A device and method for quickly measuring the matrix suction and shear strength of unsaturated soil

Abstract

The invention discloses a device and method for quickly measuring the matrix suction and shear strength of unsaturated soil. The device includes a centrifuge cabin and a secant workbench, a pressurizing system, a pressure sensor, a breathable pressure cover, a shear box, a drainage collection box, a ball, a slideway, a shear force application system, a shear force sensor and a displacement sensor: the shear box is connected to the drainage collection box and contacts the slideway of the secant workbench through the ball; the pressurizing system is installed at the center of the cabin, and the pressure acts on the sample through the breathable pressure cover; the shear force application system is installed at the bottom of the centrifuge cabin, and the shear force acts vertically upward on the lower shear box; the values ​​of force and displacement are collected by the pressure sensor, the shear force sensor and the displacement sensor. The method steps are: preparing the sample; installing the sample; measuring the matrix suction, the unsaturated strength and the water content. The invention can realize the rapid measurement of the matrix suction and unsaturated strength of the unsaturated sample, which is of great significance to the research of unsaturated soil.

Description

Technical Field

[0001] The invention belongs to the technical field of unsaturated soil mechanics experiments, and in particular relates to a device and a method for rapidly measuring the matrix suction and shear strength of unsaturated soil. Background Art

[0002] Most of the soils that can be touched by human engineering activities are unsaturated soils. How to quickly obtain the matrix suction and unsaturated strength of soils is an urgent problem to be solved. At present, the methods for measuring matrix suction include filter paper method, axis translation method and tensiometer method. Although these methods can measure the size of soil matrix suction, the measurement cycle ranges from 7 to 30 days, or even longer. Drawing a water-soil characteristic curve generally requires 6 to 8 data points, and the time required increases exponentially. At present, the commonly used instruments for measuring the unsaturated strength of soils are unsaturated direct shear instrument, unsaturated triaxial instrument and GDS unsaturated triaxial instrument. These instruments all use the axis translation method as the theoretical basis. The matrix suction is balanced by applying air pressure first, and then the shear process is carried out. The test cycle will be longer. The use of the above instruments will greatly reduce the test efficiency, extend the scientific research and engineering cycle, and cause waste of resources and economy.

[0003] At present, there are unsaturated soil capillary suction direct shear instrument and use method (CN108956331A), fully automatic direct shear instrument for studying unsaturated shear properties of high-compacted bentonite (CN109211687A), unsaturated soil evaporation dehumidification direct shear instrument and use method (CN108693049A), unsaturated soil shear strength parameter determination method and special direct shear instrument (CN107389473A), etc. Although these methods can measure the unsaturated soil matrix suction and unsaturated strength, the test efficiency is low and a lot of time is required, and the application in scientific research and engineering is greatly limited. For a patented method for measuring the unsaturated soil matrix suction in a centrifugal model test (CN110568151A), the unsaturated data measured by this patent is single and the steps are numerous, which causes a waste of resources to a certain extent. Therefore, the present invention proposes a device and method for quickly measuring the unsaturated soil matrix suction and shear strength. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a device and method for quickly measuring the matrix suction and shear strength of unsaturated soil. The present invention can accurately, quickly and efficiently measure the matrix suction and shear strength of unsaturated soil.

[0005] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0006] A device for rapidly measuring the suction and shear strength of unsaturated soil matrix, comprising a centrifuge chamber 1 and a cutting line workbench 2; a pressurizing system 3; a pressure sensor 6 installed on a horizontal force transmission rod 5; a breathable pressure cover 7; a shear box 9 connected to a drainage collection box 15; a ball bearing 16 and a slideway 17 at the bottom of the drainage collection box 15; a limiting groove 13; a shear force application system 24 installed at the bottom 27 of the chamber, a shear force sensor and a displacement sensor 22 installed on the shear force transmission rod 25; and a centrifuge chamber sealing device 20.

[0007] The experimental control system 19 is connected to the experimental device through a data transmission line 18, including the control of the centrifuge speed, the control of the axial pressure and the number of pressurized samples, the control of the shear rate, the control of the electromagnet 12, the control of the centrifuge chamber sealing device 20, and the collection of axial pressure, shear force and shear displacement.

