CN111044366B - Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range - Google Patents
Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range Download PDFInfo
- Publication number
- CN111044366B CN111044366B CN201911391628.8A CN201911391628A CN111044366B CN 111044366 B CN111044366 B CN 111044366B CN 201911391628 A CN201911391628 A CN 201911391628A CN 111044366 B CN111044366 B CN 111044366B
- Authority
- CN
- China
- Prior art keywords
- soil sample
- suction
- annular
- unit
- tension
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/066—Special adaptations of indicating or recording means with electrical indicating or recording means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0017—Tensile
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/003—Generation of the force
- G01N2203/0042—Pneumatic or hydraulic means
- G01N2203/0048—Hydraulic means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0067—Fracture or rupture
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0682—Spatial dimension, e.g. length, area, angle
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention discloses a test device for measuring the internal tensile stress and cracks of unsaturated soil in real time within a full suction range, which comprises a soil sample tension unit, a stress-strain test unit and an image acquisition unit, wherein the soil sample tension unit is an annular soil sample tension unit, a low suction force measurement device and a high suction force measurement device are detachably arranged on the annular soil sample tension unit, a camera device is arranged above the annular soil sample tension unit in a suspended manner, the annular soil sample tension unit is connected with the image acquisition unit through the camera device, the annular soil sample tension unit is electrically connected with the stress-strain test unit, and the suction force is controlled by combining a tensiometer and a saturated salt solution, so that the change range of suction force research can be further expanded, and the change of the internal tensile stress of a soil body and the development condition of cracks within the full suction range can be dynamically observed.
Description
Technical Field
The invention belongs to the technical field of geotechnical engineering, and particularly relates to a test device for measuring the internal tensile stress and the cracks of unsaturated soil in real time within a full suction range.
Background
In unsaturated soils, tensile strength and tensile stress are the two main factors controlling the development of soil cracks. The increase of suction makes the soil body shrink mummification gradually, and inside tensile stress increases gradually, and when tensile stress exceeded tensile strength, the soil body appears the crack, and it is crucial to know the mechanism that the increase of suction leads to the crack to sprout in the unsaturated soil. Many experimental methods and theoretical models have been proposed for measuring and predicting tensile strength. However, the annular test device for measuring the internal tensile stress and the crack of unsaturated soil in real time within the full suction range is rarely used in geotechnical engineering.
The change process of the tensile stress in the soil body is complex and is often related to the factors such as the particle size of the soil body, the water content, the suction force and the like. In the previous research for predicting the tensile stress of the soil body, most of the research focuses on solving the relationship between the tensile stress and the water content, and the suction force is less considered. No matter the device such as a clamp is utilized or a three-axis instrument is used, the loads applied by the traditional soil body tensile strength testing methods belong to external loads, and the tensile stress change in the soil body cannot be really measured. The suction is used as the stress state quantity in the soil body, the change process of the tensile stress can be reflected more truly, the prediction of the tensile strength of the soil is more reliable, and therefore, the change rule of the tensile stress and the suction is researched, the influence of the suction on soil body cracks is observed, and certain theoretical guidance significance and engineering practice significance are achieved. Because the suction value measured by the tensiometer is limited and is not suitable for the soil body with larger self suction, further exploration is urgently needed for the research on the change of the tensile stress and the crack in the full suction range.
Disclosure of Invention
In view of this, the invention provides a test device for measuring the tensile stress and the fracture in unsaturated soil in real time within the full suction range, which has the advantages of expanding the suction range and dynamically observing the change of the tensile stress and the development condition of the fracture in the soil body within the full suction range.
The test device for measuring the internal tensile stress and the cracks of unsaturated soil in real time within the full-suction range comprises a soil sample tension unit, a stress-strain test unit and an image acquisition unit, wherein the soil sample tension unit is an annular soil sample tension unit, a low-suction measurement device and a high-suction measurement device are detachably arranged on the annular soil sample tension unit, a camera device is arranged above the annular soil sample tension unit in a hanging mode, the annular soil sample tension unit is connected with the image acquisition unit through the camera device, and the annular soil sample tension unit is electrically connected with the stress-strain test unit.
The suction measured value of the low suction measuring device is not more than 2.6MPa, and the suction measured value of the high suction measuring device is more than 2.6 MPa.
The low-suction measuring device and the high-suction measuring device are both electrically connected with the suction display, a chip with data processing and control functions is arranged in the suction display, and the chip is a single chip microcomputer chip.
