A model test device and test method for pile-soil interaction that can create a deep water environment

Abstract

The invention discloses a pile-soil interaction model test device and a test method capable of creating a deep-water environment, belonging to the field of marine geotechnical engineering. The test device includes a model main cylinder, a sample preparation and volume increasing cylinder, a loading test cylinder, a model bearing base, a model loading top cover, a water supply and gas supply system, and a loading control and data acquisition system. The invention combines a stainless steel model cylinder with a flange to achieve sealing and withstand high water pressure and gas pressure, complete the formation of deep-sea sediments and simulate the deep-water environment; realize the displacement control of the pile foundation through the reaction support system in the loading test cylinder; control the horizontal loading system and the axial loading system to apply horizontal dynamic loads and axial static loads through the loading control and data acquisition system, and complete the research on the influence of soil disturbance on the bearing capacity of the pile foundation; comprehensively measure the data of earth pressure gauges and pore pressure sensors to determine the change law of the bearing capacity of the pile foundation under the action of horizontal dynamic loads and the time-varying evolution law of the strength of the soil around the pile.

Description

Technical Field

[0001] The invention belongs to the field of marine geotechnical engineering, and relates to a pile-soil interaction model test device and a test method capable of creating a deep-water environment, in particular to a model test device and a corresponding test method for simulating the pile-soil interaction of marine engineering structures and detecting the bearing capacity of pile foundations under different deep-water environments. Background Art

[0002] For most marine structures, the seabed foundation is the "foundation" to maintain their safety and stability, which is crucial for their long-term service. Pile foundations are widely used in marine engineering structures such as offshore wind turbines, offshore oil drilling platforms, and offshore wharves. Compared with traditional onshore pile foundations, offshore pile foundations undertake more diverse functions. They not only bear vertical loads but also horizontal dynamic loads brought by earthquakes, upper winds, waves, and mechanical equipment such as ships. In particular, the geological conditions of the working environment where the pile foundations are located are complex, and the engineering properties of marine sedimentary soil around the piles are significantly different from those of terrigenous sedimentary soil, mainly manifested in lower strength, higher compressibility, poor permeability, and obvious softening and thixotropy. Therefore, the study of pile-soil interaction under horizontal dynamic loads is of great engineering significance for revealing the change of pile bearing performance and improving the service life of marine structures. However, the current experimental studies mostly focus on onshore pile-soil interaction or only consider free water boundaries, and fail to consider the influence of deep-water environment on pile-soil interaction in the ocean. Therefore, a test device and its test method that can simulate water depth conditions and simultaneously complete horizontal dynamic load actions are very important for related research. Summary of the Invention

[0003] To achieve the simulation of different deep-water environments and simultaneously consider the pile-soil interaction research under horizontal loads such as wind, waves, and ship loads, the invention provides a model test device for simulating the pile-soil interaction of marine engineering structures and detecting the bearing capacity of pile foundations under different deep-water environments and a corresponding test method.

[0004] The test device is connected to a stainless steel model cylinder through a flange to achieve sealing and withstand high water pressure and air pressure, complete the formation of deep-sea sediments and the simulation of deep-water environments; realize the action of horizontal dynamic loads and the displacement control of pile foundations through a horizontal loading system and a reaction support system; achieve high-precision loading rate control through an axial loading system, synchronously record the change of axial pressure, and complete the test of pile bearing performance; comprehensively measure the data of earth pressure gauges and pore pressure sensors to determine the change law of pile bearing capacity under horizontal dynamic loads and the time-varying evolution law of the strength of soil around the piles.

[0005] The technical solution of the invention:

[0006] A model test device for simulating the pile - soil interaction in a deep - water environment, comprising a main model cylinder, a sample preparation and volume - increasing cylinder, a loading test cylinder, a model bearing base, a model loading top cover, a water - supply and gas - supply system, and a loading control and data - acquisition system, where the sample preparation and volume - increasing cylinder and the loading test cylinder do not exist simultaneously;

[0007] The main model cylinder is used for making soil samples and placing pile foundations. It includes a first circular model cylinder 1, a first flange chassis 6, a first flange top plate 7, a sealing rubber strip 23, and a porous stainless - steel plate 42. Among them, the bottom of the first circular model cylinder 1 is welded to the first flange chassis 6, the top of the first circular model cylinder 1 is welded to the first flange top plate 7, and the first flange top plate 7 is used to connect the second flange chassis 8 of the sample preparation and volume - increasing cylinder or the third flange chassis 10 of the loading test cylinder. Sealing rubber strips 23 are provided at the connection of the flange plates to ensure sealing. The porous stainless - steel plate 42 is arranged inside the first circular model cylinder 1 to form a gap with the model bottom plate 4 for drainage, and is supported and the gap height is controlled by a porous stainless - steel adjusting floor bolt 43;

[0008] The sample preparation and volume - increasing cylinder is used in cooperation with the main model cylinder to ensure that the slurry does not overflow during soil sample preparation. The sample preparation and volume - increasing cylinder includes a second circular model cylinder 2, a second flange chassis 8, a second flange top plate 9, and a sealing rubber strip 23. Among them, the bottom of the second circular model cylinder 2 is welded to the second flange chassis 8, and the second flange chassis 8 is connected to the first flange top plate 7. The top of the second circular model cylinder 2 is welded to the second flange top plate 9, and the second flange top plate 9 is connected to the model top cover 5. Sealing rubber strips 23 are provided at the connection of the flange plates to ensure sealing;

