Round gravel soil constitutive model construction method and system

Abstract

The invention relates to the technical field of geotechnical engineering and geomechanics, in particular to a round gravel soil constitutive model construction method and system. The method comprises the following steps: performing a triaxial consolidation drainage experiment on round gravel soil to obtain mechanical test data of the round gravel soil; according to the mechanical test data, the Duncan-Chang model is improved; and based on the improved Duncan-Chang model, constructing a roundstone soil constitutive model. According to the method, by improving the curvilinear relation between the axial strain and the lateral strain of the Duncan-Chang model, the volume strain and the tangent Poisson's ratio, the applicability of the Duncan-Chang model to the round gravel soil is improved, and the problem that under the combined action of mountainous area alluviation and lacustrine facies deposition on the rushing-lacustrine round gravel soil, the model is difficult to deform is solved. The problem that an existing constitutive model cannot accurately describe the mechanical behavior of round gravel soil is solved.

Description

Technical Field

[0001] The present invention relates to the technical fields of geotechnical engineering and geomechanics, and particularly relates to a method and system for constructing a constitutive model of cobble soil. Background Art

[0002] Cobble soil is widely distributed in various regions of China. With the continuous development of infrastructure construction in China, more and more projects are built on cobble soil layers. The safety and stability of engineering construction often depend on the mechanical properties of the soil. Due to the large differences in the formation processes of cobble soil layers in different regions, the properties of cobble soil are different, so it is impossible to use the same constitutive model to describe the mechanical behaviors of cobble soil in different regions. The constitutive model is the key to describing the stress-strain relationship of soil. An accurate constitutive model is of great significance for the design, analysis, and prediction of geotechnical engineering, and is crucial in the analysis of foundation pit stability problems.

[0003] Regarding the research on the constitutive model of soil, since the Cambridge model was proposed, it has developed rapidly. Now there are hundreds of constitutive models. The differences between the models are huge. How to select a suitable constitutive model according to the properties of the soil for the analysis of engineering stability problems has also become the focus of research.

[0004] Currently, common constitutive models such as the Duncan-Chang model can be applied to most soils, but usually, its parameters need to be specifically corrected to reflect the mechanical properties of specific soils in a certain region. For this reason, many scholars at home and abroad have carried out a large number of studies on the correction of constitutive models according to the characteristics of the soil. For example, for fine-grained soil, some scholars have conducted a large number of experiments on the constitutive model of hydrated sediments in the South China Sea, and combined with the existing constitutive models of soil to derive a corrected model reflecting the hydrated sediments in the South China Sea.

[0005] The Duncan-Chang constitutive model has strong applicability. However, due to the combined action of mountain alluvial and lacustrine sedimentation on the alluvial-lacustrine cobble soil, there are significant differences from other regions, and its material properties are relatively more complex. The Duncan-Chang constitutive model also has certain limitations, such as not considering the influence of factors such as disturbance and soil deposition history on the physical and mechanical parameters of the soil during analysis. Therefore, constructing a suitable constitutive model for alluvial-lacustrine cobble soil to solve the problem that the existing constitutive models cannot accurately describe the mechanical behavior of cobble soil under the combined action of mountain alluvial and lacustrine sedimentation is an urgent problem to be solved at present. Summary of the Invention

[0006] In view of the deficiencies of the existing methods and the requirements of practical applications, in order to improve the applicability of alluvial-lacustrine cobble soil and solve the problem that the existing constitutive models cannot accurately describe the mechanical behavior of cobble soil under the combined action of mountain alluvial and lacustrine sedimentation. On the one hand, the present invention provides a method for constructing a constitutive model of cobble soil, including the following steps: Perform a triaxial consolidated drained test on the cobble soil to obtain the mechanical test data of the cobble soil; improve the Duncan-Chang model according to the mechanical test data; construct a constitutive model of the cobble soil based on the improved Duncan-Chang model. By improving the curve relationship between the axial strain and the lateral strain, and the volumetric strain and the tangent Poisson's ratio of the Duncan-Chang model, the present invention improves the applicability of the Duncan-Chang model to the cobble soil, and solves the problem that the existing constitutive model cannot accurately describe the mechanical behavior of the cobble soil under the combined action of alluvial and lacustrine deposits in mountainous areas.

