An indoor test device and installation method for pile-soil interaction under combined cyclic loading

Abstract

The present invention discloses an indoor test device for pile-soil interaction under combined cyclic loading, which includes a reaction force system and a model box. The model box is filled with soil and soil physical and mechanical parameter acquisition components. A loading system is arranged on the reaction force system, and the loading system is located above the model box and corresponds to it. The end face of the model box facing the loading system is an open end. One end of the model pile is installed on the loading system, and the model pile is inserted into the soil and placed in the model box. A number of physical and mechanical state acquisition components are arranged inside the pile body of the model pile, and a horizontal displacement meter is arranged on the top of the model pile. The loading system includes a soil overburden pressure loading system, a horizontal loading system, and a pile vertical load loading system. The horizontal loading system has the functions of horizontal cyclic force loading and continuous force loading, and the pile vertical load loading system has the function of applying vertical load to the model pile. This test device can show the responses of the pile and the soil and the interaction law between them under the combined action of horizontal cyclic and vertical loads, can conduct pile-soil interaction tests of different soil properties (including sand and clay) under different initial stress states and different pile foundation forms under different combined loads, so as to explore the bearing performance of the pile and the response law of the soil, etc., and can also intuitively record the deformation characteristics of the pile and the soil during the test.

Description

Technical Field

[0001] The present invention relates to an indoor test device for pile - soil interaction under combined cyclic loads, and also relates to an installation method of the indoor test device for pile - soil interaction under combined cyclic loads. Background Art

[0002] As one of the important foundation forms for supporting superstructures, during the service operation of piles, in addition to the vertical loads from the superstructures, horizontal loads may also be encountered. For example, for the pile foundation of offshore wind turbines, it bears the horizontal loads of waves and the vertical loads transmitted from the upper part of the wind turbines. The pile foundation bearing both vertical and horizontal loads is collectively referred to as combined loads, and during long - term service operation, these combined loads often act cyclically on the pile foundation. Currently, during the test process of studying the response of pile foundations under combined loads, generally, the pile - soil response under monotonic combined loads is analyzed, lacking an indoor test device and its usage method for studying pile - soil interaction under combined cyclic loads. Summary of the Invention

[0003] In view of the deficiencies in the background art, the technical problem to be solved by the present invention is to provide an indoor test device for pile - soil interaction under combined cyclic loads. This test device can demonstrate the responses of piles and soil masses and the interaction laws between them under the combined action of horizontal cyclic and vertical loads, can conduct pile - soil interaction tests for different soil properties (including sandy soil and clay) under different initial stress states and different pile foundation forms under different combined loads, so as to explore the bearing capacity of piles and the response laws of soil masses, etc., and can also intuitively record the deformation characteristics of piles and soil masses during the test process.

[0004] To this end, an indoor test device for pile - soil interaction under combined cyclic loads provided by the present invention includes a reaction force system and a model box. The model box is filled with soil and multiple soil physical and mechanical parameter acquisition elements. A loading system is provided on the reaction force system. The loading system is located above the model box and corresponds to it. The end face of the model box facing the loading system is an open end. One end of a model pile is installed on the loading system, and the other part of the model pile is inserted into the soil and placed inside the model box. The model pile is provided with multiple pile - body physical and mechanical state acquisition elements. A horizontal displacement meter is arranged at the top of the model pile. The loading system includes an overburden pressure loading system for soil, a horizontal loading system, and a vertical load loading system for the pile. The horizontal loading system has the functions of horizontal cyclic force loading and continuous force loading. The vertical load loading system for the pile has the function of applying vertical loads to the model pile.

[0005] In the present invention, a horizontal loading servo motor in a horizontal loading system is used to apply a horizontal load to a model pile, and the load of a vertical loading jack is transmitted to the model pile through a universal force transmission device, so that the model pile bears a vertical load. Through the horizontal loading system and the pile vertical load loading system, the model pile bears both horizontal and vertical loads simultaneously. The response of the model pile and the soil and the interaction law between them under the combined action of horizontal and vertical loads are visually demonstrated through a model box, and pile-soil interaction tests are carried out on the soil properties (including sand and clay) under different initial stress states and different pile foundation forms under different combined loads, so as to explore the bearing performance of the pile and the response law of the soil, etc., and the deformation characteristics of the pile and the soil during the test can also be visually recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 FIG. is a schematic cross-sectional structure diagram of an indoor test device for pile-soil interaction under combined cyclic loads in the present invention;

[0007] Figure 2 is Figure 1 a schematic top view structure diagram of an indoor test device for pile-soil interaction under combined cyclic loads in;

