Device and method for measuring volume deformation of unsaturated soil in water-force coupling loading process

Abstract

The invention provides a device and a method for measuring volume deformation of unsaturated soil in a water-force coupling loading process. The device comprises a pressure chamber, a loading rod, a first pressure monitoring unit and a second pressure monitoring unit. The loading rod is arranged above the pressure chamber and penetrates through the upper cover of the pressure chamber to be in contact with an unsaturated soil sample in the pressure chamber, and the loading rod reciprocates in the vertical direction to provide loading for the unsaturated soil sample; the first pressure monitoring unit is arranged on one side in the pressure chamber, the second pressure monitoring unit is arranged on the other side in the pressure chamber, one end of the second pressure monitoring unit is flush with one end of the first pressure monitoring unit, and the other ends of the two pressure monitoring units are fixed to the pressure chamber base and communicated with the outside of the pressure chamber. In the water-force coupling loading process of the unsaturated soil sample, the two monitoring units respectively monitor the pressure difference between the two sides in the pressure chamber. According to the scheme provided by the invention, the volume variation of the unsaturated soil sample can be accurately and continuously measured under the complex water-force coupling loading condition.

Description

Technical Field

[0001] The invention relates to the technical field of experimental equipment for soil mechanics and multiphase porous material testing, and in particular to a volume deformation measuring device and method for unsaturated soil that can be used in a water-mechanical coupling loading process. Background Art

[0002] When soil is subjected to hydraulic loading (such as soil wetting and drying), mechanical loading (such as consolidation and shearing), or water-mechanical coupling loading, the soil's internal structure usually changes due to the action of external loads, resulting in a change in volume. This change is represented by volume deformation (or volume change). The volume change of soil is a basic parameter in the study of soil mechanics theoretical models and practical engineering design. Accurately measuring the volume deformation of soil samples during water-mechanical loading is an important part of soil mechanics experiments.

[0003] Generally speaking, since there are only solid phase (solid particles) and liquid phase (water) in saturated soil and both solid particles and water are incompressible, the volume change of saturated soil samples during consolidation shear can be calculated by measuring the volume of liquid discharged or absorbed by the soil sample. This method is simple and has high accuracy. It is currently a commonly used method for measuring the volume deformation of saturated soil samples in triaxial consolidation shear experiments.

[0004] However, the above method for measuring the volume deformation of saturated soil is not applicable to the measurement of the volume deformation of unsaturated soil, which is more commonly distributed in actual engineering. This is because in unsaturated soil samples, in addition to the incompressible solid phase (solid particles) and liquid phase (water), there is also a gas phase (air) that can be compressed and expanded. The change in the volume of unsaturated soil samples during water-mechanical loading is mainly due to the volume change of the gas phase and the liquid phase entering and leaving the sample. Due to the compressibility of air in unsaturated soil, the measurement of its volume change becomes complicated and difficult.

[0005] The existing methods for measuring the volume deformation of unsaturated soil samples mainly include the following categories:

[0006] (1) Use a dual-chamber measurement system. Depending on whether the inner chamber and the outer chamber are connected, the dual-chamber measurement system can be divided into two types, namely, the inner and outer pressure chambers are connected and the inner and outer pressure chambers are closed. The measurement method of the inner and outer pressure chambers are connected. See the following references: Bishop et al. (1961), Josa et al. (1987), Cui et al. (1996), Yin Zongze (1998), and Ng et al. (2002); the measurement method of the inner and outer pressure chambers are closed. See the following references: Wheeler (1986), Sivakumar (1993), Rampino et al. (1999), Yin Jianhua (2002), Mendes et al. (2012), and Mao Jiafeng (2019).

[0007] (2) The method of measuring volume deformation by measuring the volume of gas and liquid fluids in unsaturated soil samples or the change in fluid (especially gas) pressure (Wulfsohn et al. (1998), Laudahn (2005), and Li Jingshuang (2020)).

[0008] (3) The method of using non-contact Hall sensors (Clayton and Khatrush 1986; Clayton et al. 1989) or contact LVDTs (Zhao Yang et al. (2011)) to measure and estimate local strain.

[0009] (4) Non-contact digital image measurement using photoelectric technologies such as CT, DIC, or PIV (Sachanand Penumadu (2007); Higo et al. (2011); Bhadari et al. (2012) etc.).

[0010] Among the above four types of measurement methods, the first type of method belongs to the overall direct measurement method. The measurement results continuously and directly reflect the volume deformation of the unsaturated soil sample, which is the most commonly used measurement method. The main technical difficulties that need to be solved in this type of method are to ensure that the confining pressure applied on both sides of the inner chamber is equal, to ensure that the water in the inner chamber does not leak and there is no gas in the water, to ensure the accuracy of the measurement of the volume change of the water in the inner chamber and the automation of the measurement, and to exclude the interference of factors such as the evaporation of water in the inner chamber, the absorption of water by the pressure chamber wall and the influence of temperature (Xu Jianing et al. 2018). Due to the design of the double pressure chamber, the sample loading process of this type of method is very cumbersome and easy to cause disturbance to the sample; at the same time, because the double pressure chamber system needs to accommodate multiple complex components in a limited space, the size range of the sample to be tested is usually small (for example, the sample size of the most widely used GDS double pressure chamber system is usually 38mm and 50mm in diameter), which limits the testing of larger samples (such as samples composed of larger soil particles) and smaller samples (such as samples used for CT scanning). The second type of method belongs to the method of directly measuring the volume of the fluid to reflect the deformation of the overall sample volume. Compared with water, the measured air is very sensitive to temperature and air pressure during the measurement of gas volume, and the dissolution of air in water. This type of method leads to measurement limitations in principle. The accuracy of the measurement results is significantly affected by environmental factors and is not easy to calibrate the influence of environmental factors. The third type of measurement method uses local measurement results to calculate the overall volume deformation of the sample according to the approximate method. It has good accuracy for small deformation (i.e., high-order Green-Lagrange strain expression can be ignored, usually strain less than 2% can be regarded as small deformation) samples, but the measurement error is significant for large deformation (i.e., sample deformation cannot be accurately predicted by elastic theory) samples and irregular deformation samples, and it is easy to cause disturbance to the measured sample. The fourth type of measurement method can achieve non-disturbance measurement of the sample, but the measurement accuracy depends on the quality and resolution of the acquired image, and the three-axis system needs to have the conditions for installing an image acquisition device; at the same time, the image acquisition system used by the image-based measurement method is very expensive and the laboratory of the image acquisition system usually needs to be specially designed (such as the price of CT is millions of RMB and the environment requires dust-free and constant humidity).

[0011] In summary, the direct measurement method should be the first choice for the volume deformation measurement of unsaturated soil samples. The main aspects that need to be considered in the direct measurement method are: the accuracy and directness of the measurement, the dependence of the measurement method on the environment, the complexity of the measurement system and the requirements for the space of the triaxial test system, the minimum requirements for sample disturbance, and the potential for upgrading and transformation of the measurement system to be installed in the existing triaxial test system. The existing measurement methods are difficult to meet the above requirements at the same time. Therefore, it is urgent to invent a method that can be used to measure the volume deformation of unsaturated soil samples during hydraulic coupling loading. The method of directly measuring the overall volume deformation of the triaxial sample overcomes the shortcomings of the first type of method, such as difficulty in loading, disturbance to the sample, and poor applicability, and overcomes the shortcomings of the second to fourth types of methods, such as being greatly affected by the environment and only being able to indirectly or partially reflect the volume deformation of the sample, so that it is suitable for both the volume deformation measurement of samples in the micro-sized hydraulic coupling loading test system during loading and the volume deformation measurement installed in the conventional triaxial test system. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a device and method for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading, so as to achieve accurate and continuous measurement of the volume change of unsaturated soil samples under complex water-mechanical coupling loading conditions.

