Method for testing and predicting retaining wall of earth-rock mixture high landfill

Abstract

The invention relates to the technical field of geotechnical engineering and geological disaster prevention, in particular to a method for testing and predicting a retaining wall of a soil-rock mixture high landfill. The method comprises the following steps: S1, sample preparation: determining soil materials with different maximum particle sizes by adopting a rejection method, a similar gradation method and an equivalent substitution method according to a field soil material gradation curve of the soil-rock mixture; s2, large-scale direct shear test: performing direct shear test on each group of samples prepared in the step 1 by using a direct shear apparatus, and determining the shear strength of each sample. According to the method, the stability of the soil-rock mixture high landfill site can be improved, indoor tests, physical models, discrete element simulation and theoretical analysis are integrated, the stability influence main cause and the instability mechanism are accurately recognized, effective prevention and treatment measures are provided, a scientific basis can be provided for safety risk assessment and site selection optimization of the stockpiling site, and the method is suitable for popularization and application. And the land reclamation technology is combined, engineering safety and environment harmony are ensured, and remarkable social and economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering and geological disaster prevention, and in particular to a method for testing and predicting a retaining wall of a soil-rock mixture high landfill. Background Art

[0002] In major engineering projects, the disposal of earth and rock is a crucial link. However, due to the complexity and uncertainty of earth and rock mixtures, their storage and treatment often face many challenges. Traditional storage methods often fail to fully consider the physical and mechanical properties of earth and rock mixtures and their response under different working conditions, resulting in difficulty in ensuring the stability of the storage site, which may in turn cause serious geological disasters such as landslides.

[0003] As an important part of the storage site, the stability of the retaining wall of the soil-rock mixture landfill is directly related to the safety of the entire storage site. However, most of the existing retaining wall stability assessment methods are based on empirical formulas or simplified models, which are difficult to accurately reflect the actual mechanical behavior of the soil-rock mixture and its interaction with the environment. Especially under extreme conditions such as rainfall and earthquakes, the risk of instability of the retaining wall increases significantly, posing a serious threat to the surrounding environment and the safety of people's lives and property.

[0004] Therefore, there is an urgent need for a scientific, systematic and comprehensive test method that can comprehensively consider the physical and mechanical properties of soil-rock mixtures, environmental factors and retaining wall structural characteristics, and accurately predict and evaluate the stability of retaining walls of soil-rock mixture high-landfill sites. The present invention is proposed in this context, aiming to reveal the instability mechanism of soil-rock mixture high-landfill sites through a combination of indoor tests, physical model tests, discrete element simulation and theoretical analysis, and propose corresponding prevention and control measures, so as to provide technical guidance and theoretical support for the safety risk assessment and site selection optimization of storage sites. To this end, we propose a method for experimental prediction of retaining walls of soil-rock mixture high-landfill sites. Summary of the invention

[0005] The purpose of the present invention is to provide a method for testing and predicting the retaining wall of a soil-rock mixture high landfill, so as to solve the problems raised in the above-mentioned background technology.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for testing and predicting a retaining wall of a soil-rock mixture high landfill, comprising the following steps:

[0008] S1: Sample preparation. According to the on-site soil gradation curve of soil-rock mixture, the elimination method, similar gradation method and equal replacement method were used to determine soil with different maximum particle sizes, and prepare samples with relative densities of 0.1, 0.3, 0.5 and 0.8 respectively. At the same time, for each group of soil with the same maximum particle size and relative density, samples with moisture contents of 4%, 8%, 12% and 16% were prepared respectively to study the influence of scale effect, density and moisture content on shear strength;

[0009] S2: Large-scale direct shear test: using a direct shear apparatus, conduct direct shear tests on each group of samples prepared in step 1, measure the shear strength of each sample, and explore the influence of scale effect, density and moisture content on the effective internal friction angle of coarse aggregate, and establish an analytical solution for the shear strength of coarse aggregate considering the main influencing factors;

[0010] S3: Physical model test design to simulate the effects of vertical load and rainfall conditions on the stability of soil-rock mixture high-fill sites;

[0011] S4: Model test implementation: fill soil in the model test box, apply vertical load through the loading device, use the rainfall system to simulate rainfall conditions, and use soil pressure sensors and moisture content testers to monitor the changes in soil pressure and moisture content, and study the temporal and spatial evolution law of the transient saturated zone and soil pressure distribution characteristics of the soil-rock mixture high landfill site;

[0012] S5: Discrete element simulation, using the improved BPM method to establish a particle crushing model, calibrating the microscopic parameters of coarse-grained soil through numerical simulation tests, including particle contact modulus, bonding strength and friction coefficient, establishing a fluid-solid coupling model of a soil-rock mixture high-fill site, and simulating the influence of water-soil interaction on site stability during rainfall.

