Device and method for measuring volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading

Abstract

This invention provides a device and method for measuring the volumetric deformation of unsaturated soil during water-force coupled loading. The device includes a pressure chamber, a loading rod, a first pressure monitoring unit, and a second pressure monitoring unit. The loading rod is positioned above the pressure chamber, passing through the top cover of the pressure chamber and contacting the unsaturated soil sample inside. The loading rod reciprocates vertically to apply load to the unsaturated soil sample. The first pressure monitoring unit is located on one side of the pressure chamber, and the second pressure monitoring unit is located on the other side, with one end flush with one end of the first pressure monitoring unit. The other ends of both pressure monitoring units are fixed to the base of the pressure chamber and connected to the outside of the pressure chamber. During water-force coupled loading of the unsaturated soil sample, the two monitoring units monitor the pressure difference between the two sides of the pressure chamber. This invention enables accurate and continuous measurement of the volumetric change of unsaturated soil samples under complex water-force coupled loading conditions.

Description

Technical Field

[0001] This invention relates to the technical field of experimental equipment for soil mechanics and testing of multiphase porous materials. Specifically, it relates to a device and method for measuring the volume deformation of unsaturated soil during water-mechanical coupling loading. Background Technology

[0002] Soil undergoes changes in volume due to alterations in its internal structure caused by hydraulic loading (such as soil wetting and drying), mechanical loading (such as consolidation and shearing), or hydraulic-mechanical coupling loading. These changes are represented by volumetric deformation (or volume change). The volumetric change of soil is a fundamental parameter in soil mechanics theoretical modeling and practical engineering design. Accurately measuring the volumetric deformation of soil samples during hydraulic-mechanical loading is an important aspect of soil mechanics experiments.

[0003] Generally, since saturated soil contains only a solid phase (solid particles) and a liquid phase (water), and neither solid particles nor water are compressible, the volume change of a saturated soil sample during consolidation shear can be calculated by measuring the volume of liquid displaced or absorbed by the soil sample. This method is simple and has high accuracy, and is currently a commonly used method for measuring the volume deformation of saturated soil samples in triaxial consolidation shear experiments.

[0004] However, the methods described above for measuring the volumetric deformation of saturated soil are not applicable to measuring the volumetric deformation of unsaturated soil, which is more commonly found in practical engineering. This is because unsaturated soil samples contain not only incompressible solid phases (solid particles) and liquid phases (water), but also compressible and expandable gas phases (air). The volume change of unsaturated soil samples during hydrodynamic loading is mainly due to the volume change of the gas phase and the entry and exit of the liquid phase. Due to the compressibility of air in unsaturated soil, measuring its volume change becomes complex and difficult.

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

[0006] (1) Using a dual-chamber measurement system. Based on whether the inner and outer chambers are connected, dual-chamber measurement systems can be divided into two types: those with connected inner and outer pressure chambers and those with closed inner and outer pressure chambers. The measurement methods for the type with connected inner and outer pressure chambers are mainly found in 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 methods for the type with closed inner and outer pressure chambers are mainly found in 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 the volume deformation of gaseous and liquid fluids in unsaturated soil samples by measuring the volume of fluid (especially gas) pressure changes (Wulfsohn et al. (1998), Laudahn (2005), and Li Jingshuang (2020)).

[0008] (3) A method for local strain measurement and estimation using a non-contact Hall sensor (Clayton and Khatrush 1986; Clayton et al. 1989) or a contact LVDT (Zhao et al. (2011)).

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

[0010] Among the four types of measurement methods mentioned above, the first type is a direct measurement method, which provides continuous and direct results reflecting the volumetric deformation of unsaturated soil samples and is the most commonly used method. The main technical challenges of this type of method lie in ensuring equal confining pressures applied to both sides of the inner chamber, preventing water leakage and ensuring the absence of gas in the water, maintaining accuracy and automation in measuring water volume changes within the inner chamber, and eliminating interference from factors such as evaporation of water within the inner chamber, absorption of water by the pressure chamber walls, and temperature effects (Xu et al., 2018). The dual-pressure chamber design makes sample loading a very cumbersome process and prone to disturbing the sample. Furthermore, because the dual-pressure chamber system needs to accommodate multiple complex components within a limited space, the size range of the tested samples is usually small (e.g., the most widely used GDS dual-pressure chamber system typically uses samples with diameters of 38 mm and 50 mm). This limits the testing of larger samples (e.g., samples composed of larger soil particles) and smaller samples (e.g., samples used for CT scans). The second type of method directly measures the fluid volume to reflect the overall sample volume deformation. However, compared to water, the measured air volume is highly sensitive to temperature and pressure, as well as the solubility of air in water. This inherently limits the measurement accuracy, making it significantly susceptible to environmental factors and difficult to calibrate. The third type of method uses local measurement results to calculate the overall sample volume deformation using approximation methods. It has good accuracy for samples with small deformations (i.e., higher-order Green-Lagrange strain expressions can be ignored; strain less than 2% is typically considered small deformation). However, it has significant measurement errors for samples with large deformations (i.e., sample deformation cannot be accurately predicted using elastic theory) and irregularly deformed samples, and is prone to disturbing the sample. The fourth type of method allows for undisturbed measurement, but its accuracy depends on the quality and resolution of the acquired images, and the triaxial system requires the ability to mount image acquisition devices. Furthermore, image-based measurement methods use very expensive image acquisition systems, and the laboratories using such systems typically require specialized designs (e.g., CT scanners cost millions of RMB and require dust-free and constant humidity environments).

