Triaxial sample preparation device and method based on underwater deposition method

Abstract

The triaxial sample preparation device comprises a saturator, a support, a water containing base, a vacuum pump and a three-valve mechanism, the saturator is a container used for vacuumizing and saturating underwater sandy soil, a pipeline connected with a pressure-resistant pipe is arranged on a top cover of the saturator, and a first valve is arranged on the top cover of the saturator to control on-off; the other end of the pressure-resistant pipe is connected with a vacuum pump. A pipeline connected with the rubber pipe is arranged below the saturator, and a second valve is installed to control on-off. The three-valve mechanism is a three-axis sample preparation mold, and a water containing base is installed above the three-valve mechanism. The saturator is fixed above the three-valve mechanism and the water containing base through a support. According to the device, the working procedure of preparing the triaxial sample by a traditional underwater deposition method is simplified, the working procedures of heating the sample, injecting air-free water, cooling overnight, transferring a sand solution between a flask and a funnel and the like are omitted, the sample preparation time is greatly shortened, the test operation threshold is reduced, and the test reliability is improved.

Description

Technical Field

[0001] The invention relates to a sand triaxial sample preparation device, in particular to a triaxial sample preparation device and method based on an underwater sedimentation method, and belongs to the technical field of indoor geotechnical test equipment. Background Art

[0002] Water sedimentation is a method for preparing triaxial specimens of sand. This method was proposed as early as the 1980s. Its core is to immerse sand in a container containing water, expel the gas in the water by boiling, and finally prepare samples directly in the three-valve membrane by underwater sedimentation. Due to the use of sedimentation sample preparation, the underwater sedimentation method is considered to be a better way to restore the sedimentation process of sand. At the same time, this method can be used to prepare sand samples with a full density range from loose sand to dense sand. However, although this method has been developed for decades, it has never been widely used. The reasons are as follows:

[0003] (1) Although the underwater sedimentation method is theoretically sound, its actual operation requires the help of professional equipment and has a high threshold for implementation;

[0004] (2) The underwater sedimentation method requires open flame heating, which poses potential risks and is not easy to promote in laboratories;

[0005] (3) The underwater sedimentation method has a complicated sample preparation process, including sample heating, injection of air-free water, overnight cooling, and transfer of sand solution between the flask and the funnel, which takes a long time to prepare the sample;

[0006] (4) The underwater sedimentation method controls the density of the prepared sample by the sedimentation height of sand in water, but the sedimentation height in water is difficult to guarantee.

[0007] In order to solve the above-mentioned problems and promote the application of underwater sedimentation method in the preparation of triaxial specimens of sand and soil, it is necessary to propose an underwater sedimentation method sample preparation equipment. Summary of the invention

[0008] The purpose of the present invention is to provide a triaxial sample preparation device and method based on an underwater deposition method, so as to solve the problem that the underwater deposition method is difficult to be popularized and applied to triaxial sample preparation in the prior art.

[0009] To achieve the above object, the present invention provides the following technical solutions: a triaxial sample preparation device based on underwater sedimentation method, mainly comprising a saturator, a bracket, a water-containing base, a vacuum pump and a three-valve membrane mechanism;

[0010] The saturator is a container for vacuum saturation of sand and soil, and mainly includes a saturator cup, a saturator top cover, a first valve and a second valve. The saturator top cover is placed on the saturator cup, a pipeline is provided on the saturator top cover, and a first valve is installed to control the on-off. The pipeline of the saturator top cover is connected to the vacuum pump through a pressure-resistant pipe. The upper part of the saturator cup is an open hollow cylinder, and the lower part is a hollow cone. The bottom of the cone is provided with a pipeline and a second valve is installed to control the on-off.

[0011] The water holding base is installed on the top of the three-valve mechanism to increase the maximum height of the water level in the three-valve structure. The saturator is fixed above the three-valve mechanism and the water holding base through the bracket. The pipeline at the bottom of the saturator cup is connected to a rubber tube, and the rubber tube extends into the water holding base and the three-valve mechanism.

[0012] Furthermore, a rubber strip is fixed on the upper edge of the saturator cup body, and the upper part of the rubber strip is a concave crescent shape. The saturator top cover is placed above the rubber strip, and the rubber strip is used to close the gap between the saturator cup body and the saturator top cover during vacuuming.

