Sandy gravel soil mechanical behavior analysis method based on energy dissipation theory

Abstract

The invention discloses a sandy gravel soil mechanical behavior analysis method based on an energy dissipation theory. The method comprises the following steps: establishing a biaxial compression numerical model of sandy gravel soil based on an elliptical block stone shape; carrying out a biaxial compression numerical test under a certain confining pressure by adopting given mechanical parameters of rock blocks and soil matrixes; and analyzing the stress-strain behavior and the energy evolution mechanism of the sandy gravel soil in the whole process of the biaxial compression numerical test. The method has the advantages that the energy dissipation theory is introduced into the biaxial compression numerical value test of the sandy cobble soil, the influence of the random structure in the sandy cobble soil on the overall stress-strain behavior can be known more clearly, and the deformation and damage process of the sandy cobble soil can be explained from the angle of energy.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering, in particular to a method for analyzing the mechanical behavior of sand and gravel soil based on energy dissipation theory. Background Art

[0002] At present, energy dissipation theory is widely used in the crack generation, crack propagation, internal damage and progressive failure process of loaded rocks, but it is rarely used in sandy and gravel formations.

[0003] Therefore, a method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory is needed in order to more clearly understand the influence of the internal random structure of sandy gravel soil on its overall stress-strain behavior. Summary of the invention

[0004] The purpose of the present invention is to provide a method for analyzing the mechanical behavior of gravel soil based on energy dissipation theory in accordance with the above-mentioned deficiencies of the prior art, and to introduce the energy dissipation theory into the biaxial compression numerical test of gravel soil, so as to more clearly understand the influence of the internal random structure of gravel soil on its overall stress-strain behavior, and to explain its deformation and failure process from the perspective of energy. When performing numerical simulation, the energy change of each unit in the numerical model within the incremental time step △t can be calculated first, and the energy value of each unit in the current state can be accumulated, and then the energy values ​​of all units can be summed up and divided by the volume of the numerical model to obtain the energy value of the unit volume numerical model in the current state, that is, the energy density.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory, characterized in that the method comprises:

[0007] (S1) A biaxial compression numerical model of sandy gravel soil was established based on the elliptical block shape;

[0008] (S2) Using the given mechanical parameters of the rock mass and soil matrix, numerical biaxial compression tests under certain confining pressure are carried out;

[0009] (S3) Analyze the stress-strain behavior and energy evolution mechanism of sandy gravel soil during the entire biaxial compression numerical test.

[0010] In step S1:

[0011] The part of the gravel stratum with a particle size less than 20 mm is regarded as the soil matrix, and all the block stone particle size intervals of the gravel stratum are divided into 5 groups, and the equivalent block stone particle sizes of each block stone particle size interval are 150 mm, 90 mm, 70 mm, 50 mm and 30 mm respectively;

[0012] During numerical simulation, a displacement boundary condition with a fixed normal direction is applied to the bottom of the biaxial compression numerical model, and a stress boundary condition with a magnitude equal to the confining pressure is applied to both sides of the biaxial compression numerical model.

[0013] In step S2:

[0014] According to the indoor test results, the parameters of numerical simulation are calibrated;

[0015] Among them, the controlled variable method was used to carry out a series of biaxial compression numerical test simulations to study the influence of elastic modulus and internal friction angle on the stress-strain behavior of sandy gravel soil; repeated tests were carried out through the trial and error method, and the elastic modulus and internal friction angle of the soil matrix were calibrated one by one, so that the stress-strain curve obtained by numerical simulation was consistent with the indoor test results.

