Method for researching dry shrinkage fractures of rock-soil interface in stony desertification area

Abstract

The invention belongs to the technical field of rock-soil mechanics, and particularly relates to a rocky desertification area rock-soil interface shrinkage fracture research method which comprises the following steps: constructing a test container, and forming a drainage hole in the bottom of the test container; selecting a plurality of natural rock blocks and placing the natural rock blocks in a test container, wherein the heads of the rock blocks are positioned on the outer side of the test container; filling the unoccupied area of the test container with soil to form a test sample; performing any dry-wet cycle on the test sample, recording the crack development process, and recording the change of the water content in the soil in the crack development process. The device is high in flexibility and adaptability, and samples of different sizes can be designed according to actual needs; a natural rock surface or a special rock surface can be selected and researched according to needs, a plurality of soil layer thicknesses, rock surface geometric shapes, rock surface inclination angles and the like can be designed, and the test can be repeated.

Description

Technical Field

[0001] The invention belongs to the technical field of rock and soil mechanics, and in particular relates to a method for studying shrinkage cracks at a rock-soil interface in a rocky desertification area. Background Art

[0002] Soil shrinkage due to water loss is a common phenomenon in nature. Under the influence of climate change, frequent dry-wet cycles can easily lead to soil cracking and closure due to moisture increase, which directly affects soil permeability, structure and stability, and seriously affects agricultural production, civil engineering and water conservancy projects.

[0003] In rocky desertification areas, long-term karstification has caused rocks to be exposed on the surface, soil distribution to be discontinuous, and rocks and soil to be distributed in an alternating pattern. Rock-soil interfaces with abrupt contact between exposed rocks and soil are common in rocky desertification areas. This abrupt contact is mainly due to the lack of a C layer or transition layer between the matrix carbonate parent rock and the soil. Due to differences in rock and soil properties, soil in rocky desertification areas is prone to form cracks at the rock-soil interface through shrinkage under dry and wet conditions, and the cracks are closed through swelling.

[0004] Although there are relatively mature research technologies and methods for shrinkage cracks in clay or expansive soil, there are no ready-made devices and methods for shrinkage cracks in karst soil and its exposed rock boundary constraints. The existing research technologies and methods for expansive soil cracks cannot achieve the observation and research of shrinkage cracks in soil constrained by rock boundaries. Therefore, the existing technology lacks research devices and methods for shrinkage cracks at the rock-soil interface in karst rocky desertification areas.

[0005] Based on this, how to observe and study the development of shrinkage cracks at the rock-soil interface formed by soil shrinkage constrained by the exposed rock boundary and obtain accurate crack morphology analysis results is a core problem that needs to be solved urgently in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas to solve the above problems.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for studying shrinkage cracks at the rock-soil interface in a rocky desertification area comprises the following steps:

[0009] Construct a test container and provide drainage holes at the bottom of the test container;

[0010] Select a number of natural rock masses and place them in the test container, with the rock masses heads being located outside the test container;

[0011] Filling the empty area of ​​the test container with soil to form a test sample;

[0012] The test sample is subjected to any number of dry-wet cycles, the crack development process is recorded, and the change in the water content in the soil during the crack development process is recorded.

[0013] Optionally, the test container comprises:

[0014] The organic glass container has organic glass bottom holes arranged in a matrix, and the bottom of the organic glass container is paved with quartz sand.

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

[0016] Optionally, the steps of the wet-dry cycle include initial humidification, drying loss and water spraying humidification.

[0017] Optionally, the initial humidification step comprises:

[0018] Placing the test sample in a water container, wherein the water level in the water container is flush with the upper surface of the quartz sand;

[0019] Maintaining the water level in the water holding device;

[0020] After the soil surface is moistened, the water level in the water container is raised to be flush with the soil surface.

[0021] Optionally, the drying and dehydration step comprises:

[0022] The water holding device is drained, and the test sample is placed in a temperature and humidity controllable environment;

[0023] The water in the test sample evaporates through the soil surface and is discharged through the holes punched at the bottom of the organic glass container;

[0024] Observe and record the development process of shrinkage cracks;

[0025] When the mass change of the test sample after three consecutive weighings is less than 0.5%, the drying process is considered to be finished.

[0026] Optionally, the step of spraying water to increase humidity includes:

[0027] Calculate the water spraying amount, and spray the water evenly onto the rock mass and the soil surface;

[0028] After the water spraying is finished, the organic glass container is weighed after no water drips from the bottom, and photographs are taken and crack changes are recorded until the shrinkage cracks are completely closed.

