A model test device and test method for the bearing capacity of pull-out piles under vacuum negative pressure loading

Abstract

This invention relates to the field of pile foundation engineering testing technology, and discloses a vacuum negative pressure loading model test device for the tensile bearing capacity of piles. The device includes: an observation model assembly comprising a model box, in which soil samples and simulated groundwater layers are layered and placed, with a model pile vertically placed within the soil sample; a sensor array uniformly distributed within the soil sample, used to collect soil pressure, pore water pressure, and temperature; strain gauges uniformly distributed on the model pile for collecting strain data; a vacuum negative pressure system for generating tensile force; and a traction system for transmitting the tensile force generated by the vacuum negative pressure system to the observation model assembly, traction the model pile vertically, and conducting a tensile bearing capacity test on the model pile. This invention uses the tensile force generated by vacuum negative pressure to test the tensile bearing capacity of piles, which can not only test the tensile bearing capacity of piles under various complex working conditions, but also simulate the influence of different properties and water contents of soil on the tensile bearing capacity of pile foundations in the presence of groundwater.

Description

Technical Field

[0001] This invention relates to the field of pile foundation engineering testing technology, and in particular to a model test device and test method for tensile pile bearing capacity under vacuum negative pressure loading. Background Technology

[0002] When the groundwater resources on the construction site are abundant, the groundwater will exert an upward buoyancy force on the building. If the weight of the superstructure is less than the buoyancy of the water, the building may shift upwards, either entirely or partially, potentially causing damage. Therefore, it is necessary to install anti-uplift piles to resist the buoyancy force generated by groundwater, making the quality inspection of these piles particularly important.

[0003] Currently, there are two main methods for testing the uplift bearing capacity of pile foundations. One is the static load test of a single pile's vertical uplift, where jacks are used to apply force to the reaction piles on both sides of the pile foundation, causing the uplift pile to experience an upward tensile force. The other method involves directly applying an upward tensile force to the uplift pile using large hoisting equipment. Both methods can be used for both field testing and model testing. Field testing results are reliable, but the testing cycle is long, the cost is high, and the area required is large. Field testing is also not suitable when the actual geological conditions are poor. While existing model testing methods overcome some of the problems associated with field testing, they require personnel to operate large machinery, posing certain safety hazards. Furthermore, the measurement results from large machinery have significant errors, and indoor testing still requires a large space, consuming substantial manpower and resources. Summary of the Invention

[0004] The purpose of this invention is to provide a model test device and method for the tensile bearing capacity of piles under vacuum negative pressure loading. This method uses vacuum negative pressure to provide tensile force for testing the tensile bearing capacity of pile foundations, eliminating the need for large equipment and making the test simple and safe. Considering the influence of groundwater, it can simulate the tensile bearing process of pile foundations under various working conditions, providing guidance for the research and design of related tensile pile model tests. This addresses the problems existing in current pile foundation tensile bearing capacity testing methods and meets the testing needs for pile foundation construction under complex geological conditions.

[0005] This invention provides the following technical solution:

[0006] A vacuum negative pressure loading model test device for the bearing capacity of pull-out piles, comprising:

[0007] The observation model component includes a model box, in which soil samples and simulated groundwater layers are layered and placed in the model box. Model piles are placed vertically in the soil samples. Sensor groups are evenly distributed in the soil samples and are used to collect soil pressure, pore water pressure and temperature parameters in the soil samples.

[0008] Vacuum negative pressure system, used to generate tensile force;

[0009] The traction system is used to transmit the tension generated by the vacuum negative pressure system to the observation model component, and to pull the model pile in the vertical direction to conduct a pull-out bearing capacity test on the model pile.

[0010] According to some implementation methods, the simulated groundwater layer is simulated by isolating the soil sample from the water layer through two layers of waterproof membrane; heating rods are evenly distributed around the soil sample; the sensor group includes a soil pressure sensor, a pore water pressure sensor, a temperature sensor, and a corresponding data acquisition instrument; strain gauges are attached to the pile body of the model pile and transmit the strain to the strain acquisition instrument.

