Indoor pile foundation model test device and method for multiple horizontal cyclic loading working conditions

Abstract

The application discloses an indoor pile foundation model test device for various horizontal cyclic loading working conditions, which comprises a pull-out type model box with a guide rail, a vacuum consolidation system, a loading system, a PLC control system and a data acquisition system. The loading system is connected with a model pile in the model box through a pile sleeve which can be inserted and locked; an insertion rod is arranged at a force sensor port, and the force sensor is designed to be detachable; the vacuum consolidation system is arranged in the model box to simulate a real soil environment by vacuumizing from the bottom; the pull-out type and the guide rail design of the model box can quickly adjust the position of the loading system, and a plurality of tests can be performed at one time of sample preparation; the PLC control system and the electronic data acquisition system are adopted, test parameters are accurately controllable, test operation is simple and convenient, and the pile foundation indoor model test under various loading amplitudes and various loading paths such as 0-5kN unidirectional step loading, unidirectional horizontal cyclic loading, bidirectional symmetric horizontal cyclic loading and bidirectional asymmetric horizontal cyclic loading can be performed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of indoor pile foundation model test equipment, and particularly relates to an indoor pile foundation model test device for various horizontal cyclic loading conditions. BACKGROUND

[0002] In addition to vertical load, pile foundations under high-rise buildings, sea-crossing bridges, port terminals and ocean wind power also bear large horizontal loads, which are mainly caused by wind, seismic load, impact force caused by vehicles and brakes, wave load, ship impact and the like. Most of these horizontal loads are regular or irregular horizontal cyclic loads except for instantaneous loads in some extreme cases. Since on-site loading tests are time-consuming and laborious, and it is difficult to operate on-site tests for some marine pile foundations, many scholars at home and abroad use indoor model test methods to explore the load response of pile foundations under horizontal cyclic loads.

[0003] Existing researches prefer to focus on whether the results of indoor model tests can reflect real working conditions, but ignore the influence of model test devices on test accuracy, and the research on the optimization design of model test devices is slightly insufficient. Existing indoor pile foundation model test devices are mainly divided into two categories. One category is large devices using exciters or servo hydraulic loading systems. This type of device can better reflect the actual load response of pile foundations, but it is expensive and difficult to operate. It is difficult to switch for simulating different working conditions, which is time-consuming and laborious. The other category is based on the principle of torque, which realizes cyclic loading through the coordinated action of counterweight, motor, pulley and rope. This type of device is small and light, and is rich in creativity. However, when the test working condition requires a large horizontal cyclic load, the device often causes the applied load to be inaccurate due to the inertia effect and the friction effect between the rope and the pulley. Therefore, it is of great significance to develop an indoor pile foundation model test device that is suitable for various horizontal cyclic loading conditions and has economic and practical characteristics.

[0004] Patent No. CN 112160353 A, entitled "Pile-soil interaction indoor test device under combined cyclic load and installation method" discloses an indoor test device, which includes a counterforce system, a model box and a plurality of parameter acquisition elements. The test device can exhibit the response of the pile and the soil under the combined action of horizontal cyclic and vertical load and the interaction between them, and can carry out pile-soil interaction tests of different pile foundation forms under different combined loads. However, the device cannot consolidate the soil in the model box to maintain the same stress state as the in-situ soil, so the test reliability is poor. In addition, the device realizes cyclic loading through two loading electric cylinders, and it is difficult to coordinate the two loading electric cylinders, so the accuracy of the applied load is also difficult to accurately control.

[0005] CN 106088169 A, entitled "Multi-freedom cyclic loading device for indoor test research of offshore wind turbine foundation", uses a pulley system composed of a movable pulley and a fixed pulley, combined with a cyclic stepping motor, a spring base, etc. to achieve any cycle and any form of cyclic loading by controlling the moving distance and moving speed of the cyclic stepping motor. This technology cannot be applied to larger horizontal load conditions, and the test parameters such as loading cycle and loading amplitude cannot be accurately controlled. The research paper "Development and experimental study of a cyclic loading device suitable for indoor model test" is basically similar to the above patent technology solution, and also has similar problems.

