Double-control progressive stable loading method for large compression direct shear integrated tester

Abstract

According to the double-control progressive stable loading method of the large compression direct shear integrated tester, a strain control type test method and a stress control type test method are integrated, an automatic control system carries out conversion according to a preset test scheme according to test requirements, continuous and stable loading can be carried out, and the test efficiency is improved. The control mode in the specific test can be strain-stress type comprehensive control, and can also be strain type and stress type respective control. And the stress level of the sample is gradually changed, so that the stepped change of graded loading is avoided. A compression / direct shear conventional mechanical property test and a long-term compression / direct shear rheological test can be performed, and a comprehensive test combining the mechanical property test and the long-term rheological test is realized.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering tests, and in particular to a dual-control progressive stable loading method for a large-scale compression direct shear integrated testing instrument. Background Art

[0002] Strain control and stress control are two different test control methods in soil mechanics tests.

[0003] The strain control method controls the strain (deformation) rate or total strain of the specimen during the test. The specimen is loaded according to a pre-set strain change law, and the stress change process of the specimen is detected at the same time. The stress-strain relationship can be obtained to study the deformation characteristics and failure mechanism of the specimen under different strain states. The stress control method controls the magnitude and path of stress acting on the specimen during the test. The specimen is loaded or unloaded according to a pre-set stress variation law, and process parameters such as strain and deformation under the stress are measured at the same time. The stress-strain-time relationship can be obtained, and the strength-deformation performance and failure characteristics of the specimen under a specific stress level can be studied.

[0004] In conventional compression / direct shear tests, different equipment utilizes different control methods. Selecting either strain control or stress control, depending on equipment performance and test objectives, can meet the needs of conventional testing. For large-particle coarse-grained soils, such as rockfill, fully graded specimen model tests require specimens up to 300 cm in diameter and weighing over 40 tons. This requires long sample preparation and testing cycles, and complex operations. Therefore, it is necessary to simplify sample preparation and testing procedures to improve specimen utilization efficiency and test cycles. Summary of the Invention

[0005] The main purpose of the present invention is to provide a dual-control progressive stable loading method for a large-scale compression direct shear integrated testing instrument to solve the problems in the above-mentioned background technology.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: including the integration of strain control and stress control test methods. The automatic control system switches according to the preset test plan based on the test requirements and performs continuous and stable loading. The control mode in the specific test is strain and stress integrated control, or strain and stress control separately. The steps are as follows: S1. Determine the control method according to the purpose of compression / direct shear test; S2. Install servo tracking, detection and feedback devices; S3. Input control variables into the control system; S31, strain control input preset loading rate parameters or appropriate strain rate; S32, stress control input preset control stress path, using two loading paths; S321, continuous load application mode: input the stress increment value for continuous application of gradual changes; S322, mode of applying load in stages: input load pressure to be applied in stages; S4. Adjust the instrument / sample into position and adjust the initial readings of each sensor; S5. Start the automatic control system and install the control mode preset in the above steps S1 to S3 to conduct the test; When the specimen is deformed under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors and adjusts the strain rate in real time during the test through feedback control. The automatic control system collects data in real time during the test, monitors the specimen status, automatically determines whether the test stability standards are met according to the test procedures and test standards, and automatically applies the next level of pressure test; S6. When conducting long-term rheological tests, the system applies strain-controlled loads according to the above S2, S31, S4, and S5. When the sample reaches the principal consolidation stress, the system stably maintains the current stress level of the sample. At the same time, the control system switches to stress control mode by continuously applying loads according to S321. The system outputs a continuous load stabilization effect, and the stress level of the sample changes gradually, avoiding step-by-step changes in graded loading. S7. The system automatically judges according to the test end criteria, controls the corresponding load and displacement changes, and issues instructions to safely end the test.

[0007] Preferably, a comprehensive test combining mechanical test and long-term rheological test adopts a strain-stress comprehensive control method, and the method steps are as follows: According to the test plan, the stress control parameter ΔPi~t curve and the strain control parameter ε~t relationship curve are input. After the sample is ready, the automatic control system starts the strain control mode, and the sample is subjected to a continuously increasing load. When the specimen is deformed under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors and adjusts the strain rate in real time during the test through feedback control. When the specimen reaches the principal consolidation stress, the automatic control system stably maintains the current specimen stress level and automatically switches to stress control mode. The system input continuously applies a gradual stress increment value ΔPi~t curve, and the control force source cylinder outputs a continuous load stabilization effect. The stress level of the specimen changes gradually, avoiding step-by-step changes in graded loading. All test status and data are monitored and stored in real time. The automatic control system automatically judges according to the test end criteria, controls the corresponding load and displacement changes, and issues instructions to safely end the test.

