A large-size saturated homogeneous sand sample preparation device and method

Abstract

This invention discloses a device and method for preparing large-size saturated homogeneous sand samples, including a frame assembly, a sand sample preparation assembly, a model box, and a sand sample saturation assembly. The frame assembly includes a base, a vertical support, a horizontal support, and a connecting support. The horizontal support is driven to move up and down by a lifting drive device. The sand sample preparation assembly includes a rotation drive device and a sand drop box, which is driven to rotate by the rotation drive device. A first exhaust valve is provided on the first sealing cover at the top of the model box, and a geotextile is covered at the bottom water inlet and connected to a water inlet valve. The sand sample saturation assembly includes a vacuum pump and a sealed container. A second exhaust valve is provided on the second sealing cover at the top of the sealed container, and the second exhaust valve is connected to the vacuum pump. The vacuum pump is also connected to the first exhaust valve. A drain valve is provided at the bottom drain outlet of the sealed container, and the drain valve is connected to the water inlet valve. This invention can prepare homogeneous saturated sand samples suitable for large-size model tests and meeting different density requirements.

Description

Technical Field

[0001] This invention relates to the field of geotechnical testing technology, and in particular to an apparatus and method for preparing large-size saturated homogeneous sand samples. Background Technology

[0002] In geotechnical engineering, sand is widely used in indoor model tests due to its advantages such as stable properties, high reusability, and controllable physical properties like gradation. However, the density and homogeneity of sand samples directly affect the reliability of test results. Therefore, it is necessary to develop better preparation devices and methods to prepare sand samples with good density and homogeneity to meet test requirements. Currently, the main methods for preparing sand samples for indoor geotechnical tests include vibration, compaction, tamping, and sand rain methods. Among these, the sand rain method can theoretically prepare homogeneous sand samples with horizontal deposition. However, due to limitations in the sample preparation device, samples prepared using the sand rain method still have many drawbacks: for example, when using a handheld funnel to sprinkle sand, the throwing height and speed cannot be effectively controlled; when using a fixed funnel for sand dropping, although the dropping height can be controlled, the size and position of the sand outlet are difficult to adjust, and the sand surface directly below the outlet is significantly higher than the surrounding area. This results in uneven surfaces on the sand sample. When using a rotating funnel device for sand dropping, although the dropping speed and height can be controlled, there is only one outlet, which still causes unevenness on the surface of the sand sample. In addition, most sand rain method sample preparation devices are only suitable for preparing small-sized samples. For large-sized samples, it is necessary to move the sand dropping device multiple times and add sand to the device multiple times during the sample preparation process. This is complicated and easily leads to uneven sand distribution. The prepared sand sample has poor density and uniformity, low repeatability, and is difficult to meet the test requirements.

[0003] In the field of marine geotechnical engineering, saturated sand is widely used in indoor model tests. It is necessary to ensure the good density and uniformity of the sand sample and to improve the saturation of the sand. At present, there are two main methods for preparing saturated sand samples: (1) using the underwater sand rain method. In this method, sufficient saturated liquid is added to the model box first, and then sand particles are thrown into the model box. During the sample preparation process, due to the different deposition rates of each sand particle in the liquid, severe segregation will occur, resulting in poor sample uniformity; (2) preparing dry sand samples and then vacuum saturating them. In this method, the sample needs to be transferred to the saturation device during the sample preparation process, which can easily cause disturbance to the sand sample, thereby affecting the density and uniformity of the sand sample. In addition, during the back pressure saturation process, the sand sample is easily disturbed by hydraulic action, causing structural damage to the sand sample and affecting the reliability of the test results. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for preparing large-size saturated homogeneous sand samples, so as to solve the problems existing in the prior art and to prepare homogeneous saturated sand samples that are suitable for large-size model tests and meet different density requirements.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides a large-size saturated homogeneous sand sample preparation device, including a frame assembly, a sand sample preparation assembly, a model box, and a sand sample saturation assembly;

[0007] The frame assembly includes a base, a vertical support, a horizontal support, and a connecting support. The lower end of the vertical support is fixed to the base. The horizontal support is slidably disposed on the vertical support and is driven by a lifting drive device to slide up and down along the vertical support. The connecting support is fixedly connected to the horizontal support.

