A triaxial specimen preparation device and method based on underwater deposition method

Abstract

The application discloses a kind of triaxial sample preparation device and method based on underwater deposition method, including saturator, support, water base, vacuum pump and three membrane mechanism, saturator is used for the container of underwater sand soil vacuum saturation, saturator top cover is equipped with the pipeline of connecting pressure tube, and is equipped with first valve to control on-off, pressure tube other end is connected with vacuum pump.Saturator below is equipped with the pipeline of connecting rubber tube, and is equipped with second valve to control on-off.The three membrane mechanism is the mold of triaxial sample, and water base is installed on top.Saturator is fixed on the three membrane mechanism and water base by support.The device simplifies the process of preparing triaxial sample of conventional underwater deposition method, eliminates sample heating, injects airless water, overnight cooling, sand soil solution is transferred between flask and funnel and other processes, greatly shorten the time of sample preparation, reduce test operation threshold, improve test reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of sand triaxial specimen preparation device, more particularly to a kind of triaxial specimen preparation device and method based on underwater sedimentation method, belong to indoor geotechnical test equipment technical field. BACKGROUND

[0002] Water sedimentation method (Water sedimentation) is a method for preparing sand triaxial specimen. The method was proposed as early as in the 1980s, and its core is to immerse the sand in a water-containing container, and to remove the gas in the water by boiling, and finally to prepare the sample directly in the three-pellicle by underwater deposition. Since the deposition method is used, the water sedimentation method is considered to be able to better restore the deposition process of sand. At the same time, this method can be used for the preparation of sand specimen from loose sand to dense sand with full density. However, although this method has been developed for decades, it has not been widely used. The reasons are as follows:

[0003] (1) Although the water sedimentation method is theoretically complete, it needs to be assisted by professional equipment to realize the actual operation, and the threshold for implementation is high;

[0004] (2) The water sedimentation method requires open flame heating, which has potential risks and is not easy to promote in the laboratory;

[0005] (3) The water sedimentation method has complex process, including sample heating, water injection, overnight cooling, transfer of sand solution between flask and funnel, etc., and the sample preparation takes a long time;

[0006] (4) The water sedimentation method controls the density of the prepared specimen by the deposition height of sand in water, and it is difficult to guarantee the deposition height in water.

[0007] In order to solve the above-mentioned problems and promote the application of water sedimentation method in sand triaxial specimen preparation, it is necessary to propose a water sedimentation method sample preparation device. SUMMARY

[0008] The present application aims to provide a kind of triaxial specimen preparation device and method based on water sedimentation method, to solve the problem that water sedimentation method is difficult to be applied to triaxial specimen preparation in prior art.

[0009] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a kind of triaxial specimen preparation device based on water sedimentation method, mainly including saturator, support, water base, vacuum pump and three-pellicle mechanism;

[0010] The saturator is a sand vacuum saturation container, mainly comprising a saturator cup, a saturator top cover, a first valve and a second valve. The saturator top cover is placed on the saturator cup, and a pipeline is arranged on the saturator top cover and is provided with the first valve for controlling the opening and closing of the pipeline. The pipeline of the saturator top cover is connected with the vacuum pump through a pressure-resistant pipeline. The saturator cup is a hollow cylinder with an open upper part and a hollow conical body with a pipeline arranged at the bottom and provided with the second valve for controlling the opening and closing of the pipeline.

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

[0012] Further, a rubber strip is fixed on the upper edge of the saturator cup, and the upper part of the rubber strip is in a concave crescent shape. The saturator top cover is placed above the rubber strip, and the rubber strip is used to seal the gap between the saturator cup and the saturator top cover during the vacuumizing process.

[0013] Further, the saturator cup has a pressure-resistant requirement, and is preferably made of stainless steel or aluminum alloy. 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] Further, the support comprises 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 on the straight rod, and the other end is an O-shaped iron ring with an inner diameter smaller than the maximum outer diameter of the saturator to support the saturator. The large iron ring is arranged above the small iron ring, one end of the large iron ring is fixed on the straight rod, and the other end is an O-shaped iron ring with an inner diameter corresponding to the maximum outer diameter of the saturator to constrain the horizontal degree of freedom. One end of the C-shaped clamp is fixed on the straight rod, and the other end is clamped to other fixed objects to increase the stability of the support.