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

[0030] The present invention can better simulate the contact between exposed rocks and soil in rocky desertification areas, and can accurately obtain the development process of shrinkage cracks at the rock-soil interface and the critical value of soil moisture; the present invention has strong flexibility and adaptability, and can be designed into samples of different sizes according to actual needs; the samples can be selected to study natural rock surfaces or special rock surfaces according to needs, and multiple soil layer thicknesses, rock surface geometric shapes, rock surface inclinations, etc. can be designed, and the test can be repeated. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor:

[0032] Figure 1 This is a cross-sectional view of a sample showing the development of shrinkage cracks at the rock-soil interface of the present invention;

[0033] Figure 2 A top view of a sample of the present invention showing shrinkage crack development at the rock-soil interface;

[0034] Figure 3 This is a schematic diagram of uniformly punching holes on the bottom of the organic glass container of the present invention;

[0035] Figure 4 This is a schematic diagram of the development of shrinkage cracks at the straight rock-soil interface of the present invention;

[0036] Figure 5 This is a schematic diagram of the development of shrinkage cracks at the convex rock-soil interface of the present invention;

[0037] Figure 6 Schematic diagram of the development of shrinkage cracks at the concave rock-soil interface of the present invention;

[0038] Figure 7 This is a schematic diagram of the image processing result of the straight rock-soil interface shrinkage cracks of the present invention;

[0039] Figure 8 This is a schematic diagram of the image processing result of the convex rock-soil interface shrinkage cracks of the present invention;

[0040] Fig. 9 This is a schematic diagram of the image processing result of the concave rock-soil interface shrinkage cracks of the present invention;

[0041] Among them, 1. plexiglass container; 2. rock mass; 3. rock mass head; 3-1. straight rock surface; 3-2. convex rock surface; 3-3. concave rock surface; 4. soil; 5. quartz sand; 6. rock-soil interface; 7. overall inclination line of rock-soil interface; 8. inclination angle of rock-soil interface; 9. holes punched at the bottom of plexiglass container; 10. external scale of plexiglass container; 11. shrinkage cracks at rock-soil interface; 12. shrinkage cracks on soil surface. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0044] Reference Figures 1 to 9 The present invention discloses a method for studying shrinkage cracks at the rock-soil interface in rocky desertification areas, comprising the following steps:

[0045] Construct a test container and provide drainage holes at the bottom of the test container;

[0046] Select a number of natural rock masses 2 and place them in a test container, with the rock mass heads 3 of the rock masses 2 located outside the test container;

[0047] The test sample is formed by filling the empty area of ​​the test container with soil 4;

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

[0049] The present invention can better simulate the contact between exposed rocks and soil in rocky desertification areas, and can accurately obtain the development process of shrinkage cracks at the rock-soil interface and the critical value of soil moisture; the present invention has strong flexibility and adaptability, and can be designed into samples of different sizes according to actual needs; the samples can be selected to study natural rock surfaces or special rock surfaces according to needs, and multiple soil layer thicknesses, rock surface geometric shapes, rock surface inclinations, etc. can be designed, and the test can be repeated.

[0050] As an optional embodiment, the test container includes:

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

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

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

[0054] The test soil can be selected as sieved soil or non-sieved soil as soil 4 according to research needs. The sieved soil can be sieved through soil sieves with different apertures as needed. According to the size of the designed organic glass container, multiple blocks of stone with a specification of about 1 / 2 of the volume of the organic glass container 1 are selected, and one of the rock surfaces of the blocks should meet the design needs. For example, multiple blocks of stone of about 50cm×50cm×25cm are selected, and the natural rock surface of 50cm×50cm is used as the rock-soil interface 6, or a variety of rock surface shapes such as straight rock surface, convex rock surface, concave rock surface and random (not polished) are selected or polished as needed to obtain a 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 surface type and rock surface inclination of the rock-soil contact surface, and the rock mass 2 is filled in sideways, according to the principle that the soil 4 and the rock mass 2 each occupy about half; when filling the soil, the container is filled in layers from bottom to top according to the original bulk density to the surface level. At this time, the rock mass 2 and the soil 4 each occupy about 50% of the container surface, and the weight of the organic glass container 1, the rock mass 2 and the filled soil 4 are weighed and recorded respectively; the thickness of the soil layer can be divided into multiple levels such as 10, 20, 30 cm according to the experimental design, the rock surface geometry of the rock-soil contact surface is designed to be straight, convex and concave, and the rock surface inclination is designed to be 30°, 60° and 90°. Multiple gradients, each treatment is repeated more than 3 times.