[0013] In order to solve the above technical problems, an embodiment of the present invention provides a volume deformation measurement device for unsaturated soil during water-mechanical coupling loading, comprising:

[0014] A pressure chamber, used to hold unsaturated soil samples;

[0015] A loading rod is disposed above the pressure chamber, and the loading rod passes through the pressure chamber upper cover of the pressure chamber and contacts the unsaturated soil sample, and the loading rod reciprocates vertically to provide loading to the unsaturated soil sample;

[0016] A first pressure monitoring unit is disposed on one side of the pressure chamber, a first end of the first pressure monitoring unit is located above a sample cover covering the unsaturated soil sample, and a second end of the first pressure monitoring unit is fixed to a pressure chamber base of the pressure chamber and communicated with the outside of the pressure chamber; and

[0017] A second pressure monitoring unit is arranged at the other side of the pressure chamber, a first end of the second pressure monitoring unit is flush with the first end of the first pressure monitoring unit, and a second end of the second pressure monitoring unit is fixed on the pressure chamber base of the pressure chamber and communicated with the outside of the pressure chamber;

[0018] During the hydraulic-mechanical coupling loading process on the unsaturated soil sample, the first pressure monitoring unit is used to monitor the pressure difference on one side of the pressure chamber, and the second pressure monitoring unit is used to monitor the pressure difference on the other side of the pressure chamber.

[0019] In one embodiment, the first pressure monitoring unit comprises:

[0020] A first vertical tube, wherein a first end of the first vertical tube is located above the sample cover, and a second end of the first vertical tube is fixed to the pressure chamber base and communicated with the outside of the pressure chamber; and

[0021] A first differential pressure sensor is connected to the second end of the first vertical pipe. During the hydraulic-mechanical coupling loading process of the unsaturated soil sample, the first differential pressure sensor is used to monitor the pressure difference between the first vertical pipe and one side of the pressure chamber.

[0022] In one embodiment, the first pressure monitoring unit further comprises:

[0023] a first water connecting pipe, the first water connecting pipe being in communication with the second end of the first vertical pipe, and the first differential pressure sensor being disposed on one side of the first water connecting pipe; and

[0024] A first valve is disposed at the other side of the first water connecting pipe and is connected in parallel with the first differential pressure sensor.

[0025] In one embodiment, the second pressure monitoring unit comprises:

[0026] A second vertical tube, wherein a first end of the second vertical tube is flush with the first end of the first vertical tube, and a second end of the second vertical tube is fixed on the pressure chamber base and communicated with the outside of the pressure chamber; and

[0027] A second differential pressure sensor is connected to the second end of the second vertical pipe and is on the same horizontal plane as the first differential pressure sensor. During the hydraulic-mechanical coupling loading process of the unsaturated soil sample, the second differential pressure sensor is used to monitor the pressure difference between the second vertical pipe and the other side of the pressure chamber.

[0028] In one embodiment, the second pressure monitoring unit further comprises:

[0029] a second water connecting pipe, the second water connecting pipe being in communication with the second end of the second vertical pipe, and the second differential pressure sensor being disposed on one side of the second water connecting pipe; and

[0030] A second valve is disposed at the other side of the second water connecting pipe and is connected in parallel with the second differential pressure sensor.

[0031] In one embodiment, the unsaturated soil volume deformation measuring device further comprises:

[0032] an air connection pipe, one end of which passes through the pressure chamber upper cover and communicates with the pressure chamber; and

[0033] A fourth valve is arranged at the other end of the gas connecting pipeline, and the fourth valve cooperates with the gas connecting pipeline to apply sample confining pressure to the unsaturated soil sample in the pressure chamber.

[0034] In one embodiment, the unsaturated soil volume deformation measuring device further comprises:

[0035] a third water connecting pipe, one end of which is disposed on the pressure chamber base and communicated with the pressure chamber, and two sides of which are respectively communicated with the first differential pressure sensor and the second differential pressure sensor; and

[0036] A third valve is arranged at the other end of the third water connecting pipeline.

[0037] In one embodiment, the unsaturated soil volume deformation measuring device further comprises:

[0038] A linear displacement sensor is disposed above the upper cover of the pressure chamber and fixedly connected to the loading rod, and is used to monitor the displacement of the loading rod when performing vertical reciprocating motion.

[0039] In one embodiment, the top and the interior of the first vertical tube and the second vertical tube are covered with a hydrophilic coating.

[0040] An embodiment of the present invention further provides a method for measuring the volume deformation of unsaturated soil during the water-mechanical coupling loading process based on the above-mentioned device, comprising the following steps:

[0041] The unsaturated soil sample is installed in a pressure chamber;

[0042] At the initial time t of the water-mechanical coupling loading on the unsaturated soil sample 0 , open the first valve and inject air-free water into the pressure chamber through the first water connecting pipe and the first vertical pipe until the air-free water enters the second vertical pipe and reaches a preset water level height h 0 , and simultaneously record a first initial pressure difference currently monitored by the first differential pressure sensor and a second initial pressure difference currently monitored by the second differential pressure sensor;

[0043] When the unsaturated soil sample is subjected to hydraulic-mechanical coupling loading, a loading rod uniformly applies pressure to the unsaturated soil sample at a preset loading speed v' until a preset time t i , and at the preset time t i When the first differential pressure sensor monitors the first pressure difference and the second differential pressure sensor monitors the second pressure difference;

[0044] The volume change of the unsaturated soil sample during the hydraulic-mechanical coupling loading process is determined according to the first initial pressure difference, the second initial pressure difference, the first pressure difference, the second pressure difference and the preset loading speed v'.

[0045] The above solution of the present invention includes at least the following beneficial effects:

[0046] (1) The measuring device of the present invention adopts a double vertical pipe structure, which is convenient for installation in a single pressure chamber system, thereby greatly expanding the experimental capabilities of a large number of existing single pressure chamber instruments that can only be used for saturated soil experiments, making them applicable to the measurement of unsaturated soil; at the same time, the measurement principle based on the dual differential pressure sensor is adopted, and the volume deformation of the sample can be directly measured without using a dual pressure chamber system, ensuring that the measurement process is simple and reliable and the measurement results are accurate.

[0047] (2) Compared with the dual pressure chamber system, the measuring device of the present invention can greatly reduce the complexity of operation during the experiment, reduce the sample disturbance caused by the stiffness of the water pipe connected to the upper sample cover in a narrow space in the dual pressure chamber system, and avoid the common problems of water leakage in the internal pressure chamber of the dual pressure chamber system. At the same time, compared with the dual pressure chamber system measurement method, the measurement range is limited by the throat size of the internal pressure chamber. The measuring device of the present invention has a wide adaptability to the size range of the sample to be measured. For samples of different sizes, it is only necessary to adjust the ratio of the cross-sectional area of ​​the vertical pipe in the pressure monitoring unit to the cross-sectional area of ​​the pressure chamber to achieve higher accuracy.

[0048] (3) Compared with the dual pressure chamber system, the measuring device of the present invention has a simple structure and greatly reduced manufacturing cost, which is conducive to large-scale use in engineering design and is suitable for unsaturated soil volume deformation measurement in micro-experimental systems, such as soil sample measurement in the in-situ loading system of X-ray CT. It is a method that can realize continuous volume deformation measurement in the current CT in-situ loading system and is also suitable for large-scale experimental systems, such as experimental systems for super-large samples containing gravel (such as cylindrical samples with a diameter of 500 mm and a height of 1000 mm).

[0049] (4) The measuring device of the present invention is based on a single pressure chamber for sample loading and measurement. Compared with a dual pressure chamber, it can greatly reduce the structural complexity and sample installation difficulty, avoid sample collapse when installing loose sand samples or soft clay samples that are easily disturbed in the dual pressure chamber system and then installing the inner pressure chamber, thereby reducing the probability of sample loading failure.

[0050] (5) The measuring device of the present invention has wide adaptability to environmental variables such as temperature and air pressure. When the temperature or pressure environment in which the device is located changes, such as moving from a plain to a plateau, a reference curve can be calibrated at the temperature and pressure to conduct experiments without the need for complex calibration procedures.

[0051] (6) Although the measuring device and method of the present invention are proposed for measuring the volume deformation of unsaturated soil, they can measure whether the soil particles are filled with incompressible water or compressible gas or water-gas mixture, which is obviously superior to other unsaturated soil and dry soil volume deformation measurement methods. However, from its measurement principle, it can be seen that this method is also applicable to the volume deformation measurement of saturated soil samples and dry soil samples, as well as the volume deformation measurement of other multi-phase porous materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a schematic diagram of the overall structure of a device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading provided by an embodiment of the present invention;

[0053] Figure 2 It is a flow chart of a measurement method of a device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading provided by an optional embodiment of the present invention.

