CN114577608A - Test device and method for researching mechanical properties of root-unsaturated soil interface - Google Patents
Test device and method for researching mechanical properties of root-unsaturated soil interface Download PDFInfo
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- CN114577608A CN114577608A CN202210206858.8A CN202210206858A CN114577608A CN 114577608 A CN114577608 A CN 114577608A CN 202210206858 A CN202210206858 A CN 202210206858A CN 114577608 A CN114577608 A CN 114577608A
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- 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N19/00—Investigating materials by mechanical methods
- G01N19/02—Measuring coefficient of friction between materials
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- 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
Abstract
The invention relates to a test device and a method for researching mechanical properties of a root-unsaturated soil interface, wherein the device comprises the following components: the drawing system is connected with the pressure chamber system, the pressure chamber system is used for placing the root-soil complex sample, and the drawing system is used for fixing the root system of the root-soil complex sample and drawing the root-soil complex sample; the sample matrix suction control system is connected with the pressure chamber system and is used for adjusting the saturation of the root-soil complex sample; the automatic confining pressure-water supply system is connected with the pressure chamber system; the automatic confining pressure-water supply system is used for providing confining pressure for the root-soil complex sample and simulating the stress state of the root-soil complex sample; when the sample matrix suction control system and the automatic confining pressure-water supply system work together, the stress history of the root-soil composite sample is simulated. The invention realizes the accurate and simultaneous simulation of the mechanical properties of the root-unsaturated soil interface under different initial conditions.
Description
Technical Field
The invention relates to the technical field of geotechnical engineering, in particular to a test device and a method for researching mechanical characteristics of a root-unsaturated soil interface.
Background
The method is a common slope protection means for preventing shallow landslide by utilizing the reinforcement effect of plant root systems, the plant root systems and the side slope soil body form a root-soil complex, when a plant is subjected to external forces such as surface subsidence, landslide and the like, a relative sliding trend can be generated between the root systems and the soil, and the tensile strength of the plant root systems can be exerted while the sliding displacement is resisted by the friction force generated by the root-soil interface, so that the shearing strength of the root-soil complex is increased. Therefore, the study of the mechanical properties of the root-soil interface is particularly critical for analyzing the soil fixation mechanism of the root system.
In addition to factors such as plant species, diameter and mechanical properties of the root system, the mechanical properties of the root-soil interface are closely related to the saturation, stress state and stress history of the soil: the mechanical property of the root-soil interface is mainly interface friction, and the maximum frictional resistance is related to the extrusion effect of the periapical soil on the root, namely the stress state of the soil; with the progress of rainfall infiltration, the saturation of the root-soil complex gradually rises, and the mechanical properties of the root-soil interface also change due to the change of the mechanical properties of unsaturated soil; the mechanical properties of the soil are directly influenced by the super-consolidation ratio of the root-soil complex, and further the mechanical properties of a root-soil interface are influenced. The research on the root-soil interface mechanical characteristics at the present stage is mainly carried out by drawing and direct shearing equipment, although a great deal of results are obtained on the research on the influence factors such as plant varieties, soil density and water content, the influence of initial conditions such as the saturation, stress state and stress history of unsaturated soil cannot be simulated precisely, and the research on the root system soil fixation mechanism is restricted.
Disclosure of Invention
The invention aims to provide a test device and a test method for researching mechanical properties of a root-unsaturated soil interface, and aims to solve the problem that the device and the method for researching the mechanical properties of the root-unsaturated soil interface in the prior art cannot accurately simulate different initial conditions at the same time.
In order to achieve the purpose, the invention provides the following scheme:
a test device for studying root-unsaturated soil interface mechanical properties, comprising: the device comprises a drawing system, a pressure chamber system, a sample matrix suction control system and an automatic confining pressure-water supply system;
the drawing system is connected with the pressure chamber system, the pressure chamber system is used for placing a root-soil complex sample, and the drawing system is used for fixing the root system of the root-soil complex sample and drawing the root-soil complex sample;
the sample matrix suction control system is connected with the pressure chamber system and is used for adjusting the saturation of the root-soil complex sample;
the automatic confining pressure-water supply system is connected with the pressure chamber system; the automatic confining pressure-water supply system is used for providing confining pressure for the root-soil composite sample and simulating the stress state of the root-soil composite sample;
and when the sample matrix suction control system and the automatic confining pressure-water supply system work together, the stress history of the root-soil composite sample is simulated.
Optionally, the drawing system comprises: the device comprises a test pedestal, a pillar, a lifting table, a cross beam, a force sensor, a root system clamp, a probe type displacement sensor and an axial driving device;
the lifting table is arranged on the test bed seat, the axial driving device is arranged in the test bed seat, and the axial driving device is used for driving the lifting table to move;
the supporting column is fixedly connected with the test pedestal, the cross beam is detachably connected with the supporting column, the force sensor is installed on the cross beam and used for measuring the tensile force applied to the root system of the root-soil complex sample, the root system clamp is installed on the force sensor and used for fixing the root system of the root-soil complex sample;
the probe type displacement sensor is arranged on the cross beam and used for measuring the displacement of the root system of the root-soil complex sample.