[0009] The loading test cylinder is used in cooperation with the main model cylinder to provide the horizontal dynamic load, the support reaction force of the pile foundation, sensor connection, and test observation required for the model test. The loading test cylinder includes a third circular model cylinder 3, a third flange chassis 10, a first sealing connector 11, a third flange top plate 12, a sensor connection plate 13, a second sealing connector 14, a horizontal loading system 15, a reaction - force support system 22, a sealing rubber strip 23, and an observation window 21. Among them, the bottom of the third circular model cylinder 3 is welded to the third flange chassis 10, and the third flange chassis 10 is connected to the first flange top plate 7. The top of the third circular model cylinder 3 is welded to the third flange top plate 12, which is welded to connect the model top plate 5. The horizontal loading system 15 is connected to the third circular model cylinder 3 through the second sealing connector 14 to provide the horizontal dynamic load. The reaction - force support system 22 is connected to the third circular model cylinder 3 through the first sealing connector 11 to provide the support reaction force for the pile foundation and limit its displacement change. Sealing rubber strips 23 are provided at the connection to ensure sealing. The sensor connection plate 13 is used for the connection between the earth - pressure gauge, pore - pressure sensor required for different tests and the outside, and 4 - channel, 8 - channel or 12 - channel connection plates can be replaced according to needs. The observation window 21 is used to observe the situation inside the loading test cylinder during the test;

[0010] The described model load-bearing base is used to support the upper load and provide a drainage channel. It includes a model bottom plate 4, support feet 16, foot support plates 17, a drainage valve 18, and a sealing strip 23. Among them, the model bottom plate 4 is used to connect the first flange chassis 6; the support feet 16 are used to support the pile-soil interaction model test device; the foot support plates 17 are placed under the model bottom plate 4; the drainage valve 18 is placed on one side of the model bottom plate 4 and is used to drain the water during the pressure infiltration process; a sealing strip 23 is provided at the connection to ensure sealing.

[0011] The described model loading top cover is used to provide top sealing, axial pressure, and water and gas supply channels, and complete digital image observation. The model loading top cover includes a model top plate 5, a water and gas inlet valve 19, an axial loading system 20, a fixed wide-angle waterproof camera 44, and a liftable waterproof camera 45. Among them, the model top plate 5 is used to connect the third flange top plate 12 of the loading test cylinder or the second flange top plate 9 of the sample preparation and volume increase cylinder; the water and gas inlet valve 19 is used to introduce high-pressure water or high-pressure gas; the axial loading system 20 is arranged in the middle of the model top plate 5 and is used to accurately control displacement or force and measure the change in axial pressure; the fixed wide-angle waterproof camera 44 is arranged at the bottom of the model top plate 5 and is used to observe the situation inside the cylinder during the model test; the liftable waterproof camera 45 is fixed at the bottom of the model top plate 5 through a liftable metal rod and is used to observe the situation inside the cylinder along the height direction and determine the settlement of the soil sample.

[0012] The described water and gas supply system is used to provide high water pressure and high air pressure. It includes a water filling port 46, a pressure valve 47, a pressure gauge 48, a pressure chamber 49, a drainage and exhaust valve 50, an air compressor 51, and a gas supply valve 52. Among them, the water filling port 46 is used to quickly fill water when the water level in the pressure chamber 49 is insufficient; the pressure valve 47 is used to provide the required air pressure for the pressure chamber 49; the pressure gauge 48 is used to monitor the pressure situation in the pressure chamber; the pressure chamber 49 is used to store water and provide the required water pressure for the test; the drainage and exhaust valve 50 is connected to the water and gas inlet valve 19 and is used to continuously provide water pressure for the test; the air compressor 51 is used to provide the total air pressure required for the test; the gas supply valve 52 is used to connect to the pressure valve 47 and provide air pressure.

[0013] The described loading control and data acquisition system is used to control the loading device and process data. It includes a loading control module, a data acquisition module, and an automatic processing module. Among them, the loading control module is connected to the lateral loading system 15 and the axial loading system 20 through the USB interface of the computer, inputs various parameters, and controls the loading value, loading frequency, and loading waveform; the data acquisition module is used to collect the earth pressure gauges and pore pressure sensors that are pressed into the soil together with the model pile; the automatic processing module can generate the time relationship curves of axial force, axial displacement, horizontal force, and horizontal displacement in real time.

[0014] The described lateral loading system 15 includes a lateral pressure plate 28, a lateral loading extension rod 29, a lateral loading ball head 30, a lateral tie rod 31, a lateral loading rod 32, a lateral tension-compression load sensor 33, a lateral loading cylinder 34, and a lateral loading motor 35; the lateral loading motor 35 is bolted to the lateral loading cylinder 34 and is used to provide lateral forces, including static and dynamic effects; the lateral loading rod 31 is bolted to the lateral loading cylinder 34 and is used to output the lateral force to the test target; the lateral tension-compression load sensor 33 is bolted to the piston rod of the lateral loading cylinder 34 and is used to monitor the lateral force value and ensure stable stress output through closed-loop control; the lateral loading rod 32 is bolted to the lateral tension-compression load sensor 33 and is used to transfer the lateral force to the lateral tension-compression load sensor (33); the lateral loading extension rod 29 is bolted to the lateral loading rod 32 and is used to increase the length of the lateral loading rod (32) for docking with the test target; the lateral loading ball head 30 is bolted to the lateral loading extension rod 29 and is used to coordinate the position between the lateral pressure plate (28) and the test target; the lateral pressure plate 28 is connected to the lateral loading ball head 30 by bolting and is used to contact the test target and ensure good contact.

