Apparatus for measuring axial and radial strains of a sample in triaxial testing and method of use thereof

Abstract

A kind of measuring device for axial strain and radial strain of triaxial test sample and its use method, including upper positioning ring, lower positioning ring, conversion lever and two groups of LVDT micro displacement sensors.Three triaxial samples are placed in upper and lower positioning rings, and the three are coaxially arranged;Conversion lever is installed in upper positioning ring;One group of LVDT micro displacement sensors is installed in lower positioning ring for measuring the radial strain of sample, and the other group of LVDT micro displacement sensors is installed on the upper positioning ring for measuring the axial strain of sample.The radial strain of triaxial sample is converted to axial strain for measurement in the present application, which not only ensures the accuracy of radial strain measurement, but also reduces the difficulty of measurement, while greatly saving the demand of measurement device for radial space, facilitating the lightweight design of triaxial test equipment;The device has simple structure, convenient operation, high measurement precision and reliable test results, providing more convenient and effective technical means for measuring axial strain and radial strain of triaxial sample in soil test, with good popularization value.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical testing technology, and relates to a measuring device and its method for measuring axial and radial strain of a specimen in a triaxial test. Technical Background

[0002] In triaxial testing, the axial and radial strains of the specimen are crucial experimental parameters. Accurately and rapidly measuring these strains is of paramount importance for ensuring the accuracy and practicality of the test results. Currently, traditional triaxial testing typically measures the axial strain of the soil by measuring the deformation at both ends. However, due to end effects and systematic errors, the obtained soil stiffness is significantly lower than expected. Furthermore, methods for measuring the radial strain of the specimen remain relatively scarce, lacking simple and reliable testing equipment, which greatly limits experimental precision and the accuracy of the results. Therefore, accurately measuring the axial and radial strains of triaxial specimens has become an unavoidable challenge in triaxial testing.

[0003] To reduce experimental errors and improve measurement accuracy, many scholars have proposed different testing methods and techniques, such as using bending elements and resonant columns (mainly for measuring the maximum dynamic shear modulus of soil), local strain measurement techniques, laser displacement gauges, miniature inclinometers, and Hall effect sensors. Among these, bending elements and resonant columns, which derive the soil shear modulus from the shear wave rate, improve measurement accuracy, but can only obtain very small strains in the soil, and the test cannot control the strain magnitude and rate. Local strain measurement devices, applied in triaxial tests, can measure the strain range of triaxial specimens from 0.001% to 1%, but also suffer from the inability to measure strains over a larger range. Using precision testing instruments such as laser displacement gauges, miniature inclinometers, and Hall effect sensors presents problems such as high instrument costs and the susceptibility of sensors to damage during testing.

[0004] Therefore, considering the advantages and disadvantages of the various testing methods and techniques mentioned above, this invention proposes a simple, highly accurate, and environmentally friendly measuring device for measuring axial and radial strain of specimens in triaxial tests, along with its usage method. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for measuring axial and radial strain of a specimen in triaxial testing. By using this device for strain measurement in triaxial testing, the testing process can be simplified, the testing accuracy improved, and the testing cost reduced.

[0006] To achieve the above objectives, the technical solution adopted by this invention patent is as follows:

[0007] A measuring device for measuring the axial and radial strain of a specimen in a triaxial test is disclosed. The measuring device mainly includes: an upper positioning ring 100, a lower positioning ring 200, a conversion lever 300, and two sets of LVDT miniature displacement sensors 400A and 400B. The triaxial specimen 500 is placed within the upper positioning ring 100 and the lower positioning ring 200, all three arranged coaxially. The inner diameters of the upper positioning ring 100 and the lower positioning ring 200 are larger than the outer diameter of the triaxial specimen 500. The conversion lever 300 is mounted on the upper positioning ring 100 and is used to convert the radial strain of the specimen into axial strain, thereby simplifying the measurement. The LVDT miniature displacement sensor 400A is mounted on the lower positioning ring 200 and is used to measure the radial strain of the triaxial specimen 500; the LVDT miniature displacement sensor 400B is mounted on the upper positioning ring 100 and is used to measure the axial strain of the triaxial specimen 500. Specifically:

[0008] The upper positioning ring 100 mainly includes: an axial positioning hole 101, a steel support 102, a telescopic straight rod 103, a radial positioning support 104, a rotating shaft limiting hole 105, and an axial positioning support 106. The upper positioning ring 100 has a main structure of steel ring; the axial positioning holes 101 are three identical circular holes, equally spaced at angular intervals on the upper surface of the upper positioning ring 100, used for positioning the free end of the LVDT miniature displacement sensor 400B; there are six steel supports 102, each welded to one end of a telescopic rod 103, for direct contact with the triaxial sample 500; there are six telescopic rods 103, each welded at an equally spaced angular interval at one end to the inner edge of the upper positioning ring 100, so that the telescopic rods 103 can extend and retract with the deformation of the triaxial sample 500; there are three axial positioning supports 106, which are square barrels with a circular hole in the middle, each welded directly below the axial positioning hole 101, used to fix the LVDT miniature displacement sensor. The 400B has a circular hole on its outer wall for the data cable 404 of the LVDT miniature displacement sensor 400B to extend out. There are three radial positioning supports 104, which are welded to the middle position of every two axial positioning supports 106. The main body is a square barrel structure with a circular hole in the middle for fixing the LVDT miniature displacement sensor 400A. Two rectangular steel plates extend radially from the lower edge of the radial positioning support 104 on both sides of the main body upward positioning ring 100. The horizontal length of the rectangular steel plates is equal to the length of the steel round-head rod 303 in the conversion lever 300. The ends of the two rectangular steel plates have pivot limiting holes 105 for fixing the conversion lever 300. A circular hole is also opened on the outer wall of the radial positioning support 104 for the data cable 404 of the LVDT miniature displacement sensor 400A to extend out.

[0009] The lower positioning ring 200 mainly includes: steel supports 201, telescopic rods 202, and axial positioning holes 203. The main structure of the lower positioning ring 200 is a steel ring, the same size as the upper positioning ring 100. The axial positioning holes 203 are three identical circular holes, equally spaced at angular intervals on the upper surface of the lower positioning ring 200, used for positioning the LVDT miniature displacement sensor 400B probe 403. There are six steel supports 201, each welded to one end of the telescopic rod 202, for direct contact with the triaxial sample 500. There are also six telescopic rods 202, one end of which is equally spaced at angular intervals on the inner edge of the lower positioning ring 200, allowing the telescopic rods 202 to extend and retract with the deformation of the triaxial sample 500.

[0010] The aforementioned conversion lever 300 mainly includes a right-angle steel plate 301, a pivot hole 302, and a steel round-headed rod 303. The right-angle steel plate 301 is the main structure of the conversion lever 300, and is a right-angle steel plate with two arms of equal length. The pivot hole 302 is a through hole opened at the corner of the right-angle steel plate 301, used for connecting the conversion lever 300 to the upper positioning ring 100. The steel round-headed rod 303 is a non-extendable steel round rod, with one end welded to the lower edge of the outer side of the vertical surface of the right-angle steel plate, and the other end having a round head structure. During measurement, it gently presses against the triaxial sample 500. When the triaxial sample 500 deforms, the steel round-headed rod 303 can move back and forth with the deformation of the sample. The working principle of the conversion lever 300 is as follows: When the triaxial specimen 500 deforms, the steel round-headed rod 303 moves back and forth with the deformation of the triaxial specimen 500. Since the conversion lever 300 is made of a material with extremely high rigidity, when the steel round-headed rod 303 moves back and forth with the deformation of the specimen, the conversion lever 300 rotates around the pivot hole 302, thereby indirectly causing the upper surface of the right-angled steel plate 301 to move up and down with the deformation of the triaxial specimen 500. During the experiment, the probe 403 of the LVDT miniature displacement sensor 400A is positioned against the upper surface of the right-angled steel plate 301, ensuring that the distance from the probe 403 to the pivot hole 302 is equal to the length of the steel round-headed rod 303, thus converting the radial strain of the triaxial specimen 500 into axial strain for measurement.