Low suction measuring device is the tensiometer, the tensiometer includes tensiometer main part, porous argil board, diaphragm, tension foil gage, water receiver and tension cap, wherein, the diaphragm is split into first cavity and second cavity with the tensiometer main part, first cavity just is provided with the tension cap with the relative port department of diaphragm, be provided with the tension stress piece in the first cavity, the tension foil gage is connected with the suction display electricity, be provided with porous argil board in the second cavity, be provided with the water receiver between porous argil board and the diaphragm.
The high-suction measuring device is a suction control circulating system which comprises an annular soil sample closed cylinder, a saturated salt solution closed cylinder and an air circulating pump, wherein the annular soil sample closed cylinder comprises an upper cover, a lower cover and a cylinder body, the cylinder body is detachably arranged between the upper cover and the lower cover, two pipeline through holes are oppositely formed in the upper cover of the soil sample closed cylinder and the top end of the saturated salt solution closed cylinder, pipelines are respectively arranged in the pipeline through holes, the annular soil sample closed cylinder is connected with the saturated salt solution closed cylinder through two pipelines, the air circulating pump and a pressure sensor are arranged on any pipeline in the two pipelines, and the pressure sensor is electrically connected with a suction display.
The annular soil sample tension unit comprises an annular soil sample containing device, a soil sample crack capturing layer and a weighing device, wherein the weighing device is provided with the annular soil sample containing device, an annular soil sample is contained in the annular soil sample containing device, the top layer of the annular soil sample is detachably provided with the soil sample crack capturing layer, and the soil sample crack capturing layer is provided with a camera device.
The soil sample crack capturing layer is sandy soil, the weighing device is a balance, the annular soil sample containing device comprises an outer ring and an inner ring, the outer ring and the inner ring are made of PVC materials in a surrounding mode, lubricating oil is smeared in the outer ring and the inner ring, and a through hole for inserting the low-suction measuring device is formed in the outer ring.
The inner ring is internally and detachably provided with strain gauges, the strain gauges are symmetrically arranged at the center of the inner ring, the strain gauges are resistance-type strain gauges, and the annular soil sample containing device is electrically connected with the stress-strain testing unit through the strain gauges.
Stress strain test unit includes temperature moisture content display, four-channel strain data collection station, the foil gage is connected with four-channel strain data collection station electricity, temperature moisture content display sets up on weighing device, temperature moisture content display is connected with four-channel strain data collection station electricity, and temperature moisture content display is any one of liquid crystal display or charactron kind, including the controller that has data calculation processing function among the four-channel strain data collection station, the controller is any one in MCU, PC, PLC or the industrial computer.
The camera device is a CCD high-speed camera, a camera support is arranged on one side of the weighing device in a matching mode with the CCD high-speed camera, the CCD high-speed camera is electrically connected with an image acquisition unit, and the image acquisition unit is a PIV testing system.
The invention discloses an annular test device for measuring internal tensile stress and cracks of unsaturated soil in real time within a full suction range, which comprises an annular soil sample tension unit, a stress-strain test unit, an image acquisition unit, a low suction measurement device and a high suction measurement device, wherein two suction methods of a tensiometer and a saturated saline solution are jointly used for controlling the suction, the suction test is carried out by adopting the tensiometer under the pressure of not more than 2.6MPa, the suction test is carried out by adopting the saturated saline solution under the pressure of more than 2.6MPa, the change range of the suction research is further expanded, the change of the internal tensile stress of a soil body and the development condition of the cracks within the full suction range are dynamically observed, and the change of the tensile strain of the soil body is reflected from the internal state quantity of the suction, so that the stress-strain state of the soil body can be more truly reflected; and the suction value when the soil body reaches tensile failure can be obtained, and a suction reference is provided for predicting the generation of cracks.
The test device is provided with the balance, the temperature and water content display and the suction display, can obtain a soil-water characteristic curve of a soil body while observing the stress-strain state of the soil body, and can make comparison reference for other methods; in addition, a high-precision camera device is arranged right above the balance, data of each display and a soil crack displacement image can be measured in real time by means of a PIV technology, a soil sample is annular, the shape is novel, the appearance is attractive, a strain gauge and a tensiometer are convenient to install, the occupied area of the whole device is reduced, and the instrument is simple in structure, convenient to operate and easy to master.
Drawings
FIG. 1 is a schematic diagram of a test apparatus for measuring the tensile stress and cracks in unsaturated soil in real time under low suction.
FIG. 2 is a schematic diagram of a test apparatus for real-time measurement of tensile stress and cracks in unsaturated soil under high suction.
Fig. 3 is a top view of the soil sample tension unit at low suction.