[0054] Description of Figure Numbers:

[0055] 1. Loading rod; 2. Linear displacement sensor; 31. Top permeable stone; 32. Bottom permeable stone; 33. Sample cover; 34. Latex membrane; 4. First vertical pipe; 5. Pressure chamber; 51. Pressure chamber upper cover; 52. Pressure chamber base; 61. First water connecting pipe; 62. First valve; 71. Second water connecting pipe; 72. Second valve; 81. Third water connecting pipe; 82. Third valve; 91. Air connecting pipe; 92. Fourth valve; 10. O-ring; 11. Unsaturated soil sample; 12. Second vertical pipe; 13. First differential pressure sensor; 14. Second differential pressure sensor. DETAILED DESCRIPTION

[0056] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0057] In the description of the present invention, it is to be understood that the terms "include / comprise", "consist of" or any other variation thereof are intended to cover non-exclusive inclusion, so that a product, device, process or method including a series of elements includes not only those elements, but also other elements not explicitly listed when necessary, or also includes elements inherent to such product, device, process or method. In the absence of further restrictions, the elements defined by the phrases "include / comprise...", "consist of..." do not exclude the presence of other identical elements in the product, device, process or method including the elements.

[0058] It should also be understood that terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “top”, “bottom”, “inside” and “outside” to indicate directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the device, component or structure referred to must have a specific direction, be constructed or operate in a specific direction, and should not be understood as a limitation on the present invention.

[0059] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0060] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; 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 the present invention can be understood according to specific circumstances.

[0061] The measuring device provided in the following embodiments of the present invention can be used for direct measurement of volume deformation in indoor triaxial compression consolidation and shear tests of unsaturated soil samples, and is particularly suitable for the following two types of working conditions:

[0062] (1) Suitable for modifying existing conventional triaxial tests to enable direct volume deformation measurements under complex stress loading conditions;

[0063] (2) In addition to the micro-experimental system, the system is used to measure the volume deformation of the compression consolidation and shear micro-devices installed inside the X-ray CT for in-situ loading and imaging. It is also suitable for large-scale devices for large-size samples, such as experimental systems for ultra-large samples containing gravel (such as cylindrical samples with a diameter of 500 mm and a height of 1000 mm).

[0064] like Figure 1 As shown, an embodiment of the present invention provides a device and method for measuring volume deformation of unsaturated soil during hydraulic-mechanical coupling loading, which may include a pressure chamber 5, a loading rod 1, a first pressure monitoring unit, and a second pressure monitoring unit. Among them, the pressure chamber 5 is used to hold the unsaturated soil sample 11; the loading rod 1 is arranged above the pressure chamber 5, and the loading rod 1 passes through the pressure chamber upper cover 51 of the pressure chamber 5 and contacts the unsaturated soil sample 11, and the loading rod 1 reciprocates vertically to provide loading to the unsaturated soil sample 11; the first pressure monitoring unit is arranged on one side of the pressure chamber 5, the first end of the first pressure monitoring unit is located above the sample cover 33 covering the unsaturated soil sample 11, the second end of the first pressure monitoring unit is fixed on the pressure chamber base 52 of the pressure chamber 5 and communicates with the outside of the pressure chamber 5; the second pressure monitoring unit is arranged on the other side of the pressure chamber 5, the first end of the second pressure monitoring unit is flush with the first end of the first pressure monitoring unit, the second end of the second pressure monitoring unit is fixed on the pressure chamber base 52 of the pressure chamber 5 and communicates with the outside of the pressure chamber 5; in the process of hydraulic-mechanical coupling loading of the unsaturated soil sample 11, the first pressure monitoring unit is used to monitor the pressure difference on one side of the pressure chamber 5, and the second pressure monitoring unit is used to monitor the pressure difference on the other side of the pressure chamber 5.

[0065] In this embodiment, the pressure chamber 5 is a triaxial single pressure chamber with a first cavity structure, in which an unsaturated soil sample 11 is loaded; the first pressure monitoring unit and the second pressure monitoring unit are symmetrically arranged inside the pressure chamber 5, and are respectively located on both sides of the unsaturated soil sample 11, so as to monitor the pressure difference on both sides of the pressure chamber 5 during the hydraulic-mechanical coupling loading process of the unsaturated soil sample 11;

[0066] The loading rod 1 is arranged at the top of the pressure chamber 5, with one end located outside the pressure chamber 5, and the other end passing through the pressure chamber upper cover 51 of the pressure chamber 5 and penetrating into the pressure chamber 5 to contact the top of the unsaturated soil sample 11. The loading rod 1 can reciprocate vertically (i.e., the axial direction of the pressure chamber 5) to provide loading (i.e., vertical pressure) to the unsaturated soil sample 11 when the unsaturated soil sample 11 is subjected to water-mechanical coupling loading;

[0067] Before the unsaturated soil sample 11 is subjected to hydraulic-mechanical coupling loading by the measuring device of this embodiment, air-free water is first supplied to the pressure chamber 5 through the first pressure monitoring unit until the air-free water covers the unsaturated soil sample 11 and enters the second pressure monitoring unit until the water level reaches a preset water level. At this time, the preset water level serves as the initial position before the loading experiment. At the same time, the pressure difference on both sides of the pressure chamber 5 is monitored by the first pressure monitoring unit and the second pressure monitoring unit, respectively, and serves as the initial pressure difference before the loading experiment. When the hydraulic-mechanical coupling loading is performed, the unsaturated soil sample 11 is uniformly and continuously loaded by the loading rod 1, and the pressure difference is uniformly and continuously loaded by the second pressure monitoring unit. The first pressure monitoring unit and the second pressure monitoring unit monitor the pressure difference on both sides of the pressure chamber 5 during the loading process in real time; when hydraulic-mechanical coupling loading is performed and the loading is performed to a preset time, based on the principle of water balance in the entire pressure chamber 5 during the loading process (that is, the total water volume in the first pressure monitoring unit, the second pressure monitoring unit and the pressure chamber 5 remains unchanged), and according to the pressure difference on both sides of the pressure chamber 5 corresponding to the current preset time monitored by the first pressure monitoring unit and the second pressure monitoring unit and the initial pressure difference on both sides of the pressure chamber 5 before the loading starts, the volume change of the unsaturated soil sample 11 in the pressure chamber 5 during the loading process to the preset time can be determined.

[0068] The measuring device provided by the above-mentioned embodiment of the present invention is based on the measurement principle of collecting the pressure difference change in the pressure chamber 5 monitored by the first pressure monitoring unit and the second pressure monitoring unit during the deformation process of the unsaturated soil sample 11 caused by water-mechanical coupling loading, thereby ensuring high measurement accuracy and high measurement reliability; it has a wide adaptability to the size of the unsaturated soil sample 11, and the experimental system for large-size samples and small-size samples can effectively measure the volume deformation; at the same time, since the measuring device is based on a single pressure chamber for sample loading and measurement, compared with the double pressure chamber method, it can greatly reduce the structural complexity and sample installation difficulty, thereby avoiding disturbing samples such as loose sand and soft soil that are easily disturbed when loading the sample, reducing the failure rate of sample volume change measurement, so as to accurately and continuously measure the volume change of the unsaturated soil sample under complex water-mechanical coupling loading conditions.

[0069] The measuring device provided in the above embodiment of the present invention is also equipped with a data acquisition device (not shown in the figure). The data acquisition device can be arranged outside the pressure chamber 5 and connected to the loading rod 1 to collect relevant experimental data. The data acquisition device is constructed using a conventional data acquisition module and a control module to realize data acquisition.

[0070] In an optional embodiment of the present invention, the pressure chamber 5 may include a pressure chamber side wall, a pressure chamber top cover 51 fixedly connected to the top of the pressure chamber side wall, and a pressure chamber base 52 fixedly connected to the bottom of the pressure chamber side wall; the pressure chamber side wall, the pressure chamber top cover 51 and the pressure chamber base 52 are interconnected to form a first cavity structure for loading the unsaturated soil sample 11; preferably, a sealing ring may be arranged between the pressure chamber top cover 51 and the top of the pressure chamber side wall and between the pressure chamber base 52 and the bottom of the pressure chamber side wall to ensure the sealing of the pressure chamber 5.

