Testing device and method for measuring characteristic curve and shear modulus of unsaturated soil

Abstract

The invention discloses a test device for measuring an unsaturated soil characteristic curve and a shear modulus, and particularly relates to the field of unsaturated soil tests, the test device comprises a hydraulic control unit, a test cylinder, a soil-water characteristic curve test unit and a shear modulus test unit; the hydraulic control unit is communicated with the test cylinder; the test cylinder is electrically connected with a soil-water characteristic curve test unit; and the test cylinder is also electrically connected with a shear modulus test unit. The test device can measure the water content, the matrix suction and the shear wave velocity at the same time, so that the relationship between a soil-water characteristic curve and the shear modulus is established; in addition, the measuring efficiency of the soil-water characteristic curve and the shear modulus of the unsaturated soil is greatly improved, and the application prospect in engineering is wide.

Description

Technical Field

[0001] The invention relates to the field of unsaturated soil testing, in particular to a testing device and method for measuring a characteristic curve and shear modulus of unsaturated soil. Background Art

[0002] In nature, soil is mostly in an unsaturated state due to the influence of environmental factors such as rainfall and evaporation. For unsaturated soil, the soil-water characteristic curve is a curve that describes the relationship between soil water content (or saturation) and matrix suction. It is an important indicator of the basic hydraulic properties of soil and plays a very important role in studying the physical and mechanical properties of unsaturated soil. According to the theory of unsaturated soil mechanics, the strength of unsaturated soil is related to matrix suction, and there is also a close relationship between matrix suction and soil water content. When the water content is greater than the optimal water content, the shear modulus of the soil will decrease rapidly with the increase of water content. Existing studies have shown that the relationship between the soil-water characteristic curve and soil strength is complex, and it is difficult to derive an exact relationship from theory. Most of the existing experimental studies start from shear strength and establish the relationship between shear strength index and saturation. In recent years, with the increase of global rainfall and extreme rainfall events, foundation pit projects, slope projects and roadbed projects exposed to the atmosphere have been in a state of large changes in soil saturation for a long time, making their stability during construction and operation closely related to the soil-water characteristic curve and shear modulus of the soil. Therefore, it is necessary to establish the relationship between the soil-water characteristic curve of unsaturated soil and the shear modulus to provide theoretical support for the stability research of various geotechnical engineering projects during the construction and operation periods.

[0003] At present, the methods for measuring matrix suction include hygrometer, filter paper method, tensiometer method, pressure plate instrument method, etc. Through these methods, the soil-water characteristic curve of unsaturated soil can be obtained; the methods for measuring soil shear modulus mainly include resonant column method, triaxial test method, etc., but most of these methods require saturation of soil samples and can only obtain the shear modulus of saturated soil samples. Therefore, it is necessary to study a set of test devices that can simultaneously measure soil moisture content, matrix suction and shear modulus, so as to facilitate the establishment of the relationship between soil-water characteristic curve and shear modulus to serve engineering needs. Summary of the invention

[0004] The objective of the present invention is achieved through the following technical solutions: A test device for measuring the characteristic curve and shear modulus of unsaturated soil, comprising a hydraulic control unit, a test cylinder, a soil-water characteristic curve test unit and a shear modulus test unit; The hydraulic control unit is connected to the test cylinder; The test tube is electrically connected with a soil-water characteristic curve testing unit; The test cylinder is also electrically connected to a shear modulus testing unit.

[0005] Preferably, the hydraulic control unit comprises a Malvern flask and a water pipe; One end of the water pipe is connected to the valve at the bottom of the Martens flask, and the other end of the water pipe is connected to the water inlet valve at the bottom of the test cylinder. A water stop clamp for controlling water flow is installed on the water pipe, and a three-way joint for diversion is installed on the water pipe; The top end of the test cylinder is connected with a detachable top cover; A water outlet valve is installed and connected in the middle of the top cover, and a water pipe for measuring the volume of discharged water is provided in the test cylinder, and the water pipe is connected to the water outlet valve; The water inlet valve and the water outlet valve are provided with an annular hoop for sealing and preventing water from leaking out; The Martens flask is provided with a constant water head to maintain a stable seepage of water in the soil sample of the test tube.

