A method for researching rock-soil interface dry shrinkage cracks in rocky desertification area

Abstract

The present application belongs to the technical field of rock and soil mechanics, and particularly relates to a method for researching rock-soil interface dry shrinkage cracks in a rocky desertification area, comprising the following steps: constructing a test container and setting a drainage hole at the bottom of the test container; selecting a plurality of natural block rock bodies and placing them in the test container, with the rock body head being located outside the test container; filling the test container with soil in the empty area to form a test sample; performing an arbitrary number of dry-wet cycles on the test sample, recording the crack development process, and recording the change in the water content in the soil during the crack development process. The present application has high flexibility and adaptability, can be designed into test samples of different sizes according to actual needs, and can select natural rock surfaces or specially designed rock surfaces according to needs, can design multiple soil layer thicknesses, rock surface geometric shapes, rock surface inclinations, etc., and the test can be repeated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of geotechnical mechanics, and particularly relates to a method for researching dry shrinkage cracks of rock-soil interface in a stone desertification area. BACKGROUND

[0002] Soil shrinkage cracks caused by soil water loss are a common phenomenon in nature. Under the influence of climate change, frequent dry-wet cycles can easily lead to soil drying and cracking and humidification and closing, directly affecting soil permeability, structure and stability, and seriously affecting agricultural production, civil construction and water conservancy projects.

[0003] In the stone desertification area, long-term karstification causes the rocks to be exposed to the surface, the soil to be discontinuously distributed, and the rocks and soil to be staggered. The rock-soil interface between the exposed rocks and the soil on the surface is common in the stone desertification area. This abrupt contact is mainly due to the lack of C layer or transition layer between matrix carbonate parent rock and soil. Due to the difference in rock-soil characteristics, soil in the stone desertification area is prone to form cracks through dry shrinkage at the rock-soil interface and close the cracks through wet expansion under dry and wet conditions.

[0004] Although there are mature research techniques and methods for shrinkage cracks of cohesive soil or expansive soil, there is no existing device and method for shrinkage cracks of soil in karst areas and its constraint under the boundary of exposed rocks. The existing research techniques and methods for expansive soil cracks cannot achieve the observation and research of shrinkage cracks of soil constrained by rock boundaries. Therefore, there is a lack of research device and method for rock-soil interface dry shrinkage cracks in the stone desertification area in the prior art.

[0005] Therefore, how to realize the observation and research of the development of rock-soil interface dry shrinkage cracks formed by the shrinkage of soil constrained by exposed rock boundaries, and obtain accurate crack morphology analysis results, is a core problem to be solved in the field. SUMMARY

[0006] The purpose of the present application is to provide a method for researching rock-soil interface dry shrinkage cracks in a stone desertification area to solve the above problems.

[0007] To achieve the above purpose, the present application provides the following scheme:

[0008] A method for researching rock-soil interface dry shrinkage cracks in a stone desertification area, comprising the following steps:

[0009] Constructing a test container and setting a drainage hole at the bottom of the test container;

[0010] Selecting a plurality of natural block rock bodies and placing them in the test container, wherein the rock body head of the rock body is located outside the test container;

[0011] filling the soil in the free area of the test container to form a test sample;

[0012] carrying out any times of dry-wet cycles on the test sample, recording the crack development process, and recording the change of water content in the soil during the crack development process.

[0013] Optionally, the test container comprises:

[0014] the organic glass container is provided with organic glass container bottom perforations arranged in a matrix at the bottom of the organic glass container, and the quartz sand is laid at the bottom of the organic glass container.

[0015] Optionally, the volume ratio of the rock mass to the soil is 1:1.

[0016] Optionally, the step of dry-wet cycle comprises initial humidification, drying and water spraying humidification.

[0017] Optionally, the initial humidification step comprises:

[0018] placing the test sample in a water containing device, and the water level in the water containing device is flush with the upper surface of the quartz sand;

[0019] maintaining the water level in the water containing device;

[0020] after the soil surface is moistened, increasing the water level in the water containing device to be flush with the soil surface.

[0021] Optionally, the step of drying comprises:

[0022] draining the water containing device, and placing the test sample in a controllable temperature and humidity environment;

[0023] the water in the test sample is evaporated through the soil surface and discharged through the organic glass container bottom perforations;

[0024] observing and recording the development process of the dry shrinkage cracks;

[0025] when the mass change of the test sample is less than 0.5% for three times in succession, the drying process can be considered to be completed.

[0026] Optionally, the step of water spraying humidification comprises:

[0027] calculating the water spraying amount, and uniformly spraying water to the rock mass and the soil surface;

[0028] after the water spraying is completed, weighing the organic glass container after the bottom of the organic glass container does not drip water, taking a picture and recording the crack change until the dry shrinkage cracks are completely closed.