[0015] Further, the water containing base comprises a water containing base side wall, a water containing base base, a first scale and a third valve. The water containing base side wall is a thin-walled cylinder made of transparent material, and an anti-overflow hole is arranged on the upper edge of the water containing base side wall. A first scale is arranged on the side of the water containing base side wall for observing the deposition height of the sand under water. The water containing base base is fixed on the bottom of the water containing base side wall, and a circular opening is arranged in the center of the water containing base 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 to be clamped on the transparent three-valve membrane, so that the water containing base can be fixed on the three-valve membrane mechanism. The water containing base base is provided with a pipeline for draining water, and the third valve is arranged on the pipeline to control the opening and closing of the pipeline.

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

[0017] Further, the method for preparing a sample by using the triaxial sample preparation device according to any one of the preceding aspects comprises the following steps:

[0018] Step one: install the three-valve mechanism

[0019] The installation of the three-valve mechanism is consistent with the process of preparing a conventional sand triaxial sample, mainly including installing the sheepskin membrane on the triaxial base and fixing it through the O-shaped ring, then placing the water-permeable stone and filter paper on the triaxial base in turn, installing the transparent three-valve on the triaxial base and fixing it with the collar, and turning the part of the sheepskin membrane that exceeds the transparent three-valve outward on the upper part of the outer wall of the transparent three-valve.

[0020] Step two: install the water container base

[0021] The water container base is installed on the three-valve mechanism, since the diameter of the circular opening at the bottom of the water container base is equivalent to the outer diameter of the transparent three-valve, the sheepskin membrane turned outward on the upper part of the outer wall of the transparent three-valve is filled between the circular opening at the bottom of the water container base and the transparent three-valve, thereby forming a water-tight sealing structure. The height of the sheepskin membrane turned outward is about 1 cm, which has a small shielding effect on the scale on the three-valve.

[0022] Step three: install the saturator

[0023] The bracket is fixed on the test bench, the rubber tube is installed at the bottom of the saturator, and then the saturator is fixed in the small iron ring and the large iron ring of the bracket, and the position of the saturator is adjusted to align the axis of the saturator with the axis of the transparent three-valve.

[0024] Step four: prepare saturated sand

[0025] The second valve of the saturator is closed, the sand with a mass of m1 is weighed and loaded into the saturator, then distilled water is injected to a certain height to completely immerse the sand, the top cover of the saturator is installed, the top cover of the saturator is connected with the vacuum pump through the pressure-resistant pipe, the first valve and the vacuum pump are opened in turn, the vacuum negative pressure state in the saturator is maintained, and the state is maintained for at least one hour to ensure that the underwater sand is saturated.

[0026] Step five: underwater deposition preparation of the triaxial sample

[0027] Turn off the vacuum pump and remove the pressure-resistant pipe. Slowly open the first valve to restore the pressure inside the saturator to atmospheric pressure. Then, inject degaussed water into the three-valve mechanism and the water-filled base. Observe the first and second scales. Slowly open the second valve to allow the sand to fall slowly. By controlling the up-and-down movement of the saturator, control the distance between the bottom of the rubber tube and the sand deposition surface, ensuring that the distance remains constant during the deposition process, thus guaranteeing the uniform density of the sand sample. Once the sample inside the transparent three-valve membrane reaches the specified height, close the second valve.

[0028] Step Six: Remove the saturator and water-holding base

[0029] Carefully remove the saturator, taking care to prevent sand and liquid from spilling out. Slowly open the third valve on the water-containing base to drain the solution from the base, and then remove the base after draining.

