A method for predicting the relationship between lateral earth pressure and displacement of an expansive soil and a measuring device

Abstract

The application provides a prediction method and a measuring device for the relationship between lateral earth pressure and displacement of swelling soil. When measuring the lateral earth pressure of swelling soil under the condition of no displacement, a fixed block is arranged in the test device, a gradient initial constant vertical pressure is applied to the swelling soil sample for different tests, the swelling soil sample suction is gradually reduced to 0 after the sample is stable; when measuring the lateral earth pressure of swelling soil under the condition of lateral displacement, a plurality of horizontal elastic members and a plurality of horizontal displacement meters are arranged in the test device, a gradient initial constant vertical pressure is applied to the swelling soil sample for different tests, the swelling soil sample suction is gradually reduced to 0 after the sample is stable, the type of the plurality of horizontal elastic members is changed, and the test is repeated. Through fitting the test result data, the parameter value of the specific formula is determined, and then the change relationship between the lateral earth pressure of swelling soil and the lateral displacement in the humidification process is predicted.

Description

Technical Field

[0001] This invention relates to the field of soil and rock parameter testing technology, and in particular to a method and apparatus for predicting the relationship between lateral soil pressure and lateral displacement in unsaturated expansive soil during humidification. Background Technology

[0002] Expansive soil is a typical special type of soil. Rich in the expansive clay mineral montmorillonite, it exhibits significant water absorption and expansion, and water loss and shrinkage characteristics, often leading to serious engineering problems. Naturally occurring expansive soil is usually in an unsaturated state, undergoing significant three-dimensional expansion deformation under the influence of natural forces such as rainfall and rising groundwater levels. When this deformation is constrained by adjacent retaining structures (such as retaining walls, basement walls, etc.), the expansive soil can exert very large lateral earth pressures on these structures, causing damage or even failure, posing safety hazards to engineering construction. Therefore, when designing retaining structures in expansive soil areas, for the retaining structure itself, it is necessary to determine the lateral earth pressure exerted by the unsaturated expansive soil on retaining structures with different lateral stiffnesses during the wetting process; for the expansive soil itself, it is necessary to determine the relationship between the lateral earth pressure of the unsaturated expansive soil and the lateral displacement during the wetting process.

[0003] Currently, there are two main methods for studying the relationship between lateral earth pressure and lateral displacement in expansive soil, both domestically and internationally: one method uses a dilatometer to unload laterally the moistened expansive soil under lateral confinement conditions, studying the relationship between lateral earth pressure and lateral displacement during the unloading process; the other method relies on model box tests to study the relationship between lateral earth pressure and lateral displacement during the interaction and coordinated displacement of the expansive soil and the structure during the moistening and expansion process. The first method actually measures the relationship between lateral force and displacement during the unloading process, not the relationship between lateral earth pressure and lateral displacement during the moistening and expansion process. In experiments, the expansive soil is often moistened to full saturation before unloading; therefore, this method is rarely used to determine the relationship between lateral earth pressure and lateral displacement in unsaturated expansive soil. The second method relies on model box tests. Such tests involve complex preparatory processes, long testing times, and difficulty in controlling soil wetting. For unsaturated expansive soil model tests, the water content of the expansive soil inevitably fluctuates with soil depth and time. Controlling the water content and suction during the test is difficult, and the changes in lateral earth pressure and lateral displacement are coupled with changes in suction, making the analysis process quite complex. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a device and method for measuring and predicting the relationship between lateral earth pressure and displacement in expansive soil. This method is practical in engineering, accurate in measurement, and convenient to operate. It can predict the relationship between lateral earth pressure and lateral displacement changes in unsaturated expansive soil during the process of humidification and expansion, and the interaction and coordinated displacement between the soil and the structure.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for predicting the relationship between lateral earth pressure and displacement in expansive soil includes the following steps:

[0007] A measuring device is provided, comprising a rectangular cavity with a top opening. The rectangular cavity is divided into a moving area and a test area by a side-shifting baffle or a fixed block. The test area, from top to bottom, is provided with a vertical loading and displacement measuring system, a porous loading cover, a permeable stone, an expansive soil sample, a saturated clay slab, and a water cavity. The water cavity is provided with a flushing circuit, which is equipped with a circulating pump and a bubble flushing / water volume measuring device. The sidewalls of the test area are provided with multiple pressure sensors, a moisture content sensor, and a suction sensor. When the rectangular cavity is divided by the side-shifting baffle, the side-shifting baffle is movably disposed within the rectangular cavity. When the rectangular cavity is divided by the fixed block, the fixed block is fixed within the rectangular cavity.

[0008] Lubricate the measuring device, separate the rectangular cavity with a fixing block, place the entire measuring device into a sealed container, and measure the lateral soil pressure of the expansive soil sample in the measuring device without lateral displacement according to the test procedure. Apply a nominal vertical pressure of 1 kPa to the sample through the vertical loading device until the sample stabilizes, and then gradually reduce the suction force of the sample to 0. Replace the sample and select the next constant initial vertical pressure according to the vertical pressure gradient. Repeat the test until the maximum vertical stress value is reached.

[0009] In the measuring device, the rectangular cavity is divided by a lateral displacement baffle. A compression-resistant structural component and multiple horizontal displacement gauges are provided in the moving area. The lateral soil pressure of the expansive soil sample in the measuring device is measured according to the test procedure when there is lateral displacement. A nominal vertical pressure of 1 kPa is applied to the sample through a vertical loading device until the sample stabilizes. Then, the suction force of the sample is gradually reduced to 0. The sample is replaced and the next constant initial vertical pressure is selected according to the vertical pressure gradient. The test is repeated until the maximum vertical stress value is reached. The models of multiple horizontal elastic components are changed and the test is repeated.

[0010] Lateral earth pressure test results were obtained for expansive soil samples with and without lateral displacement.

[0011] Furthermore, the lateral earth pressure test results of expansive soil without lateral displacement are analyzed using the following formula:

[0012] Equation (1)

[0013] in: The lateral earth pressure of the expansive soil sample without lateral displacement; The lateral earth pressure is the pressure on an expansive soil sample when it is moistened to saturation under nominal vertical pressure without lateral displacement. The initial suction value of the expansive soil sample before wetting; This represents the suction value of the expansive soil sample. The saturated water content of the expansive soil sample; The moisture content of the expansive soil sample; This represents the vertical pressure exerted on the expansive soil sample. These are the model parameters.

[0014] Furthermore, the lateral earth pressure test results of expansive soil with lateral displacement are analyzed using the following formula:

[0015] Equation (2)

[0016] in: The lateral earth pressure of the expansive soil sample under arbitrary lateral displacement; This represents the lateral displacement of the expansive soil sample. The length of the expansive soil sample; These are the model parameters.

[0017] Furthermore, an initial constant vertical pressure is applied to the expansive soil sample using a vertical loading and displacement measurement system until the sample stabilizes. The initial suction value of the sample is measured using a suction sensor. Then, the suction of the expansive soil sample is controlled to reduce the suction to 0 in stages according to a preset gradient to simulate the humidification process. After each suction level stabilizes, the readings of the suction sensor, moisture content sensor, and pressure sensor are recorded. The gradient of vertical pressure and suction change should remain consistent in both the test without lateral displacement and the test with lateral displacement.

[0018] Furthermore, the axial translation method was used to gradually reduce the suction force of the sample to simulate the humidification process.

[0019] Furthermore, the criteria for judging the stability of vertical loading are: the change of each pressure sensor does not exceed 0.5 kPa or the change of the displacement gauge does not exceed 0.01 mm within two hours; the criteria for judging the stability of suction change are: the change of the suction sensor does not exceed 0.1% within two hours.

[0020] A device for measuring the relationship between lateral earth pressure and displacement in expansive soil, comprising:

[0021] A rectangular cavity has an opening at the top and is sealed at the bottom by a water cavity and a saturated clay plate. The rectangular cavity is divided into a moving area and a testing area by a side-shifting baffle or a fixed block. When the rectangular cavity is separated by the side-shifting baffle, the side-shifting baffle is movably disposed in the rectangular cavity. When the rectangular cavity is separated by the fixed block, the fixed block is fixed in the rectangular cavity.

[0022] The moving area is equipped with a pressure-resistant structural component and multiple horizontal displacement gauges.

[0023] The test area is arranged from top to bottom as follows: a vertical loading and displacement measurement system, a porous loading cover, a permeable stone, an expansive soil sample, a saturated clay slab, and a water cavity. The water cavity is equipped with a flushing circuit, which is equipped with a circulation pump and a bubble flushing / water volume measuring device. The side wall of the test area is equipped with multiple pressure sensors, moisture content sensors, and suction sensors.

[0024] Furthermore, the lateral displacement baffle and the rectangular cavity sidewall that contacts the expansive soil sample are provided with multiple grooves, and the pressure sensor, moisture content sensor and suction sensor are installed in the grooves.

[0025] Furthermore, the compression-resistant structural component is a transverse spring matrix formed by multiple springs evenly distributed.

[0026] Furthermore, the bubble flushing / water volume measuring device is a pressure plate instrument for measuring the soil-water characteristic curve.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] This invention provides a method and apparatus for predicting the relationship between lateral earth pressure and lateral displacement in expansive soil. During lateral earth pressure tests on expansive soil, suction sensors, moisture content sensors, displacement gauges, and pressure sensors are used to measure various data points, which are then fitted and analyzed using formulas. The experimental, analytical, and predictive method for the relationship between lateral earth pressure and lateral displacement in unsaturated expansive soil designed in this invention is applicable to both undisturbed soil in the field and remolded expansive soil in the laboratory. It has advantages such as comprehensive element control, high accuracy, simple operation, ease of promotion, and high degree of digitalization. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1This is an experimental flowchart of the method for predicting the relationship between lateral soil pressure and lateral displacement in expansive soil samples according to the present invention.

[0031] Figure 2 This is a schematic diagram of the test apparatus used in this embodiment of the invention to test the relationship between lateral earth pressure and lateral displacement (without lateral displacement) of expansive soil samples.

[0032] Figure 3 This is a schematic diagram of the test apparatus used in this embodiment of the invention to test the relationship between lateral earth pressure and lateral displacement (with lateral displacement) of expansive soil samples.

[0033] Figure 4 This is a top view of the test apparatus used in this embodiment of the invention to test the relationship between lateral earth pressure and lateral displacement (with lateral displacement) of expansive soil samples.

[0034] Figure 5 This is a side view of the test apparatus used in this embodiment of the invention to test the relationship between lateral earth pressure and lateral displacement (with lateral displacement) of expansive soil samples.

[0035] Among them, 1-rectangular cavity; 2-spring matrix; 3-lateral shift baffle; 4-displacement gauge; 5-pressure sensor; 6-moisture content sensor; 7-suction sensor; 8-permeable stone; 9-porous loading plate; 10-vertical loading and displacement measurement system; 11-saturated clay plate; 12-sealed container; 13-expansive soil sample; 14-circulation pump; 15-bubble flushing / water volume measuring device; 16-water cavity; 17-fixed block. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," 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. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0038] This invention provides a method for predicting the relationship between lateral earth pressure and displacement in expansive soil. A specialized measuring device is used to determine the variation of lateral earth pressure with lateral displacement in unsaturated expansive soil samples 13 under different vertical pressures, moisture contents, and suction levels. This method can, to some extent, solve the technical problems of limited applicability and complex operation in existing technologies. Figure 1 As shown, it includes the following steps:

[0039] Step S1: Set up the measuring device, which includes a rectangular cavity 1 with a top opening. The rectangular cavity 1 is divided into a moving area and a test area by a side-shifting baffle 3 or a fixed block 17. The test area is provided with a vertical loading and displacement measuring system 10, a porous loading cover, a permeable stone 8, an expansive soil sample 13, a saturated clay plate 11, and a water cavity 16 from top to bottom. The water cavity 16 is provided with a flushing circuit. The flushing circuit is provided with a circulating pump 14 and a bubble flushing / water volume measuring device 15. The side wall of the test area is provided with multiple pressure sensors 5, moisture content sensors 6, and suction sensors 7. When the rectangular cavity 1 is divided by the side-shifting baffle 3, the side-shifting baffle 3 is movably located inside the rectangular cavity 1. When the rectangular cavity 1 is divided by the fixed block 17, the fixed block 17 is fixed inside the rectangular cavity 1.

[0040] Step S2: Lubricate the measuring device, separate the rectangular cavity 1 with the fixing block 17, and place the entire measuring device into the sealed container 12. Measure the lateral soil pressure of the expansive soil sample 13 in the measuring device without lateral displacement according to the test procedure. Apply a nominal vertical pressure of 1 kPa to the sample through the vertical loading and displacement measurement system 10 until the sample stabilizes, then gradually reduce the suction force of the sample to 0. Replace the expansive soil sample 13 and select the next constant initial vertical pressure according to the vertical pressure gradient. Repeat the test until the maximum vertical stress value is reached.

[0041] Step S3: Lubricate the measuring device, separate the rectangular cavity 1 by the lateral displacement baffle 3, and install a compression-resistant structural component and multiple horizontal displacement gauges 4 in the moving area. Measure the lateral soil pressure of the expansive soil sample 13 in the measuring device when there is lateral displacement according to the test procedure. Apply a nominal vertical pressure of 1 kPa to the sample through the vertical loading and displacement measurement system 10 until the sample stabilizes, then gradually reduce the sample suction to 0. Replace the expansive soil sample 13 and select the next constant initial vertical pressure according to the vertical pressure gradient. Repeat the test until the maximum vertical stress value is reached. Change the model of multiple horizontal elastic components and repeat the test.

[0042] Step S4: Obtain the lateral earth pressure test results of the expansive soil samples with and without lateral displacement.

[0043] In step S4, the lateral earth pressure test results of expansive soil sample 13 without lateral displacement are analyzed using the following formula:

[0044] Equation (1)

[0045] in: The lateral earth pressure of expansive soil sample 13 without lateral displacement; The lateral earth pressure of expansive soil sample 13 when it is moistened to saturation under nominal vertical pressure without lateral displacement; The initial suction value of expansive soil sample 13 before moistening; The suction value of expansive soil sample 13; The saturated water content of expansive soil sample 13; The moisture content of expansive soil sample 13; The vertical pressure exerted on expansive soil sample 13; These are the model parameters.

[0046] The lateral earth pressure test results of expansive soil sample 13 with lateral displacement are analyzed using the following formula:

[0047] Equation (2)

[0048] in: The lateral earth pressure of expansive soil sample 13 under arbitrary lateral displacement; This represents the lateral displacement of expansive soil sample 13. The length of expansive soil sample 13; These are the model parameters.

[0049] In this invention, an initial constant vertical pressure is applied to the expansive soil sample 13 by a vertical loading and displacement measurement system 10, and the initial suction value of the sample is measured by a suction sensor 7. Then, the suction of the expansive soil sample 13 is controlled so that the suction of the sample is reduced to 0 in a preset gradient to simulate the humidification process. After each level of suction stabilizes, the readings of the suction sensor 7, the moisture content sensor 6, and the pressure sensor 5 are recorded.

[0050] Among them, the axial translation method is used to control the suction force of the sample.

[0051] The model parameters are determined by fitting the experimental data obtained in steps S2 and S3.

[0052] This invention also provides a device for measuring the relationship between lateral earth pressure and displacement in expansive soil, such as... Figures 2-5 As shown, it includes:

[0053] A rectangular cavity 1 has an opening at the top and is sealed at the bottom by a water cavity 16 and a saturated clay plate 11. The rectangular cavity 1 is divided into a moving area and a testing area by a side-shifting baffle 3 or a fixing block 17. When the rectangular cavity 1 is separated by the side-shifting baffle 3, the side-shifting baffle 3 is movably located inside the rectangular cavity 1. When the rectangular cavity 1 is separated by the fixing block 17, the fixing block 17 is fixed inside the rectangular cavity 1.

[0054] The moving area is equipped with pressure-resistant structural components and multiple horizontal displacement gauges 4;

[0055] The test area is equipped with a vertical loading and displacement measurement system 10, a porous loading cover, a permeable stone 8, an expansive soil sample 13, a saturated clay slab 11, and a water cavity 16 from top to bottom. The water cavity 16 is equipped with a flushing circuit, and the flushing circuit is equipped with a circulation pump 14 and a bubble flushing / water volume measuring device 15. The side wall of the test area is equipped with multiple pressure sensors 5, moisture content sensors 6, and suction sensors 7.

[0056] In this invention, the side-shifting baffle 3, the fixing block 17, and the side wall of the rectangular cavity 1 that contacts the expansive soil sample 13 are all provided with multiple grooves, and the pressure sensor 5, the moisture content sensor 6, and the suction sensor 7 are installed in the grooves.

[0057] In this invention, a slot is provided in the rectangular cavity 1. When the fixing block 17 is used to measure the lateral earth pressure of the expansive soil sample 13 without lateral displacement, the fixing block 17 is locked in the slot. The fixing block 17 is made of stainless steel.

[0058] In this invention, the pressure-resistant structural component is a transverse spring matrix 2 formed by multiple springs evenly distributed. One end of each spring is fixed to the side wall of the rectangular cavity 1, and the other end is fixed to the side-shifting baffle 3.

[0059] The bubble flushing / water volume measuring device 15 is a pressure plate instrument for measuring the soil-water characteristic curve.

[0060] The pressure plate apparatus for measuring soil-water characteristic curves includes a double-precision pressure gauge and a regulator. Specifically, the apparatus also features two water inlets, a cylinder pressure regulating valve and a low-pressure gauge for axial pressurization of the water supply chamber, a cylinder lifting button, a high-pressure regulating valve and a high-pressure gauge for applying pressure inside the water supply chamber, and a negative pressure display. A first regulating switch and a water injection pipe are located above the water outlet, and a second regulating switch and a drain pipe are located above the water return outlet. An exhaust pipe is located near the drain pipe, with a flexible hose connected to the bottom of the exhaust pipe and the end of the hose connected to the water chamber. An air inlet is also located on the side wall of the apparatus, connected to the water chamber via an air supply pipe.

[0061] In one implementation method, the rectangular cavity 1 is made of 304 stainless steel; the wall thickness is 20mm and the bottom thickness is 25mm; the inner cavity length is the sum of the length A1 of the expansive soil sample 13 and the length A2 of the lateral displacement baffle; the inner cavity width is consistent with the width B1 of the expansive soil sample 13 to be tested; the inner cavity height is the sum of the height H1 of the expansive soil sample 13, the height of the permeable stone 8 and the height of the porous loading plate 9; the grooves and holes in the cavity are slightly larger than the sensor diameter and have threads; the sensor accuracy is: displacement sensor 0.001mm, pressure sensor 5 0.1kPa, moisture content sensor 6 0.1%, and suction sensor 7 0.05%. The saturated clay plate 11 is 8 mm thick, and its length and width are equal to the length A1 and width B1 of the expansive soil sample 13. The length A2 of the fixing block 17 is equal to the length of the lateral baffle, the width B1 is equal to the width of the inner cavity of the rectangular cavity 1, and the height H2 is equal to the height of the inner cavity of the rectangular cavity 1. The suction control device and the vertical loading and displacement measurement system 10 are improved from the Fredlund SWCC soil-water characteristic curve pressure plate. The vertical loading of this device is pneumatic loading with a loading accuracy of 1 kPa. The suction control adopts the axis translation method, and the control accuracy is: 2 kPa for the low-range pressure gauge and 20 kPa for the high-range pressure gauge.

[0062] In the lateral earth pressure measurement of expansive soil samples without lateral displacement using a measuring device, pressure sensor 5, moisture content sensor 6, and suction sensor 7 are installed in the pre-reserved grooves on rectangular cavity 1. These sensors are threadedly connected to rectangular cavity 1, and the threads are tightened. The wires of pressure sensor 5, moisture content sensor 6, and suction sensor 7 are then arranged and connected to the data acquisition system.

[0063] The inner cavity of rectangular cavity 1 is fully lubricated.

[0064] First, the fully saturated clay plate 11 is installed at the bottom of the rectangular cavity 1. Then, the fixing block 17 is inserted into the side of the rectangular cavity 1 with the slot. Finally, the expansive soil sample 13, the permeable stone 8, and the porous loading cover are placed into the test area of ​​the rectangular cavity 1 in sequence.

[0065] Place the entire device into the sealed container 12, and connect the pipes of the circulation pump 14 and the bubble rinsing / water volume measuring device 15 to the water cavity 16 at the bottom of the saturated clay plate 11 through the pre-reserved sealing interface on the sealed container 12.

[0066] In the lateral earth pressure measurement of expansive soil samples with lateral displacement using a measuring device, pressure sensor 5, moisture content sensor 6, and suction sensor 7 are installed in the pre-reserved grooves on rectangular cavity 1. These sensors are threadedly connected to rectangular cavity 1, and the threads are tightened. The wires of pressure sensor 5, moisture content sensor 6, and suction sensor 7 are then arranged and connected to the data acquisition system.

[0067] The fully saturated clay plate 11 is first installed at the bottom of the rectangular cavity 1.

[0068] Screw one end of the high-stiffness spring into the pre-drilled slot on the side-shifting baffle 3 to form the spring matrix 2. Place the side-shifting baffle 3 into the rectangular cavity 1, and screw the other end of the high-stiffness spring into the pre-drilled slot on the inner wall of the rectangular cavity 1. Install the displacement gauge 4, so that it passes through the pre-drilled hole on the rectangular cavity 1 and contacts the side-shifting baffle 3.

[0069] The inner cavity of the rectangular cavity 1 and the side-shifting baffle 3 are fully lubricated.

[0070] The expansive soil sample 13, the permeable stone 8, and the porous loading cover were placed into the test area of ​​the rectangular cavity 1 in sequence.

[0071] Place the entire device into the sealed container 12, and connect the pipes of the circulation pump 14 and the bubble rinsing / water volume measuring device 15 to the water cavity 16 at the bottom of the saturated clay plate 11 through the pre-reserved sealing interface on the sealed container 12.

[0072] The water cavity 16 has a groove, and the saturated clay plate 11 is embedded in the groove.

[0073] In one implementation method, in step S2, a vertical loading and displacement measurement system 10 is used to load the sample. The criterion for stable vertical loading is that the change in pressure sensor 5 does not exceed 0.5 kPa or the change in displacement gauge 4 does not exceed 0.01 mm within two hours. The sample suction is controlled using an axis leveling instrument to simulate the humidification process. During humidification, the moisture content and suction of the sample are monitored in real time by suction sensor 7 to ensure that the sample remains stable after reaching the expected suction for the test until the end of the single gradient humidification. The criterion for stable suction is that the change in suction sensor 7 does not exceed 0.1% within two hours. The humidification process is carried out in stages. For the expansive soil sample 13 in one test, the suction gradient is set to change to 0 (i.e., the sample reaches saturation). Under each gradient, the next gradient humidification is carried out after the readings of pressure sensor 5 and displacement gauge 4 stabilize. After the single test is completed, the vertical pressure applied to the sample is changed. The vertical pressure should be selected starting from a certain gradient nominal vertical pressure (i.e., 1 kPa) to measure the lateral earth pressure of the expansive soil sample under no vertical pressure condition. The selectable reference values ​​for suction control are 1500, 1250, 1000, 750, 500, 250, 125, 75, 50, 25, 10, 5, and 0 kPa, while the selectable reference values ​​for vertical loading are 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 kPa.

[0074] In one implementation, in step S3, when changing the vertical pressure applied to the sample, the vertical pressure value used should be consistent with the vertical pressure value selected in step S2. When replacing the side-shifting baffle with different stiffness, first release the vertical pressure to stop the suction control, then remove the sample, and finally clean the inner cavity of the rectangular cavity 1 before reassembling the instrument. The springs are made of piano wire of standard number GB4358 with an outer diameter of 25mm, a total of 7.5 turns, and wire diameters of 6, 7, and 8mm, with single spring stiffness coefficients of 267, 580, and 1176 N / mm, respectively. The side-shifting baffle 3 is pre-applied with sealing grease to ensure that the baffle gaps are waterproof.

[0075] In one implementation, in steps S2 and S3, the lateral earth pressure of the sample should be the average value of the two pressure sensors 5 on one side, and the displacement of the lateral baffle 3 should be the average value of the two displacement gauges 4. The test is terminated when the change of each pressure sensor 5 does not exceed 0.5 kPa or the change of each displacement gauge 4 does not exceed 0.01 mm within two hours.

[0076] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for predicting the relationship between lateral earth pressure and displacement in expansive soil, characterized in that, Includes the following steps: A measuring device is provided, comprising a rectangular cavity with a top opening. The rectangular cavity is divided into a moving area and a test area by a side-shifting baffle or a fixed block. The test area, from top to bottom, is provided with a vertical loading and displacement measuring system, a porous loading cover, a permeable stone, an expansive soil sample, a saturated clay slab, and a water cavity. The water cavity is provided with a flushing circuit, which is equipped with a circulating pump and a bubble flushing / water volume measuring device. The sidewalls of the test area are provided with multiple pressure sensors, a moisture content sensor, and a suction sensor. When the rectangular cavity is divided by the side-shifting baffle, the side-shifting baffle is movably disposed within the rectangular cavity. When the rectangular cavity is divided by the fixed block, the fixed block is fixed within the rectangular cavity. Lubricate the measuring device, separate the rectangular cavity with a fixing block, place the entire measuring device into a sealed container, and measure the lateral soil pressure of the expansive soil sample in the measuring device without lateral displacement according to the test procedure. Apply a nominal vertical pressure of 1 kPa to the sample through the vertical loading device until the sample stabilizes, and then gradually reduce the suction force of the sample to 0. Replace the sample and select the next constant initial vertical pressure according to the vertical pressure gradient. Repeat the test until the maximum vertical stress value is reached. In the measuring device, the rectangular cavity is divided by a lateral displacement baffle. A compression-resistant structural component and multiple horizontal displacement gauges are provided in the moving area. The lateral soil pressure of the expansive soil sample in the measuring device is measured according to the test procedure when there is lateral displacement. A nominal vertical pressure of 1 kPa is applied to the sample through a vertical loading device until the sample stabilizes. Then, the suction force of the sample is gradually reduced to 0. The sample is replaced and the next constant initial vertical pressure is selected according to the vertical pressure gradient. The test is repeated until the maximum vertical stress value is reached. The models of multiple horizontal elastic components are changed and the test is repeated. Lateral earth pressure test results were obtained for expansive soil samples with and without lateral displacement. The results of lateral earth pressure tests on expansive soil without lateral displacement are analyzed using the following formula: Equation (1) in: The lateral earth pressure of the expansive soil sample without lateral displacement; The lateral earth pressure is the pressure on an expansive soil sample when it is moistened to saturation under nominal vertical pressure without lateral displacement. The initial suction value of the expansive soil sample before wetting; This represents the suction value of the expansive soil sample. The saturated water content of the expansive soil sample; The moisture content of the expansive soil sample; This represents the vertical pressure exerted on the expansive soil sample. These are model parameters; The results of lateral earth pressure tests on expansive soil with lateral displacement are analyzed using the following formula: Equation (2) in: The lateral earth pressure of the expansive soil sample under arbitrary lateral displacement; This represents the lateral displacement of the expansive soil sample. The length of the expansive soil sample; These are the model parameters.

2. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 1, characterized in that: An initial constant vertical pressure is applied to the expansive soil sample using a vertical loading and displacement measurement system until the sample stabilizes. The initial suction value of the sample is measured using a suction sensor. Then, the suction of the expansive soil sample is controlled to decrease to 0 in stages according to a preset gradient to simulate the humidification process. After each suction level stabilizes, the readings of the suction sensor, moisture content sensor, and pressure sensor are recorded. The gradient of vertical pressure and suction change should be consistent in both the test without lateral displacement and the test with lateral displacement.

3. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 2, characterized in that: The humidification process was simulated by gradually reducing the suction force of the sample using the axis translation method.

4. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 1 or 2, characterized in that: The criteria for judging the stability of vertical loading are: the change of each pressure sensor does not exceed 0.5 kPa or the change of the displacement gauge does not exceed 0.01 mm within two hours; the criteria for judging the stability of suction change are: the change of the suction sensor does not exceed 0.1% within two hours.

5. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 1, characterized in that: The lateral baffle and the rectangular cavity sidewall that contacts the expansive soil sample are both provided with multiple grooves, and the pressure sensor, moisture content sensor and suction sensor are installed in the grooves.

6. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 1, characterized in that: The compression-resistant structural component is a transverse spring matrix formed by multiple springs evenly distributed.

7. The method for predicting the relationship between lateral earth pressure and displacement in expansive soil according to claim 1, characterized in that: The bubble flushing / water volume measuring device is a pressure plate instrument for measuring the soil-water characteristic curve.

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