[0006] Patent No. CN111851605B, entitled "Pile foundation model loading device for vertical / horizontal cyclic loading", controls the rotation of the vertical rigid shaft by controlling the speed regulating motor, thereby driving the counterweight to move horizontally in a circular motion, achieving vertical cyclic loading and horizontal cyclic loading under different cyclic amplitudes. Still, there are problems such as low test parameter accuracy and small test loading amplitude. SUMMARY

[0007] To solve the above technical problems, the present application uses a driving electric cylinder combined with a PLC control system to expand the loading amplitude to 0~5kN, which can be applied to indoor model tests of various types of pile foundations. At the same time, the loading system can realize various horizontal cyclic loading conditions. In addition, the pull-out type model box and the guide rail design on it, as well as the detachable design of the force sensor, can perform multiple tests at once, effectively control the test variables, and make the indoor pile foundation model test operation simple and the test results accurate.

[0008] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0009] An indoor pile foundation model test device for various horizontal cyclic loading conditions, comprising:

[0010] A model box comprising multiple box unit segments, the box unit segments are connected through sealed guide rails to realize a pull-out type box structure, and the box is filled with a sand cushion layer, soil, and a sealing cover from bottom to top; a model pile is inserted into the soil in the model box;

[0011] The guide rail comprises two vertical guide rails fixedly connected with the two side walls of the model box, two longitudinal guide rails connected at the top of the vertical guide rails, and two horizontal guide rails connected between the two longitudinal guide rails, wherein the vertical guide rails can be adjusted in vertical height, the two longitudinal guide rails are arranged along the length direction of the model box, the horizontal guide rails can be adjusted in longitudinal position on the longitudinal guide rails, a driving cylinder is mounted on the horizontal guide rails, and the driving cylinder can be adjusted in horizontal position on the horizontal guide rails; the driving shaft of the driving cylinder is connected with the top of the model pile through a force sensor and a pile sleeve;

[0012] The vacuum pipe is vertically arranged, with the upper end inserted into the upper part of the soil body and the lower end communicated with a bottom pipe horizontally arranged in the sand cushion layer, one end of the bottom pipe is closed, and the other end is connected with a vacuum pump arranged outside the model box.

[0013] The drainage hole is arranged on the side wall at the bottom of the model box.

[0014] The displacement sensor is arranged on the transmission shaft connected with the driving shaft of the driving cylinder, and used for monitoring the horizontal displacement at the top of the pile.

[0015] The laser displacement meter is arranged on the inner side of the model box close to the soil body, and used for monitoring the corner of the model pile at the surface of the soil body.

[0016] The controller is connected with the driving cylinder.

[0017] The signal acquisition module is connected with the force sensor, the displacement sensor and the laser displacement meter.

[0018] Further, the side panel at the leftmost side of the entire model box is made of transparent material, and used for observing the internal condition of the model box; the side panel at the rightmost side of the entire model box can be flipped along the bottom of the box body, so as to facilitate the loading and unloading of the soil body.

[0019] Further, the range of the driving cylinder is 0-5kN.

[0020] Further, the pile sleeve comprises an insertion rod and a circular groove with holes, the insertion rod is fixed at the port of the force sensor, and one spring button is arranged on each of the upper and lower sections of the insertion rod; the circular groove with holes is fixed on the model pile, and the spring button is locked after the insertion rod is inserted into the circular groove with holes, so as to realize the locking between the insertion rod and the circular groove with holes.

[0021] Further, the driving cylinder is provided with ≥2 sets of the force sensor, and the force sensor is detachably connected with the transmission shaft.

[0022] Further, the controller is a PLC.

[0023] Further, the width of the model box is set to be greater than or equal to 2*10D, and D is the diameter of the model pile.

