An air pressure loading type one-dimensional consolidation device for unsaturated soil and a test method

Abstract

The application relates to a kind of one-dimensional consolidation devices and test methods of air pressure loading type unsaturated soil, including the sample container for placing soil sample, the loading device is installed at the bottom of sample container, the loading device is applied pressure from the bottom of sample container along the direction of central axis, the applied pressure is formed by injecting adjustable gas into the loading device, and the pressure applied by the loading device can amplify the pressure borne by the sample container;It also includes measuring device, which is arranged by the opening of the loading device relative to the sample container, for recording the external load and vertical deformation of the soil sample in real time;The application realizes one-dimensional consolidation of the sample under high stress, can carry out particle breakage test of granular material under high stress level, installs saturation control device near the bottom position in the sample container, can control the saturation in the sample container, realizes the control of the saturation of the sample, and can carry out one-dimensional consolidation test of unsaturated soil.

Description

Technical Field

[0001] This invention relates to a pneumatically loaded one-dimensional consolidation device and test method for unsaturated soil, belonging to the field of indoor geotechnical testing technology in geotechnical engineering. Background Technology

[0002] Earth-rock dams are the most widely used type of dam in hydropower projects due to their advantages such as simple material selection, simple structure, low cost, and adaptability to terrain and geology. In recent years, due to the needs of engineering construction, an increasing number of high earth-rock dams have been built worldwide. With the increase in dam height, the main material of the dam, rockfill, is subjected to significant stress. Therefore, the particle breakage rate of the rockfill in high earth-rock dams increases significantly. Particle breakage directly alters the rockfill structure and changes the shear strength of the soil. Indoor consolidation tests are one of the important methods for studying the mechanical properties of soil.

[0003] Currently, the most commonly used consolidation testing apparatuses are the lever-type consolidation apparatus and the pneumatic consolidation apparatus. The lever-type consolidation apparatus uses the principle of lever loading, applying pressure via a lever with weights. Its advantages include intuitive loading and good stability. However, this apparatus has low automation, requiring manual handling of the weights, resulting in high labor intensity; the process of adding weights generates impact forces, which can affect the test results. Traditional pneumatic consolidation apparatuses have a low upper limit for loading, and the loading stress cannot reach the particle failure strength, making it impossible to study the impact of particle breakage on the internal properties of the soil, and it cannot be used for consolidation tests on unsaturated soils.

[0004] Therefore, there is an urgent need to design a consolidation device that can apply high consolidation stress to the sample without manual operation, thereby conducting particle crushing tests of granular materials under high stress levels, and equipped with a clay plate to control the saturation of the sample for one-dimensional consolidation tests of unsaturated soil. Summary of the Invention

[0005] To address the problems mentioned in the background art, the present invention provides a pneumatically loaded one-dimensional consolidation device and test method for unsaturated soil.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A pneumatic loading type one-dimensional consolidation device for unsaturated soil includes a sample container for placing soil samples, a loading device installed at the bottom of the sample container, the loading device applying pressure from the bottom of the sample container along the central axis, the applied pressure being formed by injecting adjustable gas into the loading device, and the pressure applied by the loading device being able to amplify the pressure borne by the sample container.

[0008] A saturation control device is installed near the bottom inside the sample container to control the saturation inside the sample container.

[0009] The measuring device is arranged opposite the opening of the sample container by the loading device, and is used to record the external load and vertical deformation of the soil sample in real time;

[0010] As a further preferred embodiment of the present application, the sample container comprises a sample cylinder, the open end of the sample cylinder is covered with a sample cylinder cover, an upper water-permeable plate is arranged near the opening of the sample cylinder, and a lower water-permeable plate is arranged near the bottom of the sample cylinder, and a saturation control device is arranged at the bottom of the lower water-permeable plate;

[0011] The bottom surface of the sample cylinder is provided with a water-permeable hole, and the BSP pipe is arranged to communicate with the water-permeable hole at the bottom of the sample cylinder;

[0012] When the loading device applies pressure to the bottom of the sample container, the sample container moves along the central axis direction towards the sample cylinder cover, the upper water-permeable plate moves along the central axis direction in the opposite direction of the sample cylinder cover, and a load is generated on the soil sample in the sample cylinder;