[0015] The described reaction force support system 22 includes reaction force support rods 25, reaction force ball heads 26, and reaction force pressing heads 27; the reaction force support rods 25 are bolted to the reaction force ball heads 26 and are used to provide reaction forces; the reaction force ball heads 26 are bolted to the reaction force pressing heads 27. Among them, the reaction force ball heads 26 are used to coordinate the position between the reaction force pressing heads 27 and the test target, and the reaction force pressing heads 27 are used to contact the test target and ensure good contact.

[0016] The described axial loading system 20 includes an axial tie rod 36, an axial loading rod 37, an axial load sensor 38, an axial loading cylinder 39, an axial ball head 40, an axial pressure plate 41, and an axial loading servo motor 53; the axial loading servo motor 53 is bolted to the axial loading cylinder 39 and is used to provide axial forces and axial displacement control; the axial loading rod 37 is bolted to the axial loading cylinder 39 and is used to output the axial force to the test target; the axial load sensor 38 is bolted to the piston rod of the axial loading cylinder 39 and is used to monitor the axial force value and ensure stable stress output through closed-loop control; the axial loading rod 37 is bolted to the axial load sensor 38 and is used to transfer the axial force to the axial load sensor 38; the axial load sensor 38 is bolted to the axial loading rod 37 and is used to coordinate the position between the axial pressure plate 41 and the test target; the axial pressure plate 41 is bolted to the axial load sensor 38 and is used to contact the test target and ensure good contact.

[0017] A test method for a pile-soil interaction model test device capable of creating a deep-water environment includes the following steps:

[0018] Step 1: Connect the model base plate 4 and the model main cylinder, and at the same time close the drain valve of the model base plate 4; Place the porous stainless steel plate 42 inside the model main cylinder and determine its height through the stainless steel adjusting floor feet 43; Seal between the porous stainless steel plate 42 and the cylinder wall of the model main cylinder with sealant; Lay geotextile on the porous stainless steel plate 42, and then lay filter paper; Weigh the soil materials required for the test, make mud, and pour the mud into the model main cylinder; When the mud is about to exceed the height of the model main cylinder, connect the sample preparation and volume increase cylinder; Continue to pour the mud until the mud reaches the predetermined height; Use a mud stirrer to continue stirring until the mud is uniform and flat;

[0019] Step 2: Connect the model top cover 5, loosen the lifting waterproof camera connecting rod as the exhaust hole; Open the top water inlet and air inlet valve 19, continue to inject water until it overflows at the sealing place of the connecting rod, tighten the sealing nut, and then close the top water inlet and air inlet valve 19 to keep the pipeline in the water supply system full of water; Connect the top water inlet and air inlet valve 19 to the drain and exhaust valve 50 of the water supply and gas supply system with a pipeline, and open the drain and exhaust valve 50 of the water supply and gas supply system, the water inlet and air inlet valve 19 of the model top cover 5, and the drain valve 18 of the model base plate 4 in sequence to start soil consolidation; Observe the soil settlement position by the lifting waterproof camera 45 to determine whether the consolidation of the soil reaches the predetermined goal;

[0020] Step 3: Reduce the pressure of the water supply and gas supply system to zero, and close the drain and exhaust valve 50 of the water supply and gas supply system and the drain valve 18 of the model base plate 4; Remove the pipeline between the top water inlet and air inlet valve 19 and the drain and exhaust valve 50 of the water supply and gas supply system, and remove the model top cover 5; Pump out the water within the height range of the sample preparation and volume increase cylinder, and then remove the sample preparation and volume increase cylinder; Connect the loading test cylinder to the model main cylinder, then press the model pile together with the attached sensor into the soil to complete the embedding of the pile, connect the sensor connector to the sensor connection plate 13, and then connect it to the acquisition system;

[0021] Step 4: Make the reaction pressure head 27 of the reaction support system contact the model pile to limit the displacement of the pile; Control the lateral pressure plate 28 of the lateral loading system to contact the model pile through the loading control and data acquisition system; Inject water to reach the predetermined height; Connect the model top cover 5 to the loading test cylinder, and control the axial pressure plate 28 of the axial loading system to contact the model pile through the loading control and data acquisition system; Drain the water in the water supply and gas supply system, and then connect the top water inlet and air inlet valve 19 to the drain and exhaust valve 50 of the water supply and gas supply system with a pipeline. Open the drain and exhaust valve 50 of the water supply and gas supply system and the water inlet and air inlet valve 19 of the model top cover in sequence, and adjust the air pressure according to the required seawater depth for the test to provide pressure inside the sample cylinder to complete the simulation of the water depth environment;

[0022] Step 5: Control the axial loading system through the loading control and data acquisition system, provide slow loading and loading displacement limits, record the change of axial force in real time during the loading process, and determine the maximum axial force value after reaching the predetermined target; control the lateral loading system through the loading control and data acquisition system, apply horizontal dynamic loads by setting the dynamic load amplitude, dynamic load frequency and dynamic load waveform; after the loading is completed, control the axial loading system, provide slow loading and loading displacement limits, record the change of axial force in real time during the loading process, and determine the maximum axial force value at that time after reaching the predetermined target; repeat the axial loading according to different static time settings in the test, and finally determine the change of pile foundation bearing capacity under different static times; synchronously record the values of the buried sensors throughout the process, and output the time history curve through the automatic processing module.