[0016] In step S3:

[0017] When the volume stone content VBP of the sandy gravel soil is 50%, the stress-strain curve and energy evolution process of the sandy gravel soil are obtained through the biaxial compression numerical test;

[0018] The stress-strain curve of the sandy gravel soil has no peak point and exhibits strain hardening characteristics;

[0019] Based on the energy dissipation theory, the total strain energy U absorbed during the biaxial compression numerical test and the releasable elastic strain energy U are obtained. e and irreversible dissipated energy U d According to the evolution law of the energy evolution process of the sandy gravel soil, the entire biaxial compression numerical test process can be divided into three stages:

[0020] Stage I: As the total strain energy U increases, the elastic strain energy U e Rapidly increase from zero, dissipated energy U d The total strain energy U absorbed by the biaxial compression numerical model is completely converted into releasable elastic strain energy U e Stored, elastic strain energy accounts for U e / U is 1.0, and the dissipated energy accounts for U d / U is zero, no plastic deformation occurs, and the stress-strain relationship is approximately linear elastic;

[0021] Stage II: As the total strain energy U increases, the elastic strain energy U e Continues to increase, but the rate of increase gradually slows down, and its proportion in the total strain energy U decreases sharply; at the same time, the dissipated energy U d Rapidly increases, and the rate of increase gradually accelerates, and the proportion of dissipated energy in the total strain energy U also increases sharply, but the proportion of dissipated energy in U d / U is still less than the elastic strain energy ratio U e / U, elastic strain energy U e Still dominant; in this stage, most of the soil matrix units in the biaxial compression numerical model dissipate energy to produce irreversible plastic deformation, and the plastic deformation develops rapidly, the axial stress increases rapidly, and the stress-strain relationship is nonlinear;

[0022] Stage III: As the total strain energy U increases, the elastic strain energy U e Although it is still increasing, the growth rate is very slow, and its proportion in the total strain energy U is gradually decreasing; at the same time, the dissipated energy U d The proportion of dissipated energy in the total strain energy U also increases sharply, and the proportion of dissipated energy in the total strain energy U d / U is greater than the elastic strain energy ratio U e / U, dissipated energy U d It occupies a dominant position; in this stage, the number of units producing plastic deformation of the soil matrix in the biaxial compression numerical model further increases, the stress increases slowly, and the strain increases rapidly.

[0023] The invention has the advantages of introducing the energy dissipation theory into the biaxial compression numerical test of sandy gravel soil, being able to more clearly understand the influence of the internal random structure of sandy gravel soil on its overall stress-strain behavior, and explaining its deformation and failure process from the energy perspective. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the stress-strain behavior and energy evolution mechanism of sandy gravel soil of the present invention;

[0025] Figure 2 It is the plastic zone distribution diagram of the present invention;

[0026] Figure 3 for Figure 1 A partial enlarged view of

[0027] Figure 4 It is a schematic diagram of the elastic strain energy ratio and the dissipated energy ratio of the present invention. DETAILED DESCRIPTION

[0028] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:

[0029] Example: Figures 1 to 4 As shown, this embodiment relates to a method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory, which mainly includes:

[0030] (S1) A biaxial compression numerical model of sandy gravel soil is established based on the elliptical block shape.

[0031] Among them, the part of the gravel stratum with a particle size less than 20 mm is regarded as the soil matrix, and the minimum block particle size of the gravel stratum is 20 mm, and the maximum block particle size is 200 mm. The entire block particle size range is divided into 5 groups, namely [200mm, 100mm], [100mm, 80mm], [80mm, 60mm], [60mm, 40mm] and [40mm, 20mm]. The equivalent block particle sizes of each block particle size range are 150mm, 90mm, 70mm, 50mm and 30mm respectively. The diameter of the triaxial specimen should not be less than 5 times the maximum particle size, and the specimen height should be 2 to 2.5 times the specimen diameter. Therefore, the size of the biaxial compression numerical test can be taken as 1.0m×2.0m. The thickness direction of the model is set to 0.01m to simulate the plane strain condition.

[0032] During numerical simulation, a displacement boundary condition with a fixed normal direction is applied to the bottom of the model, and a stress boundary condition with a magnitude equal to the confining pressure is applied to both sides of the model. A stress boundary condition with a magnitude equal to the confining pressure is first applied to the top of the model to achieve equilibrium, and then a displacement boundary condition is applied for strain-controlled loading, and the simulation is performed according to the plane strain problem. The peak point of the stress-strain curve is taken as the failure point. If the stress-strain curve has no peak, the principal stress difference corresponding to an axial strain of 15% is taken as the failure strength value.