[0013] As a further preferred embodiment of the present application, the loading device comprises a counterforce frame, a bottom plate is mounted at the bottom of the counterforce frame, a gas cylinder is arranged on the surface of the bottom plate, a piston capable of moving up and down along the central axis direction is arranged in the gas cylinder, and a sample cylinder is arranged on the surface of the piston;

[0014] An upper boss is mounted at the top center of the counterforce frame towards the opening direction of the sample cylinder, the bottom of the upper boss is connected to a lower boss through a force sensor of the measuring device, and the bottom end of the lower boss is arranged to be capable of contacting the surface of the upper water-permeable plate through the sample cylinder cover;

[0015] As a further preferred embodiment of the present application, the measuring device further comprises a displacement sensor, one end of the displacement sensor is fixed to the counterforce frame, and the measurement end of the displacement sensor abuts against the surface of the sample cylinder cover;

[0016] As a further preferred embodiment of the present application, the displacement sensor is a digital height gauge electronic depth gauge percentage table measuring instrument, which is provided with a data interface and can be connected to a computer;

[0017] As a further preferred embodiment of the present application, the saturation control device is a pottery plate, and a steel ring is sleeved outside the pottery plate;

[0018] As a further preferred embodiment of the present application, a plurality of threaded holes are formed in the inner circumferential wall at the bottom of the sample cylinder, a plurality of threaded holes are also formed in the outer circumferential wall of the pottery plate, and bolts are arranged to pass through the threaded holes in the bottom of the sample cylinder and the threaded holes in the pottery plate to fix the pottery plate in the sample cylinder;

[0019] The test method based on the air pressure loading type unsaturated soil one-dimensional consolidation device specifically comprises the following steps:

[0020] Step S1: a clay plate wrapped with a steel ring is arranged at the bottom of the sample cylinder, a lower water-permeable plate is placed on the surface of the clay plate, filter paper is laid on the surface of the lower water-permeable plate, then the soil sample is loaded into the sample cylinder, a layer of filter paper is laid on the top of the soil sample, an upper water-permeable plate is arranged on the filter paper, and finally a sample cylinder cover is arranged at the opening end of the sample cylinder;

[0021] Step S2: the bottom plate is placed on the reaction frame, the air cylinder is arranged on the surface of the bottom plate, the rubber ring is arranged between the bottom plate and the air cylinder, the sample cylinder in step S1 is placed on the piston of the air cylinder, and the lower boss is aligned with the center of the sample cylinder cover; the BSP pipe is installed at the bottom of the sample cylinder and is communicated with the water-permeable hole;

[0022] Step S3: the inflation valve of the air cylinder is opened, the air cylinder is inflated, the piston pushes the sample cylinder to move towards the lower boss, when the lower boss contacts the upper water-permeable plate of the sample cylinder, the inflation valve is closed and the inflation is stopped;

[0023] Step S4: adjust the displacement sensor, the probe of the displacement sensor measurement end is attached to the sample cylinder cover, and the force sensor and the displacement sensor are connected with the computer;

[0024] Step S5: the force sensor and the displacement sensor are zeroed, the inflation valve is reopened, the air cylinder is inflated, the air pressure in the air cylinder increases, the piston pushes the sample cylinder to move towards the lower boss, at this time, the upper water-permeable plate is displaced relative to the sample cylinder, the soil sample in the sample cylinder is compressed, and at the same time, the drain valve on the BSP pipe is opened, the liquid in the soil sample is discharged through the BSP pipe in the compression process, and the force sensor and the displacement sensor monitor the consolidation stress and vertical deformation of the soil sample throughout the process until stable.

