A device and method for controlling a specific moisture content in undisturbed sandy soil samples

Abstract

This invention discloses a device and method for controlling a specific moisture content in undisturbed sandy soil samples. A main control system controls the pore pressure, flow rate, and expansion / contraction of the water pipe in the device. A pressure controller is connected to a water storage tank via a vent pipe and regulates the pressure within the tank. The water storage tank is connected to a water delivery system. The water delivery system's diversion adapter has multiple diversion outlets, each connected to a water injection needle via a water pipe. The injection needles extend into the soil. Water from the storage tank is diverted by the diversion adapter and guided by the injection needles before being evenly injected into the soil, achieving uniform control of the specific moisture content of the soil sample. The method includes assembling the device, injecting water into the storage tank, activating the pressure controller to control the pressure, and ensuring that the water in the storage tank flows evenly into the soil through the injection needles. This invention can be used to prepare sandy soil samples with specific moisture contents without disrupting the original anisotropy of the sandy soil sample, thus ensuring high homogeneity.

Description

Technical Field

[0001] This invention belongs to the field of rock and soil mechanics, and specifically relates to a device and method for controlling a specific water content of an undisturbed sandy soil sample. Background Technology

[0002] Unsaturated soil is a three-phase soil composed of solid, liquid, and gas phases, and it exists widely in nature. Whether in practical engineering or scientific exploration, the study of the engineering properties of unsaturated soil is crucial. This is a true extension and deepening of traditional saturated soil mechanics, and also one of the basic directions of modern soil mechanics development.

[0003] In geotechnical engineering and related experimental studies on unsaturated soil, remolded soil samples are usually used. The remolding process destroys the original in-situ particle size distribution characteristics of the soil sample and cannot reflect the most accurate physical and mechanical properties of the soil sample. This leads to certain differences in engineering properties between remolded soil samples and standard soil samples.

[0004] On the one hand, during actual transportation and storage, the moisture content of undisturbed soil samples may decrease over time. Therefore, it is necessary to restore the original moisture content without damaging the soil's structure. On the other hand, when studying the correlation between unsaturated soil and moisture content, a specific moisture content needs to be configured according to different experimental requirements to seek the variation law of relevant physical and mechanical properties with moisture content. For saturated soil, its permeability is mainly related to the void ratio; while for unsaturated soil, its permeability is mainly related to the void ratio and moisture content. During water injection, the moisture content of the soil sample changes continuously, and its permeability also changes continuously. Sandy soil samples have a dense, single-grain structure with larger pores, resulting in better permeability compared to clay, and are less prone to seepage path blockage and needle nozzle closure.

[0005] To prepare a specific moisture content for a soil sample, methods such as artificial dripping, spraying, or smearing on the soil surface may cause water to evaporate, leading to inaccurate moisture content. Furthermore, water only seeps from the surface of sandy soil samples, potentially resulting in a moisture content gradient that is more pronounced at the top than at the bottom, compromising uniformity. Indoor experiments on unsaturated soils offer a method for preparing moisture content that avoids the time-consuming and labor-intensive methods of spraying or smearing. These methods are also difficult to control in terms of water volume, prone to evaporation, and require a longer time to penetrate the soil and reach equilibrium. Summary of the Invention

[0006] In order to solve the problems existing in the background art, the purpose of the present invention is to provide a device and method for controlling a specific moisture content of undisturbed sandy soil samples.

[0007] The technical solution adopted in this invention is as follows:

[0008] I. A device for controlling a specific moisture content in an undisturbed sandy soil sample, characterized in that:

[0009] The device includes a main control system, a pressure controller, a water storage tank, and a water delivery system. The pressure controller and the flow controller and retractable water pipe in the water delivery system are all connected to the main control system. The main control system is used to control the pore pressure, flow rate, and the expansion and contraction of the water pipe of the entire device. The pressure controller and the water storage tank are located above the soil sample to be tested. The water storage tank stores water to be injected into the soil sample. The output end of the pressure controller is connected to the inlet of the water storage tank through a vent pipe. The pressure controller is used to regulate the pressure in the water storage tank. The outlet of the water storage tank is connected to the input end of the water delivery system. A fixed amount of water in the water storage tank flows evenly into the soil sample after passing through the water delivery system, thereby achieving uniform control of the specific moisture content of the soil sample.