[0071] Here, a latex membrane 34 with a three-dimensional cavity structure is provided in the first cavity structure of the pressure chamber 5. Preferably, the three-dimensional cavity structure is cylindrical, and a top permeable stone 31 and a bottom permeable stone 32 are respectively provided at the top and bottom of the latex membrane 34. The unsaturated soil sample 11 is loaded in a second cavity structure formed by connecting the latex membrane 34, the top permeable stone 31 and the bottom permeable stone 32. The latex membrane 34, the top permeable stone 31 and the bottom permeable stone 32 are provided to facilitate the hydraulic-mechanical testing of the unsaturated soil sample 11. Water is supplied to the unsaturated soil sample 11 before coupling loading, and water permeability is achieved during the process of water-mechanical coupling loading of the unsaturated soil sample 11; preferably, O-rings are respectively provided on the outer walls of the top and bottom of the latex membrane 34 with a three-dimensional cavity structure, and more preferably, two O-rings are respectively provided on the outer walls of the top and bottom of the latex membrane 34 at intervals, and the O-rings are sleeved on the outside of the latex membrane 34 to tighten the latex membrane 34 and seal and isolate the liquid or gas inside (sample) and outside (pressure chamber) of the latex membrane 34.

[0072] Here, the bottom of the latex membrane 34 is fixed on the pressure chamber base 52, the bottom permeable stone 32 is arranged at the bottom inside the latex membrane 34 and is fixedly connected to the pressure chamber base 52; the top permeable stone 31 is arranged at the top inside the latex membrane 34, and a sample cover 33 is arranged above the top permeable stone 31 to encapsulate the unsaturated soil sample 11; at the same time, the other end of the loading rod 11 is fixedly connected to the top of the sample cover 33, so that the vertical pressure on the unsaturated soil sample 11 is uniform and consistent during the water-mechanical coupling loading process.

[0073] In an optional embodiment of the present invention, the first pressure monitoring unit may include a first vertical tube 4 and a first differential pressure sensor 13. The first end of the first vertical tube 4 is located above the sample cover 33, and the second end of the first vertical tube 4 is fixed on the pressure chamber base 52 and communicates with the outside of the pressure chamber 5; the first differential pressure sensor 13 is connected to the second end of the first vertical tube 4, and the first differential pressure sensor 13 is used to monitor the pressure difference between the first vertical tube 4 and one side of the pressure chamber 5 during the hydraulic-mechanical coupling loading process of the unsaturated soil sample 11.

[0074] In this embodiment, the first vertical tube 4 is arranged in the first cavity structure of the pressure chamber 5 and is located on one side of the second cavity structure; the first end of the first vertical tube 4 extends into the first cavity structure of the pressure chamber 5 and the first end of the first vertical tube 4 is higher than the top of the sample cover 33; the second end of the first vertical tube 4 passes through and is fixed on the pressure chamber base 52 and is connected to the outside of the pressure chamber 5 at the same time, so as to supply air-free water to the first cavity structure of the pressure chamber 5; before hydraulic-mechanical coupling loading is performed, the air-free water injected through the first vertical tube 4 can enter the pressure chamber 5 along the first vertical tube 4 until the air-free water submerges the entire unsaturated soil sample 11.

[0075] The first differential pressure sensor 13 is disposed outside the pressure chamber 5 and connected to the second end of the first vertical pipe 4 , so as to monitor the pressure difference between the first vertical pipe 4 and one side of the pressure chamber 5 in real time during the hydraulic-mechanical coupling loading process.

[0076] In an optional embodiment of the present invention, the second pressure monitoring unit may include a second vertical pipe 12 and a second differential pressure sensor 14. The first end of the second vertical pipe 12 is flush with the first end of the first vertical pipe 4, and the second end of the second vertical pipe 12 is fixed on the pressure chamber base 52 and communicated with the outside of the pressure chamber 5; the second differential pressure sensor 14 is connected to the second end of the second vertical pipe 12 and the second differential pressure sensor 14 and the first differential pressure sensor 13 are on the same horizontal plane. The second differential pressure sensor 14 is used to monitor the pressure difference between the second vertical pipe 12 and the other side of the pressure chamber 5 during the hydraulic-mechanical coupling loading process of the unsaturated soil sample 11.

[0077] In this embodiment, the second vertical tube 12 is arranged in the first cavity structure of the pressure chamber 5 and is located on the other side of the second cavity structure; the first end of the second vertical tube 12 extends into the first cavity structure of the pressure chamber 5 and the first end of the second vertical tube 12 is flush with the first end of the first vertical tube 4; the second end of the second vertical tube 12 passes through and is fixed on the pressure chamber base 52 and is connected to the outside of the pressure chamber 5; before the hydraulic-mechanical coupling loading is performed, when air-free water is injected into the pressure chamber 5 through the first vertical tube 4 and the entire unsaturated soil sample 11 is immersed, since the first end of the first vertical tube 4 is higher than the top of the sample cover 3, when the air-free water is continuously injected, the air-free water will enter the second vertical tube 12; at this time, the amount of air-free water injected is controlled so that the air-free water in the second vertical tube 12 is at a preset height, and then the vertical pressure on the unsaturated soil sample 11 is started through the loading rod 1 to perform the hydraulic-mechanical coupling loading experiment.

[0078] The second differential pressure sensor 14 is arranged outside the pressure chamber 5 and connected to the second end of the second vertical tube 12 to monitor the pressure difference between the second vertical tube 4 and the other side of the pressure chamber 5 in real time during the water-mechanical coupling loading process; here, when the volume becomes smaller, the water surface area in the pressure chamber 5 is the total cross-sectional area inside the pressure chamber 5 minus the cross-sectional area of ​​the first vertical tube 4 and the second vertical tube 12 and the area of ​​the loading rod (the area of ​​the loading rod is generally fixed), so the accuracy and measurement range of the second differential pressure sensor 14 and the first differential pressure sensor 13 are flexibly determined by the ratio of the sum of the cross-sectional areas of the first vertical tube 4 and the second vertical tube 12 to the cross-sectional area of ​​the pressure chamber 5 and the volume change measurement accuracy requirements. Preferably, since the water level change range in the pressure chamber 5 is smaller than the water level change range in the second vertical tube 12, the accuracy of the first differential pressure sensor 13 is higher than that of the second differential pressure sensor 14, so as to ensure the measurement accuracy during the increase and decrease of the sample. The first differential pressure sensor 13 and the second differential pressure sensor 14 are at the same horizontal height outside the pressure chamber 5 to ensure the accuracy of differential pressure monitoring.

[0079] In an optional embodiment of the present invention, the first vertical tube 4 and the second vertical tube 12 are both made of transparent material to facilitate observation of the water level in the vertical tube before water-mechanical coupling loading; preferably, the transparent material can be any one of polymethyl methacrylate, inorganic glass or quartz.

[0080] In an optional embodiment of the present invention, the top and interior of the first vertical tube 4 and the second vertical tube 12 are covered with a hydrophilic coating, so that the air-free water can flow in the first vertical tube 4 and the second vertical tube 12, and smoothly flow out of the first vertical tube 4 and flow into the second vertical tube 12, thereby avoiding the problem of water blockage caused by the formation of wall water droplets and air bubbles in the first vertical tube 4 and the second vertical tube 12 in a small-size system. At the same time, the small contact angle brought by the hydrophilicity accelerates the liquid flow rate, thereby reducing the measurement hysteresis time; preferably, the controlled contact angle between the hydrophilic coating and the top and interior of the first vertical tube 4 and the top and interior of the second vertical tube 12 is less than a preset angle, and more preferably, the preset angle is less than 5°, so as to accelerate the flow rate of the air-free water, reduce the measurement hysteresis time, and thus improve the response speed of the measurement system.