[0006] Preferably, the soil-water characteristic curve testing unit comprises a data collector, a number of TDT sensors and a high-range tensiometer; Several of the TDT sensors and high-range tensiometers are pre-buried in the layered test soil in the test cylinder, and the wires of the several of the TDT sensors and high-range tensiometers are electrically connected to the data collector set up in the outside through the holes reserved in the side wall of the test cylinder.

[0007] Preferably, the shear modulus testing unit comprises a piezoelectric ceramic sheet, a signal generator, and a high-voltage amplifier; The piezoelectric ceramic sheet is electrically connected to a signal generator and a high-voltage amplifier, and is pre-buried and inserted into a test soil body in a test tube.

[0008] Preferably, the piezoelectric ceramic sheet is packaged in a brass inner cup, and the brass inner cup is further packaged with an acrylic outer cup to achieve electromagnetic shielding and waterproofing.

[0009] The test method based on the test device for measuring the characteristic curve and shear modulus of unsaturated soil comprises the following steps: S1. Prepare test soil; S2. The test soil is loaded into the test cylinder in layers, and the TDT sensor and high-range tensiometer are pre-buried in each layer of the test soil; To ensure good contact between the high-range tensiometer and the soil, before inserting the high-range tensiometer, a paste made of fine particles and water was placed in each hole of the test soil layer used to bury the high-range tensiometer; The distance between the clay head of the high-range tensiometer pre-buried in the same test soil layer and the probe of the TDT sensor is greater than 40 mm; S3, conduct soil tests, record test data from data collectors at different times, and calculate and draw soil-water characteristic curves of the test soil; Furthermore, according to the corresponding time, the waveform curve on the oscilloscope is recorded, and the shear modulus at the time corresponding to the soil-water characteristic curve of the test soil is calculated and plotted.

[0010] Preferably, the step in S1 includes: S11. Prepare soil samples, conduct screening tests, determine gradation curves, and calculate the unevenness coefficient and curvature coefficient through the gradation curves; S12. Conduct compaction test to determine the maximum dry density and optimum moisture content of the soil sample; S13. Dry the soil sample in an oven at 50°C for 24 h, then add water to reach the optimal moisture content, and then store it in a sealed container for 24 h to make the moisture uniform.

[0011] Preferably, before the test soil is loaded into the test cylinder in layers, a 5 cm gravel permeable layer is first set at the bottom of the inner cylinder of the test cylinder, and a filter net is laid on the upper part of the gravel permeable layer, and a water-permeable but soil-impermeable geotextile is wrapped around the outside.

[0012] Preferably, the soil test of S3 is divided into three stages: saturation, drainage and evaporation.

