Soil-water characteristic curve pressure plate instrument and testing method

Abstract

The present application discloses a soil-water characteristic curve pressure plate instrument and a testing method, including a soil-water characteristic curve pressure plate instrument which adopts a horizontal measuring tube, a newly designed upper pressure cover and a permeable stone structure, and a proportional valve and a PLC to gradually apply air pressure, and a testing method for using the soil-water characteristic curve pressure plate instrument to test the soil-water characteristic curve, which realizes high-precision automatic control of stress loading during the test, accurate measurement and recording of consolidation drainage, and overcomes the influence of position water head on drainage during dehumidification and water absorption during moisture absorption by adopting a horizontal measuring tube and setting the center height of the horizontal measuring tube consistent with the center height of the soil sample, which can avoid the problem of insufficient drainage of soil samples due to the influence of position water head during dehumidification measurement, and can also avoid the problem of excessive water absorption of soil samples due to the influence of position water head during moisture absorption measurement, thereby improving test accuracy and test efficiency.

Description

Technical Field

[0001] The present application belongs to the field of geotechnical engineering test technology, and specifically relates to a soil-water characteristic curve pressure plate instrument and a test method. Background Art

[0002] Unsaturated soil is a multiphase mixture, consisting of solid phase, liquid phase, gas phase and water-gas interface (also called shrinkage membrane). The two sides of the shrinkage membrane are gas phase and liquid phase respectively. The membrane has surface tension and is in a tension equilibrium state under the long-term action of gas phase pressure and liquid phase pressure. Studying the relationship between gas and liquid phases in equilibrium is of great significance to the mechanics, permeability, deformation and other studies of unsaturated soil. The difference between the gas phase pressure and the liquid phase pressure of unsaturated soil is the matrix suction, and the ratio of water to soil volume in unsaturated soil is the volume moisture content. The volume moisture content will decrease with the increase of matrix suction. For soils with the same properties, the relationship between matrix suction and volume moisture content is certain. The relationship curve between matrix suction and volume moisture content is called the soil-water characteristic curve. This curve reflects the water holding capacity of the soil and has a high status in determining important parameters such as unsaturated strength and unsaturated permeability coefficient.

[0003] The pressure plate instrument is the most commonly used device for studying soil-water characteristic curves. The working principle of this device is to place the soil sample on a clay plate, which is only permeable to water but not air within a certain pressure range. The soil sample and clay plate are placed in a sealed cylinder, and air pressure is applied in the cylinder. Due to the effect of the gas phase pressure, the water in the soil is gradually discharged through the clay plate. Only by accurately measuring the volume of the discharged water can the volumetric water content be calculated. The matrix suction is equal to the applied air pressure value, and the soil-water characteristic curve can be drawn.

[0004] The practices and shortcomings of traditional conventional pressure plate instruments are as follows:

[0005] 1. The air pressure is applied by manually rotating the pressure regulating valve. The pressure regulating valve uses a fixed throttle hole to guide the intake pressure, and uses the spring force and the twice measured pressure for dynamic balance. The control accuracy is only about 5kPa and automatic control cannot be achieved. As a result, the equipment needs to be manually adjusted step by step during the dehumidification and dehumidification process, and the accuracy is difficult to guarantee.

[0006] 2. During consolidation, part of the water in the soil sample is discharged through the permeable stone on the top. The amount of this water cannot be counted, so it is impossible to judge the completion of consolidation by the condition of drainage stability.

[0007] 3. During the dehumidification process, the soil sample discharges water into the vertical pipe for measuring the change in water volume. It needs to overcome a certain position head, resulting in less water discharge. During the moisture absorption process, water is sucked back from the vertical pipe. The existence of position head may cause the soil sample to absorb excessive water, resulting in a larger amount of water absorption.

[0008] There are also existing practices to improve conventional pressure plate instruments in the prior art, among which "a soil-water characteristic curve pressure plate instrument using an automatic pressure regulating mechanism (CN211718064U)" uses a motor to drive a pressure regulating valve for pressure regulation, "a fully automatic soil-water characteristic curve pressure plate instrument (CN206496981U)" and "a complete soil-water characteristic curve fully automatic measurement system (CN108507931A)" use a pressure volume controller to automatically apply and change the air pressure. However, there are still problems that the consolidation drainage cannot be accurately measured and the drainage during the dehumidification and moisture absorption process is affected by the position head. In addition, the equipment structure is relatively complex and the equipment cost is high.

[0009] This shows that the prior art still has certain defects. Summary of the invention

[0010] The present application provides a soil-water characteristic curve pressure plate instrument and a testing method to solve at least one of the above-mentioned technical problems.