[0008] The pressurizing system 3 includes a pressure cylinder, which is evenly divided into four pressure chambers 4. The length of the spiral piston entering the pressure chamber 4 is adjusted by the control system 19. The pressure of the pressure chamber 4 acts on the breathable pressure cover 7 with air holes through the horizontal force transmission rod 5. The signal collected by the pressure sensor 6 reversely corrects the actual pressurization value.

[0009] The shear box 9 is divided into two parts, an upper shear box 10 and a lower shear box 11. The two parts are connected by an electromagnet 12. Both parts need to be powered on during the non-shearing stage of the experiment. The power is automatically cut off at the beginning of the shearing stage. The upper shear box 10 is fixed to the limit groove 13 by screws 23, and the lower shear box 11 is in contact with the shear force transmission rod 25.

[0010] The drainage box 15 is divided into a hollow cylinder, the top surface of which has a small hole in direct contact with the sample 14, and the drainage box is connected to the shear box 9 through threads.

[0011] The slideway 17 of the cutting workbench 2 is longer than the bottom surface of the drainage collection box 15, and the ball bearing 16 can be in close contact with the slideway 17.

[0012] The shear force applying system 24 sets the shear rate through a computer, applies shear force through gear rotation, and collects shear force and shear displacement data through a sensor on the shear force transmission rod 25.

[0013] The centrifuge chamber sealing device 20 includes a sensor 21 and an electromagnetic self-locking device 22. After the chamber cover is closed, the sensor 21 sends back a signal, the electromagnetic self-locking device 22 is automatically locked, and the experimental program can be run. When the chamber rotation speed is 0r / s, the electromagnetic self-locking device 22 is powered off and unlocked, and the chamber cover can be opened.

[0014] A method for quickly measuring the matrix suction and shear strength of unsaturated soil, using the device for quickly measuring the matrix suction and shear strength of unsaturated soil, comprises the following steps:

[0015] Step 1: Prepare the sample

[0016] First, obtain the original soil core or reshaped soil material according to the experimental requirements, and take samples with a special ring knife for the original soil core experiment; for the reshaped sample, it is necessary to configure it according to the experimental requirements, and the reshaped sample is prepared in the shear box 9;

[0017] Step 2: Installation of unsaturated specimen

[0018] First, the shear box 9 is electrically connected, and the shear box 9 is taken out from the limiting groove 13, and the ring knife sample is transferred into the shear box 9 or the shear box 9 is used to prepare the reshaped sample, and the air permeable pressure cover 7 is covered, and then the shear box 9 is connected to the drainage collection box 15, and finally the shear box 9 is put back into the limiting groove and fixed with screws 23;

[0019] Step 3: Measurement of matrix suction

[0020] Make the horizontal pressure rod 5 and the breathable pressure cover 7 in close contact, adjust the shear force transmission rod 25 to be in close contact with the lower shear box 11, and close the centrifuge chamber cover; select the axial pressure size and the number of pressurization according to the experimental needs, start the pressurization system 3, and after the signal value of the pressure sensor 6 is stable, set the speed of the centrifuge chamber 1, and the matrix suction value can be calculated according to the speed;

[0021] Step 4: Measurement of unsaturated intensity

[0022] After the matrix suction is stabilized, the centrifuge chamber 1 keeps moving at the original speed, the electromagnet 12 is powered off, the shear force application system 24 is started, and the shear force sensor and the displacement sensor 26 are used to collect shear force and shear displacement data;

[0023] Step 5: Measurement of moisture content of unsaturated samples

[0024] After the shear test is completed, the pressure of the pressurizing system 3 is adjusted to zero, the rotation speed of the centrifuge chamber 1 is reduced to 0 r / s, the sample 14 is quickly taken out, the moisture content of the sample 14 is measured, and entered into the experimental control system 19 for storage and analysis.

[0025] The advantages of the present invention are:

[0026] The centrifugal force generated by the rotation of the centrifuge can discharge excess water from the sample. When equilibrium is reached, the matrix suction is equal to the centrifugal force, and the matrix suction of the soil material can be quickly measured. The shear strength of the soil material can then be measured through the built-in direct shear device, and the measurement efficiency is 15 to 30 times that of traditional instruments.