Fig. 4 is a top view of the soil sample tension unit at high suction.
Fig. 5 is a schematic view of the structure of the tensiometer.
FIG. 6 is a graph of saturated saline solution and corresponding suction values, wherein the reference numbers are as follows:
1. the device comprises a camera bracket, 2, a camera device, 3, an inner ring, 4, an outer ring, 5, a soil sample containing device, 6, a low-suction measuring device, 7, an image acquisition unit, 8, a suction display, 9, a temperature and moisture content display, 10, a four-channel strain data acquisition unit, 11, a stress and strain testing unit, 12, an annular soil sample, 13, a strain gauge, 14, a weighing device, 15, a lower cover, 16, a cylinder body, 17, an upper cover, 18, a pipeline, 19, an air circulating pump, 20, a saturated saline solution closed cylinder, 21, a tension cap, 22, a diaphragm, 23, a tension meter main body, 24, a porous clay plate, 25, a water storage device, 26, a tension strain gauge,
wherein the reference numbers are as follows:
1. the device comprises a camera support, 2 a camera device, 3 an inner ring, 4 an outer ring, 5 a soil sample containing device, 6 a low-suction measuring device, 7 an image acquisition unit, 8 a suction display, 9 a temperature and moisture content display, 10 a four-channel strain data acquisition unit, 11 a stress and strain testing unit, 12 an annular soil sample, 13 a strain gauge, 14 a weighing device, 15 a lower cover, 16 a cylinder body, 17 an upper cover, 18 a pipeline, 19 an air circulating pump, 20 a saturated saline solution closed cylinder, 21 a tension cap, 22 a diaphragm, 23 a tension meter main body, 24 a porous clay plate, 25 a water storage device and 26 a tension strain gauge.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It is understood that the described embodiments are merely some implementations, rather than all implementations, and that all other embodiments that can be derived by one of ordinary skill in the art based on the described embodiments are intended to be within the scope of the present invention.
As shown in fig. 1 to 5, the test device for measuring the internal tensile stress and the cracks of unsaturated soil in real time within a full-suction range comprises a soil sample tension unit, a stress-strain test unit 11 and an image acquisition unit 7, wherein the soil sample tension unit is an annular soil sample tension unit, a low-suction measurement device 6 and a high-suction measurement device are detachably arranged on the annular soil sample tension unit, a camera device 2 is arranged above the annular soil sample tension unit in a suspended manner, the annular soil sample tension unit is connected with the image acquisition unit 7 through the camera device 2, and the annular soil sample tension unit is electrically connected with the stress-strain test unit 11.
The suction measured value of the low suction measuring device 6 is not more than 2.6MPa, and the suction measured value of the high suction measuring device is more than 2.6 MPa.
The low-suction measuring device 6 and the high-suction measuring device are both electrically connected with the suction display 8, a chip with data processing and control functions is arranged in the suction display 8, and the chip is a single chip microcomputer chip.
The suction display 8 is positioned at the right lower part of the surface of the soil sample tension unit, and the precision is 0.001 MPa.
The low suction measuring device 6 is a tension meter, the tension meter comprises a tension meter main body 23, a porous pottery clay plate 24, a diaphragm 22, a tension strain gauge 26, a water storage device 25 and a tension cap 21, wherein the diaphragm 22 divides the tension meter main body 23 into a first chamber and a second chamber, the port of the first chamber opposite to the diaphragm 22 is provided with the tension cap 21, the first chamber is internally provided with the tension strain gauge 26, the tension strain gauge 26 is electrically connected with the suction display 8, the second chamber is internally provided with the porous pottery clay plate 24, and the water storage device 25 is arranged between the porous pottery clay plate 24 and the diaphragm 22.
The tensiometer unit is MPa, and the maximum measuring range is up to 2.6 MPa. The through hole on the outer ring 4 is arranged in the soil sample and is also contacted with the surface of the inner ring 3 through the strain gauge 13, so that the tensile strength and the suction force under the same water content can be measured. The tensiometer should be vacuum saturated for 24h before use, applying a pre-pressure of at least 1.5 MPa. The suction display 8 is electrically connected with the tension strain gauge 26, can obtain the suction value of the tensioner, and is connected with a high suction measuring device when the suction exceeds the tension gauge measuring range by 2.6 MPa.
