Vacuum falling rain type high-saturation clay rapid sample preparation device and vacuum falling rain type high-saturation clay rapid sample preparation method

Abstract

The invention belongs to the field of marine geotechnical engineering research, and provides a vacuum falling rain type high-saturation clay rapid sample preparation device and method. The sample preparation device comprises a slurry degassing device and a device for providing a high hydraulic gradient, and a test method for improving the sample preparation saturation and the sample preparation speed is designed in combination with the sample preparation device. The honeycomb degassing box in the slurry degassing device is connected with the top cover of the test box, so that the slurry can be effectively cut, gas entrained in the slurry can be released, the gas is dissipated, and the slurry saturation is remarkably improved. The device for providing the high hydraulic gradient is connected with the water tank and the test box through the air compressor, stable high pressure is provided and transmitted into the test box through water, the hydraulic gradient in slurry is improved, the consolidation process of clay samples is accelerated, and the sample preparation efficiency is improved. The sample preparation device is simple in structure, the operation method is convenient and fast, the high-saturation soil sample can be obtained only through one-time degassing treatment, and the sample preparation device is suitable for indoor model tests and other high-requirement sample preparation scenes.

Description

Technical Field

[0001] The present invention belongs to the field of marine geotechnical engineering and relates to a vacuum rain-type high-saturation clay rapid sampling device and method. Background Art

[0002] In the design process of marine engineering foundations, soil parameter analysis of marine clay and interaction tests between it and structures are key research contents. In order to reduce research costs, indoor tests have become the main research method. At present, the commonly used laboratory methods for preparing marine homogeneous clay or normally consolidated clay are usually: first stir the mud, then transfer it to a test chamber for consolidation, and finally prepare the target soil sample for testing. However, during the mud stirring and transfer process, air is easily introduced and retained in the mud, resulting in a decrease in the saturation of the final soil sample, making the saturation of the soil sample prepared indoors significantly lower than the natural state of the actual marine clay. At the same time, the existing sample preparation method has a long cycle during the consolidation process, often requiring weeks or months, and has a high time cost. The problem of low saturation can easily lead to deviations in test data, and the high time cost poses a great challenge to large-scale, repetitive tests. Summary of the Invention

[0003] This invention aims to increase the saturation of clay prepared indoors and reduce sample preparation time and costs. To this end, it proposes a vacuum-drip-type device for increasing mud saturation and a rapid sample preparation method utilizing this device. This device and method are low-cost, simple, and easy to use. They are suitable for simulating the preparation of highly saturated marine clay in current laboratories and conducting related experimental research, providing technical support for accurately reconstructing the mechanical properties of marine clay and obtaining reliable indoor experimental data.

[0004] The technical solution of the present invention:

[0005] A vacuum rain-type high-saturation clay rapid sampling device, including a mud degassing device and a high hydraulic gradient providing device;

[0006] The mud degassing device includes: a cover plate, the shape of the cover plate is consistent with the shape of the test box to facilitate sealing the test box, and a through hole is opened on the cover plate to facilitate the installation of valves and pipes; a vacuum gauge, the vacuum gauge is above the cover plate and outside the test box, and the vacuum gauge is connected to the cover plate and connected to the test box through the vacuum gauge connecting valve installed on the cover plate to measure the vacuum state inside the test box; a mud funnel, the mud funnel is used to store mud, and is connected to the cover plate through the mud funnel valve and directly connected to the honeycomb degassing box The honeycomb degassing box is composed of a short honeycomb degassing cylinder with a large diameter and small holes on the side, and a plurality of long honeycomb degassing cylinders with small diameters and small holes on the side. The top of the short honeycomb degassing cylinder is connected to the mud funnel, and there are no small holes on its upper and lower surfaces, only holes on the side; the top of the long honeycomb degassing cylinder is connected to the short honeycomb degassing cylinder, and there are no small holes on the lower surface of the long honeycomb degassing cylinder, only holes on the side; the cover is also provided with a top cover water inlet valve, which is connected to the water pipe to supply water to the test box;