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

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

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

[0059] Maintaining water level in water container;

[0060] 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 .

[0061] As an optional embodiment, the step of drying and dehydration comprises:

[0062] Drain the water storage device and place the test sample in a temperature and humidity controlled environment;

[0063] 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;

[0064] Observe and record the development process of shrinkage cracks;

[0065] 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.

[0066] As an optional embodiment, the step of spraying water to increase humidity includes:

[0067] Calculate the water spraying amount and spray the water evenly onto the surface of the rock mass 2 and the soil 4;

[0068] After the water spraying is finished, the plexiglass container 1 is weighed after no water drips from the bottom, and photographs are taken and crack changes are recorded until the shrinkage cracks are completely closed.

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

[0070] For the above test samples, initial humidification is started, and the initial humidification method of "water absorption from the bottom of the soil layer to the soil surface" is adopted, that is, the test samples are placed in a water holding device whose water level is flush with the quartz sand layer 5. The water holding device can be replaced by a larger water basin or an inflatable fish pond, etc. The water is gradually absorbed by the soil 4. At this time, the water holding device should continuously replenish water 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 holding device to be flush with the fill surface to make the soil 4 completely saturated. At this point, the humidification process is completed.

[0071] For the sample after humidification, 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 on the soil surface" is adopted, that is, the water holding device is drained, and the test sample is placed in an indoor controllable temperature and humidity environment or an outdoor natural environment with temperature and humidity changes. At this time, the water in the sample with the development of rock-soil interface shrinkage cracks can be discharged from the organic glass container 1 through leakage and through the quartz sand 5, and can be discharged from the organic glass container 1 through water vapor evaporation through the surface of the soil 4. The initial state of the sample is recorded when the drainage begins. Thereafter, as the dehydration process continues, the contact position between the surface of the soil 4 and the rock mass 2 will develop into a rock-soil interface shrinkage crack 11. Starting from the initial state, it is necessary to take photos and record the surface morphology of the sample at a certain time interval, measure and record the development of the crack depth on the outer wall with a soft ruler, and weigh the weight change of the device at the same time; when the rock-soil interface shrinkage crack appears, the interval between taking photos and weighing needs to be shortened to maximize the dynamic change process of crack enlargement; when the mass change of the sample is less than 0.5% after three consecutive weighings, it can be seen that the drying process is over, the crack development is stable, and the first humidification test is started.

[0072] For the samples after drying and water loss, the first humidification test was carried out, using the humidification method of "spraying water / rainfall on the sample surface", that is, using a pressure spray bottle to evenly spray water to the entire rock and soil surface. The amount of water sprayed each time can be calculated based on the local rainfall intensity and the sample device area. For example, according to the erosive rainfall intensity of a certain place, the maximum 30min rainfall intensity is 15.0mm / h, the rainfall is 15mm, and the sample device area is 50cm×50cm, then the water spraying volume is 3750ml, and the spraying time is 60min; 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 of the organic glass container 1 is weighed when there is no water dripping, and photos are taken to record and observe the changes in the cracks until the shrinkage cracks at the rock-soil interface are completely closed, the humidification test is completed, and the next round of drying test is started.

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

[0074] W=0.1AIt

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

[0076] The moisture content data of soil 4 is calculated by weight change analysis; considering that the test sample is heavy and difficult to move, a TDR soil moisture sensor can be used to obtain it. The soil moisture sensor should be placed horizontally, and the probe should vertically contact the rock surface of rock mass 2 (to measure the soil moisture content at the rock-soil interface), and the probe should be at least 5 cm below the surface of soil 4 to ensure that the buried TDR does not affect the development of cracks on the surface of soil 4.

[0077] Repeat the above steps to conduct multiple dry-wet cycle tests.

[0078] Based on the obtained rock-soil interface shrinkage crack images, digital image processing technology is used to extract the development indicators of the rock-soil interface shrinkage cracks, such as the total length, average width and surface crack rate. The processing steps are as follows: the central area 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 processed and analyzed. The development characteristics and related parameters of the rock-soil interface shrinkage cracks in the process of appearance, development, stability and closure are extracted or calculated by relevant software: ① Crack development characteristics: crack area, length, width, surface crack rate, etc.; ② Related parameters: soil moisture content at different times of crack appearance, development, stability, closure, etc. (calculated based on the above weighing data).

[0079] The present invention is further described below in conjunction with embodiments and drawings.