The high-suction measuring device is a suction control circulating system which comprises an annular soil sample closed cylinder, a saturated saline solution closed cylinder 20 and an air circulating pump 19, wherein the annular soil sample closed cylinder comprises an upper cover 17, a lower cover 15 and a cylinder body 16, the cylinder body 16 is detachably arranged between the upper cover 17 and the lower cover 15, through holes are formed in two opposite sides of the cylinder body 16, two pipeline 18 through holes are oppositely formed in the upper cover 17 of the soil sample closed cylinder and the top end of the saturated saline solution closed cylinder 20, pipelines 18 are respectively arranged in the pipeline 18 through holes, the annular soil sample closed cylinder is connected with the saturated saline solution closed cylinder 20 through two pipelines 18, the air circulating pump 19 and a pressure sensor are arranged on any pipeline 18 of the two pipelines 18, and the pressure sensor is electrically connected with the suction display 8.
The diameter of the outer cylinder of the annular soil sample closed cylinder is 25cm, the height of the outer cylinder is 10cm, the diameters of the upper cover 17 and the lower cover 15 are both 30cm, the heights of the upper cover 17 and the lower cover 15 are both 2.5cm, the annular soil sample is closed by combining the upper cover and the lower cover, and the sealing performance of the device is guaranteed when external suction is applied in a high-suction state. The upper cover 17 is provided with through holes, one through hole is connected with an air circulating pump, and the other through hole is connected with a saturated saline solution closed cylinder. Two through holes are correspondingly formed in the centers of two sides of the soil sample closed cylinder, one through hole is used for mounting a tension meter, and the other through hole is used for communicating the strain gauge 13 with the four-channel strain data acquisition unit 10.
The ratio of liquid to gas in the saturated brine closing cylinder 20 shown is 1: and 5, the suction force provided for the annular soil sample is changed by changing the type of the saturated salt solution connected with the system. The left and right sides of the top cover of the saturated saline solution closed cylinder 20 are respectively provided with a through hole which is respectively connected with the annular soil sample closed cylinder and the air circulating pump 19. The air circulation pump 19 circulates the pressure inside the whole system, speeding up the suction balance.
Referring to FIG. 6, the saturated saline solution and the corresponding suction force value are expressed by the relative humidity of the saturated saline solution according to the standard relative humidity of the saturated saline solution given by the national Committee for physical chemical technology (PHY), and the equation of the relative humidity of the selected saturated saline solution and the corresponding suction force relationship is as follows,
wherein:Rfor ideal gas constants (8.31441J/mol),Tin the case of absolute humidity, the humidity is,h r in order to be the relative humidity,M w is the molar mass of water, d w Is the density of the water and is,sis a suction force.
The annular soil sample tension unit comprises an annular soil sample containing device 5, a soil sample crack capturing layer and a weighing device 14, wherein the weighing device 14 is provided with the annular soil sample containing device 5, an annular soil sample 12 is contained in the annular soil sample containing device 5, the top layer of the annular soil sample 12 is detachably provided with the soil sample crack capturing layer, and the soil sample crack capturing layer is provided with a camera device 2.
The soil sample crack capturing layer is sandy soil, the weighing device 14 is a balance, the annular soil sample containing device 5 comprises an outer ring 4 and an inner ring 3, the outer ring 4 and the inner ring 3 are made of PVC materials in an enclosing mode, lubricating oil is smeared in the outer ring 4 and the inner ring 3, and a through hole for inserting the low-suction measuring device is formed in the outer ring 4.
Annular soil sample hold 5 sizes be: the diameter of the inner ring 3 is 5.5cm, the diameter of the outer ring 4 is 15.24cm, and the average height of the inner ring 3 and the outer ring 4 is 4.1 cm. The inner ring 3 is made of PVC material and has a thickness of 0.5cm, and the outer ring 4 is made of PVC material and has a thickness of 1.65 cm. The right side of the outer ring 4 is provided with a through hole with the diameter of 1.2cm for installing a tension meter.
Lubricating oil is coated on the outer periphery of the inner ring 3 and the inner periphery of the outer ring 4, so that friction generated in the sample loading process can be reduced, and the side surface and the bottom of the annular soil sample 12 are ensured to have certain water impermeability. Before starting the test, the soil sample was sealed from the bottom with a plastic film and from the circumference with a rubber film to maintain the sealability of uniform shrinkage when the soil sample shrinks radially.
The balance is used for bearing the soil sample and recording the change of the water content of the soil sample. The range of the balance is 5000g, and the precision is 0.01 g.