[0011] In summary, direct measurement methods should be the preferred approach for measuring the volumetric deformation of unsaturated soil samples. Key considerations for direct measurement include: accuracy and directness of the measurement; environmental dependence; complexity of the measurement system and its spatial requirements for the triaxial experimental system; minimization of sample disturbance; and the potential for upgrading and modifying the measurement system within existing triaxial experimental systems. Existing methods struggle to simultaneously meet all these requirements. Therefore, there is an urgent need to develop a method for measuring the volumetric deformation of unsaturated soil samples during hydraulic coupling loading. This method should directly measure the overall volumetric deformation of the triaxial sample, overcoming the shortcomings of the first type of method (difficult sample loading, sample disturbance, and poor applicability) and the limitations of the second to fourth types of methods (high susceptibility to environmental influences and the ability to only indirectly or partially reflect sample volumetric deformation). This new method would be suitable for measuring the volumetric deformation of samples in small-scale hydraulic coupling loading experimental systems and also compatible with conventional triaxial experimental systems. 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 hydro-mechanical coupling loading, so as to achieve accurate and continuous measurement of the volume change of unsaturated soil samples under complex hydro-mechanical coupling loading conditions.

[0013] To address the aforementioned technical problems, embodiments of the present invention provide a device for measuring the volumetric deformation of unsaturated soil during a hydraulic-coupling loading process, comprising:

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

[0015] A loading rod is positioned above the pressure chamber, and the loading rod passes through the pressure chamber cover and contacts the unsaturated soil sample. The loading rod reciprocates vertically to apply load to the unsaturated soil sample.

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

[0017] A second pressure monitoring unit is disposed on the other side of the pressure chamber. 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 to the pressure chamber base of the pressure chamber and communicates 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 includes:

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

[0021] The first differential pressure sensor is connected to the second end of the first vertical tube. 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 tube and one side of the pressure chamber.

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

[0023] A first water connection pipe is connected to the second end of the first vertical pipe, and the first differential pressure sensor is disposed on one side of the first water connection pipe; and

[0024] The first valve is located on the other side of the first water connection pipe and is connected in parallel with the first differential pressure sensor.

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

[0026] A second vertical tube, the first end of which is flush with the first end of the first vertical tube, and the second end of which is fixed to the pressure chamber base and communicates with the outside of the pressure chamber; and

[0027] The second differential pressure sensor is connected to the second end of the second vertical tube and is on the same horizontal plane as the first differential pressure sensor. During the water-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 tube and the other side of the pressure chamber.

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

[0029] A second water connection pipe is connected to the second end of the second vertical pipe, and the second differential pressure sensor is located on one side of the second water connection pipe; and

[0030] The second valve is located on the other side of the second water connection pipe and is connected in parallel with the second differential pressure sensor.

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

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

[0033] The fourth valve is located at the other end of the gas connection pipe and is used in conjunction with the gas connection pipe 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 includes:

[0035] A third water connection pipe, one end of which is mounted on the pressure chamber base and communicates with the pressure chamber, and both sides of the third water connection pipe are respectively connected to the first differential pressure sensor and the second differential pressure sensor; and

[0036] The third valve is located at the other end of the third water connection pipe.

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

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

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

[0040] Embodiments of the present invention also provide a measurement method for the volumetric deformation measurement device of unsaturated soil during the hydraulic-mechanical coupling loading process described above, comprising the following steps:

[0041] Unsaturated soil samples were installed in a pressure chamber;

[0042] At the initial moment t0 of the hydraulic-mechanical coupling loading of the unsaturated soil sample, the first valve is opened and de-aerated water is injected into the pressure chamber through the first water connection pipe and the first vertical pipe until the de-aerated water enters the second vertical pipe and reaches the preset water level height h0. At the same time, the first initial pressure difference monitored by the first differential pressure sensor and the second initial pressure difference monitored by the second differential pressure sensor are recorded.

[0043] When applying hydraulic-coupling loading to the unsaturated soil sample, pressure is uniformly applied to the unsaturated soil sample at a preset loading speed v' until a preset time t is reached. i And at the preset time t i At the same time, record the first pressure difference monitored by the first differential pressure sensor and the second pressure difference monitored by the second differential pressure sensor;

[0044] The volume change of the unsaturated soil sample during the hydraulic-mechanical coupling loading process is determined based on 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-described solution of the present invention has at least the following beneficial effects:

[0046] (1) The measuring device of the present invention adopts a double vertical tube structure, which is easy to install 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, it adopts the measurement principle based on dual differential pressure sensors, which can directly measure the volume deformation of the sample 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 significantly reduce the operational complexity of the experiment, reduce sample disturbance caused by the rigidity of the water pipe connected to the upper sample cover in the narrow space in the dual pressure chamber system, and avoid the common problems of water leakage in the inner pressure chamber of the dual pressure chamber system. At the same time, compared with the measurement method of the dual pressure chamber system which is limited by the size of the throat of the inner pressure chamber, the measuring device of the present invention has a wide adaptability to the size range of the sample being measured. For samples of different sizes, it is only necessary to adjust the ratio of the cross-sectional area of ​​the vertical tube in the pressure monitoring unit to the cross-sectional area of ​​the pressure chamber to achieve high accuracy.

[0048] (3) Compared with the dual-pressure chamber system, the measuring device of the present invention has a simpler structure and a significantly lower manufacturing cost, which is conducive to its large-scale application in engineering design. It is suitable for measuring the volume deformation of unsaturated soil in micro-experimental systems, such as the 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. It is also suitable for large-scale experimental systems, 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).

[0049] (4) The measuring device of the present invention loads and measures samples based on a single pressure chamber. Compared with a dual pressure chamber, it can significantly reduce the structural complexity and sample installation difficulty. It avoids sample collapse when installing loose sand or soft clay samples that are easily disturbed in a 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 is highly adaptable to environmental variables such as temperature and air pressure. When the temperature or pressure environment of the device changes, such as moving from a plain to a plateau, an experiment can be conducted by calibrating a reference curve at that temperature and pressure without the need for a complicated calibration procedure.