[0013] Furthermore, the saturator cup body has the requirement of being pressure-resistant, and is preferably made of stainless steel or aluminum alloy, and the saturator top cover is preferably made of transparent tempered glass to observe the gas precipitation condition of the sand and water mixture in the saturator.

[0014] Furthermore, the bracket includes a base, a straight rod, a C-shaped clamp, a small iron ring and a large iron ring. The straight rod is fixed on the base, one end of the small iron ring is fixed to the straight rod, and the other end is an O-shaped iron ring, and its inner diameter is smaller than the maximum outer diameter of the saturator, so as to support the saturator. The large iron ring is arranged above the small iron ring, one end of which is fixed to the straight rod, and the other end is an O-shaped iron ring, and its inner diameter is equivalent to the maximum outer diameter of the saturator, so as to constrain its horizontal degree of freedom. One end of the C-shaped clamp is fixed to the straight rod, and the other end is clamped to other fixed objects to increase the stability of the bracket.

[0015] Furthermore, the water holding base includes a water holding base side wall, a water holding base base, a first scale and a third valve. The water holding base side wall is a thin-walled cylinder made of a transparent material, with an anti-overflow hole on the upper edge and a first scale on the side for observing the height of underwater sand and soil deposition. The water holding base base is fixed to the bottom of the water holding base side wall, and a circular opening is provided in the center of the base, which extends downward to form a thin-walled cylindrical bayonet. The diameter of the circular opening is comparable to the outer diameter of the transparent three-valve membrane and can be stuck on the transparent three-valve membrane, making it easy to fix the water holding base on the three-valve membrane mechanism. The water holding base base is provided with a drainage pipe and is equipped with a third valve to control the on and off of the pipeline.

[0016] Furthermore, the three-valve membrane mechanism is a commonly used structure for triaxial tests, including a transparent three-valve membrane and a hoop. The transparent three-valve membrane is made of transparent material, and a second scale for observing the underwater deposition height of sand and soil is provided on the outer wall. The three-valve membrane mechanism is arranged on a triaxial base.

[0017] Furthermore, a method for preparing a sample using the triaxial sample preparation device described in any one of the above items may include the following specific steps:

[0018] Step 1: Install the three-valve mechanism

[0019] The installation of the three-valve mechanism is consistent with the process of preparing conventional sand triaxial specimens, which mainly includes installing the sheepskin membrane on the triaxial base and fixing it with an "O" ring, then placing permeable stone and filter paper on the triaxial base in turn, and then installing the transparent three-valve membrane on the triaxial base and fixing it with a throat clamp, and turning the part of the sheepskin membrane that exceeds the transparent three-valve membrane outside the upper part of the outer wall of the transparent three-valve membrane.

[0020] Step 2: Install the water base

[0021] The water-holding base is mounted on the three-valve membrane mechanism. Since the diameter of the circular opening of the water-holding base is equivalent to the outer diameter of the transparent three-valve membrane, the sheepskin membrane everted on the upper part of the outer wall of the transparent three-valve membrane is filled between the circular opening at the bottom of the water-holding base and the transparent three-valve membrane, thereby forming a watertight sealing structure. The everted height of the sheepskin membrane is about 1 cm, and the obstruction of the scale on the three-valve membrane is small.

[0022] Step 3: Install the saturator

[0023] Fix the bracket to the test bench, install the rubber tube at the bottom of the saturator, and then fix the saturator in the small and large iron rings of the bracket. Adjust the position of the saturator so that the axis of the saturator is aligned with the axis of the transparent three-valve membrane.

[0024] Step 4: Prepare saturated sand

[0025] Close the second valve of the saturator, weigh sand with a mass of m1 and put it into the saturator, then inject distilled water to completely immerse the sand to a certain height, install the top cover of the saturator, connect the top cover of the saturator and the vacuum pump through a pressure-resistant pipe, open the first valve and the vacuum pump in turn to maintain a vacuum negative pressure state in the saturator, and maintain it for at least hours to ensure that the underwater sand is saturated.