[0024] Further, a lockable pulley is arranged at the bottom of the model box for quickly adjusting the position of the model box.

[0025] The application further discloses a test method based on the indoor pile foundation model test device for various horizontal cyclic loading conditions.

[0026] The vacuum pump is started, and the soil in the model box is subjected to vacuum consolidation under the action of vacuum negative pressure.

[0027] The driving cylinder is adjusted to the position of the model pile in the model box through the guide rail, and the force sensor at the end of the driving cylinder is connected to the model pile.

[0028] The controller is opened, and the driving force generated by the driving cylinder is connected to the pile sleeve through the force sensor, so that the horizontal force with different loading amplitudes and different loading paths is applied to the model pile.

[0029] The controller is used for stress control and displacement control, including one-way step loading, one-way horizontal cyclic loading, two-way symmetric horizontal cyclic loading, and two-way asymmetric horizontal cyclic loading.

[0030] The signal acquisition module is used for real-time and synchronous acquisition of the data of the force sensor, the displacement sensor and the laser displacement meter, and the strain gauge data arranged on the pile body.

[0031] When the number of test groups is large, the multiple box units are pulled to the required length, multiple model piles are arranged in the model box along the length of the soil body, the driving cylinder is adjusted to different positions through the guide rail, and the model piles at different positions in the soil body are loaded.

[0032] The application has the following beneficial effects:

[0033] First, the traditional mold box type is generally set as a fixed box body, and when multiple tests are carried out, the soil body often needs to be consolidated and inserted repeatedly, which is time-consuming and laborious. The present application adopts a pull-out type model box combined with a guide rail design, which can realize the movement of the loading system at any spatial position in the model box, load the model pile at different positions in the soil body, and according to the test requirements, the soil vacuum consolidation system works once, that is, multiple working condition tests can be carried out, saving the test period.

[0034] Second, a single drive electric cylinder is used, which is inserted and locked with the model pile, and unidirectional loading can realize bidirectional loading, so that the loading amplitude is accurately controllable; at the same time, the loading amplitude range is expanded to 0~5kN, which can be applied to indoor model tests of various types of pile foundations; combined with a PLC control system, indoor model tests of pile foundations under various loading amplitudes and various loading paths can be realized.

[0035] Third, the sand cushion layer at the bottom of the model box is inserted from the bottom of the soil body through the vacuum pipe, which is different from the traditional indoor vacuum consolidation technology, in which the vacuum pipe is inserted from the upper soil body. The design of the present application enables the soil body in the model box to be quickly consolidated under the dual action of vacuum negative pressure and soil self-weight when using soft clay for experiments.

[0036] Fourth, the detachable design of the force sensor of the present application can flexibly adopt sensors of different ranges for model piles of different stiffnesses, which can make the test results more accurate.

[0037] Fifth, the right side of the model box of the present application is designed to be reversible, which is convenient for loading and unloading the test soil body. BRIEF DESCRIPTION OF DRAWINGS

[0038] Fig. 1 is a schematic diagram of the indoor model device of the present application;

[0039] Fig. 2 is a top view of the model box of the present application;

[0040] Fig. 3 is a side view of the model box of the present application;

[0041] Fig. 4 is a schematic diagram of the pile sleeve structure;

[0042] Fig. 5 is a schematic diagram of multiple cyclic loading conditions of the present application;

[0043] Explanation of the drawings: 1 - model box; 2 - model pile; 3 - drainage plate; 4 - guide rail; 5 - vacuum hole; 6 - drainage hole; 7 - pulley; 8 - vacuum pipe; 9 - sealing cover; 10 - sand cushion; 11 - vacuum pump; 12 - driving electric cylinder; 13 - transmission shaft; 14 - displacement sensor; 15 - force sensor; 16 - pile sleeve; 17 - laser displacement meter; 18 - PLC control system; 19 - data acquisition system; 20 - guide rail; 21 - positioning knob; 22 - toughened glass; 23 - right side steel plate; 24 - box sealing guide rail; 25 - insertion rod; 26 - round slot with holes; 27 spring button; 28 - round hole. DETAILED DESCRIPTION

[0044] The present application will be illustrated below according to the embodiments shown in the drawings. The embodiments disclosed this time can be considered as exemplary in all aspects and are not limited. The scope of the present application is not limited by the description of the following embodiments.

