A self-balancing static load test system for pile foundation and data equivalent superposition conversion method

Abstract

The present invention provides a self-balancing static load test system for pile foundations, comprising a steel cage, two or more load boxes, a hydraulic control unit, a deep displacement monitoring unit and an intelligent digital signal processing platform. The hydraulic control unit regulates the multi-layer load boxes, and at the same time uses an integrated multi-node deep displacement monitoring unit to monitor the displacement changes of the load boxes in real time during the test. The hydraulic control unit includes an electric control switch unit, a flexible connecting pipe and a flexible retractable connecting pipe, which can achieve remote control and stable operation. The deep displacement monitoring unit is composed of a MEMS acceleration sensor unit, a relay control unit, a fixed bracket and a rigid connecting pipe, which can accurately monitor the displacement changes of the load box. The present invention also provides a test data equivalent superposition conversion method, which can superimpose and convert the segmented test data in each load box test process to obtain a load-displacement curve equivalent to the top load.

Description

Technical Field

[0001] The invention relates to the technical field of static load detection of pile bearing capacity, and in particular to a pile self-balancing static load test system and an equivalent superposition conversion method for test data thereof. Background Art

[0002] With the increasing requirements of modern buildings for foundation bearing capacity, the design and testing of pile foundations have become particularly important in projects such as high-rise buildings, bridges, and large-span structures. Although traditional static load test methods such as the pile loading method and the anchor pile method can provide a direct evaluation of the bearing capacity of the foundation piles, they often face challenges such as limited site, large equipment requirements, and high test costs in the testing of ultra-long and large-diameter piles. Especially in projects involving large loads and special geological conditions, traditional methods can no longer meet actual needs. For this reason, self-balancing static load tests have gradually been introduced into engineering practice.

[0003] At present, the domestic self-balancing static load test usually uses a single load box, which has some limitations. First, the balance point of the test pile cannot be accurately located, and the position of the load box is difficult to determine, which will affect the measurement of the ultimate bearing capacity of the upper and lower piles, making the detection value of the vertical compressive ultimate bearing capacity of the single pile low, thus affecting the economy of the foundation pile design; under complex formation conditions, the friction resistance and pile end resistance of different soil layers are unevenly distributed, and a single load box is difficult to fully reflect the influence of different soil layers. Therefore, for long piles, the use of multiple load boxes can better reflect the bearing capacity of the foundation pile in different soil layers, reduce the problem of increased difficulty in result analysis due to different stress states, and make the test results more intuitive; it can make the detection process closer to the actual working state of the pile, and can also evaluate the bearing capacity in sections and determine the effective pile length. However, due to the immaturity of the test technology of multi-layer load boxes, it is difficult to popularize this method. Specifically, there are the following defects: (1) The increase of load boxes will make the test system complicated, the pipelines are complicated, and it is difficult to operate; (2) The traditional displacement monitoring method has large errors; (3) The data obtained from the test is the segmented loading data of each load box. The current data processing method uses the simple addition of the ultimate bearing capacity or loading value of each segment of the pile, and the result has a large error; (4) The axial force change of the pile body is monitored by installing a steel bar meter, which is not economical and the result error is also large. In view of this, the present invention proposes a self-balancing static load test system for piles based on a multi-layer load box and a data equivalent superposition conversion method. Summary of the invention

[0004] Based on the above-mentioned deficiencies in the prior art, the present invention provides a self-balancing static load test system for pile foundations. Based on the self-balancing static load test of a multi-layer load box, the present invention uses a hydraulic control unit of a continuous oil pipe to regulate the load box, and uses an integrated multi-node deep displacement monitoring unit to monitor the displacement change of the load box in real time during the test. The present invention also provides a matching test data equivalent superposition conversion method, which can superimpose and convert the segmented test data during each load box test process to obtain a load-displacement curve equivalent to the top load.