[0011] Furthermore, the LVDT miniature displacement sensors 400A and 400B are identical displacement sensors. LVDT miniature displacement sensor 400A is used to measure the radial strain of the triaxial specimen 500, and LVDT miniature displacement sensor 400B is used to measure the axial strain of the triaxial specimen 500. The LVDT miniature displacement sensors 400A and 400B mainly include a transformer 401, a measuring rod 402, a probe 403, and a data cable 404. The probe 403 is used to directly contact the measuring point of the triaxial specimen 500 and drive the measuring rod 402 to move back and forth. The measuring rod 402 is a thin, non-deformable steel rod. When the coil in the transformer 401 moves back and forth, it causes a change in voltage, thereby reflecting the displacement of the probe 403 through a voltage signal. The data cable 404 is directly connected to an industrial control computer for transmitting voltage signals.

[0012] A method for using a measuring device for measuring the axial and radial strain of a specimen in a triaxial test includes the following steps:

[0013] First, according to the test plan, mark the positions to be measured on the triaxial specimen 500; assemble the upper positioning ring 100, the lower positioning ring 200 and the conversion lever 300 according to the above steps. The LVDT miniature displacement sensors 400A and 400B can be purchased directly from the market.

[0014] Secondly, based on the dimensions of the triaxial specimen 500, first adjust the length of the telescopic straight rod 202 of the lower positioning ring 200, and put it into the upper end of the triaxial specimen 500. Use strong adhesive to bond the steel support 201 to the rubber film on the surface of the triaxial specimen 500 at the pre-marked position to ensure that it will not fall off during the test.

[0015] Third, based on the dimensions of the triaxial specimen 500, adjust the length of the telescopic rod 103 of the upper positioning ring 100 and insert it from the upper end of the triaxial specimen 500. Use strong adhesive to bond the steel support 102 to the rubber membrane on the surface of the triaxial specimen 500 at the pre-marked position to ensure that it will not fall off during the test.

[0016] Fourth, fix three LVDT miniature displacement sensors 400A and three LVDT miniature displacement sensors 400B to the inner wall of the square barrel of the radial positioning support 104 and the axial positioning support 106 respectively with glue, and extend the data cable 404 from the round hole on the side wall of the square barrel.

[0017] Fifth, place the conversion lever 300 between the two rectangular steel plates extending to the lower end of the positioning support 104, align the pivot hole 302 of the conversion lever 300 with the pivot limiting hole 105 on the radial positioning support 104, and use a steel round shaft to fix the conversion lever 300 on the radial positioning support 104, so that it can rotate freely around the steel round shaft.

[0018] Sixth, adjust the probe 403 of the LVDT miniature displacement sensor 400B so that it is exactly abutting the center of the axial positioning hole 203 of the lower positioning ring 200; the steel round-head rod 303 of the conversion lever 300 is exactly abutting the surface of the triaxial sample 500; the probe 403 of the LVDT miniature displacement sensor 400A is exactly abutting the upper surface of the right-angle steel plate 301 of the conversion lever 300, and ensure that the distance from the probe 403 to the shaft hole 302 is equal to the length of the steel round-head rod 303;

[0019] Seventh, connect the data cable 404 of each LVDT miniature displacement sensor 400A and 400B to the industrial control computer and zero it;

[0020] Eighth, the displacement transmitted by the LVDT miniature displacement sensors 400A and 400B during the test is collected in real time by an industrial control computer, which is the radial strain and axial strain of the triaxial specimen 500.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) This invention converts radial strain into axial strain for measurement, which reduces the difficulty of radial strain measurement and improves the accuracy of radial strain measurement.

[0023] (2) The LVDT miniature displacement sensor used in this invention has accurate measurement, which improves the test accuracy and ensures the accuracy of the test results;

[0024] (3) The present invention has a simple structure and is easy to install, which shortens the test time, saves human resources, reduces the workload of test personnel, and thus indirectly improves the test efficiency.

[0025] In summary, the device of this invention has a simple structure, is easy to operate, and has low time cost, improving experimental accuracy and ensuring the accuracy of experimental results. Its installation process is simple and convenient, shortening the installation time of the strain measurement device and thus indirectly improving experimental efficiency. It provides a more convenient and effective means for measuring the axial and radial strain of triaxial specimens in geotechnical testing, and has good potential for widespread application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a positioning ring on a measuring device for measuring the axial and radial strain of a specimen in a triaxial test.

[0027] Figure 2 This is a schematic diagram of the lower positioning ring of a device for measuring the axial and radial strain of a specimen in a triaxial test.

[0028] Figure 3 This is a schematic diagram of a switching lever for measuring the axial and radial strain of a specimen in a triaxial test.