[0011] The technical solution adopted in this application is:

[0012] In a first aspect, the present application provides a soil-water characteristic curve pressure plate instrument, comprising:

[0013] A soil sample chamber system, comprising a soil sample chamber for placing soil samples, and a downward pressure component arranged inside the soil sample chamber for transmitting vertical loads to the soil samples, the downward pressure component comprising an upper pressure cover, a T-shaped permeable stone and an annular metal sheet, the interior of the upper pressure cover is provided with an internal flow channel that vertically penetrates the upper pressure cover, the upper part of the upper pressure cover is provided with an inlet of the internal flow channel, and the side of the upper pressure cover facing the T-shaped permeable stone is provided with an outlet of the internal flow channel; an upper pressure cover solenoid valve is also provided at the inlet of the internal flow channel, and the upper pressure cover solenoid valve can close or open the inlet of the internal flow channel, and the internal flow channel comprises at least two concentrically arranged annular flow channels and a straight flow channel connecting the annular flow channels;

[0014] A stress loading system, used for applying a vertical load to the soil sample placed inside the soil sample chamber, and applying air pressure to the inside of the soil sample chamber;

[0015] A water quality measurement system, comprising a drainage pipe, a horizontal measuring pipe and a weighing device, wherein both ends of the drainage pipe are respectively connected to the soil sample chamber and the horizontal measuring pipe, and the weighing device is used to weigh the quality of water in the horizontal measuring pipe;

[0016] A control system, wherein the control system is respectively connected to the soil sample room system, the stress loading system and the water quality measurement system, and the soil sample room system, the stress loading system and the water quality measurement system are controlled in linkage through the control system.

[0017] In the above scheme, the linkage between the control system and the stress loading system can realize fully automatic loading of the load and can realize precise control of the axial load and the air pressure in the soil sample chamber. Compared with the traditional manually adjusted pressure regulating valve, the load control accuracy is higher and there is no need to consume manpower to adjust the load regularly every day; and by arranging an internal flow channel inside the upper pressure cover, it is convenient to inject water into the T-shaped permeable stone arranged on the top of the soil sample to saturate it before the consolidation operation. By arranging the upper pressure cover solenoid valve, the internal flow channel can be closed during the consolidation operation, so that the water in the soil sample can be prevented from being pressed into the T-shaped permeable stone on the top during the consolidation process, ensuring that all the water discharged during the consolidation process enters the horizontal measuring tube, thereby overcoming the problem of inaccurate measurement of consolidation drainage; by combining the horizontal measuring tube and the weighing device, automatic and accurate measurement of drainage and water absorption can be realized, solving the problem of increased workload caused by manual graded loading of air pressure during dehumidification and moisture absorption, and by adopting the horizontal measuring tube, the problem of inaccurate measurement of drainage / water absorption caused by the influence of position head when the soil sample is draining and absorbing water during dehumidification measurement and moisture absorption measurement is overcome.

[0018] As a preferred embodiment of the present application, along the vertical direction, the center height of the horizontal measuring tube is consistent with the center height of the soil sample.

[0019] This setting can avoid the problem of insufficient water discharge of soil samples due to the influence of positional water head during moisture discharge measurement, and can also avoid the problem of excessive water absorption of soil samples due to the influence of positional water head during moisture absorption measurement. This is beneficial to ensuring the measurement accuracy of the test results and the accuracy of drawing the final soil-water characteristic curve.

[0020] As a preferred embodiment of the present application, the stress loading system includes an air source, a pressure regulating valve, a top air circuit, a bottom air circuit, a cylinder arranged at the top of the soil sample chamber, and an axial loading rod. The air source is connected to the top air circuit and the bottom air circuit through the pressure regulating valve. The top air circuit is connected to the cylinder to drive the axial loading rod to apply a vertical load to the soil sample placed inside the soil sample chamber. The bottom air circuit is connected to the soil sample chamber for applying air pressure to the inside of the soil sample chamber. The top air circuit is provided with a cylinder proportional valve for adjusting the cylinder air pressure to adjust the vertical load applied by the axial loading rod to the soil sample. The bottom air circuit is provided with a soil sample chamber proportional valve for adjusting the air pressure inside the soil sample chamber.

[0021] In the above scheme, the precise control of the axial load and the air pressure in the soil sample chamber can be achieved through the cooperation of the control system with the cylinder proportional valve and the soil sample chamber proportional valve. Compared with the existing method of using a motor to drive a pressure regulating valve or a pressure volume controller to control the load, while ensuring high precision of the same order of magnitude, the equipment structure is simpler and the equipment cost and test cost are lower.

[0022] As a preferred embodiment of the present application, the flange of the T-shaped permeable stone is arranged between the annular metal sheet and the upper pressure cover, and the annular metal sheet is fastened to the upper pressure cover by a connecting piece and clamps the T-shaped permeable stone; the soil sample chamber system also includes a fixing member arranged inside the soil sample chamber for limiting the soil sample in the horizontal direction and a bearing assembly for supporting the fixing member, the pressing assembly and the soil sample, and the bearing assembly includes a permeable base and a clay plate arranged on the upper part of the permeable base.

[0023] As a preferred embodiment of the present application, the drainage pipe is a rigid hard pipe.

[0024] In the above scheme, since one end of the drain pipe is connected to the horizontal measuring tube, the change of the center of gravity of the drain pipe and the water inside it can easily affect the measurement accuracy of the weighing device on the change of the water volume inside the horizontal measuring tube. The drain pipe adopts a rigid hard pipe so that the drain pipe maintains the same posture and shape throughout the experiment, thereby ensuring that the center of gravity of the drain pipe and the water in the drain pipe remains unchanged throughout the experiment, thereby eliminating the influence of the change of the center of gravity on the measurement accuracy of the drainage / water absorption, which is beneficial to ensure the accuracy of drawing the soil-water characteristic curve.

[0025] As a preferred embodiment of the present application, it also includes a cylinder rack, the cylinder is arranged on the cylinder rack, the piston rod of the cylinder is connected to the axial loading rod, and the lower end portion of the axial loading rod extends into the soil sample chamber; or, the cylinder is arranged at the upper part of the soil sample chamber, the piston rod is connected to the axial loading rod and the entire axial loading rod is located in the soil sample chamber.