[0005] The technical solution adopted to achieve the above-mentioned purpose of the present invention is:

[0006] A self-balancing static load test system for pile foundation includes at least a steel cage and further includes:

[0007] There are more than two load boxes, which are distributed in the steel cage up and down and are connected and fixed to the steel cage. There are multiple jacks evenly distributed inside the load box, and the load box is provided with an oil valve connected to the jack;

[0008] A hydraulic control unit is connected to all load boxes and provides pressure to the load boxes and monitors the pressure, including a hydraulic controller, an oil pipe, an optical cable, an electric control switch, a flexible connecting pipe and a flexible telescopic connecting pipe; the hydraulic controller is connected to the oil circuit valve through the oil pipe and the electric control switch, the hydraulic controller is connected to and controls the electric control switch through the optical cable, the flexible connecting pipe and the flexible telescopic connecting pipe are both sleeved on the oil pipe and the optical cable, and the flexible telescopic connecting pipe passes through the interior of the load box and is connected to the flexible connecting pipe;

[0009] The deep displacement monitoring unit is connected to all the load boxes and monitors the displacement changes of the load boxes up and down. It includes a MEMS acceleration sensor, a signal line, a relay controller, a rigid connection tube and a rigid telescopic connection tube. The MEMS acceleration sensor is fixed on the load box. The relay controller is connected to the MEMS acceleration sensor through the signal line. The rigid connection tube and the rigid telescopic connection tube are both sleeved on the signal line, and the rigid telescopic connection tube passes through the interior of the load box and is connected to the rigid connection tube.

[0010] The intelligent digital signal processing platform is connected to the hydraulic control unit and the deep displacement monitoring unit through signal lines to obtain the hydraulic loading data and the displacement data of the load box and perform calculations.

[0011] Furthermore, three load boxes are provided, which are respectively located at the upper layer, the middle layer and the lower layer of the steel cage; the load boxes are welded to the steel cage and fixed by fixing rings, and the inner circle edge of the load box is welded and fixed to the main reinforcement of the steel cage by guide ribs.

[0012] Furthermore, two holes are reserved in the load box, which are connected vertically, and the flexible telescopic connecting tube and the rigid telescopic connecting tube are respectively installed in the two holes; the maximum elongation of the flexible telescopic connecting tube and the rigid telescopic connecting tube is twice the maximum displacement of the load box.

[0013] Furthermore, the hydraulic controller includes an electric switch control module, a pressure loading module and a pressure display module, which are respectively used to control the oil circuit switch of each load box, provide pressure to the load box and monitor the pressure.

[0014] Furthermore, the rigid connecting pipe is lined with a wire mesh to shield interference from external electronic signals.

[0015] Furthermore, a MEMS acceleration sensor is disposed above and below each load box, and the two MEMS acceleration sensors are respectively fixed to the upper and lower inner walls of the load box and are located at the top and bottom of the rigid telescopic connecting tube.

[0016] Furthermore, the deep displacement monitoring unit also includes a fixed bracket and an anti-vibration pad, the MEMS acceleration sensor is installed and fixed by the fixed bracket, and the anti-vibration pad is connected between the MEMS acceleration sensor and the load box.

[0017] Furthermore, the deep displacement monitoring unit also includes a data collector, which is connected to the relay controller via a signal line and collects and stores the displacement data of the MEMS acceleration sensor.

[0018] The present invention also provides a data equivalent superposition conversion method based on the above pile self-balancing static load test system, comprising the following steps:

[0019] Starting from the load box (2) at the bottom layer, the hydraulic loading data of each load box (2) loaded downward is equivalently superimposed and converted from bottom to top. The specific formula is: ; Where: Q is the equivalent superposition value of the load, in N; Q n is the bearing capacity of the superimposed pile, in N; Q d is the axial force at the bottom of the superimposed pile segment, obtained by linear interpolation of the equivalent superimposed value of the lower pile load, in N;

[0020] The superposition conversion formula of displacement data is:

[0021] ;

[0022] ;

[0023] Where: sis the superposition conversion value of displacement, unit: mm; s 0 is the theoretical average compression deformation of the superimposed pile, in mm; s n is the measured compression deformation of the superimposed pile segment, in mm; s d is the compression deformation caused by the residual axial force of the lower pile. s d = s n - s 0, unit: mm; α gh is the compression factor; l is the length of the superimposed pile, in mm;

[0024] When all the graded loads of the superimposed pile loading test are superimposed, if there is still graded load data on the lower pile that does not participate in the equivalent superposition of the superimposed pile, then the maximum graded load of the superimposed pile Q max On the basis of , the graded load data is further superimposed and converted, and the load amount is: , where: Q′ is the load of the lower pile that has not yet participated in the equivalent superposition, in N; the corresponding displacement calculation formula at this time is: , where: s′ The load of the lower pile that has not yet participated in the equivalent superposition Q′ The corresponding measured compression deformation, unit: mm.