[0010] The water delivery system includes a flow controller, a retractable water pipe, a diversion adapter, a needle sleeve, and an injection needle. The outlet of the water storage tank is connected to the top of the retractable water pipe via the flow controller, and the bottom of the retractable water pipe is connected to the inlet of the diversion adapter. The flow controller is used to monitor and regulate the water flow in the water delivery system. The bottom of the diversion adapter is provided with several diversion outlets. Each diversion outlet of the diversion adapter is connected to each injection needle via the needle sleeve. Each injection needle extends into the test soil sample, so that the water stored in the water storage tank is diverted by the diversion adapter and guided by the injection needles in sequence and then evenly injected into the interior of the test soil sample.

[0011] The diversion adapter is used to divert water into each injection needle tube, which is evenly distributed in the test soil sample so that the water flowing out of the injection needle tube is evenly distributed in the test soil sample.

[0012] During the water injection process, the pressure at the tip of the water injection needle is obtained according to the following formula:

[0013]

[0014] Where R is the diffusion radius of the water sphere; k w γ represents the equivalent permeability coefficient of the test soil sample; P is the pressure at the tip of the injection needle during the water injection process; r0 is the inner diameter of the injection needle; t is the water injection time; n is the porosity of the test soil sample; γ w It is the density of water.

[0015] II. A method for controlling a specific moisture content in an undisturbed sandy soil sample, comprising the following steps:

[0016] Step S1: First, complete the device assembly: Assemble the water supply system, then connect the input and output ends of the water storage tank to the pressure controller and the water supply system respectively, and then connect the pressure controller, flow controller and retractable water pipe to the main control system.

[0017] Step S2: Obtain the total water injection volume based on the target moisture content of the test soil sample, and then inject water volume greater than 1.5 times the total water injection volume into the water storage tank;

[0018] Step S3: Start the air pressure controller through the main control system to control the air pressure of the water storage tank to the preset gas pressure. Then turn on the switch of the flow controller in the water delivery system so that the water in the water storage tank flows out through the expandable water pipe, the diverter and the water injection needle in sequence. After the water flow stabilizes, it can be considered that the air has been expelled. Then insert the water injection needle into the test soil sample so that the water flows into the test soil sample. At the same time, turn on the flow control module in the main control system to count the volume of water injected into the test soil and monitor it in real time.

[0019] Step S4: When the flow display screen in the main control system shows that the water flow has reached the set flow rate, the flow controller is turned off through the main control system and the depth of the water injection needle in the test soil sample is adjusted. After the depth of the water injection needle is adjusted, the flow controller is turned on again so that the water in the water storage tank flows evenly into the test soil sample through the retractable water pipe and the water injection needle.

[0020] Step S5: Repeat step S4 multiple times until the flow rate display on the main control system shows that the injected water flow has reached the total injection volume. At this point, the moisture content of the test soil sample has stabilized and reached the target moisture content.

[0021] In steps S1 and S4, the depth to which the water injection needle is inserted into the test soil sample is obtained according to the following formula:

[0022] h k =H(1-(2k-1) / 2N)

[0023] Among them, h k H represents the depth to which the injection syringe is inserted into the soil sample for the kth time; H represents the height of the soil sample; k represents the injection sequence number; and N represents the total number of injections.

[0024] In step S2, the total water injection volume Q of the test soil sample is obtained according to the following formula:

[0025] Q=v·(Gsρ w / 1+e)·Δω

[0026] Δω=ω d -ω0=ΔS r ·e / G s

[0027] Where Q represents the total amount of water to be injected into the test soil sample; v represents the injection rate; G s ρ represents the specific gravity of soil particles. wThe density of water is represented by 'e'; the initial void ratio of the soil is represented by 'e'; Δω represents the difference in water content; ω d ω represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r This represents the difference in saturation.

[0028] In step S3, the preset gas pressure P is obtained according to the following formula:

[0029] P = γ w ·R 3 n / (3k w r0t)

[0030] R = H / N

[0031] Where, γ w R is the unit weight of water; n is the water sphere diffusion radius; n is the porosity of the test soil sample; k w The equivalent permeability coefficient of the test soil sample is represented by r0; the inner diameter of the injection syringe is represented by t; the injection time is represented by H; the height of the test soil sample is represented by H; and the total number of injections is represented by N.