[0026] In the above scheme, the cylinder rack is provided to facilitate the installation and fixation of the cylinder and is conducive to simplifying the structure of the soil sample chamber cover to facilitate the assembly and sealing of the soil sample chamber. However, this structure requires a through hole to be opened in the soil sample chamber cover for the axial loading rod to pass through to apply an axial load to the soil sample, and it is also necessary to add a sealing structure between the through hole and the axial loading rod to ensure the sealing of the soil sample chamber, and the sealing structure also has the risk of leakage and failure during long-term use; arranging the cylinder integrally in the soil sample chamber cover eliminates the need for the setting of an additional sealing structure, and even if the cylinder and the soil sample chamber cover are assembled separately and a sealing structure is required between the two, since the cylinder as a whole is fixed relative to the soil sample chamber cover, the sealing effect is also more stable.

[0027] As a preferred embodiment of the present application, the soil sample chamber system further includes an axial pressure sensor connected to the axial loading rod, and the axial pressure sensor is used to measure the vertical load applied by the axial loading rod to the top of the soil sample.

[0028] As a preferred embodiment of the present application, the fixing member is a ring knife, which has an annular cylindrical structure and has a space inside for accommodating the soil sample. The outer diameter of the annular metal sheet is the same as the inner diameter of the ring knife.

[0029] As a preferred embodiment of the present application, a pressure-bearing groove is provided at the upper center of the upper pressure cover, the inner wall of the pressure-bearing groove is an arc surface, and the lower end contour of the axial loading rod is adapted to the arc surface.

[0030] In a second aspect, the present application also provides a soil-water characteristic curve testing method, which is based on the soil-water characteristic curve pressure plate instrument mentioned above and mainly includes the following steps:

[0031] Step 1, preparation before the test: exhaust the instrument pipeline, saturate the clay plate, permeable base and drain pipe, and prepare the saturated soil sample;

[0032] Step 2, install the saturated soil sample: according to the test requirements, place the saturated soil sample in the cutter ring, then place the cutter ring and the saturated soil sample inside on the saturated clay plate, then seal and assemble the down-pressing assembly and place the down-pressing assembly on the upper part of the saturated soil sample, and inject water into the internal flow channel of the upper pressure cover until the internal flow channel and the inside of the T-shaped permeable stone are filled with water and record the water injection volume, recorded as m;

[0033] Step 3, consolidation: first, open the gas source and adjust the gas pressure output by the pressure regulating valve to always be higher than the maximum gas pressure value required during the test. The control system controls the upper gland solenoid valve to close the gas inlet port of the internal flow channel of the upper gland. Then, according to the test requirements, the control system controls the output gas pressure of the cylinder proportional valve to apply gas pressure to the gas inlet end of the cylinder, so that the cylinder piston rod drives the axial loading rod to move and drives the downward pressure assembly to apply a vertical load to the soil sample until the water displacement during the consolidation process no longer changes, and the consolidation is completed.

[0034] Step 4, dehumidification measurement: After consolidation is completed, the proportional valve of the soil sample chamber is controlled by the control system to output multiple levels of air pressure from low to high according to the test requirements, and the air pressure of each level is recorded in sequence as , , ..., ,...The control system controls the solenoid valve of the upper gland to open the entrance of the internal flow channel of the upper gland so that the gas under each level of air pressure fills the soil sample chamber and enters the internal flow channel of the upper gland to press the water in the internal flow channel and the T-shaped permeable stone into the soil sample and finally discharges into the horizontal measuring tube through the soil sample, clay plate, permeable base and drainage pipe. After the suction is balanced and the drainage volume is stable, the mass of water discharged into the horizontal measuring tube under each level of air pressure is weighed by the weighing device and the mass of water discharged into the horizontal measuring tube under each level of air pressure is recorded as , , ..., , ...Then the mass of water actually discharged from the soil sample at each level of air pressure is , , ..., , ...;

[0035] Step 5, moisture absorption measurement: After completing step 4, according to the test requirements, the control system is used to adjust the proportional valve of the soil sample chamber to gradually reduce the output pressure and record the pressure at each level as , , ..., , ...so that the water in the horizontal measuring tube is sucked into the soil sample through the drainage pipe, the permeable base and the clay plate, and at the same time, the mass of the water reduced in the horizontal measuring tube under each level of air pressure is weighed by the weighing device and the mass of the water reduced in the horizontal measuring tube under each level of air pressure is recorded as , , ..., , ...;

[0036] Step 6: Calculate the volumetric moisture content of the soil sample: According to the measurement results in step 4, the volumetric moisture content of the soil sample at each level of air pressure during the dehumidification measurement is According to the measurement results in step 5, the volume moisture content of the other soil samples at each level during the moisture absorption measurement is , where e is the porosity of the soil sample, n=1, 2, 3, ...;

[0037] Step 7, draw the soil-water characteristic curve: draw the soil-water characteristic curve of the dehumidification measurement process and the soil-water characteristic curve of the moisture absorption measurement process respectively according to the calculation results of step 6. The above test method realizes high-precision and fully automatic stress loading of the pressure plate instrument, and then realizes automatic control of the entire test process. Compared with the traditional manual timing adjustment control, it can greatly save manpower and improve the test efficiency and the accuracy of the test results. The above method can accurately measure the drainage of the consolidation process, thereby eliminating the influence of inaccurate measurement of consolidation drainage on the accuracy of the test results, and can also eliminate the influence of position head on the measurement accuracy of dehumidification drainage and moisture absorption drainage, further ensuring the accuracy of the final test results to obtain a more accurate soil-water characteristic curve.