[0013] Preferably, an optimization and verification step is also included, in which, based on the results of the physical model test and the discrete element simulation, the differences between the simulation values ​​and the test values ​​are compared and analyzed, the simulation model is optimized, and the accuracy and reliability of the simulation results are ensured.

[0014] Preferably, after the optimization and verification steps, the stability of the soil-rock mixture landfill retaining wall under different working conditions is evaluated based on the optimized simulation model, the potential instability risk is predicted, and corresponding prevention and control measures are proposed.

[0015] Preferably, the maximum particle size of the soil material used in S1 is 60 mm, 40 mm, 20 mm and 10 mm, corresponding to samples with relative densities of 0.1, 0.3, 0.5 and 0.8 respectively.

[0016] Preferably, it also includes a simulation method for the occurrence and evolution process of instability of a soil-rock mixture high-altitude landfill site, and the simulation method for the occurrence and evolution process of instability of a soil-rock mixture high-altitude landfill site includes the following steps:

[0017] Particle breakage model: adopt the improved BPM method to improve the calculation efficiency and result accuracy;

[0018] Mesoscopic parameter calibration: Establish the relationship between mesoscopic parameters and physical and mechanical parameters through numerical simulation experiments;

[0019] Fluid-solid coupling model: Based on the fluid continuity equation and Navier-Stokes equations in the Euler-Descartes coordinate system, a fluid-solid coupling model is constructed.

[0020] Preferably, the improved BPM method is as follows: when the particles are smaller than the particle size, it is assumed that the particles will no longer be broken; when the particles are larger than the particle size, the BPM method is used for the particles, which are equivalently replaced with agglomerated small particles.

[0021] Preferably, the simulation method for the occurrence and evolution of instability of soil-rock mixture high-fill sites also includes an optimization program, analyzing the simulation results according to test conditions, and optimizing the program by comparing with test values, ultimately providing a reference for actual engineering.

[0022] Preferably, the direct shear instrument in S2 is Shear Trac III, and the expression for force calculation of the direct shear instrument is:

[0023]

[0024] Among them, M is the weight of the specimen contained in the upper shear box; M1 is the weight of the upper shear box frame, M2 is the weight of the cover plate and steel balls, and is taken as 100.313N; F is the applied vertical load; T is the horizontal load of the shear box; F1 and T1 are the vertical load and horizontal load of the bottom surface of the upper shear frame and the specimen, respectively.

[0025] Preferably, the specific steps in S3 are:

[0026] a): Experimental design: design the model test system based on similarity theory, including the model test box, loading device, rainfall system, drainage system and measurement system;

[0027] b) Soil material preparation: compaction test shall be carried out to determine the optimum moisture content, and the compaction degree of indoor model test shall be controlled according to the compaction degree of the on-site embankment;

[0028] c) Test steps, including sensor sensitivity test, soil filling, vertical loading, rainfall, data collection and analysis.

[0029] It can be seen without a doubt that the above-mentioned technical solution of the present application can definitely solve the technical problem to be solved by the present application.

[0030] At the same time, through the above technical solutions, the present invention has at least the following beneficial effects:

[0031] The beneficial effects of the technical solution are mainly reflected in the following aspects:

[0032] 1. The present invention uses a comprehensive research method of indoor tests, model tests, discrete element simulation and theoretical analysis to find out the main factors affecting the stability of soil-rock mixture high-fill sites and reveal their instability mechanism. These research results provide a scientific basis for proposing targeted prevention and control measures, significantly improve the overall stability of soil-rock mixture high-fill sites, and reduce the occurrence of major destructive accidents such as landslides.

[0033] 2. The present invention provides strong technical guidance and theoretical support for the key technologies of safety risk assessment and site optimization of storage sites, as well as key technologies of land consolidation integrating earthwork utilization. This not only helps to improve the safety of related engineering projects, but also promotes the efficient use of resources and reduces environmental damage.

[0034] 3. In the sample preparation process, the present invention determines the appropriate soil particle size through elimination method, similar gradation method and equal substitution method, and prepares samples with different density and moisture content, which provides rich data support for studying the influence of different factors on the shear strength of soil-rock mixture. The precise operation process of large-scale direct shear test ensures the accuracy and reliability of the test results, and provides an effective method for analyzing the shear strength of coarse aggregate.