[0081] Here, the diameters of the first vertical tube 4 and the second vertical tube 12 do not need to be the same, and the outer cross-sectional areas of the first vertical tube 4 and the second vertical tube 12 can be specifically determined according to the size of the unsaturated soil sample 11 and the cross-sectional area of ​​the pressure chamber 5;

[0082] Preferably, the inner diameter of the second vertical pipe 12 can be determined according to the accuracy of the differential pressure sensor and the size of the unsaturated soil sample 11, with the water level change of the second vertical pipe 12 corresponding to the volume change of the unsaturated soil sample 11 being detected by the differential pressure sensor being no greater than the preset accuracy as a benchmark; preferably, the preset accuracy can be 0.5%. That is, when the volume of the unsaturated soil sample 11 increases by 0.5%, the corresponding volume of airless water in the pressure chamber 5 will flow into the second vertical pipe 12, and the water level in the second vertical pipe 12 will change, thereby causing the pressure difference change of the airless water in the second vertical pipe 12 to be a certain value, and the accuracy of the differential pressure sensor needs to be able to at least measure the certain value;

[0083] Preferably, the inner diameter of the first vertical tube 4 can be large or small, and the outer diameter is related to the diameter of the second vertical tube 12 and the size of the pressure chamber 5 .

[0084] In an optional embodiment of the present invention, the first pressure monitoring unit may further include a first water connecting pipe 61 and a first valve 62. The first water connecting pipe 61 is connected to the second end of the first vertical pipe 4, and the first differential pressure sensor 13 is arranged on one side of the first water connecting pipe 61; the first valve 62 is arranged on the other side of the first water connecting pipe 61 and is arranged in parallel with the first differential pressure sensor 13.

[0085] In this embodiment, one end of the first water connecting pipe 61 passes through and is fixed on the pressure chamber base 52 and is connected to the second end of the first vertical pipe 4. The other end of the first water connecting pipe 61 extends outside the pressure chamber base 52, and the other side of the other end of the first water connecting pipe 61 is fixedly connected to the first valve 62; here, the first differential pressure sensor 13 is connected to one side of the other end of the first water connecting pipe 61.

[0086] The first water connecting pipe 61 and the first valve 62 are arranged so as to exhaust the air in the first vertical pipe 4 before the start of the hydraulic-mechanical coupling loading experiment, inject airless water into the pressure chamber 5 after exhausting the air in the first vertical pipe 4, and exhaust the airless water in the first vertical pipe 4 after the experiment; it should be known that during the process of pushing the unsaturated soil sample 11 by the loading rod 1, the first valve 62 is always in a closed state to ensure the accuracy of the hydraulic-mechanical coupling loading experiment.

[0087] In an optional embodiment of the present invention, the second pressure monitoring unit may further include a second water connecting pipe 71 and a second valve 72. The second water connecting pipe 71 is connected to the second end of the second vertical pipe 12, and the second differential pressure sensor 14 is arranged on one side of the second water connecting pipe 71; the second valve 72 is arranged on the other side of the second water connecting pipe 71 and is arranged in parallel with the second differential pressure sensor 14.

[0088] In this embodiment, one end of the second water connecting pipe 71 passes through and is fixed on the pressure chamber base 52 and is connected to the second end of the second vertical pipe 12. The other end of the second water connecting pipe 71 extends outside the pressure chamber base 52, and the other side of the other end of the second water connecting pipe 71 is fixedly connected to a second valve 72; here, the second differential pressure sensor 14 is connected to one side of the other end of the second water connecting pipe 71 and is maintained at the same horizontal height as the first differential pressure sensor 13.

[0089] The second water connecting pipe 71 and the second valve 72 are arranged to discharge the air in the second vertical pipe 12 before the start of the water-mechanical coupling loading experiment and to discharge the airless water in the first vertical pipe 4 after the experiment; it should be known that during the process of injecting airless water into the pressure chamber 5 and pushing the unsaturated soil sample 1 through the loading rod 1, the second valve 72 is always in a closed state to ensure the accuracy of the water-mechanical coupling loading experiment.

[0090] In an optional embodiment of the present invention, the volume deformation measuring device of unsaturated soil may further include an air connection pipe 91 and a fourth valve 92. One end of the air connection pipe 91 passes through the pressure chamber upper cover 51 and is connected to the pressure chamber 5; the fourth valve 92 is arranged at the other end of the air connection pipe 91, and the fourth valve 92 cooperates with the air connection pipe 91 to apply sample confining pressure to the pressure chamber 5.

[0091] In this embodiment, the gas connecting pipe 91 is fixed to one side of the pressure chamber top cover 51, and one end of the gas connecting pipe 91 passes through the pressure chamber top cover 51 to communicate with the first cavity structure of the pressure chamber 5, and the other end of the gas connecting pipe 91 is placed outside the pressure chamber top cover 51 and is connected to a fourth valve 92, so as to facilitate the timely filling of gas into the pressure chamber 5 to apply sample confining pressure to the first cavity structure of the pressure chamber 5 to simulate the pressure conditions of unsaturated soil samples when buried at different depths below the formation.

[0092] In an optional embodiment of the present invention, the volume deformation measuring device for unsaturated soil may further include a third water connecting pipe 81 and a third valve 82. One end of the third water connecting pipe 81 is disposed on the pressure chamber base 52 and communicated with the pressure chamber 5, and both sides of the third water connecting pipe 81 are respectively communicated with the first differential pressure sensor 13 and the second differential pressure sensor 14; the third valve 82 is disposed at the other end of the third water connecting pipe 81.

[0093] In this embodiment, one end of the third water connecting pipe 81 passes through and is fixed on the pressure chamber base 52, and is connected to the first cavity structure of the pressure chamber 5 to balance the sample confining pressure applied by the gas connecting pipe 91 and the fourth valve 92; the other end of the third water connecting pipe 81 extends to the outside of the pressure chamber base 52, and a third valve 82 is fixed at the opening of the other end of the third water connecting pipe 81; and one side of the third water connecting pipe 81 is connected to one side of the first differential pressure sensor 13, and the other side of the third water connecting pipe 81 is connected to the other side of the second differential pressure sensor 14.

[0094] The third water connecting pipe 81 and the third valve 82 are arranged to discharge the air in the first cavity structure of the pressure chamber 5 before the start of the water-mechanical coupling loading experiment and to discharge the airless water in the first cavity structure of the pressure chamber 5 after the experiment, and can also balance the sample confining pressure applied in the pressure chamber 5 through the air connecting pipe 91 and the fourth valve 92.

[0095] It should be known that, during the process of injecting airless water into the pressure chamber 5 and pushing the unsaturated soil sample 1 through the loading rod 1, the second valve 72 is always in a closed state to ensure the accuracy of the water-mechanical coupling loading experiment.

[0096] In an optional embodiment of the present invention, the volume deformation measuring device for unsaturated soil may further include a linear displacement sensor 2, which is disposed above the pressure chamber upper cover 51 and fixedly connected to the loading rod 1, and is used to monitor the displacement of the loading rod 1 when performing vertical reciprocating motion.

[0097] In this embodiment, the linear displacement sensor 2 is arranged on one side of the pressure chamber top cover 51, and the fixed end of the linear displacement sensor 2 is rigidly connected to one end of the loading rod 1, and the movable contact end of the linear displacement sensor 2 contacts the pressure chamber top cover 52 to measure the up and down displacement of the loading rod 1 (also the unsaturated soil sample 11) performing vertical reciprocating motion.

[0098] When the unsaturated soil sample 11 is subjected to a water-mechanical coupling loading experiment to measure its volume change, the changes in the water levels of the first vertical tube 4, the second vertical tube 12 and the pressure chamber 5 in the measuring device are caused by the volume change of the unsaturated soil sample 11 and the volume change of the loading rod 1 immersed in airless water; wherein, the volume change of the loading rod 1 immersed in water can be converted from the diameter of the loading rod 1 and the up and down displacement monitored by the linear displacement sensor 2; the displacement change of the loading rod 1 during the loading experiment is monitored by the linear displacement sensor 2, so as to facilitate the subsequent conversion of the volume change of the unsaturated soil sample 11.

[0099] The measuring device provided by the above-mentioned embodiment of the present invention provides vertical pressure to the unsaturated soil sample 11 in the pressure chamber 5 by arranging a loading rod 1 at the top of the pressure chamber 5; provides air-free water to the pressure chamber 5 by arranging two vertical pipes in the pressure chamber 5; and monitors the pressure change in the two vertical pipes (equivalent to the pressure change in the pressure chamber 5) when the vertical pressure is provided to the unsaturated soil sample 11 by the loading rod 1 by arranging two vertical pipes in the pressure chamber 5 at the same horizontal height outside the pressure chamber 5 and respectively connected to the other ends of the two vertical pipes.