[0029] Compared with the prior art, the present application has the following advantages and technical effects:

[0030] The rock-soil interface dry shrinkage crack development sample of the present application can simulate the contact condition of bare rock and soil in a rocky desertification area, and can accurately obtain the development process of dry shrinkage cracks at the rock-soil interface and the critical value of soil moisture; the present application has high flexibility and adaptability, and can be designed into samples of different sizes according to actual needs; the sample can be selected to study natural rock surface or specially designed rock surface, and multiple soil layer thicknesses, rock surface geometric shapes, rock surface inclinations, etc. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings:

[0032] Figure 1 It is a rock-soil interface dry shrinkage crack development sample profile of the present application;

[0033] Figure 2 It is a rock-soil interface dry shrinkage crack development sample plan view of the present application;

[0034] Figure 3 It is a schematic diagram of uniformly punching the bottom of a machine glass container of the present application;

[0035] Figure 4 It is a schematic diagram of flat rock-soil interface dry shrinkage crack development of the present application;

[0036] Figure 5 It is a schematic diagram of convex rock-soil interface dry shrinkage crack development of the present application;

[0037] Figure 6 It is a schematic diagram of concave rock-soil interface dry shrinkage crack development of the present application;

[0038] Figure 7 It is a schematic diagram of flat rock-soil interface dry shrinkage crack image processing result of the present application;

[0039] Figure 8 It is a schematic diagram of convex rock-soil interface dry shrinkage crack image processing result of the present application;

[0040] Figure 9 It is a schematic diagram of concave rock-soil interface dry shrinkage crack image processing result of the present application;

[0041] 1, the organic glass container; 2, rock mass; 3, rock mass head; 3-1, flat rock surface; 3-2, convex rock surface, 3-3, concave rock surface; 4, soil; 5, quartz sand; 6, rock-soil interface; 7, overall inclined line of rock-soil interface; 8, rock-soil interface inclination; 9, organic glass container bottom hole; 10, organic glass container external scale; 11, rock-soil interface dry shrinkage crack; 12, soil surface dry shrinkage crack. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0043] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0044] Reference Figures 1 to 9 The present application discloses a method for researching rock-soil interface dry shrinkage cracks in a stone desertification area, comprising the following steps:

[0045] An experimental container is constructed, and a drainage hole is arranged at the bottom of the experimental container;

[0046] A plurality of natural block rock masses 2 are selected and placed in the experimental container, and the rock mass head 3 of the rock mass 2 is located outside the experimental container;

[0047] After the soil 4 is filled in the remaining area of the experimental container, a test sample is formed;

[0048] The test sample is subjected to any number of dry-wet cycles, the crack development process is recorded, and the change of water content in the soil 4 during the crack development process is recorded.

[0049] The present application can better simulate the contact condition of exposed rock and soil in a stone desertification area, and can accurately obtain the development process of dry shrinkage cracks at the rock-soil interface and the soil moisture critical value. The present application has strong flexibility and adaptability, and can be designed into test samples of different sizes according to actual needs. The test sample can be selected according to needs, and the natural rock surface or the specially designed rock surface can be selected. Multiple soil layer thicknesses, rock surface geometric shapes, rock surface inclination angles, etc. can be designed, and the test can be repeated.

[0050] As an optional embodiment, the experimental container comprises:

[0051] The organic glass container 1 is provided with organic glass container bottom holes 9 arranged in a matrix at the bottom of the organic glass container 1, and the quartz sand 5 is laid at the bottom of the organic glass container 1.

[0052] As an optional embodiment, the volume ratio of the rock mass 2 to the soil 4 is 1:1.

[0053] According to actual needs, square organic glass containers 1 of different sizes can be designed, and an external scale 10 is added to the outer wall of the container to observe the geometric parameters of the fissure, such as a square organic glass container 1 with a side length of 50 cm x 50 cm x 50 cm; the bottom of the container needs to be uniformly punched with 10 mm aperture organic glass container bottom punching 9 for drainage, and the circular hole density is appropriate to ensure smooth water inlet and outlet; at the same time, about 1-5 cm thick quartz sand 5 (about 50 mesh) needs to be laid at the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil 4.