[0025] Through the above technical scheme, compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The air pressure loading type one-dimensional consolidation device for unsaturated soil provided by the present application adopts an automatic operation mode, gradually increases the air pressure in the air cylinder to steadily apply vertical load to the soil sample, and avoids the influence of unstable impact force generated in the process of manually adding weights on the test results;

[0027] 2. The air pressure loading type one-dimensional consolidation device for unsaturated soil provided by the present application can enlarge the pressure (pressure intensity) borne by the sample cylinder by injecting gas into the air cylinder with a large cross-sectional area, so that a higher consolidation stress can be applied to the sample, thereby making up for the deficiency that the maximum consolidation stress of the traditional consolidation instrument loaded by weights is less than 2 MPa;

[0028] 3. The air pressure loading type one-dimensional consolidation device for unsaturated soil provided by the present application is equipped with a water-permeable hole and a clay plate to control the saturation of the sample, and can perform one-dimensional consolidation test on unsaturated soil;

[0029] 4. The air pressure loading type one-dimensional consolidation device for unsaturated soil provided by the present application adopts a frame structure, is small in size, light in weight, convenient for field use, and is controlled by a computer during the test process, so that the operation is simple and manual intervention is not needed. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application is further described below in combination with the drawings and examples.

[0031] Figure 1 is the overall schematic diagram of the preferred embodiment provided by the present application;

[0032] Figure 2 is the sectional view of the sample cylinder in the preferred embodiment provided by the present application;

[0033] Figure 3 is the top view of the sample cylinder in the preferred embodiment provided by the present application;

[0034] Figure 4 is the sectional view of the piston in the preferred embodiment provided by the present application;

[0035] Figure 5 is the sectional view of the cylinder in the preferred embodiment provided by the present application;

[0036] Figure 6 is the top view of the cylinder in the preferred embodiment provided by the present application;

[0037] Figure 7 is the sectional view of the bottom plate in the preferred embodiment provided by the present application;

[0038] Figure 8 is the top view of the bottom plate in the preferred embodiment provided by the present application.

[0039] In the figure: 1 is a counterforce frame, 2 is a bottom plate, 3 is a cylinder, 4 is a piston, 5 and 13 are BSP pipes, 6 is a steel ring, 7 is a water permeable hole, 8 is a porcelain clay plate, 9 is a lower water permeable plate, 10 is a sample cylinder, 11 is an upper water permeable plate, 12 is a sample cylinder cover, 14 is a lower boss, 15 is a displacement sensor, 16 is a force sensor, 17 is an upper boss, 18 is a threaded hole, and 19 is an annular groove. DETAILED DESCRIPTION

[0040] The application will be further described in detail below with reference to the drawings. In the description of the present application, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and "first", "second" and the like do not represent the importance of the parts, and therefore cannot be understood as a limitation on the application. The specific dimensions used in the embodiments are only used to illustrate the technical solutions and do not limit the protection scope of the application.

[0041] In order to solve the problems pointed out in the background art, the application provides a gas pressure loading type one-dimensional consolidation device for unsaturated soil, Figure 1 is a schematic diagram of the preferred embodiment of the application, which includes a sample container for placing a soil sample, a loading device is installed at the bottom of the sample container, the loading device applies pressure along the central axis direction from the bottom of the sample container, here the force applying end is applied upward along the central axis direction from the bottom of the sample container, and the applied pressure is formed by injecting adjustable gas into the loading device. This load application method can amplify the pressure or pressure received by the sample container, and when the pressure or pressure is large enough, a higher consolidation stress can be generated to study the influence of particle crushing on the internal properties of the soil. Another innovation of the application is to install a saturation control device near the bottom of the sample container, which can control the saturation in the sample container to perform one-dimensional consolidation test of unsaturated soil. It also includes a measuring device which is arranged relative to the opening of the sample container through the loading device, for recording the real-time external load and vertical deformation of the soil sample, and the measuring device is connected to a computer, without manual pressure, and can monitor the state of the soil sample in real time.

[0042] The sample container specifically includes a sample cylinder 10, which is a hollow cylinder, and the open end of the sample cylinder is covered with a sample cylinder cover 12, and the sample cylinder cover is connected with a BSP pipe 13, an upper water permeable plate 11 is arranged near the opening of the sample cylinder, and a lower water permeable plate 9 is arranged near the bottom of the sample cylinder, and the upper and lower water permeable plates are both made of cylindrical water permeable stones. A saturation control device is arranged at the bottom of the lower water permeable plate. Figure 2 As shown, a water permeable hole 7 is formed in the bottom surface of the sample cylinder, and a BSP pipe 5 is arranged in the bottom of the sample cylinder and communicates with the water permeable hole, and the BSP pipe in the bottom of the sample cylinder is used to discharge the liquid of the soil sample extruded by the load; Figure 3 As can be seen, a threaded hole 18 is formed in the bottom of the sample cylinder, and a bolt is arranged in the threaded hole to fix the sample cylinder on the surface of the piston 4. When the loading device applies pressure to the bottom of the sample container, the sample container moves along the central axis direction towards the sample cylinder cover, and the upper water permeable plate moves along the central axis direction in the opposite direction of the sample cylinder cover, thereby generating a load on the soil sample in the sample cylinder.

[0043] The loading device includes a reaction frame 1, with the bottom of the reaction frame mounted on... Figure 7 The base plate 2 shown has cylinders 3 arranged on its surface. Figure 6 It can be seen that a threaded hole is made at the bottom of the cylinder. Figure 8 As shown, threaded holes are also made on the base plate for inserting bolts to fix the cylinder to the base plate surface. A piston capable of moving up and down along the central axis is installed inside the cylinder. The piston's structure is as follows... Figure 4 As shown, a concave section is set in the middle of the bottom, and toothed structures are set on both sides of the piston. These are all to ensure a tight connection between the piston and the cylinder, preventing air leakage and avoiding the major hidden danger of unstable load caused by air leakage. Sample cylinders are arranged on the piston surface. Traditional high-pressure gas cylinders have a limited upper pressure limit, which cannot cause high-compressive-strength soil particles to break up. This makes it impossible to study the effect of particle breakage on the internal mechanical properties and deformation behavior of the soil sample. However, by injecting gas from the high-pressure gas cylinder into a cylinder with a larger cross-sectional area... Figure 5 As shown, the force on the piston is equal to the force on the sample cylinder. However, the cross-sectional area of ​​the sample cylinder is much smaller than the area of ​​the piston. According to the formula: pressure = force / area, if the ratio of the piston area to the bottom area of ​​the sample cylinder is n, the consolidation stress of the sample can be amplified to n times the pressure inside the cylinder. This means that the pressure on the sample cylinder can be amplified, thus allowing a higher consolidation stress to be applied to the sample.

[0044] To apply a load to the soil sample inside the sample cylinder, in addition to applying a load from the bottom, a top force is also required at the top of the soil sample. Here, an upper boss 17 is installed at the center of the top of the reaction frame, facing the opening of the sample cylinder. The bottom of the upper boss is connected to a lower boss 14 through a force sensor 16 of the measuring device. The bottom end of the lower boss passes through the sample cylinder cover and can contact the surface of the upper permeable plate. The upper permeable plate can move relative to the sample cylinder. The axial lifting of the piston can gradually reduce the distance between the soil sample and the upper permeable plate until the upper permeable plate abuts against the lower boss. Gas continues to be injected into the cylinder, and the soil sample continues to be loaded, with a relatively large upper limit to the load.

[0045] The force sensor used to connect the upper and lower bosses is a structure within the measuring device. The measuring device also includes a displacement sensor 15, which uses a digital altimeter / electronic depth gauge / dial gauge measuring instrument with a data interface for computer connection. To obtain the most accurate and reliable data, one end of the displacement sensor is fixed to the reaction frame, and its measuring end is attached to the sample cylinder cover.

[0046] In the application, the saturation control device is a clay plate 8, and a steel ring 6 is sleeved outside the clay plate. In order to improve the sealing performance of the structure, an annular groove 19 is formed in the bottom of the sample cylinder, and a rubber ring is installed in the annular groove to realize the sealing between the sample cylinder and the piston. At the same time, a rubber ring is also arranged between the bottom plate and the air cylinder to realize the sealing between the bottom plate and the air cylinder.

[0047] The application also provides a test method based on the gas pressure loading type unsaturated soil one-dimensional consolidation device, and specifically includes the following steps.

[0048] Step S1: A clay plate wrapped with a steel ring is arranged at the bottom of the sample cylinder, a lower water-permeable plate is placed on the surface of the clay plate, filter paper is laid on the surface of the lower water-permeable plate, then a soil sample is loaded into the sample cylinder, a layer of filter paper is laid on the top of the soil sample, an upper water-permeable plate is arranged on the filter paper, and finally a sample cylinder cover is arranged at the open end of the sample cylinder;

[0049] Step S2: The bottom plate is placed on the counterforce frame, the air cylinder is arranged on the surface of the bottom plate, a rubber ring is arranged between the bottom plate and the air cylinder, the sample cylinder in step S1 is placed on the piston of the air cylinder, and the lower boss is aligned with the center of the sample cylinder cover; and the BSP pipe is installed at the bottom of the sample cylinder and communicated with the water-permeable hole;

[0050] Step S3: The inflation valve of the air cylinder is opened, the air cylinder is inflated, the piston pushes the sample cylinder to move in the direction of the lower boss, and when the lower boss contacts the upper water-permeable plate of the sample cylinder, the inflation valve is closed and the inflation is stopped;

[0051] Step S4: The displacement sensor is adjusted, the probe at the measurement end of the displacement sensor is attached to the sample cylinder cover, and the force sensor and the displacement sensor are connected to the computer;

[0052] Step S5: The force sensor and the displacement sensor are reset to zero, the inflation valve is reopened, the air cylinder is inflated, the air pressure in the air cylinder is increased, the piston pushes the sample cylinder to move in the direction of the lower boss, at this time, the upper water-permeable plate is displaced relative to the sample cylinder, the soil sample in the sample cylinder is compressed, and at the same time, the drain valve on the BSP pipe is opened, the liquid in the soil sample is discharged through the BSP pipe in the compression process, and the force sensor and the displacement sensor monitor the consolidation stress and vertical deformation of the soil sample throughout the process until stability.

[0053] Through the above description, the gas pressure loading type unsaturated soil one-dimensional consolidation device provided by the application can flexibly replace the sample cylinder according to the test requirements to perform one-dimensional consolidation tests on different sizes of samples, and the whole structure is small in size, light in weight and convenient to use on site.

[0054] As used herein, including the appended claims, the term "and / or," means "and" or "or," or both, and "and / or" is used in the same way as "and / or" is used in the patent statutes and judgements, for example, in connection with the phrase "means plus function." Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting. Except to the extent necessary or inherent in the

[0055] As used herein, the term "and / or" means that the items are either all present or one or the other is present, but not necessarily both.

[0056] As used herein, the term "and / or" means that the items are either all present or one or the other is present, but not necessarily both.

[0057] The above description is provided as an enabling teaching of the application. Those skilled in the relevant arts will readily apply the principles described herein in view of the above description, to adapt the teachings to various situations, and the application is therefore not intended to be limited to the implementations described herein, but to be given full scope of the appended claims.

Claims

1. A pneumatically loaded one-dimensional consolidation device for unsaturated soil, characterized in that: The application relates to a soil sample testing device, which comprises a sample container for placing a soil sample, a loading device arranged at the bottom of the sample container, the loading device applying pressure to the sample container along the central axis direction, the applied pressure being formed by injecting adjustable gas into the loading device, and the loading device amplifying the pressure borne by the sample container; A saturation control device is arranged at a position close to the bottom of the sample container, and the saturation control device can control the saturation of the sample container; The device further comprises a measuring device arranged opposite the opening of the sample container through the loading device, which is used for recording the external load and vertical deformation of the soil sample in real time; The sample container comprises a sample cylinder (10), the open end of the sample cylinder (10) is covered with a sample cylinder cover (12), an upper water-permeable plate (11) is arranged at a position close to the opening of the sample cylinder (10), a lower water-permeable plate (9) is arranged at a position close to the bottom of the sample cylinder (10), and a saturation control device is arranged at the bottom of the lower water-permeable plate (9); A water-permeable hole (7) is formed in the bottom surface of the sample cylinder (10), and a BSP pipe is arranged to pass through the bottom of the sample cylinder (10) and communicate with the water-permeable hole (7); When the loading device applies pressure to the bottom of the sample container, the sample container moves along the central axis direction towards the sample cylinder cover (12), the upper water-permeable plate (11) moves along the central axis direction in the opposite direction of the sample cylinder cover (12), and a load is generated on the soil sample in the sample cylinder (10); The loading device comprises a counterforce frame (1), a bottom plate (2) is arranged at the bottom of the counterforce frame (1), a gas cylinder (3) is arranged on the surface of the bottom plate (2), a piston (4) capable of moving up and down along the central axis direction is arranged in the gas cylinder (3), and the sample cylinder (10) is arranged on the surface of the piston (4); An upper boss (17) is arranged at the top center position of the counterforce frame (1) and faces the opening direction of the sample cylinder (10), the bottom of the upper boss (17) is connected with a lower boss (14) through a force sensor (16) of the measuring device, and the bottom end of the lower boss (14) passes through the sample cylinder cover (12) and can contact the surface of the upper water-permeable plate (11).

2. The apparatus according to claim 1, wherein: The measuring device further comprises a displacement sensor (15), one end of the displacement sensor (15) is fixed with the counterforce frame (1), and the measuring end of the displacement sensor (15) abuts against the surface of the sample cylinder cover (12).

3. The apparatus according to claim 2, wherein: The displacement sensor (15) adopts a digital display height gauge electronic depth gauge percentage table measuring instrument, has a data interface, and can be connected with a computer.

4. The apparatus according to claim 2, wherein: The saturation control device is a pottery plate (8), and a steel ring (6) is sleeved outside the pottery plate (8).

5. The apparatus according to claim 4, wherein: A plurality of threaded holes (18) are formed in the inner circumferential wall of the bottom of the sample cylinder (10), a plurality of threaded holes (18) are also formed in the outer circumferential wall of the pottery plate (8), bolts pass through the threaded holes (18) of the bottom of the sample cylinder (10) and the threaded holes (18) of the pottery plate (8), and the pottery plate (8) is fixed in the sample cylinder (10).

6. The test method of the apparatus for one-dimensional consolidation test of unsaturated soil by pneumatic loading according to claim 5, characterized in that: The application further specifically comprises the following steps: Step S1: The bottom of the sample cylinder (10) is provided with a clay plate (8) wrapped with a steel ring (6), a lower water-permeable plate (9) is placed on the surface of the clay plate (8), filter paper is laid on the surface of the lower water-permeable plate (9), then the soil sample is loaded into the sample cylinder (10), a layer of filter paper is laid on the top of the soil sample, an upper water-permeable plate (11) is placed on the filter paper, and finally a sample cylinder cover (12) is covered on the open end of the sample cylinder (10); Step S2: The bottom plate (2) is placed on the counterforce frame (1), the air cylinder (3) is arranged on the surface of the bottom plate (2), the rubber ring is arranged between the bottom plate (2) and the air cylinder (3), the sample cylinder (10) in step S1 is placed on the piston (4) of the air cylinder (3), and the lower boss (14) is aligned with the center of the sample cylinder cover (12); the BSP pipe is installed at the bottom of the sample cylinder (10) and communicates with the water-permeable hole (7); Step S3: The inflation valve of the air cylinder (3) is opened, the air cylinder (3) is inflated, the piston (4) pushes the sample cylinder (10) to move towards the lower boss (14), when the lower boss (14) contacts the upper water-permeable plate (11) of the sample cylinder (10), the inflation valve is closed, and the inflation is stopped; Step S4: The displacement sensor (15) is adjusted, the probe of the measurement end of the displacement sensor (15) is attached to the sample cylinder cover (12), and the force sensor (16) and the displacement sensor (15) are connected with the computer; Step S5: The force sensor (16) and the displacement sensor (15) are zeroed, the inflation valve is reopened, the air cylinder (3) is inflated, the air pressure in the air cylinder (3) increases, the piston (4) pushes the sample cylinder (10) to move towards the lower boss (14), at this time, the upper water-permeable plate (11) is displaced relative to the sample cylinder (10), the soil sample in the sample cylinder (10) is compressed, and the drainage valve on the BSP pipe is opened, the liquid in the soil sample is discharged through the BSP pipe in the compression process, and the force sensor (16) and the displacement sensor (15) monitor the consolidation stress and vertical deformation of the soil sample throughout the process until stable.

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