[0023] Advantages of the present invention: Through the combination of the stainless steel model cylinder and the flange, the sealing is achieved and the high water pressure and air pressure are withstood, and the formation of deep-sea sediments and the simulation of the deep-water environment are completed; through the lateral loading system and the reaction support system, the dynamic load action in the horizontal direction and the displacement control of the pile foundation are realized; through the axial loading system, the influence of soil disturbance on the change of pile foundation bearing capacity is studied; by synthesizing the measured data of the earth pressure gauge and the pore pressure sensor, the change law of the bearing capacity of the pile foundation under the action of horizontal dynamic loads and the time-varying evolution law of the strength of the soil around the pile are determined. Description of the Drawings

[0024] Figure 1 It is a schematic front view of the stacked model cylinders of the test device of the present invention.

[0025] Figure 2 It is a schematic side view of the stacked model cylinders of the test device.

[0026] Figure 3 It is a schematic cross-sectional front view of the stacked model cylinders of the test device.

[0027] Figure 4 It is a schematic top view of the standard model cylinder of the test device.

[0028] Figure 5 It is a schematic top view of the loading test cylinder of the test device.

[0029] Figure 6 It is a schematic front view of the model loading top cover of the test device.

[0030] Figure 7 It is a schematic front view of the water supply and gas supply system of the test device.

[0031] In the figure: 1 first circular model cylinder, 2 second circular model cylinder, 3 third circular model cylinder, 4 model bottom plate, 5 model top plate, 6 first flange bottom plate, 7 first flange top plate, 8 second flange bottom plate, 9 second flange top plate, 10 third flange bottom plate, 11 first sealing connection piece, 12 third flange top plate, 13 sensor connection plate, 14 second sealing connection piece, 15 horizontal loading system, 16 support anchor, 17 anchor support plate, 18 drain valve, 19 water inlet and air inlet valve, 20 axial loading system, 21 observation window, 22 reaction force support system, 23 sealing strip, 24 bolt hole, 25 reaction force support rod, 26 reaction force ball head, 27 reaction force pressure head, 28 horizontal pressure plate, 29 horizontal loading extension rod, 30 horizontal loading ball head, 31 horizontal pull rod, 32 horizontal loading rod, 33 horizontal tension and compression load sensor, 34 horizontal loading cylinder, 35 horizontal loading motor, 36 axial pull rod, 37 axial loading rod, 38 axial load sensor, 39 axial loading cylinder, 40 axial ball head, 41 axial pressure plate, 42 porous stainless steel plate, 43 stainless steel adjustable anchor, 44 fixed wide-angle waterproof camera, 45 lifting waterproof camera, 46 water filling port, 47 pressure valve, 48 pressure gauge, 49 pressure chamber, 50 drain and exhaust valve, 51 air compressor, 52 air supply valve, 53 axial loading servo motor. Detailed implementation mode

[0032] The following further explains the specific implementation mode of the present invention in combination with embodiments and drawings, but does not limit the present invention.