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

[0031] The installation of the top cap and removal of the three-valve membrane mechanism are consistent with the conventional triaxial sample preparation process for sand. The main steps include: installing filter paper, permeable stone and triaxial top cap in sequence on the top of the sample; turning the sheepskin membrane that is turned outward on the upper part of the transparent three-valve membrane onto the triaxial top cap and fixing it with an "O" ring; and finally removing the hose clamp and transparent three-valve membrane in sequence to complete the sample preparation.

[0032] Step 8: Calculate the sample density

[0033] The remaining sand in the saturator is dried and weighed, with the mass recorded as m2. The dry density ρ of the sample is then calculated. d The porosity e is calculated using the following formulas:

[0034]

[0035] In the formula, V is the total volume of the sample, and G s ρ is the specific gravity of soil particles. w This is the density of water.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] This device is equipped with a saturator and a vacuum pump, allowing for the direct preparation of underwater saturated sand samples within the saturator via vacuum extraction. Compared to open flame heating for degassing, this method eliminates the need for an open flame, offering better safety and suitability for laboratory operation. Furthermore, this device simplifies the preparation of triaxial samples using underwater sedimentation, eliminating steps such as sample heating, injection of degassed water, overnight cooling, and transfer of the sand solution between the flask and funnel. This significantly reduces sample preparation time, lowers the operational threshold, and improves experimental reliability.

[0038] In addition, the density of the prepared sample is controlled by the underwater deposition height of the sand when the triaxial sample is prepared by the underwater deposition method (the deposition height will directly affect the mass of the sand sinking into the three-piece membrane (m2-m1)). The device is provided with a water containing base, the maximum height of the water level in the three-piece membrane is improved, the density range of the prepared sample is improved, the water containing base and the three-piece membrane mechanism are simultaneously made of transparent material, and are provided with scales, the sand deposition height is observed and controlled during the sample loading, and therefore the density uniformity of the sample and the reliability of the test are improved. BRIEF DESCRIPTION OF DRAWINGS

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

[0040] Figure 2 It is a front view structure diagram of the sample preparation device of the application;

[0041] Figure 3 It is a top view structure diagram of the saturator of the application;

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

[0043] Figure 5 It is an A-A sectional structure diagram of the saturator of the application;

[0044] Figure 6 It is a front view structure diagram of the water containing base of the application;

[0045] Figure 7 It is a three-dimensional top view structure diagram of the water containing base of the application;

[0046] Figure 8 It is a three-dimensional bottom view structure diagram of the water containing base of the application;

[0047] Figure 9 It is a front view structure diagram of the connection structure of the water containing base and the three-piece membrane of the application;

[0048] Figure 10 It is an A-A sectional structure diagram of the sample preparation device of the application;

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

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

[0051] Please refer to Figures 1-10 The present application provides a technical solution: a triaxial sample preparation device based on underwater deposition method, mainly comprising a saturator 1, a support 2, a water containing base 3, a vacuum pump 5 and a three-valve mechanism 6.

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

[0053] The saturator is fixed above the three-valve mechanism 6 and the water containing base 3 through the support 2. The pipeline at the bottom of the saturator cup body 101 is connected with a rubber pipe 401, which 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 mechanism 6.

[0054] The upper edge of the saturator cup body 101 is fixed with a rubber strip 103, and the upper part 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 vacuumizing process.

[0055] The saturator cup body 101 has the requirement of pressure resistance, and stainless steel or aluminum alloy material is preferably used. 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 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 to the base 201, one end of the small iron ring 204 is fixed to the straight rod 202 through a clamp, and the other end is an O-shaped iron ring, and the inner diameter of the small iron ring 204 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 the large iron ring 205 is fixed to the straight rod 202 through a clamp, and the other end is an O-shaped iron ring, and the inner diameter of the large iron ring 205 is equivalent to the maximum outer diameter of the saturator 1, so as to constrain the horizontal degree of freedom. One end of the C-shaped clamp 203 is fixed to the straight rod 202 through a clamp, and the other end is clamped to other fixed objects, so as to increase the stability of the support 2.

