CN114577608B - 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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- CN114577608B CN114577608B CN202210206858.8A CN202210206858A CN114577608B CN 114577608 B CN114577608 B CN 114577608B CN 202210206858 A CN202210206858 A CN 202210206858A CN 114577608 B CN114577608 B CN 114577608B
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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 drawing system is connected with the pressure chamber system, the pressure chamber system is used for placing the root-soil composite sample, and the drawing system is used for fixing the root system of the root-soil composite sample and drawing the root-soil composite 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; the sample matrix suction control system and the automated confining pressure-water supply system, when acting together, are used for simulating the stress history of the root-soil composite sample. The invention realizes that the mechanical properties of the root-unsaturated soil interface under different initial conditions can be accurately simulated at the same time.
Description
Technical Field
The invention relates to the technical field of geotechnical engineering, in particular to a test device and a test method for researching mechanical properties of a root-unsaturated soil interface.
Background
The reinforcing effect of the plant root system is utilized to prevent shallow landslide, the plant root system and the soil mass of the side slope form a root-soil complex, when the plant is subjected to external forces such as subsidence of the earth surface, landslide and the like, the relative sliding trend can be generated between the root system and the soil, and the tensile strength of the plant root system can be exerted while the friction force generated by the root-soil interface resists sliding displacement, so that the shear strength of the root-soil complex is increased. Therefore, the research on the mechanical properties of the root-soil interface is particularly critical to the soil consolidation mechanism of the analysis root system.
In addition to factors such as plant variety, diameter and mechanical properties of root system, the mechanical properties of root-soil interface are closely related to the saturation, stress state and stress history of soil: the mechanical property of the root-soil interface is mainly interface friction, and the maximum friction resistance is related to the squeezing action of the soil around the root on the root, namely, the stress state of the soil; as rainfall infiltration proceeds, the saturation of the root-soil complex gradually rises, and the mechanical properties of the root-soil interface change due to the change of the mechanical properties of unsaturated soil; the oversolidification ratio of the root-soil complex directly affects the mechanical properties of the soil, and thus the root-soil interface. The method is limited by a test device and a test method, the research of the mechanical properties of the root-soil interface is mainly carried out through drawing and direct shearing equipment, and although a great deal of results are obtained on the research of influence factors such as plant varieties, soil density, water content and the like, the influence of initial conditions such as saturation, stress state, stress history and the like of unsaturated soil cannot be finely simulated at the same time, so that the research of a root system soil fixing mechanism is restricted.
Disclosure of Invention
The invention aims to provide a test device and a test method for researching the mechanical properties of a root-unsaturated soil interface, so as 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.
In order to achieve the above object, the present invention provides the following solutions:
a test device for researching mechanical properties of a root-unsaturated soil interface, comprising: the drawing system, the pressure chamber system, the sample matrix suction control system and the 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 composite sample, and the drawing system is used for fixing the root system of the root-soil composite sample and drawing the root-soil composite 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;
the specimen matrix suction control system, when acting in concert with the automated confining pressure-water supply system, is used to simulate the stress history of the root-soil complex specimen.
Optionally, the drawing system includes: the device comprises a test bed, a support column, a lifting table, a cross beam, a force sensor, a root clamp, a probe type displacement sensor and an axial driving device;
the lifting table is arranged on the test bench, the axial driving device is arranged in the test bench, and the axial driving device is used for driving the lifting table to move;
the support is fixedly connected with the test bench, the cross beam is detachably connected with the support, the force sensor is arranged on the cross beam and used for measuring the tensile force born by the root system of the root-soil composite sample, the root system clamp is arranged on the force sensor and used for fixing the root system of the root-soil composite sample;
the probe type displacement sensor is arranged on the cross beam and is used for measuring the displacement of the root system of the root-soil complex sample.