Optionally, the cross beam includes two arch members and a cross bar, the two ends of the cross bar are respectively welded with one arch member, and the arch members are connected with the pillars through bolts;
the cross bar is provided with two screw holes, two ends of the force sensor are provided with two screw holes, the two screw holes on the cross bar are matched with the two screw holes on the force sensor, and the screw holes are used for fixing the force sensor;
the center of the force sensor is provided with a central screw hole, and the central screw hole is used for installing the root system clamp.
Optionally, the pressure chamber system comprises a pressure chamber cover, a pressure chamber base, a clay plate, a permeable stone, a sample cap, a marker post and a bracket;
the pressure chamber cover is connected with the pressure chamber base, the pressure chamber base is placed on the lifting table, the argil plate is placed on the pressure chamber base, the sample cap is placed above the argil plate, the permeable stone is placed above the interior of the sample cap, the marker post is connected with the pressure chamber base, the support is connected with the marker post, and the probe-type displacement sensor is in contact with the support;
the centers of the pressure chamber base and the argil plate are both provided with a small hole, and the small hole is used for penetrating roots.
Optionally, the sample matrix suction control system includes an air pressure controller, a first air compressor, a pore water pressure sensor, a drainage sensor, a first drainage pipe, a second drainage pipe, a first pipeline, a second pipeline, a third pipeline, and a plurality of valves;
one end of the first pipeline penetrates through the air pressure controller to be communicated with the first air compressor, the other end of the first pipeline penetrates through the pressure chamber base to be connected with the sample cap, and a valve is arranged on the first pipeline between the air pressure controller and the pressure chamber base; one end of a second pipeline is connected with the first drainage pipe, the other end of the second pipeline is communicated with the root-soil complex sample through the pressure chamber base, the pore water pressure sensor is installed on the second pipeline, and a valve is arranged at the joint of the pore water pressure sensor and the second pipeline; the drainage sensor is installed on the third pipeline, the joint of the drainage sensor and the third pipeline is provided with a valve, one end of the third pipeline is connected with the second drainage pipe, and the other end of the third pipeline is connected with the pressure chamber base.
Optionally, the automatic confining pressure-water supply system comprises a water supply tank, a confining pressure controller, a second air compressor, a fourth pipeline and a plurality of valves; one end of the water supply tank and one end of the confining pressure controller are both connected with one end of the fourth pipeline, and the other end of the fourth pipeline penetrates through the pressure chamber base to be communicated with the inner space of the pressure chamber; a valve is arranged at the joint of one end of the water supply tank, one end of the confining pressure controller and one end of the fourth pipeline; the other end of the water supply tank and the other end of the confining pressure controller are both connected with the second air compressor, and valves are arranged at the joints of the other end of the water supply tank, the other end of the confining pressure controller and the second air compressor.
A test method for researching mechanical properties of a root-unsaturated soil interface comprises the following steps:
preparing a root-soil complex sample;
installing the root-soil complex sample in the provided test device for researching the mechanical characteristics of the root-unsaturated soil interface;
adjusting the saturation of the root-soil complex sample, simultaneously simulating the stress state and stress history of the root-soil complex sample, and ending the initial condition simulation stage;
in the root system drawing stage, a drawing system is adjusted, and data of a probe type displacement sensor and data of a force sensor are recorded;
drawing a displacement-tension curve according to the data of the probe type displacement sensor and the data of the force sensor;
determining the maximum tensile force borne by the root system of the root-soil complex sample according to the displacement-tensile force curve;
measuring the penetration depth of the root-soil complex sample and the average root diameter of the root system of the root-soil complex sample;
determining the root-soil interface friction coefficient of the root-soil complex sample according to the penetration depth, the average diameter of the root system and the maximum tensile force borne by the root system;
and analyzing the mechanical characteristics of the root-soil interface under different initial conditions according to the friction coefficient of the root-soil interface and the displacement-tension curve.
Optionally, paraffin is filled between the argil plate and the root system of the root-soil complex sample in the sample installation stage.
Optionally, gasoline is injected into the paraffin during the root system drawing stage to dissolve the paraffin.