Can dismantle in the inner ring 3 and be provided with foil gage 13, foil gage 13 sets up in 3 center departments of inner ring for two foil gage 13 symmetries, foil gage 13 is resistance-type foil gage, annular soil sample holds device 5 and is connected with stress-strain test unit 11 electricity through foil gage 13, the foil gage be quarter bridge resistance-type foil gage, resistance is 350 omega, and the number is 2, pastes in the intermediate position of PVC inner ring surface symmetrically, highly is 2.04cm for measure the inside tensile strain of soil body.
Stress strain test unit 11 includes temperature moisture content display 9, four-channel strain data collector 10, foil gage 13 is connected with four-channel strain data collector 10 electricity, temperature moisture content display 9 sets up on weighing device 14, temperature moisture content display 9 is connected with four-channel strain data collector 10 electricity, and temperature moisture content display is any one of 9 liquid crystal display or charactron types, including the controller that has data calculation processing function among the four-channel strain data collector 10, the controller is any one of MCU, PC, PLC or the industrial computer.
The temperature water content display uses the same display screen, wherein the water content is obtained by inverse calculation of the initial state weight value and the final state weight value, the temperature display precision is 1 ℃, and the water content display precision is 0.1%.
The four-channel strain data acquisition unit 10 is positioned on the left side of the soil sample tension unit and connected with the strain gauge 13, and can continuously record the change of strain along with time. The strain gauge converts strain into stress, the average value of the two strain gauges is taken as a stress value, the formula of converting strain into stress is as follows,
wherein the content of the first and second substances,σ tm in order to obtain the desired tensile stress,ε(t) Is the average reading of the strain gauge,R or the diameter of the inner ring is the diameter of the inner ring,R ir the diameter of the outer ring is the diameter of the outer ring,R os is the outer diameter of the annular soil sample,E r the elastic modulus of the PVC material is shown to be 2.9 GPa.
The camera device 2 is a CCD high-speed camera, a camera support 1 is arranged on the CCD high-speed camera in a matching mode, the camera support 1 is arranged on one side of a weighing device 14, the CCD high-speed camera is electrically connected with an image acquisition unit 7, and the image acquisition unit 7 is a PIV testing system.
The CCD high-speed camera has the resolution of 1626 pixels multiplied by 1236 pixels, the pixel size of 4.4 mu m multiplied by 4.4 mu m, the exposure time of 100 mu s multiplied by 80ms, the acquisition rate of 200fps, and simultaneously provides a Camlink special interface.
The PIV testing system comprises a hardware system and a software system, wherein the hardware system mainly comprises a CCD high-speed camera, an image acquisition unit 7, post-processing equipment and the like, and the software system adopts DaVis 8.0 series software of Germany LaVision company and PIVview2C software to complete the analysis and display work of the soil displacement image of the whole process of the acquired crack development.
The balance is a bearing body for measuring the water content change of the annular soil sample 12, and sandy soil is uniformly sprayed on the surface of the annular soil sample 12 and is used for observing the generation of soil body cracks and calculating the displacement of the cracks; the two strain gauges 13 are symmetrically attached to the surface of the soil sample inner ring 3 and used for measuring the strain of a soil body, and the tensiometer is installed on the surface of the soil body inner ring 3 through a through hole in one side of the outer ring 4 and used for measuring the suction force of the soil body in a low-suction state and is suitable for being used when the suction force is smaller than 2.6 MPa. The strain gauge 13 and the tensiometer are both in contact with the surface of the inner ring 3, so that the measurement of the strain and the suction of a soil body under the same water content is facilitated. The suction display 8 is positioned at the lower right corner of the balance, and the temperature and moisture content display 9 is positioned at the lower left corner of the balance; the high-suction measuring device is a suction control circulating system and comprises an annular soil sample closed cylinder, a saturated saline solution closed cylinder 20 and an air circulating pump 19, is used for realizing the gradual application of suction and is used when the suction exceeds 2.6 MPa; the CCD high-speed camera is positioned at the top of the soil sample tension unit and used for monitoring and recording numerical values of all displays in real time and accurately controlling the occurrence time of cracks, and the image acquisition unit 7 is positioned at one side of the soil sample tension unit and used for capturing the displacement of the cracks and analyzing the development changes of the cracks along with time.