[0045] The present application will be illustrated below according to the embodiments shown in the drawings. The embodiments disclosed this time can be considered as exemplary in all aspects and are not limited. The scope of the present application is not limited by the description of the following embodiments.

[0046] Embodiment:

[0047] Referring to the accompanying Figs. 1-4 .

[0048] During the normal service period of offshore wind power foundation, it long-term bears horizontal cyclic loads such as wind, wave and current, which induces large cumulative deformation of pile foundation. When the deformation is too large, it may cause the wind turbine to tilt, which endangers the service life and safety of the upper structure. In order to explore the load response of offshore wind power foundation under various cyclic loads, the indoor pile model test device for various horizontal cyclic loading conditions is used to carry out model test research.

[0049] The test is designed for three groups of working conditions, respectively, single pile unidirectional step-by-step loading, single pile bidirectional symmetric cyclic loading, and single pile bidirectional asymmetric cyclic loading. The model pile 2 has a length of 1 m, a diameter of 0.05 m, and a soil depth of 0.6 m. Considering the test group number, the length and diameter of the model pile 2, and the effective stress area of the soil at the edge of the foundation, the first section of the model box is designed to have a size of 1 m x 1 m x 1 m (length x width x height), and the second and third sections of the model box have a size of 0.5 m x 1 m x 1 m, with a wall thickness of 5 mm. The model box is pulled out, and the second and third sections of the model box are gradually expanded along the box sealing guide rail 24. After expansion, the total size of the model box is 2 m x 1 m x 1 m. This design ensures that the distance between the model pile 2 and the side wall of the model box 1 is more than 10D, and the influence of the boundary effect can be ignored. It also saves the test period and improves work efficiency. The model box 1 is made of steel plates welded together, and the left side is made of tempered glass 22 for observing the internal conditions of the model box 1. The right side steel plate 23 can be flipped along the right bottom edge to form a "inclined bridge" shape, which facilitates the loading and unloading of soil. Six guide rails 20 are arranged on the model box, including two vertical guide rails fixedly connected to the side walls of the model box, two longitudinal guide rails connected to the top of the vertical guide rails, and two horizontal guide rails connected between the two longitudinal guide rails. The vertical guide rails can adjust the vertical height, the two longitudinal guide rails are arranged along the length direction of the model box, the horizontal guide rails can adjust the longitudinal position on the longitudinal guide rails, the horizontal guide rails are provided with driving cylinders, and the driving cylinders can adjust the horizontal position on the horizontal guide rails. The driving shaft of the driving cylinder is connected to the top of the model pile through a force sensor and a pile sleeve;

[0050] Each guide rail 20 is provided with a positioning knob 21, which can realize the movement and fixation of the loading system at any position on the model box.

[0051] Four lockable pulleys 7 are arranged at the bottom of the model box for quickly adjusting the position of the model box 1. According to the test scheme, the soil is placed in the model box, the model box is arranged, the vacuum pipe is arranged, and the vacuum pump is connected.

[0052] In order to drain and consolidate the soft clay in the model box 1, a vacuum consolidation system is arranged in the model box. Two rows of small holes are opened in the bottom of the model box 1, one row is a vacuum hole 5 and the other is a drainage hole 6, which are 5 cm away from the bottom surface. Drainage plates 3 are arranged on the front and rear side walls of the model box 1, and a 10 cm thick sand cushion layer 10 is arranged at the bottom to play a reverse filtration role. An L-shaped vacuum pipe 8 passes through the sand cushion layer 10 and is inserted into the upper soil (soft clay) through the vacuum hole 5. The other end of the L-shaped vacuum pipe 8 is connected to a vacuum pump 11. A sealing cover 9 is arranged on the top of the model box 1 to ensure the vacuum environment. When the vacuum pump 11 is turned on, the soil in the model box 1 is subjected to vacuum negative pressure, and the pore water in the soil passes through the drainage plate 3, the sand cushion layer 10 and the drainage hole 6 to be discharged, thereby causing vacuum consolidation.