[0011] According to some implementations, the model box is provided with at least one vertical partition for adjusting the volume of the soil sample.

[0012] According to some embodiments, the model box is made of tempered glass; the partition is made of resin glass.

[0013] According to some embodiments, the traction system includes telescopic rods, which are horizontally fixed to the inner and outer sides of one side of the model box. The telescopic rods are equipped with fixed pulleys at their ends. One end of the cable is connected to a vacuum negative pressure system outside the model box, and the other end is wound around the two fixed pulleys and connected to the top of the model pile.

[0014] According to some embodiments, the telescopic rod is provided with multiple sets of screw holes for adjusting the position of the fixed pulley, and the upper edge of the model box is provided with two rows of screw holes for fixing the telescopic rod and fixing the partition.

[0015] According to some embodiments, the vacuum negative pressure system includes a negative pressure cylinder, a piston, and a vacuum pump. A spring is provided at the bottom of the negative pressure cylinder, a barometer is provided on the piston, the barometer is connected to the inside of the negative pressure cylinder, and the top of the piston is connected to one end of the cable.

[0016] According to some embodiments, the piston includes a butyl rubber stopper that wraps around the perimeter and bottom of an acrylic piston plate; the vacuum pump draws air evenly through a plurality of vertical suction holes evenly distributed on the piston.

[0017] Secondly, the present invention provides a test method for the above-mentioned vacuum negative pressure loading anti-tension pile bearing capacity model test device, which includes the following steps:

[0018] S1: Depending on the experimental observation requirements, it is possible to choose whether to use a partition to change the amount of soil sample around the model pile, show the cross-section of the soil sample around the model pile, and facilitate the observation of the overall and local displacement of the surrounding soil sample during the pull-out process of the model pile.

[0019] S2: After loading the bottom soil sample into the model box, lay a layer of simulated groundwater, and then continue to fill the soil and bury the model pile with strain gauges. At the same time, evenly bury soil pressure sensors, pore water pressure sensors and temperature sensors around the model pile, and connect each sensor and strain gauge to the corresponding data acquisition instrument. Use the heating rods preset around the model box to heat the soil and raise the soil temperature to the required temperature.

[0020] S3: Use the telescopic rods inside the model box to place the fixed pulley directly above the model pile, and use the telescopic rods outside the model box to place the fixed pulley directly above the vacuum negative pressure system. Use a cable to connect the model pile and the piston, and connect the barometer to the inside of the negative pressure cylinder.

[0021] S4: After checking the stability and airtightness of the test device, use a vacuum pump to extract the air from the negative pressure cylinder. This external air pressure generates downward pressure on the piston. This pressure is converted into the tensile force on the model pile through the cable and fixed pulley. The test loading method is controllable. The tensile force can be controlled by controlling the air pressure of the vacuum negative pressure system, so as to realize graded loading or cyclic loading.

[0022] S5: Start the test, observe the data acquisition instrument, monitor the changes in pressure, strain and settlement in real time, and completely simulate the process of pile foundation pull-out; after the test, first unload the negative pressure cylinder, and after the pressure is unloaded, the pile foundation pull-out model test is completed.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The vacuum negative pressure loading model test device for the tensile bearing capacity of piles provided by this invention is characterized by its simple operation, safety, and short test cycle. Using this device to conduct pile foundation tensile bearing capacity tests eliminates the need for large instruments, jacks, and reaction frames. This not only saves manpower and resources but also reduces potential errors and operational mistakes that researchers may make when operating large equipment, thereby lowering the risk of safety accidents.

