Single shear test device and test method for hydrate-containing marine soil

Abstract

The invention belongs to the technical field of physical property measurement of geotechnical engineering foundations, and discloses a hydrate-containing marine soil single shear test device and a test method. The hydrate-containing marine soil single shear test device comprises a single shear stress state shear box, a multidirectional servo loading system, a hydrate in-situ generation-decomposition system, a temperature and pressure control system and a data acquisition and control system. According to the hydrate-containing marine soil simple shear testing device, a macroscopic mechanical property test of hydrate-containing marine soil in a complex field stress state can be achieved, reliable design and operation of offshore facilities such as an ocean platform are further guaranteed, and hardware support is provided for commercialized exploitation of porous medium phase change resources such as hydrates in the future in China.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering basic physical property measurement, and relates to a single shear test device and test method for hydrate-containing marine soil. Background Art

[0002] As a highly efficient new clean energy, natural gas hydrate is regarded as the most potential alternative energy source for exploitation in the 21st century because of its huge reserves, high energy density, and no dust and nitrogen oxide pollutants after combustion, and has gradually become a strategic high ground for energy competition among major global powers. Two key conditions need to be met for the commercial exploitation of natural gas hydrate: the long-term stability of the suction piles (buckets), steel pipe piles, etc. of the floating offshore platform is the premise for exploitation; the long-term stability of the drilling riser is a necessary condition during the production process. The stability analysis of the drilling riser is similar to that of the suction pile (bucket) or steel pipe pile, and should also be analyzed according to the pile foundation. In the actual hydrate exploitation project, complex marine environmental loads such as storms and waves are continuously transmitted to the shallow hydrate-containing marine soil reservoir through the anchor chain, resulting in the deterioration of the mechanical properties of the reservoir. This process will not only threaten the drilling platform and damage the production well, but may even induce geological disasters (such as triggering tsunamis and earthquakes) and ecological environment chain reactions (such as exacerbating the greenhouse effect).

[0003] Some research (Meng Xiangchuan et al., Study on the undrained shear strength characteristics of saturated clay. China Civil Engineering Journal, 2024, 57, 5) pointed out that the soil stress state in the triaxial test is very different from the in-situ stress state, and the shear strength obtained through the triaxial stress state test may be overestimated, which undoubtedly increases the risk of failure of the anchor foundations such as suction piles (buckets) and steel pipe piles; and the stress state of the indoor single shear test is similar to the shear mode of the hydrate-containing marine soil around the offshore pile foundation and the stress state of the hydrate-containing marine soil unit on the potential failure surface. However, the existing single shear instruments announced in, such as CN201710245902.5, CN201911324850.6, CN201910185363.X, and CN202211378071.6, can only achieve temperature control, cannot meet the low temperature, high pressure and other conditions for the occurrence of hydrate-containing marine soil and lack the hydrate gas source environment. Therefore, the research and development of single shear test devices for hydrate-containing marine soil is still blank at home and abroad. Accurately depicting the macroscopic mechanical properties of hydrate-containing marine soil under the actual stress state in the indoor laboratory is a prerequisite for improving the development of the special soil mechanics of hydrate-containing marine soil. This method can provide a scientific basis and technical support for the resource development of phase change in porous media and the prevention and control of regional geological disasters. Summary of the Invention

[0004] The object of the present invention is to provide a single shear test device for hydrate-containing marine soil and its test method, filling the gaps in the domestic and international single shear test technology for hydrate-containing marine soil. The present invention can accurately obtain the macroscopic mechanical properties of hydrate-containing marine soil under the single shear stress mode, and has the remarkable characteristics of simple operation, reliable data, simple structure, rich functions and in-situ stress reduction, providing hardware support for ensuring the reliable design and operation of offshore facilities such as offshore platforms and the future commercial exploitation of hydrates in China.

[0005] The technical solution of the present invention:

[0006] A single shear test device for hydrate-containing marine soil, comprising a single shear stress state shear box 1, a multi-directional servo loading system 2, a hydrate in-situ generation-decomposition system 3, a temperature and pressure control system 4, and a data acquisition and control system 5;

[0007] The single shear stress state shear box 1 includes an upper cover plate 1-1, a high-pressure cylinder 1-2, a sealing bolt 1-3, a water jacket 1-4, an upper pressing head 1-5, a permeable stone 1-6, a reinforced rubber membrane 1-7, a lower pressing head 1-8, a lower cover plate 1-9, an O-ring 1-10, hydrate-containing marine soil 1-11, a limit bolt 1-12, and a connecting bolt 1-13; among them, the high-pressure cylinder 1-2 and the upper cover plate 1-1 are connected by the sealing bolt 1-3 to ensure the sealing of the single shear stress state shear box 1 within the pressure range of 5 - 35000 kPa; a water jacket 1-4 is arranged inside the side wall of the high-pressure cylinder 1-2 for replacing the temperature inside the single shear stress state shear box 1; the lower cover plate 1-9 is located at the bottom of the high-pressure cylinder 1-2 and is equipped with pulleys; the lower pressing head 1-8 is connected to the lower cover plate 1-9 by the connecting bolt 1-13, a permeable stone 1-6 and a dry filter paper are sequentially placed on the lower pressing head 1-8, the reinforced rubber membrane 1-7 is stretched open by using a film holding cylinder, the lower part of the reinforced rubber membrane 1-7 is sealed to the lower pressing head 1-8 by the O-ring 1-10, after the matrix material of the hydrate-containing marine soil 1-11 is filled in layers in the film holding cylinder, a dry filter paper and a permeable stone 1-6 are placed in sequence, the upper pressing head 1-5 is lowered until it contacts the matrix material of the hydrate-containing marine soil 1-11, the reinforced rubber membrane 1-7 is sleeved over the upper pressing head 1-5 and sealed to the upper pressing head 1-5 by the O-ring 1-10, and the film holding cylinder is removed; the limit bolt 1-12 is installed at the bottom of the high-pressure cylinder 1-2, mainly to prevent the shear displacement of the lower cover plate 1-9 from being too large during the shear process;

[0008] The described multi-directional servo loading system 2 includes a vertical loading system 2-1 and a horizontal loading system 2-2; the vertical loading system 2-1 is located at the upper end of the single shear stress state shear box 1 and includes a vertical loading rod 2-1-1 with a cylindrical structure, a vertical servo hydraulic cylinder 2-1-2, a vertical guide ring 2-1-3, and a vertical dynamic seal ring 2-1-4; the top end of the vertical loading rod 2-1-1 is fixed to the vertical servo hydraulic cylinder 2-1-2 by a connecting bolt 1-13, and its bottom end is connected to the upper platen 1-5; the vertical guide ring 2-1-3 and the vertical dynamic seal ring 2-1-4 act on the outer wall of the vertical loading rod 2-1-1 to achieve sealed sliding of the vertical loading rod 2-1-1 in the vertical direction; the vertical dynamic seal ring 2-1-4 can still ensure the effectiveness of sealing under a pressure of 35 MPa; the horizontal loading system 2-2 is located on the side wall of the single shear stress state shear box 1 and includes a horizontal loading rod 2-2-1, a horizontal servo hydraulic cylinder 2-2-2, a horizontal guide ring 2-2-3, and a horizontal dynamic seal ring 2-2-4. The left end of the horizontal loading rod 2-2-1 is fixed to the horizontal servo hydraulic cylinder 2-2-2 by a connecting bolt 1-13, and its right end is connected to the lower cover plate 1-9; the horizontal guide ring 2-2-3 and the horizontal dynamic seal ring 2-2-4 act on the outer wall of the horizontal loading rod 2-2-1 to achieve sealed sliding of the horizontal loading rod 2-2-1 in the horizontal direction; the horizontal dynamic seal ring 2-2-4 can still ensure the effectiveness of sealing under a pressure of 35 MPa;