[0032] The main control system of this invention controls a pressure controller, a flow controller, and a retractable water pipe. The pressure controller injects gas into the water tank to compensate for the pressure inside, serving two purposes: firstly, to achieve the seepage initiation pressure, and secondly, to regulate the water injection rate, preventing seepage difficulties due to blockage. The water tank has a vent at the top for connecting to the pressure controller, and water inlets at the bottom and top for adding and discharging water. The flow controller precisely controls the amount of water injected at different stages of the injection process. A flow divider connects a micro-flow meter and an injection needle via a flexible water hose. Current research on unsaturated soil primarily focuses on remolded soil, while this invention provides a new method for preparing unsaturated soil with a specific moisture content from sandy soil samples. The method is simple, and the prepared soil has a uniform internal water content.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention uses a water injection needle to artificially increase the internal seepage path of the soil and accelerates the seepage speed by pressurizing, while preventing blockage.

[0035] 2. This invention vents the entire channel before water injection to ensure the accuracy of the water volume injected into the soil. At the same time, the method of layered water injection from bottom to top can greatly improve the uniformity of water distribution within the soil.

[0036] 3. This invention uses a syringe for water injection. Because the contact area between the syringe and the soil is very small, it has almost no impact on the structural properties of the soil. This device can be used to prepare undisturbed sandy soil samples with specific moisture contents without destroying the original anisotropy of the undisturbed sandy soil sample, ensuring high homogeneity. It can be used to study the relevant physical and mechanical properties of unsaturated soils.

[0037] 4. This invention can integrate various devices into one box, which is convenient for management and transportation, and can be used in various environments when using a power bank. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the device;

[0039] Figure 2 Schematic diagram of a four-channel flow adapter;

[0040] Figure 3 This is a schematic diagram showing the spherical diffusion of water in a sandy soil sample.

[0041] In the diagram: 1-Main control system; 2-Pneumatic controller; 3-Ventilation pipe; 4-Water storage tank; 5-Flow controller; 6-Water pipe; 7-Diverter; 8-Needle sleeve; 9-Water injection needle. Detailed Implementation

[0042] The present invention will be described in detail below with reference to specific implementation examples. These examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way.

[0043] like Figure 1 As shown, the device includes a main control system 1, a pressure controller 2, a water storage tank 4, and a water delivery system. The pressure controller 2, water storage tank 4, and water delivery system are all housed inside the device's casing. The diverter 7, needle sleeve 8, and injection needle 9 are located outside the casing. The casing must be placed above the test soil sample to ensure that the height of the water storage tank 4 is greater than that of the test soil sample. The main control system 1 is connected to the pressure controller 2, flow controller 5, and retractable water pipe 6 to control the overall pressure, flow rate, and the extension / retraction of the retractable water pipe. The pressure controller 2 and water storage tank 4 are both located above the test soil sample. The water storage tank 4 contains water to be injected into the test soil sample. The output of the pressure controller 2 is connected to the inlet of the water storage tank 4 via a vent pipe 3. The pressure controller 2 is used to regulate the pressure inside the water storage tank 4. The outlet of the water storage tank 4 is connected to the input of the water delivery system. A fixed amount of water in the water storage tank 4 flows evenly into the test soil sample through the water delivery system, thereby achieving uniform control of the specific moisture content of the test soil sample.

[0044] like Figure 2As shown, the water delivery system includes a flow controller 5, a retractable water pipe 6, a diversion adapter 7, a needle sleeve 8, and an injection needle 9. The outlet of the water storage tank 4 is connected to the top of the retractable water pipe 6 through the flow controller 5, and the bottom of the retractable water pipe 6 is connected to the inlet of the diversion adapter 7. The flow controller 5 is used to monitor and regulate the water flow in the water delivery system. The bottom of the diversion adapter 7 is provided with several diversion outlets. Each diversion outlet of the diversion adapter 7 is connected to each injection needle 9 through the needle sleeve 8. Each injection needle 9 extends into the test soil sample, so that the water stored in the water storage tank 4 is diverted by the diversion adapter 7 and guided by the injection needle 9 in sequence and then evenly injected into the interior of the test soil sample.

