Intelligent step-by-step loading control system and method for whole process of coarse-grained soil compression test

Abstract

The invention provides an intelligent step-by-step loading control system and method for the whole process of a coarse-grained soil compression test, in the test, the system synchronously controls a plurality of loading oil cylinders to move to approach a sample, and input test control parameters including multi-stage vertical loading force and loading speed corresponding to each stage are configured on the system through a predetermined test scheme; the initial dry density, the moisture content, the void ratio, the sample diameter and the sample area of a sample are input, and a digital control system is adopted to automatically judge and control loading and unloading of force in the whole process of the coarse-grained soil compression test. According to the compression test, the loading process is adjusted through a variable-structure PID control algorithm, after it is automatically judged that the sample settles stably, the next-stage load is controlled to be applied to the sample in a preset loading mode, and therefore the test steps of intelligent step-by-step loading and voltage stabilization and step-by-step load shedding and voltage stabilization without human intervention or with few human intervention are completed. And a load error compensation function and a deformation compensation function are used in a special test system, so that the synchronous control and measurement precision is improved. The whole system can work uninterruptedly and reliably, manual intervention is reduced, and test efficiency and result quality are improved.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering test equipment, and in particular to an intelligent step-by-step loading control system and method for the entire process of a coarse-grained soil compression test. Background Art

[0002] The compression test of coarse-grained soil refers to the process of compressing and deforming the soil under graded axial pressure, and measuring the relationship between the deformation and pressure, and the deformation and time of the soil under each level of loading conditions. The equipment used to implement the compression test is a geocompression instrument. When conducting compression tests on coarse-grained soil, due to factors such as the large volume of coarse-grained soil and the complexity of loading control, the existing coarse-grained soil compression requires manual judgment of the sample deformation stability under each level of loading force, and then manual operation for the next level of loading. When the test is completed, manual control is performed for unloading. During this process, the data is recorded in real time in a calculation table, and then the unit settlement, porosity, compression coefficient, compression modulus, and the relationship curves between pressure and settlement at each level, and the relationship curves between pressure and porosity at each level, etc. are calculated. When manual intervention and pressurization are performed at each graded loading force, uncertain factors are very likely to affect the test process, resulting in low test efficiency and extended cycle. Especially under the objective conditions of the site environment, heavy equipment operation, and high-demand control of ultra-large compression tests for mechanical research on coarse-grained soil with ultra-large particle size, there is an even more urgent need for a system that can be used for intelligent control of the entire test process to assist in the test, ensure smooth testing, improve control accuracy, and reduce manual intervention requirements and personnel workload. Summary of the Invention

[0003] The main purpose of the present invention is to provide an intelligent step-by-step loading control system and method for the entire process of coarse-grained soil compression test, so as to solve the problems in the above-mentioned background technology.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: during the test, the system synchronously controls multiple loading cylinders to move close to the sample. The system inputs the test control parameters through a predetermined test scheme configuration, including multi-level vertical loading force and the corresponding loading speed of each level, and inputs the initial dry density, moisture content, porosity, sample diameter, and sample area of ​​the sample. During the entire process of the coarse-grained soil compression test, a digital control system is used to automatically judge and control the loading and unloading of force.

[0005] Preferably, the loading cylinders include 5 axial loading cylinders and 3 horizontal loading cylinders, and the control system can independently or synchronously control the loading and unloading of each loading cylinder; Each loading cylinder is equipped with two sensor interfaces for detecting load and displacement. The control system also has six deformation sensor interfaces for measuring the vertical and horizontal deformation of the test.

[0006] Preferably, the control system switches the control mode in real time according to the load and displacement parameters, and switches between the control modes smoothly and dynamically during the test; The control modes include constant-speed stress, constant-speed displacement, displacement holding and force holding, among other closed-loop control modes.

[0007] Preferably, the loading process is regulated by a variable structure PID control algorithm, with a constant speed control error of ≤5% and a pressure holding control error of ≤0.5%; The control system A / D and D / A are 16 bits, and the refresh rate of each channel closed-loop control data is 2kHz. The data acquisition speed is synchronized with it, that is, the fastest sampling interval is 0.5mS, and the data acquisition time of all sensors is completely synchronized.