[0057] The water containing base 3 comprises a water containing base side wall 301, a water containing base base 303, a first scale 305 and a third valve 304. The water containing base is used to increase the maximum water level height in the three-valve mechanism, so as to increase the controllable height range of the underwater deposition of the sand. The water containing base side wall 301 is a thin-walled cylinder made of transparent material, and an anti-overflow hole 302 is arranged at the upper edge. During the sand deposition process, the overflowing water can flow out from the anti-overflow hole. The first scale 305 for observing the underwater deposition height of the sand is arranged on the side of the water containing base side wall 301. The water containing base base 303 is fixed to the bottom of the water containing base side wall 301, a circular opening is arranged in the center of the base 303 and extends downward to form a thin-walled cylindrical socket. The diameter of the circular opening is equivalent to the outer diameter of the transparent three-valve 601, and can be clamped on the transparent three-valve, so as to facilitate the fixation of the water containing base 3 on the three-valve mechanism 6. At the same time, when the three-axis sample is prepared, the transparent three-valve 601 is provided with an everted sheepskin film at the top, so as to ensure the sealing property of the connection between the water containing base 3 and the three-valve mechanism 6. The water containing base base 303 is provided with a drainage pipeline and is provided with the third valve 304, so as to control the opening and closing of the pipeline.

[0058] The three-valve mechanism 6 is a commonly used structure in triaxial tests, and comprises a transparent three-valve 601, a ring hoop 602 and a second scale 603. The main feature is that the transparent three-valve 601 is made of transparent material, and the outer wall is provided with the second scale 603 for observing the underwater deposition height of the sand.

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

[0060] Step one: install the three-valve mechanism 6

[0061] The installation of the three-lid membrane mechanism 6 is consistent with the process of conventional sand triaxial specimen preparation, mainly including installing the sheepskin membrane on the triaxial base 7 and fixing it through the "O" ring, then placing the water-permeable stone and filter paper on the triaxial base in turn, installing the transparent three-lid membrane 601 on the triaxial base 7 and fixing it with the throat clamp 602, and turning the part of the sheepskin membrane outside the transparent three-lid membrane 601 outward on the upper part of the outer wall of the transparent three-lid membrane 602.

[0062] Step two: install the water-containing base 3

[0063] The water-containing base 3 is installed on the three-lid membrane mechanism 6. Since the diameter of the circular opening of the water-containing base 3 is equivalent to the outer diameter of the transparent three-lid membrane 601, the sheepskin membrane turned outward on the upper part of the outer wall of the transparent three-lid membrane 601 fills the circular opening at the bottom of the water-containing base 3 and the transparent three-lid membrane 601, thereby forming a water-tight sealing structure. The turning height of the sheepskin membrane is about 1 cm, which has little obstruction to the scale on the three-lid membrane.

[0064] Step three: install the saturator 1

[0065] The support 2 is fixed on the test bench, the saturator 1 is fixed in the small iron ring 204 and the large iron ring 205 of the support 2 after the rubber pipe 401 is installed at the bottom of the saturator 1, and the position of the saturator 1 is adjusted to align the axis of the saturator 1 with the axis of the transparent three-lid membrane 6.

[0066] Step four: prepare saturated sand

[0067] The second valve 105 of the saturator is closed, the sand with a mass of m1 is weighed and loaded into the saturator 1, then distilled water is injected to a certain height to completely immerse the sand, the saturator top cover 102 is installed, the saturator top cover 102 and the vacuum pump 5 are connected through the pressure-resistant pipe 402, the first valve 104 and the vacuum pump 5 are opened in turn, the vacuum negative pressure state in the saturator 1 is maintained, and the state is maintained for at least 2 hours to ensure that the underwater sand is saturated.

[0068] Step five: underwater deposition preparation of triaxial specimen

[0069] The vacuum pump 5 is closed and the pressure-resistant pipe 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-lid 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 make the sand fall slowly, the distance between the bottom of the rubber pipe 401 and the deposition surface of the sand is controlled by controlling the up-and-down movement of the saturator, so that the distance between the bottom of the rubber pipe 401 and the deposition surface of the sand remains unchanged during the deposition process, thereby ensuring the uniformity of the density of the sand specimen. When the specimen in the transparent three-lid membrane 601 reaches the specified height, the second valve 105 is closed.