[0100] When the unsaturated soil sample 11 is subjected to a hydraulic-mechanical coupling loading experiment, based on the specific structure of the measuring device provided in the above embodiment and the water balance principle in the pressure chamber 5, the total amount of water in the first vertical tube 4, the second vertical tube 12 and the pressure chamber 5 remains unchanged; during the hydraulic-mechanical coupling loading process, the volume change of the unsaturated soil sample 11 during the loading process can be deduced through the pressure changes on different sides of the pressure chamber 5; the specific derivation principle is: during the hydraulic-mechanical coupling loading process, the change of the water level in the first vertical tube 4, the second vertical tube 12 and the pressure chamber 5 in the measuring device is caused by the volume change of the unsaturated soil sample 11 and the volume change of the loading rod 1 immersed in airless water; wherein, the volume change of the loading rod 1 immersed in water can be converted from the diameter of the loading rod 1 and the up and down displacement monitored by the linear displacement sensor 2; and the change of the water volume in the first vertical tube 4, the second vertical tube 12 and the pressure chamber 5 at a certain moment relative to the initial moment in the measuring device is converted from the pressure difference data monitored by the first differential pressure sensor 13 and the second differential pressure sensor 14.

[0101] When the unsaturated soil sample 11 in the pressure chamber 5 is subjected to a water-mechanical coupling loading experiment, it is required that in the initial state (before loading), the water level in the second vertical pipe 12 should be located near the bottom of the second vertical pipe 12, and the water level in the first vertical pipe 4 should be flush with the water level in the pressure chamber 5 (equivalent to the top level of the first vertical pipe 4); when loading is performed through the loading rod 1, when the volume of the unsaturated soil sample 11 is pressurized, the water overflowing from the pressure chamber 5 will overflow into the second vertical pipe 12. Since the water overflowing from the pressure chamber 5 overflows into the second vertical pipe 12 and the volume in the second vertical pipe 12 increases, the pressure in the second vertical pipe 12 will increase. The amount of water can be obtained by converting the pressure difference data monitored by the second pressure difference sensor 14, and the water levels in the pressure chamber 5 and the first vertical pipe 4 will remain unchanged at this time; when the volume of the unsaturated soil sample 11 is compressed and reduced, the water level in the first vertical pipe 4 remains unchanged while the water level in the pressure chamber 5 decreases, and the amount of water reduced in the pressure chamber 5 can be obtained by converting the pressure difference data monitored by the first pressure difference sensor 13; during the loading process, the volume of the loading rod 1 infiltrated by the pressure chamber 5 may increase or decrease, and the infiltrated volume is calculated by multiplying the cross-sectional area of ​​the loading rod 1 by the change in its vertical displacement (measured by the linear displacement sensor 2).

[0102] Based on the above derivation principle, an embodiment of the present invention further provides a measurement method 100 of a volume deformation measurement device for unsaturated soil during a hydraulic-mechanical coupling loading process based on the above embodiment. Figure 2 As shown, the specific steps include:

[0103] Step 110, installing the unsaturated soil sample 11 in the pressure chamber 5;

[0104] Step 120, at the initial time t of water-mechanical coupling loading on the unsaturated soil sample 11 0 , open the first valve 62 and inject airless water into the pressure chamber 5 through the first water connecting pipe 61 and the first vertical pipe 4 until the airless water enters the second vertical pipe 12 and reaches the preset water level h 0 At the same time, a first initial pressure difference monitored by the first differential pressure sensor 13 and a second initial pressure difference monitored by the second differential pressure sensor 14 are recorded;

[0105] Step 130, when the unsaturated soil sample 11 is subjected to hydraulic-mechanical coupling loading, the loading rod 1 uniformly applies pressure to the unsaturated soil sample 11 at a preset loading speed v' until a preset time t i , and at the preset time t i When the first differential pressure sensor 13 monitors the first differential pressure difference and the second differential pressure sensor 14 monitors the second differential pressure difference;

[0106] Step 140, determining the volume change of the unsaturated soil sample 11 during the hydraulic-mechanical coupling loading process according to the first initial pressure difference, the second initial pressure difference, the first pressure difference, the second pressure difference and the preset loading speed v'.

[0107] In this embodiment, at the initial time t before the water-mechanical coupling loading 0 (Before the loading experiment begins, that is, after the unsaturated soil sample 11 is installed), open the first valve 62 and inject airless water into the pressure chamber 5 through the first water connecting pipe 61 and the first vertical pipe 4 in sequence until the airless water in the second vertical pipe 12 reaches the preset water level h. 0 During this process, the second valve 72 and the third valve 82 need to be opened in time to exhaust all the air in the second vertical pipe 12 and the pressure chamber 5.

[0108] Since the top of the first vertical tube 4 and the second vertical tube 12 are located above the sample cover 33, the air-free water enters the air-free water in the second vertical tube 12 to a preset water level h. 0 When the water level in the first vertical pipe 4 is equal to the top port thereof, the initial water level height y in the pressure chamber 5 is 0flush with the end of the first vertical pipe 4; here, the airless water in the second vertical pipe 12 reaches the preset water level h 0 The position is the position near the bottom of the second vertical pipe 12; at the same time, the first initial pressure difference P monitored by the current first pressure difference sensor 13 is recorded. DB0 and the second initial pressure difference P monitored by the second pressure difference sensor 14 DA0 .

[0109] The air-free water is filled into the pressure chamber 5 through the first vertical pipe 4 until the air-free water in the pressure chamber 5 overflows into the second vertical pipe 12 to a preset water level h. 0 When the first valve 62, the second valve 72 and the third valve 82 are closed, the sample confining pressure is then applied through the gas connection pipe 91 and the fourth valve 92, and the unsaturated soil sample 11 is compressed by applying pressure through the loading rod 1 until the preset time t i , and record the first pressure difference monitored by the first differential pressure sensor 13 and the second pressure difference monitored by the second differential pressure sensor 14 at this time.

[0110] During the whole pressurization process, the unsaturated soil sample 11 may increase or decrease in volume. When the volume of the unsaturated soil sample 11 increases, the preset water level height h in the second vertical pipe 12 is 0 Will increase to the first water level h i , corresponding to the change in the height difference of the airless water level in the second vertical pipe 12 is Δh; when the volume of the unsaturated soil sample 11 decreases, the preset water level height h in the second vertical pipe 12 0 The initial water level in the pressure chamber 5 is constant. 0 Lower to the second water level height y i , the corresponding amount of change in the height difference of the airless water level in the pressure chamber 5 is Δy. The water level change caused by the volume change of the unsaturated soil sample 11 will cause the pressure difference on the left and right sides of the second differential pressure sensor 14 and the first differential pressure sensor 13 to change (that is, the first initial pressure difference is different from the first pressure difference; the second initial pressure difference is different from the second pressure difference).

[0111] Here, according to the first initial pressure difference and the first pressure difference, it can be obtained from the initial time t 0 Load to preset time t i When the first pressure difference change ΔP on the left and right sides of the first pressure difference sensor 13 DBi According to the second initial pressure difference and the second pressure difference, it can be obtained from the initial time t 0 Load to preset time t i When the second pressure difference change ΔP on the left and right sides of the second pressure difference sensor 14 DAi .

[0112] Furthermore, from the initial time t 0 Load to preset time t i When the first pressure difference change ΔP on the left and right sides of the first pressure difference sensor 13 is DBi , the second pressure difference change ΔP on the left and right sides of the second pressure difference sensor 14 DAi And the preset loading speed v' can be determined from the initial time t 0 Load to preset time t i The volume change of the unsaturated soil sample 11 is ΔV i .

