A testing device and method for testing the side friction of uplift piles under freeze-thaw conditions

Abstract

The application discloses a kind of test device and testing method of side friction of uplift pile under freeze-thaw condition, it is related to uplift pile test device field, the technical scheme of the present application includes pedestal, outer bin, inner bin and loading device;Outer bin and guide pile vertical sliding fit, spring is arranged between outer bin and pedestal;Outer bin is provided with liquid inlet, liquid outlet and thermometer, the side wall of inner bin uses water-tight non-woven fabric, and inner bin is filled with soil body;Loading device is set to outer support, and the output end of loading device acts on the top of outer bin downward;The upper end of model pile is sequentially slid upward and is provided with outer bin bottom, inner bin bottom, inner bin top and outer bin top.The temperature of pressure-maintaining water in the device is changed to realize the freeze-thaw cycle of soil body, and the surrounding pressure of soil body is stabilized by the means of spring, loading device and pressure-maintaining water, and the maximum side friction and residual stress change after relative displacement are tested.

Description

Technical Field

[0001] This invention relates to the field of tensile pile testing devices, and in particular to a testing device and method for testing the tensile pile side friction resistance under freeze-thaw conditions. Background Technology

[0002] Tension piles, as a mature pile foundation technology, are widely used in the pile foundations of large basements, high-rise buildings, offshore dock platforms, suspension bridges, and cable-stayed bridges. However, most current building pile foundations must consider the influence of groundwater in the soil. Therefore, in existing technologies, tension pile tests must be conducted before construction. In cold regions such as permafrost areas, the soil around the pile is affected by long-term freeze-thaw cycles, causing pore water to accumulate at the pile-soil interface, inevitably affecting the side friction resistance value of the tension pile. This makes it difficult to obtain support data for different working conditions based on past design experience in pile foundation engineering. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a testing device and method for measuring the side friction resistance of pull-out piles under freeze-thaw conditions. The device achieves a freeze-thaw cycle of the soil by changing the temperature of the pressure-holding water inside the device. Simultaneously, the confining pressure of the soil is stabilized by using springs, a loading device, and pressure-holding water, and the maximum side friction resistance and the change in residual stress after relative displacement are tested.

[0004] The technical solution adopted by the present invention to solve its technical problem is: a test device for the resistance of pull-out pile side friction under freeze-thaw conditions, including a base, an outer chamber, an inner chamber and a loading device;

[0005] The base is vertically provided with guide piles, the outer compartment is vertically slidably engaged with the guide piles, and a spring is provided between the outer compartment and the base;

[0006] The outer chamber is equipped with an inlet, an outlet and a thermometer. The inner chamber is located inside the outer chamber. The upper and lower outer tops of the inner chamber are respectively connected and fixed to the upper and lower inner tops of the outer chamber. The side walls of the inner chamber are made of waterproof non-woven fabric and the inner chamber is filled with soil.

[0007] The loading device is mounted on the outer support, and the output end of the loading device acts downward on the top of the outer compartment;

[0008] The lower end of the model pile is fixed to the base, and the upper end of the model pile slides upward through the bottom of the outer warehouse, the bottom of the inner warehouse, the top of the inner warehouse, and the top of the outer warehouse in sequence.

[0009] When using it, set up the model piles and soil, then inject solvent into it. After initialization, start the loading device downwards. The loading device pushes the outer chamber downwards as a whole. The test can be completed by collecting and calculating various data.

[0010] Preferably, the outer compartment includes a pressure-bearing base, side cylinders, and a connecting top plate;

[0011] The upper and lower openings of the side cylinder are respectively connected to the connecting top plate and the pressure-bearing base;

[0012] The pressure-bearing base extends outward and slides in cooperation with the guide pile.

[0013] The solvent flows through the outer chamber and comes into contact with the inner soil.

[0014] Preferably, the inlet is located below one side of the side cylinder, and the outlet is located above the other side of the side cylinder. This ensures that the solvent entering the outer chamber can flow and mix sufficiently within the outer chamber.