[0033] Such as Figure 1-7As shown in the figure, a model test device and testing method for pile-soil interaction that can create a deep-water environment, including a model main cylinder, a sample preparation and volume increase cylinder, a loading test cylinder, a model bearing base, a model loading top cover, a water supply and gas supply system, and a loading control system. In this embodiment, the model main cylinder is used for making soil samples and placing pile foundations; among them, the first circular model cylinder 1, the first flange chassis 6, the first flange top plate 7, and the porous stainless steel plate 42 are made of 316 stainless steel, with a plate thickness of 10 mm; the porous stainless steel plate 42 is densely distributed with 3-mm round holes, and the stainless steel adjusting floor feet 43 below it achieve height control by adding or reducing pads. The sample preparation and volume increase cylinder is used to ensure that the slurry does not overflow during soil sample preparation; among them, the second circular model cylinder 2, the second flange chassis 8, and the second flange top plate 9 are made of 316 stainless steel, with a plate thickness of 10 mm. The loading test cylinder is used to provide the horizontal dynamic load, the support reaction force of the pile foundation, sensor connection, and test observation required for the model test; it includes the third circular model cylinder 3, the third flange chassis 10, the first sealing connector 11, the third flange top plate 12, the sensor connection plate 13, the second sealing connector 14, the lateral loading system 15, the reaction force support system 22, the sealing strip 23, and the observation window 21; among them, the third circular model cylinder 3, the third flange chassis 10, the first sealing connector 11, the third flange top plate 12, the sensor connection plate 13, and the second sealing connector 14 are made of 316 stainless steel, with a plate thickness of 10 mm; the observation window 21 is made of high-strength tempered borosilicate glass, with a diameter of 100 mm and a thickness of 20 mm; the lateral loading system 15 can apply a sine wave, with a load of 1 kN and a frequency of 0.01 - 1 Hz; the reaction force support system 22 can adjust the restraint of the lateral displacement of the model pile through the position of the pressure plate. Further, the inner diameters of the model main cylinder, the sample preparation and volume increase cylinder, and the loading test cylinder are 1 m and the height is 1 m, and they can withstand a pressure of 1 MPa; the flange plates are welded to the corresponding circular model cylinders with stainless steel, and there are 28 bolt holes 24 on them, with a bolt hole diameter of 15 m; the sealing strip 23 is made of silica gel in a circular ring shape, with 28 round holes distributed on it that are consistent with the bolt holes on the flange plate, with a thickness of 5 mm and a width of 40 mm. The model bearing base is used to support the upper load and provide a drainage channel; it includes the model bottom plate 4, the support floor feet 16, the floor foot support plate 17, the drain valve 18, and the sealing strip 23; among them, the model bottom plate 4 is made of 316 stainless steel, with a plate thickness of 10 mm, and there are 28 bolt holes 24 on it, with a bolt hole diameter of 15 m; there are a total of 4 support floor feet 16, which are used to support the entire model cylinder; the drain valve 18 is connected to a pipeline with a diameter of 10 mm.The model loading top cover is used to provide top sealing, axial pressure, and water and gas supply channels, and complete digital image observation; it includes a model top plate 5, a water and gas inlet valve 19, an axial loading system 20, a fixed wide-angle waterproof camera 44, and a lifting waterproof camera 45; among them, the model top plate 5 is made of 316 stainless steel with a plate thickness of 10 mm, and there are 28 bolt holes 24 on it, with a bolt hole diameter of 15 mm; the water and gas inlet valve 19 is connected to a 10-mm diameter pipeline; the maximum load of the axial loading system 20 is 1 kN, the displacement loading accuracy is 0.1 mm, and the loading rate is 0.1 - 1 mm / min; the waterproof grades of the fixed wide-angle waterproof camera 44 and the lifting waterproof camera 45 are IP68, and the pressure resistance is >1 MPa. The water and gas supply system is used to provide high water pressure and high air pressure; it includes a water filling port 46, a pressure regulating valve 47, a pressure gauge 48, a pressure chamber 49, a drainage and exhaust valve 50, an air compressor 51, and a gas supply valve 52; among them, the pressure chamber 49 is made of an organic glass tube with a wall thickness of 20 mm, an inner diameter of 400 mm, and a height of 1000 mm, and can withstand a pressure of 1.0 MPa; the pressure gauge 48 can display 1.0 MPa with an accuracy of 0.25%; the pressure regulating valve 47, the drainage and exhaust valve 50, and the gas supply valve 52 are connected to 10-mm diameter pipelines; the air compressor 51 can provide an air pressure of 0.7 MPa. The loading control and data acquisition system is used to control the loading device and process data; it includes a loading control module, a data acquisition and automatic processing module; among them, the loading control module uses a multi-channel full-digital servo controller, the A / D converter can achieve an industrial-grade 18-bit parallel bus and a conversion frequency of 666 kHz, and the control algorithm can achieve accurate control of 3 m / s and 1500 kN / s for a single channel. It can complete displacement control, force control, and frequency setting; the acquisition frequency of the data acquisition module is 1 kHz.

[0034] The method of conducting experiments using the above system includes the following steps:

[0035] Step 1: Align the bolt holes of the model bottom plate 4 and the first flange chassis 6 on the model main cylinder, place a sealing rubber strip 23 in the middle, and connect them with 28 M12 bolts. Use a torque wrench to reach a bolt torque of 100 N·m, and at the same time close the drainage valve 18 of the model bottom plate; place the porous stainless steel plate 42 inside the cylinder and determine its height through 5 stainless steel adjusting floor bolts 43; apply sealing glue between the porous stainless steel plate 42 and the cylinder wall to ensure tightness around; lay geotextile on the porous stainless steel plate 42, and then lay filter paper; weigh the soil materials required for the experiment, make a slurry with a water content 1.5 times the liquid limit, and pour the slurry into the cylinder; when the slurry is about to exceed the cylinder height, continue to connect the sample-making volume-increasing cylinder with bolts, place a sealing rubber strip 23 between the first flange top plate 7 and the second flange chassis 8 and ensure that the bolt torque reaches 100 N·m; continue to pour the slurry until it reaches the predetermined height; use a slurry stirrer to continue stirring until the slurry is uniform and flat.

[0036] Step 2: Connect the model loading top cover and the third flange top plate 12 with 28 M12 bolts, place a sealing strip 23 in the middle and ensure that the bolt torque reaches 100 N.m; loosen the connecting rod of the lifting waterproof camera 45 as the exhaust hole; open the top water inlet and air inlet valve 19, continue to fill water until it overflows at the sealing part of the connecting rod, tighten the lifting waterproof camera 45, and then close the top water inlet and air inlet valve 19 to keep the pipeline in the water supply system full of water; connect the top water inlet and air inlet valve 19 with the drain and exhaust valve 50 of the water supply and gas supply system with a pipeline, open the drain and exhaust valve 50 of the water supply and gas supply system, the water inlet and air inlet valve 19 of the model loading top cover, and the drain valve 18 of the model bottom plate in sequence to start soil consolidation; observe the overall situation during the test by the fixed wide-angle waterproof camera 44, and observe the scale line on the cylinder wall with the lifting waterproof camera 45 to determine whether the consolidation of the soil reaches the predetermined target.