[0029] Figure 4 This is a schematic diagram of an LVDT miniature displacement sensor, a device for measuring axial and radial strain of a specimen in a triaxial test.

[0030] Figure 5 This is a schematic diagram of an overall device for measuring the axial and radial strain of a specimen in a triaxial test.

[0031] Figure 6 This is a schematic diagram of the installation of a measuring device for measuring the axial and radial strain of a specimen in a triaxial test.

[0032] Figure 7 The axial strain time history curve of a specimen measured by a measuring device for measuring axial and radial strain of a specimen in a triaxial test;

[0033] Figure 8 The radial strain time history curve of a specimen is measured by a measuring device used for measuring the axial and radial strain of a specimen in a triaxial test.

[0034] in:

[0035] Figure 1 It mainly includes: 101 axial positioning hole; 102 steel support; 103 telescopic straight rod; 104 radial positioning support; 105 rotating shaft limiting hole; 106 axial positioning support;

[0036] Figure 2 Main components include: 201 steel support; 202 telescopic straight rod; 203 axial positioning hole;

[0037] Figure 3 Main components include: 301 right-angle steel plate; 302 pivot hole; 303 steel round-head rod;

[0038] Figure 4 Main components include: 401 transformer; 402 probe; 403 probe head; 404 data cable;

[0039] Figure 5 Main components include: 100 upper positioning ring; 200 lower positioning ring; 300 conversion lever; 400 ALVDT miniature displacement sensor; 400 BLVDT miniature displacement sensor;

[0040] Figure 6 It mainly includes: 100 upper positioning ring; 200 lower positioning ring; 500 triaxial specimen. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] A measuring device for measuring the axial and radial strain of a specimen in a triaxial test is disclosed. The measuring device mainly includes: an upper positioning ring 100, a lower positioning ring 200, a switching lever 300, and LVDT miniature displacement sensors 400A and 400B.

[0043] In specific embodiments of the device of the present invention, it should be clearly stated that some terms indicating relative direction or relative position, such as "one side," "upper end," and "lower end," are used to describe the orientation or positional relationship of a specific component relative to other components. This description of orientation or position is only for the convenience and clarity of describing the specific embodiment and does not mean that it is not strictly limited in actual implementation. It can be modified according to actual information such as the size of each component.

[0044] The upper positioning ring 100 mainly includes: axial positioning holes 101, steel supports 102, telescopic straight rods 103, radial positioning supports 104, rotating shaft limiting holes 105, and axial positioning supports 106. The main structure of the upper positioning ring 100 is a steel ring; the axial positioning holes 101 are three identical circular holes, equally spaced at angular intervals on the upper surface of the upper positioning ring 100, used for positioning the free end of the LVDT miniature displacement sensor 400B; there are six steel supports 102, each welded to one end of the telescopic straight rod 103 for direct contact with the sample; there are six telescopic straight rods 103, each welded at equally spaced angular intervals at one end to the inner edge of the upper positioning ring 100, allowing the telescopic straight rods 103 to extend and retract with the sample deformation; there are three axial positioning supports 106, each a square barrel with a circular hole in the center, welded directly below the axial positioning holes 101, used to fix the LVDT miniature displacement sensor 400B. The displacement sensor 400B has a circular hole on its outer barrel wall for extending the data cable 404 of the LVDT miniature displacement sensor 400B. Three radial positioning supports 104 are welded to the middle of every two axial positioning supports 106, forming a square barrel-shaped structure with a circular hole in the center, used to fix the LVDT miniature displacement sensor 400A. Two rectangular steel plates extend radially from the lower edge of the square barrel from the upward positioning rings 100 on both sides. The horizontal length of the rectangular steel plates is equal to the length of the steel round-headed rod 303 in the conversion lever 300. The ends of the two rectangular steel plates have pivot limiting holes 105 for fixing the conversion lever 300; and a circular hole is also provided on the outer barrel wall for extending the data cable 404 of the LVDT miniature displacement sensor 400A.