[0015] Preferably, a loading cylinder is provided on the top of the outer compartment, the top of the model pile is located inside the loading cylinder, a loading disk is provided at the upper end of the loading cylinder, and the output end of the loading device acts on the loading disk. Because the recording device and the outer compartment and other structures will move downwards during the loading process, while the model pile will not change its vertical position, the use of a loading cylinder can avoid interference caused by contact between the loading device and the model pile.

[0016] Preferably, the outer top of the outer compartment is provided with a limiting groove that mates with the lower end of the loading cylinder. This can improve the stability of the contact between the loading cylinder and the outer top of the outer compartment.

[0017] Preferably, the inner compartment includes fixed supports and sidewall membranes. The two fixed supports are respectively fixed to the upper and lower tops of the outer compartment, and the upper and lower ends of the sidewall membrane are respectively connected to the fixed supports. This connects the upper and lower ends of the sidewall membrane to the fixed supports.

[0018] Preferably, the sidewall membrane comprises at least three layers of the impermeable nonwoven fabric, thereby increasing its strength.

[0019] Preferably, the external support includes a support column and a reaction frame, with both ends of the reaction frame fixed to the upper end of the support column, and the lower end of the support column fixed to the base. This facilitates the installation of a loading device.

[0020] Preferably, the inlet and outlet are each equipped with a flow valve to facilitate control of the solvent's entry and exit.

[0021] A test method for resisting the pull-out side friction of piles under freeze-thaw conditions includes the following steps:

[0022] S1, Insert the model piles into the outer and inner chambers, apply Vaseline to the top and bottom surfaces of the inner chamber, fill the inner chamber with soil, and remove excess model piles according to the height of the outer chamber and the spring.

[0023] S2, the lower end of the loading cylinder is set to correspond to the limiting groove, the loading disk is placed at the upper opening of the loading cylinder, and the output end of the loading device acts downward on the loading disk;

[0024] S3. Inject solvent into the outer chamber through the inlet until it is full. After standing for 30 minutes, wait for the temperature to stabilize. Then, open the inlet and outlet at the same time. Inject solvent at 40°C. After the thermometer shows the solvent temperature, stand for 10 minutes. Then, inject solvent at -20°C and stand for 10 minutes. Repeat this cycle 5 to 10 times. Then, close the inlet and outlet and wait for the solvent temperature inside the device to return to room temperature.

[0025] S4, start the loading device and load downwards at a speed of 1 mm / min. Record the displacement data as P, the loading time as T, the deformation modulus of spring 21 as E, the side area of ​​the model pile as S, and the axial force data as F. During the loading process, the axial force data Fmax appears as the maximum axial force. At this time, the maximum stress is Fmax / S. Record the displacement data at this time as Pmax. Continue loading. At this time, the residual stress is [F-(P-Pmax)E] / S.

[0026] Advantages of this invention:

[0027] In this invention, the model pile is connected to the bearing base, fixed bearing platform, soil and connecting top plate in sequence. All connections are sliding connections and cannot move horizontally due to device constraints. The conventional pile pulling is replaced by the vertical movement of the soil.

[0028] The soil is wrapped with impermeable non-woven fabric. The pore water in the soil is either remolded or undisturbed soil water. The water used for insulation in the device is an additive solution with a wide temperature variation range, which effectively solves the problem of pore water needing to exchange with the outside water. Moreover, the water in the device remains in a flowing state at lower temperatures, which can better ensure the soil confining pressure.

[0029] Meanwhile, the bottom of the device uses a spring-loaded non-fixed support as a reaction force device, which can provide displacement reserve as much as possible to test its participation stress. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only four of the drawings in this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of an embodiment of the present invention;

[0032] Figure 2This is a top view of the connecting top plate according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the loading disk according to an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the base according to an embodiment of the present invention.