[0008] Preferably, the stress control type and the strain control type adopt separate control modes, and the stress control or strain control mode is selected according to the test plan. The method steps are as follows: Stress control: select continuous loading mode or graded loading mode according to the test plan; Start the continuous loading mode, input the stress control parameter ΔPi~t curve, and the automatic control system applies the load according to the input conditions. The specimen deforms under the action of the continuously increasing load. The system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment. It automatically controls the continuous application of the load to continue the test or end the test. Start the graded loading mode, input the stress control parameters and graded load, the automatic control system applies the load according to the input conditions, the specimen is deformed by the current stable load, the system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment, automatically controls the test to apply the next level of load to continue the test or end the test.

[0009] Strain control: Input the strain control parameter ε~t relationship curve. The automatic control system applies the load according to the input conditions. The specimen is deformed by the current stable load. The system collects and stores test data, automatically monitors and controls the test process, and makes stability judgments. The system automatically controls the test to apply the next level of load to continue the test or end the test.

[0010] Preferably, the automatic control system controls the oil cylinder to load the sample according to a preset curve and automatically switches the loading control mode. In the strain control stage, the stress-strain relationship curve, pore water pressure, and settlement parameters of the soil can be directly obtained, and its compression modulus, compression coefficient, and shear strength parameters can be determined, and the deformation and strength characteristics of the soil can be further analyzed.

[0011] Preferably, the specimen undergoes compression / shear deformation under a continuous and stable load, thereby obtaining a continuous stress-strain-time relationship of the specimen, which improves the test method for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loads; Compression and direct shear tests can be combined with strain control and stress control loading methods to conduct comprehensive tests that combine mechanical tests with long-term rheological tests. Using one sample, the compression / direct shear test mechanical parameters and long-term deformation parameters of the sample can be obtained.

[0012] Preferably, a non-step continuous loading method is used to apply load stress to the specimen. A specific stress level is applied to the specimen within a specified time period. According to a pre-established test loading plan, the test control parameters are set to continuously apply stress increments. That is, a loading curve ΔPi~t with continuous stress growth is set in the automatic control system. Based on this curve, the force source cylinder is automatically controlled to apply a continuous load with stable increments to the specimen. Under the action of the continuous stable load, the specimen produces a gradual compression / shear deformation, thereby obtaining a gradual and continuous stress-strain-time relationship for the specimen soil, providing more accurate data for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loads.

[0013] Preferably, load stress is applied to the sample in a graded loading manner. When the deformation of the sample under the load is stable, the next level of load is applied so that the sample is subjected to specific stress levels under each level of load. The deformation of the sample soil under stress develops and stabilizes over time, so that the relationship between the deformation and pressure, and the deformation and time of the sample under each level of stress can be measured, and the relevant deformation and strength parameters can be calculated.

[0014] Preferably, vertical and horizontal hydraulic cylinder control systems are respectively provided, which can switch between compression test and direct shear test functions; The test control is set to strain control mode or stress control mode for loading.

[0015] The present invention provides a dual-control progressive stable loading method for a large-scale compression direct shear integrated testing instrument, which has the following beneficial effects: 1. For large-particle coarse-grained soil, a fully graded sample model test is conducted. The sample size reaches φ300cm and the weight is more than 40 tons. The sample preparation cycle and test cycle of such a large sample model are very long and the operation process is complicated. The present invention simplifies the sample preparation operation process and test process, thereby improving the sample use efficiency and test cycle; 2. For stress control, the present invention provides a gradual and stable loading system, which achieves a continuous and uninterrupted gradual increase in loading (stress level), avoiding the step-by-step changes of graded loading, and improving the experimental level of studying the creep and rheological deformation characteristics of rockfill bodies under long-term loading; 3. This invention provides a large-scale integrated compression and direct shear testing instrument with dual-control modes: stress-controlled and strain-controlled. Depending on the test objectives, these two control methods can be used separately for compression and direct shear tests, or they can be integrated for dual control. This meets the automated control needs of tests such as compression, direct shear, and long-term rheological (wetting) tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and examples: Figure 1It is a block diagram of the working principle of the comprehensive control of the present invention; Figure 2 It is a block diagram of the working principle of the present invention respectively controlled; DETAILED DESCRIPTION Example 1 like Figures 1 and 2 As shown, the dual-control progressive stable loading method of the large-scale integrated compression direct shear tester integrates both strain-controlled and stress-controlled test methods. The automatic control system switches according to the preset test plan based on the test requirements, enabling continuous and stable loading. The control method in specific tests can be a combination of strain-stress control, or separate strain and stress control. A large-scale integrated compression direct shear tester with a dual-control progressive stable loading system, both stress-controlled and strain-controlled, is provided. The stress level of the specimen changes gradually, avoiding the step-by-step changes of graded loading. Conventional compression / direct shear mechanical tests and long-term compression / direct shear rheological tests can be performed, enabling comprehensive testing that combines mechanical testing with long-term rheological testing.