[0045] The lower positioning ring 200 mainly includes: a steel support 201, a telescopic straight rod 202, and axial positioning holes 203. The upper positioning ring 200 has a main structure of a steel ring; the axial positioning holes 203 are three identical circular holes, equally spaced at angular intervals on the upper surface of the lower positioning ring 200, used for positioning the LVDT miniature displacement sensor 400B probe 403; there are six steel supports 201, each welded to one end of the telescopic straight rod 202, for direct contact with the sample; there are six telescopic straight rods 202, one end of which is equally spaced at angular intervals on the inner edge of the lower positioning ring 200, so that when the sample deforms, the telescopic straight rods 202 can extend and retract with the deformation of the triaxial sample 500.

[0046] The conversion lever 300 mainly includes a right-angle steel plate 301, a pivot hole 302, and a steel round-headed rod 303. The right-angle steel plate 301 is the main structure of the conversion lever 300, and is a right-angle steel plate with two arms of equal length. The pivot hole 302 is a through hole opened at the corner of the right-angle steel plate 301, used for connecting the conversion lever 300 to the upper positioning ring 100. The steel round-headed rod 303 is a non-extendable steel round rod, with one end welded to the lower edge of the outer side of the vertical surface of the right-angle steel plate, and the other end having a round head structure. During measurement, it gently presses against the triaxial sample 500. When the sample deforms, the steel round-headed rod 303 can move back and forth with the deformation of the sample.

[0047] The LVDT miniature displacement sensors 400A and 400B are identical displacement sensors. LVDT miniature displacement sensor 400A is used to measure the radial strain of the triaxial specimen 500, and LVDT miniature displacement sensor 400B is used to measure the axial strain of the triaxial specimen 500. The LVDT miniature displacement sensors 400A and 400B mainly include a transformer 401, a measuring rod 402, a probe 403, and a data cable 404. The probe 403 is used to directly contact the triaxial measuring point and drive the measuring rod 402 to move back and forth. The measuring rod 402 is a thin, non-deformable steel rod. When the coil in the transformer 401 moves back and forth, it causes a voltage change, thus reflecting the displacement of the probe 403 through a voltage signal. The data cable 404 is directly connected to an industrial control computer for transmitting voltage signals.

[0048] The following section describes how to use this invention's device, using a specific strain measurement process as an example:

[0049] First, according to the test plan, sample preparation was carried out. The test material was gravel from the panel dam of the Dashixia Hydropower Station in Xinjiang. The triaxial specimen 500 was a cylindrical specimen with a diameter of 300 mm and a height of 650 mm. After the specimen was prepared, a rubber membrane was placed over the outside of the specimen.

[0050] Second, use a plumb bob to mark four equidistant plumb lines on the triaxial specimen 500. Then, using the top circular axis of the triaxial specimen as the reference line, use a tape measure to measure the points 125mm and 525mm away from the reference line. Then, use a black ballpoint pen to mark the rubber membrane surface of the triaxial specimen 500, intersecting with the plumb lines drawn in the previous step. The intersection points serve as the positioning marks for the upper positioning ring 100 and the lower positioning ring 200.

[0051] Third, assemble the upper positioning ring 100, the lower positioning ring 200, and the conversion lever 300 according to the above steps. The LVDT miniature displacement sensors 400A and 400B can be purchased directly from the market.

[0052] Next, based on the dimensions of the triaxial specimen 500, first adjust the length of the telescopic rod 202 of the lower positioning ring 200, and slip it onto the upper end of the triaxial specimen 500. Use strong adhesive to glue the steel support 201 to the positioning mark on the rubber membrane on the surface of the triaxial specimen 500 to ensure that it will not fall off during the test.

[0053] Fourth, adjust the length of the telescopic rod 103 of the upper positioning ring 100 according to the size of the triaxial specimen 500, and put it into the upper end of the triaxial specimen 500. Use strong adhesive to glue the steel support 201 to the positioning mark of the rubber membrane on the surface of the triaxial specimen 500 to ensure that it will not fall off during the test.

[0054] Fifth, fix three LVDT miniature displacement sensors 400A and three LVDT miniature displacement sensors 400B to the inner wall of the square barrel of the radial positioning support 104 and the axial positioning support 106 respectively with glue, and extend the data cable 404 from the round hole on the side wall of the square barrel.

[0055] Sixth, place the conversion lever 300 between the two rectangular steel plates extending to the lower end of the positioning support 104, align the pivot hole 302 of the conversion lever 300 with the pivot limiting hole 105 on the radial positioning support 104, and use a steel round shaft to fix the conversion lever 300 on the radial positioning support 104, so that it can rotate freely around the steel round shaft.