[0038] In summary, due to the adoption of the above technical solution, the beneficial effects achieved by this application are as follows:

[0039] 1. It realizes the full automatic control of the pressure plate instrument and the automatic recording of test data in a long test cycle, which greatly saves manpower and greatly improves the test efficiency and test accuracy compared with the traditional manual timed adjustment of test instruments and timed handwritten test data; and under the premise of ensuring the same level of high accuracy, compared with the existing technology of using a motor to drive a pressure regulating valve or a pressure volume controller to control the load, the equipment structure is simpler, the test operation is simpler, and the equipment cost and test cost are lower;

[0040] 2. By injecting water into the internal flow channel of the upper gland and the T-shaped permeable stone and controlling the opening and closing of the upper gland solenoid valve through the control system, the water in the soil sample is prevented from being discharged into the T-shaped permeable stone during the consolidation process, and the consolidation drainage can be accurately measured and recorded;

[0041] 3. By adopting a horizontal measuring tube and setting the center height of the horizontal measuring tube to be consistent with the center height of the soil sample, the influence of the position water head on the water discharge during the dehumidification process and the water absorption during the moisture absorption process is overcome, thereby avoiding the problem of insufficient water discharge of the soil sample due to the influence of the position water head during the dehumidification measurement, and avoiding the problem of excessive water absorption of the soil sample due to the influence of the position water head during the moisture absorption measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0043] Figure 1 It is the equipment structure diagram;

[0044] Figure 2 This is a schematic diagram of the soil sample room system structure;

[0045] Figure 3 It is a schematic diagram of the bottom surface structure of the upper gland;

[0046] Figure 4 It is a schematic diagram of the top surface structure of the annular metal sheet.

[0047] List of parts and reference numerals:

[0048] 1 High-pressure gas source; 2 Pressure regulating valve; 3 Top first gas circuit; 4 Cylinder proportional valve; 5 Top second gas circuit; 6 Cylinder; 7 Axial loading rod; 8 Cylinder frame; 9 Bottom first gas circuit; 10 Soil sample chamber proportional valve; 11 Bottom second gas circuit;

[0049] 12 soil sample chamber system, 121 axial pressure sensor, 122 upper gland, 123 internal flow channel, 124 T-type permeable stone, 125 fastening screw, 126 groove and sealing ring, 127 annular metal sheet, 128 upper gland solenoid valve, 129 outlet sealing port, 1210 soil sample, 1211 ring knife, 1212 clay plate, 1213 permeable base;

[0050] 13. Drain pipe; 14. Precision balance; 15. Horizontal measuring tube; 16. PLC integrated machine. DETAILED DESCRIPTION

[0051] In order to more clearly illustrate the overall concept of the present application, a detailed description is given below in an illustrative manner in conjunction with the accompanying drawings.

[0052] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below. It should be noted that the embodiments of the present application and the features in each embodiment may be combined with each other without conflict.

[0053] In addition, in the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "top", "bottom", "inside", "outside", "axial", "radial", "circumferential", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0054] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0055] In the present application, unless otherwise clearly specified and limited, a first feature "above" or "below" a second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0056] Reference Figure 1 and Figure 2 As shown, the present application first provides a soil-water characteristic curve pressure plate instrument, which mainly includes a soil sample chamber system 12, a stress loading system, a water quality measurement system and a control system, wherein the soil sample chamber system 12 mainly includes a soil sample chamber for placing a soil sample 1210, the stress loading system includes an air source, a pressure regulating valve 2, a top air circuit, a bottom air circuit, a cylinder 6 arranged at the top of the soil sample chamber and an axial loading rod 7, the air source is connected to the top air circuit and the bottom air circuit through the pressure regulating valve 2, the top air circuit is connected to the cylinder 6 to drive the axial loading rod 7 to apply a vertical load to the soil sample 1210 placed inside the soil sample chamber, and the bottom air circuit is connected to the soil sample chamber for applying a vertical load to the inside of the soil sample chamber. Air pressure, the top air circuit is provided with a cylinder proportional valve 4 for adjusting the air pressure of the cylinder 6 to adjust the vertical load applied by the axial loading rod 7 to the soil sample 1210, and the bottom air circuit is provided with a soil sample chamber proportional valve 10 for adjusting the air pressure inside the soil sample chamber. The water quality measurement system includes a drainage pipe 13, a horizontal measuring tube 15 and a weighing device. The two ends of the drainage pipe 13 are respectively connected to the soil sample chamber and the horizontal measuring tube 15. The weighing device is used to weigh the quality of water in the horizontal measuring tube 15; the control system is respectively connected to the soil sample chamber system 12, the stress loading system and the water quality measurement system, and the soil sample chamber system 12, the stress loading system and the water quality measurement system are controlled in linkage through the control system.