[0051] (6) Although the measuring device and method of the present invention are proposed for measuring the volume deformation of unsaturated soil, they can be measured regardless of whether the soil particles are filled with incompressible water or compressible gas or a water-air mixture. This is significantly better than other methods for measuring the volume deformation of unsaturated soil and dry soil. However, based on its measurement principle, this method is also applicable to the measurement of the volume deformation of saturated soil samples and dry soil samples, as well as the measurement of the volume deformation of other multiphase porous materials. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the overall structure of the device for measuring the volume deformation of unsaturated soil during the hydraulic-mechanical coupling loading process provided in this embodiment of the invention.

[0053] Figure 2 This is a flowchart of a measurement method for a device for measuring the volumetric deformation of unsaturated soil during a water-mechanical coupling loading process, provided in an optional embodiment of the present invention.

[0054] Explanation of icon 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 tube; 5. Pressure chamber; 51. Pressure chamber cover; 52. Pressure chamber base; 61. First water connection pipe; 62. First valve; 71. Second water connection pipe; 72. Second valve; 81. Third water connection pipe; 82. Third valve; 91. Gas connection pipe; 92. Fourth valve; 10. O-ring; 11. Unsaturated soil sample; 12. Second vertical tube; 13. First differential pressure sensor; 14. Second differential pressure sensor. Detailed Implementation

[0056] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0057] In the description of this invention, it should be understood that the terms "comprising / including," "consisting of," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements includes not only those elements but may also include, where necessary, other elements not expressly listed, or elements inherent to such a product, apparatus, process, or method. Without further limitation, an element defined by the phrases "comprising / including," "consisting of," does not exclude the presence of additional identical elements in the product, apparatus, process, or method that includes said element.

[0058] It should also be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device, component or structure referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of the present invention.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0060] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] The measuring device provided in the following embodiments of the present invention can be used for direct measurement of volumetric 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) It is applicable to modifying existing conventional triaxial tests to enable them to perform direct volume deformation measurements under complex stress loading conditions.

[0063] (2) In addition to micro-experimental systems, the measurement of volumetric deformation of compression-consolidation and shear micro-devices installed inside X-ray CT for in-situ loading and imaging is also applicable to large-scale devices for large-sized samples, such as experimental systems for ultra-large samples containing gravel (e.g., 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 the volumetric deformation of unsaturated soil during a water-force coupled loading process, which may include a pressure chamber 5, a loading rod 1, a first pressure monitoring unit and a second pressure monitoring unit. The pressure chamber 5 is used to hold the unsaturated soil sample 11. A loading rod 1 is positioned above the pressure chamber 5, passing through the pressure chamber cover 51 and contacting the unsaturated soil sample 11. The loading rod 1 reciprocates vertically to apply load to the unsaturated soil sample 11. A first pressure monitoring unit is located on one side of the pressure chamber 5, with its first end positioned above the sample cover 33 covering the unsaturated soil sample 11, and its second end fixed to the pressure chamber base 52 and connected to the outside of the pressure chamber 5. A second pressure monitoring unit is located on the other side of the pressure chamber 5, with its first end flush with the first end of the first pressure monitoring unit, and its second end fixed to the pressure chamber base 52 and connected to the outside of the pressure chamber 5. During the hydro-mechanical coupling loading process on the unsaturated soil sample 11, the first pressure monitoring unit monitors the pressure difference on one side of the pressure chamber 5, and the second pressure monitoring unit monitors 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, which is filled with an unsaturated soil sample 11; the first pressure monitoring unit and the second pressure monitoring unit are symmetrically arranged inside the pressure chamber 5 and are 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 of the unsaturated soil sample 11.

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

[0067] Before applying hydraulic-mechanical coupling loading to the unsaturated soil sample 11 using the measuring device of this embodiment, de-aired water is supplied to the pressure chamber 5 through the first pressure monitoring unit until it submerges the unsaturated soil sample 11 and enters the second pressure monitoring unit until the water level reaches a preset height. This preset water level is used as the initial position before the loading experiment. Simultaneously, the pressure difference between the two sides of the pressure chamber 5 is monitored by both the first and second pressure monitoring units and used as the initial pressure difference before the loading experiment. During hydraulic-mechanical coupling loading, the loading rod 1 uniformly and continuously applies load to the unsaturated soil sample 11, and the first pressure monitoring unit... A pressure monitoring unit and a second pressure monitoring unit monitor the pressure difference on both sides of the pressure chamber 5 in real time during the loading process. When the hydraulic-mechanical coupling loading is carried out and the loading reaches the 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 based on the pressure difference on both sides of the pressure chamber 5 at the current preset time monitored by the first pressure monitoring unit and the second pressure monitoring unit, as well as 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 in the above embodiments of the present invention is based on the measurement principle of 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 caused by water-force coupling loading of unsaturated soil sample 11, ensuring high measurement accuracy and high measurement reliability; it has wide adaptability to the size of unsaturated soil sample 11 and can effectively measure volume deformation for both large and small sample experimental systems; at the same time, since the measuring device is based on single pressure chamber for sample loading and measurement, it can significantly reduce structural complexity and sample installation difficulty compared to the dual pressure chamber method, thereby avoiding disturbance of easily disturbed samples such as loose sand and soft soil during sample loading, reducing the failure rate of sample volume deformation measurement, and enabling accurate and continuous measurement of volume deformation of unsaturated soil samples under complex water-force coupling loading conditions.