Optionally, determining the root-soil interface friction coefficient of the root-soil complex sample according to the penetration depth, the average diameter of the root system and the maximum tensile force applied to the root system specifically includes:
using a formula
Calculating the root-soil interface friction coefficient; in the formula, mu is the friction coefficient between the surface of the root system and the soil body, namely the root-soil interface friction coefficient; p is confining pressure applied to the root-soil composite sample in the drawing stage; d is the average diameter of the root system; z is the depth of penetration; f. ofsThe maximum tensile force applied to the root system.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention adjusts the saturation of the root-soil complex sample through the sample matrix suction control system to simulate the states of the root-soil complex at different stages of rainfall infiltration, the automatic confining pressure-water supply system communicated with the pressure chamber can provide different confining pressures for the root-soil composite sample according to actual requirements, simulate the stress state of the root-soil composite sample, make up the defect that the traditional drawing device can only control vertical load, enable the stress environment simulated in the root-soil interface mechanical characteristic test to be closer to the natural stress state, and under the combined action of the sample substrate suction control system and the automatic confining pressure-water supply system, the method can simulate the stress history of the root-soil complex sample, and can accurately and simultaneously simulate the mechanical properties of the root-unsaturated soil interface under different initial conditions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of a test apparatus for studying the mechanical properties of a root-unsaturated soil interface provided by the present invention;
FIG. 2 is a schematic view of the drawing system according to the present invention;
FIG. 3 is a schematic view of the construction of the pressure chamber base of the present invention;
FIG. 4 is a schematic view of a clay plate configuration according to the present invention;
FIG. 5 is a schematic diagram of an initial condition simulation phase according to the present invention;
FIG. 6 is a schematic drawing stage of the present invention;
fig. 7 is a flowchart of a test method for studying mechanical properties of a root-unsaturated soil interface provided by the invention.
Description of the symbols: i, a drawing system, II, a pressure chamber system, III, a sample matrix suction control system and IV, an automatic confining pressure and water supply system;
1-a test bench seat, 2-a pillar, 3-a lifting table, 4-a beam, 5-a force sensor, 6-a root system clamp, 7-a probe type displacement sensor, 8-a pressure chamber base, 8-1-a chassis, 8-2-a base, 8-3-an upper base, 8-4-a lower base, 8-5-a small hexagon bolt, 9-a pressure chamber cover, 9-1-an exhaust hole, 10-a clay plate, 10-1-paraffin, 11-a soil complex sample, 12-a permeable stone, 13-a sample cap, 14-a mark rod, 15-a bracket, 16-an air pressure controller, 17-a first air compressor, 18-a pore water pressure sensor, 19-a first exhaust pipe, 20-a drainage sensor, 21-a water supply tank, 21-1-a water injection hole, 22-a confining pressure controller, 23-a first pipeline, 24-a second pipeline, 25-a third pipeline, 26-a fourth pipeline, 27-a second drainage pipe and 28-a second air compressor.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a test device and a test method for researching mechanical properties of a root-unsaturated soil interface, and aims to solve the problem that the device and the method for researching the mechanical properties of the root-unsaturated soil interface in the prior art cannot accurately simulate different initial conditions at the same time.
Aiming at the defects of the existing equipment for researching the mechanical properties of the root-soil interface, the invention provides a test device and a method for researching the mechanical properties of the root-soil interface under different initial conditions, wherein the test device can consider the influence of saturation, provide confining pressure for a root-soil complex sample, simulate the stress history of the root-soil complex sample, systematically research the mechanical properties of the root-soil interface, measure the frictional resistance of the root-soil interface and calculate the friction coefficient of the root-soil interface, and has the advantages of simple and convenient operation and use and accurate and reliable test results.
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the accompanying drawings and the detailed description thereof.
Fig. 1 is a schematic diagram of a test apparatus for studying root-unsaturated soil interface mechanical properties provided by the present invention, as shown in fig. 1, including: drawing system I, pressure chamber system II, sample matrix suction control system III and automatic confining pressure-water supply system IV.
Drawing system I with pressure chamber system II is connected, pressure chamber system II is used for placing root-soil complex body sample, drawing system I is used for fixing the root system of root-soil complex body sample and right root-soil complex body sample draws.
And the sample matrix suction control system III is connected with the pressure chamber system II and is used for adjusting the saturation of the root-soil complex sample.
The automatic confining pressure-water supply system IV is connected with the pressure chamber system II; and the automatic confining pressure-water supply system IV is used for providing confining pressure for the root-soil complex sample and simulating the stress state of the root-soil complex sample.
And when the sample matrix suction control system III and the automatic confining pressure-water supply system IV act together, the stress history of the root-soil complex sample is simulated.
In practical application, the automatic confining pressure-water supply system IV supplies water for the pressure chamber system II and provides confining pressure by taking water as a medium; simulating different initial conditions of the root-soil complex sample under the combined action of an automatic confining pressure-water supply system IV and the sample matrix suction control system III; after the simulation process, draw I fixed root system position of system, when providing power for the axial motion of pressure chamber, survey the pulling force that the root system receives.
Specifically, drawing system I includes: the device comprises a test bed base 1, a support column 2, a lifting table 3, a cross beam 4, a force sensor 5, a root system clamp 6, a probe type displacement sensor 7 and an axial driving device. Wherein the axial drive is not shown in the figures.
The elevating platform 3 is arranged on the test bench 1, the axial driving device is arranged in the test bench 1, and the axial driving device is used for driving the elevating platform 3 to move.
The probe type displacement sensor 7 is arranged on the cross beam 4, and the probe type displacement sensor 7 is used for measuring the displacement of the root system of the root-soil complex sample.
In practical application, the cross beam 4 penetrates through the lower part of the pressure chamber base and is detachably connected with the support column 2, the force sensor 5 is installed above the cross beam 4, and the probe type displacement sensor 7 is arranged on the right part below the cross beam 4.