[0113] Here, P DA and P DB Respectively represent the pressure difference between the second differential pressure sensor 14 and the first differential pressure sensor 13; P AL and P AR Respectively represent the absolute pressure values ​​on the left and right sides of the second differential pressure sensor 14, P BL and P BR represents the absolute pressure values ​​on the left and right sides of the first differential pressure sensor 13 (here, P DA , P DB , P AL , P AR , P BL and P BR It is only used for theoretical derivation and is not directly measured by the differential pressure sensor); γ represents the gravity of airless water (the mass of water per unit volume); Figure 1 , S A and S B represents the outer cross-sectional area of ​​the second vertical tube 12 and the first vertical tube 4 respectively; S' represents the cross-sectional area of ​​the loading rod 1; S represents the outer cross-sectional area S of the pressure chamber 5 excluding the second vertical tube 12 A , the outer cross-sectional area S of the first vertical tube 4 B and the cross-sectional area S' of the loaded rod 1; H 0 It means that at t = t 0 The initial position height of the loading rod 1 at the initial moment; H 1 It means that at t = t 1 The first position height of the loading rod 1 at the first moment; h 1 It means that at t = t 1 The third water level height of the airless water in the second vertical pipe 12 at the first moment; y 1 It means that at t = t 1 The fourth water level height of the airless water in the pressure chamber 5 at the first moment; here, the first moment t 1 Less than the preset time t i .

[0114] When hydraulic-mechanical coupling loading is performed, according to the water balance principle, that is, the total amount of water in the first vertical pipe 4, the second vertical pipe 12 and the pressure chamber 5 remains unchanged, the above-mentioned partial parameters have the following derivation relationship:

[0115] P DA =P AL -P AR =γ(hYy) (1)

[0116] P DB =P BL -P BR =γ(yy 0 ) (2)

[0117] V A =γS A h-γ(Y+y)S (3)

[0118] V chamber =V B =γ(Y+y)S (4)

[0119] Wherein, h represents the water level of the airless water in the second vertical pipe 12 at the non-initial time, Y represents the height difference between the bottom surface of the pressure chamber 5 and the pressure difference sensor, y represents the water level of the airless water in the pressure chamber 5 at the non-initial time, V A V represents the nominal air-free water volume in the corresponding second vertical pipe 12 and the pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading at a non-initial moment; B V represents the nominal air-free water volume in the corresponding first vertical pipe 4 and pressure chamber 5 that causes the first differential pressure sensor 13 to generate a reading at a non-initial time. Since the water level in the first vertical pipe 4 remains constant throughout the hydraulic loading experiment, V B It is also equal to the nominal air-free water volume V in the pressure chamber 5 at the non-initial moment. chamber The nominal air-free water volume means that during the calculation of the air-free water volume, the calculated absolute value is not the real volume but an intermediate quantity. This is because the third water connecting pipe 81 connecting the first vertical pipe 4, the second vertical pipe 12, and the bottom of the pressure chamber 5 connected to the second differential pressure sensor 14 and the first differential pressure sensor 13 is also considered to have the same cross-sectional area as the first vertical pipe 4, the second vertical pipe 12, and the pressure chamber 5 during calculation; however, this nominal quantity will not affect the actual measurement, because the actual measurement is based on the difference (such as ΔV A and ΔV B ), in the process of calculating the difference, the influence of the nominal water volume in the third water connecting pipe 81 connecting the first vertical pipe 4, the second vertical pipe 12, the bottom of the pressure chamber 5 and the second differential pressure sensor 14 and the first differential pressure sensor 13 is eliminated by subtraction.

[0120] Then the first pressure difference change ΔP on the left and right sides of the first pressure difference sensor 13 is DBi , the second pressure difference change ΔP on the left and right sides of the second pressure difference sensor 14 DAi And the preset loading speed v' can be determined from the initial time t 0 Load to the first time t 1 The volume change of the unsaturated soil sample 11 is ΔV i The specific process is as follows:

[0121] At the initial moment t of the water-mechanical coupling loading 0 :

[0122] P DA0 =P AL0 -P AR0 =γ(h 0 -Yy 0 ) (5)

[0123] P DB0 =P BL0 -P BR0 =γ(y 0 -y 0 ) (6)

[0124] V A0 =γS A h 0 -γ(Y+y 0 )S (7)

[0125] V B0 =γ(Y+y 0 )S (8)

[0126] Among them, P DA0 Indicates that at the initial time t 0 The second initial pressure difference monitored by the second differential pressure sensor 14, P DB0 Indicates that at the initial time t 0 The first initial pressure difference monitored by the first differential pressure sensor 13, V A0 Indicates that at the initial time t 0 The nominal air-free water volume in the corresponding second vertical pipe 12 and the pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading when V B0 Indicates that at the initial time t 0 The nominal air-free water volume in the corresponding first vertical pipe 4 and the pressure chamber 5 causes the first differential pressure sensor 13 to produce a reading.

[0127] When the water-mechanical coupling loading is performed to the first moment t 1 hour:

[0128] P DA1 =PAL1 -P AR1 =γ(h 1 -Yy 1 ) (9)

[0129] P DB1 =P BL1 -P BR1 =γ(y 1 -y 0 ) (10)

[0130] V A1 =γS A h 1 -γ(Y+y 1 )S (11)

[0131] V B1 =γ(Y+y 1 )S (12)

[0132] Among them, P DA1 Indicates that at the first moment t 1 The fourth pressure difference, P DB1 Indicates that at the first moment t 1 The third pressure monitored by the first differential pressure sensor 13, V A1 Indicates that at the initial time t 1 The nominal air-free water volume in the corresponding second vertical pipe 12 and the pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading when V B1 Indicates that at the initial time t 1 The nominal air-free water volume in the corresponding first vertical pipe 4 and the pressure chamber 5 causes the first differential pressure sensor 13 to produce a reading.

[0133] From the initial time t 0 Load to the first time t 1 The changes of each parameter in the process are:

[0134] ΔP DA1 =P DA1 -P DA0 =γ[(h 1 -h 0 )-(y 1 -y 0 )] (13)

[0135] ΔP DB1 =P DB1 -P DB0 =γ(y 1 -y 0 ) (14)

[0136] ΔV A1 =γSA (h 1 -h 0 )-γS(y 1 -y 0 ) (15)

[0137] ΔV B1 =γS(y 1 -y 0 ) (16)

[0138] Here, ΔP DA1 It means that from the initial time t 0 Load to the first time t 1 The fourth pressure difference change corresponding to both sides of the second vertical pipe 12 when ΔP DB1 It means that from the initial time t 0 Load to the first time t 1 The third pressure difference change corresponding to both sides of the first vertical pipe 4 when ΔV A1 It means that from the initial time t 0 Load to the first time t 1 The fourth volume change of the air-free water in the second vertical pipe 12 at ΔV B1 It means that from the initial time t 0 Load to the first time t 1 The volume change of the third air-free water in the first vertical pipe 4 at this time.

[0139] because:

[0140] Δy=y 1 -y 0 =ΔP DB1 / γ (17)

[0141] Substituting formula (17) into formula (13) yields:

[0142] Δh=h 1 -h 0 =(ΔP DA1 -ΔP DB1 ) / γ (18)

[0143] Among them, Δy represents the time from the initial time t 0 Load to the first time t 1 The first water level difference of the airless water in the pressure chamber 5 at the time t, Δh represents the height difference from the initial time t 0 Load to the first time t 1 The second water level height difference of the airless water in the second vertical pipe 12 at the time; further, by substituting formula (17) and formula (18) into formula (15) and formula (16), we can obtain:

[0144] ΔV A1 =SA (ΔP DA1 +ΔP DB1 )-SΔP DB1 (19)

[0145] ΔV B1 =SΔP DB1 (20)

[0146] ΔV H1 =S'(H 1 -H 0 )=S'v'(t 1 -t 0 ) (twenty one)

[0147] Where, ΔV H1 It means that from the initial time t 0 Load to the first time t 1 During the process, the loading rod 1 is immersed in the airless water in the pressure chamber 5 by a second volume change;

[0148] According to the water balance principle:

[0149] ΔV A1 =ΔV H1 +ΔV 1 +ΔV B1 (twenty two)

[0150] According to the first initial pressure difference, the second initial pressure difference, the third pressure difference, the fourth pressure difference and the preset loading speed v', at the initial time t 0 When loading to the first time t1, the first volume change ΔV of the unsaturated soil sample 11 is 1 It can be expressed as:

[0151]

[0152] Then further, at the initial time t 0 To the preset time t i When the volume change of the unsaturated soil sample 11 is ΔV i It can be expressed as:

[0153]

[0154] Where, ΔV Ai It means that from the initial time t 0 Load to preset time t i The volume change of the second air-free water in the second vertical pipe 12 at ΔV Bi It means that from the initial time t 0 Load to preset time t i The volume change of the first air-free water in the first vertical pipe 4 at ΔVHi It means that from the initial time t 0 Load to preset time t i The first volume change when the loading rod is immersed in the airless water in the pressure chamber 5. It can be seen from equations (13) and (14) that the liquid tension effect (pressure difference change) inside the pressure chamber 5, the second vertical tube 12 and the first vertical tube 4 is eliminated in the process of calculating the increment.