[0007] The cover plate and the test chamber are sealed together to form the outer shell of the mud degassing device. Rubber pads are placed at the joints to prevent leakage of gas, water, and mud. During operation, the mud degassing device is evacuated internally. The vacuum level is indicated by a vacuum gauge connected to the cover plate and connected to the interior of the test chamber. When the internal vacuum level is insufficient and evacuation is required, the vacuum gauge reading serves as the starting point for evacuation. The mud funnel is used to hold mud. Due to the pressure differential between the inside and outside of the test chamber, the mud is pressed into the mud funnel valve below the mud funnel and then into the honeycomb degassing box. As the mud increases, the short and long honeycomb degassing cylinders of the honeycomb degassing box are filled with mud. During this process, mud flows out through the mesh holes on the sides of the cylinders. Gas entrained in the mud is also cut and released by the mesh holes, escaping into the vacuum environment, thereby reducing the gas content. Because mud degassing is performed directly after the cover plate is attached to the test chamber, the mud drips directly into the test chamber, avoiding the traditional sample preparation process of stirring and then transferring the sample to the test chamber, further increasing the soil sample saturation.

[0008] The long honeycomb degassing cylinder and the short honeycomb degassing cylinder are connected, and the length-to-short ratio is set to 2:1; the diameter of the long honeycomb degassing cylinder is smaller than that of the short honeycomb degassing cylinder, and the long honeycomb degassing cylinder is evenly distributed below the short honeycomb degassing cylinder, and the spacing between the long honeycomb degassing cylinders is equal to twice the diameter of the long honeycomb degassing cylinder.

[0009] Because the long honeycomb degassing cylinder and the short honeycomb degassing cylinder are internally connected, the short honeycomb degassing cylinder plays a role in mud diversion, dispersing the mud into each long honeycomb degassing cylinder; the separation of mud-entrained gas is mainly completed by the side mesh; the long honeycomb degassing cylinder has a slender shape, and the mud can easily slide down the cylinder wall after precipitation, thereby avoiding mud adhesion and accumulation affecting the subsequent gas precipitation in the mud and improving the gas precipitation rate. This is also the advantage of designing a long honeycomb degassing cylinder and a short honeycomb degassing cylinder for combined use.

[0010] The side mesh diameter is only 2 mm, and the hole spacing is consistent with the hole diameter, and is evenly distributed on the side walls of the long honeycomb degassing cylinder and the short honeycomb degassing cylinder, which can effectively cut and separate the gas from the mud.

[0011] The high hydraulic gradient device includes: an air compressor, which provides a stable high pressure of at least 1 MPa for the test chamber, which is converted into a water head of more than 100 meters, far exceeding the conventional method of increasing the water head in the laboratory. It can also control the output and stop of the pressure; a water tank, which is used to hold a certain volume of water. The top cover of the water tank is equipped with a water tank water inlet valve and an air pressure regulating valve; the air pressure regulating valve can regulate the pressure transmitted to the water tank by the air compressor, and transmit the pressure to the water in the water tank after adjustment as needed; a water pipe, which is used to connect the water tank and the test chamber; and an air pipe, which is used to connect the air compressor and the water tank.

[0012] After degassing the slurry through the mud degassing device, it forms a highly saturated slurry and is collected in a test chamber for subsequent soil sample preparation. The test chamber is connected to a high hydraulic gradient device via a water pipe. Before connection, a certain amount of water must be injected into the test chamber to consolidate the slurry. The air compressor in the high hydraulic gradient device compresses air, increasing the pressure, and then transmits this pressure to the water tank through an air pipe. Because the water tank is connected to the test chamber via a water pipe, the water in the water tank is forced into the test chamber by air pressure. The test chamber contains water at the top and highly saturated slurry at the bottom. Under the pressure of the water tank, the water transfers pressure into the test chamber, increasing the water pressure inside the test chamber. Ultimately, the water pressure inside the test chamber is consistent with that of the water tank. The water pressure in the water tank can be adjusted by an air pressure regulating valve located at the top of the water tank, thereby regulating the water pressure in the test chamber and thus controlling the hydraulic gradient within the slurry. This technical solution provides stable high pressure through an air compressor and effectively improves the hydraulic gradient inside the mud with the help of the pressure transmission effect of the water body in the water tank.