[0053] In order to perform cyclic loading on the model pile, a loading system is arranged at the top of the pile, which is composed of a driving cylinder 12, a transmission shaft 13, a force sensor 15, a displacement sensor 14 and a pile sleeve 16. The driving cylinder 12 is the main source of driving force, and the transmission shaft 13 connects the driving force generated by the driving cylinder to the pile sleeve 16 through the force sensor 15, so as to realize the application of different loading amplitudes and different loading paths of horizontal force to the pile. In this test, static step loading, bidirectional symmetric cyclic loading and bidirectional asymmetric cyclic loading are included. The static step loading is used to determine the maximum horizontal bearing capacity of the model pile, so a large-range force sensor with a range of 0-5 kN is required. The loading amplitude of bidirectional cyclic loading is generally 0.1-0.5 times the maximum horizontal bearing capacity, so a small-range force sensor with a range of 0-2 kN can be switched. The pile sleeve 16 is designed with an insertion locking structure and is arranged on the model pile 2. When the insertion rod 25 on the force sensor 15 is inserted into the hole-shaped groove 26 on the pile sleeve and the spring button 27 is pressed down to the round hole 28 and then rebounds, automatic locking is realized. The transmission shaft 13 is also provided with a displacement sensor 15 for monitoring the horizontal displacement at the top of the pile. Two laser displacement meters 17 are arranged at the mud surface for monitoring the rotation angle of the model pile at the mud surface.

[0054] The PLC control system 18 is used to set the loading parameters and the loading curve. The system is programmed by a PLC controller, a signal converter and loading software, and works together with the loading system. The PLC control system can realize stress control and displacement control, and can also set the loading path, including unidirectional step loading, unidirectional horizontal cyclic loading, bidirectional symmetric horizontal cyclic loading and bidirectional asymmetric horizontal cyclic loading. At the same time, the basic parameters of the test can be set through the loading software, such as loading frequency, stress amplitude, displacement amplitude, loading cycle, loading time, cycle number, etc.

[0055] The data acquisition system 19 uses a multi-channel data acquisition device to synchronously acquire the related data of the force sensor and the displacement sensor on the loading device in real time, and can also acquire the data of the strain gauges arranged on the pile body. The data in the acquisition system can be exported as an EXCLE file for easy editing in the later stage.

[0056] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0057] It is to be understood that the application is not limited to the embodiments described above, which are presently considered exemplary only, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the present application. The scope of the application is indicated by the following claims.

Claims

1. An indoor pile foundation model test device for various horizontal cyclic loading conditions, characterized in that, include: The model box comprises multiple box units, which are connected by sealed guide rails to achieve a pull-out box structure. The box is filled with a sand cushion layer, soil, and a sealing cap from bottom to top. Model piles are inserted into the soil in the model box. The guide rails include two vertical guide rails fixedly connected to the two side walls of the model box, two longitudinal guide rails connected to the top of the vertical guide rails, and two horizontal guide rails connected between the two longitudinal guide rails. The vertical guide rails are adjustable in height. The two longitudinal guide rails are arranged along the length of the model box. The horizontal guide rails are adjustable in position longitudinally on the longitudinal guide rails. A drive cylinder is installed on each horizontal guide rail, and the drive cylinder is adjustable in position horizontally on the horizontal guide rail. The drive shaft of the drive cylinder is connected to the top of the model pile via a force sensor and a pile sleeve. The vacuum tube is set vertically, with its upper end inserted into the upper part of the soil and its lower end connected to a bottom pipe that is buried in the sand cushion layer and arranged horizontally. One end of the bottom pipe is closed and the other end is connected to a vacuum pump set outside the model box. Drainage holes are provided on one side wall of the bottom of the model box; A displacement sensor is installed on a transmission shaft connected to the drive shaft of the drive cylinder to monitor the horizontal displacement at the top of the pile. A laser displacement meter is installed inside the model box near the soil to monitor the rotation angle of the model pile at the soil surface. The controller is connected to the drive cylinder via a signal. The signal acquisition module is connected to the force sensor, displacement sensor, and laser displacement meter.

