Testing device and testing method for studying degradation of shearing strength of pile-soil interface under dynamic load

Abstract

The invention relates to a test device and a test method for studying degradation of shear strength of a pile-soil interface under dynamic load. The test device comprises a frame assembly, a sample mold assembly, a model test assembly, a dynamic disturbance load loading assembly, a vertical loading assembly and a data acquisition assembly. The test device provided by the invention can simulate the shear strength degradation characteristics of the pile-soil interface under different dynamic disturbance loads, and simulates different dynamic disturbance load strengths and disturbance times by changing the height and impact times of the loading steel ball, so that the bearing characteristics and change rules of the pile foundation under the action of the dynamic disturbance loads are further analyzed, and the test result is more accurate. The problem that the change characteristics of the pile-soil interface in the actual construction disturbance process cannot be accurately simulated in the prior art is solved, and a scientific basis is provided for engineering design and construction. According to the test device provided by the invention, the falling height of the loading steel ball can be adjusted to simulate dynamic disturbance loads with different strengths and times borne by the pile-soil system.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a test device and a test method for studying the degradation of the shear strength of a pile-soil interface under dynamic load. Background Art

[0002] Pile foundations are increasingly used in high-speed railway bridges, urban high-rise or super-high-rise building foundation engineering and other fields due to their advantages such as high bearing capacity and small deformation. However, the vibration and impact caused by factors such as high-speed railway train operation and urban subway tunnel blasting construction and excavation will have a certain degree of adverse effect on the bearing capacity of pile foundations. The pile-soil interface is an important medium for deformation and force transmission between the pile and the soil around the pile, and its shear strength largely determines the bearing capacity of the pile. Under the action of dynamic disturbance loads, the shear strength of the pile-soil interface will be affected by a certain degree of deterioration, which in turn affects the bearing capacity of the pile foundation. Therefore, further research on the degradation characteristics of the shear strength of the pile-soil interface under dynamic disturbance loads can better predict and ensure the stability of the pile foundation, and has certain practical engineering application value.

[0003] At present, the calculation of the shear strength of the pile-soil interface mainly adopts theoretical analysis, on-site pile test or indoor model test. Among them, on-site tests are often limited by cost, environment and other aspects, and are suitable for a small number of pile extraction tests. Indoor model tests have the advantages of convenient operation and low cost, and are widely used in pile foundation testing. However, the existing pile-soil interface shear strength test model test is mainly used to analyze the settlement and deformation characteristics of piles under vertical static loads or cyclic loads. It cannot simulate the variation law of the shear strength of the pile-soil interface under different dynamic disturbance loads, and thus cannot accurately analyze the bearing characteristics of the pile foundation, which is quite different from the actual engineering. Summary of the invention

[0004] In view of the above problems, a test device and a test method are provided to study the degradation of the shear strength of the pile-soil interface under dynamic loads, so as to simulate the degradation characteristics of the pile-soil interface strength and the change law of the pile foundation bearing characteristics under different impact load conditions, so as to more accurately evaluate the long-term stability and safety of the pile foundation under dynamic disturbance loads.

[0005] The specific technical solutions are as follows:

[0006] The first aspect of the present invention is to provide a test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load, comprising: a frame assembly, a sample mold assembly, a model test assembly, a dynamic disturbance load loading assembly, a vertical loading assembly and a data acquisition assembly;

[0007] The frame assembly is used to support other corresponding components of the test device;

[0008] The sample mold assembly is used to shape and obtain a pile foundation sample with an outer wall having a certain roughness;

[0009] The model test assembly is used to prepare samples of loaded pile foundations and simulate the pile-soil interface, and is movably mounted on the frame assembly;

[0010] The dynamic disturbance load loading assembly is used to apply impact loads to the pile-soil interface;

[0011] The vertical loading component is used to apply vertical load to the pile foundation sample;

[0012] The data acquisition component is used to measure the dynamic disturbance load intensity, the pile top load of the pile foundation sample and the displacement under the vertical load.

[0013] Furthermore, the frame assembly is a cubic frame.

[0014] Furthermore, the sample mold assembly includes a chassis, two side panels and multiple fixing clamps. The side panels are semi-cylindrical thin-walled structures, and the inner walls of the side panels are serrated. The bottom of the side panels can be inserted into the chassis, and the chassis and the side panels can be combined to form a cylindrical mold cavity. The fixing clamps can be mounted on the outer periphery of the side panels.