Specifically, as shown in fig. 2, the cross beam 4 includes two arch members and a cross bar, the two ends of the cross bar are respectively welded with one arch member, and the arch members are detachably connected with the pillars 2 through bolts, so that the position of the cross beam 4 can be adjusted conveniently.
The cross rod is provided with two screw holes, two ends of the force sensor 5 are provided with two screw holes, the two screw holes on the cross rod are matched with the two screw holes on the force sensor 5, and the screw holes are used for fixing the force sensor 5.
The center of the force sensor 5 is provided with a central screw hole which is used for installing the root system clamp 6. In practical applications, the diameter of the central screw hole is larger than the other two screw holes on the force sensor 5.
Specifically, the pressure chamber system II comprises a pressure chamber cover 9, a pressure chamber base 8, a clay plate 10, a permeable stone 12, a sample cap 13, a mark post 14 and a support 15.
The pressure chamber cover 9 is connected with the pressure chamber base 8, the pressure chamber base 8 is placed on the lifting table 3, the clay plate 10 is placed on the pressure chamber base 8, the sample cap 13 is placed above the clay plate 10, the permeable stone 12 is placed above the inner portion of the sample cap 13, the marker post 14 is connected with the pressure chamber base 8, the support 15 is connected with the marker post 14, and the probe type displacement sensor 7 is in contact with the support 15.
The centers of the pressure chamber base 8 and the argil plate 10 are both provided with a small hole, and the small hole is used for penetrating roots.
In practical application, the pressure chamber base 8 comprises a base 8-2 and a base; the argil plate 10 is placed on the base; the root-soil complex sample 11 is placed on a clay plate 10, a rubber membrane is wrapped outside the root-soil complex sample 11, and the permeable stone 12 and the sample cap 13 are sequentially placed on the top of the root-soil complex sample 11; the outer wall of the pressure chamber cover is made of transparent organic glass and is connected with a pressure chamber base 8 through bolts, and an exhaust hole 9-1 is formed in the top of the pressure chamber cover.
As shown in FIG. 3, the chassis 8-1 of the base 8-2 is fixedly connected with the base 8-2 with four pillars; the chassis 8-1 is a short cylindrical structure with a cylindrical groove at the center; the base comprises an upper base 8-3 and a lower base 8-4, wherein the upper base 8-3 is a hollow cylinder with the diameter slightly smaller than that of the cylindrical groove, is embedded in the concave part of the chassis 8-1 and forms a boss structure with the chassis 8-1; the lower base 8-4 is an inverted hollow cap-shaped structure, two screw holes are formed in the brim of the cap, a small hole is formed in the bottom of the cap and used for allowing a root system to penetrate through the small hole, and rubber gaskets with different opening diameters can be replaced in the small hole at the bottom of the cap so as to adapt to root systems with different diameters; the lower base 8-4 and the chassis 8-1 can be detachably connected through a pair of small hexagon bolts 8-5; a first pipeline and a fourth pipeline are arranged in the chassis 8-1; a second pipeline is arranged in the upper base 8-3; the bottom of the lower base 8-4 is internally provided with a third pipeline.
The center of the plate body of the pottery clay plate 10 is provided with a through hole which is in an inverted frustum shape and is convenient for the plant root system to penetrate out. Placing the root-soil complex sample 11 on the argil plate 10, enabling the root-soil complex sample 11 to penetrate through the hole of the argil plate 10, filling the gap between the argil plate 10 and the plant root system with melted paraffin 10-1, and enabling the paraffin 10-1 to be rapidly solidified. As shown in fig. 4.
Specifically, the sample substrate suction control system iii includes an air pressure controller 16, a first air compressor 17, a pore water pressure sensor 18, a drainage sensor 20, a first drainage pipe 19, a second drainage pipe 27, a first pipeline 23, a second pipeline 24, a third pipeline 25, and a plurality of valves.
One end of the first pipeline 23 penetrates through the air pressure controller 16 to be communicated with the first air compressor 17, the other end of the first pipeline 23 penetrates through the pressure chamber base 8 to be connected with the sample cap 13, and a valve is arranged on the first pipeline 23 between the air pressure controller 16 and the pressure chamber base 8; one end of a second pipeline 24 is connected with the first drainage pipe 19, the other end of the second pipeline 24 is communicated with the root-soil composite sample 11 through the pressure chamber base 8, the pore water pressure sensor 18 is installed on the second pipeline 24, and a valve is arranged at the connection position of the pore water pressure sensor 18 and the second pipeline 24; the drainage sensor 20 is installed on the third pipeline 25, a valve is arranged at the joint of the drainage sensor 20 and the third pipeline 25, one end of the third pipeline 25 is connected with the second drainage pipe 27, and the other end of the third pipeline 25 is connected with the pressure chamber base 8.
Specifically, the automatic confining pressure-water supply system iv comprises a water supply tank 21, a confining pressure controller 22, a second air compressor 28, a fourth pipeline 26 and a plurality of valves.