[0057] In the above scheme, the fully automatic loading of the load can be achieved through the linkage between the control system and the stress loading system, and the precise control of the axial load and the air pressure in the soil sample chamber can be achieved through the cooperation between the control system and the cylinder proportional valve 4 and the soil sample chamber proportional valve 10. Compared with the traditional manual adjustment of the pressure regulating valve 2, the load control accuracy is higher and there is no need to consume manpower to adjust the load regularly every day. At the same time, under the premise of ensuring the same level of high accuracy, the equipment structure is simpler, and the equipment cost and test cost are lower than the existing method of using a motor to drive the pressure regulating valve 2 or using a pressure volume controller to control the load; and by combining the horizontal measuring tube 15 with the weighing device, automatic and accurate measurement of the drainage and water absorption can be achieved, which solves the problem of increased workload caused by manual graded loading of air pressure during the dehumidification and dehumidification processes, and by using the horizontal measuring tube 15, the problem of inaccurate drainage / water absorption measurement caused by the influence of the position head when the soil sample 1210 is draining and absorbing water during the dehumidification and dehumidification measurements is overcome.

[0058] As a preferred embodiment of the present application, continue to refer to Figure 1 As shown, along the vertical direction, the center height of the horizontal measuring tube 15 is consistent with the center height of the soil sample 1210. With this arrangement, the problem of insufficient drainage of the soil sample 1210 due to the influence of the position water head can be avoided during the moisture discharge measurement, and the problem of excessive water absorption of the soil sample 1210 due to the influence of the position water head can be avoided during the moisture absorption measurement, which is conducive to ensuring the measurement accuracy of the test results and the drawing accuracy of the final soil-water characteristic curve.

[0059] In one example, referring to Figure 1-Figure 4 As shown, the soil sample chamber system 12 includes a soil sample chamber, a pressing assembly disposed inside the soil sample chamber for transmitting a vertical load to the soil sample 1210, a fixing member disposed inside the soil sample chamber for limiting the soil sample 1210 in the horizontal direction, a bearing assembly for bearing the fixing member, the pressing assembly and the soil sample 1210, and an axial pressure sensor 121 connected to the axial loading rod 7 for measuring the vertical load applied by the axial loading rod 7 to the top of the soil sample 1210. For details, continue to refer to Figure 2As shown, the bearing assembly includes a permeable base 1213 and a clay plate 1212 arranged on the upper part of the permeable base 1213, and the lower pressure assembly includes an upper pressure cover 122, a T-shaped permeable stone 124 and an annular metal sheet 127, and a pressure groove is provided in the upper center of the upper pressure cover 122, the inner wall of the pressure groove is an arc surface, and the lower end contour of the axial loading rod 7 is adapted to the arc surface. By providing the pressure groove and setting the inner wall of the pressure groove and the lower end contour of the axial loading rod 7 as an arc surface, it is convenient to accurately locate the force application position of the axial loading rod 7 and to achieve uniform distribution of the load to ensure the accuracy of the test results. The fixing part is a ring knife 1211, which is an annular cylindrical structure, and has a space for accommodating the soil sample 1210 inside, and the outer diameter of the annular metal sheet 127 is the same as the inner diameter of the ring knife 1211. Continue to refer to Figure 3 and Figure 4 As shown, a groove and a sealing ring 126 are provided between the upper pressure cover 122 and the annular metal sheet 127 to seal the connection structure between the upper pressure cover 122 and the annular metal sheet. Figure 2 As shown, the flange of the T-shaped permeable stone 124 is arranged between the annular metal sheet 127 and the upper pressure cover 122, and the annular metal sheet 127 is fastened to the upper pressure cover 122 by fastening screws 125 and clamps the T-shaped permeable stone 124. The interior of the upper pressure cover 122 is provided with an internal flow channel 123 that vertically penetrates the upper pressure cover 122, and the upper part of the upper pressure cover 122 is provided with an entrance of the internal flow channel 123. The side of the upper pressure cover 122 facing the T-shaped permeable stone 124 is provided with an outlet of the internal flow channel 123, and an upper pressure cover solenoid valve 128 is also provided at the entrance of the internal flow channel 123. The upper pressure cover solenoid valve 128 can close or open the entrance of the internal flow channel 123. The top of the soil sample chamber is also provided with an outlet sealing port 129, so that the axial pressure sensor 121 and the upper pressure cover solenoid valve 128 are connected to the control system through wires to realize the transmission of detection signals. Preferably, continue to refer to Figure 3 The internal flow channel 123 includes at least two concentrically arranged annular flow channels and also includes a straight flow channel connecting the annular flow channels. That is, the portion of the internal flow channel 123 facing the T-shaped permeable stone 124 is evenly distributed on the side of the upper pressure cover 122 facing the T-shaped permeable stone 124. This arrangement is conducive to improving the efficiency of injecting water into the T-shaped permeable stone 124 to saturate it before consolidation, and is also conducive to ensuring that the T-shaped permeable stone 124 is evenly pressurized through the internal flow channel 123 during the subsequent dehumidification measurement and moisture absorption measurement process, thereby ensuring that the soil sample is evenly pressurized during the subsequent dehumidification measurement and moisture absorption measurement process, and further ensuring the accuracy of the water discharge and water absorption of the soil sample during the dehumidification measurement and moisture absorption measurement process.