[0015] Furthermore, the model test assembly includes a test box, a box cover, a bottom cover for controlling the opening and closing of a bottom hole of the test box, and filling soil. The top of the test box is open, and the box cover can be extended into the test box from the top of the test box. The pile foundation sample can be installed in the test box, and the top of the pile foundation sample can pass through the box cover, and the filling soil is filled around the periphery of the pile foundation sample.

[0016] Furthermore, the dynamic disturbance load loading assembly includes a loading frame and a loading steel ball. The loading frame includes a horizontal guide rail and an inclined guide rail. The bottom of the inclined guide rail is connected to one end of the horizontal guide rail. The other end of the inclined guide rail extends upward in a direction away from the horizontal guide rail. The other end of the horizontal guide rail can extend and abut against the test box.

[0017] Furthermore, the vertical loading assembly includes a driver and a pressure rod installed on a driving head in the driver, and the driver is installed on the frame assembly.

[0018] Further, the data acquisition component includes a pressure sensor, a displacement meter and a dynamic earth pressure sensor;

[0019] The pressure sensor is used to measure the vertical load on the pile foundation sample and is installed at the bottom of the pressure rod;

[0020] The displacement meter is used to measure the vertical displacement of the pile foundation sample and is installed at the bottom of the test box;

[0021] Dynamic earth pressure sensors are used to monitor the intensity of dynamic disturbance loads and are installed in filled soil.

[0022] A second aspect of the present invention is to provide a test method for the shear strength of the pile-soil interface under a simulated disturbance load, comprising:

[0023] The sample mold assembly is assembled to form a mold, and the inner cavity of the mold is filled with fine aggregate concrete. After vibration, curing, and demoulding, a pile foundation sample with a certain roughness is obtained;

[0024] Fasten the bottom cover of the test box orifice, place the cast pile foundation sample in the test box, make the bottom of the pile foundation sample above the bottom cover of the orifice, then fill part of the soil around the pile foundation sample, compact it, bury the dynamic soil pressure sensor, repeat the filling and compaction until the soil reaches the preset height;

[0025] The loading steel ball is placed on the inclined guide rail, and is made to slide down along the inclined guide rail and the horizontal guide rail in turn, thereby forming a certain impact load on the test box. The height and number of drops of the loading steel ball are changed to simulate impact loads of different intensities and times. The dynamic soil pressure sensor is used to record the dynamic disturbance load exerted by the loading steel ball on the pile-soil interface.

[0026] Move the test box so that the pile foundation sample is located at the bottom of the pressure rod, open the bottom cover of the hole, and install the displacement meter and pressure sensor at the designated positions according to the data collection requirements;

[0027] A pressure rod is used to apply a vertical load to the pile foundation sample. During the loading process, a pressure sensor is used to record the vertical load on the pile foundation sample. A displacement meter is used to record the displacement of the pile foundation sample under the vertical load. The shear strength of the pile-soil interface is determined based on the load-displacement curve.

[0028] The shear strength of the same type of pile-soil interface without dynamic disturbance load and with dynamic disturbance load of different intensities and times is compared, and the strength degradation characteristics of the pile-soil interface and the changing law of the bearing characteristics of the pile foundation are analyzed.

[0029] Furthermore, during filling, after each layer of filling soil is filled, the box cover is extended into the test box from the top of the test box, and force is applied from the four corners of the top of the box cover to compact the filling soil to a certain density. When the pile body of the pile foundation sample is half buried, dynamic soil pressure sensors are evenly placed according to the layout point map, and the filling and compaction are repeated until the soil reaches a preset height.

[0030] Furthermore, strain-controlled loading is used when applying vertical load.

[0031] The beneficial effects of the above scheme are:

[0032] 1) The test device provided by the present invention can study the degradation characteristics of the shear strength of the pile-soil interface under different dynamic disturbance loads. By changing the height and impact number of the loaded steel ball, different impact strengths and impact numbers are simulated, so as to further analyze the bearing characteristics and change laws of the pile foundation under the dynamic disturbance load, solve the problem that the prior art cannot accurately simulate the change characteristics of the pile-soil interface during the actual construction disturbance process, and provide a scientific basis for engineering design and construction;

[0033] 2) The test device provided by the present invention can simulate dynamic disturbance loads of different strengths and times on the pile-soil interface by adjusting the height and number of drops of the loaded steel ball;

[0034] 3) In the present invention, the roughness characteristics of the pile-soil interface are taken into consideration, and a sample mold assembly that can provide different roughnesses is designed. The sample mold assembly is composed of a chassis and two identical semi-cylindrical side panels, and has strong operability and is convenient for sample preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the structure of the test device provided in an embodiment of the present invention;

[0036] Figure 2 It is a schematic diagram of the exploded structure of the sample mold assembly provided in the embodiment of the present invention.