[0013] A method for rapid sample preparation of highly saturated clay comprises the following steps:

[0014] S1, mixing the test soil to a slurry state;

[0015] S2, seal the cover plate with the test chamber, and then evacuate the air from the test chamber to achieve vacuum;

[0016] S3, pour the stirred slurry into the slurry funnel on the cover plate, and slowly press it into the honeycomb degassing box under the action of atmospheric pressure and degas;

[0017] S4. After the mud is completely degassed, close all valves, open the water inlet valve, fill the test box with water until it is full, and then connect it to the water tank through the water inlet and water pipe;

[0018] S5: Turn on the air compressor to increase the internal air pressure, and use the pressure to press the water in the water tank into the test chamber. At this time, the bottom of the test chamber remains drained. As the pressure increases, the hydraulic gradient gradually increases, and the drainage gradually increases. The soil sample can be consolidated in a relatively short time, and finally a highly saturated soil sample for the test is obtained.

[0019] S6. After consolidation is completed, turn off the air compressor, close the air compressor gas output, release the residual pressure through the water tank, and then remove the test box top cover to carry out relevant indoor tests.

[0020] Beneficial effects of the present invention:

[0021] 1. The present invention uses the circular holes on the honeycomb degassing box to completely cut and separate the stirred mud, so that the gas entrained in the mud is fully exposed and dissipated in a vacuum environment, thereby significantly reducing the gas content in the soil sample and increasing the saturation, providing technical support for reducing indoor test errors and improving sample preparation repeatability.

[0022] 2. By directly connecting the top cover equipped with a honeycomb degassing box to the test chamber, the degassed high-saturation mud falls directly into the test chamber without the need for a transfer process, effectively reducing the possibility of air mixing and further improving the saturation of the soil sample.

[0023] 3. Use a high-pressure air compressor to transfer the air pressure to the water tank, and then the water tank transfers the water pressure to the test box to quickly increase the water pressure in the test box, thereby increasing the hydraulic gradient inside the mud, shortening the strength formation time of the soil sample, speeding up the sample preparation process, and saving time and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the top cover and test chamber combined

[0025] Figure 2 Schematic diagram of the honeycomb degassing box, where (a) is a top-down view, (b) is a bottom-up view, and (c) is a schematic diagram of the internal structure after axisymmetric cutting.

[0026] Figure 3 Schematic diagram of soil sample consolidation process

[0027] In the figure: 1 vacuum pump connecting valve; 2 vacuum gauge connecting valve; 3 mud funnel valve; 4 top cover water inlet valve; 5 vacuum gauge; 6 mud funnel; 7 cover plate; 8 short honeycomb degassing cylinder; 9 long honeycomb degassing cylinder; 10 air compressor; 11 air compressor exhaust valve; 12 air pipe; 13 water tank water inlet valve; 14 water tank; 15 air pressure regulating valve; 16 water pipe; 17 test chamber; 18 test chamber drain valve. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0029] Example

[0030] This embodiment is an indoor test process for quickly preparing a highly saturated clay device. The experimental device provided in this embodiment is simple and can improve the sample preparation speed and saturation. The prepared soil samples can serve indoor experimental research in related marine geotechnical fields.

[0031] See Figure 1 、 Figure 2 In this embodiment, clay saturation is increased using short honeycomb degassing cartridges 8 and long honeycomb degassing cartridges 9. The honeycomb degassing cartridges are connected to a cover plate 7 and communicate with a mud funnel 6 on the cover plate 7. The mud funnel 6 and the cover plate 7 are connected via a mud funnel valve 3. The vacuum gauge communication valve 2, mud funnel valve 3, and top cover water inlet valve 4 on the cover plate 7 all communicate with the interior of the test chamber 17. The cover plate 7 can be modified to suit the shape of the test chamber 17; this embodiment uses a circular test chamber as an example.