[0060] In the above scheme, by setting an internal flow channel 123 inside the upper pressure cover 122, it is convenient to inject water into the T-shaped permeable stone 124 set on the top of the soil sample 1210 to saturate it before the consolidation operation. By setting the upper pressure cover solenoid valve 128, the internal flow channel 123 can be closed during the consolidation operation, so that the water in the soil sample 1210 can be prevented from being pressed into the T-shaped permeable stone 124 on the top during the consolidation process, ensuring that all the water discharged during the consolidation process enters the horizontal measuring tube 15, thereby overcoming the problem of inaccurate measurement of consolidation drainage. By setting an axial load sensor in conjunction with the control system, the size of the vertical load applied by the axial loading rod 7 can be accurately grasped and controlled in real time. Preferably, the control system in this example adopts a PLC all-in-one machine 16. The PLC control system has the advantages of simple programming, reliable operation, high flexibility, strong adaptability and low cost, and has good adaptability for the soil-water characteristic curve test.

[0061] At the same time, as a preferred embodiment of this example, the drain pipe 13 is a rigid hard pipe, and the two ends of the drain pipe 13 are respectively connected to the permeable base 1213 and the horizontal measuring tube 15, and the weighing device is a precision balance 14. Since one end of the drain pipe 13 is connected to the horizontal measuring tube 15, the change of the center of gravity of the drain pipe 13 and the water inside it can easily affect the measurement accuracy of the change of the water volume inside the horizontal measuring tube 15 by the precision balance 14, and the use of a rigid hard pipe for the drain pipe 13 allows the drain pipe 13 to maintain the same posture and shape throughout the experiment, thereby ensuring that the center of gravity of the drain pipe 13 and the water in the drain pipe 13 remains unchanged throughout the experiment to eliminate the influence of the change of the center of gravity on the measurement accuracy of the drainage volume / water absorption, which is conducive to ensuring the accuracy of drawing the soil-water characteristic curve.

[0062] It should be noted here that the above example is only a preferred example in the present application scheme. The setting method and specific structure of the soil sample room system 12 in the present application are not limited to the above example. The setting method of the soil sample room system 12 can also be adaptively modified according to actual testing needs, installation restrictions and other conditions. The present application does not make specific limitations on this.

[0063] Further, refer to Figure 1As shown, the soil-water characteristic curve pressure plate instrument in the present application also includes a cylinder frame 8, and the cylinder 6 is arranged on the cylinder frame 8. The piston rod of the cylinder 6 is connected to the axial loading rod 7, and the lower end portion of the axial loading rod 7 extends into the soil sample chamber. The cylinder frame 8 can be more convenient for the installation and fixation of the cylinder 6 and is conducive to simplifying the structure of the upper cover of the soil sample chamber to facilitate the assembly and sealing of the soil sample chamber. However, the use of this structure requires a through hole to be opened in the upper cover of the soil sample chamber for the axial loading rod 7 to pass through to apply an axial load to the soil sample 1210, and it is also necessary to add a sealing structure between the through hole and the axial loading rod 7 to ensure the sealing of the soil sample chamber, and the sealing structure also has the risk of leakage failure during long-term use. Therefore, as a preferred embodiment of the present application, the cylinder 6 in the present application can also be directly arranged on the upper part of the soil sample chamber, the piston rod is connected to the axial loading rod 7, and the axial loading rod 7 is entirely located in the soil sample chamber. Integrally arranging the cylinder 6 on the soil sample chamber cover eliminates the need for an additional sealing structure. Even if the cylinder 6 and the soil sample chamber cover are assembled separately and a sealing structure is required between the two, the sealing effect is more stable because the cylinder 6 is fixed as a whole relative to the soil sample chamber cover.

[0064] It should also be noted that the setting method of the cylinder 6 in the present application and its specific installation structure are not limited to the above examples. The above are only two preferred implementation schemes in the present application scheme, and other more different setting schemes can also be adopted. The present application does not make specific limitations on this.

[0065] Furthermore, the present application also provides a method for testing a soil-water characteristic curve using the soil-water characteristic curve pressure plate instrument, which mainly includes the following steps:

[0066] Step 1, preparation before the test: vent the instrument pipeline, saturate the clay plate 1212, the permeable base 1213 and the drainage pipe 13, and prepare the saturated soil sample 1210;

[0067] Step 2, installing the saturated soil sample 1210: according to the test requirements, the saturated soil sample 1210 is set in the ring knife 1211, and then the ring knife 1211 and the saturated soil sample 1210 inside are placed on the saturated clay plate 1212, and then the pressing assembly is sealed and assembled and the pressing assembly is set on the upper part of the saturated soil sample 1210, and water is injected into the internal flow channel 123 of the upper pressure cover 122 until the internal flow channel 123 and the T-shaped permeable stone 124 are filled with water and the water injection amount is recorded, which is recorded as m;

[0068] Step 3, consolidation: first, open the gas source and adjust the gas pressure output by the pressure regulating valve 2 to always be higher than the maximum gas pressure value required during the test. The control system controls the upper gland solenoid valve 128 to close the gas inlet port of the internal flow channel 123 of the upper gland 122. Then, according to the test requirements, the control system controls the output gas pressure of the cylinder proportional valve 4 to apply gas pressure to the gas inlet end of the cylinder 6, so that the piston rod of the cylinder 6 drives the axial loading rod 7 to move and drives the pressing assembly to apply a vertical load to the soil sample 1210 until the water displacement during the consolidation process no longer changes, and the consolidation is completed.