[0035] 4. The physical model test of the present invention is designed using similarity theory, which can simulate the stress conditions and rainfall conditions of a soil-rock mixture high-fill site under actual working conditions, accurately reflects the evolution law of the earth pressure of the coarse-grained soil embankment retaining wall under the coupling effect of vertical load and heavy rainfall, and provides an important reference for disease prevention and control in actual engineering.

[0036] 5. In the discrete element simulation, the present invention proposes an improved BPM method, which reduces the number of particles, improves the calculation efficiency, and makes the simulation results more accurate by introducing the concept of "crushing limit particle size". At the same time, through the calibration of microscopic parameters and the establishment of fluid-solid coupling model, the high consistency of simulation results and actual working conditions is ensured.

[0037] 6. The research results of this invention are not limited to theoretical research, but also have strong application value. Through the optimization program, the discrete element method can be applied to the simulation research of actual engineering, providing scientific guidance for the design, construction and maintenance of earthwork engineering, and promoting the progress and wide application of related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0039] Figure 1 It is a schematic diagram of the steps of the present invention;

[0040] Figure 2 It is a schematic diagram of the Shear TracⅢ type direct shear system of the present invention;

[0041] Figure 3 The structure and loading diagram of the Shear Trac III indoor large direct shear apparatus of the present invention;

[0042] Figure 4 It is a schematic diagram of the physical model test instrument of the present invention;

[0043] Figure 5 It is a schematic diagram of the rainfall system of the present invention;

[0044] Figure 6 This is a diagram of the sensor arrangement of the present invention. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] Example 1

[0047] Reference Figure 1-6 The specific steps of a method for experimental prediction of a soil-rock mixture high landfill retaining wall are as follows:

[0048] 1. Sample preparation

[0049] The soil-rock mixture of the present invention is sourced from the Pinglu Canal. Since its original gradation particle size is relatively large, according to the on-site soil gradation curve, the elimination method, similar gradation method and equivalent substitution method are used to determine the soil with maximum particle sizes of 60mm, 40mm, 20mm and 10mm, so as to study the influence of the scale effect on the shear strength of the soil-rock mixture. At the same time, each group of soil is prepared into four samples with relative densities of 0.1, 0.3, 0.5 and 0.8, respectively, so as to study the influence of the density on the shear strength of the soil-rock mixture. A group of soil with the same maximum particle size and relative density is selected, and the moisture content is prepared as 4%, 8%, 12% and 16%, respectively, so as to study the influence of the moisture content on the shear strength of the soil-rock mixture.

[0050] 2. Large direct shear test

[0051] a. Instruments and Equipment

[0052] It is planned to use the Shear TracⅢ direct shear instrument produced by Geocomp Corporation of the United States, which can automatically complete the direct shear test of soil and geotextiles (geotextiles, geomembranes) and geogrids. The specific parameters of the instrument are shown in the following table. According to the geotechnical test methods and standards, the particle size of the test soil should be less than 1 / 5 to 1 / 6 of the instrument size, that is, this instrument can shear samples with a maximum particle size of less than 50 mm.

[0053] Main technical indicators of Shear TracⅢ direct shear apparatus

[0054]

[0055]

[0056] The Shear TracⅢ indoor large direct shear instrument mainly consists of six parts: A shear box, B loading system, C measurement system, D terminal operation panel and E data acquisition system. The main system structure is as follows: Figure 2As shown. Among them, the A shear box consists of upper and lower shear boxes, a pressure cover plate and steel balls. The lower shear box is 100 mm longer than the upper shear box to ensure that the sample particles do not "leak sideways" during the shearing process, and the effective shear area remains constant to reduce the test error. At the same time, it can also fix geotextiles, etc., to carry out direct shear tests on the interface friction characteristics between soil and geotextiles and geogrids; the B loading system includes horizontal and vertical loading systems, which are controlled by a computer to apply horizontal and vertical loads using a micro-stepping motor; the C measurement system includes four vertical displacement sensors and one horizontal displacement sensor to measure the vertical deformation information and shear displacement of the sample during loading; the D terminal operation panel is used to adjust the load and displacement information during the loading and unloading process; the E data acquisition system can set test-related parameters such as solid load, consolidation time and shear rate according to test needs, record data information during consolidation and shearing, and also has the function of real-time display of the current test status and consolidation loading curve.