[0037] Step 3: Reduce the pressure of the water supply and gas supply system to zero, and close the drain and exhaust valve 50 of the water supply and gas supply system and the drain valve 18 of the model bottom plate; remove the pipeline between the top water inlet and air inlet valve 19 and the drain and exhaust valve 50 of the water supply and gas supply system, and remove the model loading top cover; pump out the water within the height range of the sample preparation and volume increase cylinder with a small water pump, and then remove the sample preparation and volume increase cylinder; connect the third flange chassis 10 of the loading test cylinder and the first flange top plate 7 of the model main cylinder with 28 M12 bolts, then press the model pile together with the attached sensors into the soil to complete the embedding of the pile, connect the sensor connector with the sensor connection plate 13, and then connect it with the acquisition system.

[0038] Step 4: Make the reaction pressure head 27 of the reaction support system 22 contact the model pile to limit the displacement of the pile; control the lateral pressure plate 28 of the lateral loading system 15 to contact the model pile through the loading control and data acquisition system; inject an appropriate amount of water to reach the predetermined height; connect the model loading top cover and the third flange top plate 12 of the loading test cylinder with 28 M12 bolts, and control the axial pressure plate 41 of the axial loading system 20 to contact the model pile through the loading control and data acquisition system; drain the water in the pressure chamber 49 of the water supply and gas supply system, then connect the top water inlet and air inlet valve 19 with the drain and exhaust valve 50 of the water supply and gas supply system with a pipeline, open the drain and exhaust valve 50 of the water supply and gas supply system and the water inlet and air inlet valve 19 of the model loading top cover in sequence, and adjust the air pressure according to the required seawater depth of the test to provide pressure for the sample cylinder to complete the simulation of the water depth environment.

[0039] Step 5: Control the axial loading system 20 through the loading control and data acquisition system, apply a loading rate limit of 0.1 mm / min to load a displacement of 0.5 mm, record the change in axial force in real time during the loading process, and determine the maximum axial force value after reaching the predetermined target; control the lateral loading system 15 through the loading control and data acquisition system, set the dynamic load amplitude, dynamic load frequency, dynamic load waveform, etc. in the customized software, and apply a horizontal dynamic load; after the loading is completed, control the axial loading system 20 again, apply a loading rate limit of 0.1 mm / min to load a displacement of 0.5 mm, record the change in axial force in real time during the loading process, and determine the maximum axial force value at that time after reaching the predetermined target; repeat the axial loading according to different static time settings in the test, and finally determine the change in the bearing capacity of the pile foundation under different static time; synchronously record the values of the buried sensors throughout the process, and output the time history curve through the automatic processing module.