[0070] Step six: remove the saturator 1 and the water-containing base 3

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

[0072] Step seven: install the top cap and remove the three-lip membrane mechanism 6

[0073] The installation of the top cap and the removal of the three-lip membrane mechanism 6 are consistent with the conventional sand triaxial specimen preparation process, mainly including: installing filter paper, water-permeable stone and triaxial top cap on the top end of the specimen in turn, turning the sheepskin membrane turned over on the upper part of the transparent three-lip membrane 601 to the triaxial top cap, and fixing it through the "O" ring, and finally removing the collar and the transparent three-lip membrane in order to complete the specimen preparation.

[0074] Step eight: calculate the density of the specimen

[0075] Dry the sand remaining in the saturator 1 and weigh the mass, denoted as m2, then the dry density of the specimen ρ d and the void ratio e are calculated as follows:

[0076]

[0077] In the formula, V is the total volume of the specimen, G s is the specific gravity of the soil particles, and ρ w is the density of water.

Claims

1. A triaxial specimen preparation apparatus based on an underwater deposition method, characterized by, It comprises a saturator (1), a support (2), a water containing base (3), a vacuum pump (5) and a three membrane mechanism (6). The saturator (1) is a container for saturating underwater sand with vacuum, 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), and a pipeline is arranged on the saturator top cover (102) and equipped with the first valve (104) to control the on-off state. The pipeline of the saturator top cover (102) is connected with the 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 conical body. A pipeline is arranged at the bottom of the conical body, and the second valve (105) is installed to control the on-off state. The three membrane mechanism (6) is a mold of three-axis type. The water containing base (3) is installed on the top of the three membrane mechanism (6) to increase the maximum height of the water level in the three membrane mechanism (6). The saturator is fixed above the water containing base (3) through the support (2). The pipeline at the bottom of the saturator cup (101) is connected with a rubber pipe (401), which extends into the water containing base (3) and the three membrane mechanism (6). The water containing base (3) comprises a water containing base side wall (301), a water containing base base (303) and a first scale (305). The side surface of the water containing base side wall (301) is provided with the first scale (305) for observing the underwater deposition height of the sand. The bottom of the water containing base side wall (301) is fixed with the water containing base base (303). The center of the base is provided with a circular opening, 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 membrane (601) and can be clamped on the transparent three membrane, so that the water containing base (3) is fixed on the three membrane mechanism (6).

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

3. A triaxial specimen preparation apparatus based on underwater deposition method as claimed in claim 1, wherein: The saturator cup (101) is made of stainless steel or aluminum alloy. The saturator top cover (102) is made of transparent tempered glass to observe the gas precipitation condition of the sand and water mixture in the saturator (1).

4. The triaxial specimen preparation apparatus based on underwater deposition method according to claim 1, wherein: 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 on the straight rod (202), and the other end is an O-shaped iron ring with an inner diameter smaller than the maximum outer diameter of the saturator (1) to support the saturator (1); the large iron ring (205) is arranged above the small iron ring, one end of the large iron ring (205) is fixed on the straight rod (202), and the other end is an O-shaped iron ring with an inner diameter equivalent to the maximum outer diameter of the saturator (1) to constrain the horizontal degree of freedom; one end of the C-shaped clamp (203) is fixed on the straight rod (202), and the other end is clamped to other fixed objects to increase the stability of the support (2).

5. The triaxial specimen preparation apparatus based on underwater deposition method as claimed in claim 1, wherein: The water containing base (3) further comprises a third valve (304); the sidewall (301) of the water containing base is a thin-walled cylinder made of transparent material, and the upper edge is provided with an anti-overflow hole (302); the base (303) of the water containing base is provided with a drainage pipeline and is provided with the third valve (304) to control the opening and closing of the pipeline.

