A method for establishing a constitutive model of soil based on a prototype test and a prototype test device used in the method

Abstract

The present application relates to a method for establishing a constitutive model of soil based on a prototype test and a test device used by the method, the method comprising the following steps: placing a sealed bag in a soil column test hole, injecting fluid into the sealed bag to load the soil, measuring the lateral displacement of the deep soil, calculating the yield cylindrical surface radius of the soil, the radial compressive stress at yield, and the principal stress state of the soil unit according to the circular hole expansion theory and the Lame equation, establishing the yield criterion, the subsequent yield surface, and the failure criterion, dividing the soil in the plastic deformation area into multiple concentric soil cylinders according to the graded loading, calculating the size and radial displacement of each soil cylinder from outside to inside, combining the test hole sidewall radial displacement test value, calculating the elastic parameters required by the incremental method in the elastic-plastic mechanics according to the test loading grade, establishing the constitutive model, assuming that the yield surface is a plane and the intermediate principal stress is ignored, degrading the yield criterion into the Mole-Coulomb criterion, and verifying the constitutive model through a prototype test.

Description

Technical Field

[0001] This invention relates to a method for establishing a soil constitutive model based on prototype tests in the field of elastoplastic mechanics, and the prototype test apparatus used therein. Background Technology

[0002] In the field of elastoplastic mechanics, the stress-strain relationship of soil is the foundation of geotechnical engineering calculations and analysis, also known as the constitutive model of soil. The incremental method is a commonly used calculation method in elastoplastic mechanics. The basic principle of the incremental method is to determine whether the soil has yielded based on the yield criterion. After yielding, the correlation between stress increments and strain increments at each stress level is explored, providing the elastic parameters required for elastic calculations under stress increments at each stress state. Then, calculations and analyses are performed based on elasticity calculation theory. Soil is a naturally formed material, and its material composition and the interactions between its components vary from place to place. Through long-term, persistent efforts and laboratory experiments, mechanicians have proposed numerous constitutive models for soil, attempting to solve the problems of engineering calculations and mechanical analysis of soil. However, due to the enormous volume, variable composition, and complex mechanical relationships of soil materials, the current calculation accuracy is still far from meeting engineering needs, resulting in massive engineering waste and frequent safety hazards. Finding a force sufficient to reflect the stress-strain relationship in soil and measuring its approximate displacement response under this force, thus providing reliable parameters tailored to specific conditions for engineering calculations and analyses, is a pressing scientific and technological challenge in the field of elastoplastic mechanics. The bladder compression test involves placing a fluid-filled bag in the soil and gradually increasing and decreasing the fluid pressure to measure the soil deformation caused by these changes. Summary of the Invention

[0003] The first objective of this invention is to provide a method for establishing a soil constitutive model based on prototype tests. This method can use bagged fluid to apply sufficiently large loading and unloading actions to the soil, thereby causing the soil to deform sufficiently within a certain distance range. The soil within a specific range is treated as a common load-bearing body and generates lateral displacement. By measuring the lateral displacement, the stress-deformation characteristics of the soil under loads comparable to those used in engineering applications can be determined, and the stress-strain relationship of the soil can be determined.

[0004] This method for establishing a soil constitutive model based on prototype tests includes the following steps:

[0005] a) Conduct prototype tests in soil using fluid contained in a sealed bag. This includes determining the maximum load, graded load, graded unloading, and radial displacement test requirements for single-stage loading and unloading based on the test objectives; determining the radial displacement stability criteria, termination loading criteria, and termination unloading criteria for single-stage loading and unloading; drilling test holes in the soil; constructing one or more inclinometer holes outside the test holes; placing the sealed bag in the test holes; filling the sealed bag with fluid to form a fluid column in the test holes; applying compressive stress to the sidewall of the test holes using the sealed bag and the fluid inside; calculating the magnitude of the compressive stress; and ensuring that the graded loading and unloading requirements are met. After completing the loading and unloading, measure the lateral displacement of the deep soil at different depths using one or two combinations of the test hole sidewall and inclinometer holes, according to the radial displacement test requirements.

[0006] b) Determine the soil elastic modulus and Poisson's ratio using one of the following two methods: The first method is to plot the relationship curve between the load measured in step a) and the lateral displacement of the deep soil at the same test point location, forming a hysteresis loop of the soil unloading-reloading rebound test curve. Using the circular hole expansion theory under elastic deformation conditions, calculate and determine the secant modulus of the corresponding test point as the elastic modulus of the test soil. Determine the soil Poisson's ratio using indoor tests or other tests or empirical methods. The second method is to set up one or more deep soil lateral displacement test points in the elastic deformation zone at different distances from the center of the test hole and test them simultaneously. Let one or two elastic parameters of the soil elastic modulus and Poisson's ratio be unknowns. Calculate the calculated value of the soil lateral displacement at the test point using the circular hole expansion theory. Establish an equation or a system of equations based on the equality of the calculated value and the measured value of the soil lateral displacement at the test point. Calculate the soil elastic modulus and Poisson's ratio by solving the equations or the system of equations.

[0007] c) Determine the distribution range of the yielding soil and the radial compressive stress at the boundary of the yielding soil corresponding to the first occurrence of soil yielding during the test using one of the following two methods: The first method is implemented as follows: First, based on the elastic modulus and Poisson's ratio of the soil determined in step b), calculate the radial displacement values ​​of the test hole sidewall or inclinometer hole under each level of test loading in step a), according to the circular hole expansion theory; Second, compare the calculated radial displacement values ​​of the test hole wall or inclinometer hole in step b) with the measured values ​​in step a). When the calculated value is less than the measured value, it is determined that the soil has yielded under the corresponding loading action; Third, assuming that the radius of the cylindrical surface of the yielding region boundary of the soil (hereinafter referred to as the yield cylinder surface) and the radial compressive stress at the position of the yield cylinder surface are unknowns when the soil yields for the first time, according to the circular hole expansion theory, the outer side of the yield cylinder surface is still an elastic body, and... The radius of the yield cylinder is used as the radius of the equivalent loading test hole. The radial compressive stress at the yield cylinder position is used as the equivalent circular hole test load. The deep lateral displacement of the soil at different distances from the center of the yield cylinder outside the soil is calculated. An equation system is established according to the principle of being equal to the measured value. The equation system is solved to calculate the radius of the yield cylinder and the radial compressive stress at the yield cylinder position. The second method is implemented as follows: The elastic modulus calculated in step b) is compared with the secant modulus of the soil calculated based on the test results in step a). The highest level of loading that is close to the elastic modulus is determined as the yield loading of the soil. The corresponding test point position is the yield cylinder position of the soil. Then, based on the elastic modulus, Poisson's ratio, and measured displacement at the test point when yielding, the radial and tangential compressive stresses at the yield cylinder position are calculated according to the circular hole expansion theory.

[0008] d) Establish the yield criterion of the soil according to the following method: Based on the radial compressive stress at the yield cylinder position determined in step c), determine that the soil inside the yield cylinder is in a plastic deformation state and the soil outside the yield cylinder is in an elastic deformation state. Take the radial compressive stress of the soil at the yield cylinder position calculated in step c) as the major principal stress, the tangential compressive stress as the minor principal stress, and the vertical compressive stress as the intermediate principal stress. Take the principal stress state of the soil element at the yield cylinder position as the yield point in the soil yield surface, and construct the yield surface through the yield point.

[0009] e) The subsequent yield surface of the soil and the first yield elastic modulus required for calculation using the incremental plasticity method are determined as follows: Based on the incremental plasticity method, assuming that the elastic modulus used in the incremental method calculation of the soil inside the yield cylinder determined in step c) is an unknown, after the test soil exhibits its first yield, the test soil is divided into a cylindrical soil inside the yield cylinder and a soil outside the yield cylinder, with the yield cylinder as the boundary. Then, the radial displacement of the test borehole sidewall or the lateral displacement of the deep soil at the test point location inside the yield cylinder is calculated according to the Lamé equation. Based on the fact that the calculated value equals the measured value, an equation is established, and the modulus of elasticity (hereinafter referred to as the first yield elastic calculation modulus) of the test soil after the first yield is calculated by solving the equation. The radial compressive stress at the test point on the inner side of the yield cylinder corresponding to the test load in step c) is taken as the major principal stress, and the compressive stress of the overlying soil is taken as the intermediate principal stress. The tangential normal stress at the test point on the sidewall of the test hole or the inner side of the yield cylinder is calculated by the Lamé equation as the minor principal stress. The stress state of the soil at the first subsequent yield point is determined, and the first subsequent yield surface of the soil is constructed through the subsequent yield point.

[0010] f) For the subsequent yield surfaces and corresponding yield elastic moduli generated by subsequent graded loading tests after the first yield surface established in step e), the following method is used to determine them: First, based on the yield criterion established in step d), assume that the radius of the boundary cylindrical surface between the elastic body and the plastic body in the test soil (equivalent to the yield cylindrical surface in step c, hereinafter also referred to as the yield cylindrical surface) is unknown, and the radial compressive stress at the yield cylindrical surface is equal to the radial compressive stress at the yield cylindrical surface determined in step c). Repeat the third step of the first method in step c), calculate the radius of the yield cylindrical surface, and calculate the radial displacement at the yield cylindrical surface. Then, according to the number of subsequent loading stages after the first yield of the soil, divide the soil inside the yield cylindrical surface into multiple concentric soil cylinders with the same number of subsequent loading stages, from the outside to the inside, so that the radial compressive stress on the interface of each concentric cylinder increases from low to high, and successively interacts with the soil. After yielding, the loading amounts for each test stage are the same. Using the calculated yield elastic modulus of the soil at each stage of loading, starting from the soil cylinder formed by the yield cylinder and the first subsequent yield cylinder, from the outside in, starting from the yield cylinder, the radial displacement at the interface of the soil cylinder is calculated sequentially using the incremental method in plasticity and the Lamé equation, and an equation is established. By solving the equation, the outer diameter of each soil cylinder is calculated sequentially. Then, the subsequent yield elastic modulus of the soil cylinder with the smallest outer diameter is set as an unknown under the corresponding loading action, and the radial displacement of the soil at the test hole sidewall is calculated. Based on the fact that the calculated value of the radial displacement at the test hole sidewall is equal to the measured value, an equation is established, and by solving the equation, the subsequent yield elastic modulus is calculated. Then, based on the principal stress state of the soil element at the test hole sidewall, referring to the method of establishing the soil yield criterion in step d), the subsequent yield surface is constructed through the yield point of the soil element in stress space.