[0035] The components are as follows: 1. Soil; 2. Fixed foundation; 3. Impermeable non-woven fabric; 4. Model pile; 5. Connecting top plate; 6. Loading plate; 7. Information acquisition device; 8. Loading device; 9. Bolt; 10. Limiting groove; 11. Thermometer; 12. Side cylinder; 13. Flow pipe; 14. Flow valve; 15. Guide pile; 16. Pressure bearing base; 17. Screw hole; 18. Support column; 19. Reaction frame; 20. Base; 21. Spring. Detailed Implementation

[0036] To enhance understanding of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are only used to explain the invention and do not limit the scope of protection of the invention.

[0037] Example

[0038] like Figure 1 As shown, a testing device for the resistance of pull-out pile side friction under freeze-thaw conditions includes a base 20, an outer chamber, an inner chamber, and a loading device 8. A guide pile 15 is vertically installed on the base 20, and the outer chamber slides vertically with the guide pile 15. A spring 21 is installed between the outer chamber and the base 20. The outer chamber has an inlet, an outlet, and a thermometer 11. The inner chamber is located inside the outer chamber, with its upper and lower outer tops respectively connected and fixed to the upper and lower inner tops of the outer chamber. The sidewalls of the inner chamber are made of impermeable non-woven fabric 3, and the inner chamber is filled with soil 1. The loading device 8 is installed on the outer support, and its output end acts downwards on the top of the outer chamber. The lower end of a model pile 4 is fixed to the base 20, and its upper end slides upwards through the bottom of the outer chamber, the bottom of the inner chamber, the top of the inner chamber, and the top of the outer chamber.

[0039] When using it, set up the model pile 4 and the soil 1, then inject solvent into it. After initialization, start the loading device 8 downwards. The loading device 8 pushes the outer chamber downwards as a whole. The test can be completed by collecting and calculating various data.

[0040] The loading device 8 employs an electric push rod or a cylinder, among other structures. Figure 4 As shown, the base 20 is provided with screw holes 17 for the lower end of the guide pile 15 to be fitted.

[0041] The inlet is located at the bottom of the outer chamber side, and the outlet is located at the top of the outer chamber side, consistent with the installation rules of thermometer 11. It is integrally formed with the outer chamber and is connected to the water inside. Flow valves 14 are installed outside the inlet and outlet to control the water exchange rate within the device, which, in conjunction with thermometer 11, controls the water temperature within the device. Specifically, a flow pipe 13 is connected to both the inlet and outlet, and the flow valve 14 is located within the flow pipe 13.

[0042] The outer chamber includes a pressure-bearing base 16, side cylinders 12, and a connecting top plate 5; the upper and lower openings of the side cylinders 12 are respectively connected to the connecting top plate 5 and the pressure-bearing base 16; the pressure-bearing base 16 extends outward and slides in cooperation with the guide pile 15. The solvent flows through the outer chamber and contacts the soil 1 in the inner layer.

[0043] The inlet is located below one side of the side cylinder 12, and the outlet is located above the other side of the side cylinder 12. This ensures that the solvent entering the outer chamber can flow and mix sufficiently within the outer chamber.

[0044] Combination Figure 3 As shown, a loading cylinder is provided on the top of the outer compartment, and the top of the model pile 4 is located inside the loading cylinder. A loading disk 6 is provided at the upper end of the loading cylinder, and the output end of the loading device 8 acts on the loading disk 6. Because the recording device and the outer compartment and other structures will move downwards during the loading process, while the model pile 4 will not change its vertical position, the use of a loading cylinder can avoid the loading device 8 from contacting the model pile 4 and causing interference.

[0045] Combination Figure 2 As shown, the outer top of the outer compartment is provided with a limiting groove 10 that mates with the lower end of the loading cylinder. This improves the stability of the contact between the loading cylinder and the outer top of the outer compartment. Specifically, the upper surface of the connecting top plate 5 is provided with the limiting groove 10.

[0046] The inner compartment includes fixed supports 2 and sidewall membranes. The two fixed supports 2 are respectively fixed to the upper and lower tops of the outer compartment, and the upper and lower ends of the sidewall membranes are respectively connected to the fixed supports 2. This allows the upper and lower ends of the sidewall membranes to be connected to the fixed supports 2.