[0057] The force and structure diagram of Shear TracⅢ direct shear apparatus are as follows: Figure 3 As shown, Figure 3 The numbers in the table are interpreted as follows: 1-vertical micro-stepping motor power system; 2-horizontal micro-stepping motor power system; 3-vertical displacement sensor; 4-horizontal load sensor; 5-vertical reaction steel beam; 6-horizontal reaction steel beam; 7-cover plate and steel ball; 8-upper shear box; 9-lower shear box; According to the force and balance conditions, the shear stress τ and the vertical pressure σ can be calculated by the following formula:

[0058]

[0059] Where, M is the weight of the specimen contained in the upper shear box; M1 is the weight of the upper shear box frame; M2 is the weight of the cover plate and steel ball, which is taken as 100.313N; F is the applied vertical load; T is the horizontal load of the shear box; F1 and T1 are the vertical load and horizontal load of the bottom surface of the upper shear frame and the specimen, respectively. When the material reaches its peak strength during the shear process, it is usually accompanied by shear expansion. In addition, due to the existence of shear joints, the shear frame is in a suspended state, F1 and T1 are approximately zero, and M1 can be ignored. During the test, the direct shear apparatus automatically collects the normal pressure FN and the tangential force FS, and calculates the shear stress τ and the vertical stress σ.

[0060] b. Test methods

[0061] The GDS large direct shear test machine purchased by Guangxi University was used to conduct direct shear tests on each group of samples to determine the shear strength of each sample. The effects of scale effect, density and moisture content on the effective internal friction angle of coarse aggregate were further explored, and an analytical solution to the shear strength of coarse aggregate considering the main factors was established. The specific operation process of the Shear TracⅢ direct shear tester is as follows:

[0062] a. Weigh the sample. The coarse-grained soil sample prepared shall be calculated and weighed according to the density, moisture content (5%) and sample size required by the test using the formula;

[0063] b. Set the shearing seam. Place the lower shearing box on the operating table and install the slit ring on the lower shearing box frame to control the slit size to (1 / 3~1 / 4)dmax, i.e. 3, 6 and 12mm (corresponding to the maximum particle size dmax of 10, 20 and 40mm respectively). Then, place the upper shearing box and insert the latch to fix it so that the upper and lower shearing boxes are aligned;

[0064] c. Compact by layers. According to the principle of staggered layer height and layer seam, all samples are loaded into the shear box in three layers, so the soil material also needs to be divided into three parts with the same mass and uniformity using a platform scale. Each layer is compacted and vibrated to control the layer height to meet the predetermined density requirements. After completion, the surface needs to be planed before filling the next layer. Repeat the previous steps to the last layer, calibrate with a level ruler, and level the surface of the sample;

[0065] d. Install the top cover, steel beam and sensor. Place the cover plate on the specimen surface and use a level ruler to calibrate the level. Slowly push the lower shear box to push the specimen as a whole into the direct shear apparatus, and connect the lower shear box and the horizontal micro-stepping power system with bolts. Place a steel ball in the groove of the cover plate, fine-tune the position of the cover plate so that the steel ball and the center of the pressure rod are aligned, and then install the horizontal and vertical reaction steel beams and vertical displacement sensors;

[0066] f. Reset the initial value. Open the software, load the preset project file by File-load, compare the values ​​of View and Calibrate-summary to reset the Vertical load, then set 0.01kN in Control-Verticalload-Go, adjust the contact between the vertical load sensor and the pressure ball; compare the values ​​of View and Calibrate-Summary, and reset Vertical Displacment, Horizontal load and Horizontal Displacment in turn;

[0067] g. Set the basic parameters of the test. Set the sample size to 305×305mm, the shear rate to 4mm / min (in the preliminary experiment, the peak strength is guaranteed to be obvious and the requirements of consolidation fast shear are met), and the vertical loads to 50, 100, 150 and 200kPa;

[0068] h. Consolidation and loading. Click run to start the consolidation test, and check the "vertical load-time" curve and "vertical displacement-time" curve in the view-graph. When the vertical deformation is less than 0.03mm per hour, the deformation is considered stable and the consolidation stage is completed. Remove the slit ring and the fixing pin, and conduct a direct shear test. When the shear stress reading reaches a stable state or drops significantly, it means that the specimen is in a loss state. If the shear stress reading continues to increase to 60mm or 1 / 15 to 1 / 10 of the specimen diameter, the shear displacement in this article is 30mm;

[0069] i. After the shear test is completed, export the test file in Report-export. In the operation terminal interface, use vertical-displacment-up to separate the steel ball and the pressure rod. Use horizontal-displacment-right to push the shear box to the sample loading workbench. Remove the vertical displacement sensor, reaction steel beam, cover plate and other instrument components in turn.