[0007] Optionally, the improvement of the Duncan-Chang model according to the mechanical test data includes the following steps: Improve the curve relationship between the axial strain and the lateral strain; improve the volumetric strain; improve the tangent Poisson's ratio.

[0008] Optionally, the improvement of the curve relationship between the axial strain and the lateral strain satisfies the following formula: Wherein, represents the axial strain, represents the first fitting parameter, represents the second fitting parameter, represents the lateral strain. By improving the curve relationship between the axial strain and the lateral strain, the present invention replaces the hyperbolic relationship between the axial strain and the lateral strain of the conventional Duncan-Chang model, which is beneficial to improving the applicability of the present invention to the alluvial-lacustrine cobble soil.

[0009] Optionally, the improvement of the volumetric strain satisfies the following formula: Wherein, represents the improved volumetric strain, represents the axial strain, represents the lateral strain, represents the first fitting parameter, represents the second fitting parameter. By improving the volumetric strain, the present invention accurately reflects the shear contraction law of the alluvial-lacustrine cobble soil, and further improves the applicability to the alluvial-lacustrine cobble soil.

[0010] Optionally, the improvement of the tangent Poisson's ratio satisfies the following formula: Wherein, represents the tangent Poisson's ratio, represents the axial strain, represents the lateral strain, represents the first fitting parameter, Represents the second fitting parameter. By improving the tangent Poisson's ratio, the present invention further improves the applicability to alluvial and lacustrine gravelly soil.

[0011] Optionally, the first fitting parameter satisfies the following formula: Where, Represents the first fitting parameter, Represents the linear parameter, Represents the confining pressure, Represents the standard atmospheric pressure.

[0012] Optionally, the second fitting parameter satisfies the following formula: Where, Represents the second fitting parameter, Represents the confining pressure, Represents the standard atmospheric pressure.

[0013] Optionally, the improved Duncan-Chang model satisfies the following formula: Where, Represents the elastic modulus, 、 Represents the test constant, Represents the confining pressure, Represents the standard atmospheric pressure, Represents the failure ratio, Represents the axial stress, Represents the internal friction angle, Represents the cohesion.

[0014] Optionally, the test constant satisfies the following formula: Where, Represents the initial elastic modulus, Represents the standard atmospheric pressure, Represents the confining pressure, 、 Represents the test constant.

[0015] Second aspect, to efficiently execute a method for constructing a constitutive model of cobble soil provided by the present invention, the present invention further provides a system for constructing a constitutive model of cobble soil, including a processor, an input device, an output device, and a memory. The processor, the input device, the output device, and the memory are interconnected. Among them, the memory is used to store a computer program, and the computer program includes program instructions. The processor is configured to call the program instructions to execute a method for constructing a constitutive model of cobble soil as described in the first aspect of the present invention. The system for constructing a constitutive model of cobble soil of the present invention has a compact structure and stable performance, and can stably execute a method for constructing a constitutive model of cobble soil provided by the present invention, further improving the overall applicability and practical application ability of the present invention. Description of the Drawings

[0016] Figure 1 It is a flowchart of a method for constructing a constitutive model of cobble soil provided by an embodiment of the present invention; Figure 2 It is a comparison chart of measured and calculated curves of volumetric strain under different confining pressures; Figure 3 It is a curve graph of the relationship between lateral strain and axial strain under different confining pressures; Figure 4 It is a framework diagram of a system for constructing a constitutive model of cobble soil provided by an embodiment of the present invention. Detailed Embodiments

[0017] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described here are only for illustrative purposes and do not limit the present invention. In the following description, in order to provide a thorough understanding of the present invention, a large number of specific details are set forth. However, it is obvious to those of ordinary skill in the art that the present invention does not have to employ these specific details. In other instances, well-known circuits, software, or methods have not been described in detail to avoid obscuring the present invention.