One end of the water supply tank 21 and one end of the confining pressure controller 22 are both connected to one end of the fourth pipe 26, and the other end of the fourth pipe 26 passes through the pressure chamber base 8 to communicate with the pressure chamber interior space; a valve is arranged at the joint of one end of the water supply tank 21, one end of the confining pressure controller 22 and one end of the fourth pipeline 26; the other end of the water supply tank 21 and the other end of the confining pressure controller 22 are both connected with the second air compressor 28, and valves are arranged at the connection of the other end of the water supply tank 21, the other end of the confining pressure controller 22 and the second air compressor 28. In practical application, a water injection hole 21-1 is arranged at the top of the water supply tank 21; one end of the fourth pipeline 26 passes through the chassis 8-1 to be communicated with the internal space of the pressure chamber, and the other end is a branched pipeline.
Fig. 7 is a flowchart of a test method for studying mechanical properties of a root-unsaturated soil interface provided by the present invention, as shown in fig. 7, including:
step 701: root-soil complex samples were prepared. In practical application, corresponding soil bodies and plant root systems are selected according to research targets, and root-soil complex remolded soil samples are manufactured; or directly taking an undisturbed root-soil complex sample 11, and reducing disturbance as much as possible in the field sampling process; and marking the position of the part of the root system exposed out of the soil body.
Step 702: the root-soil composite sample was set in the test apparatus for studying the mechanical properties of the root-unsaturated soil interface. In practical application, a piece of filter paper is placed on the upper surface and the lower surface of the main body part of the saturated root-soil composite sample 11, and then the sample is placed on the argil plate 10, so that the root system of the plant penetrates through the holes of the argil plate 10; in order to ensure the air tightness of the root-soil complex, filling a gap between the argil plate 10 and a plant root system with melted paraffin 10-1, and quickly solidifying the paraffin 10-1; placing a sample and a argil plate 10 on a base, wrapping the main part of the sample by using a rubber film, sequentially placing a permeable stone 12 and a sample cap 13 on the top of the sample, fastening the two ends of the sample by using rubber rings, removing air of a second pipeline 24 in the sample loading process, placing the sample, placing a pressure chamber cover 9 on a base 8-2, and fastening the sample by using a nut; and (3) sleeving a rubber gasket with a proper size at an opening at the lower end of the lower base 8-4 according to the diameter of the root system, smearing a small amount of silicone grease on the inner wall of the rubber gasket to ensure the air tightness of the device, and connecting the lower base 8-4 with the chassis 8-1 by using a small hexagonal screw after the lower base is sleeved in the root system of the plant to finish the installation of the sample.
Step 703: and adjusting the saturation of the root-soil composite sample, simulating the stress state and stress history of the root-soil composite sample, and ending the initial condition simulation stage.
In practical application, in an initial condition simulation stage, water is injected into the pressure chamber through the automatic confining pressure-water supply system IV, target confining pressure is provided for the pressure chamber, and the sample saturation and the stress history of the sample can be adjusted by utilizing the sample matrix suction control system III and the automatic confining pressure-water supply system IV according to actual needs; after the predetermined condition is reached, the initial condition simulation phase is finished, and the device of the initial condition simulation phase is as shown in fig. 5.
Example 1: and analyzing the influence of the stress state on the mechanical properties of the root-saturated soil interface. The test object is saturated soil, OCR is 1, four groups of comparison experiments are carried out, the confining pressure of each group of samples is respectively increased by 25 kPa, 50kPa, 75 kPa and 100kPa after saturation, and consolidation is considered to be completed when the pore water pressure is dissipated.
After the sample is installed, a second air compressor 28 of the automatic confining pressure-water supply system IV is started, the valve is adjusted to the position of a first branch of the fourth channel to the position of a passage, water is injected into the pressure chamber, after the water is filled, the exhaust hole 9-1 is tightly closed to enable the second branch to keep the passage, and the pressure in the pressure chamber is loaded to the preset confining pressure through the confining pressure controller 22. After the confining pressure in the pressure chamber is stabilized, adjusting a valve of the second pipeline 24 to the position communicated with the pore water pressure sensor 18, starting the pore water pressure sensor 18, and measuring the pore water pressure of the root-soil composite sample 11; and opening a valve of the third pipeline 25 to solidify and drain the sample, and closing the valve after the pore water pressure is dissipated and the initial stress state of the sample is considered to be simulated.
Example 2: and analyzing the influence of the saturation on the mechanical properties of the root-unsaturated soil interface. The test object controls the same stress state, OCR is 1, the soil-water characteristic curve of the test soil body can be measured firstly, and the change relation between the soil body saturation and the matrix suction is obtained; the influence of different corresponding saturation degrees of the matrix suction forces of 10, 50, 100 and 150kPa on the mechanical characteristics of the root-unsaturated soil interface under the net confining pressure of 100kPa is studied, four groups of comparative tests are carried out, the internal air pressure of a sample is set to be 200kPa, the test confining pressure is 300kPa, and the matrix suction force balancing stage is considered to be finished when the pore water pressures of the four samples reach 190, 150, 100 and 50kPa respectively.