[0069] Step 4, dehumidification measurement: After consolidation, the proportional valve 10 in the soil sample chamber is controlled and adjusted by the control system to output multiple levels of air pressure from low to high according to the test requirements, and the air pressures of each level are recorded in sequence as , , ..., ... the control system controls the upper gland solenoid valve 128 to open the air inlet port of the internal flow channel 123 of the upper gland 122, so that the gas under each level of air pressure fills the soil sample chamber and enters the internal flow channel 123 of the upper gland 122, so that the water in the internal flow channel 123 and the T-shaped permeable stone 124 is pressed into the soil sample 1210 and finally discharged into the horizontal measuring tube 15 through the soil sample 1210, the clay plate 1212, the permeable base 1213 and the drainage pipe 13. After the suction is balanced and the drainage volume is stable, the mass of the water discharged into the horizontal measuring tube 15 under each level of air pressure is weighed by the weighing device and the mass of the water discharged into the horizontal measuring tube 15 under each level of air pressure is recorded as , , ..., , ...Then the mass of water actually discharged from soil sample 1210 at each level of air pressure is , , ..., , ...;

[0070] Step 5, moisture absorption measurement: After completing step 4, the proportional valve 10 in the soil sample chamber is controlled and adjusted by the control system to gradually reduce the output pressure according to the test requirements and the pressure at each level is recorded as , , ..., , ...so that the water in the horizontal measuring tube 15 is sucked into the soil sample 1210 through the drainage pipe 13, the permeable base 1213 and the clay plate 1212, and at the same time, the mass of the water reduced in the horizontal measuring tube 15 under each level of air pressure is weighed by a weighing device and the mass of the water reduced in the horizontal measuring tube 15 under each level of air pressure is recorded as , , ..., , ...;

[0071] Step 6: Calculate the volume moisture content of soil sample 1210: According to the measurement results in step 4, the volume moisture content of soil sample 1210 at each level of air pressure during the dehumidification measurement is According to the measurement results in step 5, the volume moisture content of the other soil samples 1210 at each level during the moisture absorption measurement is , where e is the porosity of soil sample 1210, n = 1, 2, 3, ...;

[0072] Step seven, draw the soil-water characteristic curve: according to the calculation results of step six, draw the soil-water characteristic curve of the dehumidification measurement process and the soil-water characteristic curve of the moisture absorption measurement process respectively.

[0073] By adopting the above-mentioned test method, high-precision and fully automatic stress loading of the pressure plate instrument is achieved, thereby realizing automatic control of the entire test process. Compared with traditional manual timing adjustment control, it can greatly save manpower and improve test efficiency and the accuracy of test results. In addition, the above-mentioned method can accurately measure the drainage of the consolidation process, thereby eliminating the influence of inaccurate measurement of consolidation drainage on the accuracy of test results, and can also eliminate the influence of position head on the measurement accuracy of dehumidification drainage and moisture absorption drainage, further ensuring the accuracy of the final test results to obtain a more accurate soil-water characteristic curve.

[0074] Anything not described in this application can be achieved by adopting or drawing on existing technologies.

[0075] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0076] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A soil-water characteristic curve pressure plate instrument, characterized in that: include: A soil sample chamber system, comprising a soil sample chamber for placing soil samples, and a downward pressure component arranged inside the soil sample chamber for transmitting vertical loads to the soil samples, the downward pressure component comprising an upper pressure cover, a T-shaped permeable stone and an annular metal sheet, the interior of the upper pressure cover is provided with an internal flow channel that vertically penetrates the upper pressure cover, the upper part of the upper pressure cover is provided with an inlet of the internal flow channel, and the side of the upper pressure cover facing the T-shaped permeable stone is provided with an outlet of the internal flow channel; an upper pressure cover solenoid valve is also provided at the inlet of the internal flow channel, and the upper pressure cover solenoid valve can close or open the inlet of the internal flow channel, and the internal flow channel comprises at least two concentrically arranged annular flow channels and a straight flow channel connecting the annular flow channels; A stress loading system, used for applying a vertical load to the soil sample placed inside the soil sample chamber, and applying air pressure to the inside of the soil sample chamber; A water quality measurement system, comprising a drainage pipe, a horizontal measuring pipe and a weighing device, wherein both ends of the drainage pipe are respectively connected to the soil sample chamber and the horizontal measuring pipe, and the weighing device is used to weigh the quality of water in the horizontal measuring pipe; A control system, wherein the control system is connected to the soil sample room system, the stress loading system and the water quality measurement system respectively, and the soil sample room system, the stress loading system and the water quality measurement system are controlled in linkage through the control system; In the vertical direction, the center height of the horizontal measuring tube is consistent with the center height of the soil sample; The drainage pipe is a rigid hard pipe.

2. The soil-water characteristic curve pressure plate instrument according to claim 1, characterized in that: The stress loading system includes an air source, a pressure regulating valve, a top air circuit, a bottom air circuit, a cylinder arranged at the top of the soil sample chamber, and an axial loading rod. The air source is connected to the top air circuit and the bottom air circuit through the pressure regulating valve. The top air circuit is connected to the cylinder to drive the axial loading rod to apply a vertical load to the soil sample placed inside the soil sample chamber. The bottom air circuit is connected to the soil sample chamber for applying air pressure to the inside of the soil sample chamber. The top air circuit is provided with a cylinder proportional valve for adjusting the cylinder air pressure to adjust the vertical load applied by the axial loading rod to the soil sample. The bottom air circuit is provided with a soil sample chamber proportional valve for adjusting the air pressure inside the soil sample chamber.

