of the lower pile segment 43 are used as the tensile bearing capacity of the target pile 4. Ideally, the bearing capacity of the target pile 4 is compared with the bearing capacity determined by other existing methods such as the self-balancing method to optimize relevant parameters.

[0104] Step 7: Reinforcement of the Loading Section of the Loading Box. If the target pile 4 is used as a permanent load-bearing pile for the project, and the working space inside the steel pipe pile meets the needs of the construction personnel, the upper pile section 41 and the lower pile section 43 need to be welded to the loading section pile section 42 by the construction personnel to form an integral permanent pile. Preferably, the load box is removed, and the jacks are taken out one by one.

[0105] Step 8: Removal of steel pipe piles. If target pile 4 is not intended as a permanent engineering pile, it can be removed by vibratory pile extraction or rotary sleeve extraction, and then used for the next test after maintenance.

[0106] Step 9: Restore the test site and complete the test.

[0107] In summary, compared with existing methods for testing the vertical bearing capacity of pile foundations, such as the surcharge method and the anchor pile method, the rapid testing method proposed in this application fully leverages the advantages of the self-balancing method, eliminating the need for conventional surcharge or anchor pile testing. It is particularly suitable for field operations and pile foundations with large bearing capacity.

[0108] Compared to the self-balancing method, it overcomes the shortcomings of the traditional self-balancing method, which has negative skin friction in the upper section of the pile, resulting in different test results compared to the positive skin friction of the engineering pile, making the test results conservative. In addition, the load cell requires a certain cost and cannot be recycled. It can directly obtain the vertical compressive bearing capacity and tensile bearing capacity of the pile foundation. The test device is simple and easy to operate, and some equipment can be recycled and reused, resulting in good economic benefits and strong applicability and promotion.

[0109] Compared to the reverse self-balancing method, the existing reverse self-balancing method requires the installation of a load cell at the top of the pile and a load cell in the pile body. It also requires the pre-reserved pipe for the loading rod to pass through in the upper section of the pile. The operation is relatively cumbersome and the equipment integration is not high. Therefore, it needs to be optimized and improved.

[0110] The rapid testing method of this application optimizes and improves the existing reverse self-balancing pile testing method, which uses two sets of equipment, namely the pile top load cell and the pile body load cell, to perform load testing by moving them in opposite directions. Instead, it uses a single load cell to perform load testing by moving it in opposite directions. By simplifying the loading equipment and improving the equipment level, the pile foundation testing method is simplified.

[0111] Moreover, the rapid testing method of this application can achieve all the detection effects of the reverse self-balancing experiment, and only uses one load cell, which is simpler and easier to operate. It has a high degree of equipment integration, mature technology, low R&D difficulty, and the simplified equipment is easy to use for pile foundation testing under complex operating conditions, which has great market potential.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A bidirectional control load cell, characterized in that, include: Two fixing plates are provided and are used to connect to the pile or the reinforcing cage; Opposite moving loading jacks are located between the two fixed plates, and multiple jacks are distributed in a circular array with equal spacing around the axis of the fixed plates. The cylinder and piston rod of the opposite moving loading jacks are fixedly connected to the two fixed plates respectively. A first U-shaped commutator and a second U-shaped commutator are located between two fixed disks, and multiple sets are distributed in a circumferential array at equal intervals along the axis of the fixed disks. The openings of the first and second U-shaped commutators in the same set are relatively fitted together, and their opening ends are detachably connected to the corresponding fixed disks. The opposing moving loading jacks are connected between the closed ends of the first and second U-shaped commutators in the same group.

2. The bidirectional control load cell of claim 1, wherein, The outer contour shape of the fixed plate is the same as that of the target pile.

3. The bidirectional control load cell of claim 1, wherein, The fixed plate has a working hole through the middle.

4. A bidirectional control load cell according to claim 1, characterized in that, Both of the two fixed plates are provided with anchoring steel bars on opposite sides for connection with the pile or steel cage.