Optionally, the cross beam comprises two arched members and a cross rod, wherein two ends of the cross rod are respectively welded with one arched member, and the arched members are connected with the support column through bolts;
the transverse rod is provided with two screw holes, two ends of the force sensor are provided with two screw holes, the two screw holes on the transverse rod 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 center screw hole, and the center 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 clay plate is placed on the pressure chamber base, the sample cap is placed above the clay plate, the permeable stone is placed above the inside 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;
and the centers of the pressure chamber base and the clay plate are respectively provided with a small hole, and the small holes are used for root penetration.
Optionally, the sample matrix suction control system comprises a pneumatic 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 drain pipe, the other end of the second pipeline is communicated with a root-soil complex sample through the pressure chamber base, the pore water pressure sensor is arranged 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 arranged on the third pipeline, a valve is arranged at the joint of the drainage sensor and the third pipeline, one end of the third pipeline is connected with the second drain 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 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 internal space of the pressure chamber; valves are arranged at the joints 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 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 the mechanical properties of a root-unsaturated soil interface comprises the following steps:
preparing a root-soil complex sample;
the root-soil composite sample is arranged in the provided test device for researching the mechanical properties of the root-unsaturated soil interface;
adjusting the saturation of the root-soil composite sample, simultaneously simulating the stress state and stress history of the root-soil composite 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 applied to the root system of the root-soil composite sample according to the displacement-tensile force curve;
measuring the penetration depth of the root-soil composite sample and the root mean diameter of the root-soil composite sample;
determining a root-soil interface friction coefficient of the root-soil composite sample according to the soil penetration depth, the average diameter of the root system and the maximum tensile force born by the root system;
and analyzing the mechanical properties 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 clay plate and the root system of the root-soil composite sample during the sample mounting stage.
Optionally, gasoline is injected into the paraffin during the root system drawing stage to dissolve the paraffin.
Optionally, the determining the root-soil interface friction coefficient of the root-soil composite sample according to the depth of penetration, the average diameter of the root system and the maximum tensile force exerted by the root system specifically comprises:
using the formulaCalculating the friction coefficient of a root-soil interface; in which μ is the root surfaceCoefficient of friction of soil mass root-soil interface coefficient of friction; 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 (f) s Is the maximum pulling force applied to the root system.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
according to the invention, the saturation of the root-soil composite sample is regulated through the sample matrix suction control system to simulate the state of the root-soil composite at different stages of rainfall infiltration, different confining pressures can be provided for the root-soil composite sample according to actual demands through the automatic confining pressure-water supply system communicated with the pressure chamber, the stress state of the root-soil composite sample is simulated, the defect that the traditional drawing device can only control vertical load is overcome, the simulated stress environment in the root-soil interface mechanical property test is more similar to the natural stress state, and the stress history of the root-soil composite sample can be simulated under the combined action of the sample matrix suction control system and the automatic confining pressure-water supply system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a test device for researching the mechanical properties of a root-unsaturated soil interface;
FIG. 2 is a schematic diagram of the construction of the drawing system of 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 the construction of the clay plate according to the invention;
FIG. 5 is a schematic diagram of an initial condition simulation phase of the present invention;
FIG. 6 is a schematic drawing stage of the present invention;
FIG. 7 is a flow chart of a test method for researching the mechanical properties of a root-unsaturated soil interface.
Symbol description: i-drawing system, II-pressure chamber system, III-sample matrix suction control system, IV-automatic confining pressure-water supply system;
the device comprises a 1-test bench, a 2-pillar, a 3-elevating platform, a 4-cross beam, a 5-force sensor, a 6-root clamp, a 7-probe type displacement sensor, an 8-pressure chamber base, an 8-1-chassis, an 8-2-base, an 8-3-upper base, an 8-4-lower base, an 8-5-small hexagon bolt, a 9-pressure chamber cover, a 9-1-vent hole, a 10-clay plate, 10-1-paraffin, an 11-root-soil composite sample, 12-water permeable stone, a 13-sample cap, 14-pillar, a 15-bracket, a 16-air pressure controller, a 17-first air compressor, an 18-pore water pressure sensor, a 19-first drain pipe, a 20-drainage sensor, a 21-water supply tank, a 21-1-water injection hole, a 22-confining pressure controller, a 23-first pipeline, a 24-second pipeline, a 25-third pipeline, a 26-fourth pipeline, a 27-second drain pipe and a 28-second air compressor.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a test device and a test method for researching the mechanical properties of a root-unsaturated soil interface, so as 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.