[0045] The diversion adapter 7 is used to divert water into each water injection needle tube 9. The water injection needle tubes 9 are evenly distributed in the test soil sample in the horizontal direction, so that the water flowing out of the water injection needle tubes 9 is evenly distributed in the test soil sample.

[0046] like Figure 3 As shown, during the water injection process of the water injection needle 9, the pressure at the tip of the water injection needle 9 is obtained according to the following formula:

[0047]

[0048] Where R is the diffusion radius of the water sphere; k w γ represents the equivalent permeability coefficient of the test soil sample; P is the pressure at the tip of the injection needle 9 during the water injection process; r0 is the inner diameter of the injection needle 9; t is the water injection time; n is the porosity of the test soil sample; γ w It is the density of water.

[0049] Embodiments of the present invention include the following steps:

[0050] Step S1: First, complete the device assembly: Assemble the water supply system, connect the input and output ends of the water storage tank 4 to the pressure controller 2 and the water supply system respectively, and then connect the pressure controller 1, the flow controller 5 and the retractable water pipe 6 to the main control system 1.

[0051] Step S2: Obtain the total water injection volume based on the target moisture content of the test soil sample, and then inject water volume greater than 1.5 times the total water injection volume into the water storage tank 4;

[0052] In practice, the undisturbed sand sample is a cube with a volume of 10×10×10 cm, a void ratio e = 0.8, and a specific gravity of soil particles G. s =2.72, equivalent permeability coefficient k w Approximately 2×10 -3The initial saturation was approximately 20%, and the target saturation was 85%. The preset injection time was 3 minutes, assuming the soil volume remained constant before and after injection. The injection only filled the soil pores. The required water volume to reach the target moisture content was calculated to be 288.92 ml, and the water volume in the storage tank should be greater than 433.38 ml. Four injection needles (10 cm long, 0.5 mm inner diameter) were used, employing a four-channel converter. The injection was carried out in two layers, dividing the total water volume into eight portions and injecting them into the soil.

[0053] Before injecting water, wrap the soil thoroughly with plastic film to prevent water evaporation or leakage during the injection process. Mark the insertion points of the injection needles and mark a certain height on the injection needle tubes. Then, securely connect all the equipment in sequence to prevent detachment and leakage. Based on the required water head pressure, control the platform height to be slightly higher than the injection surface, and set the injection pressure to 12.7 kPa. Pour all the prepared water into the storage tank and seal the injection port with a rubber stopper.

[0054] Step S3: Start the air pressure controller 2 through the main control system 1 to control the air pressure of the water storage tank 4 to the preset gas pressure. Then turn on the switch of the flow controller 5 on the main control system 1 so that the water in the water storage tank 4 flows out through the expandable water pipe 6, the diverter 7 and the water injection needle 9 in sequence. After the water flow stabilizes, it can be considered that the air has been expelled. Then insert the water injection needle 9 into the test soil so that the water flows into the test soil sample. At the same time, turn on the flow control module in the main control system 1 to count the volume of water injected into the test soil and monitor it in real time.

[0055] In practice, the main control system 1 checks and turns on the air pressure controller 2 and the flow controller 5. The water injection needle 9 is placed next to the soil. When the water fills the entire pipe and there is a uniform water flow in the water injection needle 9, the flow controller is turned off to ensure that the pipe is full of water. At the same time, the reading on the flow display in the main control system 1 is cleared to ensure the accuracy of the amount of water entering the soil.

[0056] Step S4: When the flow display in the main control system 1 shows that the water flow has reached the set flow rate, the main control system 1 closes the flow controller 5 and adjusts the depth of the water injection needle 9 in the test soil sample. After the depth of the water injection needle 9 is adjusted, the flow controller 5 is opened again so that the water in the water storage tank 4 flows evenly into the test soil sample through the retractable water pipe 6 and the water injection needle 9.

[0057] Step S5: Repeat step S4 multiple times until the flow rate display in the main control system 1 shows that the injected water flow has reached the total injection volume. Then, allow the sample to stand still for a preset time. At this point, the moisture content of the test soil sample will stabilize and reach the target moisture content.