The test apparatus shown was used as follows:
a. coating a thin layer of lubricating oil on the inner surfaces of the outer ring 4 and the inner ring 3, adding soil with certain dry density and water content into the outer ring with the diameter of 15.24cm in two times, compacting each layer by using a wood stick with the diameter of 2.55cm, wherein the compacting height of the first layer is 2.05cm, and the compacting height of the second layer is 4.1 cm. A hole with the radius of 5.5cm is dug in the center of the cylindrical soil sample by a knife and a thin-wall steel ring, and the PVC inner ring is slowly inserted into the hole. To prevent evaporation of water, the sides and bottom of the sample should also be coated with lubricating oil. Before starting the test, the soil sample was sealed from the bottom with a plastic film and from the circumference with a rubber film.
b. Two strain gauges 13 are symmetrically posted on the surface of the inner ring 4, the strain gauges 13 are connected with the four-channel strain data acquisition device 10, and the saturated tensiometer is installed inside the soil sample through a through hole in the outer ring 4.
c. The annular soil sample 12 is placed on a balance and used for bearing a soil body and recording the change of various data such as the water content of the soil sample.
d. And the camera device at the top of the device records data every 10min, and measures the state change of the soil body in the natural water loss process in real time.
e. Through the operation, the change rule of the internal tensile stress of the soil body in the low-suction state along with the suction in the natural dehydration process can be measured in real time, and the tensile strength of the soil body and the corresponding suction value at the moment are obtained.
The tensiometer transmits the suction value to the suction display 8, when the suction exceeds 2.6MPa, the following operations are adopted:
f. the annular soil sample 12 is surrounded by the annular soil sample closed cylinder to form the annular soil sample closed cylinder, through holes are formed in two sides of the cylinder body 16 respectively, the through holes in the left side are used for passing through the strain gauges 13 and connecting lines of the four-channel strain data acquisition unit 10, the through holes in the right side are used for installing tensiometers, the two through holes are located in opposite corners of a rectangle, and the two strain gauges 13 are located in opposite corners of the rectangle.
g. Saturated saline solution is used for providing high suction for the system, the air circulating pump 19 is used for accelerating the circulation of the suction, the pipelines of the annular soil sample closed cylinder, the saturated saline solution closed cylinder 20 and the air circulating pump 19 are communicated with each other, and the saturated saline solution closed cylinder connected with the system is replaced to realize the gradual increase of the suction.
h. The top camera device is used for real-time measurement of data, and it is noted that when the water content of the soil body is measured, pipelines connected around the annular soil sample closed cylinder are removed so as to avoid error influence on the measured data caused by residual water in the connecting pipe.
i. Through the operation, the change rule of the internal tensile stress of the soil body within the full suction range along with the suction can be measured in real time, and the tensile strength of the soil body and the corresponding suction value at the moment are obtained.
In addition, white sandy soil is uniformly scattered on the surface of the annular soil sample 12, the using function of the PIV testing system is enriched, and the displacement of the crack is captured by using the image collector 7. The device can help clearly observe the growth condition of the cracks of the soil body on the surface, and measure the change rule of the soil body cracks in the low-suction state along with the suction in real time in the natural water loss process.
The technical means disclosed by the scheme of the invention are not limited to the technical means disclosed by the embodiment, and the technical means also comprises the technical scheme formed by any combination of the technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.
Claims (5)
1. Full suction within range real-time measurement unsaturated soil internal tensile stress and crack test device, including soil sample tension unit, stress strain test unit (11) and image acquisition unit (7), its characterized in that: the soil sample tension unit is an annular soil sample tension unit, a low-suction measuring device (6) and a high-suction measuring device are detachably arranged on the annular soil sample tension unit, a camera device (2) is arranged right above the annular soil sample tension unit in a hanging mode, the annular soil sample tension unit is connected with an image acquisition unit (7) through the camera device (2), and the annular soil sample tension unit is electrically connected with a stress-strain testing unit (11);
the low-suction measuring device (6) is a tensiometer, the tensiometer comprises a tensiometer main body (23), a porous argil plate (24), a diaphragm (22), a tension strain gauge (26), a water storage device (25) and a tension cap (21), wherein the tensiometer main body (23) is divided into a first chamber and a second chamber by the diaphragm (22), the tension cap (21) is arranged at a port of the first chamber opposite to the diaphragm (22), the tension strain gauge (26) is arranged in the first chamber, the tension strain gauge (26) is electrically connected with a suction display (8), the porous argil plate (24) is arranged in the second chamber, and the water storage device (25) is arranged between the porous argil plate (24) and the diaphragm (22);