[0032] See Figure 3 , a schematic diagram of the overall apparatus for increasing sample preparation speed according to this embodiment, comprises an air compressor 10, a water tank 14, and a test chamber 17. The air compressor 10 is the primary source of pressure, while the water tank 14 supplies water and transmits pressure to the test chamber 17. The three devices are connected via an air pipe 12 and a water pipe 16, which must be airtight. An air pressure regulating valve 15 regulates the pressure from the air compressor 10 transmitted to the water tank 14, ensuring repeatable sample preparation.

[0033] In conjunction with the accompanying drawings and technical solutions, the main steps of this embodiment are as follows:

[0034] S1, assemble the mud degassing device.

[0035] See Figure 1 and Figure 2 Design and fabricate a corresponding cover plate 7 based on the shape of the test chamber 17. Install the vacuum pump connection valve 1, vacuum gauge connection valve 2, mud funnel valve 3, top cover water inlet valve 4, vacuum gauge 5, and mud funnel 6 onto the cover plate 7. During installation, ensure that all joints are properly sealed to prevent air leakage or water seepage. Then, place the cover plate 7 on the test chamber 17 and seal it.

[0036] S2, vacuum the test chamber.

[0037] See Figures 1 to 3 , open the vacuum pump connecting valve 1 and the vacuum gauge connecting valve 2, close the mud funnel valve 3, the top cover water inlet valve 4 and the test box drain valve 18, start the vacuum pump to evacuate the test box 17, and make the reading of the vacuum gauge 5 reach below -80kPa.

[0038] S3, the amount of mud required for the stirring test.

[0039] S4, mud degassing.

[0040] Pour the stirred mud into the mud hopper 6. Open the mud hopper valve 3 appropriately, and use the pressure differential between the inside and outside of the test chamber 17 to force the mud into the short honeycomb degassing cylinder 8. Under its own weight, the mud gradually fills the short honeycomb degassing cylinder 8 and the long honeycomb degassing cylinder 9. During the mud filling process, the mud flows out through the small side holes, while being cut in the flow path between the holes. This process exposes the trapped gas to the low-pressure environment inside the test chamber 17 and allows it to escape, effectively increasing the mud saturation. It is important to note that if the mud in the mud hopper 6 is low, it should be replenished promptly to prevent gas from being drawn into the short honeycomb degassing cylinder 8.

[0041] S5, restore the test chamber air pressure.

[0042] After the mud degassing is completed, the mud funnel valve 3 is closed, and the vacuum pump connecting valve 1 and the vacuum gauge connecting valve 2 are opened to allow air to enter the test box 17 to restore the air pressure to the normal pressure level.

[0043] S6, fill the test chamber with water until it is full.

[0044] After the air pressure returns to normal, while keeping the other valves unchanged, open the mud funnel valve 3 and inject water into the mud funnel 6 until the test chamber 17 is filled with water. At this time, the open vacuum pump connecting valve 1, vacuum gauge connecting valve 2, and mud funnel valve 3 facilitate the smooth discharge of air during the water inlet process.

[0045] S7, connecting the test box 17 to the device for increasing the hydraulic gradient.

[0046] Close the vacuum pump connecting valve 1, the vacuum gauge connecting valve 2 and the mud funnel valve 3, connect the test box 17 to the top cover water inlet valve 4 through the water pipe 16, and at the same time connect the exhaust valve 11 of the air compressor 10 to the water tank 14 and the air pressure regulating valve 15 through the air pipe 12 to form a passage system between the test box 17-water tank 14-air compressor 10.

[0047] S8, increase the hydraulic gradient for consolidation.

[0048] Open the water tank inlet valve 13 to inject a certain amount of water into the water tank 14. Close the valve after the water filling is complete. Start the air compressor 10 to accumulate pressure. Once the pressure reaches the set value, open the exhaust valve 11 and apply air pressure to the water tank 14 through the air pressure regulating valve 15, thereby applying pressure to the water. Open the water inlet valve 4 of the cover plate 7 to pressurize the water in the water tank 14 into the test box 17. At the same time, open the test box drain valve 18 to promote the consolidation of the mud in the test box 17. Because the air compressor 10 can provide high air pressure, the clay consolidates faster, ultimately obtaining soil samples with a higher strength range.