[0008] Figure 3 is Figure 1 a schematic cross-sectional structure diagram of a model box of an indoor test device for pile-soil interaction under combined cyclic loads in;

[0009] Figure 4 is Figure 1 a schematic structure diagram of a horizontal loading bracket of an indoor test device for pile-soil interaction under combined cyclic loads in. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] Referring to Figure 1 and Figure 2As shown in the figure, an indoor test device for pile-soil interaction under combined cyclic loading provided in the present invention includes a reaction force system 1 and a model box 2. The model box 2 is filled with soil mass 3 and a plurality of soil physical and mechanical parameter acquisition elements 4. The soil physical and mechanical parameter acquisition elements 4 can be selected as soil pressure sensors, piezometers, or fiber optic micro soil pressure cells. A liftable loading system is provided on the reaction force system 1. The loading system is located above the model box 2 and corresponds to it. The end face of the model box 2 facing the loading system is an open end. One end of the model pile 5 is installed on the loading system, and the other part of the model pile 5 is inserted into the soil mass 3 and placed inside the model box 2. A horizontal displacement meter 6 is provided at the top of the model pile 5. The horizontal displacement meter 6 is a dial indicator or an electronic displacement acquisition device. A number of pile body physical and mechanical state acquisition elements 7 are provided on the model pile 5. The pile body physical and mechanical state acquisition elements 7 adopt FBG grating fiber optic sensors, piezoelectric strain gauges, or distributed optical fibers. The horizontal displacement meter 6 records the horizontal displacement manually or automatically by a computer. The soil physical and mechanical parameter acquisition elements 4 and the pile body physical and mechanical state acquisition elements 7 are connected to an external computer acquisition instrument for data acquisition work. The loading system includes an overburden pressure loading system for the soil mass, a horizontal loading system, and a vertical pile load loading system. The horizontal loading system has a function of horizontal cyclic force loading. The cyclic force loading means that different loading forces appear within a cyclic period time, and the loading period is repeated. The vertical pile load loading system has a function of applying a vertical load to the model pile.

[0011] The reaction force system 1 includes a reaction frame 8, a threaded rigid column 9, and a rigid base 10. The rigid base 10 is fixed at the bottom of the threaded rigid column 9. The reaction frame 8 is connected to the threaded rigid column 9 and the lifting of the reaction frame is controlled by a main electric elevator 11. A jack reaction frame 12 is fixed at the end of the reaction frame 8 facing the model box. The main electric elevator 11 is fixed below the reaction frame. The main electric elevator 11 has a driving nut. The main electric elevator 11 is sleeved on the threaded rigid column through the driving nut. The rotation of the driving nut of the main electric elevator realizes the lifting on the rigid column and controls the height of the reaction frame 8. The model box 2 is fixedly installed on the rigid base 10 through a rigid block 13. When installing the model box 2, the reaction frame 8 is adjusted to the highest position by the main electric elevator 11, then the model box 2 is placed, and the model box 2 is installed and fixed on the rigid base 10 through the rigid block 13.

[0012] The model box 2 is semi-cylindrical and consists of a rigid steel plate 14 and a transparent plate 15. There is a water-proof rubber gasket 26 at the connection between the rigid steel plate 14 and the transparent plate 15 and they are connected by waterproof glue. The transparent plate 15 is a high-strength resin transparent plate. A rubber skin is pasted on the side of the model pile 5 in contact with the transparent plate 15, and lubricating oil or vaseline is applied between the model pile 5 and the transparent plate 15 to minimize the friction between the model pile and the transparent plate. The rigid steel plate 14 is provided with a number of drain holes 16, and a number of micro-grooves 17 are arranged on the outside of the rigid steel plate 14. The micro-groove holes 17 are connected to the drain holes 16. The number and arrangement of the drain holes 16 are set according to the drainage requirements of the test. When the test requirement is the undrained condition, the drain holes 16 are sealed; when the test requires drainage consolidation of the soil mass 3, methods such as vacuum preloading can be used for consolidation and reinforcement, and the water in the soil mass 3 is discharged through the drain holes 16 and the micro-grooves 17 for soil drainage consolidation. Relevant laboratory tests are carried out under two conditions of drainage and undrainage.

[0013] The loading system includes an overburden pressure loading system for the soil mass, a horizontal loading system, and a vertical load loading system for the pile.