[0058] In practice, after preparing and inspecting the equipment, the flow controller 5 is turned on through the main control system 1. After the air is vented, water is injected into the soil sample. Initially, the injection syringe is inserted into the soil to a depth of about 7.5 cm, maintaining stable air pressure. When the flow display in the main control system 1 shows that the water volume has reached 144.5 ml, that is, when the water volume is more than half, the flow controller 5 is immediately turned off. At the same time, the height of the injection syringe 9 is adjusted to be inserted into the soil to a depth of 2.5 cm, and water injection continues until the flow display shows that the preset volume of water has been injected.

[0059] After water injection is complete, the soil is completely wrapped with plastic film again and left to stand for a period of time. This allows the capillary force formed by the tiny pores and natural gravity to balance and evenly inject water into the sandy soil sample. According to the law of unsaturated soil flow, the moisture content gradient and capillary force are considered as driving potential energy. Theoretically, the longer the standing time, the better the uniformity of moisture inside the soil, resulting in higher efficiency and practicality compared to other humidification methods.

[0060] Regarding the specific uniformity after water balance, a soil moisture meter can be used to measure the area around a cylinder with a diameter of 7cm and a height of 7cm, centered on the central probe. Four points are then taken at the center of the plane and 3.5cm from the boundary. The moisture content of different parts of the soil after humidification is measured as follows: 82%, 83%, 88%, 83%, and 85%, respectively. The average value is 84.2%, and the standard deviation is 2.39%. The smaller the data dispersion, the more uniform the water content inside the soil. This embodiment demonstrates that the present invention can guarantee good uniformity.

[0061] In steps S1 and S4, the depth to which the water injection needle 9 is inserted into the test soil sample is obtained according to the following formula:

[0062] h k =H(1-(2k-1) / 2N)

[0063] Among them, h k H represents the depth of the water injection needle 9 inserted into the test soil sample for the kth time; H represents the size and height of the test soil sample; k represents the injection sequence number (i.e., the insertion sequence number into the test soil sample); and N represents the total number of injections.

[0064] The grout diffusion radius R for each water injection is obtained according to the following formula:

[0065] R = H / N

[0066] The depth to which the water injection syringe 9 is inserted into the test soil needs to be determined based on the specific size of the soil sample and the length of the syringe. Generally speaking, soil samples with a height of less than 20cm can be injected in two layers, while samples with a height of more than 20cm can have the number of injections increased appropriately.

[0067] In step S2, the total water injection volume Q of the test soil sample is obtained according to the following formula:

[0068] Q = v·(G s ρ w / 1+e)·Δω

[0069] Δω=ω d -ω0=ΔS r ·e / G s

[0070] Where Q represents the total amount of water to be injected into the test soil sample; v represents the injection rate; G s ρ represents the specific gravity of soil particles. w The density of water is represented by 'e'; the initial void ratio of the soil is represented by 'e'; Δω represents the difference in water content; ω d ω represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r This represents the difference in saturation.

[0071] In step S3, the preset gas pressure P is obtained according to the following formula:

[0072] P = γ w ·R 3 n / (3k w r0t)

[0073] R = H / N

[0074] Where, γ w R is the unit weight of water; n is the water sphere diffusion radius; n is the porosity of the test soil sample; k w The equivalent permeability coefficient of the test soil sample is represented by r0; the inner diameter of the injection needle 9 is represented by t; the injection time is represented by H; the size and height of the test soil sample are represented by H; and the total number of injections is represented by N.

[0075] The device of this invention mainly consists of a main control system 1, a pressure controller 2, a water storage tank 4, a flow controller 5, a diversion adapter 7, and a water injection needle tube 9. The main control system 1 connects the pressure controller 2, the flow controller 5, and the retractable water pipe 6, controlling the pressure, flow rate, and expansion / contraction of the water pipe throughout the system. The pressure controller 2 increases the pressure within the water storage tank 4, accelerating the seepage rate of water within the soil. The flow controller 5 controls the amount of water injected, and the diversion adapter 7 diverts water from the water storage tank 4 into the water injection needle tube 9. The water injection needle tube 9 is fixed in the central area of ​​the equally divided soil mass to ensure the uniformity of water injection into the soil.

[0076] In this invention, the water-injected sandy soil sample is cubic, and the size of the soil sample should meet the size requirements of conventional unsaturated soil triaxial, shear, and consolidation specimens. In order to minimize the disturbance to the sandy soil sample, multiple water injection needles 9 are placed at the center of the equally divided area of ​​the soil. After water injection is completed, the sample block can be taken from the center point, thereby better avoiding the disturbance of the soil by the needles.