[0155] At this point, the unsaturated soil sample 11 in the measuring device has been completed from the initial moment of the water-mechanical coupling loading experiment to the preset moment t i Volume change ΔV i Derivation and measurement; the measurement method provided in the above embodiment can realize the continuous measurement of the volume deformation of the unsaturated soil sample 11, and the measurement time interval depends on the response time of the differential pressure sensor and the movement time of the airless water.

[0156] The above-mentioned embodiments of the present invention provide a device and method for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading. The specific corresponding structural setting of the measuring device can expand the entire measuring device to measure the volume deformation of unsaturated samples. In addition to the micro-experimental system, the sample volume deformation measurement in the micro-hydraulic coupling experimental system built into the X-ray CT is also suitable for large-scale devices for large-size samples, such as an experimental system for super-large samples containing gravel (such as cylindrical samples with a diameter of 500mm and a height of 1000mm). The measuring device is based on the structural design of a single pressure chamber, which can reduce the complexity of the overall structure of the device and the difficulty of sample installation, avoid disturbance to the sample during installation, and measure the volume deformation of unsaturated soil samples under complex water-mechanical coupling loading conditions. The volume deformation can be measured accurately and continuously to reduce the failure rate of measurement; the measurement method is based on the measurement principle of the pressure difference change caused by the change of water level in the two vertical tubes and the pressure chamber during the deformation of the sample, which ensures high measurement accuracy and high measurement reliability; and the measurement method has a wide adaptability to the size of unsaturated soil samples, and can effectively measure the volume deformation of experimental systems of large-size samples and small-size samples; in addition, since the soil particles of saturated soil are filled with water, although there are simpler and more accurate methods for saturated soil filled with incompressible water, based on the volume deformation measurement device and method of unsaturated soil during water-mechanical coupling loading provided by the above-mentioned embodiments of the present invention and the water balance principle used in the measurement process, the measurement device and method are also suitable for the measurement of saturated soil volume deformation.

[0157] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A device for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading, characterized in that: include: A pressure chamber (5) for containing an unsaturated soil sample (11); A loading rod (1) is disposed above the pressure chamber (5), and the loading rod (1) passes through a pressure chamber upper cover (51) of the pressure chamber (5) and contacts the unsaturated soil sample (11), and the loading rod (1) performs vertical reciprocating motion to provide loading to the unsaturated soil sample (11); a first pressure monitoring unit, arranged at one side of the pressure chamber (5), wherein a first end of the first pressure monitoring unit is located above a sample cover (33) covering the unsaturated soil sample (11), and a second end of the first pressure monitoring unit is fixed to a pressure chamber base (52) of the pressure chamber (5) and communicated with the outside of the pressure chamber (5); and a second pressure monitoring unit, arranged at the other side of the pressure chamber (5), wherein the first end of the second pressure monitoring unit is flush with the first end of the first pressure monitoring unit, and the second end of the second pressure monitoring unit is fixed to a pressure chamber base (52) of the pressure chamber (5) and communicated with the outside of the pressure chamber (5); During the hydraulic-mechanical coupling loading process on the unsaturated soil sample (11), the first pressure monitoring unit is used to monitor the pressure difference on one side of the pressure chamber (5), and the second pressure monitoring unit is used to monitor the pressure difference on the other side of the pressure chamber (5).

2. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 1, characterized in that: The first pressure monitoring unit comprises: a first vertical tube (4), wherein a first end of the first vertical tube (4) is located above the sample cover (33), and a second end of the first vertical tube (4) is fixed to the pressure chamber base (52) and communicates with the outside of the pressure chamber (5); and A first differential pressure sensor (13), the first differential pressure sensor (13) being connected to the second end of the first vertical pipe (4), and the first differential pressure sensor (13) being used to monitor the pressure difference between the first vertical pipe (4) and one side of the pressure chamber (5) during the hydraulic-mechanical coupling loading process on the unsaturated soil sample (11).

3. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 2, characterized in that: The first pressure monitoring unit also includes: a first water connecting pipe (61), the first water connecting pipe (61) being in communication with the second end of the first vertical pipe (4), and the first differential pressure sensor (13) being arranged on one side of the first water connecting pipe (61); and A first valve (62), wherein the first valve (62) is arranged at the other side of the first water connecting pipe (61) and is arranged in parallel with the first differential pressure sensor (13).

4. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 2, characterized in that: The second pressure monitoring unit comprises: a second vertical tube (12), wherein a first end of the second vertical tube (12) is flush with a first end of the first vertical tube (4), and a second end of the second vertical tube (12) is fixed to the pressure chamber base (52) and communicates with the outside of the pressure chamber (5); and A second differential pressure sensor (14), the second differential pressure sensor (14) is connected to the second end of the second vertical pipe (12) and the second differential pressure sensor (14) and the first differential pressure sensor (13) are located on the same horizontal plane, and the second differential pressure sensor (14) is used to monitor the pressure difference between the second vertical pipe (12) and the other side of the pressure chamber (5) during the hydraulic-mechanical coupling loading process of the unsaturated soil sample (11).

5. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 4, characterized in that: The second pressure monitoring unit also includes: a second water connecting pipe (71), the second water connecting pipe (71) being in communication with the second end of the second vertical pipe (12), and the second differential pressure sensor (14) being arranged on one side of the second water connecting pipe (71); and A second valve (72), the second valve (72) is arranged on the other side of the second water connecting pipe (71) and is arranged in parallel with the second differential pressure sensor (14).

6. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 1, characterized in that: Also includes: an air connection pipe (91), one end of which passes through the pressure chamber upper cover (51) and is in communication with the pressure chamber (5); and A fourth valve (92), the fourth valve (92) being arranged at the other end of the gas connection pipe (91), the fourth valve (92) being used in conjunction with the gas connection pipe (91) to apply a sample confining pressure to the unsaturated soil sample (11) in the pressure chamber (5).

7. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 4, characterized in that: Also includes: a third water connecting pipe (81), one end of the third water connecting pipe (81) being arranged on the pressure chamber base (52) and communicating with the pressure chamber (5), and two sides of the third water connecting pipe (81) being respectively connected with the first differential pressure sensor (13) and the second differential pressure sensor (14); and A third valve (82), the third valve (82) is arranged at the other end of the third water connecting pipe (81).

8. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 1, characterized in that: Also includes: A linear displacement sensor (2), the linear displacement sensor (2) being arranged above the pressure chamber upper cover (51) and fixedly connected to the loading rod (1), and being used for monitoring the displacement of the loading rod (1) in vertical reciprocating motion.

9. The device for measuring volume deformation of unsaturated soil during water-mechanical coupling loading according to claim 4, characterized in that: The top and the inside of the first vertical tube (4) and the second vertical tube (12) are covered with a hydrophilic coating.

10. A method for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading based on the device for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading according to any one of claims 1 to 9, characterized in that: The following steps are involved: Installing an unsaturated soil sample (11) in a pressure chamber (5); At the initial time t0 of hydraulic-mechanical coupling loading of the unsaturated soil sample (11), the first valve (62) is opened and air-free water is injected into the pressure chamber (5) through the first water connecting pipe (61) and the first vertical pipe (4) until the air-free water enters the second vertical pipe (12) and reaches a preset water level height h0, and at the same time, a first initial pressure difference monitored by the first differential pressure sensor (13) and a second initial pressure difference monitored by the second differential pressure sensor (14) are recorded; When the unsaturated soil sample (11) is subjected to hydraulic-mechanical coupling loading, a pressure is uniformly applied to the unsaturated soil sample (11) at a preset loading speed v' through the loading rod (1) until a preset time t i , and at the preset time t i When the first differential pressure sensor (13) and the second differential pressure sensor (14) are detected, a first differential pressure is recorded; The volume change of the unsaturated soil sample (11) during the hydraulic-mechanical coupling loading process is determined according to the first initial pressure difference, the second initial pressure difference, the first pressure difference, the second pressure difference and the preset loading speed v'.

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