[0017] A comprehensive test combining mechanical tests and long-term rheological tests was conducted. During the test, the strain control method was first used to complete the main consolidation stage, and then the test was automatically switched to the stress control method. The stress control method was set to continuously apply continuous loads instead of graded loads, and the specimens were subjected to continuously changing stress levels.

[0018] Preset strain-controlled and stress-controlled loading paths are available. The strain-controlled method uses a preset loading rate (ε-t curve), while the stress-controlled method uses a continuous loading method to apply a continuous load stress to the specimen, with a set stress growth loading curve (ΔPi-t curve). The automatic control system controls the cylinder to load the specimen according to the preset curve and automatically switches the loading control mode. During the strain-control phase, soil parameters such as stress-strain curve, pore water pressure, and settlement are directly obtained, allowing parameters such as compression modulus, compressibility, and shear strength to be determined, and further analysis of soil deformation and strength properties is performed. Once the specimen reaches the required principal consolidation stress level, the automatic control system maintains the current stress level and switches to stress-controlled mode according to the test presets. During the stress-control phase, the force source cylinder automatically controls the force source cylinder to apply a continuous, stable incremental load according to the ΔPi-t curve. Under the continuous, stable load, the specimen undergoes compression and shear deformation, thereby obtaining a continuous stress-strain-time relationship. This improves the experimental method for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loading.

[0019] Compression and direct shear tests can both combine strain control and stress control loading methods to conduct comprehensive tests that combine mechanical tests with long-term rheological tests. Using a single specimen, both the compression / direct shear test mechanical parameters and long-term deformation parameters of the specimen can be obtained, saving sample preparation frequency and fully improving test efficiency. This has important practical significance for ultra-large specimen models.

[0020] The stress control type presets the stress path and adopts two loading paths, namely the method of applying load continuously without step difference and the commonly used method of applying load in stages.

[0021] The specimens were loaded using a continuous, stepless loading method, maintaining a specific stress level over a specified time period. Based on a pre-defined loading scheme, the test control parameters were set to continuously apply stress increments. This meant that a loading curve with continuous stress growth (ΔPi~t curve) was set in the automatic control system. This automatically controlled the force source cylinder to apply a continuous, steady-incremental load to the specimens. Under this continuous, stable load, the specimens experienced gradual compression / shear deformation, thereby obtaining a gradual, continuous stress-strain-time relationship for the specimens. This provided more accurate data for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loading.

[0022] The load stress is applied to the specimen in a graded loading manner. When the deformation of the specimen is stable under the load, the next level of load is applied so that the specimen is subjected to a specific stress level under each level of load. The deformation of the specimen soil under stress develops and stabilizes over time, so that the relationship between the deformation and pressure, and the deformation and time of the specimen under each level of stress can be measured, and related deformation, strength and other parameters can be calculated.

[0023] like Figure 1 As shown, a comprehensive test combining mechanical and long-term rheological testing utilizes an integrated control approach. The stress control parameter ΔPi~t curve and the strain control parameter ε~t relationship curve are input according to the test plan. Once the specimen is ready, the automatic control system activates the strain control mode. The specimen is subjected to a continuously increasing load. When the specimen deforms under load, the pore water pressure within the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors the strain rate in real time and uses feedback control to adjust the strain rate. Once the specimen reaches the principal consolidation stress, the automatic control system maintains the current specimen stress level and automatically switches to stress control mode. The system inputs a continuously changing stress increment ΔPi~t curve, controlling the force source cylinder to output a steady load. This results in a gradual change in the specimen stress level, avoiding step-wise changes in loading. All test status and data are monitored and stored in real time. The automatic control system automatically determines the test termination criteria, controls the load and displacement changes accordingly, and issues a command to safely terminate the test.