[0026] Step 5: Underwater deposition preparation of triaxial specimens

[0027] Turn off the vacuum pump and remove the pressure-resistant pipe. Slowly open the first valve to restore the pressure in the saturator to atmospheric pressure, and then inject air-free water into the three-valve membrane mechanism and the water base. Observe the first scale and the second scale, slowly open the second valve to make the sand fall slowly, and control the up and down movement of the saturator to control the distance between the bottom of the rubber tube and the sand deposition surface. The distance between the bottom of the rubber tube and the sand deposition surface remains unchanged during the deposition process, thereby ensuring the uniform density of the sand sample. When the sample in the transparent three-valve membrane reaches the specified height, close the second valve.

[0028] Step 6: Remove the saturator and water base

[0029] Carefully remove the saturator to prevent the sand and liquid in the saturator from spilling out. Slowly open the third valve of the water base to drain the solution in the water base, and remove the water base after draining.

[0030] Step 7: Install the top cap and remove the three-valve membrane mechanism

[0031] The installation of the top cap and removal of the three-valve membrane mechanism are consistent with the conventional sand triaxial specimen preparation process, mainly including: installing filter paper, permeable stone and triaxial top cap on the top of the specimen in sequence, turning the sheepskin membrane on the upper part of the transparent three-valve membrane over the triaxial top cap and fixing it with an "O" ring, and finally removing the throat clamp and the transparent three-valve membrane in sequence to complete the specimen preparation.

[0032] Step 8: Calculate the density of the sample

[0033] Dry the sand remaining in the saturator and weigh its mass, recorded as m2. The dry density of the sample is ρ d and the porosity ratio e were calculated as follows:

[0034]

[0035] Where V is the total volume of the sample, G s is the specific gravity of soil particles,…….

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The device is equipped with a saturator and a vacuum pump, and can prepare underwater saturated sand samples directly in the saturator by vacuuming. Compared with the method of degassing by heating with open flames, this method does not require open flames, has good safety performance, and is suitable for operation in the laboratory. At the same time, the device simplifies the process of preparing triaxial specimens by underwater deposition, eliminating the steps of sample heating, injecting airless water, cooling overnight, and transferring sand and soil solutions between flasks and funnels, greatly shortening the sample preparation time, lowering the threshold for test operation, and improving test reliability.

[0038] In addition, when preparing triaxial specimens by underwater deposition method, the density of the prepared specimens is controlled by the underwater deposition height of the sand (the deposition height will directly affect the mass of sand sunk into the three-valve membrane (m2-m1)). The device is equipped with a water-filled base, which increases the maximum height of the water level in the three-valve membrane, and increases the density range of the prepared specimens; the water-filled base and the three-valve membrane mechanism are both made of transparent materials and are equipped with scales, which facilitates the observation and control of the sand deposition height during sample loading, thereby improving the uniformity of the specimen density and the reliability of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a three-dimensional side view structural diagram of the sample preparation device of the present invention;

[0040] Figure 2 It is a front structural diagram of the sample preparation device of the present invention;

[0041] Figure 3 This is a top view of the structure of the saturator of the present invention;

[0042] Figure 4 It is a three-dimensional front view structure diagram of the saturator of the present invention;

[0043] Figure 5 It is the AA cross-sectional structure diagram of the saturator of the present invention;

[0044] Figure 6 This is a front structural diagram of the water holding base of the present invention;

[0045] Figure 7 This is a three-dimensional top view of the water holding base of the present invention;

[0046] Figure 8 This is a three-dimensional upward structural diagram of the water-containing base of the present invention;

[0047] Fig. 9 It is a front view of the connection structure between the water-containing base and the three-petal membrane of the present invention;

[0048] Fig.10 It is the AA cross-sectional structural diagram of the sample preparation device of the present invention;

[0049] In the figure: 1. saturator; 101. saturator cup; 102. saturator top cover; 103. rubber strip; 104. first valve; 105. second valve; 2. bracket; 201. base; 202. straight rod; 203. C-shaped clamp; 204. small iron ring; 205. large iron ring; 3. water holding base; 301. side wall of water holding base; 302. overflow hole; 303. base of water holding base; 304. third valve; 305. first scale; 401. pressure-resistant tube; 402. rubber tube; 5. vacuum pump; 6. three-valve membrane mechanism; 601. transparent three-valve membrane; 602. hoop; 603. second scale; 7. three-axis base. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0051] See also Figure 1-10 , the present invention provides a technical solution: a triaxial sample preparation device based on underwater sedimentation method, mainly comprising a saturator 1, a bracket 2, a water-containing base 3, a vacuum pump 5 and a three-valve membrane mechanism 6;