Claims

1. A pile-soil interaction model test device capable of creating a deep water environment, characterized in that: The pile-soil interaction model test device capable of creating a deep-water environment comprises a model main cylinder, a sample preparation and volume expansion cylinder, a loading test cylinder, a model load-bearing base, a model loading top cover, a water supply and air supply system, and a loading control and data acquisition system, wherein the sample preparation and volume expansion cylinder and the loading test cylinder do not exist at the same time; The model main cylinder is used for making soil samples and placing pile foundations, and comprises a first circular model cylinder (1), a first flange bottom plate (6), a first flange top plate (7), a sealing rubber strip (23) and a porous stainless steel plate (42); wherein the bottom of the first circular model cylinder (1) is welded to the first flange bottom plate (6), and the top of the first circular model cylinder (1) is welded to the first flange top plate (7); the first flange top plate (7) is used to connect to the second flange bottom plate (8) of the sample preparation and volume expansion cylinder or the third flange bottom plate (10) of the loading test cylinder; a sealing rubber strip (23) is provided at the connection of the flanges to ensure sealing; the porous stainless steel plate (42) is arranged in the first circular model cylinder (1) to form a gap with the model bottom plate (4) for facilitating drainage, and the gap height is supported and controlled by the porous stainless steel adjusting foot 43; The sample preparation and volume expansion cylinder is used in conjunction with the model main cylinder to ensure that mud does not overflow when making soil samples; the sample preparation and volume expansion cylinder comprises a second circular model cylinder (2), a second flange bottom plate (8), a second flange top plate (9) and a sealing strip (23); wherein the bottom of the second circular model cylinder (2) is welded to the second flange bottom plate (8), and the second flange bottom plate (8) is connected to the first flange top plate (7); the top of the second circular model cylinder (2) is welded to the second flange top plate (9), and the second flange top plate (9) is connected to the model top plate (5); a sealing strip (23) is provided at the connection of the flange to ensure sealing; The loading test cylinder is used in conjunction with the model main cylinder to provide the horizontal dynamic load, pile foundation support reaction force, sensor connection and test observation required for the model test; the loading test cylinder comprises a third circular model cylinder (3), a third flange bottom plate (10), a first sealing connection piece (11), a third flange top plate (12), a sensor connection plate (13), a second sealing connection piece (14), a lateral loading system (15), a reaction force support system (22), a sealing strip (23) and an observation window (21); wherein the bottom of the third circular model cylinder (3) is welded to the third flange bottom plate (10), and the third flange bottom plate (10) is connected to the first flange top plate (7); the third circular model cylinder (3) The top is welded to the third flange top plate (12), and the model top plate (5) is welded to the top plate; the lateral loading system (15) is connected to the third circular model tube (3) through the second sealing connection piece (14), and is used to provide a horizontal dynamic load; the reaction force support system (22) is connected to the third circular model tube (3) through the first sealing connection piece (11), and is used to provide a support reaction force for the pile foundation to limit its displacement change; a sealing strip (23) is provided at the connection point, and is used to ensure sealing; the sensor connection plate (13) is used to connect the earth pressure gauge and pore pressure sensor required for different tests with the outside, and the 4-, 8- or 12-channel connection plate can be replaced as needed; the observation window (21) is used to load the test tube during the test process; The model load-bearing base is used to support the upper load and provide a drainage channel, and comprises a model base plate (4), a supporting foot (16), a foot support plate (17), a drainage valve (18) and a sealing strip (23); wherein the model base plate (4) is used to connect to the first flange chassis (6); the supporting foot (16) is used to support the pile-soil interaction model test device; the foot support plate (17) is placed below the model base plate (4); the drainage valve (18) is placed on one side of the model base plate (4) and is used to discharge moisture in the pressurized infiltration process; a sealing strip (23) is provided at the connection to ensure sealing; The model loading top cover is used to provide top sealing, axial pressure and water and air supply channels to complete digital image observation; the model loading top cover comprises a model top plate (5), a water inlet and air inlet valve (19), an axial loading system (20), a fixed wide-angle waterproof camera (44) and a lifting waterproof camera (45); wherein the model top plate (5) is used to connect the third flange top plate (12) of the loading test tube or the second flange top plate (9) of the sample preparation and expansion tube; the water inlet and air inlet valve (19) is used to pass high-pressure water or high-pressure gas; the axial loading system (20) is arranged in the middle of the model top plate (5) to accurately control the displacement or force and measure the axial pressure change; the fixed wide-angle waterproof camera (44) is arranged at the bottom of the model top plate (5) to observe the situation inside the tube during the model test; the lifting waterproof camera (45) is fixed to the bottom of the model top plate (5) by a liftable metal rod to observe the situation inside the tube along the height direction and determine the settlement of the soil sample; The water supply and air supply system is used to provide high water pressure and high air pressure, and comprises a water inlet (46), a pressure valve (47), a pressure gauge (48), a pressure chamber (49), a water discharge and exhaust valve (50), an air compressor (51) and an air supply valve (52); wherein the water inlet (46) is used to quickly add water when the water level in the pressure chamber (49) is insufficient; the pressure valve (47) is used to provide the required air pressure to the pressure chamber (49); the pressure gauge (48) is used to monitor the pressure in the pressure chamber; the pressure chamber (49) is used to store water and provide the water pressure required for the test; the water discharge and exhaust valve (50) is connected to the water inlet and air inlet valve (19) to continuously provide water pressure for the test; the air compressor (51) is used to provide the total air pressure required for the test; the air supply valve (52) is used to connect to the pressure valve (47) to provide air pressure; The loading control and data acquisition system is used to control and process the loading device, and comprises a loading control module, a data acquisition module and an automatic processing module; wherein the loading control module is connected to the lateral loading system (15) and the axial loading system (20) via a USB interface of a computer, inputs various parameters, and controls the loading value, loading frequency and loading waveform; the data acquisition module is used to collect data from a soil pressure gauge and a pore pressure sensor pressed in together with the model pile; and the automatic processing module can generate time relationship curves of axial force, axial displacement, horizontal force and horizontal displacement in real time.

2. The pile-soil interaction model test device according to claim 1, characterized in that: The transverse loading system (15) includes a transverse pressure plate (28), a transverse loading extension rod (29), a transverse loading ball head (30), a transverse pull rod (31), a transverse loading rod (32), a transverse tension and compression load sensor (33), a transverse loading cylinder (34) and a transverse loading motor (35); the transverse loading motor (35) is bolted to the transverse loading cylinder (34) to provide transverse force, including static force and dynamic force; the transverse loading rod (32) is bolted to the transverse loading cylinder (34) to output the transverse force to the test target; the transverse tension and compression load sensor (33) is bolted to the piston rod of the transverse loading cylinder (34) to monitor The transverse force value is measured, and the stress output is ensured to be stable through closed-loop control; the transverse loading rod (32) is bolted to the transverse tension and compression load sensor (33) to transmit the transverse force to the transverse tension and compression load sensor (33); the transverse loading extension rod (29) is bolted to the transverse loading rod (32) to increase the length of the transverse loading rod (32) so as to dock with the test target; the transverse loading ball head (30) is bolted to the transverse loading extension rod (29) to coordinate the position between the transverse pressure plate (28) and the test target; the transverse pressure plate (28) and the transverse loading ball head (30) are bolted to contact with the test target and ensure good contact.