6. A triaxial specimen preparation apparatus based on underwater deposition method as claimed in claim 1, wherein: The three-valve mechanism (6) comprises a transparent three-valve (601) and a ring clamp (602); the transparent three-valve (601) is made of transparent material, and the outer wall is provided with a second scale (603) for observing the underwater deposition height of the sandy soil; in use, the three-valve mechanism (6) is arranged on the three-axis base (7).

7. A method for preparing a triaxial specimen based on an underwater deposition method, characterized by: The three-axis sample preparation device is used for sample preparation, and the specific steps include the following: Step one: install the three-valve mechanism (6) Install the sheepskin membrane on the three-axis base (7) and fix it with an O-shaped ring, then place the water permeable stone and filter paper on the three-axis base in turn, install the transparent three-valve (601) on the three-axis base (7) and fix it with the ring clamp (602), and turn the part of the sheepskin membrane outside the transparent three-valve (601) outward on the upper part of the outer wall of the transparent three-valve (601); Step two: install the water containing base (3) Install the water containing base (3) on the three-valve mechanism (6); since the diameter of the circular opening of the base (303) of the water containing base is equivalent to the outer diameter of the transparent three-valve (601), the sheepskin membrane turned outward on the upper part of the outer wall of the transparent three-valve (601) is filled between the circular opening at the bottom of the water containing base (3) and the transparent three-valve (601), thereby forming a water-tight sealing structure; the outward turning height of the sheepskin membrane is about 1 cm, and the shielding of the scale on the three-valve is small; Step three: install the saturator (1) Fix the support (2) on the test bench, install the rubber pipe (401) at the bottom of the saturator (1), and then fix the saturator (1) on the support (2); adjust the position of the saturator (1) to align the axis of the saturator (1) with the axis of the transparent three-valve (601); Step four: prepare saturated sandy soil Close the second valve(105) of saturator, weigh the sand with mass m1 and put it into saturator(1), then inject distilled water to immerse the sand completely, install the top cover(102) of saturator, connect the top cover(102) of saturator and vacuum pump(5) through pressure tube(402), open the first valve(104) and vacuum pump(5) in turn, maintain the vacuum state in saturator(1) for at least 2 hours to ensure the saturation of sand under water; Step five: underwater deposition of triaxial sample Close the vacuum pump(5) and remove the pressure tube(402), slowly open the first valve(104) to restore the pressure in saturator(1) to atmospheric pressure, then inject water into the three-petal mechanism(6) and water container(3); observe the first scale(305) and the second scale(603), slowly open the second valve(105) to make the sand fall slowly, control the distance between the bottom of rubber tube(401) and the deposition surface of sand by controlling the up and down movement of saturator, so that the distance between the bottom of rubber tube(401) and the deposition surface of sand remains unchanged during deposition, thereby ensuring the uniformity of the density of sand sample; when the sample in transparent three-petal membrane(601) reaches the specified height, close the second valve(105); Step six: remove saturator(1) and water container(3) Remove the saturator(1) to prevent the sand and liquid in the saturator(1) from spilling out, slowly open the third valve(304) of water container(3) to remove the solution in the water container(3), and remove the water container(3) after draining; Step seven: install top cap and remove three-petal mechanism(6) Install the top cap and remove the three-petal mechanism(6) in accordance with the conventional sand triaxial sample preparation process, mainly including: install filter paper, water-permeable stone and triaxial top cap on the top end of the sample in turn, turn the sheepskin film on the upper part of the transparent three-petal membrane(601) to the triaxial top cap and fix it through the "O" ring, and finally remove the collar and transparent three-petal membrane in order to complete the sample preparation.

8. The triaxial specimen preparation method based on the underwater deposition method according to claim 7, characterized in that: The density of the obtained sample is as follows: The sand left in the saturator (1) is dried and weighed, and the mass is recorded as m2. The dry density p of the sample is then calculated d The porosity e is calculated according to the following formula: where V is the total volume of the sample, G s is the specific gravity of the soil particles, p w is the density of water.

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