[0025] Furthermore, when superimposed on the upper pile, the upward loading data of the uppermost load box (2) is first equivalently converted, and then the equivalent superposition is repeated again to generate a load-displacement variation law curve that is actually equivalent to the pile top load. The specific formula is: ; Where: Q u is the measured bearing capacity of the upper pile, in N; W is the deadweight and additional weight of the upper pile, in N; γ 1 is the conversion coefficient of the compressive friction resistance of the upper pile, which is determined through comparative tests under similar conditions and regional experience;

[0026] The equivalent superposition conversion formula of load is:

[0027] ;

[0028] The equivalent superposition conversion formula of displacement is:

[0029] .

[0030] Compared with the prior art, the pile foundation self-balancing static load test system and data equivalent superposition conversion method provided by the present invention have the following advantages: 1. The present invention adopts a hydraulic control unit of a continuous oil pipe, realizes remote control and power supply through a built-in cable, simplifies pipeline layout, and improves system controllability; 2. The multi-node deep displacement monitoring unit and high-precision MEMS acceleration sensor in the present invention improve the accuracy of displacement monitoring, and the one-piece connecting pipes simplify the pipeline layout and ensure the stability of displacement monitoring; 3. The multi-layer load box design in the present application has high reliability, and the segmented loading method solves the complex The problem that the balance point in the stratum is difficult to determine, and the test results are more accurate; 4. The test data equivalent superposition conversion method provided by the present invention takes into account the axial force transmission law and compression deformation of the foundation pile under the top load, scientifically integrates the segmented data, reduces errors, solves the problem that the test data of the multi-layer load box is not easy to integrate, and improves the practicality of the results; 5. The ground intelligent digital signal processing platform in this application can directly process and analyze the test data, and obtain the load-displacement curve equivalent to the pile top load, and analyze the changing laws of the pile body axial force, side friction resistance, and pile end resistance, thereby improving data processing efficiency and engineering application value.

[0031] The present invention effectively overcomes the limitations of the traditional self-balancing static load test system and provides a more accurate, reliable and economical means for pile bearing capacity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the pile self-balancing static load test system of the present invention;

[0033] Figure 2 It is a structural schematic diagram of the hydraulic control unit and the deep displacement monitoring unit in the present invention;

[0034] Figure 3 It is a schematic diagram of the cross-sectional structure of the load box of the present invention;

[0035] Figure 4 yes Figure 3 A partial enlarged view of the middle A part;

[0036] Figure 5 yes Figure 3 A partial enlarged view of part B in the middle;

[0037] Figure 6 It is a work flow chart of the intelligent digital signal processing platform of the present invention;

[0038] Figure 7 It is a complete load-displacement variation law curve obtained by the equivalent superposition conversion method of the pile self-balancing static load test data of the present invention;

[0039] Figure 8It is a graph showing the variation of pile shaft axial force, lateral friction resistance and pile end resistance obtained by the data equivalent superposition conversion method provided by the present invention.

[0040] Among them: 1-rebar cage, 2-load box, 3-guide rib, 4-fixing ring, 5-flexible connecting pipe, 6-hydraulic controller, 7-rigid connecting pipe, 8-relay controller, 9-data collector, 10-rigid telescopic connecting pipe, 11-intelligent digital signal processing platform, 12-signal line, 13-flexible telescopic connecting pipe, 14-fixed bracket, 15-anti-seismic pad, 16-MEMS acceleration sensor, 17-electrically controlled switch, 18-oil valve, 19-optical cable, 20-oil pipe, 21-jack. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following embodiments.