[0008] Preferably, the stability standard is set according to the compression test regulations and the pressure is applied step by step. The sensor readings are recorded in sequence at the specified time intervals under the current load pressure until the soil settlement rate is stabilized or the consolidation stability is reached according to the regulations. The control system intelligently judges and automatically controls the loading cylinder to load the next level and maintain stable pressure, entering the test cycle of the next level of pressure, thereby gradually pressurizing to the last level of pressure. When the specimen stabilizes at the last level of pressure until the end of the test, the control system automatically controls the loading cylinder to unload.

[0009] Preferably, in the unloading rebound test after the compression is completed, the stability standard is set according to the compression test regulations to reduce the pressure step by step. The control system automatically controls the unloading rate of the loading cylinder and keeps the pressure stable until the soil deformation rate is measured to be stable or the consolidation stability is reached as specified in the regulations. The control system intelligently judges and automatically controls the loading cylinder to perform the next level of load reduction and keep the pressure stable, and enters the next level of test cycle, thereby reducing the pressure step by step until the test is completed.

[0010] Preferably, a load error compensation function is used in a dedicated test system, two opposing servo cylinders are loaded step by step in opposite directions, the reading of any load sensor is used as a reference value, the difference between the other load sensor and the reference value is recorded, and a compensation curve is calculated; Through the compensation curve and load control compensation, the synchronization of the two relative servo cylinders loading towards each other can be guaranteed to the greatest extent.

[0011] Preferably, a human-computer interaction method is used to analyze and calculate the mechanical properties of the test material. During the compression test, the parameters of unit settlement, porosity, compression coefficient, and compression modulus are automatically calculated, and corresponding charts are automatically generated. On the basis of automatic analysis, the analysis results are corrected through manual intervention to improve the accuracy of the analysis.

[0012] The method for an intelligent step-by-step loading control system for the entire coarse-grained soil compression test process is as follows: S1. After the compression test begins, the control system automatically starts the test according to the previously set test control data, and automatically maintains the pressure when the vertical force value reaches the target value; S2. The control system determines the deformation state of the specimen based on the automatically collected test information. The system records the specimen deformation value at intervals. When the average deformation change of the four deformation sensors in the last time is less than the set value, it is considered that the consolidation under the current force value is stable. If the change is greater than the set value, the sample is considered unconsolidated, and the pressure is maintained for the set time before the deformation is determined. When the deformation value of the specimen under the current pressure reaches the specified stability condition, the system determines that consolidation is completed under the current load level; then, the system automatically controls the cylinder to start loading to the next load level and maintain the pressure value stable. During the loading process, the loading rate is automatically controlled according to the deformation of the specimen, and the test cycle of the next pressure level is entered; this cycle completes the compression test under the pre-set test pressure levels until the last force value is reached, and the compression test ends; S3. Unloading and rebound test: reduce pressure step by step according to the specified stability standard. The control system determines and automatically controls the unloading rate of the cylinder and maintains the pressure stable until the soil deformation rate is stable or the consolidation stability is reached according to the regulations. The control system automatically controls the loading cylinder to carry out the next level of unloading and maintain the pressure stable, and enter the next level of test cycle. In this way, the pressure is reduced step by step until the test is completed; S4. After the test, the system automatically controls the oil cylinder to unload, and automatically controls the unloading rate during the unloading process to ensure safety; S5. Data are recorded in real time during the test, and sample data can be observed in real time during the test; data are automatically extracted to form reports, and test parameters are calculated in real time to form relevant charts.

[0013] The present invention provides an intelligent step-by-step loading control system and method for the entire process of coarse-grained soil compression testing, with the following beneficial effects: 1. The compression test uses a variable structure PID control algorithm to adjust the loading process. After automatically determining that the sample settlement is stable, the next level of load is controlled and applied to the sample according to the preset loading method, thereby completing the intelligent step-by-step loading, voltage stabilization, and step-by-step unloading and voltage stabilization test steps with little or no human intervention. 2. Use load error compensation and deformation compensation functions in dedicated test systems to improve synchronous control and measurement accuracy; 3. The entire system can work reliably and uninterruptedly, reducing manual intervention and improving test efficiency and results quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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 system of the present invention; Figure 2 It is a flowchart of the system work flow of the present invention; DETAILED DESCRIPTION Example 1 like Figures 1 and 2 As shown in the figure, the intelligent step-by-step loading control system for the entire coarse-grained soil compression test process includes the system synchronously controlling the vertical movement of five servo cylinders close to the specimen during the test. The system inputs test control parameters through a predetermined test plan configuration, including multi-level vertical loading force and the corresponding loading speed for each level (the loading force and speed can be set according to the test procedure). The initial dry density, moisture content, porosity, specimen diameter, specimen area, etc. of the specimen are input. A digital control system is used to automatically judge and control the loading and unloading of force throughout the coarse-grained soil compression test process.