[0070] 3. Simulation method for the occurrence and evolution of instability in soil-rock mixture high-altitude landfill sites

[0071] a. Particle breakage model

[0072] In view of the certain defects in the current simulation of particle crushing of coarse-grained soil, an improved BPM method is proposed. This method is based on the BMP method and proposes a concept of "crushing limit particle size", that is, when the particle is smaller than this particle size, it is assumed that the particle will no longer be crushed. When the particle size is larger than this particle size, the particle is equivalently replaced by agglomerated small particles using the BPM method. The advantages of the improved method are: 1. It reduces the number of particles and improves calculation efficiency; 2. The "crushing limit particle size" can be appropriately adjusted according to the size of the model and the number of particles, making the result more accurate.

[0073] b. Micro-parameter calibration

[0074] The parameters in PFC are mesoscopic parameters, including particle contact modulus, bonding strength and friction coefficient. These parameters have no corresponding relationship with the physical and mechanical parameters of the materials actually obtained, so the parameters obtained from the experiment cannot be directly applied to PFC simulation. The parameter calibration process is generally established through numerical simulation tests (uniaxial compression, biaxial compression or Brazilian splitting test, etc.). When the results obtained from the simulation experiment are consistent with the results obtained from the corresponding indoor test, the particle mesoscopic parameters at this time are the mesoscopic parameters required for slope stability analysis. The parameter calibration of coarse-grained soil is proposed to use the coarse-grained soil particle flow model established in the previous step, and use the flexible biaxial compression model for parameter calibration. This parameter calibration model is closer to the actual situation.

[0075] c. Fluid-Structure Interaction Model

[0076] After obtaining the microscopic parameters of coarse-grained soil, a fluid-solid coupling model of soil-rock mixture high landfill site was established according to the model test. The coarse-grained soil model was obtained by the improved BMP method. The fluid continuity equation and Navier-Stokes (NS) equation in the Euler-Descartes coordinate system were used as the fluid coupling principle. The water-soil interaction is a complex nonlinear mechanical process. Seepage causes the soil to deform, and the deformed soil reacts to the seepage field. The particle flow calculation program considers the effect of water with the help of the water-soil coupling principle. By dividing the fixed fluid unit grid in the x, y, and z directions, the permeability in the fluid grid unit acts on the soil particles in the form of body force, and the movement of the particles in turn affects the movement of the fluid. The distribution and change of the water head in the slope during rainfall are calculated with the help of the unsaturated soil seepage analysis (SEEP / W) software, and the water head distribution in the particle flow model during the simulation process is adjusted based on this calculation result.

[0077] d. Optimization program

[0078] Based on the established fluid-solid coupling model of soil-rock mixture high landfill site, according to the test conditions, the stability of soil-rock mixture high landfill site under the coupling of vertical load and heavy rainfall is analyzed, and the difference between simulation results and test values ​​is compared and analyzed to optimize the program. On this basis, the discrete element method is used to simulate the actual project, providing a reference for the prevention and control of coarse-grained soil embankment retaining wall diseases under rainfall conditions.

[0079] Example 2

[0080] Reference Figure 1-6 , further optimize Example 1, specifically, the physical model test steps:

[0081] According to the actual stress conditions of the soil-rock mixture high landfill site, the model test design is carried out based on the similarity theory. The model tester is mainly composed of a model test trough, a loading device and a measurement system. Through this model tester, the influence of stress state and rainfall conditions on the stability of the soil-rock mixture high landfill site can be studied. Combined with the indoor test of Guangxi University, the main factors affecting the shear strength are obtained, and the main influencing factors of the stability of the soil-rock mixture high landfill site are clarified. Finally, the main influencing factors that will inevitably lead to instability are set to simulate the evolution process of the instability of the soil-rock mixture high landfill site under actual working conditions. Combined with discrete element simulation analysis, the instability mechanism of the soil-rock mixture high landfill site is obtained and prevention and control measures are proposed.

[0082] a. Physical model test instrument composition

[0083] This paper intends to design a model test based on the similarity theory according to the working conditions of the coarse-grained soil embankment retaining wall under actual rainfall conditions. Figure 4As shown in the figure, the physical model test system is mainly composed of a model test box, a filling area, a loading system, a rainfall system, a drainage system and a measurement system. The model tester can be used to simulate the respective vertical loading and rainfall conditions, so as to explore the evolution law of the earth pressure of the coarse-grained soil embankment retaining wall under the coupling of vertical load and heavy rainfall, and construct a calculation model that can accurately describe this law.

[0084] like Figure 4 As shown in the figure, the internal dimensions of the model test box to be used in the present invention are 2800mm (length), 1000mm (width) and 2000mm (height). One side of the model box is made of transparent organic glass to observe the seepage characteristics and deformation law of the coarse-grained soil high embankment model under the action of dynamic wetting, and the other side is made of iron sheet and has openings designed to facilitate the buried monitoring instrument. Figure 4 shown.

