Device and method for controlling specific water content of undisturbed sandy soil sample

Abstract

The invention discloses a device and a method for controlling the specific moisture content of an undisturbed sandy soil sample. The main control system is used for controlling pore pressure and flow of the device and stretching of the water pipe; the air pressure controller is connected with the water storage tank through a breather pipe and used for regulating and controlling the pressure in the water storage tank, the water storage tank is connected with the water conveying system, a flow dividing adapter of the water conveying system is provided with a plurality of flow dividing outlets, the flow dividing outlets are connected with the water injection needle tubes through water pipes respectively, and the water injection needle tubes stretch into a soil body. Water in the water storage tank is shunted by the shunting adapter and drained by the water injection needle tube and then is uniformly injected into the soil body, so that the specific water content of the soil sample is uniformly regulated and controlled; the method comprises the steps that device assembling is completed, water is injected into the water storage tank, the air pressure controller is started to control pressure, and the water in the water storage tank evenly flows into the soil body through the water injection needle tube. The device can be used for preparing the sandy soil sample with specific water content, does not damage the original structure anisotropy of the sandy soil sample, and has relatively high uniformity guarantee.

Description

Technical Field

[0001] The invention belongs to the field of rock and soil mechanics, and in particular relates to a control device and method for the specific moisture content of an original sandy soil sample. Background Art

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

[0003] In the field of geotechnical engineering and related experimental research on unsaturated soil, reshaped soil samples are usually used. The reshaping process destroys the in-situ particle size arrangement characteristics of the original soil samples and cannot reflect the most realistic physical and mechanical indicators of the soil samples. This leads to certain differences in the engineering properties of the reshaped soil samples and samples.

[0004] On the one hand, the moisture content of the original sample may decrease over time during the actual transportation and storage process. At this time, it is necessary to restore its original moisture content without destroying its structure. On the other hand, when studying the related characteristics of unsaturated soil and moisture content, it is also necessary to configure a specific moisture content according to the different needs of the test to find the change law of related physical and mechanical properties with moisture content. For saturated soil, its permeability is mainly related to the porosity; while for unsaturated soil, its permeability is mainly related to the porosity and moisture content. During the water injection process, the moisture content of the soil sample is constantly changing, and its permeability is also constantly changing. Sandy soil particles have a dense single-grain structure, large pores, and better permeability than clay. It is not easy to have seepage blockage and needle tube closure.

[0005] If you use artificial dripping, spraying, smearing and other methods on the soil surface to configure a specific moisture content of the sample, the water may evaporate, resulting in an inaccurate configured moisture content. In addition, water only penetrates from the surface of sandy soil samples, which may cause the soil moisture content gradient to be more on the top and less on the bottom, and the uniformity cannot be well guaranteed. Indoor unsaturated soil related experimental research provides a way to configure the moisture content. Spraying and smearing are not only time-consuming and labor-intensive, but also difficult to control the amount of water. It is easy to evaporate, and the time it takes for water to penetrate into the soil is long, and the time required for its equilibrium is also long. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a control device and method for the specific moisture content of an original sandy soil sample.

[0007] The technical solution adopted by the present invention is:

[0008] 1. A device for controlling the specific moisture content of an original sandy soil sample, characterized in that:

[0009] The device includes a main control system, an air pressure controller, a water storage tank and a water delivery system; the air pressure controller and the flow controller and the 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 and retraction of the water pipe of the entire device, the air pressure controller and the water storage tank are both located above the test soil sample to be tested, the water to be injected into the test soil sample is stored in the water storage tank, the output end of the air pressure controller is connected to the inlet of the water storage tank through the ventilation pipe, the air 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, and a certain amount of water in the water storage tank flows evenly into the test soil sample after passing through the water delivery system, thereby realizing uniform regulation of the specific moisture content of the test soil sample.

[0010] The water delivery system includes a flow controller, a retractable water pipe, a shunt adapter, a needle sleeve and a water injection needle; the outlet of the water storage tank is connected to the top of the retractable water pipe through the flow controller, and the bottom of the retractable water pipe is connected to the inlet connected to the shunt adapter. The flow controller is used to monitor and regulate the water flow in the water delivery system. The bottom end of the shunt adapter is provided with a plurality of shunt outlets, and each shunt outlet of the shunt adapter is respectively connected to each water injection needle through the needle sleeve, and each water injection needle extends into the test soil sample, so that the water stored in the water storage tank is evenly injected into the test soil sample after being shunted by the shunt adapter and drained by the water injection needle in turn.