[0052] The saturator 1 is a container for vacuum saturation of sand and soil, and mainly includes a saturator cup 101, a saturator top cover 102, a first valve 104 and a second valve 105. The saturator top cover 102 is placed on the saturator cup 101. A pipeline is provided in the center of the saturator top cover 102, and a first valve 104 is installed to control the on-off. The pipeline of the saturator top cover 102 is connected to the vacuum pump 5 through a pressure-resistant pipe 402. The vacuum pump 5 is used to vacuum and saturate the underwater sand and soil sample in the saturator 1. The upper part of the saturator cup 101 is an open hollow cylinder, and the lower part is a hollow cone. A pipeline is provided below the cone, and a second valve 105 is installed to control the on-off.

[0053] The saturator is fixed above the three-valve mechanism 6 and the water-containing base 3 through the bracket 2. The pipeline at the bottom of the saturator cup 101 is connected to the rubber tube 401, and the rubber tube 401 extends into the water-containing base 3 and the three-valve mechanism 6. The water-containing base 3 is installed on the top of the three-valve mechanism 6 to increase the maximum height of the water level in the three-valve structure 6.

[0054] A rubber strip 103 is fixed on the upper edge of the saturator cup 101, and the upper portion of the rubber strip 103 is a concave crescent shape. The saturator top cover 102 is placed above the rubber strip 103, and the rubber strip 103 is used to close the gap between the saturator cup 101 and the saturator top cover 102 during the vacuuming process.

[0055] The saturator cup body 101 has the requirement of being pressure-resistant, and is preferably made of stainless steel or aluminum alloy. The saturator top cover 102 is preferably made of transparent tempered glass to observe the gas precipitation condition of the sand and water mixture in the saturator 1 .

[0056] The bracket 2 includes a base 201, a straight rod 202, a C-shaped clamp 203, a small iron ring 204 and a large iron ring 205. The straight rod 202 is fixed on the base 201, one end of the small iron ring 204 is fixed to the straight rod 202 by a clamp, and the other end is an O-shaped iron ring, and its inner diameter is smaller than the maximum outer diameter of the saturator 1, so as to support the saturator 1. The large iron ring 205 is arranged above the small iron ring 204, one end of which is fixed to the straight rod 202 by a clamp, and the other end is an O-shaped iron ring, and its inner diameter is equivalent to the maximum outer diameter of the saturator 1, so as to constrain its horizontal degree of freedom. One end of the C-shaped clamp 203 is fixed to the straight rod 202 by a clamp, and the other end is clamped to other fixed objects to increase the stability of the bracket 2.

[0057] The water holding base 3 includes a water holding base side wall 301, a water holding base base 303, a first scale 305 and a third valve 304. The water holding base is used to raise the maximum water level in the three-valve membrane mechanism, thereby raising the controllable height range of the underwater deposition of sand and soil. The water holding base side wall 301 is a thin-walled cylinder made of transparent material, and an anti-overflow hole 302 is provided on the upper edge. During the deposition of sand and soil, the overflowing water can flow out from the anti-overflow hole. The side of the water holding base side wall 301 is provided with a first scale 305 for observing the underwater deposition height of sand and soil. The water holding base base 303 is fixed to the bottom of the water holding base side wall 301, and a circular opening is provided in the center of the base 303, which extends downward to form a thin-walled cylindrical bayonet. The diameter of the circular opening is equivalent to the outer diameter of the transparent three-valve membrane 601 and can be clamped on the transparent three-valve membrane, so as to facilitate the fixing of the water holding base 3 on the three-valve membrane mechanism 6. Meanwhile, when preparing the triaxial specimen, the top of the transparent three-valve membrane 601 is provided with an everted sheepskin membrane, so as to ensure the sealing of the connection between the water-containing base 3 and the three-valve membrane mechanism 6. The water-containing base base 303 is provided with a drainage pipe and a third valve 304 to control the on-off of the pipe.