[0085] In order to simulate the actual situation, the present invention arranges drainage holes at the bottom of the model box, such as Figure 4 The drainage hole of the model box is connected to the drainage pipe, which guides the water discharged from the drainage hole in the test into the water tank through the water hole pre-processed on the model tube. By measuring the water volume in the water tank in the test and combining it with the rainfall, the rainfall conditions that cause the instability of the soil-rock mixture high-fill site can be studied.

[0086] The present invention can realize the precise control of rainfall under various rainfall conditions, ensuring that the rainfall uniformity coefficient of each test is above 0.75. Figure 5 shown.

[0087] The loading device to be used in this invention is the "electro-hydraulic servo coordinated loading system" purchased by the college in 2009. The system has a maximum load of 5000kN, which fully meets the vertical loading requirements of the test. A uniform load is applied to the coarse-grained soil filler through a pressurized cover plate, thereby simulating the vertical stress of the highway embankment in actual engineering.

[0088] In order to accurately determine the temporal and spatial evolution law of the transient saturated water level and the soil pressure evolution law of the coarse-grained soil embankment under the coupling effect of vertical load and heavy rainfall, the measurement system of the present invention uses soil pressure sensors and moisture content testers to measure soil pressure and water content respectively. The buried positions of each sensor are as follows: a moisture content tester and soil pressure sensor are set every 500mm along the length direction and every 250mm along the height direction in the backfill area of ​​the retaining wall, and the moisture content tester and the corresponding vertical soil pressure sensor are on the same horizontal plane, so as to determine the temporal and spatial distribution law of the transient saturated area of ​​the backfill behind the retaining wall and the spatial distribution law of the soil pressure under the coupling effect of vertical load and heavy rainfall.

[0089] Since the present invention requires a large number of sensors, it is planned to bury the moisture content tester, vertical soil force sensor and soil pressure sensor by steel wire pasting and positioning to ensure that they are buried in the specified position. First, two buckles are symmetrically set every 500mm along the length direction at the top position of the model box, and the buckles are connected with steel wire to form a positioning steel wire. Then, according to the buried depth of the sensor, each sensor is pasted on the thin steel wire to form a sensor string, such as Figure 6 Finally, according to the plane position of the sensor, the sensor string is placed at the corresponding position, and connected to the preset buckle hole of the bottom plate of the model box through the lower steel wire to realize the positioning and fixation of the sensor position.

[0090] b. Experimental plan

[0091] The soil for the model test was taken from the Pinglu Canal. Before sample preparation, a compaction test was carried out according to the Geotechnical Test Code (JTG E40-2007) to test the dry density of each moisture content of the soil and determine the optimal moisture content corresponding to the maximum dry density. The coarse-grained soil was configured to the optimal moisture content for filling, and the compaction degree during the indoor model test was controlled according to the compaction degree of the on-site embankment to ensure that the permeability coefficient in the test was consistent with the permeability coefficient of the on-site soil, thereby ensuring that the test conditions were consistent with the actual situation. After the filling material was prepared, the specific test steps were as follows:

[0092] 1) Sensor sensitivity test. Test the sensitivity of each sensor before the test. After each sensor is fixed to the designated position, debug it again to ensure that each sensor is in good working condition before soil filling.

[0093] 2) Filling soil. Before filling, apply a layer of vaseline on the inner wall of the model to prevent rainwater from seeping into the inner wall of the model and affecting the accuracy of the test. In order to better simulate the groundwater level, coarse sand is used to fill below the water level and watered to saturation, and then coarse-grained soil is filled in layers and hammered to the compaction degree of the on-site embankment. During the compaction process, care should be taken to avoid damage to the sensors, ensure that each sensor works normally after the soil filling is completed, and record the initial value of each sensor.

[0094] 3) Vertical loading. According to the provisions of the "General Specification for Highway Bridge and Culvert Design" (JTGD60-2015) on the calculation method of soil pressure caused by vehicle loads, the vehicle loads in various cases are converted into uniformly distributed loads, and combined with the actual road load values, a loading plan that conforms to the actual situation is formulated.

[0095] 4) Rainfall. First, based on local climate data and combined with on-site rainfall data, the rainfall intensity under different rainfall conditions is reduced according to similar relationships. A rainfall plan is formulated by changing the rainfall duration and rainfall pattern, and the evolution law of coarse-grained soil pressure under rainfall conditions is studied while avoiding contradictions with actual conditions.