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

[0012] During the water injection process of the water injection needle, 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 represents the equivalent permeability coefficient of the test soil sample; P is the pressure at the tip of the injection needle during the injection process; r0 is the inner diameter of the injection needle; t is the injection time; n is the porosity of the test soil sample; γ w The weight of water.

[0015] 2. A method for controlling the specific moisture content of an original sandy soil sample comprises the following steps:

[0016] Step S1, first, complete the assembly of the device: assemble the water delivery system, then connect the input end and output end of the water storage tank to the air pressure controller and the water delivery system respectively, and then connect the air pressure controller, flow controller and retractable water pipe to the main control system;

[0017] Step S2, obtaining a total amount of water injection according to a target moisture content of the test soil sample, and then injecting water greater than 1.5 times the total amount of water injection 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 a preset air 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 retractable water pipe, the flow diversion adapter and the water injection needle in sequence, and after the water flow is stable, it can be considered that the air has been discharged, and then insert the water injection needle into the test soil sample to make water flow into the test soil sample, and 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 reaches the set flow rate, the flow controller is closed through the main control system and the depth of the water injection needle in the test soil sample is adjusted. After the depth position of the water injection needle is adjusted, the flow controller is opened 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 display screen in the main control system shows that the injected water flow reaches the total water injection amount, and at this time the moisture content of the test soil sample stably reaches the target moisture content.

[0021] In step S1 and step S4, the depth of the water injection needle inserted into the test soil sample is obtained by the following formula:

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

[0023] Among them, h k It indicates the depth of the water injection needle inserted into the test soil sample for the kth time; H indicates the size height of the test soil sample, k indicates the injection sequence, and N indicates the total number of injections.

[0024] In step S2, the total amount of water injection 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 speed; G s Represents the specific gravity of soil particles; ρ wrepresents the density of water; e represents the initial porosity of the soil; Δω represents the difference in water content; ω d represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r Indicates the saturation difference.

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

[0029] P = γ w ·R 3 n / (3k w r0t)

[0030] R=H / N

[0031] Among them, γ w is the density of water; R is the diffusion radius of the water sphere; n is the porosity of the test soil sample; k w represents the equivalent permeability coefficient of the test soil sample; r0 is the inner diameter of the injection needle; t is the injection time; H represents the size and height of the test soil sample; N represents the total number of injections.

[0032] The main control system of the present invention is used to control the air pressure controller, the flow controller and the retractable water pipe; the air pressure controller can inject gas into the water tank to compensate for the pressure in the water tank. On the one hand, it is used to reach the seepage starting pressure, and on the other hand, it is used to adjust the water injection rate to prevent the situation where seepage is difficult to proceed when blockage occurs. There is an air vent on the top of the water tank for connecting the air pressure controller, and there are water holes at the bottom and top for adding and discharging water. The flow controller is used to accurately control the amount of water injected at different water injection stages. The diverter adapter connects the micro flow meter and the water injection needle through a water hose. The current research status of unsaturated soil is basically aimed at remolded soil, and the present invention provides a new method for configuring unsaturated soil with a certain water content of sandy soil samples. The method is simple and the water body inside the prepared soil body is uniform.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention adopts the method of water injection needle tube to artificially increase the internal seepage path of the soil body, and accelerates the seepage speed by pressurizing, while preventing the occurrence of blockage.

[0035] 2. The present invention performs exhaust treatment on the entire channel before water injection to ensure the accuracy of the amount of water 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 inside the soil.

[0036] 3. The present invention uses a needle to inject water. Since the contact area between the needle and the soil is very small, it has almost no effect on the structural properties of the soil. The device can be used to configure the original sandy soil sample with a specific water content, and does not destroy the original structural anisotropy of the original sandy soil sample. It has a high uniformity guarantee and can be used to study the physical and mechanical properties related to unsaturated soil.