[0058] The three-valve membrane mechanism 6 is a commonly used structure for triaxial testing, including a transparent three-valve membrane 601, a hoop 602 and a second scale 603. Its main feature is that the transparent three-valve membrane 601 is made of transparent material, and a second scale 603 for observing the underwater deposition height of sand and soil is provided on the outer wall.

[0059] This embodiment also provides a method for preparing a sample using the device, and the specific steps are as follows:

[0060] Step 1: Install the three-valve mechanism 6

[0061] The installation of the three-valve mechanism 6 is consistent with the process of preparing conventional sand triaxial specimens, mainly including installing the amnion on the triaxial base 7 and fixing it with an "O" ring, then placing permeable stones and filter paper on the triaxial base in turn, and then installing the transparent three-valve membrane 601 on the triaxial base 7 and fixing it with a throat clamp 602, and turning the part of the amnion that exceeds the transparent three-valve membrane 601 outside the upper part of the outer wall of the transparent three-valve membrane 602.

[0062] Step 2: Install the water base 3

[0063] The water-holding base 3 is mounted on the three-valve membrane mechanism 6. Since the diameter of the circular opening of the water-holding base 303 is equivalent to the outer diameter of the transparent three-valve membrane 601, the amniotic membrane everted on the upper part of the outer wall of the transparent three-valve membrane 601 is filled between the circular opening at the bottom of the water-holding base 3 and the transparent three-valve membrane 601, thereby forming a watertight sealing structure. The everted height of the amniotic membrane is about 1 cm, and the obstruction of the scale on the three-valve membrane is small.

[0064] Step 3: Install Saturator 1

[0065] Fix the bracket 2 on the test bench, install the rubber tube 401 on the bottom of the saturator 1, and then fix the saturator 1 in the small iron ring 204 and the large iron ring 205 of the bracket 2, and adjust the position of the saturator 1 so that the axis of the saturator 1 is aligned with the axis of the transparent three-valve membrane 6.

[0066] Step 4: Prepare saturated sand

[0067] Close the second valve 105 of the saturator, weigh the sand with a mass of m1 and put it into the saturator 1, then inject distilled water until the sand is completely immersed to a certain height, install the saturator top cover 102, connect the saturator top cover 102 and the vacuum pump 5 through the pressure-resistant pipe 402, open the first valve 104 and the vacuum pump 5 in turn, maintain the vacuum negative pressure state in the saturator 1, and maintain it for at least 2 hours to ensure that the underwater sand is saturated.

[0068] Step 5: Underwater deposition preparation of triaxial specimens

[0069] Turn off the vacuum pump 5 and remove the pressure-resistant pipe 402, slowly open the first valve 104 to restore the pressure in the saturator 1 to atmospheric pressure, and then inject air-free water into the three-valve membrane mechanism 6 and the water base 3. Observe the first scale 305 and the second scale 603, slowly open the second valve 105 to make the sand fall slowly, and control the up and down movement of the saturator to control the distance between the bottom of the rubber tube 401 and the sand deposition surface, so that the distance between the bottom of the rubber tube 401 and the sand deposition surface remains unchanged during the deposition process, thereby ensuring the uniform density of the sand sample. When the sample in the transparent three-valve membrane 601 reaches the specified height, close the second valve 105.

[0070] Step 6: Remove the saturator 1 and the water base 3

[0071] Carefully remove the saturator 1 to prevent the sand and liquid in the saturator 1 from spilling out. Slowly open the third valve 304 of the water base 3 to drain the solution in the water base 3, and remove the water base 3 after draining.

[0072] Step 7: Install the top cap and remove the three-valve membrane mechanism 6

[0073] The installation of the top cap and removal of the three-valve membrane mechanism 6 is consistent with the conventional sand triaxial sample preparation process, mainly including: installing filter paper, permeable stone and three-axis top cap on the top of the sample in sequence, turning the sheepskin membrane on the upper part of the transparent three-valve membrane 601 onto the three-axis top cap and fixing it with an "O" ring, and finally removing the throat clamp and the transparent three-valve membrane in sequence to complete the sample preparation.

[0074] Step 8: Calculate the density of the sample

[0075] Dry the sand remaining in saturator 1 and weigh its mass, recorded as m2. The dry density of the sample is ρ d and the porosity ratio e were calculated as follows:

[0076]

[0077] Where V is the total volume of the sample, Gs is the specific gravity of soil particles, and ρw is the density of water.