[0014] The overburden pressure loading system for the soil mass includes a semi-circular jack 18. The semi-circular jack 18 is a semi-circular special hydraulic jack. The semi-circular jack 18 is fixed on the jack reaction frame 12 of the reaction system. The semi-circular jack 18 is placed at the central position above the model box 2. The lower end of the semi-circular jack 18 is loaded on the soil mass 3. The semi-circular jack 18 is used to provide a stable overburden pressure to ensure that the initial stress state of the soil mass is close to the in-situ condition. The semi-circular jack is controlled manually or by computer intelligence according to the test requirements. For geotechnical centrifuge tests, servo-controlled jacks are required, and mechanical control should be used as much as possible.

[0015] The horizontal loading system includes a horizontal loading bracket 19, two horizontal loading servo motors 20 and a horizontal loading force transmission rigid rod 21. The horizontal loading bracket 19 is connected to the threaded rigid column 9 of the reaction force system and controls the lifting of the horizontal loading system through a secondary electric lift 27. The height of the horizontal loading system is adjusted by controlling the lifting of the horizontal loading system through the secondary electric lift 27 to maintain a vertical and appropriate loading position with the model pile 5. The secondary electric lift 27 is fixed below the horizontal loading bracket 19. The secondary electric lift 27 has a driving nut. The secondary electric lift 27 is sleeved on the threaded rigid column through the driving nut. The secondary electric lift drives the nut to rotate to achieve lifting on the rigid column and control the height of the horizontal loading system. The two horizontal loading servo motors 20 are respectively arranged at the two ends of the horizontal loading bracket 19, the two ends of the horizontal loading force transmission rigid rod 21 are respectively connected to the horizontal loading servo motors 20 at the two ends, the horizontal loading force transmission rigid rod 21 is provided with a pile cap 22, the horizontal loading bracket 19 is provided with an arc slot 23 at the position corresponding to the pile cap 22, one end of the model pile 5 passes through the arc slot 23 and is connected to the pile cap 22, the model pile 5 is cyclically displaced in the arc slot 23, the horizontal loading system is arranged at a position close to the transparent plate 15, and the state of contact between the model pile and the surrounding soil can be observed through the transparent plate 15. In the horizontal loading system, the horizontal loading servo motor 20 can control the loading mode through a computer to perform horizontal cyclic force loading. According to different test requirements, the horizontal loading servo motor 20 selects different displacement or force control loading levels to drive the pile cap 22 to perform horizontal cyclic displacement, and the model pile 5 is horizontally cyclically displaced within the range of the arc slot 23 under the action of the pile cap 22, and the model pile body 5 bears the corresponding horizontal cyclic force load.

[0016] The pile vertical load loading system includes a vertical loading jack 24, which is fixed on the jack reaction frame 12 of the reaction system and corresponds to the position of the pile cap 22. The vertical loading jack 24 is connected to the pile cap 22 through a universal force transmission device 25, butter or vaseline is applied between the vertical loading jack 24 and the universal force transmission device 25 to increase the lubrication between the two, and the load of the vertical loading jack 24 is transmitted to the top of the model pile 5 through the universal force transmission device 25. In the horizontal loading system, the horizontal loading servo motor works, driving the pile cap 22 to perform horizontal cyclic displacement, and the universal force transmission device 25 is transmitted accordingly. The transmission of the universal torque device 25 enables the pile cap 22 to continue to perform horizontal cyclic displacement while still being able to transmit the load of the vertical loading jack 24 to the pile cap and the model pile, and will not limit the horizontal cyclic displacement of the pile cap 22. The universal force transmission device 25 belongs to conventional technology, and the structure of the universal force transmission device 25 will not be further elaborated in the present invention.

[0017] In the horizontal loading system, the horizontal loading servo motor 20 is used to model the horizontal load borne by the pile body. The universal force transmission device 25 transmits the load of the vertical loading jack 24 to the model pile, and the model pile body bears the vertical load. Through the horizontal loading system and the pile vertical load loading system, the model pile simultaneously bears the combined load under the combined action of horizontal and vertical directions. The response of the model pile and the soil under the combined action of horizontal and vertical loads and the interaction law between them are visually demonstrated through the model box.

[0018] An installation method for an indoor test device of pile-soil interaction under combined cyclic loads is as follows:

[0019] (1) According to the test requirements, determine the sizes of the model pile 5, the model box 2 and the reaction system, and determine the layout and quantity of the drainage holes 16, the quantity and layout positions of the soil physical and mechanical parameter acquisition elements 4 and the pile body physical and mechanical state acquisition elements 7. Then lay the pile body physical and mechanical acquisition elements 7 on the pile body of the model pile 5 according to the quantity and position requirements.