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

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

[0071] Here, the first cavity structure of the pressure chamber 5 is provided with a three-dimensional cavity structure of latex membrane 34. Preferably, the three-dimensional cavity structure is cylindrical, and the top and bottom of the latex membrane 34 are respectively provided with a top permeable stone 31 and a bottom permeable stone 32. The unsaturated soil sample 11 is loaded into the 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 arranged to facilitate the hydraulic 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 hydro-mechanical coupling loading of the unsaturated soil sample 11; preferably, O-rings are respectively provided on the top and bottom outer walls of the three-dimensional cavity structure latex membrane 34, more preferably, two O-rings are respectively provided at intervals on the top and bottom outer walls of the latex membrane 34, and the O-rings are fitted 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 to the pressure chamber base 52, the bottom permeable stone 32 is set inside the bottom of the latex membrane 34 and fixedly connected to the pressure chamber base 52; the top permeable stone 31 is set inside the top of the latex membrane 34, and a sample cover 33 is set 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-force 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 to 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 is used to monitor the pressure difference between the first vertical tube 4 and one side of the pressure chamber 5 during the hydro-mechanical coupling loading process on the unsaturated soil sample 11.

[0074] In this embodiment, the first vertical tube 4 is disposed in the first cavity structure of the pressure chamber 5 and 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 communicates with the outside of the pressure chamber 5, so as to supply airless water into the first cavity structure of the pressure chamber 5; before the water-mechanical coupling loading is performed, the airless water injected through the first vertical tube 4 can enter the pressure chamber 5 along the first vertical tube 4 until the airless water submerges the entire unsaturated soil sample 11.

[0075] The first differential pressure sensor 13 is located 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 water-force coupling loading process.

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

[0077] In this embodiment, the second vertical tube 12 is disposed within the first cavity structure of the pressure chamber 5 and 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 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 to the pressure chamber base 52 and communicates with the outside of the pressure chamber 5; before performing water-force coupling loading, when the first vertical tube 4 injects de-aerated water into the pressure chamber 5 and immerses the entire unsaturated soil sample 11, since the first end of the first vertical tube 4 is higher than the top of the sample cover 3, the de-aerated water will enter the second vertical tube 12 when the de-aerated water is continuously injected; at this time, the amount of de-aerated water injected is controlled so that the de-aerated water in the second vertical tube 12 is at a preset height, and then the loading rod 1 is used to start to lift the vertical pressure on the unsaturated soil sample 11 to perform the water-force coupling loading experiment.

[0078] The second differential pressure sensor 14 is located 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 during the water-force coupling loading process in real time. Here, when the volume decreases, the water surface area inside the pressure chamber 5 is the total cross-sectional area inside the pressure chamber 5 minus the cross-sectional areas of the first vertical tube 4 and the second vertical tube 12, plus the area of ​​the loading rod (the area of ​​the loading rod is generally fixed). Therefore, 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 inside the pressure chamber 5 is smaller than that 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 to ensure the measurement accuracy during the sample enlargement and reduction process. 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, both the first vertical tube 4 and the second vertical tube 12 are made of transparent material to facilitate observation of the water level in the vertical tubes before hydro-hydraulic 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 tops and interiors of the first vertical tube 4 and the second vertical tube 12 are covered with a hydrophilic coating to facilitate the flow of airless water within the first vertical tube 4 and the second vertical tube 12, as well as its smooth flow out of the first vertical tube 4 and into the second vertical tube 12. This avoids water blockage caused by the formation of water droplets or air bubbles within the first vertical tube 4 and the second vertical tube 12 in small-sized systems. Simultaneously, the small contact angle resulting from the hydrophilic coating accelerates the liquid flow rate, thereby reducing the measurement lag time. Preferably, the control contact angle between the hydrophilic coating and the tops and interiors of the first vertical tube 4 and the second vertical tube 12 is less than a preset angle; more preferably, the preset angle is less than 5°, to accelerate the flow rate of the airless water, reduce the measurement lag 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 tube 12 can be determined based on the accuracy of the differential pressure sensor and the size of the unsaturated soil sample 11, with the reference being that the differential pressure sensor can detect the water level change corresponding to the second vertical tube 12 when the volume change of the unsaturated soil sample 11 is no greater than a preset accuracy; 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 tube 12, and the water level in the second vertical tube 12 will change, resulting in a certain value of differential pressure change of the airless water in the second vertical tube 12, and the accuracy of the differential pressure sensor needs to be able to measure at least this 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 connection pipe 61 and a first valve 62. The first water connection pipe 61 is connected to the second end of the first vertical pipe 4, and the first differential pressure sensor 13 is disposed on one side of the first water connection pipe 61; the first valve 62 is disposed on the other side of the first water connection pipe 61 and is disposed in parallel with the first differential pressure sensor 13.

[0085] In this embodiment, one end of the first water connection pipe 61 passes through and is fixed to 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 connection pipe 61 extends to the outside of the pressure chamber base 52, and a first valve 62 is fixedly connected to the other side of the other end of the first water connection pipe 61. Here, the first differential pressure sensor 13 is connected to one side of the other end of the first water connection pipe 61.

[0086] The first water connection pipe 61 and the first valve 62 are designed to facilitate the removal of air from the first vertical pipe 4 before the start of the water-force coupling loading experiment, the injection of de-aired water into the pressure chamber 5 after the air in the first vertical pipe 4 is removed, and the removal of de-aired water from the first vertical pipe 4 after the experiment. It should be noted that the first valve 62 is always closed during the process of pushing the unsaturated soil sample 11 through the loading rod 1 to ensure the accuracy of the water-force coupling loading experiment.