Claims

1. A triaxial sample preparation device based on underwater deposition method, characterized in that: It comprises a saturator (1), a bracket (2), a water-containing base (3), a vacuum pump (5) and a three-valve membrane mechanism (6); The saturator (1) is a container for vacuum saturation of sandy soil under water, comprising a saturator cup (101), a saturator top cover (102), a first valve (104) and a second valve (105); the saturator top cover (102) is placed on the saturator cup (101), a pipeline is provided on the saturator top cover (102), and a first valve (104) is installed to control on and off, and the pipeline of the saturator top cover (102) is connected to a vacuum pump (5) through a pressure-resistant pipe (402); the upper part of the saturator cup (101) is an open hollow cylinder, and the lower part is a hollow cone, a pipeline is provided at the bottom of the cone, and a second valve (105) is installed to control on and off; The three-valve mechanism (6) is a three-axis sample-making mold, and the water-containing base (3) is installed on the top of the three-valve mechanism (6) to increase the maximum height of the water level in the three-valve mechanism (6); the saturator is fixed above the water-containing base (3) through the bracket (2), and the pipeline at the bottom of the saturator cup (101) is connected to the rubber tube (401), and the rubber tube (401) extends into the water-containing base (3) and the three-valve mechanism (6).

2. The triaxial sample preparation device based on the underwater deposition method according to claim 1, characterized in that: A rubber strip (103) is fixed to the upper edge of the saturator cup body (101), the upper portion of the rubber strip (103) is in a concave crescent shape, the saturator top cover (102) is placed above the rubber strip (103), and the rubber strip (103) is used to seal the gap between the saturator cup body (101) and the saturator top cover (102) during the vacuuming process.

3. The triaxial sample preparation device based on underwater deposition method according to claim 1, characterized in that: The saturator cup body (101) is made of stainless steel or aluminum alloy, and the saturator top cover (102) is made of transparent tempered glass for observing the gas precipitation condition of the sand and water mixture in the saturator (1).

4. The triaxial sample preparation device based on underwater deposition method according to claim 1, characterized in that: The support (2) comprises a base (201), a straight rod (202), a C-shaped clamp (203), a small iron ring (204) and a large iron ring (205); the straight rod (202) is fixed on the base (201); one end of the small iron ring (204) is fixed to the straight rod (202), and the other end is an O-shaped iron ring, and its inner diameter is smaller than the maximum outer diameter of the saturator (1), so as to support the saturator (1); the large iron ring (205) is arranged above the small iron ring, one end of which is fixed to the straight rod (202), and the other end is an O-shaped iron ring, and its inner diameter is equivalent to the maximum outer diameter of the saturator (1), so as to constrain its horizontal degree of freedom; one end of the C-shaped clamp (203) is fixed to the straight rod (202), and the other end is clamped to other fixed objects, so as to increase the stability of the support (2).

5. The triaxial sample preparation device based on underwater deposition method according to claim 1, characterized in that: The water holding base (3) comprises a water holding base side wall (301), a water holding base base (303), a first scale (305) and a third valve (304); the water holding base side wall (301) is a thin-walled cylinder made of a transparent material, an anti-overflow hole (302) is provided on the upper edge, and a first scale (305) for observing the underwater sedimentation height of sand and soil is provided on the side; a water holding base base (303) is fixed to the bottom of the water holding base side wall (301), a circular opening is provided at the center of the base, and extends downward to form a thin-walled cylindrical bayonet; the diameter of the circular opening is equivalent to the outer diameter of the transparent three-valve membrane (601) and can be clamped on the transparent three-valve membrane, so that the water holding base (3) is fixed on the three-valve membrane mechanism (6); the water holding base base (303) is provided with a drainage pipe and is equipped with a third valve (304) to control the on-off of the pipeline.

6. The triaxial sample preparation device based on underwater deposition method according to claim 1, characterized in that: The three-valve membrane mechanism (6) comprises a transparent three-valve membrane (601) and a hoop (602). The transparent three-valve membrane (601) is made of a transparent material and has an outer wall provided with a second scale (603) for observing the underwater deposition height of sand and soil. When in use, the three-valve membrane mechanism (6) is arranged on a three-axis base (7).