[0077] In addition, a plastic film should be applied to the surface of the soil sample before water injection to prevent moisture evaporation. Before inserting the injection syringe 9 into the soil, the flow controller 5 is turned on via the main control system 1. Once the water fills the entire pipe and a uniform flow appears in the injection syringe 9, the flow controller is turned off to ensure all air is expelled from the pipe. Simultaneously, the reading on the flow display on the main control system 1 is reset to zero to ensure the accuracy of the water volume entering the soil. Stable air pressure must be maintained during the water injection process. When the water injection flow rate in each soil zone reaches the target, the flow controller is turned off, and the injection syringe 9 is pulled up to the preset position. When the flow display on the main control system 1 shows that the injected water volume has reached the preset volume, the flow controller 5 is turned off, and the injection syringe 9 is pulled out. After injection, the sandy soil sample is carefully wrapped again with the plastic film. After a period of time, the capillary force and water content gradient formed by the tiny channels inside the soil will automatically even out the water distribution, thus achieving higher uniformity.

[0078] The water injection device can adjust the water head pressure as needed. Through the control of the main control system 1, the air pressure controller 2 can adjust the pressure inside the water storage tank 4 to increase the water injection rate. The flow controller 5 is used for precise control of the area's water volume. For example... Figure 2 As shown, the diversion adapter 7 includes a diversion inlet and multiple diversion outlets. The single-channel diversion inlet must be in the exact center, and the diversion outlets must be symmetrically distributed about the center point. The diversion adapter 7 can divert water from the water tank to different injection needles 9. The multiple injection needles 9 are long and slender, allowing insertion into different planar positions in the soil. The insertion depth at different injection stages can be adjusted to ensure uniform water distribution without damaging the initial soil structure. A pressure controller 2 is used to regulate the water head pressure and prevent clogging. The use of multiple long and slender injection needles 9 avoids excessive disturbance to the soil. The adjustable insertion depth of the injection needles 9 at different injection stages ensures uniform soil wetting. A plastic film is applied to the sample surface before injection to prevent water evaporation.

[0079] Water diffuses in a spherical pattern in sandy soil samples, as shown in the attached image. Figure 3As shown, after measuring parameters such as the permeability coefficient and porosity of the soil, specific indicators such as the required pressure, water injection time, and injection needle diameter of the soil in different sub-regions can be preliminarily calculated using formulas. After water injection is completed, the soil is wrapped again with plastic film and left to stand for a period of time. The water content gradient and local capillary force in the soil act as the driving potential energy of the internal water, balancing the soil to ensure the uniformity of the water.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for controlling a specific moisture content in an undisturbed sandy soil sample, characterized in that: It includes a main control system (1), a pressure controller (2), a water storage tank (4), and a water delivery system; the pressure controller (2) and the water delivery system are both connected to the main control system (1), the pressure controller (2) and the water storage tank (4) are both located above the soil sample to be tested, the water storage tank (4) stores water to be injected into the soil sample, the output end of the pressure controller (2) is connected to the inlet of the water storage tank (4) through the air pipe (3), the pressure controller (2) is used to regulate the pressure in the water storage tank (4), the outlet of the water storage tank (4) is connected to the input end of the water delivery system, a certain amount of water in the water storage tank (4) flows evenly into the soil sample after passing through the water delivery system, thereby realizing the uniform regulation of the specific moisture content of the soil sample; The water delivery system includes a flow controller (5), a retractable water pipe (6), a diversion adapter (7), a needle sleeve (8), and an injection needle (9). The outlet of the water storage tank (4) is connected to the top of the retractable water pipe (6) through the flow controller (5), and the bottom of the retractable water pipe (6) is connected to the inlet of the diversion adapter (7). The flow controller (5) is used to monitor and regulate the water flow in the water delivery system. The bottom of the diversion adapter (7) is provided with several diversion outlets. Each diversion outlet of the diversion adapter (7) is connected to each injection needle (9) through the needle sleeve (8). Each injection needle (9) extends into the test soil sample, so that the water stored in the water storage tank (4) is diverted by the diversion adapter (7) and guided by the injection needle (9) and then evenly injected into the test soil sample.

