Double-control progressive stable loading method of large-scale compression and direct shear integrated testing instrument

Abstract

The application provides a double-control progressive stable loading method of a large compression and direct shear integrated tester, integrates strain control type and stress control type two test methods, and an automatic control system is switched according to a preset test scheme according to test requirements, can perform sustained stable loading, and the control mode in specific tests can be strain stress type comprehensive control, or strain type and stress type control respectively. The stress level borne by the sample is progressively changed, so that the stepwise change of the grading loading is avoided. The compression / direct shear conventional mechanical property test, long-term compression / direct shear rheological test can be performed, and the comprehensive test combining the mechanical property test and the long-term rheological test is realized.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering testing, specifically to a dual-control progressive stable loading method for a large-scale integrated compression and shear testing instrument. Background Technology

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

[0003] Strain control involves controlling 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, and the deformation characteristics and failure mechanism of the specimen under different strain states can be studied. Stress-controlled testing involves controlling 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 change pattern, and process parameters such as strain and deformation under the stress are measured simultaneously. This allows for the determination of the stress-strain-time relationship, enabling the study of the specimen's strength, deformation performance, and failure characteristics under a specific stress level.

[0004] In conventional compression / direct shear tests, different equipment employs different control methods. Strain control or stress control is selected based on equipment performance and test objectives to meet the needs of conventional tests. For coarse-grained soils with large particle sizes, such as riprap, full-gradation sample model tests are conducted. Sample sizes reach φ300cm, and weights exceed 40 tons. The sample preparation and testing cycles are very long, and the operation is complex. Therefore, it is essential to simplify sample preparation and testing procedures to improve sample utilization efficiency and test duration. Summary of the Invention

[0005] The main objective of this invention is to provide a dual-control progressive stable loading method for a large-scale integrated compression and shear testing instrument, thereby solving the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: it includes two test methods: integrated strain control and stress control. The automatic control system switches according to the test requirements and the preset test plan to carry out continuous and stable loading. In the specific test, the control method is integrated strain and stress control, or strain control and stress control respectively. The steps are as follows: S1. Determine the control method based on the purpose of the 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 parameter or suitable strain rate; S32, stress-controlled input preset control stress path, adopts 2 loading paths; S321, Method of continuously applying load: Input the value of the gradually increasing stress increment for continuous application; S322, Method of applying load in stages: Input the load pressure 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 test the control modes preset in steps S1 to S3 above. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. For this purpose, the automatic control system monitors and provides feedback control to adjust the strain rate in real time during the test. The automatic control system collects data in real time during the test, monitors the state of the sample, automatically determines whether the test stability standard is met according to the test procedure and test standard, 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-mentioned S2, S31, S4, and S5. When the specimen reaches the principal consolidation stress, the system stably maintains the current stress level of the specimen. At the same time, the system switches to stress control mode according to the continuous load application mode in S321. The system outputs a continuous load stabilizing effect, and the stress level of the specimen changes gradually, avoiding the step-like changes of graded loading. S7. The system automatically judges the test end criteria, controls the corresponding load and displacement changes, and issues a command to safely end the test.

[0007] Preferably, the comprehensive test combining mechanical testing and long-term rheological testing adopts a strain-stress integrated control method, the steps of which 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 specimen is ready, the automatic control system starts the strain control mode and the specimen is subjected to a continuously increasing load. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. For this purpose, the automatic control system monitors and provides feedback control to adjust the strain rate in real time during the test. Once the specimen reaches the principal consolidation stress, the automatic control system stably maintains the current stress level of the specimen. At the same time, the automatic control switches to stress control mode. The system inputs a gradually changing stress increment value ΔPi~t curve and controls the output of the power source cylinder to continuously stabilize the load. The stress level of the specimen changes gradually, avoiding the step-like changes of graded loading. All test statuses and data are monitored and stored in real time. The automatic control system automatically judges the test end criteria, controls the corresponding load and displacement changes, and issues a command to safely end the test.