[0096] 5) Data collection and analysis. During the loading and rainfall process, the data acquisition instrument is used to collect the readings of each sensor throughout the process. By analyzing the data of the soil pressure sensor and the moisture content sensor, the temporal and spatial evolution law of the transient saturated zone of the soil-rock mixture high landfill and the distribution characteristics and change law of the soil pressure can be obtained.

[0097] From the above, we can know that:

[0098] The present invention is directed to the technical problem that due to the complexity and uncertainty of soil-rock mixtures, their storage and processing often face many challenges. Traditional storage methods often find it difficult to fully consider the physical and mechanical properties of soil-rock mixtures and their responses under different working conditions, which makes it difficult to ensure the stability of the storage site, and may further cause serious geological disasters such as landslides. As an important component of the storage site, the retaining wall of the soil-rock mixture high-landfill site is directly related to the safety of the entire storage site. However, most of the existing retaining wall stability assessment methods are based on empirical formulas or simplified models, which are difficult to accurately reflect the actual mechanical behavior of soil-rock mixtures and their interaction with the environment. Especially under extreme working conditions such as rainfall and earthquakes, the risk of instability of the retaining wall increases significantly, posing a serious threat to the surrounding environment and the safety of people’s lives and property; adopting the technical solutions of the above-mentioned embodiments and through the above-mentioned settings, the present application will certainly be able to solve the above-mentioned technical problems, and at the same time, achieve the following technical effects:

[0099] 1. The present invention uses a comprehensive research method of indoor tests, model tests, discrete element simulation and theoretical analysis to find out the main factors affecting the stability of soil-rock mixture high-fill sites and reveal their instability mechanism. These research results provide a scientific basis for proposing targeted prevention and control measures, significantly improve the overall stability of soil-rock mixture high-fill sites, and reduce the occurrence of major destructive accidents such as landslides.

[0100] 2. The present invention provides strong technical guidance and theoretical support for the key technologies of safety risk assessment and site optimization of storage sites, as well as key technologies of land consolidation integrating earthwork utilization. This not only helps to improve the safety of related engineering projects, but also promotes the efficient use of resources and reduces environmental damage.

[0101] 3. In the sample preparation process, the present invention determines the appropriate soil particle size through elimination method, similar gradation method and equal substitution method, and prepares samples with different density and moisture content, which provides rich data support for studying the influence of different factors on the shear strength of soil-rock mixture. The precise operation process of large-scale direct shear test ensures the accuracy and reliability of the test results, and provides an effective method for analyzing the shear strength of coarse aggregate.

[0102] 4. The physical model test of the present invention is designed using similarity theory, which can simulate the stress conditions and rainfall conditions of a soil-rock mixture high-fill site under actual working conditions, accurately reflects the evolution law of the earth pressure of the coarse-grained soil embankment retaining wall under the coupling effect of vertical load and heavy rainfall, and provides an important reference for disease prevention and control in actual engineering.

[0103] 5. In the discrete element simulation, the present invention proposes an improved BPM method, which reduces the number of particles, improves the calculation efficiency, and makes the simulation results more accurate by introducing the concept of "crushing limit particle size". At the same time, through the calibration of microscopic parameters and the establishment of fluid-solid coupling model, the high consistency of simulation results and actual working conditions is ensured.

[0104] 6. The research results of this invention are not limited to theoretical research, but also have strong application value. Through the optimization program, the discrete element method can be applied to the simulation research of actual engineering, providing scientific guidance for the design, construction and maintenance of earthwork engineering, and promoting the progress and wide application of related technologies.

[0105] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0106] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. The preferred embodiments of the present invention are given in the accompanying drawings, but they do not limit the patent scope of the present invention. The present invention can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Although the present invention has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned specific embodiments, or to perform equivalent replacements for some of the technical features therein. Any equivalent structure made using the contents of the specification and drawings of the present invention, directly or indirectly used in other related technical fields, is also within the scope of patent protection of the present invention.