2. The device for controlling a specific moisture content of an undisturbed sandy soil sample according to claim 1, characterized in that: The diversion adapter (7) is used to divert water into each water injection needle (9). The water injection needles (9) are evenly distributed in the test soil sample so that the water flowing out of the water injection needles (9) is evenly distributed in the test soil sample.

3. The device for controlling a specific moisture content of an undisturbed sandy soil sample according to claim 1, characterized in that: During the water injection process of the water injection needle (9), the pressure at the tip of the water injection needle (9) is obtained according to the following formula: Where R is the diffusion radius of the water sphere; k w γ represents the equivalent permeability coefficient of the test soil sample; P is the pressure at the tip of the injection needle (9) during the water injection process; r0 is the inner diameter of the injection needle (9); t is the water injection time; n is the porosity of the test soil sample; γ w It is the density of water.

4. A method for controlling a specific moisture content in an undisturbed sandy soil sample applied to the apparatus described in any one of claims 1-3, characterized in that, Includes the following steps: Step S1: First, complete the device assembly: assemble the water supply system, then connect the input and output ends of the water storage tank (4) to the pressure controller (2) and the water supply system respectively, and then connect the pressure controller (2), flow controller (5) and retractable water pipe (6) to the main control system (1). Step S2: Obtain the total water volume based on the target moisture content of the test soil sample, and then inject water that is more than 1.5 times the total water volume into the water storage tank (4); Step S3: Start the air pressure controller (2) through the main control system (1) to make the air pressure control of the water storage tank (4) set to the preset gas pressure. Then turn on the switch of the flow controller (5) in the water supply system so that the water in the water storage tank (4) flows out through the expandable water pipe (6), the diversion adapter (7) and the water injection needle (9) in sequence. After the water flow stabilizes, insert the water injection needle (9) into the test soil sample so that the water flows into the test soil sample. At the same time, turn on the main control system (1) to count the volume of water injected into the test soil and monitor it in real time. Step S4: When the flow display screen in the main control system (1) shows that the water flow has reached the set flow rate, the flow controller (5) is turned off by the main control system (1) and the depth of the water injection needle (9) in the test soil sample is adjusted. After the depth position of the water injection needle (9) is adjusted, the flow controller (5) is turned on again so that the water in the water storage tank (4) flows evenly into the test soil sample through the retractable water pipe (6) and the water injection needle (9). Step S5: Repeat step S4 multiple times until the flow rate display screen in the main control system (1) shows that the injected water flow has reached the total injection volume. At this time, the moisture content of the test soil sample has reached the target moisture content.

5. The method for controlling a specific moisture content in an undisturbed sandy soil sample according to claim 4, characterized in that: In steps S1 and S4, the depth to which the water injection needle (9) is inserted into the test soil sample is obtained according to the following formula: h k =H(1-(2k-1) / 2N) Among them, h k H represents the depth of the water injection needle (9) inserted into the test soil sample for the kth time; H represents the size and height of the test soil sample; k represents the injection sequence number; and N represents the total number of injections.

6. The method for controlling a specific moisture content in an undisturbed sandy soil sample according to claim 4, characterized in that: In step S2, the total water injection volume Q of the test soil sample is obtained according to the following formula: Q=v·(G s r w / 1+e)·See Give = oh d -ω0=ΔS r ·e / G s Where Q represents the total amount of water to be injected into the test soil sample; v represents the injection rate; G s ρ represents the specific gravity of soil particles. w The density of water is represented by 'e'; the initial void ratio of the soil is represented by 'e'; Δω represents the difference in water content; ω d ω represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r This represents the difference in saturation.

7. The method for controlling a specific moisture content in an undisturbed sandy soil sample according to claim 4, characterized in that: In step S3, the preset gas pressure P is obtained according to the following formula: P=γ w ·R 3 n / (3k w r0t) R = H / N Where, γ w R is the unit weight of water; n is the water sphere diffusion radius; n is the porosity of the test soil sample; k w The equivalent permeability coefficient of the test soil sample is represented by r0; the inner diameter of the injection needle (9) is represented by t; the injection time is represented by H; the size and height of the test soil sample are represented by H; and the total number of injections is represented by N.

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