[0008] The sand sample preparation assembly includes a rotary drive device and a sand drop box. The sand drop box is connected to the bottom of the connecting bracket and is driven to rotate by the rotary drive device. The bottom of the sand drop box is provided with a sand drop plate, and the sand drop plate is evenly provided with a plurality of sand drop holes. The bottom of the sand drop box is provided with a switch baffle that can be opened and closed to control the sand drop.

[0009] When the model box is placed below the sand drop box, the sand drop box is driven to rotate by the rotation drive device, and the sand in the sand drop box can fall evenly into the model box. The top of the model box is provided with a removable first sealing cover, and the first sealing cover is provided with a first exhaust valve. The bottom of the model box is provided with a water inlet, and the water inlet is covered with geotextile and connected to a water inlet valve.

[0010] The sand sample saturation assembly includes a vacuum pump and a sealed container. The sealed container is used to hold distilled water. A second vent valve is provided on the second sealing cap at the top of the sealed container. The second vent valve is connected to the vacuum pump through a pipeline. The vacuum pump is also connected to the first vent valve through a pipeline. A drain outlet is provided at the bottom of the sealed container. The drain outlet is provided with a drain valve. The drain valve is connected to the water inlet valve through a pipeline.

[0011] Preferably, the lifting drive device includes a reel, a suspension line, and a fixed pulley. A vertical guide rail is provided on one side of the vertical support, and the horizontal support is slidably mounted on the vertical guide rail via a pulley. The reel is provided on the other side of the vertical support, and the fixed pulley is provided at the top of the vertical support. One end of the suspension line is wound around the reel, and the other end passes over the fixed pulley and is connected to the horizontal support.

[0012] Preferably, the vertical support has a graduated scale on its front side.

[0013] Preferably, the first sealing cover is provided with a first pressure gauge, the second sealing cover is provided with a second pressure gauge, and the first sealing cover is a transparent sealing cover.

[0014] Preferably, a sealing ring is provided at the connection between the bottom of the first sealing cover and the model box; the first sealing cover is connected to the model box by two steel fixing clips, and the steel fixing clips are provided with fastening screws for fastening the connection between the first sealing cover and the model box.

[0015] Preferably, the sand-falling box is a square iron box that is open at both the top and bottom. The lower part of the front and back sides of the sand-falling box is provided with a plurality of small holes at equal intervals. A hard plastic rod is inserted into each pair of oppositely arranged small holes. The sand-falling plate is supported on each of the hard plastic rods and the sand-falling holes are staggered from the hard plastic rods.

[0016] Preferably, the model box is a cylindrical steel barrel, and multiple steel ribs are uniformly welded to the outer wall of the model box along the circumference; each of the bottom two sides of the model box is provided with a water inlet, and each water inlet is covered with geotextile and connected to a water inlet valve.

[0017] This invention also provides a method for preparing large-size saturated homogeneous sand samples, using the aforementioned apparatus for preparing large-size saturated homogeneous sand samples, and comprising the following steps:

[0018] S1: Select the sand dropping plate with corresponding aperture holes according to the particle size of the sand sample. Adjust the height of the sand dropping box according to the specific sand gradation through the lifting drive device, thereby adjusting the sand dropping height. Adjust the rotation speed of the sand dropping box by adjusting the rotation speed of the rotation drive device, thereby adjusting the sand dropping speed. Perform a relative compaction test on the scattered sand to determine the corresponding sand dropping height and sand dropping speed for sand samples under different compaction conditions. Select an appropriate sand dropping height and sand dropping speed according to the sand test sample preparation requirements.

[0019] S2: After closing the water inlet valve and determining the sand drop height and speed, fill the sand drop box with sand, open the switch baffle, and turn on the rotary drive device. The sand drop box starts rotating at the set speed, and the sand falls evenly into the model box through the sand drop hole to prepare a sand sample. During the sand sample preparation process, the height of the sand drop box is adjusted at any time using the lifting drive device to keep the sand drop distance constant. The sand drop distance is the distance between the sand drop plate and the sand surface. If the target density requirement of the sand sample changes with depth, the sand drop height and the sand drop distance are adjusted at any time during the sample preparation process to ensure that the sand sample reaches the target density.

[0020] S3: After the sand sample preparation is completed, the first sealing cap is sealed and fixed on the model box, and the vacuum pump and the first exhaust valve are opened to expel the air in the model box;

[0021] S4: Close the drain valve, fill the sealed container with distilled water, open the vacuum pump and the second exhaust valve to expel the air from the sealed container, and prepare gas-free distilled water;

[0022] S5: Connect the drain valve to the inlet valve through a pipeline, open the inlet valve and the drain valve to allow the airless distilled water in the sealed bucket to enter the model box until the sand sample is completely below the water surface, the saturated sand sample preparation is completed, and close the drain valve and the inlet valve.

[0023] The present invention achieves the following technical effects compared to the prior art:

[0024] 1. The sand-falling device of the present invention can be adapted to the size of the model box, and can prepare large-size homogeneous samples. It is especially suitable for the preparation of large-size saturated homogeneous sand samples in arm centrifuge tests. Furthermore, the sand-falling device does not need to be moved during the sample preparation process, and sand can be added to the sand-falling box at any time. The sample can be prepared in one go.

[0025] 2. The present invention can prepare sand samples with different densities according to specific needs, and the samples have good uniformity and repeatability. In addition, the present invention can also prepare homogeneous sand samples with density varying with depth by adjusting the sand falling speed and height at any time during the sample preparation process.

[0026] 3. The present invention allows for the selection of a sand drop plate with an appropriate drop hole diameter based on the particle size of the sand particles, so that the sand particles fall at a uniform speed during the sample preparation process, thereby preparing a sand sample with good density and uniformity. Furthermore, the sand drop plate can be disassembled and reused, making the operation simple.

[0027] 4. The model box used in this invention can be directly used to prepare saturated sand samples without transferring the prepared sand samples to other saturation devices, thus reducing disturbance to the sand samples during transportation and ensuring the uniformity of the sand samples. Furthermore, the lower water inlet of the model box used in this invention is wrapped with geotextile. Geotextile has a denser texture and provides better control over the water flow rate than commonly used mesh, allowing for reasonable control of the water inlet speed and reducing disturbance to the sand samples caused by hydraulic flow.

[0028] 5. This invention prepares degassing distilled water for saturating sand samples, further improving the saturation degree of the sand samples. Furthermore, this invention uses a single vacuum pump to complete both the preparation of degassing distilled water and the preparation of saturated sand samples, demonstrating efficient use of equipment and a simple setup.

[0029] 6. The model box used in this invention can be directly placed on an arm centrifuge after the large-size sand sample is prepared to carry out geotechnical tests under hypergravity environment; and two water inlets are reserved at the bottom of the model box in advance, and water inlet valves are provided for control. Later, it can be directly connected to the model box through a connecting hose to achieve double-sided drainage and meet the requirements of arm centrifuge test. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure for preparing homogeneous sand samples using a frame assembly, a sand sample preparation assembly, and a model box in this invention.

[0032] Figure 2 This is a schematic diagram of the structure for preparing saturated sand samples using a model box and a sand sample saturation assembly in this invention;

[0033] Figure 3 This is a front view structural diagram of the sand drop box in this invention;

[0034] Figure 4 This is a side view of the structure of the sand box bottom switch baffle when it is open in this invention;

[0035] Figure 5 This is a schematic diagram of the sand-falling plate in this invention.

[0036] In the diagram: 1-Base, 2-Vertical support, 3-Horizontal support, 4-Roller, 5-Suspension line, 6-Fixed pulley, 7-Rotation drive device, 8-Connecting bracket, 9-Sand box, 10-Sand plate, 11-Hard plastic rod, 12-Steel rib, 13-Model box, 14-Geotextile, 15-Water inlet valve, 16-First water inlet hose, 17-Sand drop hole, 18-Second water inlet hose, 19-Sealing ring, 20-Steel fixing clamp, 21-First sealing cover, 22-First pressure gauge, 23-First exhaust valve, 24-First exhaust hose, 25-Second pressure gauge, 26-Second sealing cover, 27-Second exhaust valve, 28-Second exhaust hose, 29-Vacuum pump, 30-Sealed bucket, 31-Drain valve, 32-Switch baffle. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The purpose of this invention is to provide a device and method for preparing large-size saturated homogeneous sand samples to solve the problems existing in the prior art, and to prepare homogeneous saturated sand samples that are suitable for large-size model tests and meet different density requirements.

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] like Figures 1-5 As shown, this embodiment provides a large-size saturated homogeneous sand sample preparation device, including a frame assembly, a sand sample preparation assembly, a model box 13, and a sand sample saturation assembly;

[0041] The frame assembly includes a base 1, a vertical support 2, a horizontal support 3, and a connecting support 8. The lower end of the vertical support 2 is fixed to the base 1. The horizontal support 3 is slidably mounted on the vertical support 2 and is driven by a lifting drive device to slide up and down along the vertical support 2. The connecting support 8 is fixedly connected to the horizontal support 3.

[0042] The sand sample preparation assembly includes a rotary drive device 7 and a sand drop box 9. The sand drop box 9 is connected to the bottom of the connecting bracket 8 and is driven to rotate by the rotary drive device 7. The bottom of the sand drop box 9 is provided with a sand drop plate 10. Multiple sand drop holes 17 are evenly provided on the sand drop plate 10. The bottom of the sand drop box 9 is provided with a switch baffle 32 that can be opened and closed to control the sand drop.

[0043] When the model box 13 is placed below the sand box 9, the sand box 9 is driven to rotate by the rotation drive device 7, and the sand in the sand box 9 can fall evenly into the model box 13. The top of the model box 13 is provided with a removable first sealing cover 21, and the first sealing cover 21 is provided with a first exhaust valve 23. The bottom of the model box 13 is provided with a water inlet, and the water inlet is covered with geotextile 14 and connected to a water inlet valve 15.

[0044] The sand sample saturation assembly includes a vacuum pump 29 and a sealed container 30. The sealed container 30 is used to hold distilled water. A second exhaust valve 27 is provided on the second sealing cover 26 at the top of the sealed container 30. The second exhaust valve 27 is connected to the vacuum pump 29 through a pipeline. The vacuum pump 29 is also connected to the first exhaust valve 23 through a pipeline. A drain outlet is provided at the bottom of the sealed container 30. The drain outlet is provided with a drain valve 31. The drain valve 31 is connected to the water inlet valve 15 through a pipeline.

[0045] In use, a sand-falling plate 10 with a suitable aperture 17 can be selected according to the particle size of the sand particles, ensuring that the sand particles fall uniformly and at a constant speed during sample preparation, thus producing a sand sample with good density and uniformity. The falling height and speed can be flexibly adjusted according to the requirements of the sand sample preparation, thereby producing a sand sample with density and uniformity that meets the test requirements. The model box 13 used in this device can be directly used to prepare saturated sand samples without transferring the prepared sand samples to other saturation devices, reducing disturbance to the sand samples during transportation and ensuring the uniformity of the sand samples. The lower water inlet of the model box 13 is wrapped with geotextile 14. The geotextile is relatively dense and has a better control effect on the water flow rate than commonly used mesh, allowing for reasonable control of the water inlet speed, reducing disturbance to the sand samples by hydraulic flow, and ensuring the uniformity of the sand samples. This device uses a vacuum pump to complete the preparation of airless distilled water and saturated sand samples, making reasonable use of the instrument and simplifying the device.

[0046] In this embodiment, the rotary drive device 7 can be a rotary motor, which drives the sand box 9 to rotate and controls the rotation speed of the sand box 9.

[0047] In this embodiment, the lifting drive device includes a reel 4, a suspension line 5, and a fixed pulley 6. A vertical guide rail is provided on one side of the vertical support 2, and the horizontal support 3 is slidably mounted on the vertical guide rail via pulleys. A reel 4 is provided on the other side of the vertical support 2, and a fixed pulley 6 is provided at the top of the vertical support 2. One end of the suspension line 5 is wound around the reel 4, and the other end passes over the fixed pulley 6 and connects to the horizontal support 3. The lifting and lowering of the vertical support 2 is controlled by manipulating the length of the suspension line 5 wound around the reel 4, thereby adjusting the height of the sand box 9. The structure is simple and the operation is convenient.

[0048] In this embodiment, the vertical support 2 is provided with a scale on the front, and the height of the horizontal support 3 can be precisely adjusted and controlled by the scale, thereby adjusting the sand drop height.

[0049] In this embodiment, a first pressure gauge 22 is provided on the first sealing cover 21, and a second pressure gauge 25 is provided on the second sealing cover 26. The first sealing cover 21 is a transparent sealing cover. When the air inside the model box 13 or the sealed barrel 30 is extracted by the vacuum pump 29, the reading of the pressure gauge is observed to determine whether the internal air has been completely expelled.

[0050] In this embodiment, a sealing ring 19 is provided at the connection between the bottom of the first sealing cover 21 and the model box 13 to ensure the sealing performance after the first sealing cover 21 is connected to the model box 13; the first sealing cover 21 is connected to the model box 13 by two steel fixing clips 20, and the steel fixing clips 20 are provided with fastening screws to fasten the connection between the first sealing cover 21 and the model box 13, making it easy to disassemble and assemble the first sealing cover 21.

[0051] In this embodiment, the sand drop box 9 is a square iron box that is open at both the top and bottom. Multiple small holes with equal spacing are provided on the lower part of the front and back sides of the sand drop box 9. A hard plastic rod 11 is inserted into each pair of oppositely arranged small holes. The sand drop plate 10 is supported on each hard plastic rod 11, and the sand drop holes 17 are staggered from the hard plastic rods 11, allowing the sand to fall smoothly through each sand drop hole 17. Furthermore, the sand drop plate 10 can be disassembled and reused, making operation simple. The length of the sand drop box 9 is slightly larger than the inner diameter of the model box 13, and the diameter of the sand drop holes 17 is slightly larger than the sand particle size, ensuring that the sand particles fall uniformly and at a constant speed during sample preparation, thereby producing a sand sample with good density and uniformity.

[0052] In this embodiment, the model box 13 is a cylindrical steel barrel, and multiple steel ribs 12 are uniformly welded along the circumference of the outer wall of the model box 13. Each side of the bottom of the model box 13 has a water inlet, each inlet is covered with geotextile 14 and connected to a water inlet valve 15. The two water inlet valves 15 can be connected to a first water inlet hose 16 and a second water inlet hose 18 respectively, for convenient and reasonable use according to experimental needs later. The sealed barrel 30 is a cylindrical transparent acrylic product.

[0053] A method for preparing large-size saturated homogeneous sand samples, using the aforementioned apparatus for preparing large-size saturated homogeneous sand samples, includes the following steps:

[0054] S1: Select a sand dropping plate 10 with corresponding pore size 17 according to the particle size of the sand sample. According to the specific sand gradation, adjust the height of the sand dropping box 9 by the lifting drive device, and then adjust the sand dropping height. Adjust the rotation speed of the sand dropping box 9 by the rotation drive device 7, and then adjust the sand dropping speed. Perform a relative compaction test on the scattered sand to determine the corresponding sand dropping height and sand dropping speed for sand samples under different compaction conditions. Select a suitable sand dropping height and sand dropping speed according to the sand test sample preparation requirements.