[0025] 2. The experimental device provided by this invention directly displays the cross-section of the soil through a transparent model box, and the position of the partition can be adjusted according to the experimental requirements, allowing for direct observation of the displacement changes of the soil at different radii centered on the model pile. In the actual construction of pile foundations, soil conditions are often complex and variable, and the device of this invention fully meets the needs of researchers. It allows for direct adjustment of soil sample type and moisture content during the experiment; it also allows for the use of heating rods to change the soil temperature and the use of a waterproof membrane to simulate groundwater, making the model experiment more closely resemble actual conditions and thus obtaining more reliable experimental results.

[0026] 3. The test device provided by the present invention uses an acrylic piston plate and a butyl rubber stopper. Under the premise of ensuring the airtightness of the negative pressure cylinder, the external atmospheric pressure is used to generate pressure on the acrylic piston plate, and then the pressure is converted into the tensile force of the model pile through the fixed pulley, so that there is no need to use a jack or rely on external load to provide tensile force.

[0027] 4. The screw holes reserved on the upper part of the model box and the telescopic rod in the device of the present invention facilitate researchers to conduct pull-out bearing capacity tests on pull-out piles of different sizes and forms, and can also conduct pull-out bearing capacity tests considering the group pile effect.

[0028] 5. The strain gauges arranged on the model pile body and the soil pressure sensor, pore water pressure sensor and temperature sensor evenly distributed around the pile in this invention can help researchers monitor the required data in real time, thereby helping researchers to grasp the entire development process of the pile foundation's tensile bearing capacity.

[0029] 6. In the device of this invention, the spring installed at the bottom of the negative pressure cylinder ensures the safety of the test. It prevents the acrylic piston plate from shifting downwards instantaneously when the model pile is pulled away from the soil, thus preventing damage to the test device. Attached Figure Description

[0030] Figure 1 This is an overall schematic diagram of the vacuum negative pressure loading anti-uplift pile bearing capacity model test device provided in the embodiment of the present invention.

[0031] Figure 2 This is a top view of the vacuum negative pressure loading anti-uplift pile bearing capacity model test device provided in the embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the model box provided in an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of the traction system provided in an embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram of the vacuum negative pressure system provided in an embodiment of the present invention.

[0035] In the diagram: 1-Soil sample, 2-Tempered glass model box, 3-Model pile, 4-Fixed pulley, 5-Telescopic rod, 6-Cable, 7-Hook, 8-Heating rod, 9-Waterproof membrane, 10-Dial gauge, 11-Base beam, 12-Soil pressure sensor, 13-Pore water pressure sensor, 14-Temperature sensor, 15-Soil pressure sensor, 16-Pore water pressure sensor, 17-Temperature sensor, 18-Strain gauge, 19-Vacuum pump, 20-Acrylic piston plate, 21-Butyl rubber stopper, 22-Spring, 23-Barometer, 24-Negative pressure cylinder, 25-Evacuation hole, 26-Resin glass partition, 27-Snap fastener, 28-Screw hole, 29-Nut and bearing, 30-Rubber tube, 31-Flat tube clamp, 32-Hex bolt, 33-Strain sensor, 34-Adhesive. Detailed Implementation

[0036] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "front," and "rear," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0038] This invention proposes a vacuum negative pressure loading model test device and method for the tensile bearing capacity of piles. This method utilizes the vacuum negative pressure system and traction system of the test device to provide an upward tensile force to the model pile. When the vacuum pump extracts air from inside the negative pressure cylinder, the atmospheric pressure outside the cylinder exerts a downward pressure on the acrylic piston plate. This pressure is then converted into tensile force on the model pile through cables and pulleys within the device, thus enabling the pile foundation tensile bearing capacity model test. This test method does not rely on large machinery, jacks, or reaction frames to provide tensile force, making it convenient and safe to operate. It also solves the problems of large floor space requirements and the inconvenience of providing tensile force to the model pile indoors. The use of a waterproof membrane and heating rods can also comprehensively simulate the effects of temperature and groundwater on the tensile bearing capacity of the pile foundation. This test device and method provide a more accurate, safe, and reliable testing method for the study of pile foundation tensile bearing capacity.