[0037] In the attached figure: 1. Pile foundation sample preparation; 2. Chassis; 3. Side plate; 4. Fixing clamp; 5. Test box; 6. Box cover; 7. Filling soil; 8. Loading steel ball; 9. Horizontal guide rail; 10. Inclined guide rail; 11. Pressure rod; 12. Pressure sensor; 13. Displacement meter; 14. Dynamic soil pressure sensor; 15. Driving rod; 16. Servo motor. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0040] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0041] like Figure 1 , Figure 2As shown, the test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load provided in the embodiment of the present invention comprises: a frame assembly, a sample mold assembly, a model test assembly, a dynamic disturbance load loading assembly, a vertical loading assembly and a data acquisition assembly; the frame assembly is used to support other corresponding components of the test device; the sample mold assembly is used to shape and obtain a pile foundation sample 1 with a certain roughness on the outer wall; the model test assembly is used to load the pile foundation sample 1 and simulate the pile-soil interface, and is movably installed on the frame assembly; the dynamic disturbance load loading assembly is used to apply an impact load to the pile-soil interface; the vertical loading assembly is used to apply a vertical load to the pile foundation sample 1; the data acquisition assembly is used to measure the dynamic disturbance load intensity, the pile top load of the pile foundation sample 1 and the displacement of the pile foundation sample 1 under the vertical load.

[0042] In the present invention, a pile foundation sample 1 with an outer wall having a certain roughness is obtained by using a sample mold assembly, and then loaded on a model test assembly, filled with soil, and then an impact load is applied by using a dynamic disturbance load loading assembly, and the dynamic disturbance load intensity around the pile foundation sample 1 is measured and recorded at this time; then the pile foundation sample 1 is adjusted by the model test assembly, and a vertical load is applied to the pile foundation sample 1 by using a vertical loading assembly, and the displacement of the pile foundation sample 1 under the vertical load is measured and recorded.

[0043] As a specific example, Figure 2 As shown, the sample mold assembly provided by the present invention includes a chassis 2, two side panels 3 and a plurality of fixing clamps 4. The side panels 3 are semi-cylindrical thin-walled structures. The bottom of the side panels 3 can be inserted into the groove in the chassis 2, so that the chassis 2 and the side panels 3 are combined to form a cylindrical mold cavity, and then the plurality of fixing clamps 4 are sleeved on the periphery of the side panels 3 (the outer wall of the side panels 3 is smooth) from top to bottom in an interval manner, so as to obtain a stable sample mold. When in use, the mold cavity can be filled with fine aggregate concrete, and the pile foundation sample 1 can be obtained after vibration, curing and demoulding. In order to obtain a pile foundation sample 1 with a certain surface roughness, a serrated structure can also be provided on the inner wall of the side panel 3 in the present invention, so that the surface roughness of the pile foundation sample 1 can be changed by the serrated structure formed by the side panel 3 pressing on the surface of the pile foundation sample 1.

[0044] As a specific example, Figure 1 As shown, the model test assembly provided by the present invention includes a test box 5, a box cover 6, and an orifice bottom cover for controlling the opening and closing of the orifice at the bottom of the test box 5 (the orifice bottom cover is Figure 1The top of the test box 5 is open. When loading the pile foundation sample 1, the bottom hole of the test box 5 can be closed by using the bottom cover of the hole, and then the pile foundation sample 1 can be fixed in the test box 5, so that the bottom of the pile foundation sample 1 is inserted into the bottom hole, and a small amount of filling soil 7 is filled in the test box 5. The box cover 6 is extended into the test box 5 from the top of the test box 5, and a force is applied from the four corners of the top of the box cover 6 to compact the filling soil 7 with the help of the box cover 6. Repeat the filling and compaction, so as to load the pile foundation sample 1 with the test box 5. In order to facilitate the loading of the pile foundation sample 1 and subsequent tests, the test box 5 in the present invention can be movably installed on the cubic frame through rollers or a slide groove-slide rail structure.