[0011] In the above method for establishing a soil constitutive model based on prototype tests, in step d), the soil yield surface can be assumed to be a plane, and the yield surface can be determined based on the yield point.

[0012] In the above method for establishing a soil constitutive model based on prototype tests, in step e) or step f), it can be assumed that the subsequent yield surface of the soil is a plane, and the subsequent yield surface is determined according to the yield point.

[0013] In the above-mentioned method for establishing a soil constitutive model based on prototype tests, in step e) or step f), when the test borehole wall experiences a sudden increase in radial displacement or an unacceptable amount of displacement under single-stage loading, it can be determined that the soil has failed, and the soil yield surface of the test borehole wall determined by the corresponding upper-stage loading can be used as the soil failure surface.

[0014] In the above-mentioned method for establishing a soil constitutive model based on prototype tests, in step f), the loading and unloading conditions can be determined and the calculation parameters selected as follows: Using steps b) to f), an elastic zone, yield surface, successive yield surfaces at various levels, and failure surface are constructed in the stress space. The stress space of the tested soil element is divided into three regions: elastic zone, yield hardening zone, and failure zone. The elastic parameters required for the incremental method of soil elastic-plasticity calculation and the successive yield elastic modulus calculated for each level of yield surface before failure are tested. In the incremental method calculation process, firstly, the region corresponding to the stress state of the calculation element in the stress space is determined, and the loading and unloading conditions are determined as follows: First, based on the current principal stress state of the calculation element; second, the current stress state of the calculation element is placed in a three-dimensional stress space containing the soil yield surface, successive yield surface, and failure surface. When the calculation point is in the yield hardening zone, the yield surface where the stress state of the calculation element is located is further determined; third, assuming that the calculation element is in one of the loading or unloading states, the incremental method is used for the next calculation, and the successive yield elastic modulus is selected for loading calculation or the successive yield elastic modulus is selected for loading calculation. The soil elastic modulus is unloaded to calculate the principal stress state of the soil element, and the first step is repeated. In the fourth step, the relative positions of the principal stress states of the soil element calculated in the third step and the principal stress states of the soil element calculated in the first step in the soil stress space are determined. If the principal stress state of the soil element calculated in the third step is closer to the next yield surface of the soil under test loading than the principal stress state of the soil element calculated in the first step, it is determined to be a loading process; otherwise, it is determined to be an unloading process. If the judgment result in this step is consistent with the assumptions of the loading or unloading calculation in the third step, the calculation is valid; otherwise, the assumptions of the calculation in the third step are changed and the calculation is repeated.

[0015] In the above method for establishing a soil constitutive model based on prototype tests, in step a), graded loading, graded unloading, and graded loading are performed in the soil, and the lateral displacement of the test hole sidewall and the deep soil at the test point is measured simultaneously, and a soil unloading and reloading rebound test is conducted.

[0016] In the above method for establishing a soil constitutive model based on prototype tests, in step a), a clinometer hole is set in the test hole, and the radial displacement of the test hole sidewall is measured through the clinometer hole.

[0017] In the above method for establishing a soil constitutive model based on prototype tests, in step a), a slant hole with the function of measuring the deep lateral displacement of the soil is constructed near the test hole. The deep lateral displacement of the soil in the slant hole is measured simultaneously. The horizontal distance between the test hole and the slant hole on each horizontal plane is calculated by measuring the inclination of the test hole and the distance between the hole openings.

[0018] In the above method for establishing a soil constitutive model based on prototype tests, in step a), the maximum compressive stress in the termination loading criterion matches the magnitude of the actual additional stress in the soil of the proposed project at the test site.

[0019] In the above method for establishing a soil constitutive model based on prototype tests, in step a), during tunnel excavation, advance boreholes are drilled in the soil through the tunnel face, and these advance boreholes are used as test holes to conduct advance tests during construction.

[0020] In the above method for establishing a soil constitutive model based on prototype tests, the test holes in step a) are set vertically, inclined, or horizontally.

[0021] In the above method for establishing a soil constitutive model based on prototype tests, in step a), a vertical shaft is first constructed in the soil, and the shaft is used as the operating surface to drill oblique or horizontal holes in the soil as test holes.

[0022] In the above method for establishing a soil constitutive model based on prototype tests, in step a), the pore pressure reaction method is used to perform water-stopping treatment at the orifice of the test hole.

[0023] In the above method for establishing a soil constitutive model based on prototype tests, in step a), the difference in the test hole sidewall displacement values ​​of the same soil layer under different seepage path conditions is used to calculate the soil deformation and time correlation parameters.

[0024] In the above method for establishing a soil constitutive model based on prototype tests, in step a), the measured loading duration at each test point is divided by the square of the equivalent seepage path to normalize the effect of seepage conditions, so as to calculate the difference in test parameters caused by soil consolidation or shorten the test time.

[0025] The second objective of this invention is to provide a prototype testing apparatus for a method of establishing a soil constitutive model based on prototype tests, which can perform prototype tests on soil.

[0026] The prototype test apparatus used in this method for establishing a soil constitutive model based on prototype tests includes six parts: a sealed bag, a pore size measuring device, a distance measuring device, a fluid pressure measuring device, a sealing connection, and a fluid input / output device. The sealed bag is a bag-shaped component made of flexible material with sealing performance, and it contains fluid. The pore size measuring device is a device that can measure the cross-sectional size of the test hole, and it is equipped with a device that can sink or float in the fluid. The pore size measuring device is enclosed in a sealed shell. The distance measuring device is a device that can measure the position of the pore size measuring device in the test hole. The fluid pressure measuring device is a device that can measure the fluid pressure. The fluid input / output device is a device that can input or output fluid into or out of the sealed bag. The sealing connection is a component that seals the sealed bag and the fluid input / output device together.

[0027] In the prototype test apparatus used in the above-mentioned method for establishing a soil constitutive model based on prototype tests, one or a combination of the above-mentioned aperture measuring device and distance measuring device can be one or a combination of optical distance measuring instruments and acoustic distance measuring instruments.

[0028] In the prototype test apparatus used in the above-mentioned method for establishing a soil constitutive model based on prototype tests, an inclination measuring device can be installed at the lower part of the above-mentioned aperture measuring device.

[0029] In the prototype test apparatus used in the above-mentioned method for establishing a soil constitutive model based on prototype tests, the aforementioned aperture measuring device is a combination of a clinometer tube buried in the test hole and a clinometer placed in the clinometer tube.

[0030] In the prototype test apparatus used in the above-mentioned method for establishing a soil constitutive model based on prototype tests, the above-mentioned aperture measuring device is equipped with a variable volume sealed airbag, and the sealed airbag is connected to an air tube and a gas input and output device.

[0031] The present invention relates to a method for establishing a soil constitutive model based on prototype tests and the prototype test apparatus used therein. The constitutive model is theoretically sound, with simple parameters that can be obtained from soil prototype tests. The method for establishing the constitutive model is simple and easy to implement. The prototype test apparatus can apply a huge load to the soil using a combination of water and air, so that the load level borne by the soil during the test is comparable to the load level borne in actual engineering. This makes the various displacement test values ​​during the test comparable to the actual values ​​in engineering practice. Therefore, the model parameters are reliable and stable, the test equipment is simple to operate, highly accurate, low in cost, and highly reliable. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the test hole, inclinometer hole, and soil layer distribution profile used in the prototype test of the first embodiment of the present invention.

[0033] Figure 2 This is a schematic cross-sectional view of the prototype testing apparatus used in the first embodiment of the present invention.

[0034] Figure 3 This is a diagram showing the relationship between the loading and unloading amount of the prototype test chamber and the radial displacement of the test hole sidewall used in the first embodiment of the present invention.

[0035] Figure 4 A schematic diagram showing the relationship between radial displacement of the test hole sidewall and test time under single-stage bladder compression loading during the prototype test used in the first embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the horizontal test hole, vertical shaft, and soil layer distribution profile used in the first embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the cross-sectional structure of the test hole used in the second embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of the cross-sectional structure of the test hole used in the second embodiment of the present invention;

[0039] Figure 8 Photograph of the upper part of the test hole in the prototype test for bladder compression loading used in the third embodiment of the present invention;

[0040] Figure 9 This is a plan view of the test holes and test points for the prototype test of the bladder compression loading used in the third embodiment of the present invention;

[0041] Figure 10 This is a plan view of the test holes and test points for the prototype test of the bladder compression rebound and recompression used in the third embodiment of the present invention;

[0042] Figure 11 The test curves of horizontal displacement of deep soil under different loading conditions for the test hole sidewall of the prototype test of the bladder compression loading used in the third embodiment of the present invention;

[0043] Figure 12 The prototype test of the bladder compression loading used in the third embodiment of the present invention is used to test the horizontal displacement curves of the deep soil at the WC7 test point under different loading conditions.

[0044] Figure 13 The test curves of horizontal displacement of deep soil at the WC2 test point under different loading conditions are shown in the third embodiment of the present invention.

[0045] Figure 14The curve showing the relationship between horizontal displacement and loading amount of soil at test points 3-7.5m deep on the sidewall of the test hole in the prototype test of the bladder compression loading test used in the third embodiment of the present invention;

[0046] Figure 15 The curve showing the relationship between horizontal displacement and loading amount of soil at a depth of 7.5–9.5 m on the sidewall of the test hole in the prototype test of the bladder compression loading test used in the third embodiment of the present invention;

[0047] Figure 16 The curve showing the relationship between the horizontal displacement of the soil at a depth of 9.5–11.5 m in the test hole at the test point on the sidewall of the prototype test hole used in the third embodiment of the present invention and the loading amount.

[0048] Figure 17 The curves showing the relationship between horizontal displacement and loading amount of soil at depths of 11.5–18.5 m on the sidewall of the test hole in the prototype test of the bladder compression loading test used in the third embodiment of the present invention;

[0049] Figure 18 The curve showing the relationship between horizontal displacement and loading amount of soil at a depth of 2.5–7.5 m in the WC7 test point of the prototype test for bladder compression loading used in the third embodiment of the present invention;

[0050] Figure 19 The curve showing the relationship between horizontal displacement and loading amount of soil at a depth of 7.5–9.5 m in the WC7 test point of the prototype test for bladder compression loading used in the third embodiment of the present invention;

[0051] Figure 20 The curve showing the relationship between horizontal displacement and loading amount of soil at a depth of 9.5–11.5 m in the prototype test WC7 for the bladder compression loading used in the third embodiment of the present invention.