[0018] Throughout the specification, the reference to "one embodiment", "an embodiment", "one example", or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment", "in an embodiment", "one example", or "an example" appearing throughout the specification do not necessarily all refer to the same embodiment or example. In addition, the specific features, structures, or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. In addition, those of ordinary skill in the art should understand that the drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0019] Please refer to Figure 1, in order to improve the applicability of alluvial-lacustrine cobble soil and solve the problem that the existing constitutive model cannot accurately describe the mechanical behavior of cobble soil under the combined action of mountain alluvial and lacustrine sedimentation, the present invention provides a method for constructing a constitutive model of cobble soil, as Figure 1 shown. In one embodiment, the method includes the following steps: S1. Conduct a triaxial consolidated drained test on the cobble soil to obtain the mechanical test data of the cobble soil.

[0020] In the embodiment, the foundation pit of a water purification plant in Kunming is located in the northern urban area of Kunming. According to the geological exploration report, the site is a typical alluvial-lacustrine stratum, and 85% of the exposed strata are cobble strata.

[0021] Furthermore, samples of cobble soil are taken from the bottom of the center of the foundation pit. After air-drying and sieving, the proportion of particles with a particle size greater than 60 mm in the soil sample is 0.48%. Considering that the maximum allowable particle size of the test instrument cannot be greater than 60 mm, the oversize soil sample is scaled down according to the "Standard for Geotechnical Test Methods" (GB / T 50123-2019).

[0022] The experimental instrument uses a DJSZ-150 large-scale coarse-grained soil dynamic and static triaxial testing machine. The allowable sample size for the experiment is 300×600 mm, the maximum axial load is 1500 kN, and the maximum confining pressure can reach 3.0 MPa. The testing machine can automatically test parameters such as axial stress, strain, confining pressure, pore pressure, sample volume change, saturated water inflow, and consolidated drainage volume.

[0023] Furthermore, the experimental conditions during the triaxial experiment are controlled as consolidated drainage, and the confining pressures in the experiment are designed as 100 kPa, 200 kPa, 300 kPa, and 400 kPa respectively.

[0024] Further, remold the soil sample according to the particle size distribution, wet density, and water content. The amount of soil filled is determined according to the size and density of the sample cylinder. The experiment is carried out in 5 times, and equal amounts of soil samples are filled in separately, covered with filter paper, permeable plate, and pressure cap. Tie the rubber membrane and fix it on the pressure cap, evacuate to the sample cylinder does not fall over, and carry out subsequent operations after half an hour. After the sample preparation is completed, use the lifting equipment in the laboratory to lift the pressure chamber above the sample, lower the pressure chamber until it contacts the base, fasten the pressure chamber and the base, and start to fill the pressure chamber with water until it is full. Open the saturated water inlet valve and the vacuum valve. After two bottles of water are filled in the suction flask, close the vacuum valve and the vacuum pump, and open the upper drain valve to saturate the sample for 18 to 24 hours (the pore pressure coefficient B is greater than or equal to 0.95). During consolidation, turn on the testing machine, apply the confining pressure of the experiment, open the upper and lower drain valves of the testing machine, and observe the curve relationship between the drainage volume and time during consolidation until it reaches a stable state. After the sample consolidation is completed, set the loading rate and automatically load until the compression displacement of the sample reaches 15% of the sample height. Save the experimental data, push out the pressure chamber, lift off the pressure chamber and take pictures, remove the rubber mold, and unload the soil sample.

[0025] S2. Improve the Duncan-Chang model according to the mechanical test data.

[0026] Specifically, the improvement of the Duncan-Chang model according to the mechanical test data includes the following steps: S21. Improve the curve relationship between axial strain and lateral strain.

[0027] In the embodiment, the improvement of the curve relationship between axial strain and lateral strain satisfies the following formula: Among them, represents axial strain, represents the first fitting parameter, represents the second fitting parameter, represents lateral strain.

[0028] In the embodiment, the above formula is used to process the triaxial test data of cobble soil. Through the fitting analysis of the processed data, it can be seen that the fitting correlation coefficient R 2 is 0.9998 under different confining pressures, all greater than 0.97, and the fitting result has a high degree of coincidence with the calculation result, indicating that the improvement method can well replace the hyperbolic relationship between axial strain and lateral strain of the Duncan-Chang model.

[0029] S22. Improve the volumetric strain.