[0056] Seventh, adjust the probe 403 of the LVDT miniature displacement sensor 400B so that it is exactly abutting the center of the axial positioning hole 203 of the lower positioning ring 200; the steel round-head rod 303 of the conversion lever 300 should be exactly abutting the surface of the triaxial sample 500; the probe 403 of the LVDT miniature displacement sensor 400A should be exactly abutting the upper surface of the right-angle steel plate 301 of the conversion lever 300, and ensure that the distance from the probe 403 to the shaft hole 302 is equal to the length of the steel round-head rod 303. The final installed state is as follows. Figure 6 As shown.

[0057] Eighth, connect the data lines 404 of each LVDT miniature displacement sensor 400A and 400B to the industrial control computer and zero them.

[0058] Ninth, the voltage values ​​transmitted by the LVDT miniature displacement sensors 400A and 400B during the test were acquired in real time using an industrial control computer. The voltage data of the obtained axial strain and radial strain were processed to obtain the time history curves of the axial strain and radial strain of the triaxial specimen, as shown below. Figure 7 and Figure 8 As shown.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A measuring device for axial and radial strain of a specimen in a triaxial test, characterized in that: The measuring device includes: an upper positioning ring (100), a lower positioning ring (200), a conversion lever (300), and two sets of first LVDT micro displacement sensors (400A) and second LVDT micro displacement sensors (400B). The triaxial specimen (500) is placed inside the upper positioning ring (100) and the lower positioning ring (200), and the three are arranged coaxially. The inner diameter of the upper positioning ring (100) and the lower positioning ring (200) is larger than the outer diameter of the triaxial specimen (500). The conversion lever (300) is mounted on the upper positioning ring (100). The first LVDT micro displacement sensor (400A) is mounted on the lower positioning ring (200) and is used to measure the radial strain of the triaxial specimen (500). The second LVDT micro displacement sensor (400B) is mounted on the upper positioning ring (100) and is used to measure the axial strain of the triaxial specimen (500). The upper positioning ring (100) includes axial positioning holes (101), steel supports (102), telescopic rods (103), radial positioning supports (104), shaft limiting holes (105), and axial positioning supports (106). The main structure of the upper positioning ring (100) is a steel ring. The three axial positioning holes (101) are equally spaced on the upper surface of the upper positioning ring (100) for positioning the free end of the second LVDT miniature displacement sensor (400B). There are six steel supports (102) in total, which are welded to one end of the telescopic rods (103) for direct contact with the triaxial sample (500). There are six telescopic rods (103) in total, one end of which is equally spaced on the inner edge of the upper positioning ring (100) for use when the triaxial sample (500) deforms. The telescopic rod (103) can extend and retract with the deformation of the sample; there are three axial positioning supports (106), which are square barrels with a circular hole in the middle, and are welded directly below the axial positioning hole (101) to fix the second LVDT miniature displacement sensor (400B); there are three radial positioning supports (104), which are welded in the middle of every two axial positioning supports (106), and are square barrels with a circular hole in the middle to fix the first LVDT miniature displacement sensor (400A). Two rectangular steel plates extend radially from the upper positioning rings (100) on both sides of the square barrel. The horizontal length of the rectangular steel plates is equal to the length of the steel round-head rod (303) in the conversion lever (300). The ends of the two rectangular steel plates are provided with pivot limiting holes (105) to fix the conversion lever (300); The lower positioning ring (200) includes a steel support (201), a telescopic rod (202), and an axial positioning hole (203). The main structure of the lower positioning ring (200) is a steel ring. The axial positioning hole (203) consists of three identical circular holes, spaced at equal angles on the upper surface of the lower positioning ring (200), used for positioning the probe (403) of the second LVDT miniature displacement sensor (400B). There are six steel supports (201) in total, each welded to one end of the telescopic rod (202), for direct contact with the triaxial sample (500). There are six telescopic rods (202) in total, one end of which is welded at equal angles to the inner edge of the lower positioning ring (200), so that when the triaxial sample (500) deforms, the telescopic rod (202) can extend and retract with the deformation of the triaxial sample (500). The aforementioned conversion lever (300) includes a right-angle steel plate (301), a pivot hole (302), and a steel round-head rod (303); the right-angle steel plate (301) is the main structure of the conversion lever (300), and is a right-angle steel plate with two arms of equal length; the pivot hole (302) is a through hole opened at the corner of the right-angle steel plate (301), used for connecting the conversion lever (300) and the upper positioning ring (100); the steel round-head rod (303) is a non-extendable steel round rod, one end of which is welded to the lower edge of the outer side of the vertical surface of the right-angle steel plate, and the other end has a round head structure. During measurement, it gently presses against the triaxial sample (500). When the triaxial sample (500) deforms, the steel round-head rod (303) can move back and forth with the deformation of the sample.