[0027] The four pressure chambers 4 of the axial pressurization system 3 can work independently. One experiment can measure the unsaturated soil matrix suction and shear strength under four axial load conditions. The sensor on the horizontal force transmission rod 5 can record the actual pressure value acting on the sample and reversely correct the pressure value of the corresponding pressure chamber 4, so that the experimental data obtained is more accurate.

[0028] The shear box 9 is divided into an upper shear box 10 and a lower shear box 11, which are connected by an electromagnet 12, and the reshaped sample is directly prepared therein, thereby solving the disturbance problem of the reshaped sample during the transfer process.

[0029] The shear force sensor and displacement sensor installed on the shear force transmission rod 21 can record the shear force and shear displacement of the sample in real time, and the obtained experimental data is more accurate.

[0030] The device only needs to manually measure the moisture content of the sample after the test. The experimental process is automatically completed by the control program, which reduces a lot of manpower input and saves a lot of time for the test personnel.

[0031] The breathable pressure cover 7 is provided with breathable holes 28 in the cover body to prevent negative pressure from being generated near the cover body during the matrix suction measurement process, thereby solving the influence of negative pressure on matrix suction.

[0032] This experimental device can accurately and quickly measure the matrix suction and shear strength of unsaturated soil, greatly improving the experimental efficiency and having important significance for the study of unsaturated soil properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a top view of a test device for a device and method for quickly measuring the matrix suction and shear strength of unsaturated soil.

[0034] Figure 2 It is the left view of the complete test of sample No. ① of the present invention.

[0035] In the figure: 1-centrifuge cabin; 2-secting workbench; 3-pressurization system; 4-pressure chamber; 5-horizontal force transmission rod; 6-pressure sensor; 7-breathable pressure cover; 8-contact groove; 9-shear box; 10-upper shear box; 11-lower shear box; 12-electromagnet; 13-limiting groove; 14-sample; 15-drainage collection box; 16-ball; 17-slide 17; 18-data transmission line; 19-control system; 20-centrifuge cabin closing device; 21-sensor; 22-electromagnetic self-locking device; 23-screw; 24-shear force application system; 25-shear force transmission rod; 26-shear force sensor and displacement sensor; 27-cabin bottom. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0037] like Figure 1 , 2 As shown, a device for quickly measuring the suction and shear strength of unsaturated soil matrix includes a centrifuge chamber 1 and a cutting line workbench 2; a pressurizing system 3; a horizontal force transmission rod equipped with a pressure sensor in contact with the contact groove of a breathable pressure cover; a breathable pressure cover 7 in contact with a sample 14; a shear box 9 connected to a drainage collection box 15 and placed in a limiting groove 13; a ball bearing 16 and a slideway 17 at the bottom of the drainage collection box 15; a shear force application system 24 installed at the bottom 27 of the chamber, a shear force transmission rod 25 equipped with a shear force sensor and a displacement sensor 26 in contact with the lower shear box 11; and a centrifuge chamber sealing device 20.

[0038] Figure 1 In the experiment, the experimental control system 19 is connected to the designed device through the data transmission line 18, so as to control the centrifuge speed, axial pressure, number of sample pressurization, shear rate, and electromagnet 12, and obtain the axial pressure, shear force and shear displacement of the sample 14 in real time.

[0039] Figure 1 In the cabin axial pressurization system 3, the pressure cylinder is evenly divided into four pressure chambers 4 by steel plates. The length of each spiral piston entering the pressure chamber 4 is individually controlled by the control system 19. The pressure of the pressure chamber 4 acts on the breathable pressure cover 7 with air holes through the horizontal force transmission rod 5, thereby applying axial pressure to the sample. The magnitude of the axial pressure value is obtained by the pressure sensor 6 of the horizontal force transmission rod 5, and the actual pressure value in the pressure chamber is reversely corrected.