[0033] (S2) Using the given mechanical parameters of the rock mass and soil matrix, numerical biaxial compression tests under certain confining pressure are carried out.

[0034] Among them, the parameters of numerical simulation are calibrated according to the results of indoor tests. The effect of soil-rock interface is not considered for the time being. It is assumed that both soil matrix and block rock obey the Mohr-Coulomb model in numerical simulation. In fact, friction slip at soil-rock interface is a factor affecting energy dissipation during biaxial compression. However, the development of shear path is closely related to the strength of soil matrix and soil-rock interface. When the strength of soil matrix is ​​greater than the strength of soil-rock interface, the shear path develops in soil matrix; on the contrary, when the strength of soil matrix is ​​less than the strength of soil-rock interface, the shear path develops along soil-rock interface. It can be seen that the mechanical parameters of soil matrix and soil-rock interface have a great influence on the overall mechanical behavior and energy evolution characteristics of gravel soil. However, for the three-component material composed of soil matrix, soil-rock interface and block rock, how to reasonably calibrate their respective parameters is a huge challenge. Therefore, the influence of soil-rock interface is not considered here for the time being. The soil matrix and soil-rock interface are regarded as a whole, and only the influence of the difference in mechanical properties between soil matrix and block rock on the overall mechanical behavior is concerned.

[0035] Since individual pebbles are generally hard, have a monolithic or blocky structure, and have high uniaxial compressive strength, according to the surrounding rock classification method, the pebbles can be qualitatively classified as Class II surrounding rock, and the basic physical and mechanical parameters of the pebbles can be obtained by looking up the table. On the other hand, since the critical size of the pebbles and the soil matrix is ​​20 mm, the soil matrix should be a mixture of sand and small-size gravel. According to the classification method of gravel soil, the soil matrix can be qualitatively classified as Class V surrounding rock, and the density and Poisson's ratio of the soil matrix can be obtained by looking up the table. In addition, since the clay content in sandy and gravel soil is generally low, the cohesion of the soil matrix is ​​assumed to be zero. Finally, through parameter inversion, the elastic modulus and internal friction angle of the soil matrix, which have a greater impact on the overall mechanical properties of sandy and gravel soil, are calibrated. The calibration process is as follows: Using the control variable method, a series of biaxial compression numerical simulations are carried out to study the influence of elastic modulus and internal friction angle on the stress-strain behavior of sandy gravel soil. The results show that when the deviator stress increment is constant, the overall strength of sandy gravel soil increases with the increase of the internal friction angle of the soil matrix, while the axial strain increment decreases with the increase of the elastic modulus of the soil matrix, that is, the larger the elastic modulus, the steeper the stress-strain curve. Then, through repeated tests by trial and error, the elastic modulus and internal friction angle of the soil matrix are calibrated one by one, so that the stress-strain curve obtained by numerical simulation is consistent with the indoor test results.

[0036] (S3) Analyze the stress-strain behavior and energy evolution mechanism of sandy gravel soil during the entire biaxial compression numerical test.

[0037] Among them, Figures 1 to 3 As shown in the figure, taking the volume stone content VBP = 50% of sandy gravel soil as an example, the typical stress-strain curve and energy evolution process obtained from the biaxial compression numerical test of sandy gravel soil can be obtained. It can be seen that the stress-strain curve of sandy gravel soil has no peak point and shows strain hardening characteristics. At the same time, based on the energy dissipation theory, the total strain energy U absorbed during the biaxial compression process and the releasable elastic strain energy U e and irreversible dissipated energy U d The evolution law of Figure 4 As shown in the figure, the elastic strain energy ratio (U e / U) and dissipated energy ratio (U d / U) situation. According to the energy evolution process, the entire biaxial compression process can be divided into three stages:

[0038] In the first stage of loading (OA segment): With the increase of total strain energy, elastic strain energy increases rapidly from zero, dissipated energy remains zero and remains unchanged, the total strain energy absorbed by the numerical model is completely converted into releasable elastic strain energy and stored, the elastic strain energy accounts for 1.0, the dissipated energy accounts for zero, no plastic deformation occurs, and the stress-strain relationship is approximately linear elastic. When the stress-strain curve reaches point A, the soil matrix unit in the numerical model yields and begins to produce plastic deformation.