[0055] S2: After closing the water inlet valve 15 and determining the sand drop height and speed, fill the sand drop box 9 with sand, open the switch baffle 32, and turn on the switch of the rotary drive device 7. The sand drop box 9 starts to rotate at the set rotation speed, and the sand falls evenly into the model box 13 through the sand drop hole 17 to prepare a sand sample. During the preparation of the sand sample, observe the height of the sand accumulation. According to the scale on the vertical support 2, adjust the height of the sand drop box 9 at any time through the winding wheel 4 to keep the height of the sand drop plate 10 from the sand surface constant, that is, ensure that the sand drop height remains constant. If the target density requirement of the sand sample changes with the depth, adjust the sand drop height and distance at any time during the sample preparation process to make the sand sample reach the target density. During the sample preparation process, observe the amount of sand remaining in the sand drop box 9 and add sand as needed.

[0056] S3: After the sand sample preparation is completed, the first sealing cap 21 is sealed and fixed on the model box 13. The first exhaust valve 23 is connected to the first exhaust hose 24 and the vacuum pump 29. The vacuum pump 29 and the first exhaust valve 23 are opened to exhaust the air in the model box 13. The reading of the first pressure gauge 22 is observed. After the air in the model box 13 is exhausted, the first exhaust valve 23 and the vacuum pump 29 are closed, and the first exhaust hose 24 connected to the vacuum pump 29 is removed.

[0057] S4: Close the drain valve 31, fill the sealed container 30 with distilled water, connect the second exhaust valve 27 to the second exhaust hose 28 and connect it to the vacuum pump 29, open the vacuum pump 29 and the second exhaust valve 27 to expel the air in the sealed container 30, prepare degassing distilled water, observe the reading of the second pressure gauge 25 until all the air in the sealed container 30 is expelled, close the second exhaust valve 27 and the vacuum pump 29, and disconnect the second exhaust hose 28 connected to the vacuum pump 29. The prepared degassing distilled water is stored in the sealed container 30.

[0058] S5: Connect the drain valve 31 to the inlet valve 15 through the first inlet hose 16, open the inlet valve 15 and the drain valve 31, and during the back pressure process, allow the airless distilled water in the sealed container 30 to enter the model box 13 to prepare a saturated sand sample; observe the water level in the model box 13 through the transparent first sealing cover 21 until the sand sample is completely below the water surface, the preparation of the saturated sand sample is completed, and close the drain valve 31 and the inlet valve 15.

[0059] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A device for preparing large-size saturated homogeneous sand samples, characterized in that: Includes frame components, sand sample preparation components, model box, and sand sample saturation components; The frame assembly includes a base, a vertical support, a horizontal support, and a connecting support. The lower end of the vertical support is fixed to the base. The horizontal support is slidably disposed on the vertical support and is driven by a lifting drive device to slide up and down along the vertical support. The connecting support is fixedly connected to the horizontal support. The sand sample preparation assembly includes a rotary drive device and a sand drop box. The sand drop box is connected to the bottom of the connecting bracket and is driven to rotate by the rotary drive device. The bottom of the sand drop box is provided with a sand drop plate, and the sand drop plate is evenly provided with a plurality of sand drop holes. The bottom of the sand drop box is provided with a switch baffle that can be opened and closed to control the sand drop. When the model box is placed below the sand drop box, the sand drop box is driven to rotate by the rotation drive device, and the sand in the sand drop box can fall evenly into the model box. The top of the model box is provided with a removable first sealing cover, and the first sealing cover is provided with a first exhaust valve. The bottom of the model box is provided with a water inlet, and the water inlet is covered with geotextile and connected to a water inlet valve. The sand sample saturation assembly includes a vacuum pump and a sealed container. The sealed container is used to hold distilled water. A second vent valve is provided on the second sealing cap at the top of the sealed container. The second vent valve is connected to the vacuum pump through a pipeline. The vacuum pump is also connected to the first vent valve through a pipeline. A drain outlet is provided at the bottom of the sealed container. The drain outlet is provided with a drain valve. The drain valve is connected to the water inlet valve through a pipeline.

2. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: The lifting drive device includes a reel, a suspension line, and a fixed pulley. A vertical guide rail is provided on one side of the vertical support. The horizontal support is slidably mounted on the vertical guide rail via a pulley. The reel is provided on the other side of the vertical support. The fixed pulley is provided at the top of the vertical support. One end of the suspension line is wound around the reel, and the other end passes over the fixed pulley and is connected to the horizontal support.

3. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: The vertical support has a graduated scale on the front.

4. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: The first sealing cover is equipped with a first pressure gauge, and the second sealing cover is equipped with a second pressure gauge. The first sealing cover is a transparent sealing cover.

5. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: A sealing ring is provided at the connection between the bottom of the first sealing cover and the model box; the first sealing cover is connected to the model box by two steel fixing clips, and the steel fixing clips are provided with fastening screws for fastening the connection between the first sealing cover and the model box.

6. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: The sand-falling box is a square iron box that is open at both the top and bottom. The lower part of the front and back sides of the sand-falling box has multiple small holes at equal intervals. A hard plastic rod is inserted into each pair of opposite small holes. The sand-falling plate is supported on each of the hard plastic rods, and the sand-falling holes are staggered from the hard plastic rods.

7. The apparatus for preparing large-size saturated homogeneous sand samples according to claim 1, characterized in that: The model box is a cylindrical steel barrel, and multiple steel ribs are uniformly welded to the outer wall of the model box along the circumference; each of the bottom two sides of the model box is provided with a water inlet, and each water inlet is covered with geotextile and connected to a water inlet valve.

8. A method for preparing large-size saturated homogeneous sand samples, characterized in that, The preparation apparatus for large-size saturated homogeneous sand samples according to any one of claims 1 to 7 includes the following steps: S1: Select the sand dropping plate with corresponding aperture holes according to the particle size of the sand sample. Adjust the height of the sand dropping box according to the specific sand gradation through the lifting drive device, thereby adjusting the sand dropping height. Adjust the rotation speed of the sand dropping box by adjusting the rotation speed of the rotation drive device, thereby adjusting the sand dropping speed. Perform a relative compaction test on the scattered sand to determine the corresponding sand dropping height and sand dropping speed for sand samples under different compaction conditions. Select an appropriate sand dropping height and sand dropping speed according to the sand test sample preparation requirements. S2: After closing the water inlet valve and determining the sand drop height and speed, fill the sand drop box with sand, open the switch baffle, and turn on the rotary drive device. The sand drop box starts rotating at the set speed, and the sand falls evenly into the model box through the sand drop hole to prepare a sand sample. During the sand sample preparation process, the height of the sand drop box is adjusted at any time using the lifting drive device to keep the sand drop distance constant. The sand drop distance is the distance between the sand drop plate and the sand surface. If the target density requirement of the sand sample changes with depth, the sand drop height and the sand drop distance are adjusted at any time during the sample preparation process to ensure that the sand sample reaches the target density. S3: After the sand sample preparation is completed, the first sealing cap is sealed and fixed on the model box, and the vacuum pump and the first exhaust valve are opened to expel the air in the model box; S4: Close the drain valve, fill the sealed container with distilled water, open the vacuum pump and the second exhaust valve to expel the air from the sealed container, and prepare gas-free distilled water; S5: Connect the drain valve to the inlet valve through a pipeline, open the inlet valve and the drain valve to allow the airless distilled water in the sealed bucket to enter the model box until the sand sample is completely below the water surface, the saturated sand sample preparation is completed, and close the drain valve and the inlet valve.

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