Claims

1. A method for testing and predicting the retaining wall of a soil-rock mixture landfill, characterized in that: The following steps are involved: S1: Sample preparation. According to the on-site soil gradation curve of soil-rock mixture, the elimination method, similar gradation method and equal replacement method were used to determine soil with different maximum particle sizes, and prepare samples with relative densities of 0.1, 0.3, 0.5 and 0.8 respectively. At the same time, for each group of soil with the same maximum particle size and relative density, samples with moisture contents of 4%, 8%, 12% and 16% were prepared respectively to study the influence of scale effect, density and moisture content on shear strength; S2: Large-scale direct shear test: using a direct shear apparatus, conduct direct shear tests on each group of samples prepared in step 1, measure the shear strength of each sample, and explore the influence of scale effect, density and moisture content on the effective internal friction angle of coarse aggregate, and establish an analytical solution for the shear strength of coarse aggregate considering the main influencing factors; S3: Physical model test design to simulate the effects of vertical load and rainfall conditions on the stability of soil-rock mixture high-fill sites; S4: Model test implementation: fill soil in the model test box, apply vertical load through the loading device, use the rainfall system to simulate rainfall conditions, and use soil pressure sensors and moisture content testers to monitor the changes in soil pressure and moisture content, and study the temporal and spatial evolution law of the transient saturated zone and soil pressure distribution characteristics of the soil-rock mixture high landfill site; S5: Discrete element simulation, using the improved BPM method to establish a particle crushing model, calibrating the microscopic parameters of coarse-grained soil through numerical simulation tests, including particle contact modulus, bonding strength and friction coefficient, establishing a fluid-solid coupling model of a soil-rock mixture high-fill site, and simulating the influence of water-soil interaction on site stability during rainfall.

2. The method for testing and predicting the retaining wall of a soil-rock mixture landfill according to claim 1 is characterized in that: It also includes optimization and verification steps. According to the results of physical model tests and discrete element simulation, the differences between simulation values ​​and experimental values ​​are compared and analyzed, the simulation model is optimized, and the accuracy and reliability of the simulation results are ensured.

3. The method for testing and predicting the retaining wall of a soil-rock mixture landfill according to claim 2 is characterized in that: After the optimization and verification steps, the stability of the retaining wall of the soil-rock mixture landfill under different working conditions is evaluated based on the optimized simulation model, the potential instability risk is predicted, and corresponding prevention and control measures are proposed.

4. The method for testing and predicting the retaining wall of a soil-rock mixture landfill according to claim 1, characterized in that: The maximum particle sizes of the soil materials used in S1 are 60 mm, 40 mm, 20 mm and 10 mm, corresponding to samples with relative densities of 0.1, 0.3, 0.5 and 0.8 respectively.

5. The method for testing and predicting the retaining wall of a soil-rock mixture high landfill according to claim 2 is characterized in that: The invention also includes a method for simulating the occurrence and evolution of instability of a soil-rock mixture high-fill site, and the method for simulating the occurrence and evolution of instability of a soil-rock mixture high-fill site includes the following steps: Particle breakage model: adopt the improved BPM method to improve the calculation efficiency and result accuracy; Mesoscopic parameter calibration: Establish the relationship between mesoscopic parameters and physical and mechanical parameters through numerical simulation experiments; Fluid-structure coupling model: Based on the fluid continuity equation and Navier-Stokes equations in the Euler-Descartes coordinate system, a fluid-structure coupling model is constructed.

6. The method for testing and predicting the retaining wall of a soil-rock mixture landfill according to claim 5, characterized in that: The improved BPM method is specifically as follows: when the particles are smaller than the particle size, it is assumed that the particles will no longer be broken; when the particles are larger than the particle size, the BPM method is used for the particles, which are equivalently replaced with agglomerated small particles.

7. The method for testing and predicting the retaining wall of a soil-rock mixture high landfill according to claim 5 is characterized in that: The simulation method for the occurrence and evolution of instability of a soil-rock mixture high-fill site also includes an optimization program, analyzing simulation results according to test conditions, and optimizing the program by comparing with test values, ultimately providing a reference for actual engineering.

8. The method for testing and predicting the retaining wall of a soil-rock mixture high landfill according to claim 1, characterized in that: The direct shear apparatus in S2 is Shear TracⅢ, and the expression for force calculation of the direct shear apparatus is: Among them, M is the weight of the specimen contained in the upper shear box; M1 is the weight of the upper shear box frame, M2 is the weight of the cover plate and steel balls, and is taken as 100.313N; F is the applied vertical load; T is the horizontal load of the shear box; F1 and T1 are the vertical load and horizontal load of the bottom surface of the upper shear frame and the specimen, respectively.

9. The method for testing and predicting the retaining wall of a soil-rock mixture landfill according to claim 1, characterized in that: The specific steps in S3 are: a): Experimental design: design the model test system based on similarity theory, including the model test box, loading device, rainfall system, drainage system and measurement system; b) Soil material preparation: compaction test shall be carried out to determine the optimum moisture content, and the compaction degree of indoor model test shall be controlled according to the compaction degree of the on-site embankment; c) Test steps, including sensor sensitivity test, soil filling, vertical loading, rainfall, data collection and analysis.

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