[0009] The described in-situ hydrate formation-decomposition system 3 includes a hydrate gas tank 3-1, a pressure regulating valve 3-2, a degassed water volume controller 3-3, valve a 3-4, valve b 3-5, valve c 3-6, a drainage pipeline 3-7, a drainage valve 3-8, a pressure reducing valve 3-9, a gas flowmeter 3-10, and an exhaust pipeline 3-11; after passing through the pressure regulating valve 3-2 and valve c 3-6, the hydrate gas tank 3-1 is divided into two branches. One branch passes through valve b 3-5 and a gas-water pressure sensor 5-5 and then communicates with the gas-water hole on the lower platen 1-8, jointly providing hydrate gas for the synthesis of hydrate-bearing marine soil 1-11 with the hydrate gas tank 3-1 and providing the gas pressure required for hydrate synthesis. The other branch is connected to the inlet end of the degassed water volume controller 3-3 through valve a 3-4. After the synthesis of hydrate-bearing marine soil 1-11, the pressure regulating valve 3-2 and valve c 3-6 are closed. The degassed water volume controller 3-3, valve a 3-4, and valve b 3-5 work together for the gas displacement saturation of hydrate-bearing marine soil 1-11. The drainage valve 3-8 is connected to the channel hole on the upper platen 1-5 through the drainage pipeline 3-7, providing a channel for hydrate gas and degassed water during the gas displacement saturation of hydrate-bearing marine soil 1-11. The gas flowmeter 3-10 and the pressure reducing valve 3-9 are sequentially connected to the decomposed hydrate gas channel hole on the lower platen 1-8, providing a gas channel for the decomposition of hydrate-bearing marine soil 1-11 to generate hydrate gas by adjusting the temperature and pressure conditions inside the single shear stress state shear box 1, and quantitatively measuring the decomposition degree of hydrate-bearing marine soil 1-11 through the gas flowmeter 3-10; the above pipelines are all made of soft stainless steel pipelines; the degassed water volume controller 3-3 is a screw pump controlled by a microprocessor, which can accurately control and measure the fluid pressure and volume changes, and can provide a degassed water pressure of not less than 30 MPa;

[0010] The described temperature and pressure control system 4 mainly provides a suitable temperature and pressure environment for the synthesis of hydrate-bearing marine soil 1-11, including a water area device 4-1, a silicon oil cylinder 4-2, a confining pressure volume controller 4-3, valve d 4-4, valve e 4-5, and valve f 4-6; among them, the water area device 4-1 is hermetically connected to the water area jacket 1-4 through a soft stainless steel pipeline, and the two work together to achieve temperature control, providing temperature guarantee for the single shear stress state shear box 1; the silicon oil cylinder 4-2 and the confining pressure volume controller 4-3 are respectively connected to the confluence pipeline after passing through valve e 4-5 and valve f 4-6, and the confluence pipeline leads into the high-pressure cylinder 1-2. A confining pressure sensor 5-6 and valve d 4-4 are arranged on the confluence pipeline, providing pressure guarantee for the single shear stress state shear box 1; the confining pressure volume controller 4-3 is a screw pump controlled by a microprocessor, which can accurately control and measure the fluid pressure and volume changes, and can provide a confining pressure of not less than 35 MPa;

[0011] The described data acquisition and control system 5 includes various sensors, a data acquisition instrument, and a host computer, mainly realizing the automatic control and acquisition of the hydrate-containing marine soil single shear test device to ensure the reliability of test data. Specifically, a vertical displacement sensor 5-1 and a vertical force sensor 5-2 are fixed to the vertical loading rod 2-1-1 to monitor the vertical displacement and vertical force of the hydrate-containing marine soil 1-11 during the test; a horizontal displacement sensor 5-3 and a horizontal force sensor 5-4 are fixed to the horizontal loading rod 2-2-1 to monitor the horizontal displacement and horizontal force of the hydrate-containing marine soil 1-11 during the test; a gas-water pressure sensor 5-5 is used to monitor the pore pressure inside the hydrate-containing marine soil 1-11; a confining pressure sensor 5-6 is used to monitor the confining pressure inside the high-pressure cylinder 1-2; a temperature sensor 5-7 is fixed to the upper cover plate 1-1 as close as possible to the hydrate-containing marine soil 1-11 to monitor the temperature inside the high-pressure cylinder 1-2; these sensors are jointly connected to the data acquisition instrument 5-9 through a data acquisition line 5-8, and the test data is input into the host computer 5-10 after being converted by the signal of the data acquisition instrument 5-9, realizing the automatic acquisition and control of data.

[0012] Furthermore, the material of the high-pressure cylinder 1-2 is 7075 aviation aluminum alloy, and the upper cover plate 1-1 is made of 1-1316L stainless steel specially;

[0013] Furthermore, the lower pressing head 1-8 is provided with bolt holes, gas-water holes, and decomposed hydrate gas channel holes, the lower pressing head 1-8 is integrally cast, and the lower cover plate 1-9 is composed of a steel plate made of 316L stainless steel, bolt holes, and rollers;

[0014] Furthermore, a limit bolt 1-12 is arranged at the bottom of the high-pressure cylinder 1-2 to fix the displacement range of the lower cover plate 1-9, mainly to avoid excessive shear displacement of the lower cover plate 1-9 during the shearing process, causing test accidents such as sensor overlimit;

[0015] Furthermore, the hydrate gas in the hydrate gas tank 3-1 can be methane gas with a purity of 99.99%, carbon dioxide gas with a purity of 99.99%, or xenon gas with a purity of 99.99%;

[0016] Furthermore, the sensors can all be used in environments with high and low pressure differences (5 - 35000 kPa) and high and low temperature differences (-20 - 65 °C), and the measurement accuracy is ±0.1 %.

[0017] Furthermore, the data acquisition and control system 5 adopts two control methods: stress control and strain control. Among them, stress control uses the stress increment change rate as the control method, while strain control uses the displacement change rate as the control method.

[0018] A test method for a hydrate-containing marine soil single shear test device includes:

[0019] S1. Line connection: After the sensors in the data acquisition and control system 5 are connected to the corresponding pipelines, each sensor is connected to the data acquisition instrument 5-9 and the upper computer 5-10 in sequence. The digital control system is connected through the data acquisition control software in the upper computer 5-10, that is, the vertical loading system 2-1, the horizontal loading system 2-2, the air-free water volume controller 3-3, the water area device 4-1, and the confining pressure volume controller 4-3 are controlled by the upper computer 5-10. It should be noted that at this time, each system is controlled by displacement. The purpose of doing this is that displacement control is relatively stable and experimental accidents can be avoided. After ensuring that each system operates reliably, zero each sensor.