2. The measuring device for axial and radial strain of a specimen in a triaxial test according to claim 1, characterized in that: The first LVDT miniature displacement sensor (400A) and the second LVDT miniature displacement sensor (400B) are identical displacement sensors. Both the first LVDT miniature displacement sensor (400A) and the second LVDT miniature displacement sensor (400B) include a transformer (401), a measuring rod (402), a probe (403), and a data line (404). The probe (403) is used to directly contact the measuring point of the triaxial sample (500) and drive the measuring rod (402) to move back and forth. The measuring rod (402) is a thin, non-deformable steel rod. When the coil in the transformer (401) moves back and forth, it causes a change in voltage, thereby reflecting the displacement of the probe (403) through the voltage signal. The data line (404) is directly connected to the industrial control computer and is used to transmit voltage signals.

3. The measuring device for axial and radial strain of a specimen in a triaxial test according to claim 2, characterized in that: The outer wall of the axial positioning support (106) has a round hole for extending the data line (404) of the second LVDT miniature displacement sensor (400B); the outer wall of the radial positioning support (104) has a round hole for extending the data line (404) of the first LVDT miniature displacement sensor (400A).

4. A method of using the measuring device for axial and radial strain of a specimen in a triaxial test as described in any one of claims 1-3, characterized in that, Includes the following steps: First, according to the test plan, mark the positions to be measured on the triaxial specimen (500); and assemble the upper positioning ring (100), the lower positioning ring (200) and the conversion lever (300) respectively. Second, based on the dimensions of the triaxial specimen (500), first adjust the length of the telescopic rod (202) of the lower positioning ring (200), and put it into the upper end of the triaxial specimen (500). Use strong adhesive to bond the steel support (201) to the rubber film on the surface of the triaxial specimen (500) at the pre-marked position to ensure that it will not fall off during the test. Third, based on the dimensions of the triaxial specimen (500), adjust the length of the telescopic rod (103) of the upper positioning ring (100), and fit it onto the upper end of the triaxial specimen (500). Use strong adhesive to bond the steel support (102) to the rubber film on the surface of the triaxial specimen (500) at the pre-marked position to ensure that it will not fall off during the test. Fourth, three first LVDT miniature displacement sensors (400A) and three second LVDT miniature displacement sensors (400B) are fixed to the inner walls of the square barrel of the radial positioning support (104) and the axial positioning support (106) respectively with glue, and the data cable (404) extends out from the round hole on the side wall of the square barrel. Fifth, place the conversion lever (300) between the two rectangular steel plates extending from the lower end of the radial positioning support (104), align the pivot hole (302) of the conversion lever (300) with the pivot limiting hole (105) on the radial positioning support (104), and use a steel round shaft to fix the conversion lever (300) on the radial positioning support (104) so ​​that it can rotate freely around the steel round shaft; Sixth, adjust the probe (403) of the second LVDT miniature displacement sensor (400B) so that it just touches the center of the axial positioning hole (203) of the lower positioning ring (200); the steel round-head rod (303) of the conversion lever (300) just touches the surface of the triaxial sample (500); the probe (403) of the first LVDT miniature displacement sensor (400A) just touches the upper surface of the right-angle steel plate (301) of the conversion lever (300), and ensure that the distance from the probe (403) to the shaft hole (302) is equal to the length of the steel round-head rod (303); Seventh, connect the data lines (404) of each of the first LVDT miniature displacement sensors (400A) and the second LVDT miniature displacement sensors (400B) to the industrial control computer and perform zeroing; Eighth, the displacement of the first LVDT miniature displacement sensor (400A) and the second LVDT miniature displacement sensor (400B) during the test was collected in real time using an industrial control computer, and the radial strain and axial strain of the triaxial specimen (500) were finally obtained.

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