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 test method capable of simulating the mechanical properties of the root-unsaturated soil interface under different initial conditions, the test device can consider the influence of saturation, can provide confining pressure for a root-soil composite sample, can simulate the stress history of the root-soil composite sample, and can 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.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
FIG. 1 is a schematic diagram of a test device for researching mechanical properties of a root-unsaturated soil interface, which is provided by the invention, and as shown in FIG. 1, the test device comprises: drawing system I, pressure chamber system II, sample matrix suction control system III and automatic confining pressure-water supply system IV.
The drawing system I is connected with the pressure chamber system II, the pressure chamber system II is used for placing a root-soil composite sample, and the drawing system I is used for fixing the root system of the root-soil composite sample and drawing the root-soil composite sample.
The sample matrix suction control system III is connected with the pressure chamber system II, and the sample matrix suction control system III 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; the automatic confining pressure-water supply system IV is used for providing confining pressure for the root-soil composite sample and simulating the stress state of the root-soil composite sample.
And the sample matrix suction control system III and the automatic confining pressure-water supply system IV are used for simulating the stress history of the root-soil complex sample when acting together.
In practical application, the automatic confining pressure-water supply system IV supplies water for the pressure chamber system II and supplies confining pressure by taking water as a medium; the root-soil complex sample simulates different initial conditions under the combined action of an automatic confining pressure-water supply system IV and a sample matrix suction control system III; after the simulation process is finished, the position of the root system is fixed by the drawing system I, and the tensile force born by the root system is measured while power is provided for the axial movement of the pressure chamber.
Specifically, the drawing system i includes: test bench 1, pillar 2, elevating platform 3, crossbeam 4, force transducer 5, root anchor clamps 6, probe displacement sensor 7 and axial drive device. Wherein the axial drive is not shown in the figures.
The lifting table 3 is arranged on the test bed 1, the axial driving device is arranged inside the test bed 1, and the axial driving device is used for driving the lifting table 3 to move.
The support column 2 is fixedly connected with the test bed 1, the cross beam 4 is detachably connected with the support column 2, the force sensor 5 is installed on the cross beam 4, the force sensor 5 is used for measuring tensile force born by a root system of the root-soil composite sample, the root system clamp 6 is installed on the force sensor 5, and the root system clamp 6 is used for fixing the root system of the root-soil composite sample. In practical application, root system anchor clamps 6 divide into upper and lower two parts, and upper portion is a pulling force anchor clamps, and the lower part is a bolt structure, and the external screw thread of bolt structure and the screw thread of force sensor 5 center screw inner wall mutually support to realize root system anchor clamps 6 and force sensor 5's connection.
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 beam 4 passes through the lower part of the pressure chamber base and is detachably connected with the support column 2, the force sensor 5 is arranged above the beam 4, and the probe type displacement sensor 7 is arranged at the right part below the beam 4.
Specifically, as shown in fig. 2, the cross beam 4 includes two arch members and a cross beam, two ends of the cross beam are respectively welded with one arch member, and the arch members are detachably connected with the support posts 2 through bolts, so that the position of the cross beam 4 can be conveniently adjusted.
Two screw holes are formed in the cross rod, two screw holes are formed in two ends of the force sensor 5, the two screw holes in the cross rod are matched with the two screw holes in 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 center screw hole, and the center screw hole is used for installing the root clamp 6. In practical application, 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 marker post 14 and a bracket 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 inside 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 contacted with the support 15.
The centers of the pressure chamber base 8 and the clay plate 10 are provided with a small hole, and the small hole is used for root penetration.