[0045] As a specific example, Figure 1 As shown, the dynamic disturbance load loading assembly provided by the present invention includes a loading frame and a loading steel ball 8, the loading frame includes a horizontal guide rail 9 and an inclined guide rail 10, the bottom of the inclined guide rail 10 is connected to one end of the horizontal guide rail 9, the other end of the inclined guide rail 10 extends upward in a direction away from the horizontal guide rail 9, and the other end of the horizontal guide rail 9 can extend and abut against the test box 5; during the test, the loading steel ball 8 can be placed on the inclined guide rail 10, and after being released, the loading steel ball 8 rolls along the inclined guide rail 10 and the horizontal guide rail 9 under the action of gravity and hits the test box 5 located at the end of the horizontal guide rail 9, thereby forming a certain impact load on the test box 5. Under the above principle, multiple tests can be carried out by using loading steel balls 8 of different masses or changing the height at which the loading steel balls 8 fall to simulate impact loads of different intensities and times. During the simulation process, a dynamic soil pressure sensor 14 is used to record the dynamic disturbance load applied by the loading steel ball 8 to the pile-soil interface.

[0046] As a specific example, Figure 1 As shown, the vertical loading assembly in the present invention includes a driver (which may be composed of a driving rod 15 and a servo motor 16) and a pressure rod 11 installed on a driving head in the driver, and the driver is installed on a cubic frame; under the above structure, when the pile foundation sample 1 is adjusted to below the pressure rod 11 through the test box 5, the vertical load can be applied to the pile foundation sample 1 through the pressure rod 11.

[0047] As a specific example, Figure 1 As shown, the data acquisition component in the present invention includes a pressure sensor 12, a displacement meter 13 and a dynamic soil pressure sensor 14; the pressure sensor 12 is used to measure the vertical load on the pile foundation sample 1 and is installed at the bottom of the pressure rod 11; the displacement meter 13 is used to measure the displacement of the pile foundation sample 1 in the vertical direction and is installed at the bottom of the test box 5; the dynamic soil pressure sensor 14 is used to monitor the intensity of the dynamic disturbance load and is installed in the filling soil 7.

[0048] An embodiment of the present invention provides a test method for studying the degradation of the shear strength of the pile-soil interface under dynamic disturbance loads using the above method, comprising:

[0049] The sample mold assembly is assembled to form a mold, and the inner cavity of the mold is filled with fine aggregate concrete. After vibration, curing, and demoulding, a pile foundation sample 1 with a certain roughness is obtained;

[0050] Place the cast pile foundation sample 1 in the test box 5 so that the bottom of the pile foundation sample 1 is located above the orifice, and then fill the pile foundation sample 1 with a 5 cm thick filling soil 7 and compact it. Repeat the filling and compaction until half of the pile of the pile foundation sample 1 is buried. Evenly place the dynamic soil pressure sensors 14 according to the layout point diagram, and repeat the filling and compaction until the soil reaches a preset height.

[0051] The loading steel ball 8 is placed on the inclined guide rail 10, and the loading steel ball 8 slides down along the inclined guide rail 10 and the horizontal guide rail 9 in sequence, thereby forming a certain impact load on the test box 5, and the height and number of drops of the loading steel ball 8 are changed to simulate impact loads of different strengths and times, and the dynamic soil pressure sensor 14 is used to record the dynamic disturbance load applied by the loading steel ball 8 to the pile-soil interface;

[0052] Move the test box 5 so that the pile foundation sample is located at the bottom of the pressure rod 11, open the bottom cover of the hole, and install the displacement meter 13 and the pressure sensor 12 at the designated positions according to the data collection requirements;

[0053] A vertical load is applied to the pile foundation sample 1 in a strain-controlled loading mode by using a pressure rod 11. During the loading process, a pressure sensor 12 is used to record the vertical load on the pile foundation sample 1. A displacement meter 13 is used to record the displacement of the pile foundation sample 1 under the vertical load. The shear strength of the pile-soil interface is determined according to a load-displacement curve.

[0054] The shear strength of the same type of pile-soil interface without dynamic disturbance load and with dynamic disturbance load of different intensities and times is compared, and the strength degradation characteristics of the pile-soil interface and the changing law of the bearing characteristics of the pile foundation are analyzed.

[0055] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load, characterized in that: Including: frame assembly, sample mold assembly, model test assembly, dynamic disturbance load loading assembly, vertical loading assembly and data acquisition assembly; The frame assembly is used to support corresponding components of the test device; The sample mold assembly is used to shape and obtain a pile foundation sample with an outer wall having a certain roughness; The model test assembly is used to load the pile foundation sample and simulate the pile-soil interface, and is movably installed on the frame assembly; The dynamic disturbance load loading assembly is used to apply a dynamic disturbance load to the pile-soil interface; The vertical loading assembly is used to apply vertical load to the pile foundation sample; The data acquisition component is used to measure the dynamic disturbance load intensity, the pile top load of the pile foundation sample and the displacement under the vertical load.

2. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 1 is characterized in that: The frame assembly is a cubic frame structure.

3. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 1, characterized in that: The sample mold assembly includes a chassis, two side plates and a plurality of fixing clamps. The side plates are semi-cylindrical thin-walled structures. The inner walls of the side plates are serrated. The bottoms of the side plates can be inserted into the chassis. The chassis and the side plates can be combined to form a cylindrical mold cavity. The fixing clamps can be sleeved on the outer periphery of the side plates.

4. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 3 is characterized in that: The model test assembly includes a test box, a box cover, an orifice bottom cover for controlling the opening and closing of a bottom orifice of the test box, and a filling soil body. The top of the test box is open, and the box cover can extend into the test box from the top of the test box. The pile foundation sample can be installed in the test box, and the top of the pile foundation sample can pass through the box cover, and the filling soil body is filled around the periphery of the pile foundation sample.

5. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 4, characterized in that: The dynamic disturbance load loading assembly includes a loading frame and a loading steel ball. The loading frame includes a horizontal guide rail and an inclined guide rail. The bottom of the inclined guide rail is connected to one end of the horizontal guide rail. The other end of the inclined guide rail extends upward in a direction away from the horizontal guide rail. The other end of the horizontal guide rail can extend and abut against the test box.

6. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 5, characterized in that: The vertical loading assembly comprises a driver and a pressure rod installed on a driving head in the driver, and the driver is installed on the frame assembly.

7. The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load according to claim 6, characterized in that: The data acquisition component includes a pressure sensor, a displacement meter and a dynamic soil pressure sensor; The pressure sensor is used to measure the vertical load on the pile foundation sample and is installed at the bottom of the pressure rod; The displacement meter is used to measure the displacement of the pile foundation sample in the vertical direction and is installed at the bottom of the test box; The dynamic soil pressure sensor is used to monitor the intensity of dynamic disturbance load and is installed in the filled soil.

8. A test method for studying the degradation of the shear strength of the pile-soil interface under dynamic disturbance load, characterized in that: The test device for studying the degradation of the shear strength of the pile-soil interface under dynamic load as claimed in claim 7 comprises: The sample mold assembly is assembled to form a mold, and the inner cavity of the mold is filled with fine aggregate concrete. After vibration, curing, and demoulding, a pile foundation sample with a certain roughness is obtained; The bottom cover of the test box orifice is fastened, and the cast pile foundation sample is placed in the test box so that the bottom of the pile foundation sample is located above the bottom cover of the orifice, and then the soil is partially filled around the pile foundation sample, compacted, and a dynamic soil pressure sensor is buried, and the filling and compaction are repeated until the soil reaches a preset height; A loading steel ball is placed on the inclined guide rail, and the loading steel ball slides down along the inclined guide rail and the horizontal guide rail in sequence, thereby forming a certain impact load on the test box, and the height and number of drops of the loading steel ball are changed to simulate impact loads of different intensities and times, and a dynamic soil pressure sensor is used to record the dynamic disturbance load applied by the loading steel ball to the pile-soil interface; Move the test box so that the pile foundation sample is located at the bottom of the pressure rod, open the bottom cover of the orifice, and install a displacement meter and a pressure sensor at designated positions according to data collection requirements; The pressure rod is used to apply a vertical load to the pile foundation sample, the pressure sensor is used to record the vertical load on the pile foundation sample during the loading process, the displacement meter is used to record the displacement of the pile foundation sample under the vertical load, and the shear strength of the pile-soil interface is determined according to the load-displacement curve; The shear strength of the same type of pile-soil interface without dynamic disturbance load and with dynamic disturbance load of different intensities and times is compared, and the strength degradation characteristics of the pile-soil interface and the changing law of the bearing characteristics of the pile foundation are analyzed.

9. The test method for the shear strength of the pile-soil interface under simulated disturbance load according to claim 8, characterized in that: During filling, after each layer of the filling soil is filled, the box cover is extended into the test box from the top of the test box, and force is applied from the four corners of the top of the box cover to compact the filling soil to a certain density. When the pile body of the pile foundation sample is half buried, the dynamic soil pressure sensors are evenly placed according to the layout point map, and the filling and compaction are repeated until the soil reaches a preset height.

10. The test method for the shear strength of the pile-soil interface under simulated disturbance load according to claim 8, characterized in that: Strain-controlled loading is used when applying vertical loads.

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