[0024] like Figure 2 As shown, the stress control type and the strain control type adopt separate control methods, and the stress control or strain control method is selected according to the test plan.

[0025] Stress control: Select continuous loading mode or graded loading mode according to the test plan.

[0026] Start the continuous loading mode, input the stress control parameter ΔPi~t curve, and the automatic control system applies the load according to the input conditions. The specimen is deformed by the continuously increasing load. The system collects and stores test data, automatically monitors and controls the test process, makes stability judgments, and automatically controls the continuous application of load to continue the test or end the test.

[0027] Start the graded loading mode, input the stress control parameters and graded load, the automatic control system applies the load according to the input conditions, the specimen is deformed by the current stable load, the system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment, automatically controls the test to apply the next level of load to continue the test or end the test.

[0028] Strain control: Input the strain control parameter ε~t relationship curve. The automatic control system applies the load according to the input conditions. The specimen is deformed by the current stable load. The system collects and stores test data, automatically monitors and controls the test process, and makes stability judgments. The system automatically controls the test to apply the next level of load to continue the test or end the test.

[0029] Example 2 Further explanation is given in conjunction with Example 1: The method steps are as follows: S1. Determine the control method according to the purpose of compression / direct shear test; S2. Install servo tracking, detection, and feedback devices. The accuracy of the pressure sensor is 0.2% FS, the accuracy of the displacement sensor is 0.2% FS, and the accuracy of the pore water pressure sensor is 0.5% FS.

[0030] S3. Input control variables into the control system; S31, strain control input preset loading rate parameters or appropriate strain rate; S32, stress control input preset control stress path, using two loading paths; S321, continuous load application mode: input the stress increment value for continuous application of gradual changes; S322, mode of applying load in stages: input load pressure to be applied in stages; S4. Adjust the instrument / sample into position and adjust the initial readings of each sensor; S5. Start the automatic control system and install the control mode preset in the above steps S1 to S3 to conduct the test; When the specimen is deformed under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors and adjusts the strain rate in real time during the test through feedback control. The automatic control system collects data in real time during the test, monitors the specimen status, automatically determines whether the test stability standards are met according to the test procedures and test standards, and automatically applies the next level of pressure test; S6. When conducting long-term rheological tests, the system applies strain-controlled loads according to the above S2, S31, S4, and S5. When the sample reaches the principal consolidation stress, the system stably maintains the current stress level of the sample. At the same time, the control system switches to stress control mode by continuously applying loads according to S321. The system outputs a continuous load stabilization effect, and the stress level of the sample changes gradually, avoiding step-by-step changes in graded loading. S7. The system automatically judges according to the test end criteria, controls the corresponding load and displacement changes, and issues instructions to safely end the test.

[0031] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. The dual-control progressive stable loading method of the large-scale compression direct shear integrated tester is characterized by: It includes two test methods: strain control and stress control. The automatic control system switches according to the preset test plan based on the test requirements and performs continuous and stable loading. The control mode in the specific test is strain-stress integrated control, or strain and stress control respectively. The steps are as follows: S1. Determine the control method according to the purpose of compression / direct shear test; S2. Install servo tracking, detection and feedback devices; S3. Input control variables into the control system; S31, strain control input preset loading rate parameters or appropriate strain rate; S32, stress control input preset control stress path, using two loading paths; S321, continuous load application mode: input the stress increment value for continuous application of gradual changes; S322, mode of applying load in stages: input load pressure to be applied in stages; S4. Adjust the instrument / sample into position and adjust the initial readings of each sensor; S5. Start the automatic control system and install the control mode preset in the above steps S1 to S3 to conduct the test; When the specimen is deformed under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors and adjusts the strain rate in real time during the test through feedback control. The automatic control system collects data in real time during the test, monitors the specimen status, automatically determines whether the test stability standards are met according to the test procedures and test standards, and automatically applies the next level of pressure test; S6. When conducting long-term rheological tests, the system applies strain-controlled loads according to the above S2, S31, S4, and S5. When the sample reaches the principal consolidation stress, the system stably maintains the current stress level of the sample. At the same time, the control system switches to stress control mode by continuously applying loads according to S321. The system outputs a continuous load stabilization effect, and the stress level of the sample changes gradually, avoiding step-by-step changes in graded loading. S7. The system automatically judges according to the test end criteria, controls the corresponding load and displacement changes, and issues instructions to safely end the test.