After the sample is installed, an air compressor of the automatic confining pressure-water supply system IV is started, the position of a hand valve is adjusted to the position of a first branch of a fourth channel to a passage, water is injected into the pressure chamber, after the water is filled, an exhaust hole 9-1 is closed to enable a second branch passage to be communicated, the pressure in the pressure chamber is loaded to 300kPa through a confining pressure controller 22, meanwhile, a relevant valve of the first channel is opened, the target air pressure value of an air pressure controller 16 is set, the air compressor is started, 200kPa air pressure is applied to the interior of the sample, a relevant valve of the second three channels is opened, a drainage sensor 20 and a pore water pressure sensor 18 are started to dehumidify the sample, after the pore water pressure reaches a target value, the substrate suction balance stage is considered to be finished, and the sample reaches the target saturation.
Example 3: and analyzing the influence of stress history (OCR) on the mechanical properties of the root-saturated soil interface. The test object is saturated soil, four groups of comparative experiments are carried out by controlling the same stress state, different super consolidation ratios are drawn up, OCR is 0.5, 1, 1.5 and 2, each group of samples are respectively loaded with 25, 50, 75 and 100kPa confining pressure for early consolidation after saturation, the confining pressure is added/unloaded to 50kPa confining pressure after consolidation, and consolidation is considered to be completed when the pore water pressure is dissipated.
After the sample is installed, an air compressor of the automatic confining pressure-water supply system IV is started, the position of a hand valve is adjusted to the position of a first branch of a fourth channel to a passage, water is injected into the pressure chamber, after the water is filled, an exhaust hole 9-1 is tightly closed to enable a second branch to keep the passage, and the internal pressure of the pressure chamber is loaded to the preset early consolidation pressure through the confining pressure controller 22. After the confining pressure in the pressure chamber is stabilized, adjusting a valve of the second pipeline 24 to the position communicated with the pore water pressure sensor 18, starting the pore water pressure sensor 18, and measuring the pore water pressure of the root-soil complex sample 11; and opening a valve of the third pipeline 25 to enable the sample to be solidified and drained, and closing the valve of the third pipeline 25 when the pore water pressure is dissipated and the early solidification is considered to be completed. And then the internal pressure of the pressure chamber is added/unloaded to 50kPa by the confining pressure controller 22, a valve of the third pipeline 25 is opened to wait for the consolidation of the sample, and the valve is closed when the consolidation is considered to be completed after the pore water pressure is dissipated, and the sample reaches the corresponding consolidation exceeding ratio.
Step 704: and in the root system drawing stage, the drawing system I is adjusted, and the data of the probe type displacement sensor 7 and the data of the force sensor 5 are recorded.
In the root system drawing stage, the cross beam 4 is adjusted to a proper position according to the root system length of the root-soil complex sample 11, and the cross beam 4 is fixed on the pillar 2 through a bolt; after the lower base 8-4 is taken down, gasoline is injected into the paraffin 10-1 filled between the pottery clay plate 10 and the root system to be dissolved; carefully fixing the root system penetrating out of the pottery clay plate 10 on a root system clamp 6; the probe-type displacement sensor 7 is positioned in contact alignment with the support 15 of the pressure chamber base 8. Setting the strain rate of the axial driving device to be 10mm/min, under the action of the axial driving device, the lifting table 3 drives the pressure chamber to axially lift, and drives the main body part of the root-soil composite body sample 11 to axially lift, so as to generate a drawing force, and the device in the drawing stage is shown as fig. 6. The probe type displacement sensor 7 is used for acquiring displacement data, namely the length of the root system pulled out from the soil body, and the force sensor 5 is used for acquiring the tensile force applied to the root system. The root system is pulled out or slides out of the soil sample, namely the test is finished; the experiment that the root system slipped out of the soil sample was recorded as a successful experiment.
Step 705: and drawing a displacement-tension curve according to the data of the probe type displacement sensor and the data of the force sensor.
Step 706: and determining the maximum tensile force borne by the root system of the root-soil complex sample according to the displacement-tensile force curve.
In practical application, data recorded by the probe type displacement sensor and the force sensor are analyzed to obtain a displacement-tension relation curve of the root system in the drawing process under different initial conditions, and the maximum tension borne by the root system is the root system drawing force.
Step 707: and measuring the penetration depth of the root-soil complex sample and the average root diameter of the root system of the root-soil complex sample.
In practical application, the root system of the root-soil complex sample 11 which is successfully tested is taken out, the penetration depth z of the root system and the diameters of the upper part, the middle part and the lower part of the root system penetration part are measured by a vernier caliper, and the average diameter of the root system penetration depth z and the diameters of the upper part, the middle part and the lower part of the root system penetration part are calculated.
Step 708: and determining the root-soil interface friction coefficient of the root-soil complex sample according to the penetration depth, the average diameter of the root system and the maximum tensile force borne by the root system.