[0049] The above embodiments are merely preferred technical solutions of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A vacuum rain-type high-saturation clay rapid sample preparation device, characterized in that: The vacuum rain-type high-saturation clay rapid sampling device includes a mud degassing device and a high hydraulic gradient providing device; The mud degassing device includes: a cover plate, the shape of the cover plate is consistent with the shape of the test box to facilitate sealing the test box, and the cover plate is provided with through holes to facilitate the installation of valves and pipes; a vacuum gauge, the vacuum gauge is located above the cover plate and outside the test box, and the vacuum gauge is connected to the cover plate and the test box through a vacuum gauge connecting valve installed on the cover plate to measure the vacuum state inside the test box; a mud funnel, the mud funnel is used to store mud, and is connected to the cover plate through a mud funnel valve and directly connected to the honeycomb degassing box; a top cover water inlet valve is also provided on the cover plate, and the top cover water inlet valve is connected to a water pipe to supply water to the test box; The device for providing high hydraulic gradient includes: an air compressor, which provides stable high pressure for the test chamber and can also control the output and stop of pressure; a water tank, which is used to hold a certain volume of water, and the top cover of the water tank is attached with a water tank water inlet valve and an air pressure regulating valve; the air pressure regulating valve can regulate the pressure transmitted to the water tank by the air compressor, and transmit the pressure to the water in the water tank after adjustment as needed; a water pipe, which is used to connect the water tank and the test chamber; and an air pipe, which is used to connect the air compressor and the water tank.

2. The vacuum rain-type high-saturation clay rapid sample preparation device according to claim 1, characterized in that: The honeycomb degassing box is composed of a short honeycomb degassing cylinder with a large diameter and small holes on the side and a plurality of long honeycomb degassing cylinders with small diameters and small holes on the side. The top of the short honeycomb degassing cylinder is connected to the mud funnel. There are no small holes on the upper and lower surfaces of the short honeycomb degassing cylinder, and only holes are opened on the side. The upper part of the long honeycomb degassing cylinder is connected to the short honeycomb degassing cylinder. The lower surface of the long honeycomb degassing cylinder has no small holes, and only holes are opened on the side.

3. The vacuum rain-type high-saturation clay rapid sample preparation device according to claim 2, characterized in that: The long honeycomb degassing cylinder and the short honeycomb degassing cylinder are connected, and the length-to-short ratio is set to 2:1; the diameter of the long honeycomb degassing cylinder is smaller than that of the short honeycomb degassing cylinder, and the long honeycomb degassing cylinder is evenly distributed below the short honeycomb degassing cylinder, and the spacing between the long honeycomb degassing cylinders is equal to twice the diameter of the long honeycomb degassing cylinder.

4. The vacuum rain-type high-saturation clay rapid sample preparation device according to claim 2, characterized in that: The side mesh holes have a diameter of 2 mm, and the hole spacing is consistent with the hole diameter, and are evenly distributed on the side walls of the long honeycomb degassing cylinder and the short honeycomb degassing cylinder.

5. A rapid sample preparation method for highly saturated clay, characterized in that: The steps include: S1, mixing the test soil to a slurry state; S2, seal the cover plate with the test chamber, and then evacuate the air from the test chamber to achieve vacuum; S3, pour the stirred slurry into the slurry funnel on the cover plate, and slowly press it into the honeycomb degassing box under the action of atmospheric pressure and degas; S4. After the mud is completely degassed, close all valves, open the water inlet valve, fill the test box with water until it is full, and then connect it to the water tank through the water inlet and water pipe; S5: Turn on the air compressor to increase the internal air pressure, and use the pressure to press the water in the water tank into the test chamber. At this time, the bottom of the test chamber remains drained. As the pressure increases, the hydraulic gradient gradually increases, and the drainage gradually increases. The soil sample completes consolidation in a relatively short time, and finally a highly saturated soil sample for the test is obtained. S6. After consolidation is completed, turn off the air compressor, close the air compressor gas output, release the residual pressure through the water tank, and then remove the top cover of the test chamber to carry out relevant indoor tests.

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