[0015] The system features eight control channels, each for controlling five axial loading cylinders and three horizontal loading cylinders. These eight control channels can be loaded independently or in a coordinated, synchronized manner. The control system includes two sensor interfaces for each of the five axial and three horizontal loads (one for load and one for displacement), as well as six deformation sensor interfaces for measuring the specimen's vertical and horizontal deformation. The control system switches control modes in real time based on load, displacement, and other parameters, allowing for smooth dynamic switching between control modes during the test. Multiple closed-loop control modes are available, including constant-speed stress, constant-speed displacement, displacement hold, and force hold. A variable-structure PID control algorithm is used to regulate the loading process, achieving a constant-speed control error of ≤5% and a pressure-holding control error of ≤0.5%. The control system's A / D and D / A functions are 16-bit. The closed-loop control data refresh rate for each channel is 2kHz, synchronized with the data acquisition speed, with a minimum sampling interval of 0.5mS. Data acquisition from all sensors is fully synchronized.

[0016] According to the compression test regulations, the stability standard is set and the pressure is applied step by step. Under the current load pressure, the sensor readings are recorded in sequence at the specified time intervals until the soil settlement rate is determined to be stable (or the time required to reach consolidation stability is specified in the regulations); the control system intelligently judges and automatically controls the loading cylinder to load the next level and maintain the pressure stable, entering the test cycle of the next level of pressure, and gradually pressurizing to the last level of pressure. When the sample is stable at the last level of pressure until the end of the test, the control system automatically controls the loading cylinder to unload.

[0017] For the unloading rebound test after the compression is completed, the stability standard is set according to the compression test regulations and the pressure is reduced step by step. The control system automatically controls the unloading rate of the loading cylinder and maintains the pressure stable until the measured soil deformation rate is stable (or the time required to reach consolidation stability is as specified in the regulations). The control system intelligently judges and automatically controls the loading cylinder to carry out the next level of load reduction and maintain the pressure stable, and enters the next level of test cycle, thereby reducing the pressure step by step until the test is completed.

[0018] To improve load synchronization accuracy, a dedicated test system utilizes load error compensation. Two opposing servo cylinders are loaded step by step. Using the reading of one load sensor as a baseline, the difference between the readings of the other load sensor and the baseline is recorded, and a compensation curve (load-to-load difference curve) is calculated. During formal testing, this curve is used in load control compensation to maximize synchronization of the opposing servo cylinders' loading.

[0019] The machine uses human-computer interaction to analyze and calculate the mechanical properties of the test material. During the compression test, parameters such as unit settlement, void ratio, compression coefficient, and compression modulus are automatically calculated and corresponding charts are automatically generated. In addition to the automatic analysis, manual intervention can also be used to correct the analysis results to improve accuracy.

[0020] like Figure 1 As shown, the intelligent step-by-step loading control system for the entire coarse-grained soil compression test process includes 8 system control channels, which are used for 5 axial and 3 horizontal loading controls respectively. The 8 control channels can be loaded independently or in a coordinated and synchronous manner. The control system is equipped with 2 sensor interfaces for each of the 8 channels (for load and displacement respectively), and 6 deformation sensor interfaces for measuring the vertical and horizontal deformation of the sample. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process uses human-computer interaction to analyze and calculate the mechanical performance indicators of the test material. After automatically determining that the sample settlement is stable, it controls the next level of load to be applied to the sample according to the preset loading method, and automatically calculates the data in real time.

[0021] like Figure 2 As shown in the figure, the working process of the intelligent step-by-step loading control system for the whole process of the coarse-grained soil compression test is as follows: before the start of the test, the pressure value sequence of the compression test load is input (the test specification program is 50kpa / 100kpa / 200kpa / 400kpa / 800kpa / 1600kpa / 3200kpa...), and then the loading speed of each level and other sample parameters are input.