2. The indoor pile foundation model test device for various horizontal cyclic loading conditions according to claim 1, characterized in that, The leftmost panel of the model box is made of transparent material to allow observation of the inside of the model box; the rightmost panel can be flipped along the bottom of the box for easy loading and unloading of soil.

3. The indoor pile foundation model test device for various horizontal cyclic loading conditions according to claim 1, characterized in that, The range of the drive electric cylinder is 0~5kN.

4. The indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, characterized in that, The pile sleeve includes an insertion rod and a perforated circular groove. The insertion rod is fixed at the port of the force sensor, and a spring button is provided on the upper and lower sections of the insertion rod. The perforated circular groove is fixed on the model pile. When the insertion rod is inserted into the perforated circular groove, the spring button locks, thereby locking the insertion rod and the perforated circular groove.

5. The indoor pile foundation model test device for multiple horizontal cyclic loading conditions according to claim 1, characterized in that, The drive cylinder is equipped with ≥2 sets of force sensors, and the force sensors are detachably connected to the drive shaft.

6. The indoor pile foundation model test device for various horizontal cyclic loading conditions according to claim 1, characterized in that, The controller is a PLC.

7. The indoor pile foundation model test device for various horizontal cyclic loading conditions according to claim 1, characterized in that, The width of the model box is set to ≥2*10D, where D is the diameter of the model pile.

8. The indoor pile foundation model test device for various horizontal cyclic loading conditions according to claim 1, characterized in that, The bottom of the model box is equipped with lockable casters for quick adjustment of the model box position.

9. A test method for an indoor pile foundation model test apparatus for multiple horizontal cyclic loading conditions based on any one of claims 1 to 8, characterized in that, According to the test plan, soil was placed in the mold box, vacuum tubes were laid in the mold box, and a vacuum pump was connected; When the vacuum pump is turned on, the soil in the model box is under vacuum negative pressure. The pore water in the soil is discharged through the drainage board, sand cushion layer and drainage hole, resulting in vacuum consolidation. Adjust the drive cylinder to the position of the model pile inside the model box via the guide rail, and connect the force sensor at the end of the drive cylinder to the model pile; When the controller is turned on, the drive shaft connects the driving force generated by the electric cylinder to the pile sleeve through the force sensor, thereby applying horizontal forces with different loading amplitudes and different loading paths to the model pile. The controller is used to achieve stress control and displacement control, including unidirectional progressive loading, unidirectional horizontal cyclic loading, bidirectional symmetrical horizontal cyclic loading, and bidirectional asymmetrical horizontal cyclic loading. At the same time, the basic parameters of the test are set through the loading software, including loading frequency, stress amplitude, displacement amplitude, loading period, loading time, and number of cycles. The signal acquisition module can collect data from the force sensor, displacement sensor and laser displacement meter in real time and synchronously. It can also collect data from strain gauges installed on the pile body. The data in the acquisition system can be exported as an EXCLE file for easy editing later. When there are many test groups, multiple box units are pulled out to the required length for the test. Multiple model piles are inserted at intervals along the length of the soil in the box. The electric cylinder is driven to adjust to different positions through the guide rail to load the model piles at different positions in the soil. The vacuum consolidation system can perform multiple test conditions in one operation, saving test cycles.

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