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] Example 1

[0041] like Figures 1-5 As shown, this embodiment provides a vacuum negative pressure loading anti-tension pile bearing capacity model test device, including a soil sample 1, a tempered glass model box 2, a model pile 3, a fixed pulley 4, a telescopic rod 5, a cable 6, a hook 7, a heating rod 8, a waterproof membrane 9, a dial gauge 10, a reference beam 11, a soil pressure acquisition instrument 12, a pore water pressure acquisition instrument 13, a temperature acquisition instrument 14, a soil pressure sensor 15, a pore water pressure sensor 16, a temperature sensor 17, a strain gauge 18, a vacuum pump 19, an acrylic piston plate 20, a butyl rubber stopper 21, a spring 22, a barometer 23, a negative pressure cylinder 24, an extraction hole 25, a resin glass partition 26, a buckle 27, a screw hole 28, a nut and bearing 29, a rubber tube 30, a flat pipe clamp 31, a hexagonal bolt 32, a strain acquisition instrument 33, and an adhesive 34.

[0042] Soil sample 1 was layered and placed into tempered glass model box 2. To simulate the effect of groundwater buoyancy in the model test, after soil sample 1 was placed at the bottom of tempered glass model box 2, a layer of waterproof membrane 9 was placed in it, water was added, and then another layer of waterproof membrane 9 was placed in it. The waterproof membrane 9 is to prevent soil particles in soil sample 1 from directly contacting the water in the waterproof membrane 9, which would affect the model test results. After the waterproof membrane 9 was placed, soil sample 1 was added again. While the soil sample 1 was being compacted in layers, soil pressure sensors 15, pore water pressure sensors 16, temperature sensors 17, and strain gauges 18 were placed vertically around model pile 3 and on the pile body. Then, heating rods 8 were arranged around tempered glass model box 2. After the internal devices of tempered glass model box 2 were placed, reference beams 11 were placed on the left and right sides of model pile 3, and a dial gauge 10 was connected to each side to calibrate whether model pile 3 was placed vertically and the tilt of model pile 3 during pull-out.

[0043] The test apparatus includes telescopic rods 5 facing both sides and fixed pulleys 4, and a single telescopic rod 5 and fixed pulley 4 facing the vacuum negative pressure system, as shown below. Figure 4 As shown, the fixed pulley 4 facing the vacuum negative pressure system and the telescopic rod 5 facing the model pile 3 are the same. The telescopic rod 5 and the fixed pulley 4 are assembled together using nuts and bearings 29, and then fixed to the telescopic rod 5 and the fixed pulley 4 in the pre-drilled screw holes 28 in the upper row of the tempered glass model box 2 using hexagonal bolts 32. The telescopic rod 5 is adjusted for extension and retraction through the screw holes 28 and hexagonal bolts 32. The clip 27 is fixed through the pre-drilled screw holes 28 and hexagonal bolts 32 in the second row of the tempered glass model box 2, and then the resin glass partition 26 is fixed using the clip 27. Both the tempered glass model box 2 and the resin glass partition 26 are made of transparent material and are used to observe the displacement changes of the soil at different radii centered on the model pile 3.

[0044] Adhesive 34 is applied to the perimeter and bottom surface of the acrylic piston plate 20. The acrylic piston plate 20 is then placed into the butyl rubber stopper 21 until the adhesive 34 firmly bonds the acrylic piston plate 20 and the butyl rubber stopper 21 together. The bonded acrylic piston plate 20 and butyl rubber stopper 21 are then vertically placed into the negative pressure cylinder 24, forming a closed space. To ensure airtightness, the butyl rubber stopper 21 has three outer rings, with a diameter 3mm larger than the diameter of the negative pressure cylinder 24. A barometer 23 is placed on the acrylic piston plate 20 and connected to the inside of the negative pressure cylinder 24 to monitor the system pressure and airtightness. A rubber tube 30 is fitted over the evacuation hole 25, and then a flat tube clamp 31 is used to clamp the rubber tube 30 to the evacuation hole 25, ensuring the airtightness of the inside of the negative pressure cylinder 24.