[0030] Specifically, the improvement of the volumetric strain satisfies the following formula: Among them, denotes the improved volumetric strain, denotes the axial strain, denotes the lateral strain, denotes the first fitting parameter, denotes the second fitting parameter.

[0031] Taking as an unknown to solve the equation, we get: It can be understood that the expression obtained by solving improves the theoretical derivation process of the volumetric strain formula, making the theoretical logic of the improvement of the entire constitutive model more rigorous.

[0032] In practical applications, when the axial strain and the fitting parameters L and T are known, the lateral strain can be accurately calculated using this formula. Furthermore, the volumetric strain can be calculated according to the volumetric strain formula, which is crucial for accurately describing the deformation characteristics of cobble soil under different stress states and helps to more precisely construct the constitutive model of cobble soil.

[0033] Please refer to Figure 2 to compare and analyze the relationship curve between the original volumetric strain and axial strain and the curve calculated by the improved volumetric strain calculation formula. From Figure 2 it can be seen that the fitting curve calculated using the improved volumetric strain formula is relatively close to the measured value of the volumetric strain. The variation law of the curve is the same as the measured result, and it can more accurately reflect the shear contraction law of alluvial cobble soil.

[0034] S23. Improve the tangent Poisson's ratio.

[0035] Specifically, the improvement of the tangent Poisson's ratio satisfies the following formula: where denotes the tangent Poisson's ratio, denotes the axial strain, denotes the lateral strain, denotes the first fitting parameter, denotes the second fitting parameter.

[0036] Please refer to Figure 3 . In the embodiment, the Poisson's ratio of cobble soil under different confining pressure conditions is calculated by improving the tangent Poisson's ratio. From Figure 3It can be seen that the fitting degree between the improved tangent Poisson's ratio and the measured Poisson's ratio is relatively high. The greater the confining pressure, the smaller the Poisson's ratio. As the axial strain increases, the tangent Poisson's ratio of the gravelly soil first increases, then tends to be stable, and finally stabilizes at about 0.48.

[0037] Furthermore, the first fitting parameter satisfies the following formula: where, represents the first fitting parameter, represents the linear parameter, represents the confining pressure, represents the standard atmospheric pressure.

[0038] The second fitting parameter satisfies the following formula: where, represents the second fitting parameter, represents the confining pressure, represents the standard atmospheric pressure.

[0039] In the embodiment, from the relationship fitting curve, the first fitting parameter , the second fitting parameter are shown in Table 1.

[0040] Table 1 Nonlinear fitting parameters In the embodiment, the first fitting parameter relationship fitting curve satisfies: That is , , .

[0041] Furthermore, the improved Duncan-Chang model satisfies the following formula: where, represents the elastic modulus, , represent the test constants, represents the confining pressure, represents the standard atmospheric pressure, represents the failure ratio, represents the axial stress, represents the internal friction angle, represents the cohesion.

[0042] Even further, the test constants satisfy the following formula: Among them, represents the initial elastic modulus, represents the standard atmospheric pressure, represents the confining pressure, and represents the test constant.

[0043] S3. Based on the improved Duncan-Chang model, a constitutive model of cobblestone soil is constructed.

[0044] Specifically, the parameters of the improved Duncan-Chang model are fitted through the mechanical test data of cobblestone soil, the threshold of particle crushing strength is introduced to correct the tangent elastic modulus. Furthermore, the friction angle is corrected by combining with the fractal dimension of cobblestone soil gradation. Then, the hyperbola-exponential hybrid function is used to describe the volumetric strain, and the gradation influence coefficient is increased. The improved Duncan-Chang model is implemented in FLAC3D or ABAQUS through user subroutines (such as UMAT).

[0045] Please refer to Figure 4 , in the embodiment, in order to efficiently execute a method for constructing a constitutive model of cobblestone soil provided by the present invention, the present invention also provides a system for constructing a constitutive model of cobblestone soil, including: an input device, an output device, a processor, and a memory. The input device, the output device, the processor, and the memory are interconnected. The memory contains program instructions, and the program instructions are used for the steps of the method for constructing a constitutive model of cobblestone soil. The system for constructing a constitutive model of cobblestone soil of the present invention has a compact structure and stable performance, and can stably execute the method for constructing a constitutive model of cobblestone soil of the present invention, further improving the overall applicability and practical application ability of the present invention.