[0037] 4. The present invention can integrate various devices into one box, which is convenient for management and transportation, and can be applied to various usage environments when a mobile power supply is used. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2 This is a schematic diagram of a four-channel flow adapter;

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

[0041] In the figure: 1-main control system; 2-air pressure controller; 3-ventilation pipe; 4-water storage tank; 5-flow controller; 6-water pipe; 7-diversion adapter; 8-needle sleeve; 9-water injection needle. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with specific implementation cases. The following implementation cases will help those skilled in the art to further understand the present invention, but will not limit the present invention in any form.

[0043] like Figure 1 As shown, the device includes a main control system 1, an air pressure controller 2, a water storage tank 4 and a water delivery system; the air pressure controller 2, the water storage tank 4 and the water delivery system are all placed inside the chassis of the device, and the shunt adapter 7, the needle sleeve 8 and the water injection needle 9 are all located outside the chassis. The chassis must be placed above the test soil sample to ensure that the height of the water storage tank 4 is greater than the test soil sample; the main control system 1 is connected with the air pressure controller 2, the flow controller 5 and the telescopic water pipe 6 to control the air pressure, flow and telescopic of the entire device; the air pressure controller 2 and the water storage tank 4 are both located above the test soil sample to be tested, and the water storage tank 4 stores water to be injected into the test soil sample. The output end of the air pressure controller 2 is connected to the inlet of the water storage tank 4 through the ventilation pipe 3. The air 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. The quantitative water in the water storage tank 4 flows evenly into the test soil sample after passing through the water delivery system, thereby realizing the uniform regulation 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 diverter adapter 7, a needle sleeve 8 and a water 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 end of the retractable water pipe 6 is connected to the inlet connected to the diverter adapter 7. The flow controller 5 is used to monitor and regulate the water flow in the water delivery system. The bottom end of the diverter adapter 7 is provided with a plurality of diverter outlets, and each diverter outlet of the diverter adapter 7 is respectively connected to each water injection needle 9 through the needle sleeve 8. Each water injection needle 9 extends into the test soil sample, so that the water stored in the water storage tank 4 is evenly injected into the test soil sample after being diverted by the diverter adapter 7 and drained by the water injection needle 9 in turn.

[0045] The flow diversion adapter 7 is used to divert water to each water injection needle tube 9. The water injection needle tube 9 is evenly arranged in the test soil sample in the horizontal direction, so that the water flowing out of the water injection needle tube 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 tube 9, the pressure at the needle tip of the water injection needle tube 9 is obtained according to the following formula:

[0047]

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

[0049] An embodiment of the present invention comprises the following steps:

[0050] Step S1, first, complete the assembly of the device: assemble the water delivery system, connect the input end and output end of the water storage tank 4 to the air pressure controller 2 and the water delivery system respectively, and then connect the air pressure controller 1, the flow controller 5 and the retractable water pipe 6 to the main control system 1;

[0051] Step S2, obtaining a total amount of water injection according to a target moisture content of the test soil sample, and then injecting water greater than 1.5 times the total amount of water injection into the water storage tank 4;

[0052] In the specific implementation, the volume of the original sand sample is a cube of 10×10×10 (cm), the porosity ratio e=0.8, and the specific gravity of the soil particles G s =2.72, equivalent permeability coefficient k w About 2×10 -3cm / s, the initial saturation is about 20%, and the target saturation is 85%. The preset injection time is 3 minutes. Assuming that the soil volume remains unchanged before and after water injection, the preset injection time is 3 minutes. Water injection is just to fill the pores of the soil. The amount of water required to achieve the target moisture content is calculated. The volume of water required to be injected into the test soil is 288.92 ml, and the volume of water in the water storage tank should be greater than 433.38 ml. The injection needle is selected to be 10 cm long and 0.5 mm in inner diameter. Four injection needles are used, that is, a four-channel converter is used; the injection is divided into two layers, that is, the total water volume is divided into eight parts and injected into the soil.