3. The soil-water characteristic curve pressure plate instrument according to claim 2, characterized in that: The flange of the T-shaped permeable stone is arranged between the annular metal sheet and the upper pressure cover, and the annular metal sheet is fastened to the upper pressure cover through a connecting piece and clamps the T-shaped permeable stone; the soil sample chamber system also includes a fixing piece arranged inside the soil sample chamber for limiting the soil sample in the horizontal direction and a bearing assembly for bearing the fixing piece, the pressing assembly and the soil sample, and the bearing assembly includes a permeable base and a clay plate arranged on the upper part of the permeable base.

4. The soil-water characteristic curve pressure plate instrument according to claim 2, characterized in that: It also includes a cylinder frame, the cylinder is arranged on the cylinder frame, the piston rod of the cylinder is connected to the axial loading rod, and the lower end portion of the axial loading rod extends into the soil sample chamber; Alternatively, the cylinder is arranged at the upper part of the soil sample chamber, the piston rod is connected to the axial loading rod and the axial loading rod is entirely located in the soil sample chamber.

5. The soil-water characteristic curve pressure plate instrument according to claim 2, characterized in that: The soil sample chamber system further comprises an axial pressure sensor connected to the axial loading rod, and the axial pressure sensor is used to measure the vertical load applied by the axial loading rod to the top of the soil sample.

6. The soil-water characteristic curve pressure plate instrument according to claim 3, characterized in that: The fixing member is a ring knife, which is in the form of an annular cylindrical structure with a space inside for accommodating the soil sample. The outer diameter of the annular metal sheet is the same as the inner diameter of the ring knife.

7. The soil-water characteristic curve pressure plate instrument according to claim 2, characterized in that: A pressure-bearing groove is provided at the center of the upper portion of the upper pressure cover, the inner wall of the pressure-bearing groove is an arc surface, and the contour of the lower end of the axial loading rod is adapted to the arc surface.

8. A soil-water characteristic curve testing method, characterized in that: The soil-water characteristic curve pressure plate instrument according to any one of claims 1 to 7 comprises the following steps: Step 1, preparation before the test: exhaust the instrument pipeline, saturate the clay plate, permeable base and drain pipe, and prepare the saturated soil sample; Step 2, install the saturated soil sample: according to the test requirements, place the saturated soil sample in the cutter ring, then place the cutter ring and the saturated soil sample inside on the saturated clay plate, then seal and assemble the down-pressing assembly and place the down-pressing assembly on the upper part of the saturated soil sample, and inject water into the internal flow channel of the upper pressure cover until the internal flow channel and the inside of the T-shaped permeable stone are filled with water and record the water injection volume, recorded as m; Step 3, consolidation: first, open the gas source and adjust the gas pressure output by the pressure regulating valve to always be higher than the maximum gas pressure value required during the test. The control system controls the upper gland solenoid valve to close the entrance of the internal flow channel of the upper gland. Then, according to the test requirements, the control system controls the output gas pressure of the cylinder proportional valve to apply gas pressure to the air inlet end of the cylinder, so that the cylinder piston rod drives the axial loading rod to move and drives the downward pressure assembly to apply a vertical load to the soil sample until the water displacement during the consolidation process no longer changes, and the consolidation is completed. Step 4, dehumidification measurement: After consolidation is completed, the proportional valve of the soil sample chamber is controlled by the control system to output multiple levels of air pressure from low to high according to the test requirements, and the air pressure of each level is recorded in sequence as , , ..., ,...The control system controls the solenoid valve of the upper gland to open the entrance of the internal flow channel of the upper gland so that the gas under each level of air pressure fills the soil sample chamber and enters the internal flow channel of the upper gland to press the water in the internal flow channel and the T-shaped permeable stone into the soil sample and finally discharges into the horizontal measuring tube through the soil sample, clay plate, permeable base and drainage pipe. After the suction is balanced and the drainage volume is stable, the mass of water discharged into the horizontal measuring tube under each level of air pressure is weighed by the weighing device and the mass of water discharged into the horizontal measuring tube under each level of air pressure is recorded as , , ..., , ...Then the mass of water actually discharged from the soil sample at each level of air pressure is , , ..., , ...; Step 5, moisture absorption measurement: After completing step 4, according to the test requirements, the control system is used to adjust the proportional valve of the soil sample chamber to gradually reduce the output pressure and record the pressure at each level as , , ..., , ...so that the water in the horizontal measuring tube is sucked into the soil sample through the drainage pipe, the permeable base and the clay plate, and at the same time, the mass of the water reduced in the horizontal measuring tube under each level of air pressure is weighed by the weighing device and the mass of the water reduced in the horizontal measuring tube under each level of air pressure is recorded as , , ..., , ...; Step 6: Calculate the volumetric moisture content of the soil sample: According to the measurement results in step 4, the volumetric moisture content of the soil sample at each level of air pressure during the dehumidification measurement is According to the measurement results in step 5, the volume moisture content of the other soil samples at each level during the moisture absorption measurement is , where e is the porosity of the soil sample, n=1, 2, 3, ...; Step seven, draw the soil-water characteristic curve: according to the calculation results of step six, draw the soil-water characteristic curve of the dehumidification measurement process and the soil-water characteristic curve of the moisture absorption measurement process respectively.

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