[0054] According to research needs, sieved soil or non-sieved soil can be selected as the soil 4, and the sieved soil can be sieved through different aperture soil sieves according to needs; according to the size of the designed organic glass container, multiple stones with a size of about 1 / 2 of the volume of the organic glass container 1 are selected, and one of the rock surfaces of the stones should meet the design needs, such as selecting multiple stones with a size of about 50 cm x 50 cm x 25 cm, taking the natural rock surface of 50 cm x 50 cm as the rock-soil interface 6, or selecting or polishing the rock surface to be flat, convex, concave, and random (without polishing) according to needs to obtain the rock mass 2.

[0055] According to the prepared soil 4 and rock mass 2, the rock mass 2 is filled into the square organic glass container 1 according to the designed rock-soil contact surface rock surface type and rock surface inclination, and the rock mass 2 is filled along the edge according to the principle that the soil 4 and the rock mass 2 each occupy about half; when filling the soil, the soil is filled into the container from bottom to top according to the original container weight, and the surface is leveled at this time, at which time the rock mass 2 and the soil 4 each occupy about 50% of the surface of the container, and the weights of the organic glass container 1, the rock mass 2, and the filled soil 4 are measured and recorded; the soil layer thickness can be divided into multiple levels such as 10 cm, 20 cm, and 30 cm according to the test design, the rock-soil contact surface rock surface geometric shape is designed to be flat, convex, and concave, and the rock surface inclination is designed to be multiple gradients such as 30°, 60°, and 90°, and each treatment has more than 3 repetitions.

[0056] As an optional embodiment, the steps of dry-wet cycle include initial humidification, drying and water loss, and water spraying humidification.

[0057] As an optional embodiment, the initial humidification step includes:

[0058] The test sample is placed in a water container, and the water level in the water container is flush with the upper surface of the quartz sand 5;

[0059] The water level in the water container is maintained;

[0060] After the surface of the soil 4 is moistened, the water level in the water container is raised to the level of the surface of the soil 4.

[0061] As an optional embodiment, the step of drying and losing water includes:

[0062] The water container is drained, and the test sample is placed in a controllable temperature and humidity environment.

[0063] The moisture in the test sample is evaporated through the surface of the soil 4 and discharged through the bottom hole 9 of the organic glass container;

[0064] The development process of the dry shrinkage crack is observed and recorded.

[0065] When the mass change of the test sample is less than 0.5% for three consecutive times, the drying process is considered to be completed.

[0066] As an optional embodiment, the step of spraying water for humidification includes:

[0067] The amount of water sprayed is calculated, and the water is uniformly sprayed to the surface of the rock mass 2 and the soil 4.

[0068] After the spraying is completed, the organic glass container 1 is weighed, photographed, and the crack change is recorded until the dry shrinkage crack is completely closed.

[0069] Based on the above-prepared test sample, tests on the development process of the dry shrinkage crack of the rock-soil interface under different time scales such as indoor dry-wet cycles, simulated rainfall, or natural rainfall can be carried out. Taking the indoor dry-wet cycle as an example, the steps are as follows:

[0070] For the above test sample, initial humidification is started, and the initial humidification method of "water absorption from the bottom of the soil layer to the surface of the soil" is adopted, that is, the test sample is placed in a water container with the water level being flush with the quartz sand 5 layer. The water container can be replaced by a larger water basin or an inflatable fish tank, and the moisture is gradually absorbed by the soil 4. At this time, the water container should be constantly replenished to ensure that the soil 4 can fully absorb water and humidify. Finally, after the surface of the soil 4 is humidified, water is added to the water container to the level of the surface of the filled soil, so that the soil 4 is completely saturated, and the humidification process is completed.

[0071] For the humidified sample, the first drying test is carried out by using "soil bottom drainage + soil surface evaporation" water loss method, that is, the water containing device is drained, and the test sample is placed in a controllable temperature and humidity environment indoors or in a natural environment with changing temperature and humidity outdoors, at this time the water in the rock-soil interface dry shrinkage crack developed sample can be drained through seepage and discharged from the quartz sand 5 of the organic glass container 1, and at the same time the water vapor can be discharged from the organic glass container 1 through the soil surface evaporation. When the drainage starts, it is recorded as the initial state of the sample. After that, with the continuous progress of the water loss process, the soil surface and the rock mass 2 contact position will develop into rock-soil interface dry shrinkage crack 11. After the initial state, the surface morphology of the sample needs to be recorded by taking pictures at certain time intervals, the crack depth development is measured and recorded by using a flexible ruler on the outer wall, and the weight change of the device is weighed; after the rock-soil interface dry shrinkage crack appears, the interval time of photographing and weighing needs to be shortened to maximize the dynamic change process of crack increase; when the mass change of the sample is less than 0.5% for three consecutive times, the drying process can be considered to be completed, the crack development is stable, and the first humidification test begins.