[0020] (2) Build the reaction system. Anchor the reaction frame 8 and the jack reaction frame 12 together by rivets. Connect the reaction frame 8 with the threaded rigid column 9 and control the lifting through the main electric elevator 11. Adjust the reaction frame 8 and the jack reaction frame 12 to the highest position by the main electric elevator 11. Place the model box 2 and fix the model box on the rigid base 10 through the rigid block 13. Fix the annular jack 18 and the vertical loading jack 24 on the jack reaction frame respectively, and install a universal force transmission device at the bottom of the vertical loading jack 24.

[0021] (3) Install the horizontal loading bracket 19. Connect the horizontal loading bracket 19 with the threaded rigid column 9 and install the secondary electric elevator 27. Control the lifting of the horizontal loading bracket through the secondary electric elevator 27, and first adjust the horizontal loading bracket to the highest position.

[0022] (4) Lay the model pile body physical and mechanical state acquisition elements 7 on the pile body of the model pile 5, lay the soil body 3 in the model box 2 and arrange the soil physical and mechanical parameter acquisition elements 4 in the soil body. Place the model pile with the pile body physical and mechanical acquisition elements 7 laid on it in the soil body, and perform pre-treatment on the soil body to be tested according to the differences in the test and the soil property 3.

[0023] (5) Install the horizontal loading system. Install the horizontal loading servo motors 20 on both sides of the horizontal loading bracket respectively. Install the pile cap 22 on the horizontal loading force transmission rigid rod 21, and connect both ends of the horizontal loading force transmission rigid rod 21 with the horizontal loading servo motors 20 on both sides respectively for installation in place. Install and connect the top of the pile cap 22 with the universal force transmission device.

[0024] (6) Control the lifting of the annular jack 18 through the main electric lift, adjust the annular jack 18 until the lower end face of the jack abuts against the soil surface, control the pile cap through the secondary electric lift, adjust the pile cap 22 above the model pile and install and fix it on the model pile 5. Adjust each system to the appropriate position and conduct experiments. Adjust each system that has completed the above work to the appropriate position and conduct experiments.

[0025] The soil in the model box 2 can be selected according to the actual soil with different soil properties, such as sand and clay, to construct the stress state of the soil. The model pile selects different pile foundation forms according to the actual pile size and pile type. The model pile determines the quantity and position of the arrangement of the pile body physical and mechanical state acquisition components 7 pasted on the pile body according to the requirements of the test. Conduct pile-soil interaction tests of different soil properties (including sand and clay) in different initial stress states and different pile foundation forms under different combined loads. Intuitively display the dynamic shear friction law of the contact between the model pile 5 and the soil 3 under the combined action of horizontal load and vertical load through the transparent plate 15, explore the bearing performance of the pile and the response law of the soil, etc., and intuitively observe the physical response of the pile body and the deformation characteristics of the soil, etc. In order to be able to collect the intuitive pile-soil contact characteristics in real time, a high-speed high-definition digital camera can be used to record the pile-soil contact friction process during the test. The soil physical and mechanical parameter acquisition components and the pile body physical and mechanical parameter acquisition components are connected to the external computer acquisition instrument for data acquisition work, providing reasonable test comparison data for theoretical and numerical analysis and verification.

[0026] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0027] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An indoor test device for pile-soil interaction under combined cyclic loading, characterized in that: It includes a reaction force system and a model box. The model box is filled with soil and multiple soil physical and mechanical parameter acquisition components. A loading system is provided on the reaction force system. The loading system is located above the model box and corresponds to it. The end face of the model box facing the loading system is an open end. One end of the model pile is installed on the loading system, and the other parts of the model pile are inserted into the soil and placed inside the model box. The model pile is provided with multiple pile body physical and mechanical state acquisition components. A horizontal displacement meter is arranged at the top of the model pile. The loading system includes an overburden pressure loading system for soil, a horizontal loading system, and a vertical load loading system for the pile. The horizontal loading system has the functions of horizontal cyclic force loading and sustained force loading. The vertical load loading system for the pile has the function of applying a vertical load to the model pile; The horizontal loading system includes a horizontal loading bracket, two horizontal loading servo motors, and a horizontal loading force transmission rigid rod. The horizontal loading bracket is connected to the reaction force system and the lifting of the horizontal loading system is controlled by a secondary electric elevator. The two horizontal loading servo motors are respectively fixed on the horizontal loading bracket. The two ends of the horizontal loading force transmission rigid rod are respectively connected to the two horizontal loading servo motors. A pile cap is arranged on the horizontal loading force transmission rigid rod. One end of the model pile is installed on the pile cap. The horizontal cyclic force loading means that different loading forces appear within a cyclic period. The loading cycle repeats. According to different test requirements, the horizontal loading servo motor selects different displacements or forces to control the loading magnitude, driving the pile cap to perform horizontal cyclic displacement; The vertical load loading system for the pile includes a vertical loading jack. The vertical loading jack is fixed on the reaction force system and corresponds to the position of the pile cap. The vertical loading jack is connected to the pile cap through a universal force transmission device, and the load of the vertical loading jack is transmitted to the top of the model pile through the universal force transmission device; The reaction force system includes a reaction frame, a threaded rigid column, and a rigid base. The rigid base is fixed at the bottom of the threaded rigid column. The reaction frame is connected to the threaded rigid column and the lifting of the reaction frame is controlled by a main electric elevator. A jack reaction frame is fixed at the end of the reaction frame facing the model box. The overburden pressure loading system for soil includes a semi-circular jack. The semi-circular jack and the vertical loading jack are respectively fixedly connected to the jack reaction frame.