[0020] S2. Specimen preparation, installation and airtightness detection: Open the upper cover plate 1-1 of the single shear stress state shear box 1. After fixing the lower cover plate 1-9 with the limit bolt 1-12, fix the lower pressing head 1-8 on the lower cover plate 1-9 through the connecting bolt 1-13. Then, place the permeable stone 1-6 and dry filter paper on the lower pressing head 1-8 from bottom to top. Then, use the membrane cylinder to turn the reinforced rubber membrane 1-7 inside out and put it on the lower pressing head 1-8, and seal it with the O-ring 1-10. Use the compaction hammer to compact the matrix material of the hydrate-containing marine soil 1-11 prepared by weighing in layers in the membrane cylinder with the reinforced rubber membrane 1-7 inside to reach the designed porosity. Each layer is scraped with a metal wire to connect. Similarly, place dry filter paper and permeable stone 1-6 on the top of the matrix material of the hydrate-containing marine soil 1-11. Lower the upper pressing head 1-5 until it contacts the matrix material of the hydrate-containing marine soil 1-11, turn the reinforced rubber membrane 1-7 inside out and put it on the upper pressing head 1-5, and seal it with the O-ring 1-10. Connect the vacuum pump to the drain valve 3-8 and close all other valves. After starting the vacuum pump, open the drain valve 3-8 to pump out the air in the pipeline and the matrix material of the hydrate-containing marine soil 1-11. The extraction process lasts for 15 minutes. After that, let it stand for 30 minutes and observe the reading of the air-water pressure sensor 5-5. If it shows a negative pressure and the reading is relatively stable, it proves that the test airtightness is good and the test can be continued. If the airtightness is poor, the problems should be checked, such as air leakage of the reinforced rubber membrane 1-7, pipeline leakage, etc. After troubleshooting, repeat this step until the requirements are met and the test can be continued. The negative pressure environment is also beneficial to the self-standing of the specimen. Remove the membrane cylinder and adjust the limit bolt 1-12 to the appropriate position. Then, lower the upper cover plate 1-1 and fix it through the sealing bolt 1-3 to seal the high-pressure cylinder 1-2. Zero the sensor again to eliminate the disturbance to the sensor during the sample loading process and improve the accuracy of the test.

[0021] S3. Synthesis of hydrate-bearing marine soil: Open the valves d4-4 where the silicone oil cylinder 4-2 and the confining pressure volume controller 4-3 converge and connect to the internal pipeline of the high-pressure cylinder 1-2, the valve e4-5 that controls the confining pressure volume controller 4-3, and the valve f4-6 that controls the silicone oil cylinder 4-2 to inject silicone oil into the single shear stress state shear box 1. At the same time, adjust the confining pressure volume controller 4-3 to its maximum range. After filling, close the valve f4-6 that controls the silicone oil cylinder 4-2. Apply the set confining pressure (8000 kPa) to the displacement-controlled confining pressure volume controller 4-3; Open the water area device 4-1 and adjust the temperature to 2 °C. After the temperature stabilizes, close the valve a3-4, and successively open the pressure regulating valve 3-2 of the hydrate gas tank 3-1, the valve b3-5 where the hydrate gas tank 3-1 communicates with the gas-water hole on the lower platen 1-8, and the valve c3-6 on the pipeline between the pressure regulating valve 3-2 of the hydrate gas tank 3-1 and the valve a3-4 that controls the gas-free water volume controller 3-3 to provide the required hydrate gas (methane gas with a purity of 99.99% or carbon dioxide gas with a purity of 99.99% or xenon gas with a purity of 99.99%) and the designed pore pressure (790 kPa) for the hydrate-bearing marine soil 1-11. It should be noted that the reading of the gas-water pressure sensor 5-5 should always be less than that of the confining pressure sensor 5-6. Finally, the reading of the gas-water pressure sensor 5-5 is 790 kPa, and the reading of the confining pressure sensor 5-6 is 800 kPa. Then close the valve b3-5. The temperature and pressure conditions at this time satisfy the formation of methane hydrate solids inside the hydrate-bearing marine soil 1-11. When the reading of the gas-water pressure sensor 5-5 stabilizes, it is considered that the formation of the hydrate-bearing marine soil 1-11 is completed. Record the termination air pressure and use the gas consumption method to determine the true hydrate saturation of the hydrate-bearing marine soil 1-11.

[0022] S4. Saturation and consolidation of hydrate-bearing marine soil specimens: After the hydrate formation of the hydrate-bearing marine soil 1-11 is completed, it is necessary to expel the hydrate gas in the specimen with nitrogen to prevent the excess hydrate gas and the gas-free water during the water saturation process from forming hydrates again under stable temperature and pressure conditions. Adjust the gas-free water pressure of the gas-free water volume controller 3-3 to the pore pressure inside the hydrate-bearing marine soil 1-11. Open the valve a3-4 and the valve b3-5. After the reading of the gas-water pressure sensor 5-5 stabilizes, open the drain valve 3-8 a little at a time for multiple times until the gas-free water that is 3 times the pore volume inside the hydrate-bearing marine soil 1-11 appears. Then it is considered that the hydrate-bearing marine soil 1-11 is a water-saturated specimen.

[0023] According to the specific experimental conditions, adjust the pressure control of the confining pressure volume controller 4-3 to the target value, and consolidate the hydrate-bearing marine soil 1-11 under this state. When the vertical displacement of the hydrate-bearing marine soil 1-11 is less than 0.05 % / min, it is considered that the consolidation is completed and the test can continue.

[0024] S5. Static mechanical tests of hydrate-bearing marine soil under single shear stress state: During the test, the temperature in the shear box 1 under the single shear stress state is maintained constant to ensure that the hydrate does not decompose during the static shear process. After the pressure of the vertical loading system 2-1 is controlled to the designed value, the upper computer 5-10 is used to adjust the test static single shear program to control the horizontal servo hydraulic cylinder 2-2-2 to apply horizontal shear stress, and the horizontal shear stress acts on the hydrate-bearing marine soil 1-11 through the horizontal loading rod 2-2-1 until the shear strain of the hydrate-bearing marine soil 1-11 reaches 20% of the diameter of the hydrate-bearing marine soil 1-11, then the test is stopped.

[0025] S6. After the test is completed, turn off the water area device 4-1, and sequentially remove the pressure inside the shear box 1 under the single shear stress state through the degassed water volume controller 3-3 and the confining pressure volume controller 4-3. It should be noted that the reading of the gas-water pressure sensor 5-5 inside the hydrate-bearing marine soil 1-11 should always be less than the reading of the confining pressure sensor 5-6 to avoid bursting of the reinforced rubber membrane 1-7 and polluting the confining pressure fluid. When the reading of the confining pressure sensor 5-6 is less than 100 kPa, open the valve d4-4 and the valve f4-6 to drain all the silicone oil inside the shear box 1 under the single shear stress state. Open the shear box 1 under the single shear stress state, sequentially remove the specimens, and clean the test bench. After closing each system through the upper computer 5-10, exit the software and turn off the upper computer 5-10, and save and process the test data.