[0080] Embodiment 1: A device and method for studying shrinkage cracks at the rock-soil interface in a rocky desertification region, comprising the following steps:

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

[0082] According to the method of the present invention, a plexiglass container 1 with a side length of 30 cm×30 cm×30 cm is designed, and an plexiglass container external scale 10 is added to the outer wall of the container to observe the geometric parameters of the cracks; the bottom of the container is evenly punched with holes 9 with a hole diameter of 10 mm for drainage, and the density meets the requirement of smooth water inlet and outlet; at the same time, quartz sand 5 (50 mesh) with a thickness of about 1 cm is laid on the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil.

[0083] Step 2: Prepare soil 4 and rock 2

[0084] According to the method of the present invention, soil 4 is taken from rocky desertification land in a certain area of ​​Guizhou Province. The soil 4 is air-dried and then sieved through a 2 mm sieve to serve as test soil. According to the size of the designed organic glass container 1, a plurality of blocks of about 30 cm × 30 cm × 15 cm are selected to prepare a rock mass 2, and the natural rock surface of the 30 cm × 30 cm portion of the rock mass 2 is used as a rock-soil interface 6. Here, a rock with a straight rock surface 3-1 is selected for indoor dry-wet process simulation experiments.

[0085] Step 3: Prepare the specimen with developed shrinkage cracks at the rock-soil interface

[0086] According to the method of the present invention, a rock mass 2 on a straight rock surface is filled into a square organic glass container 1 according to a rock-soil interface inclination angle 8 of 90° (i.e., the angle between the overall inclination line 7 of the rock-soil interface and the horizontal line of the quartz sand 5), and the rock mass 2 is filled in close to the edge, and the soil 4 and the rock mass 2 are filled in according to the principle of each occupying about half; when filling the soil, the container is filled in layers from bottom to top according to the original bulk density (1.10 g / cm3) to the surface level, at which time the rock mass 2 and the soil 4 each occupy about 50% of the container surface, and the weights of the organic glass container 1, the rock mass 2 and the filled soil 4 are weighed and recorded respectively; the soil layer thickness is divided into three levels of 10, 20, and 30 cm, the rock surface geometry of the rock-soil contact surface is designed to be straight, the rock-soil interface inclination angle 8 is designed to be 90°, and each treatment is repeated more than 3 times.

[0087] Step 4: Wetting test and drying test of the specimen with shrinkage crack development at the rock-soil interface

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

[0089] For the above-mentioned samples, initial humidification is started, and the initial humidification method of "water absorption from the bottom of the soil layer to the soil surface" is adopted, that is, the sample is placed in a water holding device whose water level is flush with the quartz sand layer 5. The water holding device is replaced by a larger inflatable fish pond. The water is gradually absorbed by the soil 4. At this time, the water holding device should continuously replenish water 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 holding device to be flush with the fill surface to make the soil sample completely saturated. At this point, the humidification process is completed.

[0090] For the humidified sample, the first drying water loss test was carried out, using the "drainage at the bottom of the soil layer + evaporation on the soil surface" water loss method, that is, the water storage device was drained, and the sample was placed in a well-ventilated greenhouse for a dry-wet cycle test, and the temperature was controlled at 24°C to 32°C (the average daily maximum temperature in this area from May to September). At this time, the moisture in the sample can be discharged from the test device through leakage and quartz sand 5, and can also be discharged from the test device through water vapor evaporation through the soil surface. The initial state of the sample is recorded when drainage begins. After that, as the water loss process continues, the contact position between the soil surface and the rock will develop into a rock-soil interface shrinkage crack 11. Starting from the initial state, photographs are taken continuously at intervals of 8 hours to record the surface morphology of the sample, and a soft ruler is used to measure and record the development of the crack depth on the outer wall, while the weight change of the weighing device is measured; when shrinkage cracks appear at the rock-soil interface, the interval between photographing and weighing is shortened to 4 hours to maximize the dynamic change process of crack enlargement; when the mass change of the sample is less than 0.5% after three consecutive weighings, the drying process is considered to be over, the crack development is stable, and the first humidification test is started.