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

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

[0089] The second water connection pipe 71 and the second valve 72 are designed to discharge air from the second vertical pipe 12 before the start of the water-force coupling loading experiment and to discharge airless water from the first vertical pipe 4 after the experiment. It should be noted that the second valve 72 is always closed during the process of injecting airless water into the pressure chamber 5 and pushing the unsaturated soil sample 1 through the loading rod 1, so as to ensure the accuracy of the water-force coupling loading experiment.

[0090] In an optional embodiment of the present invention, the unsaturated soil volume deformation measuring device 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 cover 51 and communicates with the pressure chamber 5; the fourth valve 92 is disposed at the other end of the air connection pipe 91, and the fourth valve 92, in conjunction with the air connection pipe 91, is used to apply sample confining pressure to the pressure chamber 5.

[0091] In this embodiment, the gas connection pipe 91 is fixed to one side of the pressure chamber top cover 51, and one end of the gas connection pipe 91 passes through the pressure chamber top cover 51 and communicates with the first cavity structure of the pressure chamber 5. The other end of the gas connection pipe 91 is placed outside the pressure chamber top cover 51 and is connected to a fourth valve 92 so as to promptly fill the pressure chamber 5 with gas to apply sample confining pressure to the first cavity structure of the pressure chamber 5, so as to simulate the pressure situation of unsaturated soil samples when buried at different depths below the stratum.

[0092] In an optional embodiment of the present invention, the unsaturated soil volume deformation measuring device may further include a third water connection pipe 81 and a third valve 82. One end of the third water connection pipe 81 is disposed on the pressure chamber base 52 and communicates with the pressure chamber 5; both sides of the third water connection pipe 81 are respectively connected to 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 connection pipe 81.

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

[0094] The third water connection pipe 81 and the third valve 82 are designed to allow air to be discharged from the first cavity structure of the pressure chamber 5 before the start of the water-force coupling loading experiment and to discharge the airless water from the first cavity structure of the pressure chamber 5 after the experiment. They can also balance the sample confining pressure applied to the pressure chamber 5 by the air connection pipe 91 and the fourth valve 92.

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

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

[0097] In this embodiment, the linear displacement sensor 2 is disposed 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. The movable contact end of the linear displacement sensor 2 is in contact with the pressure chamber top cover 52 to measure the vertical displacement of the loading rod 1 (which is also the unsaturated soil sample 11) during vertical reciprocating motion.

[0098] When measuring the volume change of unsaturated soil sample 11 in a water-mechanical coupling loading experiment, the changes in the water levels in the first vertical tube 4, the second vertical tube 12, and the pressure chamber 5 of the measuring device are caused by the volume change of unsaturated soil sample 11 and the volume change of loading rod 1 immersed in de-aired water. The volume change of loading rod 1 immersed in water can be calculated from the diameter of loading rod 1 and the vertical displacement monitored by linear displacement sensor 2. The displacement change of loading rod 1 during the loading experiment is monitored by linear displacement sensor 2 to facilitate the subsequent calculation of the volume change of unsaturated soil sample 11.

[0099] The measuring device provided in the above embodiments of the present invention provides vertical pressure to the unsaturated soil sample 11 inside the pressure chamber 5 by setting a loading rod 1 at the top of the pressure chamber 5; provides airless water to the pressure chamber 5 by setting two vertical tubes inside the pressure chamber 5; and monitors the pressure changes in the two vertical tubes (equivalent to the pressure changes in the pressure chamber 5) when vertical pressure is provided to the unsaturated soil sample 11 through the loading rod 1.

[0100] When performing a water-mechanical coupling loading experiment on unsaturated soil sample 11, 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 water volume in the first vertical pipe 4, the second vertical pipe 12, and the pressure chamber 5 remains constant. During the water-mechanical coupling loading process, the volume change of unsaturated soil sample 11 during the loading process can be derived from the pressure changes on different sides of the pressure chamber 5. The specific derivation principle is as follows: During the water-mechanical coupling loading process, the changes in the water levels in the first vertical pipe 4, the second vertical pipe 12, and the pressure chamber 5 in the measuring device are caused by the volume change of unsaturated soil sample 11 and the volume change of loading rod 1 immersed in airless water. The volume change of loading rod 1 immersed in water can be converted from the diameter of loading rod 1 and the vertical displacement monitored by linear displacement sensor 2. The water volume change in the first vertical pipe 4, the second vertical pipe 12, and the pressure chamber 5 at a certain moment relative to the initial moment is converted from the pressure difference data monitored by the first differential pressure sensor 13 and the second differential pressure sensor 14.

[0101] When conducting a hydraulic-mechanical coupling loading experiment on the unsaturated soil sample 11 in pressure chamber 5, it is required that, in the initial state (before loading), the water level in the second vertical pipe 12 should be near the bottom of the second vertical pipe 12, and the water level in the first vertical pipe 4 should be level with the water level in pressure chamber 5 (equivalent to the top of the first vertical pipe 4 being horizontal). When loading is applied through the loading rod 1, as the volume of the unsaturated soil sample 11 increases under pressure, the water overflowing from pressure chamber 5 will spill into the second vertical pipe 12. Because the water overflowing from pressure chamber 5 spills into the second vertical pipe 12, and the volume of the second vertical pipe 12 increases... The amount of water can be calculated from the differential pressure data monitored by the second differential pressure sensor 14. At this time, the water levels in the pressure chamber 5 and the first vertical pipe 4 will remain unchanged. When the volume of the unsaturated soil sample 11 decreases due to pressure, the water level in the first vertical pipe 4 remains unchanged while the water level in the pressure chamber 5 decreases. The amount of water that decreases in the pressure chamber 5 can be calculated from the differential pressure data monitored by the first differential pressure sensor 13. During the loading process, the volume of the loading rod 1 that is wetted by the pressure chamber 5 may increase or decrease. The wetted 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, embodiments of the present invention also provide a measurement method 100 for a volumetric deformation measurement device for unsaturated soil during a hydraulic-mechanical coupling loading process, as provided in the above embodiments. Figure 2 As shown, the specific steps include:

[0103] Step 110: Install the unsaturated soil sample 11 into the pressure chamber 5;

[0104] Step 120: At the initial moment t0 of the water-mechanical coupling loading of the unsaturated soil sample 11, open the first valve 62 and inject de-aired water into the pressure chamber 5 through the first water connection pipe 61 and the first vertical pipe 4 until the de-aired water enters the second vertical pipe 12 and reaches the preset water level height h0. At the same time, record the first initial pressure difference monitored by the first differential pressure sensor 13 and the second initial pressure difference monitored by the second differential pressure sensor 14.

[0105] Step 130: When applying hydraulic-mechanical coupling loading to the unsaturated soil sample 11, pressure is uniformly applied to the unsaturated soil sample 11 through the loading rod 1 at a preset loading speed v' until a preset time t is reached. i And at the preset time t i At the same time, 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 are recorded;

[0106] Step 140: Determine the volume change of unsaturated soil sample 11 during the water-mechanical coupling loading process based on 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 moment t0 before the water-force coupling loading (before the loading experiment begins, that is, after the unsaturated soil sample 11 is installed), the first valve 62 is opened and airless water is injected into the pressure chamber 5 through the first water connection pipe 61 and the first vertical pipe 4 until the airless water in the second vertical pipe 12 reaches the preset water level height h0. During this process, the second valve 72 and the third valve 82 need to be opened in a timely manner to discharge all the air in the second vertical pipe 12 and the pressure chamber 5.

[0108] Since the tops of the first vertical tube 4 and the second vertical tube 12 are above the sample cover 33, when the airless water entering the second vertical tube 12 reaches the preset water level height h0, the water level in the first vertical tube 4 will be level with the water level at its top port, and the initial water level height y0 in the pressure chamber 5 will be level with the water level at the port of the first vertical tube 4; here, the airless water in the second vertical tube 12 reaching the preset water level height h0 is near the bottom of the second vertical tube 12; at the same time, the first initial pressure difference P monitored by the first differential pressure sensor 13 is recorded. DB0and the second initial pressure difference P monitored by the second differential pressure sensor 14 DA0 .

[0109] Anhydrous water is filled into pressure chamber 5 through the first vertical pipe 4 until it overflows into the second vertical pipe 12 to a preset water level height h0. Then, the first valve 62, the second valve 72, and the third valve 82 are closed. Afterward, the sample is subjected to confining pressure through the air connection pipe 91 and the fourth valve 92, and then pressure is applied through the loading rod 1 to compress the unsaturated soil sample 11 to a preset time t. i The system records the first differential pressure difference monitored by the first differential pressure sensor 13 and the second differential pressure difference monitored by the second differential pressure sensor 14 at this time.

[0110] During the entire pressurization process, the unsaturated soil sample 11 may experience two scenarios: volume increase or volume decrease. When the volume of the unsaturated soil sample 11 increases, the preset water level height h0 in the second vertical pipe 12 will increase to the first water level height h. i The change in the water level difference in the second vertical tube 12 corresponding to the airless water level is Δh; when the volume of the unsaturated soil sample 11 decreases, the preset water level h0 in the second vertical tube 12 remains unchanged, while the initial water level y0 in the pressure chamber 5 decreases to the second water level y0. i The change in the height difference of the airless water level in pressure chamber 5 is Δy. The change in water level caused by the volume change of the unsaturated soil sample 11 will cause the pressure difference between 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, based on the first initial pressure difference and the first pressure difference, the loading from the initial time t0 to the preset time t can be obtained. i The change in the first pressure difference ΔP between the left and right sides of the first differential pressure sensor 13 DBi Based on the second initial pressure difference and the second pressure difference, the loading from the initial time t0 to the preset time t can be obtained. i The change in the second pressure difference ΔP between the left and right sides of the second differential pressure sensor 14 DAi .

[0112] Furthermore, loading from the initial time t0 to the preset time t i At that time, based on the change in the first pressure difference ΔP between the left and right sides of the first differential pressure sensor 13... DBi The change in the second pressure difference ΔP between the left and right sides of the second differential pressure sensor 14 DAi And the preset loading speed v' can determine the loading time from the initial time t0 to the preset time t. i Volume change ΔV of unsaturated soil sample 11 i.

[0113] Here, P DA and P DB These represent the pressure difference between the second differential pressure sensor 14 and the first differential pressure sensor 13, respectively; P AL and P AR P represents the absolute pressure values ​​on the left and right sides of the second differential pressure sensor 14, respectively. BL and P BR These represent the absolute pressure values ​​on the left and right sides of the first differential pressure sensor 13, respectively (here, P...). DA P DB P AL P AR P BL and P BR (This is for theoretical derivation purposes only and is not obtained directly from a differential pressure sensor); γ represents the specific gravity of degassed water (mass of water per unit volume); combined with the appendix... Figure 1 S A and S B S 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 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 The cross-sectional area remaining after the cross-sectional area S' of loading rod 1; H0 represents the initial position height of loading rod 1 at the initial moment t = t0; H1 represents the first position height of loading rod 1 at the first moment t = t1; h1 represents the third water level height of the second vertical pipe 12 without air or water at the first moment t = t1; y1 represents the fourth water level height of the pressure chamber 5 without air or water at the first moment t = t1; here, the first moment t1 is less than the preset moment t i .

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

[0115] P DA =P AL -P AR =γ(hYy) (1)

[0116] P DB =P BL -P BR =γ(y-y0) (2)

[0117] V A =γS A h-γ(Y+y)S (3)

[0118] V chamber =V B =γ(Y+y)S (4)

[0119] Where h represents the water level height of the airless water in the second vertical pipe 12 at non-initial moments, Y represents the height difference between the bottom surface of pressure chamber 5 and the differential pressure sensor, y represents the water level height of the airless water in pressure chamber 5 at non-initial moments, and V A This represents the nominal airless water volume within the second vertical tube 12 and pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading at a non-initial time; V B This represents the nominal volume of airless water in the first vertical pipe 4 and pressure chamber 5 that causes the first differential pressure sensor 13 to generate a reading at non-initial moments. 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 volume of airless water V in pressure chamber 5 at non-initial time. chamber The nominal volume of airless water represents the absolute value of the airless water volume calculated during the calculation process. This is because the third water connection pipe 81, which connects the first vertical pipe 4, the second vertical pipe 12, and the bottom of the pressure chamber 5 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 the calculation. However, this nominal value will not affect the actual measurement, because the actual measurement is based on the difference (e.g., ΔV). A and ΔV B During the calculation of the difference, the influence of the nominal water volume in the third water connection pipe 81, which connects the bottom of the first vertical pipe 4, the second vertical pipe 12, and the pressure chamber 5 to the second differential pressure sensor 14 and the first differential pressure sensor 13, is subtracted and canceled out.

[0120] The above is based on the change in the first pressure difference ΔP between the left and right sides of the first differential pressure sensor 13. DBi The change in the second pressure difference ΔP between the left and right sides of the second differential pressure sensor 14 DAi With the preset loading rate v', the volume change ΔV of the unsaturated soil sample 11 from the initial time t0 to the first time t1 can be determined. i The specific process is as follows:

[0121] At the initial moment t0 of the hydro-mechanical coupling loading:

[0122] P DA0 =P AL0 -P AR0 =γ(h0-Y-y0) (5)

[0123] P DB0 =PBL0 -P BR0 =γ(y0-y0) (6)

[0124] V A0 =γS A h0-γ(Y+y0)S (7)

[0125] V B0 =γ(Y+y0)S (8)

[0126] Among them, P DA0 P represents the second initial pressure difference monitored by the second differential pressure sensor 14 at the initial time t0. DB0 V represents the initial pressure difference monitored by the first differential pressure sensor 13 at the initial time t0. A0 This represents the nominal volume of airless water in the second vertical pipe 12 and pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading at the initial time t0; V B0 This represents the nominal volume of airless water in the first vertical tube 4 and pressure chamber 5 that caused the first differential pressure sensor 13 to generate a reading at the initial time t0.

[0127] During the first moment t1 of the hydro-mechanical coupling loading:

[0128] P DA1 =P AL1 -P AR1 =γ(h1-Y-y1) (9)

[0129] P DB1 =P BL1 -P BR1 =γ(y1-y0) (10)

[0130] V A1 =γS A h1-γ(Y+y1)S (11)

[0131] V B1 =γ(Y+y1)S (12)

[0132] Among them, P DA1 This represents the fourth pressure difference monitored by the second differential pressure sensor 14 at the first time t1, P. DB1 V represents the third pressure monitored by the first differential pressure sensor 13 at the first time t1. A1 This represents the nominal volume of airless water in the second vertical pipe 12 and pressure chamber 5 that causes the second differential pressure sensor 14 to generate a reading at the initial time t1; V B1 This represents the nominal volume of airless water in the first vertical tube 4 and pressure chamber 5 that caused the first differential pressure sensor 13 to generate a reading at the initial time t1.

[0133] The changes in each parameter during the loading process from the initial time t0 to the first time t1 are as follows:

[0134] ΔP DA1 =P DA1 -P DA0 =γ[(h1-h0)-(y1-y0)] (13)

[0135] ΔP DB1 =P DB1 -P DB0 =γ(y1-y0) (14)

[0136] ΔV A1 =γS A (h1-h0)-γS(y1-y0) (15)

[0137] ΔV B1 =γS(y1-y0) (16)

[0138] Here, ΔP DA1 ΔP represents the change in the fourth pressure difference between the two sides of the second vertical pipe 12 from the initial time t0 to the first time t1. DB1 ΔV represents the change in the third pressure difference between the two sides of the first vertical pipe 4 from the initial time t0 to the first time t1. A1 ΔV represents the change in the volume of the fourth airless water in the second vertical pipe 12 from the initial time t0 to the first time t1. B1 This represents the change in the volume of the third airless water in the first vertical pipe 4 from the initial time t0 to the first time t1.

[0139] because:

[0140] Δy=y1-y0=ΔP DB1 / γ (17)

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

[0142] Δh=h1-h0=(ΔP DA1 -ΔP DB1 ) / γ (18)

[0143] Where Δy represents the first water level difference between the pressure chamber 5 and the first water level difference between the initial time t0 and the first time t1 when loading begins, and Δh represents the second water level difference between the second vertical pipe 12 and the first water level difference when loading begins, from the initial time t0 to the first time t1; further, substituting formulas (17) and (18) into formulas (15) and (16) yields:

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

[0145] ΔV B1 =SΔP DB1 (20)

[0146] ΔV H1 =S'(H1-H0)=S'v'(t1-t0) (21)

[0147] Where, ΔV H1 This represents the second volume change of the loading rod 1 as it is submerged in the airless water in the pressure chamber 5 during the process from the initial time t0 to the first time t1.

[0148] Based on the principle of water balance:

[0149] ΔV A1 =ΔV H1 +ΔV1+ΔV B1 (twenty two)

[0150] Based on the first initial pressure difference, the second initial pressure difference, the third pressure difference, the fourth pressure difference, and the preset loading rate v', the first volume change ΔV1 of the unsaturated soil sample 11 from the initial time t0 to the first time t1 can be expressed as:

[0151]

[0152] Furthermore, from the initial time t0 to the preset time t i At that time, the volume change ΔV of unsaturated soil sample 11 i It can be represented as:

[0153]

[0154] Where, ΔV Ai This indicates loading from the initial time t0 to the preset time t. i The change in volume of the second airless water in the second vertical pipe 12 at that time; ΔV Bi This indicates loading from the initial time t0 to the preset time t. i The change in volume of the first airless water in the first vertical pipe 4 at time; ΔV Hi This indicates loading from the initial time t0 to the preset time t. i The first volume change when the loading rod is submerged in the airless water in the pressure chamber 5. As can be seen from equations (13) and (14), the effect of liquid tension (pressure difference change) inside the pressure chamber 5, the second vertical pipe 12 and the first vertical pipe 4 is eliminated in the process of calculating the increment.

[0155] Thus, the unsaturated soil sample 11 within the measuring device was successfully loaded from the initial moment of the hydraulic-mechanical coupling loading experiment to the preset time t. i Change in volume ΔV i The derivation and measurement of the above embodiments; the measurement method provided above can realize the continuous measurement of the volume deformation of 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 present invention provides a device and method for measuring the volumetric deformation of unsaturated soil during hydraulic-coupled loading, as described in the above embodiments. The specific structural design of the measuring device allows it to be extended to measure the volumetric deformation of unsaturated samples. Besides miniature experimental systems and sample volumetric deformation measurements within miniature hydraulic-coupled experimental systems integrated with X-ray CT, it is also suitable for large-scale devices with large samples, such as experimental systems for ultra-large samples containing gravel (e.g., cylindrical samples with a diameter of 500 mm and a height of 1000 mm). Furthermore, the single-pressure-chamber design of the measuring device reduces the overall structural complexity and sample installation difficulty, avoiding disturbance to the sample during loading and installation, thus enabling the measurement of unsaturated soil samples under complex hydraulic-coupled loading conditions. The volume deformation is measured accurately and continuously, reducing the failure rate. The measurement method is based on the principle of pressure difference change caused by the water level change in the two vertical tubes and pressure chamber during the sample deformation process, ensuring high measurement accuracy and reliability. Moreover, the measurement method has wide adaptability to unsaturated soil sample size and can effectively measure volume deformation for both large and small sample experimental systems. In addition, since the soil particles in saturated soil are filled with water, although there are simpler and more accurate methods for saturated soil filled with incompressible water, the measurement device and method for measuring the volume deformation of unsaturated soil during water-force coupled loading provided in the above embodiments of the present invention, as well as the water balance principle applied in the measurement process, are also applicable to the measurement of volume deformation of saturated soil.

[0157] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A device for measuring the volumetric deformation of unsaturated soil during a water-mechanical coupled loading process, characterized in that, include: Pressure chamber (5) is used to hold unsaturated soil samples (11); A loading rod (1) is positioned above the pressure chamber (5), and the loading rod (1) passes through the pressure chamber cover (51) of the pressure chamber (5) and contacts the unsaturated soil sample (11). The loading rod (1) reciprocates vertically to provide loading to the unsaturated soil sample (11). A first pressure monitoring unit is disposed on one side inside 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), and the second end of the first pressure monitoring unit is fixed to the pressure chamber base (52) of the pressure chamber (5) and communicates with the outside of the pressure chamber (5). The first pressure monitoring unit includes: a first vertical tube (4), 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 to the pressure chamber base (52) and communicates with the outside of the pressure chamber (5); and The second pressure monitoring unit is located 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). The second pressure monitoring unit includes: a second vertical tube (12). 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) is fixed on the pressure chamber base (52) and communicates 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 the volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading as described in claim 1, characterized in that, The first pressure monitoring unit further includes: The first differential pressure sensor (13) is connected to the second end of the first vertical tube (4). During the process of hydraulic coupling loading of the unsaturated soil sample (11), 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).

3. The device for measuring the volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading according to claim 2, characterized in that, The first pressure monitoring unit further includes: A first water connection pipe (61) is connected to the second end of the first vertical pipe (4), and a first differential pressure sensor (13) is disposed on one side of the first water connection pipe (61); and The first valve (62) is located on the other side of the first water connection pipe (61) and is connected in parallel with the first differential pressure sensor (13).

4. The device for measuring the volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading according to claim 2, characterized in that, The second pressure monitoring unit also includes: The second differential pressure sensor (14) is connected to the second end of the second vertical tube (12) and is on the same horizontal plane as the first differential pressure sensor (13). During the hydraulic-mechanical coupling loading process of the unsaturated soil sample (11), the second differential pressure sensor (14) is used to monitor the pressure difference between the second vertical tube (12) and the other side of the pressure chamber (5).

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

6. The device for measuring the volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading according to claim 1, characterized in that, Also includes: A gas connection pipe (91) is provided, one end of which passes through the upper cover (51) of the pressure chamber and is connected to the pressure chamber (5). as well as The fourth valve (92) is located at the other end of the gas connection pipe (91). The fourth valve (92) works in conjunction with the gas connection pipe (91) to apply sample confining pressure to the unsaturated soil sample (11) in the pressure chamber (5).

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

8. The device for measuring the volumetric deformation of unsaturated soil during hydraulic-mechanical coupling loading according to claim 1, characterized in that, Also includes: A linear displacement sensor (2) is disposed above the pressure chamber cover (51) and fixedly connected to the loading rod (1) to monitor the displacement of the loading rod (1) during vertical reciprocating motion.

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

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