[0045] Soil pressure sensor 15, pore water pressure sensor 16, temperature sensor 17, and strain gauge 18 are respectively connected to soil pressure acquisition device 12, pore water pressure acquisition device 13, temperature acquisition device 14, and strain acquisition device 33 via wires. Vacuum pump 19 is connected to rubber hose 30 for vacuuming.

[0046] This embodiment also provides a test method for testing the pull-out bearing capacity of pile foundations using the above-mentioned vacuum negative pressure loading model test device, including the following steps:

[0047] 1) First, depending on the experimental observation requirements, it is possible to choose whether to use the resin glass partition 26 to adjust the amount of soil sample 1 around the model pile, or to show the cross-section of the soil sample 1 around the model pile, so as to help observe the overall displacement and local displacement of the surrounding soil sample 1 during the pull-out process of the model pile 3.

[0048] 2) After placing the bottom soil sample 1 into the tempered glass model box 2, lay a layer of waterproof film 9, add a large amount of water to simulate groundwater in the natural environment, and then lay another layer of waterproof film 9 (the size of the waterproof film 9 can be slightly larger than the tempered glass model box 2, or Vaseline can be applied to the edges to ensure the separation of the soil layer and the water layer). Then, fill the soil and bury the model pile 3 with strain gauges 18 arranged. With the model pile 3 as the center, evenly bury the soil pressure sensor 15, pore water pressure sensor 16 and temperature sensor 17. Use the heating rods 8 preset around the tempered glass model box 2 to heat the soil and raise the temperature of the soil sample 1 to the required temperature.

[0049] 3) Using the telescopic rod 5 inside the tempered glass model box 2, the fixed pulley 4 is placed directly above the model pile 3. The telescopic rod 5 outside the tempered glass model box 2 is used to place the fixed pulley 4 directly above the vacuum negative pressure tension system. The model pile 3 is connected to the acrylic piston plate 20 using the cable 6 and hook 7. The barometer 23 is connected to the inside of the cylindrical tempered glass cylinder 24 to monitor the air pressure and airtightness, ensuring the normal operation of the vacuum negative pressure system.

[0050] 4) After the stability and airtightness of the test device are checked, the air in the negative pressure cylinder 24 is extracted by the vacuum pump 19, so that the internal air pressure is lower than the external air pressure. This external air pressure generates downward pressure on the acrylic piston plate 20. This pressure is converted into the tensile force on the model pile 3 through the cable 6 and the fixed pulley 4. The test loading method is controllable. The tensile force can be controlled by controlling the air pressure of the vacuum negative pressure system, so as to realize graded loading or cyclic loading.

[0051] 5) During the experiment, soil pressure acquisition instrument 12, pore water pressure acquisition instrument 13, temperature acquisition instrument 14, strain acquisition instrument 33, and dial gauge 10 were used to monitor the changes in pressure, strain, and settlement in real time, thus fully simulating the pull-out process of the pile foundation. If a resin glass partition 26 is used for observation, Vaseline should be applied around the perimeter of the resin glass partition 26 to prevent the soil sample 1 and water in the tempered glass model box 2 from being lost. After the experiment, the valve of the negative pressure cylinder 24 was first opened to release air. After the pressure was unloaded, the equipment was retrieved, completing the pile foundation pull-out model test.

[0052] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A vacuum negative pressure loading anti-pulling pile bearing capacity model test device, characterized in that: include: The observation model component includes a model box, in which soil samples and simulated groundwater layers are layered and placed in the model box. Model piles are placed vertically in the soil samples. Sensor groups are evenly distributed in the soil samples and are used to collect soil pressure, pore water pressure and temperature parameters in the soil samples. A vacuum negative pressure system is used to generate downward pressure; The traction system is used to convert the downward pressure generated by the vacuum negative pressure system into an upward tension force and transmit it to the observation model component to pull the model pile in the vertical direction and conduct a pull-out bearing capacity test on the model pile; The traction system includes telescopic rods, which are horizontally fixed to the inner and outer sides of one side of the model box. The ends of the telescopic rods are equipped with fixed pulleys. One end of the cable is connected to the vacuum negative pressure system outside the model box, and the other end is wound around the two fixed pulleys and connected to the top of the model pile.