The method specifically comprises the following steps: and (4) analyzing the mechanical characteristics of the root-soil interface. The subjects of this trial were plant individuals, assuming: the plant root system is a rigid rod piece, and the tiny deformation of the plant root system in the stretching process is ignored; the surface of the plant root system is uniform in texture, i.e. the friction coefficients of the surface of the root system are the same (Unevenness of the surface of the root system, and small-amplitude bending within a certain length interval are considered in the friction coefficient); the extrusion effect of the soil around the root on the root system has little influence compared with the confining pressure, and the secondary term is ignored. The drawing force of the root system is the maximum static friction force f between the root and the soilsAnd if the buried depth is z, the maximum static friction force borne by the plant root system is as follows:
fsμ P pi Dz; in the formula, mu is the friction coefficient between the surface of the plant root system and the soil body; p is confining pressure Pa applied to the sample in the drawing stage; d is the average diameter of the plant root system, m; z is the root system penetration depth m. The root-soil interface friction coefficient can be calculated as:
step 709: and analyzing the mechanical characteristics of the root-soil interface under different initial conditions according to the friction coefficient of the root-soil interface and the displacement-tension curve. In practical application, the mechanical characteristics of the root-soil interface under different initial conditions are analyzed, and basic test data are provided for deep research of a root system soil fixation mechanism.
The working principle of the invention is as follows:
placing the saturated root-soil complex sample 11 in a pressure chamber, enabling the root system of the plant to penetrate through a lower base 8-4, sealing the gap between the root system and a pottery clay plate 10 by adopting paraffin 10-1, under the condition of ensuring good air tightness of the sample, the automatic confining pressure-water supply system IV supplies water to the pressure chamber, water is used as a confining pressure transmission medium to realize the application of the confining pressure of the sample, the automatic confining pressure-water supply system IV and the sample matrix suction control system III can simulate the saturation and the stress history of the sample, after the simulation phase to different initial conditions, by the fixed plant roots of root system anchor clamps 6 of drawing system I, drive the pressure chamber upward movement by axial drive arrangement, along with axial displacement's further increase, plant roots breaks or the roll-off soil body, and the stress process that the stage was drawn to probe-type displacement sensor 7 and the continuous force sensor 5 record root system with root system anchor clamps 6.
Compared with the prior art, the invention has the following beneficial effects:
1. with the continuous progress of rainfall infiltration, the saturation degree of the root-soil complex is gradually increased, and the friction force between the root-soil interfaces is changed along with the saturation degree. The sample matrix suction control system can adjust the saturation of the sample to simulate the state of the root-soil complex at different stages of rainfall infiltration so as to realize the research on the mechanical characteristics of the root-unsaturated soil interface.
2. The invention relates to a test device for researching the mechanical characteristics of a root-soil interface in the drawing process, an automatic confining pressure-water supply system communicated with a pressure chamber can provide different confining pressures according to actual requirements, the defect that the traditional drawing device can only control vertical load is overcome, and the stress environment simulated in the mechanical characteristics test of the root-soil interface is closer to a natural stress state.
3. Under the combined action of a sample matrix suction control system and an automatic confining pressure-water supply system, the stress history of a sample can be simulated, and the influence of the hypercuring ratio on the root-soil interface mechanical characteristics during root system drawing can be researched.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. A test device for studying root-unsaturated soil interface mechanical properties, comprising: the device comprises a drawing system, a pressure chamber system, a sample matrix suction control system and an automatic confining pressure-water supply system;
the drawing system is connected with the pressure chamber system, the pressure chamber system is used for placing a root-soil complex sample, and the drawing system is used for fixing the root system of the root-soil complex sample and drawing the root-soil complex sample;
the sample matrix suction control system is connected with the pressure chamber system and is used for adjusting the saturation of the root-soil complex sample;
the automatic confining pressure-water supply system is connected with the pressure chamber system; the automatic confining pressure-water supply system is used for providing confining pressure for the root-soil composite sample and simulating the stress state of the root-soil composite sample;
and when the sample matrix suction control system and the automatic confining pressure-water supply system work together, the stress history of the root-soil composite sample is simulated.
2. The experimental device for studying root-unsaturated soil interface mechanical properties as claimed in claim 1, wherein said drawing system comprises: the device comprises a test pedestal, a pillar, a lifting table, a cross beam, a force sensor, a root system clamp, a probe type displacement sensor and an axial driving device;
the lifting table is arranged on the test bed seat, the axial driving device is arranged in the test bed seat, and the axial driving device is used for driving the lifting table to move;
the supporting column is fixedly connected with the test pedestal, the cross beam is detachably connected with the supporting column, the force sensor is installed on the cross beam and used for measuring the tensile force applied to the root system of the root-soil complex sample, the root system clamp is installed on the force sensor and used for fixing the root system of the root-soil complex sample;
the probe type displacement sensor is arranged on the cross beam and used for measuring the displacement of the root system of the root-soil complex sample.