the high-suction measuring device is a suction control circulating system which comprises an annular soil sample closed cylinder, a saturated salt solution closed cylinder (20) and an air circulating pump (19), wherein the annular soil sample closed cylinder comprises an upper cover (17), a lower cover (15) and a cylinder body (16), the cylinder body (16) is detachably arranged between the upper cover (17) and the lower cover (15), through holes are formed in the two opposite sides of the cylinder body (16), two pipeline (18) through holes are oppositely formed in the upper cover (17) of the soil sample closed cylinder and the top end of the saturated salt solution closed cylinder (20), pipelines (18) are respectively arranged in the pipeline (18) through holes, the annular soil sample closed cylinder is connected with the saturated salt solution closed cylinder (20) through the two pipelines (18), and the air circulating pump (19) and a pressure sensor are arranged on any pipeline (18) of the two pipelines (18), the pressure sensor is electrically connected with the suction display (8);
the annular soil sample tension unit comprises an annular soil sample containing device (5), a soil sample crack capturing layer and a weighing device (14), wherein the weighing device (14) is provided with the annular soil sample containing device (5), an annular soil sample (12) is contained in the annular soil sample containing device (5), the top layer of the annular soil sample (12) is detachably provided with the soil sample crack capturing layer, and the soil sample crack capturing layer is provided with a camera device (2);
the soil sample crack capturing layer is sandy soil, the weighing device (14) is a balance, the annular soil sample containing device (5) comprises an outer ring (4) and an inner ring (3), the outer ring (4) and the inner ring (3) are made of PVC materials in an enclosing manner, lubricating oil is coated in the outer ring (4) and the inner ring (3), and a through hole for inserting the low-suction measuring device is formed in the outer ring (4);
can dismantle in inner ring (3) and be provided with foil gage (13), foil gage (13) are two foil gage (13) symmetries and set up in inner ring (3) center department, foil gage (13) are resistance-type foil gage, annular soil sample holds device (5) and is connected with stress-strain test unit (11) electricity through foil gage (13).
2. The test device for real-time measurement of tensile stress and cracks in unsaturated soil in the full suction range according to claim 1, wherein: the suction measured value of the low suction measuring device (6) is not more than 2.6MPa, and the suction measured value of the high suction measuring device is more than 2.6 MPa.
3. The test device for real-time measurement of tensile stress and cracks in unsaturated soil in the full suction range according to claim 1, wherein: the low-suction measuring device (6) and the high-suction measuring device are both electrically connected with a suction display (8), a chip with data processing and control functions is arranged in the suction display (8), and the chip is a single chip microcomputer chip.
4. The test device for real-time measurement of tensile stress and cracks in unsaturated soil in the full suction range according to claim 1, wherein: stress strain test unit (11) are including temperature moisture content display (9), four-channel strain data collection station (10), foil gage (13) are connected with four-channel strain data collection station (10) electricity, temperature moisture content display (9) set up on weighing device (14), temperature moisture content display (9) are connected with four-channel strain data collection station (10) electricity, and temperature moisture content display is (9) any one of liquid crystal display or charactron kind, including the controller that has data calculation processing function in four-channel strain data collection station (10), the controller is in MCU, PC, PLC or the industrial computer any one.
5. The test device for real-time measurement of tensile stress and cracks in unsaturated soil in the full suction range according to claim 1, wherein: the camera device (2) is a CCD high-speed camera, a camera support (1) is arranged in a matched mode with the CCD high-speed camera, the camera support (1) is arranged on one side of the weighing device (14), the CCD high-speed camera is electrically connected with the image acquisition unit (7), and the image acquisition unit (7) is a PIV testing system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201911391628.8A CN111044366B (en) | 2019-12-30 | 2019-12-30 | Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201911391628.8A CN111044366B (en) | 2019-12-30 | 2019-12-30 | Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN111044366A CN111044366A (en) | 2020-04-21 |
| CN111044366B true CN111044366B (en) | 2022-06-07 |
Family
ID=70241477
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201911391628.8A Active CN111044366B (en) | 2019-12-30 | 2019-12-30 | Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111044366B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113820313A (en) * | 2021-10-19 | 2021-12-21 | 中国电建集团华东勘测设计研究院有限公司 | Deformation testing system and method for cohesive soil in moisture desorption process |