2. The vacuum negative pressure loading uplift pile bearing capacity model test device according to claim 1, characterized in that: The simulated groundwater layer is simulated by isolating the soil sample from the water layer through two layers of waterproof membrane; heating rods are evenly distributed around the soil sample; the sensor group includes a soil pressure sensor, a pore water pressure sensor, a temperature sensor, and a corresponding data acquisition instrument; strain gauges are attached to the pile body of the model pile and transmit the strain to the strain acquisition instrument.

3. The device for testing the bearing capacity of the uplift pile under vacuum negative pressure loading according to claim 2, characterized in that: The model box is equipped with at least one vertical partition for adjusting the volume of the soil sample.

4. The vacuum negative pressure loading model test device for the tensile bearing capacity of piles according to claim 3, characterized in that: The model box is made of tempered glass; the partition is made of resin glass.

5. The vacuum negative pressure loading model test device for the tensile bearing capacity of piles according to claim 4, characterized in that: The telescopic rod is provided with multiple sets of screw holes for adjusting the position of the fixed pulley, and the upper edge of the model box is provided with two rows of screw holes for fixing the telescopic rod and fixing the partition.

6. The vacuum negative pressure loading model test device for the tensile bearing capacity of piles according to claim 5, characterized in that: The vacuum negative pressure system includes a negative pressure cylinder, a piston, and a vacuum pump. A spring is installed at the bottom of the negative pressure cylinder, and a barometer is installed on the piston. The barometer is connected to the inside of the negative pressure cylinder, and the top of the piston is connected to one end of the cable.

7. The vacuum negative pressure loading model test device for the tensile bearing capacity of piles according to claim 6, characterized in that: The piston includes a butyl rubber stopper that wraps around the perimeter and bottom of an acrylic piston plate; the vacuum pump draws air evenly through several vertical suction holes evenly distributed on the piston.

8. A test method for a model test device for the bearing capacity of pull-out piles under vacuum negative pressure loading according to claim 7, characterized in that: Includes the following steps: S1: Depending on the experimental observation requirements, it is possible to choose whether to use a partition to change the amount of soil sample around the model pile, show the cross-section of the soil sample around the model pile, and facilitate the observation of the overall and local displacement of the surrounding soil sample during the pull-out process of the model pile. S2: After loading the bottom soil sample into the model box, lay a layer of simulated groundwater, and then continue to fill the soil and bury the model pile with strain gauges. At the same time, evenly bury soil pressure sensors, pore water pressure sensors and temperature sensors around the model pile, and connect each sensor and strain gauge to the corresponding data acquisition instrument. Use the heating rods preset around the model box to heat the soil and raise the soil temperature to the required temperature. S3: Use the telescopic rods inside the model box to place the fixed pulley directly above the model pile, and use the telescopic rods outside the model box to place the fixed pulley directly above the vacuum negative pressure system. Use a cable to connect the model pile and the piston, and connect the barometer to the inside of the negative pressure cylinder. S4: After checking the stability and airtightness of the test device, the air in the negative pressure cylinder is extracted using a vacuum pump. This external air pressure generates downward pressure on the piston, which is then converted into tensile force on the model pile through a cable and a fixed pulley. The test loading method is controllable. The tensile force can be controlled by controlling the air pressure of the vacuum negative pressure system, thus achieving graded loading or cyclic loading. S5: Start the test, observe the data acquisition instrument, monitor the changes in pressure, strain and settlement in real time, and completely simulate the process of pile foundation pull-out; after the test, first unload the negative pressure cylinder, and after the pressure is unloaded, the pile foundation pull-out model test is completed.

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