[0042] The pile self-balancing static load test system provided in this embodiment has an overall structure as follows: Figure 1 As shown, due to space limitations, Figure 1 The installation of the steel cage 1 and the pouring of the foundation piles are not shown. The main body of the system provided by the present invention is a steel cage, which is connected with a three-layer load box unit, a hydraulic unit controlled by a coiled tubing and a multi-node deep displacement monitoring unit.

[0043] The cross-sectional structure of the load box 2 is as follows: Figure 3 As shown, the load box is a box-type load box, which is composed of four mutually symmetrical jacks 21. An oil circuit valve 18 is left on the jack, which is controlled by a hydraulic controller 6 on the ground. Holes are reserved inside for the flexible telescopic connecting pipe 13 and the rigid telescopic connecting pipe 10 to pass through. The load box is welded to the steel cage and fixed by a fixing ring 4. The inner circle edge of the load box is welded and fixed to the main reinforcement of the steel cage by a guide rib 3. Each load box is connected to the hydraulic system through an oil pipe 20, and a MEMS acceleration sensor 16 is provided above and below each load box.

[0044] The hydraulic control unit of the coiled tubing is used to provide hydraulic power to the load boxes at each layer, including the underground oil pressure transportation module and the ground hydraulic control module, which are used to ensure that the oil pressure reaches the designated load box stably during the test and to control the pressure of the load box. Figure 2 , wherein the underground oil pressure transport module includes a flexible connecting pipe 5 and a flexible telescopic connecting pipe 13, the flexible telescopic connecting pipe is embedded in the reserved hole of each layer of the load box, and contains an electric control switch 17 which is sealed and connected with the oil circuit valve 18 of the load box. During the test, the flexible telescopic connecting pipe can be extended with the expansion of the load box to ensure the safe operation of the internal structure. Figure 5As shown; the flexible connecting tube contains an optical cable 19 and an oil pipe 20, one end of the optical cable is connected to the electric control switch, and the oil pipe transmits oil pressure to each load box through the oil circuit valve. The ground hydraulic control module is a hydraulic controller 6, which can select the load box to be pressurized by controlling the electric control switch during the test, and can display and adjust the specific value of the pressure of each load box, and upload it to the intelligent digital signal processing platform 11 through the signal line 12.

[0045] The multi-node deep displacement monitoring unit is used to monitor and record the displacement changes of the pile sections under pressure from the load boxes at each layer during the test. Figure 2 , mainly including underground monitoring module and ground receiving management module, which are used for real-time monitoring of underground foundation pile displacement, data transmission and ground signal reception management during the test. The underground monitoring module is composed of a rigid connecting pipe 7 and a rigid telescopic connecting pipe 10. The rigid connecting pipe is lined with a steel mesh to shield external electronic signal interference. The pipe is wrapped with a signal line 12 for signal transmission; the rigid telescopic connecting pipe is located in the reserved holes of each layer of the load box and is interconnected by the rigid connecting pipe. During the test, the rigid telescopic connecting pipe can be extended with the expansion of the load box to ensure the safe operation of the internal structure. Figure 4 As shown, the rigid telescopic connecting tube contains two MEMS acceleration sensors 16 located on a fixed bracket 14, which are respectively fixed to the upper and lower inner walls of the load box, and an anti-vibration pad 15 is added at the connection to ensure that the acceleration sensor can stably monitor the displacement change of the bottom of the section during the expansion and contraction of the load box. The ground receiving management module includes a relay controller 8 and a data collector 9. The relay controller 8 is connected to the underground monitoring module through a signal line to receive the monitoring digital signal of the acceleration sensor and optimize the signal; the data collector 9 can further store and process the monitoring data.

[0046] The workflow and principle of the intelligent digital signal processing platform 11 are as follows Figure 6 As shown, it is respectively connected to the hydraulic controller 6 of the hydraulic control unit and the data collector 9 in the multi-node deep displacement monitoring unit, and is used to receive the loading data during the test and the real-time displacement data of the foundation pile, and integrates and analyzes the received data through the equivalent superposition conversion method of the foundation pile self-balancing static load test data proposed by the present invention, converts the segmented loading data of each load box into equivalent superposition data under the top load, and draws a complete load-displacement variation curve of the foundation pile. Furthermore, the intelligent digital signal processing platform can also obtain the variation law diagram of the pile body axial force, lateral friction resistance and pile end resistance of the foundation pile under the top load, and can intuitively analyze the bearing characteristics of the foundation pile.