[0053] Before water injection, wrap the soil with plastic film to prevent water from evaporating or flowing out during the water injection process, mark the position where the needle is inserted, and mark the needle at a certain height. Then connect each device firmly in turn to prevent falling off and water leakage. According to the required head pressure, control the platform height slightly higher than the water injection surface, and set the water injection pressure to 12.7kPa. Pour all the prepared water into the water storage tank and seal the water 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 a preset air 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 retractable water pipe 6, the flow diversion adapter 7 and the water injection needle 9 in sequence, and after the water flow is stable, it can be considered that the air has been discharged, and then insert the water injection needle 9 into the test soil body to make the water flow into the test soil sample, and 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 body, and monitor it in real time;

[0055] In the specific implementation, the air pressure controller 2 and the flow controller 5 are checked and opened through the main control system 1, and the water injection needle 9 is placed next to the soil. When the water flow fills the entire pipeline and the water injection needle 9 has a uniform water flow, the flow controller is closed to ensure that the pipeline is full of water. At the same time, the reading on the flow display in the main control system 1 is cleared to zero to ensure the accuracy of the amount of water entering the soil.

[0056] Step S4, when the flow indicator in the main control system 1 shows that the water flow reaches the set flow rate, the flow controller 5 is closed through the main control system 1 and the depth of the water injection needle tube 9 in the test soil sample is adjusted. After the depth position of the water injection needle tube 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 tube 9;

[0057] Step S5, repeat step S4 multiple times until the flow indicator in the main control system 1 shows that the injected water flow reaches the total amount of water injection, and then stays still for a preset time, at which time the moisture content of the test soil sample stably reaches the target moisture content.

[0058] In the specific implementation, after the equipment is prepared and checked, the flow controller 5 is opened through the main control system 1, and water is injected into the soil sample after the exhaust is completed. Initially, the water injection needle is inserted into the soil to a depth of about 7.5 cm, and the air pressure is kept stable. When the water volume displayed on the flow display in the main control system 1 reaches 144.5 ml, that is, when the water injection volume is more than half, the flow controller 5 is immediately closed, and the height of the water injection needle 9 is adjusted at the same time, and inserted to 2.5 cm from the soil body, and water injection is continued until the flow display shows that the preset volume of water has been injected.

[0059] After the water injection is completed, the soil is wrapped again with plastic film and left to stand for a period of time to allow the capillary force formed by the tiny gaps and the natural gravity to balance and evenly inject water into the sandy soil sample. According to the law of unsaturated soil flow, the water content gradient and capillary force are considered as driving potential energy. In theory, the longer the standing time, the better the uniformity of water inside the soil, which has higher efficiency and practicality compared to other humidification methods.

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

[0061] In steps S1 and S4, the depth of the water injection needle 9 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 It represents the depth of the water injection needle 9 inserted into the test soil sample for the kth time; H represents the size height of the test soil sample, k represents the injection sequence (i.e. the sequence number inserted into the test soil sample), and N represents the total number of injections.

[0064] Among them, the grouting diffusion radius R of each injection of water is obtained according to the following formula:

[0065] R=H / N

[0066] The depth of the water injection needle 9 inserted into the test soil needs to be determined according to the specific size of the soil sample and the length of the needle. Generally speaking, soil samples with a height of less than 20 cm can be injected in two layers, and samples with a height greater than 20 cm can be appropriately humidified and injected several times.

[0067] In step S2, the total amount of water injection 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 speed; G s Represents the specific gravity of soil particles; ρ w represents the density of water; e represents the initial porosity of the soil; Δω represents the difference in water content; ω d represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r Indicates the saturation difference.

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

[0072] P = γ w ·R 3 n / (3k w r0t)

[0073] R=H / N

[0074] Among them, γ w is the density of water; R is the diffusion radius of the water sphere; n is the porosity of the test soil sample; k w represents the equivalent permeability coefficient of the test soil sample; r0 is the inner diameter of the water injection needle 9; t is the water injection time; H represents the size height of the test soil sample; N represents the total number of injections.

[0075] The device of the present invention is mainly composed of a main control system 1, an air pressure controller 2, a water storage tank 4, a flow controller 5, a shunt adapter 7, a water injection needle tube 9, etc. The main control system 1 is connected to the air pressure controller 2, the flow controller 5 and the retractable water pipe 6 to control the air pressure, flow and retraction of the water pipe of the whole system; the air pressure controller 2 can increase the pressure in the water storage tank 4 to accelerate the seepage speed of water flow inside the soil. The flow controller 5 is used to control the amount of injected water, and the shunt adapter 7 can shunt the water in the water storage tank 4 to the water injection needle tube 9. The water injection needle tube 9 is fixed in the central area of ​​the soil body to ensure the uniformity of soil water injection as much as possible.