In practical application, the pressure chamber base 8 comprises a base 8-2 and a base; the clay plate 10 is placed on a base; the root-soil composite sample 11 is placed on the clay plate 10, a rubber membrane is wrapped outside the root-soil composite sample 11, and the permeable stone 12 and the sample cap 13 are sequentially placed on the top of the root-soil composite sample 11; the outer wall of the pressure chamber cover is made of transparent organic glass, the pressure chamber cover is connected with the pressure chamber base 8 through bolts, and the top of the pressure chamber cover is provided with an exhaust hole 9-1.
As shown in fig. 3, the chassis 8-1 of the base 8-2 is fixedly connected with the base 8-2 with four struts; 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 of an inverted hollow cap-shaped structure, two screw holes are formed in the cap peak, a small hole is formed in the bottom of the cap peak and is used for enabling root systems to penetrate out of the cap peak, and rubber washers with different opening diameters can be replaced in the small hole in the bottom of the cap peak 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; a third pipeline is arranged in the bottom of the lower base 8-4.
The clay plate 10 has a through hole in the center of the plate body, which is in the shape of an inverted truncated cone, and is convenient for the plant root system to pass through. The root-soil composite sample 11 was placed on the clay plate 10 such that the root-soil composite sample 11 penetrated out of the holes of the clay plate 10, the gap between the clay plate 10 and the plant root system was filled with melted paraffin 10-1, and the paraffin 10-1 was rapidly solidified. As shown in fig. 4.
Specifically, the sample matrix suction control system III comprises a pneumatic 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 drain 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 arranged on the second pipeline 24, and a valve is arranged at the joint 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 connected with one end of the fourth pipeline 26, and the other end of the fourth pipeline 26 passes through the pressure chamber base 8 to be communicated with the internal space of the pressure chamber; valves are arranged at the joints 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 connected with the second air compressor 28, and valves are arranged at the joints 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, the top of the water supply tank 21 is provided with a water injection hole 21-1; 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 branch pipeline.
FIG. 7 is a flow chart of a test method for researching mechanical properties of a root-unsaturated soil interface, which is provided by the invention, and is shown in FIG. 7, and comprises the following steps:
step 701: root-soil complex samples were prepared. In practical application, selecting corresponding soil and plant root systems according to a research target, and manufacturing a root-soil composite weight plastic soil sample; or directly taking the undisturbed root-soil composite sample 11, and reducing disturbance as much as possible in the field sampling process; marking the position of the root system exposing out of the soil body.
Step 702: the root-soil composite sample was mounted in the test apparatus for studying the mechanical properties of the root-unsaturated soil interface described above. In practical application, placing a piece of filter paper on the upper and lower surfaces of the main body part of the saturated root-soil composite sample 11, and then placing the sample on the clay plate 10 to make the plant root system penetrate out of the holes of the clay plate 10; filling gaps between the clay plates 10 and plant root systems with melted paraffin 10-1 to ensure the air tightness of the root-soil complex, and rapidly solidifying the paraffin 10-1; placing a sample and a clay plate 10 on a base, wrapping a sample main body part by using a rubber film, sequentially placing a permeable stone 12 and a sample cap 13 on the top of the sample, fastening two ends of the sample by using a rubber ring, removing air of a second pipeline 24 in the sample loading process, placing a pressure chamber cover 9 on a base 8-2 after the sample is placed, and fastening by using a nut; the rubber gasket with proper size is selected according to the diameter of the root system and sleeved at the opening at the lower end of the lower base 8-4, a small amount of silicone grease is smeared on the inner wall of the rubber gasket, the air tightness of the device is ensured, the lower base 8-4 is sleeved into the root system of the plant, and then the lower base 8-4 is connected with the chassis 8-1 by a small hexagonal screw, so that the installation of the sample is completed.
Step 703: and (3) adjusting the saturation of the root-soil composite sample, simultaneously simulating the stress state and the stress history of the root-soil composite sample, and ending the initial condition simulation stage.