[0026] Through the above test methods, the static mechanical test and dynamic mechanical test of hydrate-bearing marine soil under single shear stress state can be realized.

[0027] Preferably, in step S5, adjust the test program to a dynamic single shear program, and the dynamic mechanical test of hydrate-bearing marine soil under single shear stress state can be realized.

[0028] Preferably, replace the upper platen 1-5 and the lower platen 1-8 with a bending element upper platen and a bending element lower platen with a bending element device respectively, and the bending element test of hydrate-bearing marine soil under single shear stress state can be realized, and the shear modulus and damping ratio parameters of hydrate-bearing marine soil under single shear stress state can be obtained.

[0029] Use the temperature and pressure control system to adjust the temperature and pressure conditions inside the shear box 1 under the single shear stress state, so as to realize the static mechanical test and dynamic mechanical test of hydrate-bearing marine soil under single shear stress state under different decomposition modes / decomposition times / decomposition gradients.

[0030] Preferably, the hydrate gas tank 3-1 can be replaced with methane gas with a purity of 99.99%, carbon dioxide gas with a purity of 99.99%, xenon gas with a purity of 99.99%, or hydrogen gas with a purity of 99.99%, so as to realize marine soil containing methane hydrate, marine soil containing carbon dioxide hydrate, marine soil containing xenon hydrate, and marine soil containing hydrogen hydrate. In short, the present invention can achieve the macroscopic mechanical properties of the occurrence sediments of the phase change resources in porous media under the single shear state.

[0031] Advantages of the present invention:

[0032] (1) Innovatively develop the first set of single shear test device for hydrate-containing marine soil, filling the domestic and foreign research and development gaps of single shear test devices for hydrate-containing marine soil, improving the realization of the single shear test method for hydrate-containing marine soil, and truly simulating the mechanical response characteristics of hydrate-containing marine soil under complex stress states. The instrument is easy to operate, and the test method is systematic and simple.

[0033] (2) Use a reinforced rubber membrane to replace the shear ring required for traditional indoor single shear tests. While having the function of a shear ring, the reinforced rubber membrane avoids the influence of the expansion or contraction of the shear ring caused by changes in the temperature and pressure conditions of the synthetic hydrate-containing marine soil, improving the reliability of the results.

[0034] (3) Can accurately characterize the static and dynamic mechanical behaviors of hydrate-containing marine soil under the single shear stress state; can use the special upper and lower pressing heads of the bending element to realize the real-time measurement of the shear modulus of hydrate-containing marine soil under the single shear stress state; can use the temperature and pressure control system to adjust the temperature and pressure conditions inside the shear box under the single shear stress state, so as to realize the static and dynamic mechanical tests of hydrate-containing marine soil under the single shear stress state under different decomposition methods / decomposition times / decomposition gradients. It has the remarkable characteristics of multi-function and strong comprehensiveness, providing hardware support for ensuring the reliable design and operation of offshore facilities such as offshore platforms and the commercial exploitation of phase change resources in porous media such as future hydrates in China. Description of the drawings

[0035] Figure 1 is a schematic structural diagram of the shear box under the single shear stress state described in the present invention;

[0036] Figure 2 is a schematic diagram of the structural details of a single shear test device for hydrate-containing marine soil described in the present invention;

[0037] Figure 3 is a schematic diagram of the true overall system of a single shear test device for hydrate-containing marine soil described in the present invention;

[0038] Figure 4 is a schematic structural diagram of the vertical loading system described in the present invention;

[0039] Figure 5 It is a schematic diagram for comparing the test results of Example 1 obtained by a single-shear test device for hydrate-bearing marine soil described in the present invention with the results obtained by a traditional triaxial test for hydrate-bearing marine soil.

[0040] Figure 6 It is a schematic structural diagram of the horizontal loading system described in the present invention. In the figure: 1 single-shear stress state shear box; 2 multi-directional servo loading system; 3 in-situ hydrate generation-decomposition system; 4 temperature and pressure control system; 5 data acquisition and control system; 1-1 upper cover plate; 1-2 high-pressure cylinder; 1-3 sealing bolt; 1-4 water jacket; 1-5 upper pressure head; 1-6 permeable stone; 1-7 reinforced rubber membrane; 1-8 lower pressure head; 1-9 lower cover plate; 1-10 O-ring seal; 1-11 hydrate-bearing marine soil; 1-12 limit bolt; 1-13 connecting bolt; 2-1 vertical loading system; 2-2 horizontal loading system; 2-1-1 vertical loading rod; 2-1-2 vertical servo hydraulic cylinder; 2-1-3 vertical guide ring; 2-1-4 vertical dynamic seal ring; 2-2-1 horizontal loading rod; 2-2-2 horizontal servo hydraulic cylinder; 2-2-3 horizontal guide ring; 2-2-4 horizontal dynamic seal ring; 3-1 hydrate gas tank; 3-2 pressure regulating valve; 3-3 degassed water volume controller; 3-4 valve a; 3-5 valve b; 3-6 valve c; 3-7 drainage pipeline; 3-8 drain valve; 3-9 pressure reducing valve; 3-10 gas flowmeter; 3-11 exhaust pipeline; 4-1 water area device; 4-2 silicon oil cylinder; 4-3 confining pressure volume controller; 4-4 valve d; 4-5 valve e; 4-6 valve f; 5-1 vertical displacement sensor; 5-2 vertical force sensor; 5-3 horizontal displacement sensor; 5-4 horizontal force sensor; 5-5 gas-water pressure sensor; 5-6 confining pressure sensor; 5-7 temperature sensor; 5-8 data acquisition; 5-9 data acquisition instrument; 5-10 upper computer. Specific embodiments

[0041] The following further describes the specific embodiments of the present invention in combination with the accompanying drawings and technical solutions.