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

[0077] In addition, a layer of plastic film is attached to the surface of the soil sample before water injection to prevent water evaporation. Before the water injection needle tube 9 is placed inside the soil, the flow controller 5 is opened through the main control system 1. When the water flow fills the entire pipeline and the water injection needle tube 9 has a uniform water flow, the flow controller is closed to ensure that the air in the pipeline is removed. At the same time, the reading on the flow display on the main control system 1 is cleared to ensure the accuracy of the amount of water entering the soil. In the process of injecting water into the soil, it is necessary to ensure the stability of the air pressure. When the water injection flow rate of the soil area reaches the target, the flow controller is first closed, and then the water injection needle tube 9 is pulled up to the preset position. When the flow display on the main control system 1 shows that the amount of water injected has reached the preset volume, the flow controller 5 is closed and the water injection needle tube 9 is pulled out at the same time. After the injection is completed, the sandy soil sample is rewrapped with plastic film. After a period of time, the capillary force and water content gradient formed by the fine channels inside the soil will automatically evenly distribute the water, thereby achieving higher uniformity.

[0078] The water injection device can adjust the water head pressure according to demand. Through the regulation of the main control system 1, the air pressure controller 2 can adjust the pressure in the water storage tank 4 to increase the water injection rate. The flow controller 5 is used to accurately control the water volume in the area. Figure 2 As shown, the diversion adapter 7 includes a diversion inlet and multiple diversion outlets. The diversion inlet of a single channel must be in the middle, and the diversion outlets must be symmetrically distributed about the center point. The diversion adapter 7 can divert the water in the water tank to different water injection needles 9. The multiple water injection needles 9 are slender in shape and can be inserted into different plane positions of the soil. At the same time, the depth of penetration into the soil at different water injection stages can be adjusted to ensure the uniformity of moisture without destroying the initial structure of the soil. The air pressure controller 2 is used to regulate the head pressure and prevent clogging. Multiple slender water injection needles 9 are used to avoid excessive disturbance to the soil. The depth of penetration into the soil of the water injection needle 9 at different water injection stages can be adjusted to ensure the uniformity of soil humidification as much as possible. Before water injection, a layer of plastic film is pasted on the sample surface to prevent water evaporation.

[0079] Water diffuses in a spherical shape in sandy soil samples. Figure 3As shown in the figure, after measuring the permeability coefficient, porosity and other parameters of the soil, the required pressure of the soil in different sub-areas, injection time, injection needle diameter and other specific indicators can be preliminarily calculated through the formula. After the injection is completed, the soil is wrapped again with plastic film. After standing for a period of time, the moisture content gradient and local capillary force in the soil serve as the driving potential energy of the internal water body, balancing the interior of the soil to ensure the uniformity of the water body.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for controlling the specific moisture content of an original sandy soil sample, characterized in that: The invention comprises a main control system (1), an air pressure controller (2), a water storage tank (4) and a water delivery system; the air pressure controller (2) and the water delivery system are both connected to the main control system (1); the air pressure controller (2) and the water storage tank (4) are both located above a test soil sample to be tested; the water storage tank (4) stores water to be injected into the test soil sample; the output end of the air pressure controller (2) is connected to the inlet of the water storage tank (4) through a vent pipe (3); the air 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 test soil sample after passing through the water delivery system, thereby realizing even regulation of the specific water content of the test soil sample.

2. The device for controlling the specific moisture content of an original sandy soil sample according to claim 1, characterized in that: The water delivery system comprises a flow controller (5), a telescopic water pipe (6), a flow diversion adapter (7), a needle sleeve (8) and a water injection needle tube (9); the outlet of the water storage tank (4) is connected to the top of the telescopic water pipe (6) through the flow controller (5), the bottom of the telescopic water pipe (6) is connected to the inlet connected to the flow diversion adapter (7), the flow controller (5) is used to monitor and control the water flow in the water delivery system, the bottom of the flow diversion adapter (7) is provided with a plurality of flow diversion outlets, each flow diversion outlet of the flow diversion adapter (7) is respectively connected to each water injection needle tube (9) through the needle sleeve (8), and each water injection needle tube (9) extends into the test soil sample, so that the water stored in the water storage tank (4) is evenly injected into the test soil sample after being diverted by the flow diversion adapter (7) and drained by the water injection needle tube (9) in sequence.