[0040] Figure 1 In the shear box 9, the upper shear box 10 and the lower shear box 11 are connected by an electromagnet 12, and the other end of the lower shear box 11 is connected to the drainage collection box 15; the other end of the drainage collection box 15 is installed with a ball 16, and a slide 17 is provided on the cutting workbench 2, and the ball 16 is in close contact with the slide 17; the upper shear box 10 is fixed to the limit groove 13 by a screw 23.

[0041] Figure 1 In the experiment, the sensor 21 and the electromagnetic self-locking device 22 in the centrifuge chamber closing device 20 are installed on the equipment box. When the sensor 21 transmits the cabin cover closing signal, the electromagnetic self-locking device 27 is energized and the experimental procedure begins; when the cabin rotation speed is 0r / s, the electromagnetic self-locking device 22 is de-energized and unlocked, and the cabin cover can be opened.

[0042] Figure 2 In the embodiment, the shear force applying system 24 is installed at the bottom 27 of the cabin, the shear rate is set by a computer, and the shear force and shear displacement data are collected by the sensor on the shear force transmission rod 25.

[0043] The above-mentioned device and method for quickly measuring the matrix suction and shear strength of unsaturated soil include the following steps:

[0044] Step 1: Prepare the specimen

[0045] First, obtain the original soil core or reshaped soil material according to the experimental needs, and take samples with a special ring knife for the original soil core experiment; for the reshaped samples, they need to be configured according to the experimental requirements, and the reshaped samples are prepared in a shear box.

[0046] Step 2: Installation of unsaturated specimen

[0047] First, connect the shear box 9 with electricity, take out the shear box 9 from the limiting groove 13, transfer the original ring knife sample into the shear box 9 or use the shear box 9 to prepare a reshaped sample, cover it with the breathable pressure cover 7, and then connect the shear box 9 to the drainage collection box 15, and finally put the shear box 9 back into the limiting groove 13 and fix it with screws 23.

[0048] Step 3: Measurement of matrix suction

[0049] Make the horizontal pressure rod 5 and the breathable pressure cover 7 in close contact, adjust the shear force transmission rod 25 to be in close contact with the lower shear box 11, and close the centrifuge chamber cover; select the axial pressure size and the number of pressurizations according to experimental needs, start the pressurization system 3, and after the signal value of the pressure sensor 6 is stable, set the rotation speed of the centrifuge chamber 1, and the matrix suction value can be calculated through the rotation speed.

[0050] Step 4: Measurement of unsaturated intensity

[0051] After the matrix suction is stabilized, the centrifuge chamber 1 keeps rotating at the original speed, the electromagnet 12 is powered off, the shear force applying system 24 is started, and the shear force sensor and displacement sensor 26 collect shear force and shear displacement data.

[0052] Step 5: Measurement of moisture content of unsaturated samples

[0053] After the shear test is completed, the pressure of the pressurizing system 3 is adjusted to zero, the rotation speed of the centrifuge chamber 1 is reduced to 0 r / s, the sample 14 is quickly taken out, the moisture content of the sample 14 is measured, and entered into the experimental control system 19 for storage and analysis.

[0054] The invention is applicable to sandy soil, gravel soil and over-consolidated soil.

[0055] The above embodiment is only one implementation mode of the present invention and is not intended to limit the protection scope of the present invention. All equivalent replacements and improvements to the present invention are included in the protection scope of the present invention.

Claims

1. A device for rapidly measuring the matrix suction and shear strength of unsaturated soil, characterized in that: The invention comprises a centrifuge chamber (1) and a cutting line workbench (2); a pressurizing system (3); a pressure sensor (6) installed on a horizontal force transmission rod (5); a breathable pressure cover (7); a shear box (9) connected to a drainage collection box (15); a ball (16) and a slideway (17); a limit groove (13); a shear force application system (24) installed on the bottom of the chamber (27); a shear force sensor and a displacement sensor (26) installed on the shear force transmission rod (25); a centrifuge chamber sealing device (20); an experimental control system (19); the experimental control system (19) is connected to the experimental device through a data transmission line (18), and comprises the control of the centrifuge speed, the control of the axial pressure and the number of pressurized samples, the control of the shear rate, the control of the electromagnet (12), the control of the centrifuge chamber sealing device (20), and the collection of axial pressure, shear force and shear displacement; the pressurizing system (3) comprises a pressure cylinder, which is evenly divided into four pressure chambers (4), and the pressure chamber is sealed by the experimental control system (19). The test control system (19) adjusts the length of the spiral piston entering the pressure chamber (4), and the pressure of the pressure chamber (4) acts on the breathable pressure cover (7) with a breathable hole through the horizontal force transmission rod (5). The signal collected by the pressure sensor (6) reversely corrects the actual pressure value; the shear box (9) is divided into an upper shear box (10) and a lower shear box (11), and the two parts are connected by an electromagnet (12). In the non-shearing stage of the experiment, both parts need to be electrically connected. When the shearing stage starts, the shear box (9) is automatically The power is automatically cut off, the upper shear box (10) is fixed to the limit groove (13) by a screw (23), and the lower shear box (11) contacts the shear force transmission rod (25); the centrifuge chamber closing device (20) includes a sensor (21) and an electromagnetic self-locking device (22), after the chamber cover is closed, the sensor (21) sends back a signal, the electromagnetic self-locking device (22) is automatically locked, and the experimental program runs; when the chamber rotation speed is 0r / s, the electromagnetic self-locking device (22) is powered off and unlocked, and the chamber cover is opened.

2. A device for rapidly measuring the matrix suction and shear strength of unsaturated soil according to claim 1, characterized in that: The drainage collection box (15) is a hollow cylinder, the top surface of which is provided with a small hole for direct contact with the sample (14), and the drainage collection box (15) is connected to the shear box (9) via threads.

3. The device for rapidly measuring the matrix suction and shear strength of unsaturated soil according to claim 1, characterized in that: The slideway (17) is longer than the bottom surface of the drainage collection box (15), and the ball (16) is in close contact with the slideway (17).

4. The device for rapidly measuring the matrix suction and shear strength of unsaturated soil according to claim 1, characterized in that: The shear force applying system (24) sets the shear rate through a computer, applies shear force through gear rotation, and collects shear force and shear displacement data through a sensor on the shear force transmission rod (25).

5. A method for rapidly measuring the matrix suction and shear strength of unsaturated soil, using the device for rapidly measuring the matrix suction and shear strength of unsaturated soil as claimed in claim 1, characterized in that The usage steps include the following: Step 1: Prepare the sample First, obtain the original soil core or reshaped soil material according to the experimental requirements, and take samples with a special ring cutter for the original soil core experiment; the reshaped sample needs to be configured according to the experimental requirements, and the reshaped sample is prepared in a shear box (9); Step 2: Installation of unsaturated specimen First, the shear box (9) is electrically connected, the shear box (9) is taken out from the limiting groove (13), the original ring knife sample is transferred into the shear box (9) or the shear box (9) is used to prepare a reshaped sample, the air-permeable pressure cover (7) is covered, and the shear box (9) is connected to the drainage collection box (15), and finally the shear box (9) is put back into the limiting groove (13) and fixed with screws (23); Step 3: Measurement of matrix suction The horizontal force transmission rod (5) and the air permeable pressure cover (7) are in close contact, the shear force transmission rod (25) is adjusted to be in close contact with the lower shear box (11), and the centrifuge chamber cover is closed; The axial pressure and the number of pressurizations are selected according to experimental needs, and the pressurization system (3) is started. After the signal value of the pressure sensor (6) is stabilized, the rotation speed of the centrifuge chamber (1) is set, and the matrix suction value can be calculated according to the rotation speed; Step 4: Measurement of unsaturated intensity After the matrix suction is stabilized, the centrifuge chamber (1) keeps rotating at the original speed, the electromagnet (12) is powered off, the shear force application system (24) is started, and the shear force sensor and the displacement sensor (26) are used to collect shear force and shear displacement data; Step 5: Measurement of moisture content of unsaturated samples After the shear test is completed, the pressure of the pressurizing system (3) is adjusted to zero, the rotation speed of the centrifuge chamber (1) is reduced to 0 r / s, the sample (14) is quickly taken out, the moisture content of the sample (14) is measured, and entered into the experimental control system (19) for storage and analysis.

Images