[0047] The data equivalent superposition conversion method provided in this embodiment includes the following steps:

[0048] Starting from the load box at the bottom layer, the hydraulic loading data of each load box loaded downward is equivalently superimposed and converted from bottom to top. The specific formula is: ; Where: Q is the equivalent superposition value of the load, in N; Q n is the bearing capacity of the superimposed pile, in N; Q d is the axial force at the bottom of the superimposed pile segment, obtained by linear interpolation of the equivalent superimposed value of the lower pile load, in N;

[0049] The superposition conversion formula of displacement data is:

[0050] ;

[0051] ;

[0052] Where: s is the superposition conversion value of displacement, unit: mm; s 0 is the theoretical average compression deformation of the superimposed pile, in mm; s n is the measured compression deformation of the superimposed pile segment, in mm; s d is the compression deformation caused by the residual axial force of the lower pile. s d = s n - s 0, unit: mm; α gh is the compression factor; l is the length of the superimposed pile, in mm;

[0053] When all the graded loads of the superimposed pile loading test are superimposed, if there is still graded load data on the lower pile that does not participate in the equivalent superposition of the superimposed pile, then the maximum graded load of the superimposed pile Q max On the basis of , the graded load data is further superimposed and converted, and the load amount is: , where: Q′ is the load of the lower pile that has not yet participated in the equivalent superposition, in N; the corresponding displacement calculation formula at this time is: , where: s′ The load of the lower pile that has not yet participated in the equivalent superposition Q′ The corresponding measured compression deformation, unit: mm.

[0054] When superimposed on the upper pile, the upward loading data of the uppermost load box is first converted equivalently, and then the equivalent superposition is repeated again to generate the load-displacement variation curve equivalent to the pile top load. The specific formula is: ; Where: Q u is the measured bearing capacity of the upper pile, in N; W is the deadweight and additional weight of the upper pile, in N; γ 1 is the conversion coefficient of the compressive friction resistance of the upper pile, which is determined through comparative tests under similar conditions and regional experience;

[0055] The equivalent superposition conversion formula of load is:

[0056] ;

[0057] The equivalent superposition conversion formula of displacement is:

[0058] .

[0059] In this embodiment, the above pile self-balancing static load test system is used, and according to the above data equivalent superposition conversion method, reference is made to Figure 6 , a self-balancing static load test was carried out on a test pile with a pile diameter of 900mm and a pile length of 57m under a three-layer load box. The specific process is as follows:

[0060] The pile foundation self-balancing static load test system based on multi-layer load boxes provided in this embodiment determines the loading range and installation position of each layer of load boxes according to the characteristics of the soil layer before the test begins. The ultimate bearing capacity of the three load boxes from top to bottom are 8400kN, 15000kN, and 10000kN, respectively, and the installation positions are 34.5m, 13m, and 1m away from the pile end respectively; then Figure 1 The steel cage body, guide ribs, fixing rings, load box and underground oil pressure transport module in the hydraulic control unit and underground monitoring module of the multi-node deep displacement monitoring unit of the steel cage part shown are assembled, and the sealing of each component is checked. After the trial operation is normal, the whole is sunk into the hole, and concrete is poured to complete the pile foundation. After curing for at least 28 days, a self-balancing static load test of the pile is carried out. During the test, the ground part and underground part of the hydraulic control unit and the multi-node deep displacement monitoring unit of the system are assembled and connected, and finally matched with the intelligent digital signal processing platform, and the functional connection and operation of each part of the system are checked to be normal.

[0061] The specific working steps of the pile self-balancing static load test system based on the multi-layer load box provided in this embodiment are as follows:

[0062] 1. Start the MEMS acceleration sensor through the intelligent digital signal processing platform, perform initial calibration on each sensor to ensure that it meets the accuracy requirements of the test, and adjust the static initial displacement of each sensor to 0.

[0063] 2. Start the hydraulic controller and pressurize the load box. The test sequence for the three-layer load box is to test the lowest load box first. During the test, the electric control switch is controlled to open the oil circuit valve of the load box, and the oil circuit valves of the middle and upper load boxes are closed at the same time; according to the loading table, the lower load box is controlled to apply graded pressure to the upper and lower directions at the same time, and the displacement change displayed in the intelligent digital signal processing platform is observed. When the displacement change rate reaches a relatively stable level, the next level of load is applied.

[0064] 3. Use the hydraulic controller to drain the oil from the load box and unload it. The unloading amount of each level is twice the graded load during loading. Each level of load is maintained for 1 hour. After the load is unloaded to 0, it is left to stand for 3 hours. The displacement changes of the upper and lower ends of the lower load box are monitored throughout the process by the MEMS acceleration sensor.

[0065] 4. Continue to carry out the loading test of the middle load box and the upper load box from bottom to top. Repeat steps 2 and 3 in the test process. The difference is that when carrying out the loading test of the middle load box and the upper load box, first open the downward oil drain valve of the load box, so that the load box is first loaded downward in stages, and when the downward displacement suddenly increases or the cumulative downward displacement is large and not greater than the sum of the upper and lower residual deformations of the lower load box, close the downward oil drain valve of the load box, open the upward oil drain valve of the load box, and load the load box upward in stages.

[0066] 5. After all the load box tests are completed, the test data will be collected on the intelligent digital signal processing platform. Some of the results are shown in the following table:

[0067] ,

[0068] The platform integrates and analyzes the received data through the equivalent superposition conversion method of the self-balancing static load test data of the pile, converts the segmented loading data of each load box into equivalent superposition data under the top load, and draws the complete load-displacement variation curve of the pile, such as Figure 7 shown.

[0069] 6. The intelligent digital signal processing platform generates a graph of the change of pile axial force, lateral friction and pile end resistance under top load based on the test data, such as Figure 8 shown.

Claims

1. A data equivalent superposition conversion method based on a pile foundation self-balancing static load test system, the pile foundation self-balancing static load test system comprising at least a steel cage (1), and further comprising: There are two or more load boxes (2), which are distributed vertically in the steel cage (1) and are fixedly connected to the steel cage (1). A plurality of jacks (21) are evenly distributed inside the load box (2). An oil circuit valve (18) connected to the jacks (21) is provided in the load box (2); A hydraulic control unit is connected to all the load boxes (2) and provides pressure to the load boxes (2) and monitors the pressure, comprising a hydraulic controller (6), an oil pipe (20), an optical cable (19), an electric control switch (17), a flexible connecting pipe (5) and a flexible telescopic connecting pipe (13); the hydraulic controller (6) is connected to the oil circuit valve (18) through the oil pipe (20) and the electric control switch (17); the hydraulic controller (6) is connected to and controls the electric control switch (17) through the optical cable (19); the flexible connecting pipe (5) and the flexible telescopic connecting pipe (13) are both sleeved on the oil pipe (20) and the optical cable (19); the flexible telescopic connecting pipe (13) passes through the interior of the load box (2) and is connected to the flexible connecting pipe (5); A deep displacement monitoring unit is connected to all the load boxes (2) and monitors the displacement changes of the load boxes (2) up and down, and comprises a MEMS acceleration sensor (16), a signal line (12), a relay controller (8), a rigid connection tube (7) and a rigid telescopic connection tube (10), wherein the MEMS acceleration sensor (16) is fixed on the load box (2), the relay controller (8) is connected to the MEMS acceleration sensor (16) via the signal line (12), the rigid connection tube (7) and the rigid telescopic connection tube are both sleeved on the signal line (12), and the rigid telescopic connection tube passes through the interior of the load box (2) and is connected to the rigid connection tube (7); An intelligent digital signal processing platform (11) is connected to a hydraulic control unit and a deep displacement monitoring unit via a signal line (12) to obtain hydraulic loading data and displacement data of a load box (2) and perform calculations; It is characterized in that: the data equivalent superposition conversion method comprises the following steps: Starting from the load box (2) at the bottom layer, the hydraulic loading data of each load box (2) loaded downward is equivalently superimposed and converted from bottom to top. The specific formula is: ; Where: Q is the equivalent superposition value of the load, unit N; Q n is the bearing capacity of the superimposed pile, in N; Q d is the axial force at the bottom of the superimposed pile segment, obtained by linear interpolation of the equivalent superimposed value of the lower pile load, in N; The superposition conversion formula of displacement data is: ； ； Where: s is the superposition conversion value of displacement, unit: mm; s0 is the theoretical average compression deformation of the superposition pile, unit: mm; s n is the measured compression deformation of the superimposed pile, in mm; s d is the compression deformation caused by the residual axial force of the lower pile, s d =s n _ s0, unit: mm; α gh is the compression coefficient; l is the length of the superimposed pile, in mm; When all the graded loads of the superimposed pile loading test are superimposed, if there is still graded load data on the lower pile that does not participate in the equivalent superposition of the superimposed pile, then the maximum graded load Q max On the basis of , the graded load data is further superimposed and converted, and the load amount is: , where: Q′ is the load of the lower pile that has not yet participated in the equivalent superposition, unit N; the corresponding displacement calculation formula at this time is: , where: s′ is the measured compression deformation corresponding to the load Q′ of the lower pile that has not yet participated in the equivalent superposition, unit: mm.

2. The data equivalent superposition conversion method according to claim 1, characterized in that: When superimposed on the upper pile, the upward loading data of the uppermost load box (2) is first equivalently converted, and then the equivalent superposition is repeated again to generate a load-displacement variation curve that is actually equivalent to the pile top load. The specific formula is: ; Where: Q u is the measured bearing capacity of the upper pile, in N; W is the deadweight and additional weight of the upper pile, in N; γ1 is the conversion coefficient of the compressive friction resistance of the upper pile, which is determined through comparative tests under similar conditions and regional experience; The equivalent superposition conversion formula of load is: ; The equivalent superposition conversion formula of displacement is: .

3. The data equivalent superposition conversion method according to claim 1 is characterized in that :: Three load boxes (2) are provided, respectively located at the upper layer, the middle layer and the lower layer of the steel cage (1); the load boxes (2) are welded to the steel cage (1) and fixed by a fixing ring (4); the inner circle edge of the load box (2) is fixed to the main reinforcement of the steel cage (1) by welding through a guide rib (3).

4. The data equivalent superposition conversion method according to claim 1, characterized in that: Two holes are reserved in the load box (2) and are connected vertically. The flexible telescopic connecting tube (13) and the rigid telescopic connecting tube (10) are respectively installed in the two holes. The maximum elongation of the flexible telescopic connecting tube (13) and the rigid telescopic connecting tube (10) is twice the maximum displacement of the load box (2).

5. The data equivalent superposition conversion method according to claim 1, characterized in that: The hydraulic controller (6) comprises an electric switch control module, a pressure loading module and a pressure display module, which are respectively used to control the oil circuit switch of each load box (2), provide pressure to the load box (2) and monitor the pressure level.

6. The data equivalent superposition conversion method according to claim 1, characterized in that: The rigid connecting pipe (7) is lined with a steel mesh to shield interference from external electronic signals.

7. The data equivalent superposition conversion method according to claim 1 is characterized in that: A MEMS acceleration sensor (16) is arranged above and below each load box (2); the two MEMS acceleration sensors (16) are respectively fixed to the upper and lower inner walls of the load box (2) and are located at the top and bottom of the rigid telescopic connecting tube (10).

8. The data equivalent superposition conversion method according to claim 1, characterized in that: The deep displacement monitoring unit further comprises a fixed bracket (14) and an anti-vibration pad (15); the MEMS acceleration sensor (16) is installed and fixed via the fixed bracket (14); and the anti-vibration pad (15) is connected between the MEMS acceleration sensor (16) and the load box (2).

9. The data equivalent superposition conversion method according to claim 1, characterized in that: The deep displacement monitoring unit further comprises a data collector (9), which is connected to the relay controller (8) via a signal line (12) and collects and stores displacement data of the MEMS acceleration sensor (16).

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