3. The pile-soil interaction model test device according to claim 1, characterized in that: The reaction force support system (22) comprises a reaction force support rod (25), a reaction force ball head (26) and a reaction force pressure head (27); the reaction force support rod (25) is bolted to the reaction force ball head (26) to provide a supporting reaction force; the reaction force ball head (26) is bolted to the reaction force pressure head (27), wherein the reaction force ball head (26) is used to coordinate the position between the reaction force pressure head (27) and the test target, and the reaction force pressure head (27) is used to contact the test target and ensure good contact.

4. The pile-soil interaction model test device according to claim 1, characterized in that: The axial loading system (20) comprises an axial pull rod (36), an axial loading rod (37), an axial load sensor (38), an axial loading cylinder (39), an axial ball head (40), an axial pressure plate (41) and an axial loading servo motor (53); the axial loading servo motor (53) is bolted to the axial loading cylinder (39) to provide axial force and axial displacement control; the axial loading rod (37) is bolted to the axial loading cylinder (39) to output the axial force to the test target; the axial load sensor ( The axial load rod (38) is bolted to the piston rod of the axial loading cylinder (39) to monitor the axial force value and ensure the stability of stress output through closed-loop control; the axial loading rod (37) is bolted to the axial load sensor (38) to transmit the axial force to the axial load sensor (38); the axial ball head (40) is bolted to the axial loading rod (37) to coordinate the position between the axial pressure plate (41) and the test target; the axial pressure plate (41) is bolted to the axial ball head (40) to contact the test target and ensure good contact.

5. A testing method for the pile-soil interaction model test device capable of creating a deep water environment as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Connect the model bottom plate (4) and the model main tube, and close the drainage valve of the model bottom plate (4); place the porous stainless steel plate (42) in the model main tube, and determine its height through the stainless steel adjusting feet 43; The porous stainless steel plate (42) and the wall of the model main tube are sealed by a sealant; a geotextile is laid on the porous stainless steel plate (42), and then a filter paper is laid; soil materials required for the test are weighed to make mud, and the mud is poured into the model main tube; when the mud is about to exceed the height of the model main tube, a sample preparation and expansion tube is connected; the mud is continuously poured until the mud reaches a predetermined height; and a mud agitator is used to continue stirring until the mud is uniform and smooth; Step 2: Connect the model top plate (5), loosen the lifting waterproof camera connecting rod to serve as an exhaust hole; open the top water inlet and air inlet valve (19), continue to inject water until the sealing part of the connecting rod overflows, tighten the sealing nut, and then close the top water inlet and air inlet valve (19) to keep the pipes in the water supply system full of water; The top water inlet and air inlet valve (19) is connected to the water and air discharge valve (50) of the water and air supply system by pipelines, and the water and air discharge valve (50) of the water and air supply system, the water inlet and air inlet valve (19) of the model top plate (5), and the water discharge valve (18) of the model bottom plate (4) are opened in sequence to start soil consolidation; the soil settlement position is observed by a lifting waterproof camera (45) to determine whether the soil consolidation has reached a predetermined target; Step 3: Reduce the pressure of the water supply and air supply system to zero, close the water and air discharge valve (50) of the water supply and air supply system and the water discharge valve (18) of the model bottom plate (4); remove the pipeline between the top water inlet and air inlet valve (19) and the water and air discharge valve (50) of the water supply and air supply system, and remove the model top plate (5); extract the water within the height range of the sample preparation and expansion cylinder, and then remove the sample preparation and expansion cylinder; connect the loading test cylinder with the model main cylinder, and then press the model pile together with the attached sensor into the soil to complete the pile burial, connect the sensor connector with the sensor connecting plate (13), and then connect it to the acquisition system; Step 4: contact the reaction pressure head (27) of the reaction support system with the model pile to limit the displacement of the pile; control the lateral pressure plate (28) of the lateral loading system to contact the model pile through the loading control and data acquisition system; inject water until it reaches a predetermined height; connect the model top plate (5) with the loading test cylinder, and control the lateral pressure plate (28) of the axial loading system to contact the model pile through the loading control and data acquisition system; remove the water in the water supply and air supply system, and then connect the top water inlet and air inlet valve (19) with the water supply and air supply system drainage and exhaust valve (50) by pipeline, open the water supply and air supply system drainage and exhaust valve (50) and the model top cover water inlet and air inlet valve (19) in turn, adjust the air pressure according to the seawater depth required for the test, provide pressure for the sample cylinder, and complete the water depth environment simulation; Step 5: Control the axial loading system through the loading control and data acquisition system, provide slow loading and loading displacement limits, record the axial force changes in real time during the loading process, and determine the maximum axial force value after reaching the predetermined target; control the lateral loading system through the loading control and data acquisition system, and apply horizontal dynamic loads by setting the dynamic load amplitude, dynamic load frequency and dynamic load waveform; after loading, control the axial loading system, provide slow loading and loading displacement limits, record the axial force changes in real time during the loading process, and determine the maximum axial force value at that time after reaching the predetermined target; repeat the axial loading according to the different static times set in the test, and finally determine the changes in the pile foundation bearing capacity at different static times; synchronously record the values ​​of the embedded sensors during the whole process, and output the time history curve through the automatic processing module.

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