[0022] After the test begins, the intelligent step-by-step loading control system (hereinafter referred to as the system) for the entire coarse-grained soil compression test process will uniformly load to the first-level compression force value according to the given loading speed. After reaching the target force value, the servo valve is controlled to keep the servo cylinder at the current force value unchanged, and the system begins to record the deformation. The system records the settlement at each time point according to the previously set settlement rate time point sequence. After all time series are recorded, the system begins to measure the consolidation stability of the sample. The current data of the four deformation sensors are recorded at each specified time interval. The four sets of data measured in the last measurement are automatically compared with the previous data for judgment (the difference between the deformation of the last set and the deformation of the previous set). The difference in deformation of any of the four sets of data is as follows: If the value is greater than 0.05mm (the value set before the test starts), the system determines that the sample is not fully consolidated and will continue to maintain pressure for a predetermined time period until the difference in any set of deformations is less than 0.05mm and the sample deformation is stable. The system will then determine that the consolidation of the current level is completed, and then the load pressure target value will automatically jump to the next level, and start loading to the force target value at a given loading speed, and then continue to record and judge according to the previous method. This will be repeated until the last level of consolidation is stable, that is, the test is completed. When the last level of consolidation is completed, the system automatically jumps to the force unloading mode, and unloads at a given force speed to the given force unloading target value. After reaching the target value, the system automatically stops and the test ends.

[0023] Example 2 like Figures 1 and 2 As shown, further described in combination with Example 1, the method steps of the intelligent step-by-step loading control system for the entire process of the coarse-grained soil compression test are as follows: After the compression test begins, the control system automatically starts the test according to the previously set test control data, and automatically maintains the pressure when the vertical force value reaches the target value.

[0024] The control system determines the deformation state of the specimen based on the automatically collected test information. The system records the specimen deformation value once at each interval (this time can be set according to the specific situation). When the change in the average deformation of the four deformation sensors in the last time is less than 0.05mm (this value can be set according to the specific situation), it is considered that the consolidation under the current force value has stabilized (if the change is greater than 0.05, the specimen is considered unconsolidated, and the pressure is maintained for the set time as specified in the regulations before continuing to determine the deformation). When the specimen deformation value under the current pressure reaches the specified stability condition, the system determines that consolidation under the current load level is complete; then, the system automatically controls the cylinder to start loading to the next load level and maintain the pressure value stable. During the loading process, the loading rate is automatically controlled according to the specimen deformation, and the test cycle for the next pressure level is entered. This cycle completes the compression test under the pre-set test pressure levels until the last force value is reached, at which point the compression test ends.

[0025] In the unloading rebound test, the pressure is reduced step by step according to the specified stability standard. The control system determines and automatically controls the unloading rate of the cylinder and maintains the pressure stable until the soil deformation rate is measured to be stable (or the time required to reach consolidation stability is specified in the regulations). The control system automatically controls the loading cylinder to carry out the next level of load reduction and maintain the pressure stable, and enters the next level of test cycle, thereby reducing the pressure step by step until the end of the test.

[0026] After the test, the system automatically controls the cylinder to unload, and automatically controls the unloading rate during the unloading process to ensure safety.

[0027] During the test, data is recorded in real time, and sample data can be observed in real time. Data is automatically extracted and generated into reports, and test parameters are calculated in real time and generated into relevant charts.

[0028] 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 intelligent step-by-step loading control system for the entire coarse-grained soil compression test process is characterized by: During the test, the system synchronously controls multiple loading cylinders to move close to the specimen. The system inputs test control parameters through a predetermined test plan configuration, including multi-level vertical loading force and the corresponding loading speed for each level. The initial dry density, moisture content, porosity, specimen diameter, and specimen area of ​​the specimen are input. A digital control system is used to automatically determine and control the loading and unloading of forces throughout the coarse-grained soil compression test.

2. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: The loading cylinders include 5 axial loading cylinders and 3 horizontal loading cylinders. The control system can independently or synchronously control the loading and unloading of each loading cylinder; Each loading cylinder is equipped with two sensor interfaces for detecting load and displacement. The control system also has six deformation sensor interfaces for measuring the vertical and horizontal deformation of the test.

3. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: The control system switches the control mode in real time according to the load and displacement parameters. During the test, the control modes are switched smoothly and dynamically. The control modes include constant-speed stress, constant-speed displacement, displacement holding and force holding, among other closed-loop control modes.

4. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: The loading process is regulated by the variable structure PID control algorithm, with the constant speed control error ≤5% and the pressure holding control error ≤0.5%; The control system A / D and D / A are 16 bits, and the refresh rate of closed-loop control data of each channel is 2kHz. The data acquisition speed is synchronized with it, and the data acquisition time of all sensors is synchronized.

5. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: According to the compression test regulations, set the stability standard and pressurize step by step. Under the current load pressure, record the sensor readings at the specified time intervals until the soil settlement rate is stable or the consolidation stability is reached as specified in the regulations. The control system intelligently judges and automatically controls the loading cylinder to load the next level and maintain stable pressure, entering the test cycle of the next level of pressure, thereby gradually pressurizing to the last level of pressure. When the specimen stabilizes at the last level of pressure until the end of the test, the control system automatically controls the loading cylinder to unload.

6. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: For the unloading rebound test after the compression is completed, the stability standard is set according to the compression test regulations to reduce the pressure step by step. The control system automatically controls the unloading rate of the loading cylinder and keeps the pressure stable until the soil deformation rate is measured to be stable or the consolidation stability is reached as specified in the regulations. The control system intelligently judges and automatically controls the loading cylinder to carry out the next level of load reduction and keep the pressure stable, and enters the next level of test cycle, thereby reducing the pressure step by step until the end of the test.

7. The intelligent step-by-step loading control system for the whole process of coarse-grained soil compression test according to claim 1 is characterized by: The dedicated test system uses the load error compensation function. Two opposing servo cylinders are loaded step by step in opposite directions. The reading of any load sensor is used as the reference value. The difference between the other load sensor and the reference value is recorded, and the compensation curve is calculated. Through compensation curve and load control compensation, the synchronization of the two relative servo cylinders loading towards each other is guaranteed to the maximum extent.

8. The intelligent step-by-step loading control system for the entire coarse-grained soil compression test process according to claim 1 is characterized by: The mechanical properties of the test materials are analyzed and calculated using human-computer interaction. During the compression test, the parameters of unit settlement, void ratio, compression coefficient, and compression modulus are automatically calculated and corresponding charts are automatically generated. Based on the automatic analysis, the analysis results are corrected through manual intervention to improve the accuracy of the analysis.

9. The method for controlling the intelligent step-by-step loading of the entire coarse-grained soil compression test process according to any one of claims 1 to 8, wherein the method comprises the following steps: S1. After the compression test begins, the control system automatically starts the test according to the previously set test control data, and automatically maintains the pressure when the vertical force value reaches the target value; S2. The control system determines the deformation state of the specimen based on the automatically collected test information. The system records the specimen deformation value at intervals. When the average deformation change of the four deformation sensors in the last time is less than the set value, it is considered that the consolidation under the current force value is stable. If the change is greater than the set value, the sample is considered unconsolidated, and the pressure is maintained for the set time before the deformation is determined. When the deformation value of the specimen under the current pressure reaches the specified stability condition, the system determines that consolidation is completed under the current load level; then, the system automatically controls the cylinder to start loading to the next load level and maintain the pressure value stable. During the loading process, the loading rate is automatically controlled according to the deformation of the specimen, and the test cycle of the next pressure level is entered; this cycle completes the compression test under the pre-set test pressure levels until the last force value is reached, and the compression test ends; S3. Unloading and rebound test: reduce pressure step by step according to the specified stability standard. The control system determines and automatically controls the unloading rate of the cylinder and maintains the pressure stable until the soil deformation rate is stable or the consolidation stability is reached according to the regulations. The control system automatically controls the loading cylinder to carry out the next level of unloading and maintain the pressure stable, and enter the next level of test cycle. In this way, the pressure is reduced step by step until the test is completed; S4. After the test, the system automatically controls the cylinder to unload, and automatically controls the unloading rate during the unloading process to ensure safety; S5. Data are recorded in real time during the test, and sample data can be observed in real time during the test; data are automatically extracted to form reports, and test parameters are calculated in real time to form relevant charts.

Images