3. The control device for the specific moisture content of an original sandy soil sample according to claim 2, characterized in that: The flow diversion adapter (7) is used to divert water into each water injection needle tube (9), and the water injection needle tubes (9) are evenly arranged in the test soil sample, so that the water flowing out of the water injection needle tubes (9) is evenly distributed in the test soil sample.

4. The device for controlling the specific moisture content of an original sandy soil sample according to claim 2, characterized in that: During the water injection process of the water injection needle tube (9), the pressure at the needle tip of the water injection needle tube (9) is obtained according to the following formula: Where R is the diffusion radius of the water sphere; k w represents the equivalent permeability coefficient of the test soil sample; P is the pressure at the tip of the water injection needle (9) during the water injection process; r0 is the inner diameter of the water injection needle (9); t is the water injection time; n is the porosity of the test soil sample; γ w The weight of water.

5. A method for controlling the specific moisture content of an original sandy soil sample applied to the device described in any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1, first, complete the assembly of the device: assemble the water delivery system, then connect the input end and output end of the water storage tank (4) to the air pressure controller (2) and the water delivery system respectively, and then connect the air pressure controller (2), the flow controller (5) and the retractable water pipe (6) to the main control system (1); Step S2, obtaining a total amount of water injection according to a target water content of the test soil sample, and then injecting a water body greater than 1.5 times the total amount of water injection into the water storage tank (4); Step S3, starting the air pressure controller (2) through the main control system (1) so that the air pressure of the water storage tank (4) is controlled to a preset air pressure, and then turning on the switch of the flow controller (5) in the water delivery system, so that the water in the water storage tank (4) flows out through the retractable water pipe (6), the flow diversion adapter (7) and the water injection needle tube (9) in sequence, and after the water flow stabilizes, inserting the water injection needle tube (9) into the test soil sample so that water flows into the test soil sample, and at the same time turning on the main control system (1) to count the volume of water injected into the test soil, and monitoring it in real time; Step S4, when the flow display screen in the main control system (1) shows that the water flow reaches the set flow rate, the flow controller (5) is closed through the main control system (1) and the depth of the water injection needle tube (9) in the test soil sample is adjusted. After the depth position of the water injection needle tube (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 tube (9); Step S5, repeating step S4 multiple times until the flow display screen in the main control system (1) shows that the injected water flow reaches the total water injection amount, and at this time, the moisture content of the test soil sample stably reaches the target moisture content.

6. The method for controlling the specific moisture content of an original sandy soil sample according to claim 5, characterized in that: In step S1 and step S4, the depth of the water injection needle (9) inserted into the test soil sample is obtained by processing according to the following formula: <h2 style=";text-align:left;direction:ltr">h<h2 style=";text-align:left;direction:ltr"> k <h2 style=";text-align:left;direction:ltr"> (H(1-(2k-1) / 2N) Among them, h k represents the depth of the water injection needle (9) inserted into the test soil sample for the kth time; H represents the size height of the test soil sample, k represents the injection sequence, and N represents the total number of injections.

7. The method for controlling the specific moisture content of an original sandy soil sample according to claim 5, characterized in that: In step S2, the total amount of water injection 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 speed; G s Represents the specific gravity of soil particles; ρ w represents the density of water; e represents the initial porosity of the soil; Δω represents the difference in water content; ω d represents the target moisture content of the soil; ω0 represents the initial moisture content of the soil; ΔS r Indicates the saturation difference.

8. The method for controlling the specific moisture content of an original sandy soil sample according to claim 5, characterized in that: In step S3, the preset gas pressure P is obtained by processing according to the following formula: P=γ w ·R 3 n / (3k w r0t) R=H / N Among them, γ w is the density of water; R is the diffusion radius of the water sphere; n is the porosity of the test soil sample; k w represents the equivalent permeability coefficient of the test soil sample; r0 is the inner diameter of the water injection needle (9); t is the water injection time; H represents the size height of the test soil sample; and N represents the total number of injections.

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