| CN115014951A (en) * | 2021-12-29 | 2022-09-06 | 华北水利水电大学 | Unsaturated soil static cone penetration test device based on PIV technology real-time measurement suction |
| CN118090432B (en) * | 2024-04-25 | 2024-06-28 | 湖南大学 | Soil body fracture toughness testing system and testing method in full suction range |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105823716A (en) * | 2016-03-24 | 2016-08-03 | 华北水利水电大学 | Testing device for conducting real-time observation on rock and soil mass cracks under suction measurement condition |
| CN106289979A (en) * | 2016-09-09 | 2017-01-04 | 中国地质大学（武汉） | Unsaturated soil tensile strength test device and method of testing |
| CN106645633A (en) * | 2016-10-13 | 2017-05-10 | 桂林理工大学 | Deformation simulation device for expansion and shrinkage soil roadbed in dry and wet alternative environment and simulation method |
| US9670409B1 (en) * | 2015-12-23 | 2017-06-06 | King Fahd University Of Petroleum And Minerals | Method for reducing swell potential of expansive clayey soil with nano-level constitutive modeling |
| CN108362729A (en) * | 2018-01-31 | 2018-08-03 | 河海大学 | A kind of device for expanding soil scene differentiation |
-
2019
- 2019-12-30 CN CN201911391628.8A patent/CN111044366B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9670409B1 (en) * | 2015-12-23 | 2017-06-06 | King Fahd University Of Petroleum And Minerals | Method for reducing swell potential of expansive clayey soil with nano-level constitutive modeling |
| CN105823716A (en) * | 2016-03-24 | 2016-08-03 | 华北水利水电大学 | Testing device for conducting real-time observation on rock and soil mass cracks under suction measurement condition |
| CN106289979A (en) * | 2016-09-09 | 2017-01-04 | 中国地质大学（武汉） | Unsaturated soil tensile strength test device and method of testing |
| CN106645633A (en) * | 2016-10-13 | 2017-05-10 | 桂林理工大学 | Deformation simulation device for expansion and shrinkage soil roadbed in dry and wet alternative environment and simulation method |
| CN108362729A (en) * | 2018-01-31 | 2018-08-03 | 河海大学 | A kind of device for expanding soil scene differentiation |
Non-Patent Citations (2)
| Title |
|---|
| Soil-water retention behavior of compacted soil with different densities over a wide suction range and its prediction;You Gao 等;《Computers and Geotechnics》;20170630;第91卷;第17-26页 * |
| 宽广吸力范围内弱膨胀土的抗剪强度及其预测;张俊然 等;《岩土工程学报》;20160630;第38卷(第6期);第1064-1070页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN111044366A (en) | 2020-04-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN111044366B (en) | Test device for real-time measurement of tensile stress and crack in unsaturated soil in full-suction range | |
| US7412875B2 (en) | Centrifuge permeameter for unsaturated soils system | |
| Kurup et al. | Calibration chamber studies of piezocone test in cohesive soils | |
| CN107782640B (en) | Method for detecting water-containing uniformity of rock test piece and calculating diffusion coefficient | |
| CN106018740B (en) | Hole pressure touching methods demarcate can system | |
| CN110426336A (en) | A kind of subgrade soils Unsaturated Hydraulic Conductivity measuring system and its relevant measurement method | |
| Dautriat et al. | Axial and radial permeability evolutions of compressed sandstones: end effects and shear-band induced permeability anisotropy | |
| CN108593883A (en) | Strain type lateral expansion force testing device and measuring method | |
| Li et al. | Evaluating a new method for simultaneous measurement of soil water retention and shrinkage curves | |
| CN110196255A (en) | The pressure plate apparatus and its measurement method of rapid survey soil-water characteristic curve | |
| CN110426337A (en) | Rock And Soil seepage deformation test device and its test method under low-stress | |
| US20070131023A1 (en) | Centrifuge permeameter for unsaturated soils system | |
| Li et al. | A new approach to measure soil shrinkage curve | |
| CN204165840U (en) | A kind of multi-functional unsaturated soil consolidometer | |
| CN209821099U (en) | Multifunctional compact gas reservoir dynamic parameter joint measurement device based on nuclear magnetic resonance | |
| Laloui et al. | Advances in volume measurement in unsaturated soil triaxial tests | |
| RU2382350C2 (en) | Method of laboratory determination of cyclical strength and deformability of ground under controlled triaxial load and device for its implementation | |
| Voyiadjis et al. | Preparation of large-size cohesive specimens for calibration chamber testing | |
| CN208506041U (en) | A kind of multifunctional visible joint consolidation apparatus device | |
| CN110836799A (en) | Suction control type rapid unsaturated soil sample preparation control system and method | |
| CN110567429A (en) | Device and method for measuring actual Poisson ratio of foundation soil body under lateral limit stress condition | |
| CN111024503A (en) | Annular test device for measuring internal tensile stress and crack development of soil body in real time | |
| CN110849729A (en) | Limited cohesive soil active and passive soil pressure model test device behind flexible retaining wall of foundation pit | |
| CN115979880A (en) | Device and method for testing near-surface soil water retention curve in low-stress environment | |
| CN205898837U (en) | Thin sight flow field observation device during liquefaction in granule hole |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |