A device and method for measuring the collapsible deformation modulus of loess

Abstract

The invention discloses a device and method for measuring the collapsible deformation modulus of loess, comprising a circular tube and a measuring cavity; a groove is arranged on the circumferential surface of the circular tube as a water injection chamber, the water injection chamber is connected to a water source through a water injection chamber water inlet pipe inside the circular tube pipeline, and a water-permeable plate is provided on the top of the water injection chamber for sealing; the measuring chamber is made of an elastic membrane with an internal hollow seal, and is tubular in shape, nested and fixed on the circumferential surface of the circular tube, the inner wall of the measuring chamber is connected to a water source and a water pressure controller through a measuring chamber water inlet pipe inside the circular tube pipeline, the inner wall of the measuring chamber is connected to a measuring chamber exhaust pipe inside the circular tube pipeline, when the circular tube is placed vertically, the free end height of the measuring chamber exhaust pipe is higher than the setting height of the measuring chamber, and an exhaust valve is provided at the free end of the measuring chamber exhaust pipe. The measurement of the deformation modulus at different depths inside the loess layer is realized, and the drawback that the on-site immersion load can only measure the collapsible deformation modulus of shallow loess is effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering detection, and relates to a device and method for measuring the collapsible deformation modulus of loess. Background Art

[0002] The influence of loess collapsibility on geotechnical engineering structures is mainly reflected in two aspects: the total collapsibility of loess and the sensitivity of loess to waterlogging. Even if the size of loess collapsibility is the same, its development may be rapid or slow, that is, loess has different sensitivities to collapsibility. The stronger the sensitivity to collapsibility, the greater the harm to geotechnical engineering structures. Therefore, studying the sensitivity of loess to collapsibility has practical significance.

[0003] In existing studies, the collapsible deformation modulus, that is, the ratio of the stress increment to the strain increment of a water-saturated soil sample, is one of the important indicators for quantitatively describing the collapsible sensitivity of loess. At present, the collapsible deformation modulus of loess is mainly measured through indoor compression tests to obtain the stress-strain curve of loess, and the collapsible deformation modulus of loess is obtained by calculating the slope of the straight line segment on the curve. However, it is impossible to avoid disturbing the loess sample during sampling and transportation, and the experimental results are likely to be misjudged; on the other hand, the field test method for determining the collapsible deformation modulus of loess is mainly through immersion load tests, but the field immersion load tests on the loess collapsible site are long in construction time and costly. Due to the limitations of the test methods, only the collapsible deformation of the shallow loess layer on the surface can be measured, and the change law of the collapsible deformation modulus with depth cannot be obtained. However, the thickest collapsible loess layer in the loess area can reach 30 meters or even deeper. Therefore, a device and method for measuring the collapsible deformation of loess layers in deep strata is needed. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a device and method for measuring the collapsible deformation modulus of loess, so as to realize the measurement of the deformation modulus at different depths inside the loess layer, and effectively solve the disadvantage that on-site immersion load can only measure the collapsible deformation modulus of shallow loess.

[0005] A loess collapsible deformation modulus measuring device comprises a round tube and a measuring cavity;

[0006] A groove is provided on the circumference of the circular tube as a water injection chamber, the water injection chamber is connected to a water source through a water injection chamber water inlet pipe inside the circular tube, and a water-permeable plate is provided on the top of the water injection chamber to seal;

[0007] The measuring cavity is made of an elastic membrane with an internal hollow seal and is tubular in shape. It is nested and fixed on the circumferential surface of the circular tube. The inner wall of the measuring cavity is connected to a water source and a water pressure controller through a measuring cavity water inlet pipe inside the circular tube. The inner wall of the measuring cavity is connected to a measuring cavity exhaust pipe inside the circular tube. When the circular tube is placed vertically, the free end height of the measuring cavity exhaust pipe is higher than the set height of the measuring cavity, and an exhaust valve is provided at the free end of the measuring cavity exhaust pipe.

[0008] Preferably, an upper auxiliary chamber and a lower auxiliary chamber are respectively provided at both ends of the measuring chamber. The upper auxiliary chamber and the lower auxiliary chamber are made of a hollow seal inside an elastic membrane, are tubular in shape, and are nested and fixed on the circumferential surface of the circular tube. The upper auxiliary chamber and the lower auxiliary chamber are connected to the air compressor through the auxiliary chamber air inlet pipe inside the circular tube.

[0009] Preferably, the water injection chamber is an annular groove surrounding the circumference of the circular tube.

[0010] Furthermore, a water injection chamber is respectively provided at the upper and lower ends of the circular tube.

[0011] Furthermore, the circular tube includes an upper circular tube, a middle circular tube and a lower circular tube, and the two ends of the middle circular tube are respectively threadedly connected to the bottom end of the upper circular tube and the top end of the lower circular tube, and the threaded connection position is a groove portion.

[0012] Preferably, a metal plate is provided in a sealed manner in the area between the interior of the water injection chamber and the water-permeable plate, and a plurality of through holes are provided on the metal plate.

[0013] Furthermore, the water-permeable plate and the metal plate are connected to the water injection chamber via O-rings.

[0014] A method for measuring the collapsible deformation modulus of loess based on any one of the above-mentioned devices, comprising the following steps:

[0015] Step 1: drilling the loess measurement area to form a borehole, and the diameter of the measurement hole is equal to the diameter of the circular tube;

[0016] Step 2: Open the exhaust valve, and inject water into the measuring chamber through the water inlet pipe of the measuring chamber. The air in the measuring chamber is discharged through the exhaust pipe of the measuring chamber until the water exceeds the exhaust valve. Close the exhaust valve and stop injecting water into the measuring chamber. Measure the volume V0 of the measuring chamber at this time.

[0017] Step 3, placing the device into the specified depth position in the measuring well;

[0018] Step 4: The water source reaches the water injection tank through the water injection tank inlet pipe, passes through the permeable plate and enters the soil, so that the soil is soaked and moistened. The water injection rate is greater than the permeability coefficient of the soil, and the water injection time is not less than 1 day;

[0019] Step 5: After the water filling tank is filled with water, the water source injects water into the measuring chamber through the measuring chamber water inlet pipe, and the water pressure control device is turned on to pressurize the measuring chamber. The pressure is increased in a step-by-step manner, and the loading pressure increment is 25 kPa. Before and after each level of load is added, the water volume change in the measuring chamber is measured and recorded once. When the water injection volume increases sharply, stop injecting water into the measuring chamber and terminate the test;

[0020] Step six, implement steps one, two, three and five, calculate the deformation modulus E1 of the soil in the natural state; implement steps one to five, calculate the deformation modulus E2 of the soil in the humidified state, and obtain the difference between the deformation modulus of the soil in the natural state and the humidified state.

[0021] Preferably, in step five, while water is being injected into the measuring cavity, the air compressor is turned on to inject air into the upper auxiliary cavity and the lower auxiliary cavity to ensure that the measuring cavity is expanded and pressurized in the radial direction.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention discloses a device for measuring the collapsible deformation modulus of loess. A measuring cavity is connected to a water source and a water pressure controller, and then is nested and fixed on a circular pipe. A water injection chamber is arranged on the circular pipe and connected to the water source. The soil body can be immersed in water and humidified by the water injection chamber, and the measuring cavity is pressurized by water injection, so that radial deformation of the soil body in a lateral pressure measuring hole is achieved, and the deformation modulus at different depths inside the loess layer is measured, which effectively solves the problem that the on-site immersion load can only measure the collapsible deformation modulus of shallow soil body.

[0024] Furthermore, an upper auxiliary chamber and a lower auxiliary chamber connected to an air compressor are provided at both ends of the measuring chamber to ensure that the pressure applied by the measuring chamber is radial pressure parallel to the hole, thereby reducing the pressure of the soil on the measuring chamber in other directions and improving the measurement accuracy.

[0025] Furthermore, the water injection chamber is an annular groove surrounding the circular pipe, and the soil around the circular pipe is evenly soaked with water.

[0026] Furthermore, O-rings are provided on both the water-permeable plate and the metal plate to increase the stability of the water-permeable plate and the metal plate and reduce hard contact with the round tube.

[0027] The present invention also discloses a method for measuring the collapsible deformation modulus of loess, which comprises the steps of immersing the soil in water to increase humidity through a water injection chamber, injecting water into a measuring cavity to increase pressure, and measuring the volume change and pressure change of the measuring cavity to achieve radial deformation of the soil in a lateral pressure measuring hole, thereby obtaining the deformation modulus of the soil in a natural state and a humidified state. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a cross-sectional view of the device structure of the present invention;

[0029] Figure 2 For the present invention Figure 1 Exploded view of the boxed area;

[0030] Figure 3 It is a test curve diagram of pressure-volume change under the natural state and the humidified state of the soil of the present invention.

[0031] Among them: 1-upper circular tube; 2-middle circular tube; 3-lower circular tube; 4-metal plate; 5-permeable stone plate; 6-O-ring; 7-upper auxiliary chamber; 8-measuring chamber; 9-lower auxiliary chamber; 10-water inlet pipe of water filling tank; 11-water inlet pipe of measuring chamber; 12-exhaust pipe of measuring chamber; 13-air inlet pipe of auxiliary chamber; 14-water tank; 15-servo water pressure controller; 16-air compressor; 17-water filling tank water stop valve; 18-water stop valve of measuring chamber; 19-exhaust valve; 20-through hole. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0033] like Figure 1 As shown, the present invention discloses a device and method for measuring the collapsible deformation modulus of loess, the device includes a circular tube, a metal plate 4, a permeable stone plate 5, an O-ring 6, an upper auxiliary cavity 7, a measuring cavity 8, a lower auxiliary cavity 9, a water injection chamber water inlet pipe 10, a measuring cavity water inlet pipe 11, a measuring cavity exhaust pipe 12, an auxiliary cavity air inlet pipe 13, a water tank 14, a servo water pressure controller 15, an air compressor 16, a water injection chamber water stop valve 17, a measuring cavity water stop valve 18, an exhaust valve 19 and a through hole 20.

[0034] The circular tube is made of metal, and includes an upper circular tube 1, a middle circular tube 2 and a lower circular tube 3. A first groove is provided on the inner wall at both ends of the middle circular tube 2, and an internal thread is provided on the first groove. The bottom end of the upper circular tube 1 and the top end of the lower circular tube 3 extend toward the middle circular tube 2, and the outer diameter of the extended part is the same as the inner diameter of the first groove, and an external thread is provided. The two ends of the middle circular tube 2 are respectively threadedly connected with the bottom end of the upper circular tube 1 and the top end of the lower circular tube 3; the bottom end of the lower circular tube 3 is closed.

[0035] like Figure 2 As shown, the outer walls of the two ends of the middle circular tube 2, the bottom end of the upper circular tube 1 and the top end of the lower circular tube 3 are all provided with step surfaces around the circumference. When the upper circular tube 1, the middle circular tube 2 and the lower circular tube 3 are connected, the step surfaces form a second groove in pairs at the two ends of the middle circular tube 2, forming an upper and lower water filling chamber. The water filling chamber is sealed from the inside to the outside with an annular metal plate 4 and an annular permeable plate. The upper circular tube 1 and the lower circular tube 3 are provided with through holes 20. The water filling chamber water inlet pipe 10 passes through the through holes 20 to connect the two water filling chambers with the ground water tank 14. The water filling chamber water inlet pipe 10 is provided with a water filling chamber water stop valve 17.

[0036] The inner and outer diameters of the upper circular tube 1 and the lower circular tube 3 are the same, the inner diameter of the middle circular tube 2 is equal to the inner diameters of the upper circular tube 1 and the lower circular tube 3, and the outer diameter of the middle circular tube 2 is slightly smaller than the outer diameters of the upper circular tube 1 and the lower circular tube 3, so that the permeable plate of the water injection tank is fully in contact with the soil to soak the soil.

[0037] The metal plate 4 is made of a 1 cm thick steel plate with multiple through holes 20. The water in the water injection tank enters the permeable plate through the through holes 20. The permeable plate adopts a permeable stone plate 5, which is made of a 1 cm thick metal permeable stone to prevent soil from entering the water injection tank and blocking the through holes 20 of the metal plate 4 during the process of immersing water into the soil.

[0038] The upper circular tube 1, the middle circular tube 2 and the lower circular tube 3 are provided with U-shaped grooves at the corresponding positions where the permeable stone plate 5 and the metal plate 4 are installed. O-rings 6 are placed at the U-shaped grooves. When the circular tubes, the middle circular tube 2 and the lower circular tube 3 are connected by threaded fixing, the metal plate 4 and the permeable stone plate 5 can be sealed and fixed at the connection to form two water injection chambers. Placing the O-rings 6 in the U-shaped grooves can ensure the stability of the metal plate 4 and the permeable stone plate 5 and reduce the hard contact between the metals.

[0039] An upper auxiliary chamber 7, a measuring chamber 8 and a lower auxiliary chamber 9 are nested and fixed on the outer wall of the middle circular tube 2 in sequence from top to bottom; the measuring chamber 8 is a water pressure measuring chamber 8 formed by a hollow seal inside an elastic membrane, and is tubular in shape. It is connected to a ground water tank 14 and a water pressure controller through a measuring chamber water inlet pipe 11, and is used to pressurize the soil and measure the deformation of the soil. A measuring chamber water stop valve 18 is provided at the connection between the measuring chamber water inlet pipe 11 and the water tank 14. The preferred water pressure controller in this embodiment adopts a servo water pressure controller 15; the upper auxiliary chamber 7 and the lower auxiliary chamber 9 are air pressure chambers formed by a hollow seal inside an elastic membrane, and are tubular in shape. They are connected to an air compressor 16 through an auxiliary chamber air inlet pipe 13, and are used to ensure that the pressure applied by the water pressure measuring chamber 8 is radial pressurization.

[0040] The measuring chamber 8 is connected to the measuring chamber exhaust pipe 12. When the circular tube is placed vertically, the free end height of the measuring chamber exhaust pipe 12 is higher than the setting height of the measuring chamber 8, and the free end of the measuring chamber exhaust pipe 12 is provided with an exhaust valve 19. When the exhaust valve 19 is opened, excess air inside the measuring chamber 8 is discharged by injecting water into the measuring chamber 8.

[0041] The water inlet pipe 10 of the water injection chamber, the water inlet pipe 11 of the measuring chamber, the exhaust pipe 12 of the measuring chamber and the air inlet pipe 13 of the auxiliary chamber are all arranged inside the circular tube, which does not affect the use and measurement of the device.

[0042] The device is used to measure the collapsible deformation modulus of loess, including the following steps:

[0043] Step 1: Drill holes in the loess measurement area to form drill holes, and the diameter of the measuring hole is equal to the diameter of the circular tube.

[0044] Step 2: Open the measuring chamber water stop valve 18 and the exhaust valve 19 so that the water in the water tank 14 flows into the entire measuring chamber 8, and the air in the measuring chamber 8 is discharged through the measuring chamber exhaust pipe 12 until the water exceeds the exhaust valve 19. When there is no air in the measuring chamber 8, close the measuring chamber water stop valve 18 and the exhaust valve 19.

[0045] Step three: Place the device at the specified depth of the measurement well.

[0046] Step 4, open the water injection tank stop valve 17, the water in the water tank 14 reaches the water injection tank through the water injection tank inlet pipe 10, passes through the metal plate 4 and the permeable stone plate 5 into the soil, so that the soil is soaked and humidified, and the water injection time is not less than 1 day.

[0047] Step five, after the water filling chamber is filled with water, the soil is humidified, and the air compressor 16 is turned on to expand the elastic membranes of the upper auxiliary chamber 7 and the lower auxiliary chamber 9. At the same time, the measuring chamber water stop valve 18 and the servo water pressure control device are opened to pressurize the measuring chamber 8. The upper auxiliary chamber 7 and the lower auxiliary chamber 9 have the same radial expansion degree as the measuring chamber 8. The measuring chamber 8 is pressurized in a step-by-step manner, and the loading pressure increment is 25 kPa. Before and after each level of load is added, the change in water volume in the measuring chamber 8 is measured and recorded once. When the water injection volume increases sharply, stop injecting water into the measuring chamber 8, terminate the test, and close the measuring chamber water stop valve 18 and the servo water pressure control device.

[0048] Step 6: The pressure-volume change test curves under the natural state and the humidified state of the soil can be drawn, such as Figure 3 As shown, curve α is the pressure-volume change test curve under the natural state of the soil, and curve β is the pressure-volume change test curve under the moistened state of the soil. The deformation modulus of the soil in the natural state and moistened state can be calculated based on the curve, which provides basic data for evaluating the collapsibility sensitivity of loess and the initial pressure of collapsibility. The deformation modulus calculation formula is as follows:

[0049]

[0050] Where: i = 1 represents the natural moisture content state, i = 2 represents the humidified moisture content state;

[0051] V0—initial volume of measuring cavity 8,

[0052] Unit: cm 3 ;

[0053] — is the volume corresponding to the starting point of the straight line segment in the pressure-volume change measurement curve, in cm 3 ;

[0054] — is the volume corresponding to the end point of the straight line segment in the pressure-volume change measurement curve, in cm 3 ;

[0055] μ—Poisson’s ratio of soil;

[0056] — is the pressure corresponding to the starting point of the straight line segment in the pressure-volume change measurement curve, in kPa;

[0057] — is the pressure corresponding to the starting point of the straight line segment in the pressure-volume change measurement curve, in kPa.

[0058] Implement steps one, two, three and five to calculate the deformation modulus E1 of the soil in the natural state; implement steps one to five to calculate the deformation modulus E2 of the soil in the humidified state, and obtain the difference between the soil in the natural state and the humidified state.

[0059] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A loess collapsible deformation modulus measuring device, characterized in that: It includes a round tube and a measuring cavity (8); A groove is provided on the circumferential surface of the circular tube as a water injection chamber, the water injection chamber is connected to a water source via a water injection chamber water inlet pipe (10) inside the circular tube, and a water-permeable plate is provided on the top of the water injection chamber for sealing; The measuring cavity (8) is made of an elastic membrane with an internal hollow seal and is tubular in shape. It is nested and fixed on the circumferential surface of the circular tube. The inner wall of the measuring cavity (8) is connected to a water source and a water pressure controller through a measuring cavity water inlet pipe (11) inside the circular tube. The inner wall of the measuring cavity (8) is connected to a measuring cavity exhaust pipe (12) inside the circular tube. When the circular tube is placed vertically, the free end height of the measuring cavity exhaust pipe (12) is higher than the setting height of the measuring cavity (8), and an exhaust valve (19) is provided at the free end of the measuring cavity exhaust pipe (12). The water injection chamber is an annular groove that surrounds the circumference of the circular pipe; A water injection chamber is provided at each of the upper and lower ends of the circular tube; A metal plate (4) is provided in a sealed manner in the area between the interior of the water injection chamber and the water permeable plate, and a plurality of through holes (20) are provided on the metal plate (4).

2. The loess collapsible deformation modulus measuring device according to claim 1, characterized in that: An upper auxiliary chamber (7) and a lower auxiliary chamber (9) are respectively provided at both ends of the measuring chamber (8); the upper auxiliary chamber (7) and the lower auxiliary chamber (9) are made of an elastic membrane with an internal hollow seal and are tubular in shape and are nested and fixed on the circumferential surface of the circular tube; the upper auxiliary chamber (7) and the lower auxiliary chamber (9) are connected to an air compressor (16) via an auxiliary chamber air inlet pipe (13) inside the circular tube.

3. The device for measuring the collapsible deformation modulus of loess according to claim 1, characterized in that: The circular tube comprises an upper circular tube (1), a middle circular tube (2) and a lower circular tube (3), and the two ends of the middle circular tube (2) are respectively threadedly connected to the bottom end of the upper circular tube (1) and the top end of the lower circular tube (3), and the threaded connection position is a groove portion.

4. The device for measuring the collapsible deformation modulus of loess according to claim 1, characterized in that: The water-permeable plate and the metal plate (4) are both connected to the water injection tank via an O-ring (6).

5. A method for measuring the collapsible deformation modulus of loess based on the device according to any one of claims 1 to 4, characterized in that: The steps include: Step 1: drilling the loess measurement area to form a borehole, and the diameter of the measurement hole is equal to the diameter of the circular tube; Step 2: Open the exhaust valve (19), and inject water into the measuring chamber (8) through the measuring chamber water inlet pipe (11). The air in the measuring chamber (8) is discharged through the measuring chamber exhaust pipe (12) until the water exceeds the exhaust valve (19). Then, close the exhaust valve (19), stop injecting water into the measuring chamber (8), and measure the volume of the measuring chamber (8) at this time. ; Step 3, placing the device into the specified depth position in the measuring well; Step 4: water is fed into the water injection tank through the water injection tank inlet pipe (10), and then passes through the water permeable plate into the soil, so that the soil is soaked and moistened. The water injection rate is greater than the permeability coefficient of the soil, and the water injection time is not less than 1 day. Step 5: After the water filling tank is filled with water, the water source injects water into the measuring chamber (8) through the measuring chamber water inlet pipe (11), and the water pressure control device is turned on to increase the pressure of the measuring chamber (8). The pressure is increased in a step-by-step manner, and the loading pressure increment is 25 kPa. Before and after each level of load is added, the change in the water volume of the measuring chamber (8) is measured and recorded once. When the water injection volume increases sharply, the injection of water into the measuring chamber (8) is stopped, and the test is terminated; Step 6: Implement steps 1, 2, 3 and 5 to calculate the deformation modulus of the soil in its natural state. ; Implement steps 1 to 5 to calculate the deformation modulus of the soil under the moistening state , and obtain the difference in deformation modulus of soil in natural state and moistened state.

6. A method for measuring the collapsible deformation modulus of loess according to claim 5, characterized in that: In step five, while water is being injected into the measuring chamber (8), the air compressor (16) is turned on to inject air into the upper auxiliary chamber (7) and the lower auxiliary chamber (9) to ensure that the measuring chamber (8) is expanded and pressurized in the radial direction.

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