[0052] Figure 21 The curve showing the relationship between horizontal displacement and loading amount of soil at depths of 11.5–19 m using the WC7 test point in the prototype test of the bladder compression loading used in the third embodiment of the present invention;

[0053] Figure 22 The curves showing the relationship between horizontal displacement and loading of soil at depths of 5m and 8m in the WC2 test point of the prototype test of the bladder-compression rebound recompression of the third embodiment of the present invention are shown.

[0054] Figure 23 The curves showing the relationship between horizontal displacement and loading of soil at depths of 13m and 14m in the WC2 test point of the prototype test of the bladder-rebound recompression of the third embodiment of the present invention are shown.

[0055] Figure 24 The curve showing the relationship between horizontal displacement and loading amount of soil at a depth of 16-18m in the WC2 test point of the prototype test of the bladder-compression rebound recompression test used in the third embodiment of the present invention;

[0056] Figure 25 This is a schematic diagram illustrating the test hole and the division principle of the yield cylindrical surfaces at each level used in the third embodiment of the present invention. Detailed Implementation

[0057] Explanation of reference numerals in the attached drawings: 1-Backfill; 2-Silt; 3-Clayey soil; 4-Sand; 5-Test hole; 6-Sealing bag; 7-Sealing connection; 8-Windlass; 9-Distance measuring device; 10-Centering control plate; 11-Fluid input / output device; 12-Fluid pressure measuring device; 13-Controller; 14-Sealed outer shell; 15-Aperture measuring device; 16-Inclination measuring device; 17-Counterweight; 18-Shaft; 19-Inclination measuring hole; 20-Fluid; 21-Medium-coarse sand filler; 22-Surface settlement test point;

[0058] As a first embodiment of the present invention, the following is combined with Figures 1-5 This paper introduces the structure, working principle, and in-situ testing steps of the first prototype testing device used in the method for establishing a soil constitutive model based on prototype tests according to the present invention. Firstly, in conjunction with... Figure 2This invention introduces the structure and working principle of the prototype pressure testing device for a bladder. The testing device comprises six parts: a sealed bag, an aperture measuring device, a distance measuring device, a fluid pressure measuring instrument, a sealing connection, and a fluid input / output device. The sealed bag is a bag-shaped component made of flexible material with sealing properties, containing fluid. The aperture measuring device measures the cross-sectional dimensions of the sealed bag from within. The distance measuring device measures the position of the aperture measuring device within the sealed bag. The fluid pressure measuring instrument measures fluid pressure. The fluid input / output device inputs or outputs fluid into or out of the sealed bag. The sealing connection seals the sealed bag to the fluid input / output device. In this embodiment, the sealed bag can be a long strip made of a flexible membrane or waterproof fabric, with its bottom and sidewalls sealed, and its upper part connected to the sealing connection. The fluid is one or a combination of gas and liquid, which exerts compressive stress on the sidewalls of the sealed bag. In this embodiment, an elastic sealed bag can be used to accommodate the expansion of the sealed bag diameter after fluid pressure is introduced. In this embodiment, a larger diameter sealing bag can be folded and placed into the test hole. The sealing bag has the function of expanding its diameter after being filled with fluid. In this embodiment, a transparent sealing bag can be used to facilitate observation and imaging of the changes in the state of the test hole sidewall during the test. In this embodiment, the aperture measuring device or distance measuring device can be an optical rangefinder or an acoustic rangefinder, such as a laser tester or an ultrasonic drilling aperture tester. In this embodiment, the aperture measuring device can also be a displacement sensor. Multiple displacement sensors can be installed in the horizontal plane, arranged radially along the circular cross-section of the test hole. The measurement data of the aperture measuring device can preferably be directly transmitted to a recorder for recording and storage. In this embodiment, the aperture measuring device can be surrounded by a transparent and sealed shell to protect the relevant parts of the aperture measuring device from fluid immersion. In this embodiment, the aperture measuring device can be surrounded by a transparent and sealed shell, and the shell can be spherical to ensure that the aperture measuring device is perpendicular to the axis of the test hole during operation. In this embodiment, the line connecting the center of gravity of the aperture measuring device and the center of gravity of the outer casing is parallel to the axis of the test hole. An inclinometer can be installed at the lower part of the aperture measuring device, and a counterweight can also be installed at the lower part of the inclinometer. This ensures that the operating surface of the aperture measuring device remains perpendicular to the axis of the test hole while floating, facilitating the measurement of the test hole's diameter. In this embodiment, a transparent, elastic, sealed outer casing with a cylindrical center can also be wrapped around the aperture measuring device. The interior of the sealed casing is filled with one or a combination of two types of gas or liquid with a pressure not less than the fluid pressure inside the test hole. During testing, the middle sidewall of the sealed casing remains in close contact with the test hole wall, and the diameter of the test hole is calculated by measuring the diameter of the sealed casing.In this embodiment, the distance measuring device can be a measuring rope. The length of the measuring rope can measure the depth to which the aperture measuring device enters the test hole. Simultaneously, the aperture can be measured at various depths within the test hole by retracting and extending the measuring rope. In this embodiment, a measuring rope alignment control plate can be installed within the sealed connection. By passing the measuring rope through a central opening in the control plate, the measuring rope is controlled to remain centered on the test hole's axis. In this embodiment, a winch and controller can be installed on the upper part of the sealed connection to facilitate rope retraction and extension. An electric winch can also be installed on the sealed connection to move the aperture measuring device vertically. Alternatively, a sealing airbag can be installed on the aperture measuring device. Inflation and deflating of the sealing airbag via a connected air pipe controls its volume. The buoyancy of the airbag controls the aperture measuring device's ascent or descent, and the position of the aperture measuring device can be calculated by measuring the pressure of the sealing airbag. In this embodiment, the fluid pressure measuring instrument can be one or a combination of gas or liquid pressure measuring instruments. In this embodiment, the fluid can be a combination of water and air, with a barometer used as the fluid pressure measuring instrument and an air compressor as the fluid input / output device. The advantage of choosing a water and gas combination in this embodiment is that, on the one hand, the water pressure balances the groundwater pressure in the soil, and on the other hand, the gas pressurization above the water maintains stable pressure inside the sealed bag through gas compression, simplifying the operation. In this embodiment, a test loading pressure can also be applied to the sidewalls of the sealed bag using a water tower or similar device. Furthermore, both water and air are transparent, facilitating experimental measurements using optical instruments.