2. The dual-control progressive stable loading method of the large-scale compression direct shear integrated testing instrument according to claim 1 is characterized by: The comprehensive test combining mechanical test and long-term rheological test adopts strain-stress comprehensive control method, and the method steps are as follows: According to the test plan, the stress control parameter ΔPi~t curve and the strain control parameter ε~t relationship curve are input. After the sample is ready, the automatic control system starts the strain control mode, and the sample is subjected to a continuously increasing load. When the specimen is deformed under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. To this end, the automatic control system monitors and adjusts the strain rate in real time during the test through feedback control. When the specimen reaches the principal consolidation stress, the automatic control system stably maintains the current specimen stress level and automatically switches to stress control mode. The system input continuously applies a gradual stress increment value ΔPi~t curve, and the control source cylinder outputs a continuous load stabilization effect. The stress level of the specimen changes gradually, avoiding step-by-step changes in graded loading. All test status and data are monitored and stored in real time. The automatic control system automatically judges according to the test end criteria, controls the corresponding load and displacement changes, and issues instructions to safely end the test.

3. The dual-control progressive stable loading method of the large-scale compression direct shear integrated testing instrument according to claim 1 is characterized by: Stress control and strain control adopt separate control methods. Stress control or strain control is selected according to the test plan. The method steps are as follows: Stress control: select continuous loading mode or graded loading mode according to the test plan; Start the continuous loading mode, input the stress control parameter ΔPi~t curve, and the automatic control system applies the load according to the input conditions. The specimen deforms under the action of the continuously increasing load. The system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment. It automatically controls the continuous application of the load to continue the test or end the test. Start the graded loading mode, input the stress control parameters and graded load, the automatic control system applies the load according to the input conditions, the specimen is deformed by the current stable load, the system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment, automatically controls the test to apply the next level of load to continue the test or end the test. Strain control: Input the strain control parameter ε~t relationship curve. The automatic control system applies the load according to the input conditions. The specimen is deformed by the current stable load. The system collects and stores test data, automatically monitors and controls the test process, and makes stability judgments. The system automatically controls the test to apply the next level of load to continue the test or end the test.

4. The dual-control progressive stable loading method for a large-scale integrated compression direct shear tester according to claim 2 is characterized by: The automatic control system controls the oil cylinder to load the sample according to the preset curve and automatically switches the loading control mode. In the strain control stage, the stress-strain relationship curve, pore water pressure, and settlement parameters of the soil can be directly obtained, and its compression modulus, compression coefficient, and shear strength parameters can be determined, and the deformation and strength characteristics of the soil can be further analyzed.

5. The dual-control progressive stable loading method of the large-scale compression direct shear integrated testing instrument according to claim 2 is characterized by: The specimen undergoes compression / shear deformation under continuous and stable loads, thereby obtaining a continuous stress-strain-time relationship for the specimen, improving the experimental method for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loads. Compression and direct shear tests can be combined with strain control and stress control loading methods to conduct comprehensive tests that combine mechanical tests with long-term rheological tests. Using one sample, the compression / direct shear test mechanical parameters and long-term deformation parameters of the sample can be obtained.

6. The dual-control progressive stable loading method for a large-scale integrated compression direct shear tester according to claim 3 is characterized by: The load stress is applied to the specimen using a non-step continuous loading method. A specific stress level is applied to the specimen within a specified time period. According to a pre-established test loading plan, the test control parameters are set to continuously apply stress increments. That is, a loading curve ΔPi~t with continuous stress growth is set in the automatic control system. Based on this curve, the force source cylinder is automatically controlled to apply a continuous load with stable increments to the specimen. Under the action of the continuous stable load, the specimen produces a gradual compression / shear deformation, thereby obtaining a gradual and continuous stress-strain-time relationship for the specimen soil. This provides more accurate data for studying the creep and rheological deformation characteristics of rockfill bodies under long-term loads.

7. The dual-control progressive stable loading method for a large-scale integrated compression direct shear tester according to claim 3 is characterized by: The load stress is applied to the specimen in a graded loading manner. When the deformation of the specimen under the load is stable, the next level of load is applied so that the specimen is subjected to a specific stress level under each level of load. The deformation of the specimen soil under stress develops and stabilizes over time, so that the relationship between the deformation and pressure, and the deformation and time of the specimen under each level of stress can be measured, and the relevant deformation and strength parameters can be calculated.

8. The dual-control progressive stable loading method for a large-scale integrated compression direct shear tester according to claim 1 is characterized by: The vertical and horizontal hydraulic cylinder control systems are set up separately, which can switch between compression test and direct shear test functions; The test control is set to strain control mode or stress control mode for loading.

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