[0039] In the second stage of loading (segment AB): With the increase of total strain energy, elastic strain energy continues to increase, but the rate of increase gradually slows down, and its proportion in the total strain energy decreases sharply; at the same time, dissipated energy increases rapidly, and the rate of increase gradually accelerates, and its proportion in the total strain energy also increases sharply, but the proportion of dissipated energy is still less than that of elastic strain energy, and elastic strain energy still dominates; in this stage, most of the soil matrix units in the numerical model dissipate energy to produce irreversible plastic deformation, and the plastic deformation develops rapidly, the axial stress increases rapidly, and the stress-strain relationship is nonlinear. When the stress-strain curve reaches point B, the elastic strain energy is equal to the dissipated energy, and most of the soil matrix units have plastic deformation, and because the mechanical parameters between the block stone and the soil matrix are quite different, the block stone basically maintains elastic behavior, and the plastic zone develops "around the stone".

[0040] In the loading stage III (BC section): With the increase of total strain energy, although the elastic strain energy continues to increase, the growth rate is very slow, and the proportion of total strain energy gradually decreases; at the same time, the dissipated energy increases sharply, and the proportion of total strain energy also gradually increases, and the proportion of dissipated energy is greater than that of elastic strain energy, and dissipated energy occupies a dominant position; in this stage, the number of units in the soil matrix that produce plastic deformation in the numerical model increases further, the stress increases slowly, and the strain increases rapidly. When the stress-strain curve reaches point C, almost all soil matrix units enter the plastic state, the axial strain reaches 15%, and the axial stress reaches the failure strength value, but at this time most of the block rock units are still in the elastic state, and the phenomenon of "around stone" development in the failure zone is significant; finally, the elastic strain energy of the entire model accounts for about 0.15, and the dissipated energy accounts for about 0.85, and the dissipated energy accounts for much more than the elastic strain energy.

[0041] Specifically, the essence of material destruction is an instability phenomenon driven by energy. Studying and establishing the law of energy change in the process of rock and soil destruction will help us understand the deformation and destruction process of rock and soil more clearly. From the perspective of energy, the deformation and destruction process of rock and soil under the action of external forces is a process of energy input, accumulation, dissipation and release. Assuming that a unit volume of rock and soil unit is deformed under the action of external forces, and there is no heat exchange with the external environment in this process, then according to the first law of thermodynamics, the following relationship exists:

[0042] U=U e +U d ;

[0043] Where U represents the total input energy generated by the external force doing work on the rock and soil unit, that is, the total strain energy of the rock and soil unit; U e It represents the releasable elastic strain energy accumulated inside the rock and soil unit, which is bidirectionally reversible under certain conditions; U d It indicates the energy dissipated when damage and plastic deformation occur inside the rock and soil unit, which is unidirectional and irreversible. It is worth noting that the three energies here are actually energy density, and the unit is kJ / m 3 .

[0044] In the principal stress space, the total strain energy U and elastic strain energy U per unit volume of soil element are e The calculation formula is as follows:

[0045]

[0046] and

[0047]

[0048] in, is the elastic strain in the three principal stress directions. According to the generalized Hooke's law, its calculation formula is as follows:

[0049]

[0050] Among them, E i and μ i (i=1,2,3) are the unloading elastic modulus and unloading Poisson’s ratio respectively. For the convenience of calculation, they can be approximately taken as the initial elastic modulus and Poisson’s ratio.

[0051] The beneficial technical effect of this embodiment is that the energy dissipation theory is introduced into the biaxial compression numerical test of sandy gravel soil, which can more clearly understand the influence of the internal random structure of sandy gravel soil on its overall stress-strain behavior and explain its deformation and failure process from the perspective of energy.

[0052] Although the above embodiments have described in detail the concepts and embodiments of the present invention with reference to the accompanying drawings, ordinary technicians in this field can recognize that various improvements and changes can still be made to the present invention without departing from the scope of the claims, so they are not described one by one here.

Claims

1. A method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory, characterized in that The method comprises: (S1) A biaxial compression numerical model of sandy gravel soil is established based on the elliptical block shape; (S2) Using the given mechanical parameters of the rock mass and soil matrix, numerical biaxial compression tests are carried out under a certain confining pressure; (S3) Analyze the stress-strain behavior and energy evolution mechanism of sandy gravel soil during the entire biaxial compression numerical test.

2. A method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory as claimed in claim 1, characterized in that In step S1: The part of the sandy gravel stratum with a particle size less than 20 mm is regarded as the soil matrix, and all the block stone particle size intervals of the sandy gravel stratum are divided into 5 groups, and the equivalent block stone particle sizes of each block stone particle size interval are 150 mm, 90 mm, 70 mm, 50 mm and 30 mm respectively; During numerical simulation, a displacement boundary condition with a fixed normal direction is applied to the bottom of the biaxial compression numerical model, and a stress boundary condition with a magnitude equal to the confining pressure is applied to both sides of the biaxial compression numerical model.

3. A method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory as claimed in claim 2, characterized in that In step S2: According to the indoor test results, the parameters of numerical simulation are calibrated; Among them, the controlled variable method was used to carry out a series of biaxial compression numerical test simulations to study the influence of elastic modulus and internal friction angle on the stress-strain behavior of sandy gravel soil; repeated tests were carried out through the trial and error method, and the elastic modulus and internal friction angle of the soil matrix were calibrated one by one, so that the stress-strain curve obtained by numerical simulation was consistent with the indoor test results.

4. A method for analyzing the mechanical behavior of sandy gravel soil based on energy dissipation theory as claimed in claim 3, characterized in that In step S3: When the volume content of the sandy gravel soil is VBP =50%, the stress-strain curve and energy evolution process of the sandy gravel soil are obtained through the biaxial compression numerical test; The stress-strain curve of the sandy gravel soil has no peak point and exhibits strain hardening characteristics; Based on the energy dissipation theory, the total strain energy absorbed during the biaxial compression numerical test was obtained. U , releasable elastic strain energy U e and irreversible dissipation energy U d According to the evolution law of the energy evolution process of the sandy gravel soil, the entire biaxial compression numerical test process can be divided into three stages: Phase I: With the total strain energy U The increase in elastic strain energy U e Rapidly increase from zero, dissipating energy U d The total strain energy absorbed by the biaxial compression numerical model is U All converted into releasable elastic strain energy U e Stored, elastic strain energy accounts for U e / U is 1.0, the dissipated energy accounts for U d / U When it is zero, there is no plastic deformation and the stress-strain relationship is approximately linear elastic. Phase II: With the total strain energy U The increase in elastic strain energy U e Continue to increase, but the rate of increase gradually slows down, and in the total strain energy U The proportion of energy dissipation decreases sharply; at the same time, U d Rapidly increases, and the speed of increase gradually accelerates. U The proportion of dissipated energy also increases sharply, but the proportion of U d / U Still less than the elastic strain energy U e / U , elastic strain energy U e Still dominant; in this stage, most of the soil matrix units in the biaxial compression numerical model dissipate energy to produce irreversible plastic deformation, and the plastic deformation develops rapidly, the axial stress increases rapidly, and the stress-strain relationship is nonlinear; Stage III: With the total strain energy U The increase in elastic strain energy U e Although it is still increasing, the growth rate is very slow. U The proportion of dissipated energy gradually decreases; at the same time, U d The total strain energy increases sharply. U The proportion of dissipated energy is also gradually increasing, and the proportion of dissipated energy is U d / U Greater than the elastic strain energy ratio U e / U , dissipated energy U d It occupies a dominant position; in this stage, the number of units producing plastic deformation of the soil matrix in the biaxial compression numerical model further increases, the stress increases slowly, and the strain increases rapidly.

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