[0047] The soil body 1 is cylindrical, that is, the inner chamber is cylindrical. The sides of the soil body 1 are wrapped with waterproof non-woven fabric 3 to restrict the exchange of pore water in the soil body 1 with water in the outer chamber. The top and bottom surfaces of the soil body 1 are connected to the fixed support 2, and the contact interface is uniformly coated with Vaseline. The diameter is the same as that of the fixed support 2.

[0048] The sidewall membrane comprises at least three layers of the impermeable nonwoven fabric 3, thereby increasing its strength.

[0049] The external support includes a support column 18 and a reaction frame 19. Both ends of the reaction frame 19 are fixed to the upper end of the support column 18, and the lower end of the support column 18 is fixed to the base 20. This facilitates the installation of the loading device 8.

[0050] The inlet and outlet are each equipped with a flow valve 14 to facilitate control of the solvent flow.

[0051] The fixed support platform 2 of the inner chamber, the pressure-bearing base 16 of the outer chamber, and the connecting top plate 5 are respectively provided with through holes corresponding to the model pile 4, which can slide relative to the model pile 4.

[0052] The pressure-bearing base 16 is a circular plate with a central hole of the same diameter as the model pile 4. After connection with the model pile 4, the model pile 4 is allowed to slide up and down. Four pin holes are provided on the pressure-bearing base 16 for connecting and fixing the bearing platform 2 via bolts 9. Four circular holes are provided on the edge of the pressure-bearing base 16 for sliding engagement with the guide pile 15, thus limiting horizontal displacement through this sliding connection. The reaction frame 19 is equipped with an information acquisition device 7.

[0053] A test method for resisting the pull-out side friction of piles under freeze-thaw conditions includes the following steps:

[0054] S1, insert the model pile 4 through the outer chamber and the inner chamber, apply Vaseline to the upper and lower inner top surfaces of the inner chamber, fill the inner chamber with soil 1, and remove the excess model pile 4 according to the height of the outer chamber and the spring 21.

[0055] S2, the lower end of the loading cylinder is set to correspond to the limiting groove 10, the loading disk 6 is placed at the upper opening of the loading cylinder, and the output end of the loading device 8 acts downward on the loading disk 6.

[0056] S3, inject solvent into the outer chamber through the inlet until it is full, let it stand for 30 minutes, and wait for the temperature to stabilize. Then, open the inlet and outlet at the same time, injecting solvent at 40°C. After the thermometer 11 shows the solvent temperature, let it stand for 10 minutes. Then, inject solvent at -20°C and let it stand for 10 minutes. Repeat this cycle 5 to 10 times. Then, close the inlet and outlet and wait for the solvent temperature in the device to return to room temperature.

[0057] S4, start loading device 8, load downwards at a speed of 1mm / min, record displacement data as P, loading time as T, deformation modulus of spring 21 as E, side area of ​​model pile 4 as S, axial force data as F. During loading, the axial force data Fmax appears as the maximum axial force, and the maximum stress at this time is Fmax / S. Record the displacement data at this time as Pmax. Continue loading, and the residual stress at this time is [F-(P-Pmax)E] / S.

[0058] In this invention, the model pile 4 is sequentially connected to the bearing base 16, the fixed bearing platform 2, the soil 1, and the connecting top plate 5. All connections are sliding connections, and the pile cannot move horizontally due to the constraints of the device. This replaces the conventional pile pulling with the vertical movement of the soil 1. The soil 1 is wrapped with impermeable non-woven fabric 3. The pore water inside the soil 1 is either remolded or undisturbed soil water. The water used for insulation inside the device is an additive solution with a wide temperature range, which effectively solves the problem of pore water needing to exchange with external water. Moreover, the water inside the device remains in a flowing state at lower temperatures, which can better ensure the confining pressure of the soil 1. At the same time, the bottom of the device uses a spring 21 non-fixed support as a reaction force device, which can provide displacement reserve as much as possible to test its participation stress.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A testing device for the resistance of pile side friction under freeze-thaw conditions, characterized in that, Includes a base (20), an outer compartment, an inner compartment, and a loading device (8); The base (20) is vertically provided with a guide pile (15), the outer compartment is vertically slidably engaged with the guide pile (15), and a spring (21) is provided between the outer compartment and the base (20); The outer chamber is provided with an inlet, an outlet and a thermometer (11). The inner chamber is provided inside the outer chamber. The upper and lower outer tops of the inner chamber are respectively connected and fixed to the upper and lower inner tops of the outer chamber. The side walls of the inner chamber are made of impermeable non-woven fabric (3). The inner chamber is filled with soil (1). The loading device (8) is mounted on the outer support, and the output end of the loading device (8) acts downward on the top of the outer compartment; The lower end of the model pile (4) is fixed to the base (20), and the upper end of the model pile (4) slides upward through the bottom of the outer warehouse, the bottom of the inner warehouse, the top of the inner warehouse and the top of the outer warehouse in sequence.

2. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 1, characterized in that: The outer chamber includes a pressure-bearing base (16), a side cylinder (12), and a connecting top plate (5); The upper and lower openings of the side cylinder (12) are respectively connected to the connecting top plate (5) and the pressure-bearing base (16); The pressure-bearing base (16) extends outward and slides in cooperation with the guide pile (15).

3. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 2, characterized in that: The liquid inlet is located below one side of the side cylinder (12), and the liquid outlet is located above the other side of the side cylinder (12).

4. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 1, characterized in that: The outer top of the outer compartment is provided with a loading cylinder, the top of the model pile (4) is located inside the loading cylinder, the upper end of the loading cylinder is provided with a loading disk (6), and the output end of the loading device (8) acts on the loading disk (6).

5. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 4, characterized in that: The outer top of the outer compartment is provided with a limiting groove (10) that connects with the lower end of the loading cylinder.

6. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 1, characterized in that: The inner compartment includes a fixed support platform (2) and a side wall membrane. The two fixed supports (2) are respectively fixed to the upper and lower tops of the outer compartment, and the upper and lower ends of the side wall membrane are respectively connected to the fixed support platform (2).

7. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 6, characterized in that: The sidewall membrane comprises at least three layers of the impermeable nonwoven fabric (3).

8. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 1, characterized in that: The external support includes a support column (18) and a reaction frame (19). The two ends of the reaction frame (19) are fixed to the upper end of the support column (18), and the lower end of the support column (18) is fixed to the base (20).

9. The testing device for the resistance to pull-out pile side friction under freeze-thaw conditions according to claim 1, characterized in that: The inlet and outlet are each equipped with a flow valve (14).

10. The method for testing the pull-out pile side friction resistance under freeze-thaw conditions according to claim 1, characterized in that: Includes the following steps: S1, insert the model pile (4) through the outer chamber and the inner chamber, apply Vaseline to the upper and lower inner top surfaces of the inner chamber, fill the inner chamber with soil (1), and remove the excess model pile (4) according to the height of the outer chamber and the spring (21). S2, the lower end of the loading cylinder is set to the corresponding limiting groove (10), the loading disk (6) is placed at the upper cylinder opening of the loading cylinder, and the output end of the loading device (8) acts downward on the loading disk (6). S3, inject solvent into the outer chamber through the inlet until it is full, let it stand for 30 minutes, wait for the temperature to stabilize, open the inlet and outlet at the same time, inject the solvent at 40°C, wait for the thermometer (11) to show the temperature of the solvent, let it stand for 10 minutes, then inject the solvent at -20°C, let it stand for 10 minutes, repeat this cycle 5 to 10 times, then close the inlet and outlet, and wait for the solvent temperature in the device to return to room temperature; S4, start the loading device (8) and load downwards at a speed of 1 mm / min. Record the displacement data as P, the loading time as T, the deformation modulus of the spring (21) as E, the lateral area of ​​the model pile (4) as S, and the axial force data as F. During the loading process, the axial force data Fmax appears as the maximum axial force. At this time, the maximum stress is Fmax / S. Record the displacement data at this time as Pmax. Continue loading. At this time, the residual stress is [F-(P-Pmax)E] / S.

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