[0013] The beneficial effects of the present invention are as follows: the purpose of the present invention is to provide a test device capable of simultaneously measuring the characteristic curve and shear modulus of unsaturated soil, and the test device can realize the simultaneous measurement of the soil-water characteristic curve and shear modulus of unsaturated soil; through the test device, the moisture content, matrix suction and shear wave velocity can be measured simultaneously, so as to establish the relationship between the soil-water characteristic curve and the shear modulus, fill the gap in this field and greatly improve the measurement efficiency, and have broad application prospects in engineering; and through the test method, the soil-water characteristic curve of the soil can be obtained more conveniently, and can be used to help establish the relationship between the soil-water characteristic curve and the soil strength, which can provide great help for the mechanical properties of unsaturated soil and the study of roadbed stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an overall configuration diagram of a test device for measuring characteristic curve and shear modulus of unsaturated soil according to an embodiment of the present invention; Figure 2 It is a schematic diagram of the installation of a piezoelectric ceramic sheet in a shear modulus testing system according to an embodiment of the present invention; Figure 3 It is a schematic diagram of the overall configuration of the shear modulus testing system according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a test cylinder model according to an embodiment of the present invention; In the figure: 1-Marsh flask, 2-water pipe, 3-water inlet valve, 4-gravel permeable layer, 5-filter, 6-test cylinder, 8-water outlet valve, 9-top cover, 10-high voltage amplifier, 11-signal generator, 12-oscilloscope, 13-charge amplifier, 14-transmitter piezoelectric ceramic sheet, 15-receiver piezoelectric ceramic sheet, 16-brass inner cup, 17-acrylic outer cup, 18-data collector. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0016] like Figure 1-4As shown, a test device for measuring the characteristic curve and shear modulus of unsaturated soil, the test device can simultaneously measure the water content, matrix suction and shear wave velocity, so as to establish the relationship between the soil-water characteristic curve and the shear modulus, and greatly improve the measurement efficiency. The designed and assembled test device includes a hydraulic control unit, a test cylinder 6, a soil-water characteristic curve test unit and a shear modulus test unit; the hydraulic control unit is connected to the test cylinder 6; the test cylinder 6 is electrically connected to the soil-water characteristic curve test unit; the test cylinder 6 is also electrically connected to the shear modulus test unit. In an embodiment, the hydraulic control unit of the entire test device includes a Martens flask 1 and a water pipe 2; one end of the water pipe 2 is connected to the valve at the bottom of the Martens flask 1, and the other end of the water pipe 2 is connected to the water inlet valve 3 at the bottom of the test cylinder 6, and a water stop clamp for controlling water flow is installed on the water pipe 2, and a three-way joint for diversion is installed on the water pipe 2. The top of the test cylinder 6 is connected with a detachable top cover 9; the middle of the top cover 9 is installed with a water outlet valve 8, and a water pipe for measuring the volume of discharged water is provided in the test cylinder 6, and the water pipe is connected with the water outlet valve 8. The water inlet valve 3 and the water outlet valve 8 are arranged with an annular hoop for sealing and preventing water from seeping out; the Malchnitz flask 1 is provided with a constant water head to maintain the seepage of water in the soil sample of the test cylinder 6. In the embodiment, the soil-water characteristic curve test unit includes a data collector 18, a plurality of TDT sensors and a high-range tensiometer; the plurality of TDT sensors and the high-range tensiometer are respectively pre-buried in the layered test soil in the test cylinder 6, and the wires of the plurality of TDT sensors and the high-range tensiometer are all electrically connected to the data collector 18 arranged in the outside through the holes reserved in the side wall of the test cylinder 6. In addition, the shear modulus test unit includes a piezoelectric ceramic sheet, and the piezoelectric ceramic sheet includes a transmitting end piezoelectric ceramic sheet 14 and a receiving end piezoelectric ceramic sheet 15. The transmitting end piezoelectric ceramic sheet 14 of the piezoelectric ceramic sheet is inserted into the test soil in the test tube, and the receiving end piezoelectric ceramic sheet 15 of the piezoelectric ceramic sheet is electrically connected to the oscilloscope 12 and the charge amplifier 13; the piezoelectric ceramic sheet 14 is packaged in a brass inner cup 16, and the brass inner cup 16 is further packaged with an acrylic outer cup 17 for electromagnetic shielding and waterproofing. The above is the overall connection structure of the designed test device. After the test device is installed and debugged, the test is carried out.