2. The indoor test device for pile-soil interaction under combined cyclic loading according to claim 1, characterized in that: The semi-circular jack is fixed on the reaction force system. The semi-circular jack is placed at the central position above the model box. The lower end of the semi-circular jack is loaded on the upper surface of the soil.

3. The indoor test device for pile-soil interaction under combined cyclic loading according to claim 1 or 2, characterized in that: The model box is semi-cylindrical. The model box is composed of a rigid steel plate and a transparent plate. There is a water-proof rubber pad at the connection between the rigid steel plate and the transparent plate and they are connected by glue. A number of drainage holes are distributed on the rigid steel plate, and a number of micro-grooves are arranged outside the rigid plate.

4. An indoor test device for pile-soil interaction under combined cyclic loading according to claim 3, characterized in that: The soil physical and mechanical parameter acquisition components are soil pressure sensors, piezometers, or fiber optic micro soil pressure cells. The pile body physical and mechanical state acquisition components are FBG grating fiber optic sensors, piezoelectric strain gauges, or distributed optical fibers.

5. An indoor test device for pile-soil interaction under combined cyclic loading according to claim 1 or 2 or 4, characterized in that: An arc-shaped slot is provided at the position of the horizontal loading bracket corresponding to the pile cap. One end of the model pile passes through the slot and is connected to the pile cap, and the model pile undergoes cyclic displacement within the arc-shaped slot.

6. The indoor test device for pile-soil interaction under combined cyclic loading according to claim 5, wherein: A rubber sheet is pasted on the surface of the model pile in contact with the transparent plate, and lubricating oil is applied between the model pile and the transparent plate.

7. The installation method of an indoor test device for pile-soil interaction under combined cyclic loading according to claim 1, characterized in that: The steps are as follows: (1) According to the test requirements, determine the dimensions of the model pile, model box, and reaction system, and determine the layout and quantity of drainage holes, as well as the quantity and layout positions of the soil physical and mechanical parameter acquisition components and the pile body physical and mechanical state acquisition components. Then, lay the pile body physical and mechanical state acquisition components on the pile body of the model pile according to the quantity and position requirements. (2) Build the reaction system. Anchor the reaction frame and the jack reaction frame together with rivets. Connect the reaction frame to the threaded rigid column and control its lifting through the main electric elevator. Adjust the reaction frame and the jack reaction frame to the highest position through the main electric elevator. Place the model box and fix the model box on the rigid base with rigid blocks. Fix the semi-circular jack and the vertical loading jack on the jack reaction frame respectively, and install a universal force transmission device at the bottom of the vertical loading jack. (3) Install the horizontal loading bracket. Connect the horizontal loading bracket to the threaded rigid column and install a secondary electric elevator to control the lifting of the horizontal loading bracket. First, adjust the horizontal loading bracket to the highest position. (4) Lay the model pile body physical and mechanical state acquisition components on the pile body of the model pile, lay the soil body and arrange the soil physical and mechanical parameter acquisition components in the model box, place the model pile with the pile body physical and mechanical acquisition components laid on it in the soil body, and perform pre-treatment on the soil body to be tested according to the differences in tests and soil properties. (5) Install the horizontal loading system. Install the horizontal loading servo motors on both sides of the horizontal loading bracket, install the pile cap on the horizontal loading force transmission rigid rod, and connect the two ends of the horizontal loading force transmission rigid rod to the horizontal loading servo motors on both sides respectively for installation. Connect and install the top of the pile cap to the universal force transmission device. Control the lifting of the semi-circular jack through the main electric elevator, adjust the semi-circular jack until the lower end face of the jack abuts against the soil surface. Control the pile cap through the secondary electric elevator, adjust the pile cap above the model pile and install and fix it with the model pile. Adjust each of the above-mentioned systems to the appropriate positions and conduct the experiment.

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