3. The experimental device for researching mechanical properties of a root-unsaturated soil interface as claimed in claim 2, wherein the cross beam comprises two arch members and a cross bar, the two ends of the cross bar are respectively welded with one arch member, and the arch members are connected with the pillars through bolts;
the cross bar is provided with two screw holes, two ends of the force sensor are provided with two screw holes, the two screw holes on the cross bar are matched with the two screw holes on the force sensor, and the screw holes are used for fixing the force sensor;
the center of the force sensor is provided with a central screw hole, and the central screw hole is used for installing the root system clamp.
4. The experimental apparatus for studying root-unsaturated soil interface mechanical properties as claimed in claim 3, wherein said pressure chamber system comprises a pressure chamber cover, a pressure chamber base, a clay plate, a permeable stone, a sample cap, a mark post and a bracket;
the pressure chamber cover is connected with the pressure chamber base, the pressure chamber base is placed on the lifting table, the argil plate is placed on the pressure chamber base, the sample cap is placed above the argil plate, the permeable stone is placed above the interior of the sample cap, the marker post is connected with the pressure chamber base, the support is connected with the marker post, and the probe-type displacement sensor is in contact with the support;
the centers of the pressure chamber base and the argil plate are both provided with a small hole, and the small hole is used for penetrating roots.
5. The experimental device for studying root-unsaturated soil interface mechanical properties as claimed in claim 4, wherein said specimen matrix suction control system comprises an air pressure controller, a first air compressor, a pore water pressure sensor, a drainage sensor, a first drainage pipe, a second drainage pipe, a first pipeline, a second pipeline, a third pipeline and a plurality of valves;
one end of the first pipeline penetrates through the air pressure controller to be communicated with the first air compressor, the other end of the first pipeline penetrates through the pressure chamber base to be connected with the sample cap, and a valve is arranged on the first pipeline between the air pressure controller and the pressure chamber base; one end of a second pipeline is connected with the first drainage pipe, the other end of the second pipeline is communicated with the root-soil complex sample through the pressure chamber base, the pore water pressure sensor is installed on the second pipeline, and a valve is arranged at the joint of the pore water pressure sensor and the second pipeline; the drainage sensor is installed on the third pipeline, the joint of the drainage sensor and the third pipeline is provided with a valve, one end of the third pipeline is connected with the second drainage pipe, and the other end of the third pipeline is connected with the pressure chamber base.
6. The experimental device for studying root-unsaturated soil interface mechanical properties according to claim 5, wherein the automatic confining pressure-water supply system comprises a water supply tank, a confining pressure controller, a second air compressor, a fourth pipeline and a plurality of valves;
one end of the water supply tank and one end of the confining pressure controller are both connected with one end of the fourth pipeline, and the other end of the fourth pipeline penetrates through the pressure chamber base to be communicated with the inner space of the pressure chamber; a valve is arranged at the joint of one end of the water supply tank, one end of the confining pressure controller and one end of the fourth pipeline; the other end of the water supply tank and the other end of the confining pressure controller are both connected with the second air compressor, and valves are arranged at the joints of the other end of the water supply tank, the other end of the confining pressure controller and the second air compressor.
7. A test method for researching mechanical properties of a root-unsaturated soil interface is characterized by comprising the following steps:
preparing a root-soil complex sample;
installing the root-soil composite sample in a test device for studying root-unsaturated soil interface mechanical properties according to any one of claims 1 to 6;
adjusting the saturation of the root-soil complex sample, simultaneously simulating the stress state and stress history of the root-soil complex sample, and ending the initial condition simulation stage;
in the root system drawing stage, a drawing system is adjusted, and data of a probe type displacement sensor and data of a force sensor are recorded;
drawing a displacement-tension curve according to the data of the probe type displacement sensor and the data of the force sensor;
determining the maximum tensile force borne by the root system of the root-soil complex sample according to the displacement-tensile force curve;
measuring the penetration depth of the root-soil complex sample and the average diameter of the root system of the root-soil complex sample;
determining the root-soil interface friction coefficient of the root-soil complex sample according to the penetration depth, the average diameter of the root system and the maximum tensile force borne by the root system;
and analyzing the mechanical characteristics of the root-soil interface under different initial conditions according to the friction coefficient of the root-soil interface and the displacement-tension curve.
8. The method as claimed in claim 7, wherein paraffin is filled between the clay plate and the root system of the root-soil complex sample during the sample installation stage.
9. The test method for researching mechanical properties of the root-unsaturated soil interface as claimed in claim 8, wherein gasoline is injected into the paraffin wax during the root system drawing stage to dissolve the paraffin wax.
10. The test method for studying root-soil unsaturated interface mechanical properties of claim 7, wherein the determining the root-soil interface friction coefficient of the root-soil complex sample according to the penetration depth, the average diameter of the root system and the maximum tensile force applied to the root system specifically comprises:
using formulas
Calculating root-soil interface friction systemCounting; in the formula, mu is the friction coefficient between the surface of the root system and the soil body; p is confining pressure applied to the root-soil composite sample in the drawing stage; d is the average diameter of the root system; z is the depth of penetration; f. ofsThe maximum tensile force applied to the root system.
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