[0017] Further, in the test embodiment, the Martens flask 1 is horizontally placed on a plane at a certain height, a constant water head of 0.45m is set, a valve is opened at the bottom, and it is connected to the two water inlet holes at the bottom of the test tube 6 through the water pipe 2, and a water stop clamp is set to control the flow of water. The test tube 6 is made of acrylic board, with a diameter of 30cm, a height of 65cm, and a wall thickness of 1cm; a 5cm uniform gravel permeable layer 4 is laid at the bottom of the test tube 6 to play a role of water permeability. A filter screen 5 is laid on top of the gravel permeable layer 4, and a layer of water-permeable and soil-impermeable geotextile is wrapped around the outside to isolate the upper soil; the top cover 9 is connected to the cylinder body with bolts, and a layer of rubber ring is placed to ensure sealing, and liquid thread glue is applied to the threads to achieve the effect of sealing and preventing loosening; a water outlet valve 8 is opened at the center of the top cover, and a water pipe is connected to discharge gas and water; the test cylinder 6 is symmetrically provided with two water inlet holes at a distance of 5 cm from the bottom of the cylinder, and the water inlet holes are respectively installed with water inlet valves 3, which are connected through pipelines and connected to the Malchnitz flask 1 through the water pipe 2 (through-connected), and each pipeline connection is tightened with a hoop to prevent water from seeping out.

[0018] Further, the soil samples were prepared, sieving tests were conducted to determine the grading curve, and the unevenness coefficient and curvature coefficient were calculated through the grading curve; compaction tests were conducted to determine the maximum dry density and the best moisture content of the soil samples; the soil samples were dried in an oven at 50°C for 24 hours, and then water was added to achieve the best moisture content, and then placed in a sealed container for 24 hours to make the moisture uniform. The required test soil was prepared.

[0019] The test soil samples are filled in the test cylinder 6 in layers. Before filling, they are sieved, dried, and then watered to form the soil samples with the best moisture content. A layer of plastic wrap is covered to prevent water loss. The soil samples are left to stand for 24 hours to make the moisture content uniform. Then, they are compacted by a compaction hammer to the maximum dry density according to the volume-mass method. The Malchnitz flask 1 is set with a constant water head of 0.45m and is connected to the water inlet valve 3 at the bottom of the test cylinder 6 through a water pipe 2. A water stop clamp is provided at the water pipe 2 to control the water level. The Malchnitz flask 1 is filled with water through the upper conduit. When the water in the Malchnitz flask 1 is insufficient during the infiltration process, water needs to be added in time. In order to protect the piezoelectric ceramic sheet, it is encapsulated with epoxy resin in a brass inner cup 16 with an outer diameter of 20 mm and a depth of 20 mm. The final protruding end of the piezoelectric ceramic sheet has a length of 12 mm to ensure good coupling between the piezoelectric ceramic sheet and the soil sample. The brass inner cup 16 is placed in the acrylic outer cup 17 and finally embedded in the reserved holes of the test tube 6. The gaps are also filled with epoxy resin for electromagnetic shielding and waterproofing.

[0020] The test cylinder 6 is provided with a 5cm gravel permeable layer 4 at the bottom, and a customized filter screen 5 is laid on the top of the gravel permeable layer 4. The filter screen 5 has an aperture of 1cm, a diameter of 30cm, and a thickness of 1.5cm. The outer surface is wrapped with a water-permeable but soil-impermeable geotextile to isolate the upper soil and the lower gravel permeable layer 4. The test cylinder 6 is filled with the test soil to be tested in layers above the geotextile. The test soil is poured into the test cylinder 6, and a layer is filled at 15, 25, 35, 45, and 55cm from the bottom of the test cylinder 6, and each layer is compacted. Correspondingly, the test cylinder 6 reserves a TDT sensor hole with a diameter of 1.5cm (the bending element hole opened in the test cylinder 6) at 15, 25, 35, 45, and 55cm from the bottom of the cylinder; at the same height, a number of high-range tensiometer holes with a diameter of 2cm are arranged at a position 90° from the TDT sensor hole (also the bending element hole opened in the test cylinder 6). Specifically, high-range tensiometer holes Z1, Z2, Z3, Z4, Z5 and TDT sensor test holes T1, T2, T3, T4, T5 are arranged at 90 degrees at positions 15 cm, 25 cm, 35 cm, 45 cm and 55 cm from the bottom; further, bending element holes W1 and W2 with a diameter of 4 cm are symmetrically arranged at a position 20 cm from the bottom.

[0021] In addition, two curved holes with a diameter of 4 cm are symmetrically opened in the test tube 6 at a distance of 20 cm from the bottom of the tube. Piezoelectric ceramic sheets are buried in the test soil in the test tube 6, that is, the transmitting end piezoelectric ceramic sheet 14 and the receiving end piezoelectric ceramic sheet 15 are both buried in the test soil in the test tube 6; at the same time, the transmitting end piezoelectric ceramic sheets of the piezoelectric ceramic sheets 14 are electrically connected to the oscilloscope 12 and the charge amplifier 13. In addition, the transmitting end piezoelectric ceramic sheet 14 and the receiving end piezoelectric ceramic sheet 15 can realize the mutual conversion of electric energy and kinetic energy; vibration is generated when an electric signal is received, and an electric signal is generated when vibration is received. The electric signal generated by the vibration of the receiving end piezoelectric ceramic sheet 14 is captured by the oscilloscope 12 after being amplified by the charge amplifier 13. The signal generator 11 is used to generate a sine wave, and the frequency range generally selected is between 1kHz-50kHz, and the amplitude is between 1V and 12V. The high-voltage amplifier 10 is used to amplify the voltage signal and provide a 50-fold gain to ensure that the emitted signal can be captured by the piezoelectric ceramic piece 14 at the receiving end. The dual-channel digital storage oscilloscope 12 is used to receive, display, and store the drive signal from the high-voltage amplifier 10 and the signal from the piezoelectric ceramic piece 15 at the receiving end, and to determine the propagation time of the wave in the soil sample through a time ruler to calculate the shear wave velocity. The signal lines of the instrument are all high-performance shielded cables to prevent electromagnetic interference. The computer is used to store and display the measured emission, receiving signals, and read the propagation time of the shear wave. Data can be directly transmitted to the computer through the signal line of the oscilloscope 12.

[0022] In addition, the test tube 6 has a water outlet at the top cover 9 to discharge gas and water; the water outlet is connected to the water pipe with a stainless steel joint and tied with a hoop. The TDT sensor and the high-range tensiometer in the embodiment are used to test the moisture content and matrix suction. The TDT sensor is buried in the test soil in the test tube 6, and the sensor wire passes through the TDT sensor hole reserved on the wall of the test tube 6. The gap between the TDT sensor hole and the TDT sensor wire is evenly coated with epoxy resin A and B glue to play a waterproof and fixed role. To ensure good contact between the high-range tensiometer and the soil, before inserting the high-range tensiometer, a paste made of fine particles and water is placed in each layer of test soil hole for pre-embedded high-range tensiometer; the distance between the clay head of the high-range tensiometer pre-embedded in the same layer of test soil and the probe of the TDT sensor is greater than 40mm; and the wire of the high-range tensiometer passes through the hole of the high-range tensiometer. Similarly, the gap between the hole of the high-range tensiometer and the wire of the high-range tensiometer is evenly coated with epoxy resin A and B glue. The wires of the TDT sensor and the high-range tensiometer are electrically connected to the data acquisition device 18 set in the outside. In addition, in the embodiment, the air intake value of the clay head of the high-range tensiometer is 100kPa. In order to prevent the internal water of the high-range tensiometer from being lost too quickly, thereby shortening the service life, the high-range tensiometer is tilted 4 to 5 degrees and inserted into the test soil in the test tube 6 through the reserved hole.

[0023] Furthermore, a soil test is finally carried out to record the test data of the data collector 18 at different times, and to calculate and draw the soil-water characteristic curve of the experimental soil.

[0024] In an embodiment, Figure 2 As shown, taking the group B filler at the bottom layer of the high-speed railway foundation as an example, the implementation steps are: (1) Assemble the test cylinder 6, adjust the water head of the Martens flask 1, and connect the water pipe; (2) Prepare group B filler, with coarse sand and fine particles in a ratio of 1:9. Determine its maximum dry density and optimum moisture content through compaction test, and determine the gradation curve of the filler through screening test; (3) Dry the soil sample in an oven at 105°C for 24 h, then add water to the sample using a mixer to achieve the optimal moisture content, and then store the sample in a sealed container for 24 h to allow the moisture content to be uniform. (4) A uniform gravel permeable layer 4 with a thickness of 50 mm and a particle size of 10 mm to 20 mm is evenly spread on the bottom of the test tube 6; a filter net 5 is laid on the top of the gravel permeable layer 4, and a geotextile that is permeable to water but not to soil is wrapped around the outside; (5) According to the compaction degree of 0.95, calculate the actual filling density. Compact according to the volume-mass method, fill the filler into the test cylinder 6 and compact it to the specified height with a compacting hammer; (6) Fill the layer by layer with a thickness of 0.1m per layer. When filling to the position where the TDT sensor and high-range tensiometer are buried, place the TDT probe and a metal rod of the same size as the high-range tensiometer on the compacted layer (replace the metal rod with the high-range tensiometer after saturation). The distance between the tip of the high-range tensiometer and the TDT sensor probe should be greater than 40mm. Connect the data acquisition instrument to test whether the sensor can be used normally. (7) After the soil sample is filled, insert the bending element mold through the reserved hole and connect the instruments of the shear modulus test system with a BNC connector; (8) Open the valve of the Martens flask 1 and maintain a constant water head of 0.45 m to flow into the test tube 6. Water is observed to flow out of the outlet valve 8. After 1 day, the soil sample is considered to be saturated. After saturation, the metal rod is pulled out and replaced with a high-range tensiometer. (9) Drainage stage: uniformly set the time of the data acquisition device 18, signal generator 11, oscilloscope 12 and charge amplifier 13 to keep the time of the four consistent. Open the two valves at the bottom and disconnect them from the head Martens flask 1. Start draining several times and close the bottom valve after each drainage. After each drainage, use the data acquisition device 18 to record the readings of the TDT sensor and the high-range tensiometer. The signal generator 11 excites the signal once at a certain interval, and the oscilloscope 12 is used to record the waveform each time. After several drainages, there is no obvious water flow out of the bottom valve, indicating the completion of the drainage stage; (10) Evaporation stage: Open the upper cover 9, close the bottom valve, and start evaporation. During the entire evaporation process, the readings of the TDT sensor and the high-range tensiometer are recorded at regular intervals. The signal generator 11 excites the signal at regular intervals, and the oscilloscope 12 receives and stores the signal. When the reading of the high-range tensiometer is stable, the evaporation stage is considered to be over, and the test is over; (11) By recording the readings of the TDT sensor and the high-range tensiometer during the drainage and evaporation stages, the soil-water characteristic curve of the soil during the entire process can be drawn; by recording the waveform of the oscilloscope 12, the shear modulus at the corresponding moment can be calculated.

[0025] During the test, the waveform of the oscilloscope 12 should be recorded, and the propagation time of the shear wave should be determined by the time difference between the first vertex of the transmitted wave and the received wave. The propagation speed of the shear wave can be calculated by formula 1. ; Further, the shear modulus can be calculated from the elastic wave theory formula 2 .

[0026] , , In the formula is the distance the shear wave travels, To deduct the time after the system delay, is the bulk density of the soil sample, is the shear wave velocity.

[0027] Through this test device, the moisture content, matrix suction and shear wave velocity can be measured simultaneously, so as to establish the relationship between the soil-water characteristic curve and the shear modulus, which greatly improves the measurement efficiency and data accuracy, and has broad application prospects in engineering. In addition, through this test method, it can provide a basis and guidance for the accuracy of measurement data, help overcome the complex relationship between the characteristic curve and soil strength, and provide great help for soil research.

[0028] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the embodiments in the above description. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A test device for measuring characteristic curve and shear modulus of unsaturated soil, characterized in that: It includes a hydraulic control unit, a test cylinder, a soil-water characteristic curve test unit and a shear modulus test unit; The hydraulic control unit is connected to the test cylinder; The test tube is electrically connected with a soil-water characteristic curve testing unit; The test cylinder is also electrically connected to a shear modulus testing unit.

2. A test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 1, characterized in that: The hydraulic control unit comprises a Martens flask and a water pipe; One end of the water pipe is connected to the valve at the bottom of the Martens flask, and the other end of the water pipe is connected to the water inlet valve at the bottom of the test cylinder. A water stop clamp for controlling water flow is installed on the water pipe, and a three-way joint for diversion is installed on the water pipe; The top end of the test cylinder is connected with a detachable top cover; A water outlet valve is installed and connected in the middle of the top cover, and a water pipe for measuring the volume of discharged water is provided in the test cylinder, and the water pipe is connected to the water outlet valve; The water inlet valve and the water outlet valve are provided with an annular hoop for sealing and preventing water from leaking out; The Martens flask is provided with a constant water head to maintain a stable seepage of water in the soil sample of the test tube.

3. A test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 2, characterized in that: The soil-water characteristic curve testing unit includes a data collector, a number of TDT sensors and a high-range tensiometer; Several of the TDT sensors and high-range tensiometers are pre-buried in the layered test soil in the test cylinder, and the wires of the several of the TDT sensors and high-range tensiometers are electrically connected to the data collector set up in the outside through the holes reserved in the side wall of the test cylinder.

4. A test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 3, characterized in that: The shear modulus testing unit includes a piezoelectric ceramic sheet, a signal generator, and a high-voltage amplifier; The piezoelectric ceramic sheet is electrically connected to a signal generator and a high-voltage amplifier, and is pre-buried and inserted into a test soil body in a test tube.

5. A test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 4, characterized in that: The piezoelectric ceramic sheet is packaged in a brass inner cup, and the brass inner cup is further packaged with an acrylic outer cup to achieve electromagnetic shielding and waterproofing.

6. A test method based on the test device for measuring characteristic curve and shear modulus of unsaturated soil according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Prepare test soil; S2. The test soil is loaded into the test cylinder in layers, and the TDT sensor and high-range tensiometer are pre-buried in each layer of the test soil; To ensure good contact between the high-range tensiometer and the soil, before inserting the high-range tensiometer, a paste made of fine particles and water was placed in each hole of the test soil layer used to bury the high-range tensiometer; The distance between the clay head of the high-range tensiometer pre-buried in the same test soil layer and the probe of the TDT sensor is greater than 40 mm; S3, conduct soil tests, record test data from data collectors at different times, and calculate and draw soil-water characteristic curves of the test soil; Furthermore, according to the corresponding time, the waveform curve on the oscilloscope is recorded, and the shear modulus at the time corresponding to the soil-water characteristic curve of the test soil is calculated and plotted.

7. The test method of the test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 6, characterized in that: The steps in S1 include: S11. Prepare soil samples, conduct screening tests, determine gradation curves, and calculate the unevenness coefficient and curvature coefficient through the gradation curves; S12. Conduct compaction test to determine the maximum dry density and optimum moisture content of the soil sample; S13. Dry the soil sample in an oven at 50°C for 24 h, then add water to reach the optimal moisture content, and then store it in a sealed container for 24 h to make the moisture uniform.

8. The test method of the test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 6, characterized in that: Before the test soil is loaded into the test cylinder in layers, a 5 cm gravel permeable layer is first set at the bottom of the inner cylinder of the test cylinder, and a filter net is laid on the top of the gravel permeable layer, and a water-permeable but soil-impermeable geotextile is wrapped around the outside.

9. The test method of the test device for measuring characteristic curve and shear modulus of unsaturated soil according to claim 6, characterized in that: The soil test of S3 is divided into three stages: saturation, drainage and evaporation.

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