[0008] Preferably, stress-controlled and strain-controlled methods are used separately. The stress-controlled or strain-controlled method is selected according to the test plan, and the method steps are as follows: Stress control: Select continuous loading or staged loading methods according to the test plan; The continuous loading mode is activated, and the stress control parameter ΔPi~t curve is input. The automatic control system applies the load according to the input conditions. The specimen deforms under 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 load to continue the test or terminate the test. The graded loading mode is activated, and the stress control parameters are input for graded loads. The automatic control system applies the load according to the input conditions. The specimen deforms under the current stable load. The system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment. The system then automatically controls the test to apply the next level of load to continue the test or terminate the test.

[0009] Strain control: Input the strain control parameter ε~t relationship curve, and the automatic control system applies the load according to the input conditions. The specimen deforms under the current stable 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 test to apply the next level of load to continue the test or terminate the test.

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

[0011] Preferably, the specimen undergoes compressive / shear deformation under continuous stable load, thereby obtaining a continuous stress-strain-time relationship of the specimen, which improves the experimental method for studying the creep and rheological deformation characteristics of rockfill under long-term load. Both compression and direct shear tests can be combined with strain control and stress control loading methods to conduct comprehensive tests that combine mechanical testing with long-term rheological testing. The mechanical parameters of compression / direct shear tests and the long-term deformation parameters of a specimen can be obtained using a single specimen.

[0012] Preferably, a continuous loading method without step differences 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 the pre-established test loading scheme, the test control parameters are set to continuously apply stress increment values. That is, the automatic control system sets a loading curve ΔPi~t curve with continuous stress growth. Based on this, the power source cylinder is automatically controlled to apply a stable incremental continuous load to the specimen. Under the action of continuous stable load, the specimen produces gradual compression / shear deformation, thereby obtaining the gradually continuous stress-strain-time relationship of the soil specimen. This provides more accurate data for studying the creep and rheological deformation characteristics of rockfill under long-term load.

[0013] Preferably, a graded loading method is used to apply load stress to the specimen. After the specimen has stabilized under the load, the next level of load is applied, so that the specimen is subjected to specific stress levels under each level of load. The deformation of the soil specimen under stress develops and stabilizes over time. Thus, the relationship between the deformation and pressure, and the deformation and time of the specimen under each level of stress can be determined, and relevant deformation and strength parameters can be calculated.

[0014] Preferably, a vertical and a horizontal hydraulic cylinder control system are set up respectively, which can switch between compression test and direct shear test functions; The test controls were set to apply load using either strain control or stress control methods.

[0015] This invention provides a dual-control progressive stable loading method for a large-scale integrated compression and shear testing instrument, with the following beneficial effects: 1. For coarse-grained soil with large particle size, a full-gradation sample model test is conducted. The sample size reaches φ300cm and the weight is over 40 tons. Such a large sample model has a long sample preparation cycle and test cycle, and the operation process is complicated. This invention simplifies the sample preparation operation procedure and test process, and improves the sample use efficiency and test cycle. 2. For stress-controlled loading, this invention provides a gradual stable loading system, which realizes a continuous and uninterrupted gradual increase in load (stress level), avoiding the step-like changes in graded loading, and improving the experimental level for studying the creep and rheological deformation characteristics of rockfill under long-term load. 3. This invention provides a dual-control testing method for a large-scale integrated compression and direct shear testing apparatus, employing both stress-controlled and strain-controlled modes. Depending on the testing objective, these two control methods can be used separately in compression and direct shear tests, or they can be integrated into a dual-control system. This meets the automatic control requirements for tests such as compression tests, direct shear tests, and long-term rheological (humidification) tests. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1This is a block diagram illustrating the working principle of the integrated control system of this invention; Figure 2 This is a block diagram illustrating the working principle of the separate control of this invention; Detailed Implementation Example 1 like Figures 1-2 As shown, a dual-control progressive stable loading method in a large-scale integrated compression / direct shear testing apparatus integrates strain-controlled and stress-controlled testing methods. The automatic control system switches according to the preset test scheme based on the test requirements, enabling continuous and stable loading. In specific tests, the control method can be a combined strain-stress control or separate strain and stress control. A dual-control progressive stable loading system with stress control and strain control is provided for this large-scale integrated compression / direct shear testing apparatus. The stress level on the specimen changes progressively, avoiding the step-like changes of graded loading. It can perform conventional compression / direct shear mechanical tests and long-term compression / direct shear rheological tests, achieving a comprehensive test combining mechanical and long-term rheological testing.

[0017] A comprehensive test combining mechanical 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 stress control mode. The stress control mode was set to continuously apply a continuous load rather than applying a graded load, so the specimen was subjected to a continuously and gradually changing stress level.

[0018] The test employs preset strain-controlled and stress-controlled loading paths. Strain-controlled loading uses a preset loading rate (ε~t relationship curve), while stress-controlled loading applies continuous stress to the specimen, establishing a stress growth loading curve (ΔPi~t curve). The automatic control system controls the hydraulic cylinders to load the specimen according to the preset curves and automatically switches the loading control mode. During the strain control phase, parameters such as the soil's stress-strain relationship curve, pore water pressure, and settlement can be directly obtained, allowing for the determination of parameters such as compression modulus, compression coefficient, and shear strength. Further analysis of the soil's deformation and strength characteristics is also possible. Once the specimen reaches the required principal consolidation stress level, the automatic control system maintains the current stress level and switches to stress control mode according to the test presets. During the stress control phase, the automatic control system applies a continuous and stable incremental load to the specimen according to the ΔPi~t curve. Under this continuous and stable load, the specimen undergoes compression / shear deformation, thus obtaining a continuous stress-strain-time relationship. This improves the experimental method for studying the creep and rheological deformation characteristics of rockfill under long-term loading.

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

[0020] The stress-controlled preset stress path employs two loading paths: a continuous load application method without step differences and a commonly used graded load application method.

[0021] A continuous, stepless loading method was used to apply stress to the specimens, applying 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, i.e., a continuously increasing stress loading curve (ΔPi~t curve) was set in the automatic control system. Accordingly, the hydraulic cylinder was automatically controlled to apply a stable incremental continuous load to the specimens. Under this continuous stable load, the specimens exhibited gradual compression / shear deformation, thus obtaining a gradually continuous stress-strain-time relationship in the soil sample. This provides more accurate data for studying the creep and rheological deformation characteristics of rockfill under long-term loading.

[0022] The specimen is subjected to load stress by a graded loading method. After the specimen stabilizes under the load, the next grade of load is applied, so that the specimen is subjected to specific stress levels under each load. The deformation of the soil under stress develops and stabilizes over time. Thus, the relationship between the deformation and pressure, and the deformation and time of the specimen under each stress level can be determined, and relevant parameters such as deformation and strength can be calculated.

[0023] like Figure 1 As shown, the comprehensive test combining mechanical and long-term rheological testing employs an integrated control method. Based on the test plan, the stress control parameter ΔPi~t curve and the strain control parameter ε~t relationship curve are input. After the specimen is ready, the automatic control system initiates strain control mode. The specimen is subjected to a continuously increasing load. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3%~20% of the applied axial pressure. Therefore, the automatic control system monitors and provides feedback to adjust the strain rate in real time during the test. When the specimen reaches the principal consolidation stress, the automatic control system stably maintains the current stress level and simultaneously switches to stress control mode. The system inputs a continuously applied, gradually changing stress increment value ΔPi~t curve, controlling the power source cylinder to output a continuous load for stabilization. The stress level on the specimen changes gradually, avoiding the step-like changes caused by graded loading. All test states and data are monitored and stored in real time. The automatic control system automatically judges according to the test completion criteria, controls the corresponding load and displacement changes, and issues a command to safely terminate the test.

[0024] like Figure 2 As shown, stress-controlled and strain-controlled methods are used separately, and the stress-controlled or strain-controlled method is selected according to the test plan.

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

[0026] The continuous loading mode is activated, and the stress control parameter ΔPi~t curve is input. The automatic control system applies the load according to the input conditions. The specimen deforms under 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 load to continue the test or terminate the test.

[0027] The graded loading mode is activated, and the stress control parameters are input for graded loads. The automatic control system applies the load according to the input conditions. The specimen deforms under the current stable load. The system collects and stores the test data, automatically monitors and controls the test process, and makes a stability judgment. The system then automatically controls the test to apply the next level of load to continue the test or terminate the test.

[0028] Strain control: Input the strain control parameter ε~t relationship curve, and the automatic control system applies the load according to the input conditions. The specimen deforms under the current stable 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 test to apply the next level of load to continue the test or terminate the test.

[0029] Example 2 Further explanation based on Example 1: The method steps are as follows: S1. Determine the control method based on the purpose of the compression / direct shear test; S2. Install servo tracking, detection, and feedback devices. The accuracy of the pressure sensor is 0.2%FS, the displacement sensor is 0.2%FS, and 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 parameter or suitable strain rate; S32, stress-controlled input preset control stress path, adopts 2 loading paths; S321, Method of continuously applying load: Input the value of the gradually increasing stress increment for continuous application; S322, Method of applying load in stages: Input the load pressure 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 test the control modes preset in steps S1 to S3 above. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. For this purpose, the automatic control system monitors and provides feedback control to adjust the strain rate in real time during the test. The automatic control system collects data in real time during the test, monitors the state of the sample, automatically determines whether the test stability standard is met according to the test procedure and test standard, 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-mentioned S2, S31, S4, and S5. When the specimen reaches the principal consolidation stress, the system stably maintains the current stress level of the specimen. At the same time, the system switches to stress control mode according to the continuous load application mode in S321. The system outputs a continuous load stabilizing effect, and the stress level of the specimen changes gradually, avoiding the step-like changes of graded loading. S7. The system automatically judges the test end criteria, controls the corresponding load and displacement changes, and issues a command to safely end the test.

[0031] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A dual-control progressive stable loading method for a large-scale integrated compression and direct shear testing instrument, characterized by: It includes two test methods: integrated strain control and stress control. The automatic control system switches according to the test requirements and the preset test plan to carry out continuous and stable loading. In the specific test, the control method is integrated strain-stress control, or strain-type and stress-type control respectively. The steps are as follows: S1. Determine the control method based on the purpose of the 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 parameter or suitable strain rate; S32, stress-controlled input preset control stress path, adopts 2 loading paths; S321, Method of continuously applying load: Input the value of the gradually increasing stress increment for continuous application; S322, Method of applying load in stages: Input the load pressure 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 test the control modes preset in steps S1 to S3 above. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. For this purpose, the automatic control system monitors and provides feedback control to adjust the strain rate in real time during the test. The automatic control system collects data in real time during the test, monitors the state of the sample, automatically determines whether the test stability standard is met according to the test procedure and test standard, 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-mentioned S2, S31, S4, and S5. When the specimen reaches the principal consolidation stress, the system stably maintains the current stress level of the specimen. At the same time, the system switches to stress control mode according to the continuous load application mode in S321. The system outputs a continuous load stabilizing effect, and the stress level of the specimen changes gradually, avoiding the step-like changes of graded loading. S7. The system automatically judges the test end criteria, controls the corresponding load and displacement changes, and issues a command to safely end the test.

2. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing instrument according to claim 1, characterized in that: The comprehensive test combining mechanical testing and long-term rheological testing adopts a strain-stress integrated 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 specimen is ready, the automatic control system starts the strain control mode and the specimen is subjected to a continuously increasing load. When the specimen deforms under load, the pore water pressure inside the specimen should be less than 3% to 20% of the applied axial pressure. For this purpose, the automatic control system monitors and provides feedback control to adjust the strain rate in real time during the test. Once the specimen reaches the principal consolidation stress, the automatic control system stably maintains the current stress level of the specimen. At the same time, the automatic control switches to stress control mode. The system inputs a gradually changing stress increment value ΔPi~t curve and controls the output of the power source cylinder to continuously stabilize the load. The stress level of the specimen changes gradually, avoiding the step-like changes of graded loading. All test statuses and data are monitored and stored in real time. The automatic control system automatically judges the test end criteria, controls the corresponding load and displacement changes, and issues a command to safely end the test.

3. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 1, characterized in that: Stress-controlled and strain-controlled experiments employ separate control methods. The choice between stress-controlled and strain-controlled methods is based on the experimental plan, and the steps are as follows: Stress control: Select continuous loading or staged loading methods according to the test plan; The continuous loading mode is activated, and the stress control parameter ΔPi~t curve is input. The automatic control system applies the load according to the input conditions. The specimen deforms under 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 load to continue the test or terminate the test. The graded loading mode is activated, stress control parameters are input for graded loads, and the automatic control system applies loads according to the input conditions. The specimen deforms under the current stable load. The system collects and stores test data, automatically monitors and controls the test process, makes stability judgments, and automatically controls the test to apply the next level of load to continue the test or terminate the test. Strain control: Input the strain control parameter ε~t relationship curve, and the automatic control system applies the load according to the input conditions. The specimen deforms under the current stable 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 test to apply the next level of load to continue the test or terminate the test.

4. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 2, characterized in that: The automatic control system controls the hydraulic cylinder to load the sample according to the preset curve and automatically switches the loading control mode. During the strain control stage, the stress-strain relationship curve, pore water pressure, and settlement parameters of the soil can be directly obtained, and the parameters of its compression modulus, compression coefficient, and shear strength can be determined. Furthermore, the deformation and strength characteristics of the soil can be analyzed.

5. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 2, characterized in that: The specimen undergoes compressive / shear deformation under continuous stable load, thereby obtaining a continuous stress-strain-time relationship of the specimen, which improves the experimental method for studying the creep and rheological deformation characteristics of rockfill under long-term load. Both compression and direct shear tests can be combined with strain control and stress control loading methods to conduct comprehensive tests that combine mechanical testing with long-term rheological testing. The mechanical parameters of compression / direct shear tests and the long-term deformation parameters of a specimen can be obtained using a single specimen.

6. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 3, characterized in that: A continuous, stepless loading method was used to apply stress to the specimens. A specific stress level was applied to the specimens within a specified time period. According to the pre-established test loading scheme, the test control parameters were set to continuously apply stress increments. That is, the automatic control system was set with a continuous stress growth loading curve ΔPi~t curve. Based on this, the hydraulic cylinder of the force source was automatically controlled to apply a stable incremental continuous load to the specimens. Under the action of continuous stable load, the specimens produced gradual compression / shear deformation, thereby obtaining the gradually continuous stress-strain-time relationship of the soil specimens. This provides more accurate data for studying the creep and rheological deformation characteristics of rockfill under long-term loading.

7. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 3, characterized in that: The specimen is subjected to load stress in stages. After the specimen has stabilized under the load, the next level of load is applied, so that the specimen is subjected to specific stress levels under each level of load. The deformation of the soil specimen under stress develops and stabilizes over time. Thus, the relationship between the deformation and pressure, and the deformation and time of the specimen under each level of stress can be determined, and relevant deformation and strength parameters can be calculated.

8. The dual-control progressive stable loading method for the large-scale integrated compression and shear testing apparatus according to claim 1, characterized in that: Separate vertical and horizontal hydraulic cylinder control systems are set up, which can switch between compression test and direct shear test functions; The test controls were set to apply load using either strain control or stress control methods.

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