[0042] A single-shear test device for hydrate-bearing marine soil includes:

[0043] As Figure 1As shown in the figure, the single-shear stress state shear box 1 includes an upper cover plate 1-1, a high-pressure cylinder 1-2, a sealing bolt 1-3, an upper pressing head 1-5, a permeable stone 1-6, a reinforced rubber membrane 1-7, a lower pressing head 1-8, a lower cover plate 1-9, an O-ring 1-10, hydrate-containing marine soil 1-11, a limit bolt 1-12, and a connecting bolt 1-13. The high-pressure cylinder 1-2 and the upper cover plate 1-1 are hermetically connected by the sealing bolt 1-3, which can ensure the effective sealing of the single-shear stress state shear box 1 within the pressure range of 5 - 35000 kPa; the material of the high-pressure cylinder 1-2 is 7075 aviation aluminum alloy, the material of the upper cover plate 1-1 is made of 316L stainless steel, and the sealing bolt 1-3 is made of tungsten steel with high strength and hardness; a water jacket 1-4 is arranged inside the side wall of the high-pressure cylinder 1-2, and the inside is designed with spiral lines to ensure the rapid heat exchange of the single-shear stress state shear box 1. The upper pressing head 1-5 made of 316L stainless steel, the permeable stone 1-6, the reinforced rubber membrane 1-7, the lower pressing head 1-8 made of 316L stainless steel, and the O-ring 1-10 provide support for the hydrate-containing marine soil 1-11. Specifically, open the upper cover plate 1-1 of the single-shear stress state shear box 1, fix the lower cover plate 1-9 with the limit bolt 1-12, then fix the lower pressing head 1-8 on the lower cover plate 1-9 through the connecting bolt 1-13. After placing the permeable stone 1-6 and dry filter paper on the lower pressing head 1-8 from bottom to top in sequence, use a membrane support cylinder to turn the reinforced rubber membrane 1-7 inside out over the lower pressing head 1-8 and seal it with the O-ring 1-10; use a compaction hammer to compact the matrix material of the prepared hydrate-containing marine soil 1-11 in layers inside the membrane support cylinder with the reinforced rubber membrane 1-7 to reach the designed porosity, and scratch each layer with metal wire for connection; also place dry filter paper and the permeable stone 1-6 on the top of the matrix material of the hydrate-containing marine soil 1-11, lower the upper pressing head 1-5 until it contacts the hydrate-containing marine soil 1-11, turn the reinforced rubber membrane 1-7 inside out over the upper pressing head 1-5 and seal it with the O-ring 1-10;

[0044] As Figure 2As shown, the multi-directional servo loading system 2 includes a vertical loading system 2-1 and a horizontal loading system 2-2. Further, the connecting bolts 1-13 fix the upper and lower ends of the vertically loading rod 2-1-1, which is a cylindrical structure made of special 316L stainless steel, to the upper pressure head 1-5 and the vertical servo hydraulic cylinder 2-1-2 respectively. The vertical guide ring 2-1-3 and the vertical dynamic seal ring 2-1-4 act together on the outer wall of the vertically loading rod 2-1-1 to achieve the sealed sliding of the vertically loading rod 2-1-1 in the vertical direction; the horizontal loading system 2-2 is located on the side wall of the single shear stress state shear box 1. The connecting bolts 1-13 fix the left and right ends of the horizontally loading rod 2-2-1, which is a cylindrical structure made of 316L stainless steel, to the lower cover plate 1-9 and the horizontal servo hydraulic cylinder 2-2-2 respectively. The horizontal guide ring 2-2-3 and the horizontal dynamic seal ring 2-2-4 act together on the outer wall of the horizontally loading rod 2-2-1 to achieve the sealed sliding of the horizontally loading rod 2-2-1 in the vertical direction; preferably, the vertical dynamic seal ring 2-1-4 and the horizontal dynamic seal ring 2-2-4 can still ensure the sealing effectiveness of the vertical loading system 2-1 under a pressure of 30 MPa.

[0045] The in-situ hydrate formation-decomposition system 3 includes a hydrate gas tank 3-1, a pressure regulating valve 3-2, a gas-free water volume controller 3-3, valve a 3-4, valve b 3-5, valve c 3-6, a drainage pipeline 3-7, a drainage valve 3-8, a pressure reducing valve 3-9, a gas flowmeter 3-10, and an exhaust pipeline 3-11. Among them, after passing through the pressure regulating valve 3-2 and valve c 3-6, the hydrate gas tank 3-1 is divided into two branches. One branch passes through valve b 3-5 and a gas-water pressure sensor 5-5 and then communicates with the gas-water hole on the lower platen 1-8, jointly providing hydrate gas for the synthesis of hydrate-containing marine soil 1-11 with the hydrate gas tank 3-1 and providing the gas pressure required for hydrate synthesis. The other branch is connected to the inlet end of the gas-free water volume controller 3-3 through valve a 3-4. After the synthesis of hydrate-containing marine soil 1-11, the gas-free water volume controller 3-3, valve a 3-4, and valve b 3-5 work together for the gas displacement saturation of hydrate-containing marine soil 1-11. The drainage valve 3-8 is connected to the channel hole on the upper platen 1-5 through the drainage pipeline 3-7, providing a channel for hydrate gas and gas-free water during the gas displacement saturation process of hydrate-containing marine soil 1-11. The above pipelines are all made of soft stainless steel. The gas-free water volume controller 3-3 is a screw pump controlled by a microprocessor, which can accurately control and measure fluid pressure and volume changes and can provide a gas-free water pressure of not less than 35 MPa. The pressure reducing valve 3-9 and the gas flowmeter 3-10 are sequentially connected to the decomposed hydrate gas channel hole on the lower platen 1-8. Specifically, the gas-free water volume controller 3-3, valve a 3-4, and drainage valve 3-8 work together to provide technical support for the water saturation process of hydrate-containing marine soil 1-11. The gas-free water volume controller 3-3 is a screw pump controlled by a microprocessor, which can accurately control and measure fluid pressure and volume changes and can provide a gas-free water pressure of not less than 30 MPa.

[0046] The temperature and pressure control system 4 mainly provides a suitable temperature and pressure environment for the synthesis of hydrate-containing marine soil 1-11, including a water area device 4-1, a silicon oil cylinder 4-2, a confining pressure volume controller 4-3, valve d 4-4, valve e 4-5, and valve f 4-6. Among them, the water area device 4-1 is hermetically connected to the water area jacket 1-4 through a soft stainless steel pipeline, and the two work together to achieve temperature control, providing temperature guarantee for the single shear stress state shear box 1. The silicon oil cylinder 4-2 and the confining pressure volume controller 4-3 are respectively connected to the confluence pipeline after passing through valve e 4-5 and valve f 4-6. The confluence pipeline leads into the high-pressure cylinder 1-2. A confining pressure sensor 5-6 and valve d 4-4 are arranged on the confluence pipeline, providing pressure guarantee for the single shear stress state shear box 1. The confining pressure volume controller 4-3 is a screw pump controlled by a microprocessor, which can accurately control and measure fluid pressure and volume changes and can provide a confining pressure of not less than 35 MPa.

[0047] The data acquisition and control system 5 includes various sensors, a data collector, and a host computer, mainly realizing the automatic control and acquisition of the hydrate-containing marine soil single shear test device to ensure the reliability of test data. Specifically, the vertical displacement sensor 5-1 and the vertical force sensor 5-2 are fixed on the vertical loading rod 2-1-1 to monitor the vertical displacement and vertical force of the hydrate-containing marine soil 1-11 during the test; the horizontal displacement sensor 5-3 and the horizontal force sensor 5-4 are fixed on the horizontal loading rod 2-2-1 to monitor the horizontal displacement and horizontal force of the hydrate-containing marine soil 1-11 during the test; the gas-water pressure sensor 5-5 is located on the branch connecting the hydrate gas tank 3-1 and the gas-water hole on the lower platen 1-8 to monitor the pore pressure inside the hydrate-containing marine soil 1-11, and the confining pressure sensor 5-6 is located on the confluence pipeline of the silicon oil cylinder 4-2 and the confining pressure volume controller 4-3 to monitor the confining pressure inside the high-pressure cylinder 1-2; the temperature sensor 5-7 is fixed on the upper cover plate 1-1 as close as possible to the hydrate-containing marine soil 1-11 to monitor the temperature inside the high-pressure cylinder 1-2; these sensors are jointly connected to the data collector 5-9 through the data acquisition line 5-8, and the test data is input into the host computer 5-10 after being converted by the signal of the data collector 5-9 to realize the automatic acquisition and control of data. All control systems can be manually or automatically controlled by a computer. Preferably, the sensors can be used in an environment with high and low pressure differences (5 - 35000 kPa) and high and low temperature differences (-20 - 65 °C), and the measurement accuracy is ±0.1 %. Preferably, the data acquisition and control system 5 of the instrument adopts two control methods: stress control and strain control. Among them, stress control uses the stress increment change rate as the control method, while strain control uses the displacement change rate as the control method.

[0048] Example 1

[0049] A test method for a hydrate-containing marine soil single shear test device, specifically a method description for static and dynamic mechanical tests under the single shear stress state of hydrate-containing marine soil, includes the following steps:

[0050] S1. Line connection: After ensuring that all pipelines and sensors are reliably connected, connect the data collector 5-9 and the host computer 5-10 in sequence. After logging in to the data acquisition control software, connect the digital control system, and then the operation of the vertical loading system 2-1, the horizontal loading system 2-2, the gas-free water volume controller 3-3, the water area device 4-1, and the confining pressure volume controller 4-3 can be controlled through the host computer 5-10. It should be noted that at this time, each system is controlled by displacement. The purpose of doing this is that displacement control is more stable and can avoid test accidents. After ensuring that each system runs reliably, zero each sensor.

[0051] S2. Specimen preparation, installation and airtightness detection: Open the upper cover plate 1-1 of the single shear stress state shear box 1. After fixing the lower cover plate 1-9 with the limit bolt 1-12, fix the lower pressure head 1-8 to the lower cover plate 1-9 through the connecting bolt 1-13. Then, place the dried permeable stone 1-6 and dry filter paper of appropriate size in sequence. Use the film bearing cylinder to turn the reinforced rubber membrane 1-7 over the lower pressure head 1-8 and seal it with the O-ring 1-10. Use the compaction hammer to compact the matrix material of the hydrate-containing marine soil 1-11 prepared by weighing in layers to achieve the target porosity, and scrape the surface with metal wire for each layer for connection. Similarly, place the dried permeable stone 1-6 and dry filter paper of appropriate size on the top of the matrix material. Lower the upper pressure head 1-5 until it contacts the matrix material, turn the reinforced rubber membrane 1-7 over the upper pressure head 1-5 and seal it with the O-ring 1-10.

[0052] Connect the vacuum pump to the drain valve 3-8 and close all other valves. After starting the vacuum pump, connect and open the drain valve 3-8 to evacuate the air in the pipeline and the specimen. The extraction process lasts for 15 minutes. After that, let it stand for 30 minutes and observe the reading of the air-water pressure sensor 5-5. If it shows a negative pressure and the reading is relatively stable, it proves that the test airtightness is good and the test can be continued; if the airtightness is poor, problems should be checked, such as air leakage of the reinforced rubber membrane 1-7 and pipeline air leakage, etc. After troubleshooting, repeat this step until the requirements are met and the test can be continued. Remove the film bearing cylinder and adjust the limit bolt 1-12 to an appropriate position. Then, lower the upper cover plate 1-1 and fix it through the sealing bolt 1-3 to seal the high-pressure cylinder 1-2. Zero the sensor again to eliminate the disturbance to the sensor during the sample loading process and improve the accuracy of the test.

[0053] S3. Synthesis of hydrate-bearing marine soil: Open valves d4-4, e4-5, and f4-6 to inject silicone oil into the single shear stress state shear box 1. At the same time, adjust the confining pressure volume controller 4-3 to its maximum range. After filling, close valve f4-6. Apply the designed confining pressure (8000 kPa) by controlling the displacement of the confining pressure volume controller 4-3 to ensure that the silicone oil fills the single shear stress state shear box 1. Open the water area device 4-1 and adjust the temperature to 2 °C. After the temperature stabilizes, close valve a3-4, and then open the pressure regulating valve 3-2, valve b3-5, and valve c3-6 in sequence to provide the required hydrate gas (methane gas with a purity of 99.99% or carbon dioxide gas with a purity of 99.99% or xenon gas with a purity of 99.99%) and a pore pressure of 7900 kPa for the hydrate-bearing marine soil 1-11. It should be noted that the reading of the gas-water pressure sensor 5-5 should always be less than that of the confining pressure sensor 5-6. Finally, the reading of the gas-water pressure sensor 5-5 is 7900 kPa, and the reading of the confining pressure sensor 5-6 is 8000 kPa. Then close valve b3-5. The current temperature and pressure conditions (temperature 2 °C, pore pressure 7900 kPa) are suitable for the formation of hydrate solids inside the hydrate-bearing marine soil 1-11. When the reading of the gas-water pressure sensor 5-5 stabilizes, it is considered that the hydrate-bearing marine soil 1-11 is formed. Record the final gas pressure, and use the gas consumption method to determine the true hydrate saturation of the hydrate-bearing marine soil 1-11.

[0054] S4. Saturation and consolidation of hydrate-bearing marine soil specimens: After the hydrate formation of the hydrate-bearing marine soil 1-11 is completed, nitrogen gas is needed to expel the hydrate gas in the specimen to prevent the excess hydrate gas from reacting with the gas-free water during the water saturation process to form hydrates again under stable temperature and pressure conditions. Adjust the gas-free water pressure of the gas-free water volume controller 3-3 to the pore pressure inside the hydrate-bearing marine soil 1-11. Open valves a3-4 and b3-5. After the reading of the gas-water pressure sensor 5-5 stabilizes, open the drain valve 3-8 in small amounts multiple times until the amount of gas-free water is three times the pore volume of the hydrate-bearing marine soil 1-11, then the hydrate-bearing marine soil 1-11 is considered a water-saturated specimen. According to the specific experimental conditions, adjust the force control of the confining pressure volume controller 4-3 to the designed target value, and consolidate the hydrate-bearing marine soil 1-11 under this state. When the vertical displacement of the hydrate-bearing marine soil 1-11 is less than 0.05 % / min, it is considered that the consolidation is completed, and the test can continue.

[0055] S5. Static mechanical tests of hydrate-bearing marine soil under single shear stress state: During the test, the temperature in the pressure chamber was maintained constant to ensure that the hydrate did not decompose during the shearing process. Taking the static single shear test of hydrate-bearing marine soil as an example, after the pressure of the vertical loading system 2-1 was controlled to the designed value, the upper computer 5-10 was used to adjust the test static single shear program to control the horizontal servo hydraulic cylinder 2-2-2 to apply horizontal shear stress, and it acted on the hydrate-bearing marine soil 1-11 through the horizontal loading rod 2-2-1 until the horizontal shear strain of the hydrate-bearing marine soil 1-11 reached 20% of the diameter of the hydrate-bearing marine soil 1-11, and then the test was stopped.

[0056] S6. After the test was completed, the water area device 4-1 was closed, and the pressure inside the single shear stress state shear box 1 was removed successively through the degassed water volume controller 3-3 and the confining pressure volume controller 4-3. It should be noted that the reading of the gas-water pressure sensor 5-5 inside the hydrate-bearing marine soil 1-11 should always be less than the reading of the confining pressure sensor 5-6 to avoid bursting of the reinforced rubber membrane 1-7 and polluting the confining pressure liquid. When the reading of the confining pressure sensor 5-6 was less than 100 kPa, the valve d4-4 and the valve f4-6 were opened to drain all the silicone oil inside the single shear stress state shear box 1. The single shear stress state shear box 1 was opened, and the specimens were removed successively and the test bench was cleaned. After closing each system through the upper computer 5-10, the software was exited and the upper computer 5-10 was shut down, and the test data was saved and processed.

[0057] Through the above test methods, the static mechanical test and the dynamic mechanical test of the hydrate-bearing marine soil in Example 1 under the single shear stress state can be realized.

[0058] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An apparatus for single shear test of hydrate-containing marine soil, characterized in that, The hydrate-bearing marine soil simple shear test device includes a simple shear stress state shear box (1), a multi-directional servo loading system (2), a hydrate in-situ generation-decomposition system (3), a temperature and pressure control system (4), and a data acquisition and control system (5); The simple shear stress state shear box (1) includes an upper cover plate (1-1), a high-pressure cylinder (1-2), a water jacket (1-4), an upper pressure head (1-5), a permeable stone (1-6), a reinforced rubber membrane (1-7), a lower pressure head (1-8), a lower cover plate (1-9), an O-ring (1-10), and hydrate-bearing marine soil (1-11); among them, the high-pressure cylinder (1-2) is hermetically connected to the upper cover plate (1-1); a water jacket (1-4) is arranged inside the side wall of the high-pressure cylinder (1-2); the lower cover plate (1-9) is located at the bottom of the high-pressure cylinder (1-2); the lower pressure head (1-8) is fixed on the lower cover plate (1-9), a permeable stone (1-6) and a dry filter paper are sequentially placed on the lower pressure head (1-8), the reinforced rubber membrane (1-7) propped open by a membrane cylinder is reversely sleeved on the lower pressure head (1-8), the matrix material of the hydrate-bearing marine soil (1-11) is filled in layers in the membrane cylinder, after filling is completed, a dry filter paper and a permeable stone (1-6) are sequentially placed on the matrix material, an upper pressure head (1-5) is placed on the permeable stone (1-6), and the reinforced rubber membrane (1-7) is reversely sleeved on the upper pressure head (1-5); The multi-directional servo loading system (2) includes a vertical loading system (2-1) and a horizontal loading system (2-2); the vertical loading system (2-1) is located at the upper end of the simple shear stress state shear box (1) and is connected to the upper pressure head (1-5) to realize the vertical movement of the upper pressure head (1-5); the horizontal loading system (2-2) is located on the side wall of the simple shear stress state shear box (1) and is connected to the lower cover plate (1-9) to realize the horizontal movement of the lower cover plate (1-9); The hydrate in-situ generation-decomposition system (3) includes a hydrate gas tank (3-1), a pressure regulating valve (3-2), a degassed water volume controller (3-3), valves, a drainage pipeline (3-7), a drainage valve (3-8), a pressure reducing valve (3-9), a gas flowmeter (3-10), and an exhaust pipeline (3-11); the hydrate gas tank (3-1) is divided into two branches after passing through the pressure regulating valve (3-2) and valve c (3-6), one branch passes through valve b (3-5) and a gas-water pressure sensor (5-5) and then communicates with the gas-water hole on the lower pressure head (1-8); the other branch passes through valve a (3-4) and is connected to the inlet end of the degassed water volume controller (3-3); the drainage valve (3-8) is connected to the channel hole on the upper pressure head (1-5) through the drainage pipeline (3-7); the exhaust pipeline (3-11) is connected to the decomposed hydrate gas channel hole on the lower pressure head (1-8), and a gas flowmeter (3-10) and a pressure reducing valve (3-9) are sequentially arranged on it, and the decomposition amount of the hydrate-bearing marine soil (1-11) is quantified through the gas flowmeter (3-10); The described temperature and pressure control system (4) mainly provides a suitable temperature and pressure environment for the synthetic hydrate-containing marine soil (1-11), and includes a water area device (4-1), a silicon oil cylinder (4-2), a confining pressure volume controller (4-3) and valves; among them, the water area device (4-1) is hermetically connected to the water area jacket (1-4); the silicon oil cylinder (4-2) and the confining pressure volume controller (4-3) are respectively joined after the pipelines pass through valve e (4-5) and valve f (4-6), and the joined pipeline leads into the inside of the high-pressure cylinder (1-2). A confining pressure sensor (5-6) and a valve d (4-4) are arranged on the joined pipeline to provide pressure guarantee for the single shear stress state shear box (1). The described data acquisition and control system (5) includes sensors, a data acquisition instrument and a host computer. The sensors are jointly connected to the data acquisition instrument (5-9) through data acquisition lines (5-8). The test data is input into the host computer (5-10) after being converted by the signals of the data acquisition instrument (5-9), mainly realizing the automatic acquisition and control of the hydrate-containing marine soil single shear test device.

2. The single shear test device for hydrate-containing marine soil according to claim 1, characterized in that The described vertical loading system (2-1) includes a vertical loading rod (2-1-1) with a cylindrical structure, a vertical servo hydraulic cylinder (2-1-2), a vertical guide ring (2-1-3) and a vertical dynamic seal ring (2-1-4); the top end of the vertical loading rod (2-1-1) is fixed on the vertical servo hydraulic cylinder (2-1-2), and its bottom end is connected to the upper pressure head (1-5); the vertical guide ring (2-1-3) and the vertical dynamic seal ring (2-1-4) act on the outer wall of the vertical loading rod (2-1-1) to realize the sealed sliding of the vertical loading rod (2-1-1) in the vertical direction. The described horizontal loading system (2-2) includes a horizontal loading rod (2-2-1), a horizontal servo hydraulic cylinder (2-2-2), a horizontal guide ring (2-2-3) and a horizontal dynamic seal ring (2-2-4). The left end of the horizontal loading rod (2-2-1) is fixed on the horizontal servo hydraulic cylinder (2-2-2), and its right end is connected to the lower cover plate (1-9); the horizontal guide ring (2-2-3) and the horizontal dynamic seal ring (2-2-4) act on the outer wall of the horizontal loading rod (2-2-1) to realize the sealed sliding of the horizontal loading rod (2-2-1) in the horizontal direction.

3. The single shear test device for hydrate-containing marine soil according to claim 2, characterized in that The sensors include a vertical displacement sensor (5-1), a vertical force sensor (5-2), a horizontal displacement sensor (5-3), a horizontal force sensor (5-4), a gas-water pressure sensor (5-5), a confining pressure sensor (5-6) and a temperature sensor (5-7); the vertical displacement sensor (5-1) and the vertical force sensor (5-2) are fixed on the vertical loading rod (2-1-1) for monitoring the vertical displacement and vertical force of the hydrate-bearing marine soil (1-11) during the test; the horizontal displacement sensor (5-3) and the horizontal force sensor (5-4) are fixed on the horizontal loading rod (2-2-1) for monitoring the horizontal displacement and horizontal force of the hydrate-bearing marine soil (1-11) during the test; the gas-water pressure sensor (5-5) is used for monitoring the pore pressure inside the hydrate-bearing marine soil (1-11); the confining pressure sensor (5-6) is used for monitoring the confining pressure inside the high-pressure cylinder (1-2); the temperature sensor (5-7) is fixed on the upper cover plate (1-1) as close as possible to the hydrate-bearing marine soil (1-11) for monitoring the temperature inside the high-pressure cylinder (1-2).

4. The hydrate-bearing marine soil simple shear test device according to claim 3, wherein, The simple shear stress state shear box (1) further includes a limit bolt (1-12), which is installed at the bottom of the high-pressure cylinder (1-2) to mainly prevent the shear displacement of the lower cover plate (1-9) from being too large during the shear process.

5. The hydrate-bearing marine soil simple shear test device according to claim 4, wherein, An O-ring seal (1-10) is used for sealing between the lower pressure head (1-8) and the reinforced rubber membrane (1-7), and between the reinforced rubber membrane (1-7) and the upper pressure head (1-5).

6. A testing method for the hydrate-bearing marine soil simple shear testing device according to claim 5, characterized in that, The steps are as follows: S1. Circuit connection: Connect each sensor to the data acquisition instrument (5-9) and the upper computer (5-10) in sequence, and control the operation of the vertical loading system (2-1), the horizontal loading system (2-2), the gas-water-free volume controller (3-3), the water area device (4-1) and the confining pressure volume controller (4-3) through the upper computer (5-10); S2. Specimen preparation, installation and airtightness detection: Open the upper cover plate (1-1) of the single shear stress state shear box (1). After fixing the lower cover plate (1-9) with the limit bolt (1-12), fix the lower pressing head (1-8) on the lower cover plate (1-9). After placing the permeable stone (1-6) and dry filter paper on the lower pressing head (1-8) in sequence, use the film-bearing cylinder to turn the reinforced rubber membrane (1-7) over the lower pressing head (1-8) and seal it with an O-ring (1-10); Use a compaction hammer to compact the matrix material of the hydrate-containing marine soil (1-11) in layers in the film-bearing cylinder with the reinforced rubber membrane (1-7) to reach the designed porosity, and each layer of the matrix material of the hydrate-containing marine soil (1-11) is scraped and connected with metal wire; Similarly, place dry filter paper and permeable stone (1-6) on the top of the matrix material of the hydrate-containing marine soil (1-11), then lower the upper pressing head (1-5) until it contacts the matrix material of the hydrate-containing marine soil (1-11), turn the reinforced rubber membrane (1-7) over the upper pressing head (1-5) and seal it with an O-ring (1-10); Connect the vacuum pump to the drain valve (3-8) and close all other valves. After starting the vacuum pump, open the drain valve (3-8) to pump out the air in the pipeline and the matrix material of the hydrate-containing marine soil (1-11); The pumping process lasts for 15 minutes. After that, let it stand for 30 minutes, observe the reading of the gas-water pressure sensor (5-5) to ensure that it shows a negative pressure and the reading is relatively stable, and then continue the test; Remove the film-bearing cylinder and adjust the limit bolt (1-12) to the appropriate position; Subsequently, fix and seal the upper cover plate (1-1) on the high-pressure cylinder (1-2) and zero the sensor again; S3. Synthesis of hydrate-containing marine soil: Open valve d (4-4), valve e (4-5) and valve f (4-6) to inject silicone oil into the single shear stress state shear box (1). At the same time, adjust the confining pressure volume controller (4-3) to the maximum range. After filling with silicone oil, close valve f (4-6); Set the confining pressure of the confining pressure volume controller (4-3); Open the water circulation 4-1 and adjust the temperature to 2 °C. After the temperature is stable, close valve a (3-4), and then open the pressure regulating valve (3-2), valve b (3-5) and valve c (3-6) in sequence to provide the required hydrate gas and designed pore pressure for the hydrate-containing marine soil (1-11); During the process, ensure that the reading of the gas-water pressure sensor (5-5) is less than that of the confining pressure sensor (5-6), and close valve b (3-5); When the reading of the gas-water pressure sensor (5-5) is stable, the hydrate-containing marine soil (1-11) is generated. Record the final gas pressure and use the gas consumption method to determine the true hydrate saturation of the hydrate-containing marine soil (1-11); S4. Saturation and consolidation of hydrate-bearing marine soil specimens: After the hydrate formation is completed, nitrogen gas needs to be used to expel the hydrate gas; adjust the gas-free water pressure of the gas-free water volume controller (3-3) to the pore pressure inside the hydrate-bearing marine soil (1-11), open valve a (3-4) and valve b (3-5), and after the readings of the gas-water pressure sensor (5-5) are stable, open the drain valve (3-8) until the volume of gas-free water is three times the pore volume inside the hydrate-bearing marine soil (1-11), then the hydrate-bearing marine soil (1-11) is considered a water-saturated specimen; adjust the pressure of the confining pressure volume controller (4-3) to the target value, and consolidate the hydrate-bearing marine soil (1-11) under this condition. When the vertical displacement of the hydrate-bearing marine soil (1-11) is less than 0.05% / min, it is considered that the consolidation is completed and the test can continue; S5. Static mechanical test of hydrate-bearing marine soil under single shear stress state: During the test, maintain the temperature inside the shear box (1) under the single shear stress state constant to ensure that the hydrate does not decompose during the static shear process; after keeping the pressure of the vertical loading system (2-1) controlled to the design value, use the upper computer (5-10) to control the horizontal servo hydraulic cylinder (2-2-2) to apply horizontal shear stress, and act on the hydrate-bearing marine soil (1-11) through the horizontal loading rod (2-2-1) until the horizontal shear strain of the hydrate-bearing marine soil (1-11) reaches 20% of the diameter of the hydrate-bearing marine soil (1-11), then stop the test; S6. After the test is completed, close the water area device (4-1), and sequentially remove the pressure inside the single shear stress state shear box (1) through the gas-free water volume controller (3-3) and the confining pressure volume controller (4-3), ensuring that the reading of the gas-water pressure sensor (5-5) inside the hydrate-bearing marine soil (1-11) is less than the reading of the confining pressure sensor (5-6) to avoid bursting the reinforced rubber membrane (1-7) and polluting the confining pressure liquid; when the reading of the confining pressure sensor (5-6) is less than 100 kPa, open valve d (4-4) and valve f (4-6) to drain all the silicone oil inside the single shear stress state shear box (1); open the single shear stress state shear box (1), sequentially remove the specimens, save the test data and process it.

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