[0072] For the dried sample, the first humidification test is carried out by using "sample surface water spraying / rainfall" humidification method, that is, the water is uniformly sprayed on the surface of the rock and soil by using air pressure spray pot, the amount of water sprayed each time can be calculated according to the local rainfall intensity and the area of the sample device, for example, according to the maximum 30min rainfall intensity of 15.0mm / h in a certain place, the rainfall is 15mm, the area of the sample device is 50cm×50cm, then the amount of water sprayed is 3750ml, and the spraying time is 60min; during the spraying process, the soil structure is ensured not to be damaged and no water accumulation is generated, after the spraying is completed, the organic glass container 1 is weighed when there is no dripping water at the bottom, the crack change is recorded by taking pictures, and the observation is carried out until the rock-soil interface dry shrinkage crack is completely closed, the humidification test is completed, and the next round of drying test begins.

[0073] The calculation formula of the amount of water sprayed is:

[0074] W=0.1AIt

[0075] Wherein, W represents the amount of water sprayed (ml), I represents the rainfall intensity (mm / h), t represents the rainfall time or spraying time (h), A represents the area of the sample device (cm 2 ), and 0.1 represents the unit conversion factor.

[0076] The soil water content data is analyzed and calculated by weight change; considering that the test sample is relatively heavy and difficult to move, at this time the TDR soil moisture sensor can be used, the soil moisture sensor should be placed horizontally, and the probe should be vertically contacted with the rock surface of the rock mass 2 (to measure the soil water content at the rock-soil interface), and the probe should be at least 5cm below the soil surface to ensure that the buried TDR does not affect the development of the soil surface crack.

[0077] Repeat the above steps, and the dry-wet cycle test can be carried out for multiple times.

[0078] For the obtained rock-soil interface dry shrinkage crack picture, the digital image processing technology is used to extract the development indexes of the rock-soil interface dry shrinkage crack, such as total length, average width and surface crack rate. The processing steps are as follows: the central region of the sample is cut out as the processing object (such as 40cm*40cm) to eliminate the boundary influence of the container edge, and then the image preprocessing, crack identification and quantification are carried out for processing analysis, and the development characteristics and related parameters in the appearance, development, stability and closure process of the rock-soil interface dry shrinkage crack are extracted or calculated by the related software: ① crack development characteristics: crack area, length, width, surface crack rate and the like; ② related parameters: soil moisture content at different times (calculated according to the weighing data) such as crack appearance, development, stability and closure.

[0079] The application will be further described in combination with the embodiments and the drawings.

[0080] Embodiment 1: A rock-soil interface dry shrinkage crack research device and method in a rocky desertification area, comprising the following steps:

[0081] Step 1: Constructing a rock-soil interface dry shrinkage crack test device

[0082] In the method, an organic glass container 1 with a side length of 30cm*30cm*30cm is designed, an organic glass container outer scale 10 is added to the outer wall of the container to observe the crack geometric shape parameters; the organic glass container bottom punching 9 with a 10mm aperture is uniformly punched at the bottom of the container to drain water, and the density satisfies smooth water inlet and outlet; at the same time, about 1cm thick quartz sand 5 (50 mesh) is laid at the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil.

[0083] Step 2: Preparing soil 4 and rock mass 2

[0084] In the method, the soil 4 is taken from a rocky desertification land in a certain region of Guizhou Province, and the soil 4 is dried and passed through a 2mm sieve to be used as the test soil. According to the size of the designed organic glass container 1, a plurality of stone blocks with a size of about 30cm*30cm*15cm are selected to prepare the rock mass 2, and the 30cm*30cm natural rock surface of the rock mass 2 is taken as the rock-soil interface 6. Here, the flat rock surface 3-1 is selected for indoor dry-wet process simulation experiment.

[0085] Step 3: Preparing a rock-soil interface dry shrinkage crack development sample

[0086] With the method of the application, the rock mass 2 of the flat rock surface is filled into the square organic glass container 1 according to the rock-soil interface inclination 8 of 90° (that is, the angle between the overall inclined line 7 of the rock-soil interface and the horizontal line of the quartz sand 5), and the rock mass 2 is filled on the side according to the principle that the soil 4 and the rock mass 2 each occupy about half; when filling the soil, the soil is filled into the container in layers from bottom to top according to the original container weight (1.10 g / cm3) until the surface is level, at this time the rock mass 2 and the soil 4 each occupy about 50% of the surface of the container, and the weights of the organic glass container 1, the rock mass 2 and the filled soil 4 are measured and recorded; the thickness of the soil layer is divided into 10, 20, 30 cm and the like, the rock surface geometry of the rock-soil interface is designed as a flat type, the rock-soil interface inclination 8 is designed as 90°, and each treatment is repeated more than three times.

[0087] Step 4: Moistening test and drying test of rock-soil interface dry shrinkage crack development test sample

[0088] With the method of the application, based on the rock-soil interface dry shrinkage crack development test sample prepared above, indoor dry-wet cycle test is carried out, and the steps are as follows:

[0089] For the above-mentioned test sample, initial moistening is started, and the initial moistening method of "water absorption from the bottom of the soil layer to the surface of the soil" is adopted, that is, the test sample is placed in a water level flush with the quartz sand 5 layer of a water containing device, which is replaced by a larger aerated fish pond, and the water is gradually absorbed by the soil 4, at this time the water containing device should be constantly replenished with water to ensure that the soil 4 can fully absorb water and moisten; finally, after the surface of the soil 4 is fully moistened, water is added to the water containing device to flush with the surface of the filled soil, so that the soil sample is fully saturated, and thus the moistening process is completed.

[0090] For the moistened test sample, the first drying and water loss test is carried out, and the water loss method of "drainage at the bottom of the soil layer + evaporation at the surface of the soil" is adopted, that is, the water containing device is drained, and the test sample is placed in a well-ventilated greenhouse for dry-wet cycle test, and the temperature is controlled at 24-32℃ (which is the average daily maximum temperature in the region from May to September), at this time the water in the rock-soil interface dry shrinkage crack development test sample can be discharged from the test device through seepage and through the quartz sand 5, and at the same time can be discharged from the test device through water vapor evaporation at the surface of the soil. When the drainage starts, it is recorded as the initial state of the test sample, and thereafter, as the water loss process continues, the soil surface and the rock contact position will develop into rock-soil interface dry shrinkage cracks 11. From the initial state, the surface morphology of the test sample is recorded by taking pictures at 8h intervals, the crack depth development is measured and recorded on the outer wall with a flexible ruler, and the weight change of the device is measured; after the rock-soil interface dry shrinkage cracks appear, the interval time for photographing and weighing is shortened to 4h to maximize the dynamic change process of crack growth; when the mass change of the test sample is less than 0.5% for three consecutive times, the drying process can be considered to be completed, the crack development is stable, and the first moistening test is started.

[0091] For the sample after drying and water loss, the first wetting test was carried out, and the wetting method of "spraying water on the sample surface" was adopted, that is, a pressure spraying bottle was used to evenly spray water to the entire rock mass 2 and soil 4 surface. According to the local erosive rainfall intensity, the maximum 30-min rainfall intensity is 15.0 mm / h, the rainfall is 15 mm, and the sample device area is 30 cm×30 cm. The water spraying volume is 1350 ml and the spraying time is 60 min. During the water spraying process, it is ensured that the soil 4 structure is not damaged and no water accumulation is generated. After the water spraying is completed, the bottom is weighed and no water is dripping. Photos are taken and the changes in cracks are observed until the shrinkage cracks at the rock-soil interface are completely closed. The wetting test is completed and the next round of drying test is started.

[0092] Considering that the test device is heavy and difficult to move, a TDR soil moisture sensor is used here. The soil moisture sensor is placed horizontally, and the probe is in vertical contact with the rock surface (to measure the soil moisture content at the rock-soil interface). The probe is 5 cm below the soil surface to ensure that the buried TDR does not affect the development of cracks on the soil surface.

[0093] Step 5: Image processing and data extraction

[0094] Using the method of the present invention, digital image processing techniques are used to extract developmental indicators such as the total length, average width, and surface crack rate of rock-soil interface shrinkage cracks 11, as well as the length and average width of soil surface shrinkage cracks 12, from images of rock-soil interface shrinkage cracks. The processing steps are as follows: a central area of ​​the specimen is cropped as the processing target (e.g., 25 cm x 25 cm) to eliminate the influence of the container edge boundary. The image is then processed and analyzed through image preprocessing, crack identification, and quantification. The developmental characteristics and related parameters of rock-soil interface shrinkage cracks during their emergence, development, stabilization, and closure are extracted or calculated using relevant software: ① Crack development characteristics: crack area, length, width, surface crack rate, etc.; ② Related parameters: soil moisture content at different moments of crack emergence, development, stabilization, and closure (calculated based on the aforementioned weighing data).

[0095] Example 2: A device and method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas, comprising the following steps:

[0096] Step 1: Construct a rock-soil interface shrinkage crack test device

[0097] According to the method of the present invention, a 30 cm × 30 cm × 30 cm organic glass container is designed, and an organic glass container external scale 10 is added to the outer wall of the container to observe the geometric parameters of the cracks; circular holes with a diameter of 10 mm are evenly punched in the bottom of the container for drainage, and the density meets the requirements for smooth water inflow and drainage; at the same time, quartz sand (50 mesh) with a thickness of about 1 cm is laid on the bottom of the device to ensure smooth water inflow and outflow and good hydraulic contact with the soil.

[0098] Step 2: Preparation of soil 4 and rock mass 2

[0099] According to the method of the present application, the soil 4 is taken from a rocky desertification land in Guizhou Province, and after being dried, it is passed through a 2mm sieve for use as test soil. According to the size of the designed plexiglass container 1, a plurality of stone blocks of about 30cm x 30cm x 15cm are selected to prepare the rock mass 2, and the natural rock surface of 30cm x 30cm of the rock mass 2 is taken as the rock-soil interface 6. Here, the rock of the convex rock surface 3-2 is selected for indoor dry-wet process simulation experiment.

[0100] Step 3: Preparation of rock-soil interface dry shrinkage crack development sample

[0101] According to the method of the present application, according to the prepared soil 4 and rock mass 2, the rock mass 2 of the convex rock surface is filled into the square plexiglass container 1 at a rock surface inclination of 90°, and the rock mass 2 is filled along the side according to the principle that the soil 4 and the rock mass 2 each occupy about half; when filling the soil, the original container weight (1.10g / cm 3 ) is layered from bottom to top to fill the container to the surface level, at which time the rock mass 2 and the soil 4 each occupy about 50% of the surface of the container, and the weights of the plexiglass container 1, the rock mass 2 and the filled soil 4 are measured and recorded; the soil layer thickness is divided into 10, 20, 30cm, etc. three levels, the rock-soil contact surface rock surface geometry is designed as convex type, and the rock-soil interface inclination 8 is designed as 90°, with more than 3 repetitions for each treatment.

[0102] Step 4: Moistening test and drying test of rock-soil interface dry shrinkage crack development sample

[0103] According to the method of the present application, based on the above prepared rock-soil interface dry shrinkage crack development sample, indoor dry-wet cycle test is carried out, and the steps are as follows:

[0104] For the above sample, initial moistening is started, and the initial moistening method of "water absorption from the bottom of the soil layer to the surface of the soil" is adopted, that is, the rock-soil interface dry shrinkage crack sample is placed in a water containing device with the water level flush with the quartz sand 5, and a larger aerated fish pond is used instead. The water is gradually absorbed by the soil 4, at which time the water containing device should be constantly replenished with water to ensure that the soil 4 can fully absorb water and moisten; finally, after the surface of the soil 4 is moistened, water is added to the water containing device to flush with the filled soil surface, so that the soil sample is completely saturated, and thus the moistening process is completed.

[0105] For the humidified sample, the first drying test is carried out, and the "soil bottom drainage + soil surface evaporation" water loss method is adopted, that is, the water containing device is drained, and the sample is placed in a well-ventilated greenhouse for dry-wet cycle test, and the temperature is controlled at 24-32°C (the average daily maximum temperature in this region from May to September), at this time the water in the rock-soil interface dry shrinkage crack developed sample can be drained through the quartz sand 5 and evaporated through the soil 4 surface. When the drainage starts, it is recorded as the initial state of the sample. After that, with the continuous progress of the water loss process, the soil 4 surface and the rock mass 2 contact position will develop into rock-soil interface dry shrinkage crack 11. From the initial state, take pictures every 8 hours to record the surface morphology, measure and record the crack depth development on the outer wall with a flexible ruler, and weigh the device; when the rock-soil interface dry shrinkage crack appears, the interval time for photographing and weighing is shortened to 4 hours to maximize the dynamic change process of crack increase; when the sample mass change is less than 0.5% for three consecutive times, the drying process can be considered to be completed, the crack development is stable, and the first humidification test begins.

[0106] For the dried and water lost sample, the first humidification test is carried out, and the "sample surface water spraying" humidification method is adopted, that is, the water is uniformly sprayed to the surface of the rock and soil by using a pressure sprayer, according to the maximum 30min rainfall intensity in the local area, that is, 15.0mm / h, the rainfall is 15mm, the sample device area is 30cm×30cm, then the water spraying amount is 1350ml, and the spraying time is 60min; during the spraying process, the soil structure is not damaged and no water accumulation is generated, after the spraying is completed, the bottom is not dripping, the weight is weighed, the crack change is recorded and observed, until the rock-soil interface dry shrinkage crack is completely closed, the humidification test is completed, and the next round of drying test begins.

[0107] Considering that the test device is relatively heavy and difficult to move, TDR soil moisture sensor is used here to obtain the soil moisture sensor, which is placed horizontally and the probe is vertically contacted with the rock surface (to measure the soil moisture content at the rock-soil interface), and the probe is 5cm below the soil surface, which ensures that the buried TDR does not affect the development of soil surface cracks.

[0108] Step 5: image processing and data extraction

[0109] With the method, the total length, average width and surface crack rate of the rock-soil interface dry shrinkage crack 11, the length and average width of the soil surface dry shrinkage crack 12 and other development indexes are extracted by using digital image processing technology on the obtained rock-soil interface dry shrinkage crack picture. The processing steps are: cutting out the central area of the sample as the processing object (such as 25cm×25cm) to eliminate the boundary influence of the container edge, and then processing and analyzing by image preprocessing, crack identification and quantification, and obtaining the development characteristics and related parameters in the appearance, development, stability and closure process of the rock-soil interface dry shrinkage crack by related software: ① crack development characteristics: crack area, length, width, surface crack rate, etc.; ② related parameters: soil moisture content at different times (calculated according to the weighing data) such as crack appearance, development, stability and closure.

[0110] Embodiment 3: A rock-soil interface dry shrinkage crack research device and method in a stone desertification area, comprising the following steps:

[0111] Step 1: Constructing a rock-soil interface dry shrinkage crack test device

[0112] With the method, an organic glass container 1 with a side length of 30cm×30cm×30cm is designed, an organic glass container outer scale 10 is added to the outer wall of the container to observe the crack geometric shape parameters; a circular hole with a 10mm aperture is uniformly punched on the bottom of the container to drain water, and the density meets the smooth water inlet and outlet; at the same time, about 1cm thick quartz sand (50 mesh) is laid on the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil.

[0113] Step 2: Preparing soil 4 and rock mass 2

[0114] With the method, the test soil is taken from a stone desertification land in a certain area of Guizhou Province, and the soil is dried and passed through a 2mm sieve to be used as test soil. According to the size of the designed organic glass container, a plurality of 30cm×30cm×15cm stone blocks are selected, and the natural rock surface of 30cm×30cm is taken as the rock-soil interface 6. Here, the rock with concave rock surface is selected for indoor dry-wet process simulation experiment.

[0115] Step 3: Preparing a rock-soil interface dry shrinkage crack development sample

[0116] With the method, according to the prepared soil 4 and rock mass 2, the rock mass 2 with concave rock surface is filled into the square organic glass container 1 according to the rock surface inclination angle of 90°, and the rock mass 2 is filled on the side according to the principle that the soil 4 and the rock mass 2 each occupy about half; when filling the soil, the original container weight (1.10g / cm 3) The container is filled in layers to the surface level, at which time the rock and soil each account for about 50% of the surface of the container, and the weights of the plexiglass container 1, rock mass 2 and filled soil 4 are measured and recorded respectively; the soil layer thickness is divided into 10, 20, 30 cm and the like, the rock-soil contact surface is designed to be concave, and the rock surface inclination is designed to be 90°, and each treatment has more than 3 repetitions.

[0117] Step 4: Moistening test and drying test of the rock-soil interface dry shrinkage crack development sample

[0118] Based on the prepared rock-soil interface dry shrinkage crack development sample, the indoor dry-wet cycle test is carried out by the method, and the steps are as follows:

[0119] For the above sample, initial moistening is started, and the initial moistening method of "water absorption from the bottom of the soil layer to the surface of the soil" is adopted, that is, the rock-soil interface dry shrinkage crack sample is placed in a water level device with quartz sand 5 flush, and the water level device is replaced by a larger inflatable fish pond, and the water is gradually absorbed by the soil 4, at which time the water level device should be continuously supplemented with water to ensure that the soil 4 can fully absorb water and moisten; finally, after the surface of the soil 4 is moistened, water is added to the water level device to flush with the surface of the filled soil, so that the soil sample is completely saturated, and the moistening process is completed.

[0120] For the moistened sample, the first drying water loss test is carried out, and the water loss method of "drainage at the bottom of the soil layer + evaporation at the surface of the soil" is adopted, that is, the water level device is drained, and the sample is placed in a well-ventilated greenhouse for dry-wet cycle test, and the temperature is controlled at 24-32℃ (the average daily maximum temperature in this region from May to September), at which time the water in the rock-soil interface dry shrinkage crack development sample can be discharged from the test device through seepage and quartz sand 5, and at the same time, the water vapor can be discharged from the test device through the soil surface evaporation. When the drainage starts, it is recorded as the initial state of the sample, and thereafter, with the continuous progress of the water loss process, the soil surface and the rock contact position will develop into a rock-soil interface dry shrinkage crack 11. From the initial state, the surface morphology of the sample is continuously photographed and recorded at an interval of 8h, the crack depth development is measured and recorded on the outer wall with a flexible ruler, and the weight change of the device is measured; when the rock-soil interface dry shrinkage crack appears, the interval time of photographing and weighing is shortened to 4h to maximize the dynamic change process of crack growth; when the mass change of the sample is less than 0.5% for three consecutive times, the drying process can be considered to be completed, the crack development is stable, and the first moistening test is started.

[0121] For the sample after drying, the first humidification test is carried out, and the humidification mode of "water spraying on the surface of the sample" is adopted, that is, the water is uniformly sprayed on the surface of the whole rock and soil by using a gas pressure watering can, according to the local erosion rainfall intensity of maximum 30min rainfall intensity, that is, 15.0mm / h, the rainfall is 15mm, the sample device area is 30cm*30cm, then the water spraying amount is 1350ml, the spraying time is 60min; during the water spraying process, the soil structure is ensured not to be damaged and no water accumulation is generated, after the water spraying is completed, the bottom is not dripped, the weight is measured, the picture is recorded and the crack change is observed, until the rock-soil interface dry shrinkage crack is completely closed, the humidification test is completed, and the next round of drying test is started.

[0122] Considering that the test device is relatively heavy and is difficult to move, the TDR soil moisture sensor is adopted to obtain the soil moisture sensor, the soil moisture sensor is horizontally placed, and the probe directly contacts the rock surface (to measure the soil moisture content at the rock-soil interface), and the probe is 5cm below the soil surface, so that the buried TDR does not affect the development of the soil surface crack.

[0123] Step 5: image processing and data extraction

[0124] According to the method of the present application, for the obtained rock-soil interface dry shrinkage crack picture, the digital image processing technology is adopted to extract the total length, average width and surface crack rate of the rock-soil interface dry shrinkage crack 11, the length and average width of the soil surface dry shrinkage crack 12 and other development indexes. The processing steps are: cutting out the central region of the sample as the processing object (such as 25cm*25cm) to eliminate the boundary influence of the container edge, and then performing processing analysis through image preprocessing, crack identification and quantification, and obtaining the development characteristics and related parameters in the appearance, development, stability and closure process of the rock-soil interface dry shrinkage crack through related software extraction or calculation: ① crack development characteristics: crack area, length, width, surface crack rate and the like; ② related parameters: soil moisture content at different times (calculated according to the weighing data) such as crack appearance, development, stability and closure.

[0125] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0126] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas, characterized in that: The steps include: constructing a test container, and providing drainage holes at the bottom of the test container; Selecting a number of natural rock masses (2) and placing them in the test container, with the rock mass heads (3) of the rock masses (2) located outside the test container; Filling the empty area of ​​the test container with soil (4) to form a test sample; The soil (4) is in contact with the bottom of the test container; The test sample is subjected to any number of dry-wet cycles, and the crack development process is recorded, and the change in the water content in the soil (4) during the crack development process is recorded.

2. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 1, characterized in that: The test container comprises: An organic glass container (1) is provided with organic glass container bottom holes (9) arranged in a matrix at the bottom of the organic glass container (1), and quartz sand (5) is laid on the bottom of the organic glass container (1).

3. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 2, characterized in that: The volume ratio of the rock mass (2) to the soil (4) is 1:

1.

4. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 2, characterized in that: The steps of the wet-dry cycle include initial humidification, drying loss and water spraying humidification.

5. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 4, characterized in that: The initial humidification step comprises: The test sample is placed in a water container, wherein the water level in the water container is flush with the upper surface of the quartz sand (5); maintaining the water level in the water holding device; After the surface of the soil (4) is moistened, the water level in the water container is raised to be flush with the surface of the soil (4).

6. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 5, characterized in that: The step of drying and dehydration comprises: The water holding device is drained, and the test sample is placed in a temperature and humidity controllable environment; The water in the test sample evaporates through the surface of the soil (4) and is discharged through the holes (9) in the bottom of the organic glass container; Observe and record the development process of shrinkage cracks; When the mass change of the test sample after three consecutive weighings is less than 0.5%, the drying process is considered to be completed.

7. The method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas according to claim 4, characterized in that: The step of spraying water to increase humidity comprises: Calculate the amount of water sprayed and evenly spray the water onto the surface of the rock mass (2) and the soil (4); After the water spraying is completed, the organic glass container (1) is weighed until there is no water dripping from the bottom, and photographs are taken and crack changes are recorded until the shrinkage cracks are completely closed.

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