[0046] In an embodiment, the so-called processor may be a Central Processing Unit (CPU), and the processor may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The input device may be used to obtain data information. The output device may be used to output the result obtained from the program instructions included in the computer program stored in the memory provided by the present invention. The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory.

[0047] In a possible implementation manner, the memory may include a program storage area and a data storage area. Among them, the program storage area may store an operating system, and application programs required for at least one function, etc.; the data storage area may store the data created during use. In addition, the memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include NVRAM. The memory stores an operating system and operation instructions, executable modules, or data structures, or subsets thereof, or extended sets thereof. Among them, the operation instructions may include various operation instructions for implementing various operations. The operating system may include various system programs for implementing various basic tasks and processing hardware-based tasks.

[0048] The embodiment also provides a storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned gravel soil constitutive model construction method are implemented.

[0049] The storage medium may include: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs.

[0050] In summary, the present invention improves the applicability of the Duncan-Chang model to cobble soil by modifying the curve relationships between axial strain and lateral strain, and between volumetric strain and tangent Poisson's ratio, and solves the problem that existing constitutive models cannot accurately describe the mechanical behavior of cobble soil under the combined action of alluvial and lacustrine depositions in mountainous areas.

[0051] Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0052] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope recorded by the present invention.

Claims

1. A method for constructing a constitutive model of gravelly soil, characterized in that Including the following steps: Conduct a triaxial consolidated drained test on the gravelly soil to obtain the mechanical test data of the gravelly soil; Improve the Duncan-Chang model according to the mechanical test data; Construct a constitutive model of the gravelly soil based on the improved Duncan-Chang model.

2. The method for constructing the constitutive model of cobble soil according to claim 1, characterized in that, The improvement of the Duncan-Chang model according to the mechanical test data includes the following steps: Improve the curve relationship between the axial strain and the lateral strain; Improve the volumetric strain; Improve the tangent Poisson's ratio.

3. The method for constructing the constitutive model of cobble soil according to claim 2, characterized in that The improvement of the curve relationship between the axial strain and the lateral strain satisfies the following formula: Among them, represents the axial strain, represents the first fitting parameter, represents the second fitting parameter, represents the lateral strain.

4. The method for constructing the constitutive model of cobble soil according to claim 2, wherein The improvement of the volumetric strain satisfies the following formula: Among them, represents the improved volumetric strain, represents the axial strain, represents the lateral strain, represents the first fitting parameter, represents the second fitting parameter.

5. The method for constructing the constitutive model of cobble soil according to claim 2, wherein, The improvement of the tangent Poisson's ratio satisfies the following formula: Among them, represents the tangent Poisson's ratio, represents the axial strain, represents the lateral strain, represents the first fitting parameter, represents the second fitting parameter.

6. The method for constructing the constitutive model of cobble soil according to any one of claims 3-5, characterized in that, The first fitting parameter satisfies the following formula: Among them, represents the first fitting parameter, represents the linear parameter, represents the confining pressure, represents the standard atmospheric pressure.

7. The method for constructing the constitutive model of cobble soil according to any one of claims 3-5, characterized in that, The second fitting parameter satisfies the following formula: Among them, represents the second fitting parameter, represents the confining pressure, represents the standard atmospheric pressure.

8. The method for constructing the constitutive model of cobble soil according to claim 1, characterized in that The improved Duncan-Chang model satisfies the following formula: Among them, represents the elastic modulus, and represent test constants, represents the confining pressure, represents the standard atmospheric pressure, represents the failure ratio, represents the axial stress, represents the internal friction angle, represents the cohesion.

9. The method for constructing the constitutive model of cobble soil according to claim 8, characterized in that The test constant satisfies the following formula: Among them, represents the initial elastic modulus, represents the standard atmospheric pressure, represents the confining pressure, 、 represent test constants.

10. A constitutive model construction system for cobble soil, characterized in that, The constitutive model construction system of the gravelly soil includes: an input device, an output device, a processor, and a memory. The input device, the output device, the processor, and the memory are interconnected. The memory includes program instructions for executing the gravelly soil constitutive model construction method according to any one of claims 1-9.

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