7. A triaxial specimen preparation method based on underwater deposition method, characterized in that: The sample preparation is realized by using the triaxial sample preparation device as described in any one of claims 1 to 6, and the specific steps include the following: Step 1: Install the three-valve mechanism (6) The sheepskin membrane is mounted on the three-axis base (7) and fixed by an "O" ring, and then a permeable stone and filter paper are placed on the three-axis base in sequence, and then the transparent three-valve membrane (601) is mounted on the three-axis base (7) and fixed by a throat clamp (602), and the part of the sheepskin membrane that exceeds the transparent three-valve membrane (601) is turned outward on the upper part of the outer wall of the transparent three-valve membrane (602); Step 2: Install the water base (3) The water-holding base (3) is mounted on the three-valve membrane mechanism (6). Since the diameter of the circular opening of the base (303) of the water-holding base is equivalent to the outer diameter of the transparent three-valve membrane (601), the sheepskin membrane everted on the upper part of the outer wall of the transparent three-valve membrane (601) is filled between the circular opening at the bottom of the water-holding base (3) and the transparent three-valve membrane (601), thereby forming a watertight sealing structure; the everted height of the sheepskin membrane is about 1 cm, and the obstruction of the scale on the three-valve membrane is small; Step 3: Install the saturator (1) The support (2) is fixed to the test bench, the rubber tube (401) is installed at the bottom of the saturator (1), and then the saturator (1) is fixed to the support (2), and the position of the saturator (1) is adjusted so that the axis of the saturator (1) is aligned with the axis of the transparent three-valve membrane (6); Step 4: Prepare saturated sand The second valve (105) of the saturator is closed, sand with a mass of m1 is weighed and loaded into the saturator (1), and then distilled water is injected until the sand is completely submerged to a certain height, and then the top cover (102) of the saturator is installed, and the top cover (102) of the saturator and the vacuum pump (5) are connected through a pressure-resistant pipe (402), and the first valve (104) and the vacuum pump (5) are opened in sequence to maintain a vacuum negative pressure state in the saturator (1) and maintain it for at least 2 hours to ensure that the underwater sand is saturated; Step 5: Underwater deposition preparation of triaxial specimens The vacuum pump (5) is turned off and the pressure-resistant tube (402) is removed. The first valve (104) is slowly opened to restore the pressure in the saturator (1) to atmospheric pressure. Then, air-free water is injected into the three-valve membrane mechanism (6) and the water-containing base (3). The first scale (305) and the second scale (603) are observed. The second valve (105) is slowly opened to allow the sand to fall slowly. By controlling the saturator to move up and down, the distance between the bottom of the rubber tube (401) and the sand deposition surface is controlled so that the distance between the bottom of the rubber tube (401) and the sand deposition surface remains unchanged during the deposition process, thereby ensuring that the density of the sand sample is uniform. When the sample in the transparent three-valve membrane (601) reaches a specified height, the second valve (105) is closed. Step 6: Remove the saturator (1) and water base (3) The saturator (1) is taken out to prevent the sand and liquid in the saturator (1) from spilling out, and the third valve (304) of the water holding base (3) is slowly opened to drain the solution in the water holding base (3). After draining, the water holding base (3) is removed; Step 7: Install the top cap and remove the three-valve membrane mechanism (6) The installation of the top cap and removal of the three-valve membrane mechanism (6) is consistent with the conventional sand triaxial sample preparation process, mainly comprising: installing filter paper, permeable stone and the three-axis top cap on the top of the sample in sequence, turning the sheepskin membrane on the upper part of the transparent three-valve membrane (601) onto the three-axis top cap and fixing it with an "O" ring, and finally removing the throat clamp and the transparent three-valve membrane in sequence to complete the sample preparation.

8. The triaxial specimen preparation method based on underwater deposition method according to claim 7, characterized in that: The density of the obtained sample is specifically: Dry the sand remaining in the saturator (1) and weigh its mass, recorded as m2. The dry density of the sample is ρ d and the porosity ratio e were calculated as follows: Where V is the total volume of the sample, G s is the specific gravity of soil particles, ρ w is the density of water.

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