In actual application, in an initial condition simulation stage, water is injected into a pressure chamber through an automatic confining pressure-water supply system IV, and target confining pressure is provided for the pressure chamber, so that the sample saturation and the stress history of the sample can be adjusted by utilizing a 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 ended, and the apparatus of the initial condition simulation phase is 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=1, four groups of comparison experiments are carried out, each group of samples are respectively added with 25, 50, 75 and 100kPa confining pressure after saturation, and consolidation is considered to be completed after pore water pressure dissipation.
After the sample is installed, the second air compressor 28 of the automatic confining pressure-water supply system IV is started, the valve position is adjusted to the position from the first branch of the fourth channel to the channel position, water is injected into the pressure chamber, after the water is filled, the exhaust hole 9-1 is closed to enable the second branch to keep the channel, 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 a 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, solidifying the sample for drainage, and closing the valve when the initial stress state of the sample is simulated to be completed after the pore water pressure is dissipated.
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=1, and the soil-water characteristic curve of the test soil body can be measured first to obtain the change relation between the soil body saturation and the matrix suction; four groups of comparison tests are conducted to study the influence of corresponding saturation of different matrix suction forces 10, 50, 100 and 150kPa on the mechanical characteristics of a root-unsaturated soil interface under the net confining pressure of 100kPa, the internal air pressure of a sample is set to be 200kPa, the confining pressure of the test 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 an automatic confining pressure-water supply system IV is started, the hand valve is adjusted to be positioned at a first branch passage to a passage position of a fourth passage, water is injected into a pressure chamber, after the water is filled, an exhaust hole 9-1 is closed to enable a second branch passage, the internal pressure of the pressure chamber is loaded to 300kPa through a confining pressure controller 22, meanwhile, a first passage related valve is opened, a target air pressure value of an air pressure controller 16 is set, the air compressor is started, 200kPa air pressure is applied to the inside of the sample, a second three-passage related valve is opened, a drainage sensor 20 and a pore water pressure sensor 18 are started, the sample is dehumidified, and after the pore water pressure reaches a target value, the matrix suction balance stage is considered to be ended, and the sample reaches target saturation.
Example 3: the effect of stress history (OCR) on the mechanical properties of the root-saturated soil interface was analyzed. The test objects are saturated soil, the same stress state is controlled, four groups of comparison experiments are carried out, different oversolidation ratios are drawn, OCR=0.5, 1, 1.5 and 2, each group of samples are respectively loaded with 25, 50, 75 and 100kPa confining pressure for preliminary consolidation after saturation, and are all loaded/unloaded to 50kPa confining pressure after consolidation, and the consolidation is considered to be completed after pore water pressure dissipation.
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 from a first branch of a fourth channel to a channel position, water is injected into a pressure chamber, after the water is filled, the exhaust hole 9-1 is closed to enable a second branch to keep the channel, and the internal pressure of the pressure chamber is loaded to a 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 a 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, solidifying the sample to drain water, and closing the valve of the third pipeline 25 when the pore water pressure is dissipated to be the prior solidification is completed. And then the internal pressure of the pressure chamber is increased/unloaded to 50kPa through the confining pressure controller 22, a valve of the third pipeline 25 is opened, the sample is waited for consolidation, the consolidation is considered to be completed after the pore water pressure is dissipated, at the moment, the sample reaches the corresponding oversolidation ratio, and the valve is closed.
Step 704: and in the root system drawing stage, a 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 composite sample 11, and the cross beam 4 is fixed on the support column 2 through bolts; after the base 8-4 is taken down, injecting gasoline into the paraffin 10-1 filled between the clay plate 10 and the root system to dissolve the paraffin; carefully fixing the root penetrating out of the clay plate 10 on the root holder 6; the position of the probe displacement sensor 7 is adjusted to be 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 sample 11 to axially lift, so that the drawing force is generated, and the device in the drawing stage is shown in fig. 6. The probe type displacement sensor 7 collects displacement data, namely the length of the root system pulled out of the soil body, and the force sensor 5 collects the tensile force exerted on the root system. The root system is pulled out or slides out of the soil sample, namely the test is finished; experiments with root sliding out of the soil samples were noted as successful experiments.
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 exerted on the root system of the root-soil composite sample according to the displacement-tensile force curve.
In practical application, the 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 of the root system is the root system drawing force.
Step 707: measuring the penetration depth of the root-soil composite sample and the root mean diameter of the root-soil composite sample.
In practical application, the root system of the root-soil composite sample 11 which is successfully tested is taken out, the soil penetration depth z of the root system and the diameters of the upper part, the middle part and the lower part of the soil penetration part of the root system are measured by a vernier caliper, and the average diameter is obtained.
Wherein D is 1 、D 2 、D 3 The diameters of the upper part, the middle part and the lower part of the plant root system are respectively m.
Step 708: and determining the root-soil interface friction coefficient of the root-soil composite sample according to the soil penetration depth, the average diameter of the root system and the maximum tensile force born by the root system.
The method specifically comprises the following steps: and (5) analyzing the mechanical properties of the root-soil interface. The study subject of this test was a single plant, assuming: the plant root system is a rigid rod piece, and tiny deformation of the plant root system in the stretching process is ignored; the plant root system surface materials are uniform, namely the friction coefficients of the root system surfaces are the same (the concave-convex unevenness of the root system surfaces and the small-amplitude bending in a certain length interval are all considered in the friction coefficients); the extrusion effect of the surrounding soil on the root system has little influence compared with confining pressure, and the minor term is ignored. The pulling force of the root system is the maximum static friction force f between the root and the soil s Then the plant root system with the burial depth z receives the maximum static friction force as follows:
f s =μpρ pi Dz; wherein mu is the friction coefficient between the surface of the plant root system and the soil body; p is the confining pressure applied to the sample in the drawing stage, and Pa; d is the average diameter of plant root system, m; z is the depth of the root system entering the soil and m. The root-soil interface friction coefficient can be calculated as follows:
step 709: and analyzing the mechanical properties 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 properties of the root-soil interface under different initial conditions are analyzed, and basic test data are provided for in-depth research of a root system soil fixing mechanism.
The working principle of the invention is as follows:
the saturated root-soil composite sample 11 is placed in a pressure chamber, a plant root system penetrates out of a lower base 8-4, a gap between the root system and a clay plate 10 is sealed by adopting paraffin 10-1, water is supplied to the pressure chamber through an automatic confining pressure-water supply system IV under the condition that the sample is good in air tightness, water serves as confining pressure transmission media to realize application of the confining pressure of the sample, the saturation and stress history of the sample can be simulated by the automatic confining pressure-water supply system IV and a sample matrix suction control system III, after the simulation stage of different initial conditions is finished, the plant root system is fixed by a root system clamp 6 of a drawing system I, the pressure chamber is driven to move upwards by an axial driving device, and the plant root system is pulled out or slides out of a soil body along with further increase of axial displacement, and a stress process of the root system drawing stage is recorded by a probe type displacement sensor 7 and a force sensor 5 connected with the root system clamp 6.
Compared with the prior art, the invention has the following beneficial effects:
1. as the infiltration of rainfall proceeds, the saturation of the root-soil complex increases gradually, and the friction force between the root-soil interface changes accordingly. 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 exploration of the mechanical properties of the root-unsaturated soil interface.
2. The invention relates to a test device for researching the mechanical properties of a root-soil interface in a 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 test of the mechanical properties of the root-soil interface is more similar to a natural stress state.
3. Under the combined action of the sample matrix suction control system and the automatic confining pressure-water supply system, the invention can simulate the stress history of the sample and can study the influence of oversolidification comparison on the mechanical characteristics of a root-soil interface during root system drawing.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (4)
1. A test device for researching mechanical properties of a root-unsaturated soil interface is characterized by comprising: the drawing system, the pressure chamber system, the sample matrix suction control system and the 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 composite sample, and the drawing system is used for fixing the root system of the root-soil composite sample and drawing the root-soil composite sample;
the pressure chamber system comprises a pressure chamber cover, a pressure chamber base, a clay plate, paraffin, gasoline, permeable stones, a sample cap, a marker post and a bracket; the drawing system includes: the device comprises a test bed, a support column, a lifting table, a cross beam, a force sensor, a root clamp, a probe type displacement sensor and an axial driving device;
the pressure chamber cover is connected with the pressure chamber base, the pressure chamber base is arranged on the lifting table, the clay plate is arranged on the pressure chamber base, and the clay plate is used for fixing the root system of the root-soil composite sample; the paraffin is filled between the clay plate and the root system of the root-soil composite sample; the gasoline is used for dissolving the paraffin; the sample cap is arranged above the clay plate, the permeable stone is arranged above the inside 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 clay plate are respectively provided with a small hole, and the small holes are used for root penetration;
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 sample matrix suction control system comprises a pneumatic 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 a pressure chamber base of the pressure chamber system to be connected with a sample cap of the pressure chamber system, 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 drain pipe, the other end of the second pipeline is communicated with a root-soil complex sample through the pressure chamber base, the pore water pressure sensor is arranged 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 arranged on the third pipeline, a valve is arranged at the joint of the drainage sensor and the third pipeline, one end of the third pipeline is connected with the second drain pipe, and the other end of the third pipeline is connected with the pressure chamber base;
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;
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 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 internal space of the pressure chamber; valves are arranged at the joints 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 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;
the specimen matrix suction control system, when acting in concert with the automated confining pressure-water supply system, is used to simulate the stress history of the root-soil complex specimen.
2. The test device for researching mechanical properties of a root-unsaturated soil interface according to claim 1, wherein the lifting table is arranged on the test table seat, the axial driving device is arranged in the test table seat, and the axial driving device is used for driving the lifting table to move;
the support is fixedly connected with the test bench, the cross beam is detachably connected with the support, the force sensor is arranged on the cross beam and used for measuring the tensile force born by the root system of the root-soil composite sample, the root system clamp is arranged on the force sensor and used for fixing the root system of the root-soil composite sample;
the probe type displacement sensor is arranged on the cross beam and is used for measuring the displacement of the root system of the root-soil complex sample.
3. The test device for studying the mechanical properties of a root-unsaturated soil interface according to claim 2, wherein the cross beam comprises two arched members and a cross beam, wherein two ends of the cross beam are respectively welded with one arched member, and the arched members are connected with the support column through bolts;
the transverse rod is provided with two screw holes, two ends of the force sensor are provided with two screw holes, the two screw holes on the transverse rod 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 center screw hole, and the center screw hole is used for installing the root system clamp.
4. A test method for researching the 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 the test device for researching the mechanical properties of the root-unsaturated soil interface according to any one of claims 1 to 3, and filling paraffin between a clay plate and the root system of the root-soil composite sample;
adjusting the saturation of the root-soil composite sample, simultaneously simulating the stress state and stress history of the root-soil composite sample, and ending the initial condition simulation stage;
in the stage of root system drawing, adjusting a drawing system, injecting gasoline into the paraffin to dissolve the paraffin, and recording data of a probe type displacement sensor and data of a force sensor;
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 applied to the root system of the root-soil composite sample according to the displacement-tensile force curve;
measuring the penetration depth of the root-soil composite sample and the root mean diameter of the root-soil composite sample;
determining a root-soil interface friction coefficient of the root-soil composite sample according to the soil penetration depth, the average diameter of the root system and the maximum tensile force born by the root system;
the root-soil interface friction coefficient of the root-soil composite sample is determined according to the soil penetration depth, the average diameter of the root system and the maximum tensile force born by the root system, and the method specifically comprises the following steps:
using the formulaCalculating the friction coefficient of a root-soil interface; in (1) the->The friction coefficient between the surface of the root system and the soil body; />Confining pressure applied to the root-soil composite sample in the drawing stage; />Is the average diameter of the root system; />Is the depth of the soil; />The maximum pulling force is applied to the root system;
and analyzing the mechanical properties of the root-soil interface under different initial conditions according to the friction coefficient of the root-soil interface and the displacement-tension curve.
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