[0059] The following sections of this first embodiment mainly describe the specific implementation methods and steps for conducting prototype soil tests using the prototype testing device of this invention. Based on the testing objective, the maximum loading amount, graded loading and unloading amounts, radial displacement test requirements for single-stage loading and unloading, radial displacement stability criteria after single-stage loading and unloading, termination loading criteria, and termination unloading criteria are determined, and test holes are drilled in the soil. In this step, the testing objective for the soil layer can be to test the mechanical properties of the soil. In this case, the maximum loading amount should be applied until the soil reaches yield or failure. When the objective is to meet engineering requirements, the maximum loading amount can be determined by considering the ultimate load that the tested soil needs to bear in engineering activities. The determination of graded loading amounts generally needs to consider the testing accuracy requirements and testing time control. The more grades, the longer the testing time, the higher the testing cost, and the higher the testing accuracy. In geotechnical engineering applications, it is generally possible to choose 8 to 12 equal loading grades and 4 to 6 equal unloading grades, that is, to use twice the single-stage loading amount as the single-stage unloading amount. The requirements for radial displacement testing of test holes at each loading and unloading stage mainly refer to the testing interval. Radial displacement at each depth should be measured immediately after each loading. Considering the large testing volume, the first radial displacement measurement can be completed within 10-30 minutes after loading, and then repeated every 30-60 minutes thereafter. Of course, automated monitoring technology can be used to improve monitoring efficiency and shorten the time interval. The displacement stability standard after a single loading or unloading stage is related to the test hole diameter, the size of the single-stage loading, the mechanical properties of the soil, and the required testing accuracy. Generally, a radial displacement rate of less than 0.05-1 mm / h under each load stage can be taken as the radial displacement stability standard for each loading stage. The next loading stage can only be carried out after the radial displacement of each loading stage has stabilized. The displacement stability standard for a single unloading stage can also be taken as 0.05-1 mm / h. In this step, the loading termination standard is implemented when one of the following conditions is met: (i) the maximum loading requirement is reached; (ii) during the test, the radial displacement of the test hole becomes unstable after the next loading stage. Regarding point (ii), one of the following two criteria can be used for judgment: (A) The lateral displacement of the test hole sidewall in the subsequent loading stage reaches or exceeds 5 times the lateral displacement in the previous loading stage; (B) The logarithmic relationship curve between the radial displacement and the test time in the subsequent loading stage shows a clear inflection point; (C) The sealing bag reaches its maximum diameter. Another task in this step is to drill holes in the soil as test holes. The drilling in this step should penetrate the rock or soil layer being tested. The testing accuracy can be improved by increasing the diameter of the test hole. In this step, one or more inclinometer holes for testing the deep lateral displacement of the soil can be constructed at different distances near the test hole. In this step, advance testing can be carried out in conjunction with tunnel excavation, that is, advance drilling can be carried out in the soil through the tunnel face, and the advance drilling holes can be used as test holes.In this step, test holes can be set up vertically, inclined, or horizontally as needed to match engineering requirements or to test the anisotropic mechanical properties of the soil. When using inclined or horizontal test holes in this step, a vertical shaft can be constructed in the soil first, and then the shaft can be used as an operating face to drill inclined or horizontal holes into the soil as test holes, for example. Figure 5 As shown. In this step, when the borehole opening is below the groundwater level, the borehole opening can be sealed using the pore pressure reaction method. After drilling, a sealing bag is placed in the test hole. A rod-shaped component such as a steel pipe can be placed inside the sealing bag, and the flexible sealing bag is folded and inserted into the test hole. In this step, when the borehole opening requires sealing measures, the pore pressure reaction method used in the first step can be used for sealing. After the sealing bag is installed, fluid is filled into the sealing bag, forming a bag-filled fluid column with a sufficiently large slenderness ratio in the test hole. The fluid can be water or a combination of water and air, requiring the bag-filled fluid column to have a sufficiently large slenderness ratio to meet the assumptions of the columnar circular hole expansion calculation theory. The sealing bag and the fluid inside it are used to apply compressive stress to the sidewall of the test hole, and the magnitude of the compressive stress is calculated, meeting the requirements for graded loading to complete a single-stage pore pressure loading. During loading, the radial displacement of the test hole sidewall under the applied compressive stress should be measured according to the radial displacement test requirements until the radial displacement after loading meets the single-stage loading stability standard. After multiple stages of loading and testing, the loading is stopped until the termination criteria determined in the first step are met. Once the maximum load is reached, tiered unloading and corresponding tests are performed. Alternatively, depending on testing needs, unloading can be followed by loading tests and simultaneous testing, including soil rebound tests. The prototype testing device of this invention can apply enormous pressure to the soil using a bag-like fluid, causing splitting and fracturing of the soil during the test, fully testing the soil's deformation characteristics under conditions equivalent to the bearing capacity required for the project. As described above in this embodiment, multi-stage loading and unloading can be achieved, with each stage of loading or unloading performing multiple deformation tests. Each deformation test can be conducted segment by segment along the depth of the test hole, thus providing rich test data and various calculation parameters. For example, for a single test point under a single load, similar data can be provided. Figure 4 The radial displacement Ur ~ t curve of the test hole is shown, which reflects the consolidation characteristics of the in-situ soil. For a single test point, after loading and unloading, a curve resembling [the curve's shape] can be provided. Figure 3 The compressive stress p shown z The correlation curve with radial displacement Ur, according to Figure 3 It can calculate the secant modulus E corresponding to each loading level. pz In addition to the soil resilient modulus Eur, for test points that reach the failure criterion, the ultimate load p of the bladder compression can also be measured. zk .exist Figure 3In this process, the radial displacement data should be processed using the theory of circular hole expansion to calculate the bladder compression deformation modulus. For example... Figure 1 As shown in the soil layer distribution, this test can also measure the displacement of the third layer of cohesive soil at the same time under different seepage path conditions at distances from the top and bottom of the layer after any level of loading. Therefore... Figure 1 The soil layer distribution shown is as follows: the first layer of fill (1) is followed by sandy soil (2), then by cohesive soil (3), and the bottom of the cohesive soil (3) is sandy soil (4). Before the deformation stabilizes, the radial displacement of the top and bottom of the cohesive soil (3) is greater than the calculated value, which can reflect the consolidation deformation characteristics of the soil. In this embodiment, during the loading and unloading process of the test, the radial displacement of the test hole sidewall and the lateral displacement of the deep soil at each depth of the inclinometer hole are measured simultaneously to provide test parameters for verifying the correctness of the constitutive model of the soil. For the elastic model parameters, the following method can be used for the test: (i) Before the test begins, three or more inclinometer holes are set up at three or more different distances from the central axis of the test hole, r1, r2, and r3. And select appropriate values ​​of r1, r2, and r3 so that the corresponding three inclinometer holes are always located in the elastic deformation region during the test; (ii) Assume that during the test, the interface between the elastic region and the plastic region of the soil is at a distance of r from the central axis of the test. E The radial compressive stress at the test point on the cylindrical surface is p. E The elastic modulus of the soil is E, and that of the pine board is υ (which can also be obtained from laboratory tests). The lateral displacements of the inclinometer hole under the corresponding load, which are on the same horizontal plane as the test point, are U1, U2, and U3, respectively. Then, the equation system f(p) can be established based on the elastic deformation orifice expansion theory. E E, r, υ, U i ) = 0 (i = 1, 2, 3, 4). Therefore, we can solve for (p). E (ii) Calculate the stress at the r-cylinder surface, which is the stress state of the soil when it yields; (iii) Solve for the yield cylindrical surface r0 at the end of the previous loading stage using the same method as (ii), and let dr = r - r0; (iv) Assuming the soil conforms to the rigid-plastic model, calculate the distance between the yield cylindrical surfaces before and after the current loading stage: dr g =r g -r g0 (v) Compare dr and dr g The size when dr-dr g When dr = 0, it indicates that the soil satisfies the rigid-plastic model. g When < 0, it indicates soil hardening under load; when dr - dr g When the value is greater than 0, it indicates that the soil softens under load.

[0060] As a second embodiment of the present invention, it mainly combines Figures 6-7This paper introduces the structure and working principle of the second prototype testing device used in the method for establishing a soil constitutive model based on prototype tests according to the present invention. This embodiment is similar to the first embodiment described above, with the main differences being in the following two aspects: An inclinometer is placed between the sealing bag and the sidewall of the test hole; the change in the diameter of the test hole is calculated by measuring the lateral displacement of the deep soil and the displacement at the top of the inclinometer. The gap between the sealing bag, the inclinometer tube, and the test hole wall is backfilled with coarse sand. Another difference is that during the test, a channel for venting excess pore water pressure is formed on the test hole wall.

[0061] As a third embodiment of the present invention, combined with Figures 8 to 25 This paper details the specific implementation steps of the method for establishing a soil constitutive model based on prototype tests according to the present invention.

[0062] The first step is to prepare for and implement the prototype test. This mainly includes determining the maximum loading, graded loading and unloading, radial displacement test requirements for single-stage loading and unloading, radial displacement stability criteria for single-stage loading and unloading, termination loading criteria, and termination unloading criteria. In addition, boreholes are drilled in the soil as test holes, and one or more inclinometer holes are constructed outside the test holes.

[0063] In this embodiment, the soil layer distribution and main physical and mechanical properties of each soil layer at the selected prototype test site are shown in Table 1.

[0064] Table 1. Main Influencing Factors on Conventional Physical and Mechanical Properties of Soil Layers at the Test Site

[0065]

[0066]

[0067] In this embodiment, two prototype tests conducted by the inventors are described. The first test is a bladder compression loading test, and the second test is a bladder compression rebound and recompression test.

[0068] 1. Burr compression loading test

[0069] Between December 2021 and January 2022, the inventor employed the following method: Figure 6 and Figure 7The pressure testing apparatus shown was tested. Two inclinometer tubes were installed in the test borehole, which had a diameter of 400 mm. A double-layered sealed bag was used during the test: an inner sealed bag with a diameter of 200 mm and an outer sealed bag with a diameter of 400 mm. Before the test, the bottoms of the outer and inner sealed bags were sealed and fixed relative to each other, and the bottom of the inner sealed bag was filled with 2 m of coarse sand. After drilling, the outer sealed bag, along with the inner sealed bag and the inclinometer tubes installed at the bottom, was placed into the borehole. Then, the inner sealed bag was filled with sand at the borehole opening. The gap between the outer sealed bag and the borehole wall was then filled with coarse sand, sealing the outer sealed bag. To prevent the outer sealed bag from being punctured by sharp obstacles in the backfill under fluid pressure, a steel protective pipe was installed within 1.6 m below ground level, and the space between the steel protective pipe and the outer sealed bag was filled with coarse sand. The test borehole is 21.5m deep. After installation, the outer and inner sealing bags are in tight contact. Sand is filled into the inner sealing bag to ensure a 200mm diameter pressure hole is formed. The top of the test borehole is installed as follows... Figure 8 As shown, the test holes and monitoring holes are arranged in a planar manner as follows: Figure 9 As shown in Table 2, the groundwater level in the test well was 1.6m deep, and the loading process was as shown in Table 2. The stability control standard for each loading stage was set at 3 hours.

[0070] Table 2 Loading grading of the bladder compression test

[0071]

[0072] 2. Bag compression rebound and recompression test

[0073] To determine the elastic modulus E of the in-situ soil at various depths and layers in the test site, in-situ soil compression-rebound-recompression tests were conducted. The test borehole diameter was 300 mm. No inclination test holes or coarse sand backfill were installed on the borehole wall; the sealed bag was directly attached to the sidewall of the borehole. The top of the bag containing fluid was buried at a depth of 3 m, and the bottom depth was 24 m. The loading-rebound-reloading test was completed from January 20th to 22nd, 2022. The layout of the test borehole and monitoring plane is shown below. Figure 10 As shown in the figure. During the test, the applied load was measured using the height of the water column connected to the inside of the sealed bag. The loading and unloading stages of the rebound and recompression test are shown in Table 3, and the stability control standard for each load stage was set at 2 hours.

[0074] Table 3. Grading of Loading in Bulb Compression Rebound and Recompression Tests

[0075]

[0076] During the prototype test, a sealed bag was placed in the test hole, and fluid was filled into the sealed bag to form a fluid column with a sufficiently large slenderness ratio. The sealed bag and the fluid inside it were used to apply compressive stress to the sidewall of the test hole. The magnitude of the compressive stress was calculated, and the requirements for graded loading were met to complete a single-stage loading. According to the radial displacement test requirements, the lateral displacement of the test hole sidewall and the inclinometer hole at different depth test points was measured. Then, the next stage of loading was carried out, and the lateral displacement of the test hole sidewall and the inclinometer hole at different depth test points under the corresponding loading was measured until the loading termination criteria were met.

[0077] In the bladder compression test, the soil depth-lateral displacement relationship curves measured on the test hole sidewall under different loading amounts are shown below. Figure 11 As shown, the soil depth-lateral displacement relationship curves of the WC7 inclinometer borehole (1.100m from the borehole center) under different loading amounts are as follows: Figure 12 As shown.

[0078] The main tests of the bladder compression loading test include deep soil inclination measurement, loading amount, and surface settlement monitoring. The loading adopts equal-volume graded loads, and the loading amount is maintained stable by injecting water into the water tower. Each loading stage is maintained for 3 hours. A water meter is installed on the inlet pipe to measure the water inflow at each loading stage. Generally, the water inflow tends to stabilize 0.5 to 1 hour after loading.

[0079] In the bladder-rebound-recompression test, under various load conditions, the lateral displacement-depth relationship curves of the deep soil measured at the WC2 test point are as follows: Figure 13 As shown. This completes the prototype testing, thus completing the first step of the invention, and we proceed to the second step.

[0080] Second, the second step involves determining the soil's elastic modulus and Poisson's ratio using one of the following two methods: The first method involves plotting the relationship curve between the measured load and the lateral displacement of the deep soil at the same test point location, forming a hysteresis loop in the soil unloading and reloading test curve. Using the circular hole expansion theory under elastic deformation conditions, the unloading-reloading modulus at the corresponding test point is calculated as the elastic modulus of the test soil. The Poisson's ratio is then determined using indoor tests or other experimental or empirical methods. The second method involves setting up one or more deep soil lateral displacement test points at different distances from the center of the test hole within the elastic deformation zone and testing them simultaneously. One or both elastic parameters of the soil's elastic modulus and Poisson's ratio are set as unknowns. The calculated lateral displacement value of the soil at the test point is calculated using the circular hole expansion theory. Based on the principle that the calculated lateral displacement value of the soil at the test point is equal to the measured value, an equation or a system of equations is established. The soil's elastic modulus and Poisson's ratio are then solved by solving the equation or system of equations.

[0081] First, combined Figures 14-21 , Figures 22-24This paper introduces the first method for measuring the elastic modulus of soil. Based on the lateral displacement test results of deep soil at various depths during the first step of the bladder compression test (i.e., as shown in the image),... Figure 11 and Figure 12 The test data shown shows the relationship between the lateral displacement of the deep soil at each test point and the test load. Figures 14-21 As shown; based on the lateral displacement test results of the deep soil at various depths in the first step of the bladder compression rebound and recompression test (i.e., as shown in the figure); Figure 13 The test data shown shows the relationship between lateral displacement and loading of deep soil at typical test points, as illustrated in the curve. Figures 22-24 As shown.

[0082] For homogeneous soil layers, the elastic modulus E and Poisson's ratio v can be calculated through loading tests during the elastic phase. In the test, whether the soil yields can be determined based on, for example... Figures 22-24 The elastic modulus E is calculated according to equation (1) in the rebound and recompression test shown. In this embodiment, the calculated value of elastic modulus E is shown in Table 4.

[0083]

[0084] In the formula:

[0085] -Radial displacement of the test point in the elastic zone;

[0086] Δp j -Difference in test loading;

[0087] v - Tests the Poisson's ratio of the soil;

[0088] E - Tests the elastic modulus of soil;

[0089] r0 - radius of the test hole;

[0090] R - Horizontal distance between the center of the test hole and the test point.

[0091] Table 4. Calculation of Elastic Modulus in Burr Compression Rebound and Recompression Test

[0092]

[0093]

[0094] Note: The change in v value has little impact on the calculation results, and the range of v value change is small. It can be selected according to empirical values. In this embodiment, the v value of layer ②3 sandy silt is taken as 0.33, and the v value of layer ④ silty clay is taken as 0.42.

[0095] Third, the third step involves determining the test load, the distribution range of the yielding soil, and the radial compressive stress at the boundary of the yielding soil when the soil first yields during the test. This can be achieved in three steps: First, based on the soil's elastic modulus and Poisson's ratio determined in the second step, and according to the circular hole expansion theory, calculate the radial displacement of the test hole sidewall under each level of test loading in the first step. Second, compare the calculated radial displacement of the test hole sidewall in the first step with the measured value in the first step. If the calculated value is less than the measured value, it is determined that the soil has yielded under the corresponding loading. The third step involves setting the radius of the cylindrical surface at the boundary of the soil yielding region (hereinafter referred to as the yield cylinder surface) and the radial compressive stress at the position of the yield cylinder surface as unknowns. Based on the theory of circular hole expansion, the radius of the yield cylinder surface is set to the radius of the equivalent circular hole loading test hole of the elastic body, and the radial compressive stress at the position of the yield cylinder surface is set to the equivalent circular hole test loading amount. The deep lateral displacement of the soil at different distances from the center of the yield cylinder surface is calculated. An equation system is established according to the principle of being equal to the measured value. The equation system is solved to calculate the radius of the yield cylinder surface and the radial compressive stress at the position of the yield cylinder surface.

[0096] The third step mentioned above can be implemented through the following steps:

[0097] (1) The radius of the first yield cylinder surface of the test soil is marked as r. E The corresponding experimental loading is P. F The corresponding principal stresses on the yield cylindrical surface of the soil are {σ1, σ2, σ3}; after the first stage of yield loading, the yield cylindrical surface r... E The soil between the test borehole and the soil mass can be calculated as an elastic body with an elastic modulus of E1, and denoted by a cylindrical surface r. E As the boundary, cylindrical surface r E The soil other than that is calculated as an elastic body with an elastic modulus of E.

[0098] (2) Before the test begins, two or more inclinometer holes shall be set up at two or more different distances R1 and R2 from the centerline of the test hole. Appropriate values ​​for R1 and R2 shall be selected so that a sufficient number of inclinometer holes are available for calculation within the elastic zone during the test.

[0099] For displacement calculation within the elastic region, it can be considered as displacement on the cylindrical surface r. E A load of magnitude p was applied at the location. E The problem of columnar hole expansion is calculated. Using the two-dimensional circular hole expansion theory, equation (2) holds in the elastic region.

[0100]

[0101] In the formula:

[0102] -Radial displacement of test points in the elastic zone when the test soil yields;

[0103] r0 - Radius of the test loading hole;

[0104] r E - Radius of the first yielding cylindrical surface;

[0105] p E - Yielding cylindrical surface r E Radial additional stress generated by loading at the point;

[0106] R j - The horizontal distance between the j-th inclinometer hole and the center of the test hole at the test point;

[0107] The meanings of the other symbols are the same as before.

[0108] (3) Based on the experimental test values ​​of radial displacement at different points, p is solved using equation (2). E r E value.

[0109] By measuring the values ​​from a large number of inclinometer boreholes at different distances, and solving the equation set, the various mechanical property parameters in equation (2) can be calculated. Considering the workload and accuracy control of the test, the soil elastic modulus E and v values ​​can be obtained by means of the bladder compression rebound recompression test in the second step, or by measuring the E and v values ​​during the early loading process. Alternatively, the Poisson's ratio v value can be obtained by combining laboratory tests to reduce the workload of inclinometer testing. After completing the third step, proceed to the fourth step.

[0110] Fourth, the yield criterion of the soil is established according to the following method: Based on the radial compressive stress determined at the yield cylinder in step three, it is determined that the soil inside the yield cylinder is in a plastic deformation state, and the soil outside the yield cylinder is in an elastic deformation state. The major principal stress of the soil element at the yield cylinder is the radial compressive stress calculated in step three, the minor principal stress is the tangential principal stress at the yield cylinder, and the intermediate principal stress is the vertical compressive stress. The principal stress state of the soil element at the yield cylinder is taken as the yield point in the soil yield surface, and the yield surface is constructed using the yield point. Specifically, the method for constructing the yield surface from the yield points of soil elements can be as follows:

[0111] According to the solution of elasticity of circular hole expansion, the principal stress of soil element is calculated as shown in equation (3) at and outside the yield cylindrical surface of soil.

[0112]

[0113] In the formula:

[0114] σ1 - The principal stress in the principal stress space of the soil element;

[0115] σ² - the middle principal stress in the principal stress space of a soil element;

[0116] σ3 - Minor principal stress in the principal stress space of a soil element;

[0117] σ r -Radial compressive stress at the yield cylindrical surface of the soil;

[0118] σ z - Vertical compressive stress at the yield cylindrical surface of the soil;

[0119] σθ - Tangential compressive stress at the yield cylindrical surface of the soil;

[0120] P0 - Earth pressure at rest;

[0121] γ-Soil weight;

[0122] h - Yield surface embedment depth;

[0123] r - the distance from the calculated point of the soil on the outer side of the yield cylinder to the center of the test hole;

[0124] r iE - Radius of the cylindrical surface at each yield point of the soil;

[0125] The meanings of other symbols in the formula are the same as before.

[0126] According to equation (3), based on the yield cylindrical surface r iE The stress state at the location can be obtained as shown in equation (4).

[0127]

[0128] The meanings of the symbols in the formula are the same as before.

[0129] Equation (4) represents a stress state when soil yields during a bladder compression test, which is a point on the soil yield surface and a solution to the yield surface equation. It is related to the static earth pressure at the test point, the calculated radial compressive stress on the yield cylinder surface, and the depth of the test point. The first method to determine the soil yield surface is to construct the soil yield surface by fitting a sufficient number of test points in the same soil layer.

[0130] A second method for determining the soil yield surface is to assume certain characteristics of the soil yield surface and construct the soil yield surface.

[0131] Equation (4) is equivalent to Equation (4a).

[0132]

[0133] The meanings of the symbols in the formula are the same as before.

[0134] When the soil yield surface is assumed to be a plane, the soil yield equation can be assumed to be a linear function of the three principal stresses of the soil element. σ2 in equation (4a) is only related to the location of the test point, and the yield criterion expression shown in equation (5) can be obtained.

[0135]

[0136] In the formula:

[0137] c p -Mechanical property parameters reflecting the yield characteristics of soil when the soil yield surface is assumed to be a plane;

[0138] k0 - the coefficient of earth pressure at rest of the tested soil;

[0139] The meanings of the other symbols in the formula are the same as before.

[0140] Equation (5) can also be written as Equation (6).

[0141]

[0142] The meanings of the symbols in the formula are the same as before.

[0143] For the form of equation (6), when the influence of the intermediate principal stress is not considered, the yield criterion degenerates into the Mohr-Coulomb strength criterion.

[0144] In the yield criteria expressed as in equations (5) and (6), p is contained E 、k0、c p The three experimental constants are elastoplastic mechanical characteristic constants reflecting soil yielding and are independent of the test point depth. The at-rest earth pressure coefficient k0 can be determined through a pressure test. Specifically, a spherical borehole is buried at a depth of [insert depth here] before drilling the test hole. During the test, the test load corresponding to the lateral displacement of the test point returning to its initial value before drilling is the at-rest earth pressure P0. Dividing the at-rest earth pressure P0 by the weight of the overlying soil at the test point location yields the at-rest earth pressure coefficient k0. The experimental constant p of the soil in the yield criterion can be calculated using the aforementioned third step. E Experimental constant c p The equation can be constructed and solved by using the test results from another test point where the same layer of soil yields, different from the third step.

[0145] In this step, the yield cylinder of the test soil can also be determined by comparing it with the elastic modulus calculated from the equivalent load of the test soil. When the elastic modulus is smaller, it indicates that the soil has begun to yield, and the load at which the test soil yields can be determined accordingly. Figure 13 and Figures 22-24In the soil loading and rebound-reloading tests described, the soil yielded at a depth of 14m under a loading of 0.273MPa. Before yielding, the secant modulus calculated from the tests showed good agreement with that from the rebound-recompression tests. After the yield point, the secant modulus decreased significantly, as shown in the figure. Figure 23 As shown. In the same soil layer, the shallower the burial depth, the smaller the secant modulus. Therefore, for the ④th layer of silty clay in this test, in the soil stress space, the yield surface is located at a depth of 14m under a loading of 0.273MPa, and the stress state corresponding to the WC2 test point in the rebound and recompression test is 2.18mm. Using the same analysis method, it can be determined that for the ②3rd layer of sandy silt, the yield surface is located at a depth of 8m under a loading of 0.273MPa, and the stress state corresponding to the WC2 test point in the rebound and recompression test is 1.44mm. Figure 22 As shown.

[0146] After completing step four, proceed to step five.

[0147] Fifth, the first subsequent yield surface of the soil and the elastic modulus of the soil after the first yield required for calculation using the incremental method of plasticity are determined as follows: Based on the incremental method of plasticity, let the elastic modulus used for the incremental calculation of the soil after yielding inside the yield cylinder determined in step three be the unknown E1. After the test soil exhibits its first yield, the first yield cylinder (with radius r) is used as the reference point. E Using the cylindrical surface of the yield cylinder as the boundary, the test soil is divided into a soil cylinder inside the yield cylinder and a soil body outside the yield cylinder. The radial displacement of the test hole sidewall is calculated according to the Lamé equation, so that the calculated radial displacement of the test hole is equal to the measured value. The equation for calculating the lateral displacement of the test hole sidewall is established. The modulus of elasticity (hereinafter referred to as the first yield elastic calculation modulus E1) of the test soil after the first yield is solved by solving the equation. The test loading corresponding to the fourth step is taken as the major principal stress, the overlying soil pressure stress is taken as the intermediate principal stress, and the tangential normal stress of the soil test hole sidewall is calculated according to the Lamé equation as the minor principal stress. Based on the fourth step, the first subsequent yield surface of the test soil is established. According to the Lamé equation, the equation for calculating E1 can be expressed as (7):

[0148]

[0149] In the formula:

[0150] -Radial displacement at the first yielding cylindrical surface;

[0151] The meanings of other symbols in the formula are the same as before.

[0152] The value of E1 can be calculated from equation (7) according to equation (8) or (9) as shown.

[0153]

[0154] The meanings of the symbols in the formula are the same as before.

[0155]

[0156] The meanings of the symbols in the formula are the same as before.

[0157] When the test soil is found to be yielding through inclinometer measurement, the soil on the test borehole wall is in a subsequent yielding state and can be considered as the first subsequent yielding cylindrical surface measured in the test. In subsequent loading tests, the soil at the test borehole sidewall will further generate multiple subsequent yielding cylindrical surfaces. Correspondingly, for equal-volume graded loading tests, the subsequent yielding loading amount [p] F +(i-1)Δp] can be used to calculate the principal stress state of the subsequent yield cylinder surface through the Lamé equation, and the subsequent yield surface can be established with reference to step four.

[0158] The subsequent yield surface of the soil element at the test hole sidewall corresponding to the yield criterion shown in Equation (5) is shown in Equation (10).

[0159]

[0160] In the formula:

[0161] i - The number of loading levels after soil yielding occurs in the prototype test of equal-quantity graded loading;

[0162] Δp - Test graded loading amount;

[0163] The meanings of other symbols in the formula are the same as before.

[0164] When i = 1, equation (10) is the first successor yield surface.

[0165] According to Table 4, the vertical compressive stress generated by the buoyant unit weight of the soil at a depth of 8m is 0.0861MPa, and the vertical compressive stress generated by the buoyant unit weight of the soil at a depth of 14m is 0.1289MPa. Therefore, the calculated load value corresponding to the yield strength of the test soil at a depth of 8m is 0.1468MPa, and the calculated test load value corresponding to the yield strength of the test soil at a depth of 14m is 0.1559MPa.

[0166] In the rebound and recompression test, the soil between the test hole wall and the WC2 test point is in a yielding state. Let the elastic modulus of this part of the soil be E1 in the incremental method calculation. Let the first subsequent yield surface be the principal stress state of the test hole wall under the loading of 0.273MPa. E1 can be calculated using the Lamé equation as shown in Equation (9). The first subsequent yield surface and the corresponding first subsequent yield elastic modulus E1 of the ②3 layer of sandy silt at a depth of 8m and the ④ layer of silty clay at a depth of 14m are shown in Table 5.

[0167] Table 5. Calculation of Yield Surface and Elastic Modulus after Burr Compression Rebound and Recompression Tests

[0168]

[0169] Note: ② The v value of the silty sand layer 3 is taken as 0.25, and the v value of the silty clay layer ④ is taken as 0.42.

[0170] After completing step five, proceed to step six.

[0171] VI. Step Six, the following parts of this embodiment, in conjunction with... Figure 25 For the subsequent yield surface and corresponding yield elastic modulus generated by subsequent graded test loading after the first subsequent yield cylindrical surface established in step five, the following method is used to determine them: when the test soil begins to yield, the soil yields at a rate of r... E The cylindrical surface is the interface, r E The part outside the cylindrical surface is an elastic body, r E The area inside the cylindrical surface is the soil that has undergone its first yielding. Then, the process is carried out in the following steps:

[0172] (1) Calculate the boundary cylindrical surface between the yield cylindrical surface of the test soil and the elastic body.

[0173] After the first loading stage following soil yielding, soil yielding manifests in the following two aspects: First, the yield cylinder of the soil expands outward to r. 1E Cylindrical surface; secondly, in r 1E cylindrical surface and r E The soil between the cylindrical surfaces exhibits its first loading yield at r E A second yielding occurred within the cylindrical surface. Assuming that at the r1 cylindrical surface, after soil yielding, the stress state after the second loading is the same as the stress state at the r0 cylindrical surface after the first yielding, E1 can be used as the stress state between the r1 cylindrical surface and the r0 cylindrical surface. 1E Soil modulus calculation between, r 1EThe elastic modulus E is used for soil outside the cylindrical surface, and E1 is used as the calculation modulus for soil inside the cylindrical surface r1. This process continues, for the second and subsequent equal-volume graded loading after soil yielding, following the above method, after the i-th (i = 2, 3, 4…) loading after the test soil yields, refer to… Figure 25 The yielding soil is divided into i adjacent cylindrical elements: from the outside to the inside, the outer diameter of each cylindrical element is r. iE r1, r2, r3…r i-1 The inner diameters of each cylindrical unit are r1, r2, r3…r i-1 From the outside to the inside, the radial compressive stress on the outer surface of each cylindrical unit is p, r0; E p F p F +Δp、p F +2Δp…p F +(i-2)Δp; From the outside to the inside, the radial compressive stress on the inner surface of each cylindrical unit is successively p F p F +Δp、p F +2Δp…p F +(i-2)Δp、p F +(i-1)Δp; From the outside to the inside, the elastic modulus used in the incremental loading method for each cylindrical element is E1, E2, E3…E i-1 E i .

[0174] For r iE The elastic soil on the outer side of the cylindrical surface, at r iE The position of the cylindrical surface can be considered as being applied to r. iE The test load on the cylindrical surface is p E For the radial displacement calculation of the elastic body, because in r iE The cylindrical surface remains in an elastic state at this point; therefore, r iE The radial displacement of the soil outside the cylindrical surface is independent of the loading stress path, i.e., equation (11) holds.

[0175]

[0176] In the formula:

[0177] - The radial displacement of the test points in the elastic zone of the soil after the i-th (i = 2, 3, 4...) loading following the yielding of the test soil; r iE - The radius of the expanded yield cylinder after the i-th (i = 2, 3, 4...) loading of the test soil after it yields;

[0178] R j -in r iEThe horizontal distance between the test point of the inclinometer hole in the outer elastic zone soil and the centerline of the test hole;

[0179] The meanings of the other symbols are the same as before.

[0180] The test can be performed using an inclinometer hole located in the elastic zone of the test soil. Substitute into equation (11) and solve for r using equation (12). iE value.

[0181]

[0182] In the formula: the meanings of each symbol are the same as before.

[0183] (2) Calculate the radius r of the yield cylinder corresponding to the subsequent yield surface stress state when the test soil yields. i

[0184] The solution can be obtained by following these steps: Figure 25 The yield cylinder r corresponding to the subsequent yield surface stress state shown i :

[0185] (A) Calculate r according to equation (12) iE ;

[0186] (B) Calculation of the yield cylindrical surface r using the cylindrical hole expansion theory iE The displacement at that point is calculated using equation (13).

[0187]

[0188] In the formula:

[0189] Ur iE - Radial displacement of the initial yield cylindrical surface position;

[0190] The meanings of other symbols in the formula are the same as before.

[0191] (C) Regarding such Figure 25 The outer diameter r shown iE For a soil cylinder with an inner diameter of r1, calculate the yield cylindrical surface r using Lamé's equations and the incremental method in elastoplastic calculations. iE Displacement at point Establish the equation as shown in equation (14).

[0192]

[0193] In the formula:

[0194] r1 - the radius of the first successor yield cylinder;

[0195] E1 - The elastic modulus used for soil elasticity calculation when the test soil is in the stress state between the first yield surface and the first subsequent yield surface;

[0196] The meanings of other symbols in the formula are the same as before.

[0197] (D) Calculate the radius r1 of the cylindrical surface of the test soil after the first subsequent yield using formula (14).

[0198] (E) Regarding such Figure 25 The outer diameter r shown iE For a soil cylinder with an inner diameter of r1, calculate the displacement at the yielding cylindrical surface r1 using Lamé's equations and the incremental method in elastoplastic calculations. That is, the radial displacement at the first subsequent yield cylindrical surface r1 is calculated using equation (15).

[0199]

[0200] In the formula:

[0201] -Radial displacement at the first subsequent yielding cylindrical surface r1;

[0202] The meanings of other symbols in the formula are the same as before.

[0203] (3) Calculate the elastic modulus E at the i-th subsequent yield. i

[0204] For example Figure 25 For the other soil cylinders shown, repeat steps C) to E) of step (2) above, using the previously calculated radius r of the yield cylinder of the test soil. i-2 and Until the calculation is as follows Figure 25 The r shown i-1 In each calculation, the stress state of the test soil at adjacent subsequent yielding cylindrical surfaces is divided into an elastic stage and various subsequent yielding stages, respectively, according to... Figure 25 The elastic modulus, which is adapted to the stress state of the yield surface, is used for calculation. Using the fact that the calculated and measured values ​​of the radial displacement of the test borehole sidewall are equal, an equation as shown in equation (16) is established. Equation (16) is solved to calculate the elastic modulus E selected for the i-th subsequent yield of the test soil. i .

[0205]

[0206] In the formula:

[0207] - The radial displacement value measured on the test borehole wall after the (i-1)th loading following the yielding of the test soil;

[0208] The meanings of other symbols in the formula are the same as before.

[0209] In the above-mentioned method for establishing a soil constitutive model through prototype testing, in the fifth or sixth step, when the radial displacement of the test borehole wall suddenly increases or an unacceptable displacement occurs under a single-stage loading, it can be determined that the soil has failed. The yield surface of the test borehole sidewall soil determined by the corresponding upper-level load can be used as the soil failure surface. That is, during the test, when the radial displacement of the test borehole sidewall soil suddenly increases or an unacceptable displacement occurs under a single-stage loading, it can be determined that the soil has failed. The yield surface of the test borehole sidewall soil determined by the corresponding upper-level load can be used as the soil failure surface. The soil failure criterion can be determined by referring to the method of determining the yield criterion. The soil failure surface can be constructed by calculating the principal stress state of multiple failure points of the same layer of soil. When the soil failure surface is assumed to be planar, the soil failure criterion can be expressed by equation (17).

[0210]

[0211] In the formula:

[0212] i * - The number of subsequent equal loading stages when the soil in the test borehole wall fails after the soil yields;

[0213] The meanings of other symbols in the formula are the same as before.

[0214] In this embodiment, according to as follows Figure 12 , Figure 21 , Figure 20 , Figure 13 , Figure 23 and Figure 24 The test data shown indicates that after the fourth layer of silt-clay reached its yield point, the lateral displacement of the deeper soil under the next loading stage suddenly increased significantly, exceeding five times the displacement generated by the previous load (calculated on an equal basis). From the perspective of deformation control, it can be determined that the soil has reached failure; therefore, the yield surface of this soil layer can be identified as the failure surface. The second and third layers of sandy silt (below 8.5m depth) and the fifth layer of clay (below 18m depth) did not show a sudden and significant increase in lateral displacement after yielding. However, soil work hardening occurred with increasing loading. According to... Figure 12 , Figure 14 , Figure 15 , Figure 18 , Figure 19 The test data shown indicates that, for the loose sandy silt layer ②3, after yielding under load, there was a phenomenon of compaction and increased stiffness of the loose sandy silt. In this embodiment, the changes in vertical displacement of the ground surface before and after the test were monitored, and the monitoring results showed that the changes in vertical displacement were not significant.

[0215] In the aforementioned method for establishing a soil constitutive model based on prototype tests, in step six, the loading and unloading conditions can be determined and calculation parameters selected as follows: Using steps two through six, an elastic zone, yield surface, successive yield surfaces at various levels, and failure surface are constructed in the stress space. The elastic parameters (E and v) required for soil elastoplastic calculation are tested, as well as the successive yield elastic modulus E corresponding to each yield surface before failure after yielding. i In the incremental method calculation process, firstly, the region corresponding to the stress state at the calculation point in the stress space (such as the elastic region, yield hardening region, or failure region) is determined, and the loading and unloading conditions are determined according to the following method:

[0216] (1) Place the current stress state of the calculated soil element in a three-dimensional stress space containing the soil yield surface and failure surface, and determine whether the region where the calculated element is located in the soil stress space is an elastic zone, a yield hardening zone or a failure zone.

[0217] (2) Assume that the soil element is under loading and select elastic calculation parameters that are appropriate for the region where the soil element is located in the stress space, or assume that the soil element is under unloading and use the soil elastic modulus E and the Poisson's ratio v under elastic conditions to perform the next step of calculation using the elastoplastic mechanical incremental method to calculate the stress state of the soil element after loading or unloading.

[0218] (3) Determine the relative position of the soil element stress state calculated in step (2) in the soil stress space. When the soil element stress state calculated in step (2) is closer to the soil element stress state after the soil test loading than the soil element stress state calculated in step (1), it is determined to be the loading process; otherwise, it is determined to be the unloading process.

[0219] Thus, a soil constitutive model is established based on prototype tests. The methods and apparatus used in this embodiment can be used as a reference in rock masses. This patent includes, but is not limited to, other similar methods and apparatus that can be used by those skilled in the art.

Claims

1. A method for establishing a soil constitutive model based on prototype tests, comprising the following steps: of a) Conduct prototype tests in soil using fluid contained in a sealed bag. This includes determining the maximum load, graded load, graded unloading, and radial displacement test requirements for single-stage loading and unloading based on the test objectives; determining the radial displacement stability criteria, termination loading criteria, and termination unloading criteria for single-stage loading and unloading; drilling test holes in the soil; constructing one or more inclinometer holes outside the test holes; placing the sealed bag in the test holes; filling the sealed bag with fluid to form a fluid column in the test holes; applying compressive stress to the sidewalls of the test holes using the sealed bag and the fluid inside; calculating the magnitude of the compressive stress; and ensuring that the graded loading and unloading requirements are met. After completing the loading and unloading, measure the lateral displacement of the test hole sidewalls and inclinometer holes at different depths of deep soil according to the radial displacement test requirements. b) Determine the soil elastic modulus and Poisson's ratio using one of the following two methods: The first method is to plot the relationship curve between the load measured in step a) and the lateral displacement of the deep soil at the same test point location, forming a hysteresis loop of the soil unloading and reloading rebound test curve, and using the circular hole expansion theory under elastic deformation conditions to calculate and determine the secant modulus of the corresponding test point as the elastic modulus of the test soil, and determine the soil Poisson's ratio using indoor tests or other tests or empirical methods; The second method is to set up one or more deep soil lateral displacement test points in the elastic deformation zone at different distances from the center of the test hole and test them simultaneously, making one or two elastic parameters of the soil elastic modulus and Poisson's ratio unknown, using the circular hole expansion theory to calculate the calculated value of the soil lateral displacement at the test point, and establishing an equation or a set of equations based on the equality of the calculated value and the measured value of the soil lateral displacement at the test point, and calculating the soil elastic modulus and Poisson's ratio by solving the equation or the set of equations, and calculating the elastic modulus E according to equation (1): In the formula: -Radial displacement of the test point in the elastic zone; Δp j -Difference in test loading; v - Tests the Poisson's ratio of the soil; E - Tests the elastic modulus of soil; r0 - radius of the test hole; R - Horizontal distance between the center of the test hole and the test point; c) Determine the distribution range of the yielding soil and the radial compressive stress at the boundary of the yielding soil corresponding to the first occurrence of soil yielding during the test using the following method: First, based on the elastic modulus and Poisson's ratio of the soil determined in step b), calculate the radial displacement values ​​of the test hole sidewall or inclinometer hole under each level of test loading in step a), according to the circular hole expansion theory; Second, compare the calculated radial displacement values ​​of the test hole wall or inclinometer hole calculated in step b) with the measured values ​​in step a). When the calculated value is less than the measured value, it is determined that the soil has yielded under the corresponding loading action. The third step involves assuming that the radius of the cylindrical surface at the boundary of the soil yield zone and the radial compressive stress at the yield cylinder surface are unknowns when the soil first yields. This cylindrical surface at the boundary of the soil yield zone is simply referred to as the yield cylinder surface. Based on the theory of circular hole expansion, the outer side of the yield cylinder surface remains an elastic body. The radius of the yield cylinder surface is taken as the radius of the equivalent loading test hole, and the radial compressive stress at the yield cylinder surface is taken as the equivalent circular hole test load. The deep lateral displacement of the soil at different distances from the center of the yield cylinder surface is calculated. A system of equations is established according to the principle of equality with the measured values. The system of equations is solved to calculate the radius of the yield cylinder surface and the radial compressive stress at its location. This third step is achieved through the following steps: (1) The radius of the first yield cylinder surface of the test soil is marked as r. E The corresponding test load is PF, and the corresponding principal stresses on the yield cylinder surface of the soil are {σ1, σ2, σ3}; after the first level of yield loading, the yield cylinder surface r E The soil between the test borehole and the soil mass is calculated as an elastic body with an elastic modulus of E1, and is represented by a cylindrical surface r. E As the boundary, cylindrical surface r E The soil other than that is calculated as an elastic body with an elastic modulus of E; (2) Using the two-dimensional circular hole expansion theory, establish equation (2) in the elastic region: In the formula: -Radial displacement of test points in the elastic zone when the test soil yields; r0 - Radius of the test loading hole; r E - Radius of the first yielding cylindrical surface; p E - Yielding cylindrical surface r E Radial additional stress generated by loading at the point; R j - The horizontal distance between the j-th inclinometer hole and the center of the test hole at the test point; The meanings of other symbols are the same as before; (3) Based on the experimental test values ​​of radial displacement at different points, p is solved using equation (2). E r E value; d) Establish the yield criterion of the soil according to the following method: Based on the radial compressive stress at the yield cylinder position determined in step c), determine that the soil inside the yield cylinder is in a plastic deformation state, and the soil outside the yield cylinder is in an elastic deformation state. Take the radial compressive stress at the yield cylinder position calculated in step c) as the major principal stress, the tangential compressive stress as the minor principal stress, and the vertical compressive stress as the intermediate principal stress. Take the principal stress state of the soil element at the yield cylinder position as the yield point in the soil yield surface. Construct the yield surface through the yield points. The specific method for constructing the yield surface from the yield points of soil elements is as follows: According to the elasticity solution of the circular hole expansion, the principal stress of the soil element outside the yield cylindrical surface is calculated as shown in equation (3): In the formula: σ1 - The principal stress in the principal stress space of the soil element; σ² - the middle principal stress in the principal stress space of a soil element; σ3 - Minor principal stress in the principal stress space of a soil element; σ r -Radial compressive stress at the yield cylindrical surface of the soil; σ z - Vertical compressive stress at the yield cylindrical surface of the soil; σ θ - Tangential compressive stress at the yield cylindrical surface of the soil; P0 is the earth pressure at rest. γ-Soil weight; h - Yield surface embedment depth; r - the distance from the calculated point of the soil on the outer side of the yield cylinder to the center of the test hole; r iE - Radius of the cylindrical surface at each yield point of the soil; The meanings of other symbols in the formula are the same as before; According to equation (3), based on the yield cylindrical surface r iE The stress state at the location yields equation (4): The meanings of the symbols in the formula are the same as before; Equation (4) represents a stress state when the soil yields during the bladder compression test, which is a point on the soil yield surface and a solution to the yield surface equation. The method to determine the soil yield surface is to use enough test points in the same layer of soil and fit them to form the soil yield surface. e) The first subsequent yield surface of the soil and the elastic modulus of the soil after the first yield required for calculation using the incremental plasticity method are determined as follows: According to the incremental plasticity method, let the elastic modulus used for the incremental calculation of the soil after yielding inside the yield cylinder determined in step c) be the unknown E1. After the test soil exhibits its first yield, the radius of the first yield cylinder is marked as r, with the first yield cylinder as the boundary. E The test soil is divided into a soil cylinder inside the yield cylinder and a soil outside the yield cylinder. The radial displacement of the test hole sidewall is calculated according to the Lamé equation. The calculated radial displacement of the test hole is equal to the measured value. The equation for calculating the lateral displacement of the test hole sidewall is established. The modulus used for elastic calculation after the first yield of the test soil is solved by solving the equation. The modulus used for elastic calculation after the first yield is called the first yield elastic calculation modulus and is marked as E1. The test loading amount corresponding to step d) is taken as the major principal stress and the overlying soil pressure stress is taken as the intermediate principal stress. The tangential normal stress of the soil test hole sidewall is calculated by the Lamé equation as the minor principal stress. According to step d), the first subsequent yield surface of the test soil is established. The specific method is as follows: According to the Lamé equation, the equation for calculating E1 is expressed as (7): In the formula: -Radial displacement at the first yielding cylindrical surface; The meanings of other symbols in the formula are the same as before; From equation (7), calculate the value of E1 according to equation (8) or (9): The meanings of the symbols in the formula are the same as before; The meanings of the symbols in the formula are the same as before; When the test soil is found to be yielding through inclinometer measurement, the soil on the test borehole wall is in a subsequent yielding state, serving as the first subsequent yielding cylindrical surface measured in the test. Subsequent loading tests will generate multiple more subsequent yielding cylindrical surfaces on the test borehole sidewall. Correspondingly, for equal-volume graded loading tests, the subsequent yielding loading amount [p]... F +(i-1)Δp], calculate the principal stress state of the subsequent yield cylinder surface using the Lamé equation, and establish the subsequent yield surface with reference to step d); f) For the subsequent yield surface and corresponding calculated elastic modulus of yield generated by subsequent graded test loading after the first subsequent yield cylindrical surface established in step e), the following method shall be used to determine: when the test soil begins to yield, the soil yields at a rate of r... E The cylindrical surface is the interface, r E The part outside the cylindrical surface is an elastic body, r E The area inside the cylindrical surface is the soil that has undergone its first yielding. Then, the process is carried out in the following steps: (1) Calculate the boundary cylindrical surface between the yield cylindrical surface of the test soil and the elastic body: After the first loading stage following soil yielding, soil yielding manifests in the following two aspects: First, the yield cylinder of the soil expands outward to r. 1E Cylindrical surface; secondly, in r 1E cylindrical surface and r E The soil between the cylindrical surfaces exhibits its first loading yield at r E A second yielding occurred within the cylindrical surface; assuming that at the r1 cylindrical surface, after soil yielding, the stress state after the second loading is the same as the stress state at the r0 cylindrical surface after the first yielding, let E1 be the stress state of the r1 cylindrical surface and r... 1E Soil modulus calculation between, r 1E The elastic modulus E is used for the soil outside the cylindrical surface, and E1 is used as the calculation modulus for the soil inside the cylindrical surface r1; and so on. For the second and subsequent equal-volume graded loading after the soil yields, following the above method, after the i-th (i = 2, 3, 4...) loading after the test soil yields, the yielded soil is divided into i adjacent cylindrical elements: from the outside to the inside, the outer diameter of each cylindrical element is r iE r1, r2, r3…r i-1 The inner diameters of each cylindrical unit are r1, r2, r3…r i-1 From the outside to the inside, the radial compressive stress on the outer surface of each cylindrical unit is p, r0; E p F p F +Δp、p F +2Δp…p F +(i-2)Δp; From the outside to the inside, the radial compressive stress on the inner surface of each cylindrical unit is successively p F p F +Δp、p F +2Δp…p F +(i-2)Δp、p F +(i-1)Δp; From the outside to the inside, the elastic modulus used in the incremental loading method for each cylindrical element is E1, E2, E3…E i-1 E i ; For r iE The elastic state of the soil on the outer side of the cylindrical surface is established by equation (11): In the formula: - The radial displacement of the test points in the elastic zone of the soil after the i-th (i = 2, 3, 4...) loading following the yielding of the test soil; r iE - The radius of the expanded yield cylinder after the i-th (i = 2, 3, 4...) loading of the test soil after it yields; R j -in r iE The horizontal distance between the test point of the inclinometer hole in the outer elastic zone soil and the centerline of the test hole; The meanings of other symbols are the same as before; The test was conducted using an inclinometer hole located in the elastic zone of the test soil. Substitute into equation (11) and solve for r using equation (12). iE value: The meanings of the symbols in the formula are the same as before; (2) Solve for the yield cylindrical surface r corresponding to the subsequent yield surface stress state according to the following steps. i : (A) Calculate r according to equation (12) iE ; (B) Calculate using formula (13) In the formula: - Radial displacement of the initial yield cylindrical surface position; The meanings of other symbols in the formula are the same as before; (C) For an outer diameter of r iE For a soil cylinder with an inner diameter of r1, calculate the yield cylindrical surface r using Lamé's equations and the incremental method in elastoplastic calculations. iE Displacement at point Establish the equation as shown in equation (14): In the formula: r1 - the radius of the first successor yield cylinder; E1 - The elastic modulus used for soil elasticity calculation when the test soil is in the stress state between the first yield surface and the first subsequent yield surface; The meanings of other symbols in the formula are the same as before; (D) Calculate the radius r1 of the cylindrical surface of the test soil after the first subsequent yield using formula (14); (E) For an outer diameter of r iE For a soil cylinder with an inner diameter of r1, the radial displacement at the first subsequent yielding cylindrical surface r1 is calculated using Equation (15) according to Lamé's equation: In the formula: -Radial displacement at the first subsequent yielding cylindrical surface r1; The meanings of other symbols in the formula are the same as before; (3) Calculate the elastic modulus E at the i-th subsequent yield. i : For other soil cylinders, repeat steps C) to E) of step (2) above, using the previously calculated radius r of the yield cylinder of the test soil. i-2 and Until r is calculated i-1 Each time, the stress state of the test soil at the adjacent subsequent yielding cylindrical surface is divided into an elastic stage and each subsequent yielding stage. The elastic modulus is calculated according to the stress state of the yielding surface. The calculated value of the radial displacement of the test hole sidewall is equal to the measured value. The equation shown in equation (16) is established. Equation (16) is solved to calculate the elastic modulus E selected for the i-th subsequent yielding of the test soil. i : In the formula: - The radial displacement value measured on the test borehole wall after the (i-1)th loading following the yielding of the test soil; The meanings of other symbols in the formula are the same as before.

2. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step d) above, it is assumed that the soil yield surface is a plane, and the yield surface is determined based on the yield point.

3. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step e) or f) above, it is assumed that the subsequent yield surface of the soil is a plane, and the subsequent yield surface is determined based on the yield point.

4. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step e) or f) above, when the test borehole wall experiences a sudden increase in radial displacement or an unacceptable amount of displacement under single-stage loading, the yield surface of the test borehole wall soil determined by the corresponding upper-stage loading is taken as the soil failure surface.

5. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step f) above, the loading and unloading conditions are determined and the calculation parameters are selected according to the following method: Using steps b) to f), an elastic zone, yield surface, successive yield surfaces at each level, and failure surface are constructed in the stress space. The stress space of the test soil unit is divided into three regions: elastic zone, yield hardening zone, and failure zone. The elastic parameters required for the incremental method of soil elastic-plasticity calculation and the successive yield elastic modulus of each yield surface before failure after yielding are tested. In the incremental method calculation process, firstly, the region corresponding to the stress state of the calculation unit in the stress space is determined. The loading and unloading conditions are determined according to the following method: First step, based on the current principal stress state of the calculation unit; The second step is to place the current stress state of the calculation unit in a three-dimensional stress space containing the soil yield surface, subsequent yield surface, and failure surface. When the calculation point is in the yield hardening region, the yield surface where the stress state of the calculation unit is located is further determined. The third step is to assume that the calculation unit is in either a loading or unloading state, and to perform the next calculation using the incremental method. The subsequent yield elastic modulus is selected for loading calculation, or the soil elastic modulus is selected for unloading calculation. The principal stress state of the soil unit is calculated, and the first step is repeated. The fourth step is to determine the relative position of the principal stress state of the soil unit calculated in the third step and the principal stress state of the soil unit calculated in the first step in the soil stress space. When the principal stress state of the soil unit calculated in the third step is closer to the next yield surface of the soil test loading than the principal stress state of the soil unit calculated in the first step, it is determined to be a loading process. Conversely, if the result is determined to be an unloading process, the calculation is valid if the result of this step is consistent with the assumptions of the loading or unloading calculation in the third step; otherwise, the assumptions of the calculation in the third step are changed and the calculation is repeated.

6. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step a) above, graded loading, graded unloading, and graded loading are completed in the soil, and the lateral displacement of the test hole sidewall and the deep soil at the test point is measured simultaneously, and the soil unloading and reloading rebound test is carried out.

7. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step a) above, an inclinometer hole is set inside the test hole, and the radial displacement of the sidewall of the test hole is measured through the inclinometer hole.

8. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step a) above, a slant hole with the function of measuring the deep lateral displacement of the soil is constructed near the test hole. The deep lateral displacement of the soil in the slant hole is measured simultaneously. The horizontal distance between the test hole and the slant hole on each horizontal plane is calculated by measuring the inclination of the test hole and the distance between the hole openings.

9. The method for establishing a soil constitutive model based on prototype tests according to claim 1, characterized in that... In step a) above, the difference in the test values ​​of the sidewall displacement of the test hole under different seepage path conditions in the same soil layer is used to calculate the soil deformation and time correlation parameters.

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