5. A rapid testing method for pile foundation bearing capacity, based on a bidirectional controlled load cell as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Determine the rated bearing capacity of the bidirectional control load box and the outer contour dimensions of the fixed plate based on the design bearing capacity of the target pile; S2. Based on the geological environment parameters of the target pile, determine the equilibrium point of the target pile and define it as the installation location of the loading section and the bidirectional control load box; S3. Based on the equilibrium point position, the target pile is divided into an upper pile section and a lower pile section. The upper pile section and the lower pile section are connected by two fixing plates, or the upper pile section reinforcement cage and the lower pile section reinforcement cage are connected by two fixing plates. The final target pile is formed by pile construction according to the traditional method. S4. Connect the oil pipe of the bidirectional control load box to the oil pump and perform equipment debugging; S5. First, start the opposing moving loading jacks, record the output axial force and piston rod elongation of the opposing moving loading jacks, and record the axial force displacement curves of the upper and lower pile sections respectively. Determine the compressive bearing capacity and tensile bearing capacity according to the pile foundation design code. Then, control the oil return of the opposing moving loading jacks, start the opposing moving loading jacks, record the output axial force and piston rod elongation of the opposing moving loading jacks, and record the axial force displacement curves of the upper and lower pile sections respectively. Determine the tensile bearing capacity and compressive bearing capacity according to the pile foundation design code. S6. Based on the principle of calculating the bearing capacity of reverse self-balancing pile foundations, the compressive bearing capacity of the upper pile segment and the compressive bearing capacity of the lower pile segment are taken as the target pile compressive bearing capacity; Similarly, the pull-out bearing capacity of the upper pile segment and the pull-out bearing capacity of the lower pile segment are taken as the target pile pull-out bearing capacity; S7. Reinforce the loading section between the upper and lower pile sections; S8. The test site is restored, and the test is completed.

6. The rapid testing method for pile foundation bearing capacity according to claim 5, characterized in that, By applying load using the opposing-moving loading jacks, the two fixed discs are moved in opposite directions, and the negative bearing capacity of the upper pile section is measured. and the positive bearing capacity of the lower pile section ; By applying load using the opposing moving jacks, the two fixed discs move towards each other, allowing the positive bearing capacity of the upper pile section to be measured. and the negative bearing capacity of the lower pile body ; The ultimate vertical compressive bearing capacity of the target pile is the sum of the positive bearing capacity of the upper and lower pile sections, plus the self-weight of the target pile. ; The ultimate vertical uplift bearing capacity of the target pile is the sum of the negative bearing capacity of the upper pile segment and the negative bearing capacity of the lower pile segment, minus the self-weight of the target pile. ; Where W is the self-weight of the target pile.

7. The rapid testing method for pile foundation bearing capacity according to claim 5, characterized in that, If the target pile is a permanent cast-in-place concrete pile, the loading section is reinforced by grouting through pre-embedded grouting pipes. After pile foundation quality certification, an integral permanent pile body is formed.

8. The rapid testing method for pile foundation bearing capacity according to claim 7, characterized in that, Before reinforcing the loading section in step S7, the bidirectional control load box is first removed and recycled. Then, a steel reinforcement section is set in the loading section to connect the upper pile reinforcement cage and the lower pile reinforcement cage. Finally, concrete is poured.

9. The rapid testing method for pile foundation bearing capacity according to claim 5, characterized in that, If the target pile is a segmental assembled steel pipe pile, the target pile is divided into the upper pile body, the loading pile body and the lower pile body according to the position of the balance point, and the outer diameter of the fixing plate is less than or equal to the inner diameter of the target pile; The upper and lower pile sections are fixed to the inner walls of the pile body with mounting rings. Two fixing discs are connected to the upper and lower pile sections respectively through the mounting rings. The loading section is sleeved outside the bidirectional control load box and is not connected to the upper and lower pile sections.

10. A rapid testing method for pile foundation bearing capacity according to claim 9, characterized in that, In step S7, if the target pile is used as a permanent pile for the engineering load and the working space inside the steel pipe pile meets the work needs of the construction personnel, the bidirectional control load box is first removed and taken out, and then the construction personnel weld the upper pile body, the lower pile body and the loading section pile body to form an integral permanent pile body. If the target pile is not intended to be a permanent load-bearing pile for the project, it can be removed by vibratory pile extraction or rotary sleeve extraction, and then used for the next test after maintenance.

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