[0091] For the samples after drying and dehydration, the first humidification test was carried out, and the humidification method of "spraying water on the sample surface" was adopted, that is, a pressure spraying pot 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 30min rainfall intensity is 15.0mm / h, the rainfall is 15mm, and the sample device area is 30cm×30cm. The water spraying volume is 1350ml and the spraying time is 60min. 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 when there is no dripping, and photos are taken to record and observe the changes in cracks until the shrinkage cracks at the rock-soil interface are completely closed. The humidification 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] According to the method of the present invention, the total length, average width and surface crack rate of the rock-soil interface shrinkage cracks 11, the length and average width of the soil surface shrinkage cracks 12 and other development indicators are extracted by digital image processing technology for the obtained rock-soil interface shrinkage cracks pictures. The processing steps are: cutting out the area in the center of the sample as the processing object (such as 25cm×25cm) to eliminate the boundary influence of the edge of the container, and then processing and analyzing it through image preprocessing, crack identification and quantification, etc., and extracting or calculating the development characteristics and related parameters of the rock-soil interface shrinkage cracks in the process of appearance, development, stability and closure through relevant software: ① Crack development characteristics: crack area, length, width, surface crack rate, etc.; ② Related parameters: soil moisture content at different times of crack appearance, development, stability, closure, etc. (calculated according to the above weighing data).

[0095] Embodiment 2: A device and method for studying shrinkage cracks at the rock-soil interface in a rocky desertification region, 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 plexiglass container with a side length of 30 cm×30 cm×30 cm is designed, and an external plexiglass container 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 at the bottom of the container for drainage, and the density meets the requirement of smooth water inlet and outlet; at the same time, quartz sand (50 mesh) with a thickness of about 1 cm is laid at the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil.

[0098] Step 2: Prepare soil 4 and rock 2

[0099] According to the method of the present invention, soil 4 is taken from rocky desertification land in a certain area of ​​Guizhou Province. The soil 4 is air-dried and then sieved through a 2 mm sieve to serve as test soil. According to the size of the designed organic glass container 1, a plurality of blocks of about 30 cm×30 cm×15 cm are selected to prepare a rock mass 2, and the natural rock surface of the 30 cm×30 cm portion of the rock mass 2 is used as a rock-soil interface 6. Here, the rock of the outer convex rock surface 3-2 is selected for the indoor dry-wet process simulation experiment.

[0100] Step 3: Prepare the specimen with developed shrinkage cracks at the rock-soil interface

[0101] According to the method of the present invention, the rock mass 2 on the outer convex 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 sideways, and the soil 4 and the rock mass 2 are filled in according to the principle that each accounts for about half; when filling the soil, the original bulk density (1.10g / cm 3 ) are filled into the container in layers to the surface level. At this time, the rock mass 2 and the soil 4 each occupy about 50% of the container surface. The weights of the plexiglass container 1, the rock mass 2 and the filled soil 4 are weighed and recorded respectively; the soil layer thickness is divided into three levels of 10, 20, and 30 cm. The rock surface geometry of the rock-soil contact surface is designed to be convex, and the rock-soil interface inclination 8 is designed to be 90°. Each treatment is repeated more than 3 times.

[0102] Step 4: Wetting test and drying test of the specimen with shrinkage crack development at the rock-soil interface

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

[0104] For the above samples, initial humidification is started, and the initial humidification method of "water absorption from the bottom of the soil layer to the soil surface" is adopted, that is, the rock-soil interface shrinkage crack sample is placed in a water holding device with a water level flush with the quartz sand 5. The water holding device is replaced by a larger inflatable fish pond. The water is gradually absorbed by the soil 4. At this time, the water holding device should continuously replenish water 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 holding device to be flush with the fill surface to make the soil sample completely saturated. At this point, the humidification process is completed.

[0105] For the humidified sample, the first drying water loss test was carried out, using the "drainage at the bottom of the soil layer + evaporation on the soil surface" water loss method, that is, the water storage device was drained, and the sample was placed in a well-ventilated greenhouse for a dry-wet cycle test, and the temperature was controlled at 24°C to 32°C (the average daily maximum temperature in this area from May to September). At this time, the water in the sample with the development of rock-soil interface shrinkage cracks can be discharged from the test device through leakage and quartz sand 5, and can also be discharged from the test device through water vapor evaporation through the surface of soil 4. The initial state of the sample is recorded when drainage begins. Thereafter, as the water loss process continues, the contact position between the surface of soil 4 and rock mass 2 will develop into rock-soil interface shrinkage cracks 11. Starting from the initial state, photographs are taken continuously at intervals of 8 hours to record the surface morphology of the sample, and a soft ruler is used to measure and record the development of the crack depth on the outer wall, while the weight change of the weighing device is measured; when shrinkage cracks appear at the rock-soil interface, the interval between photographing and weighing is shortened to 4 hours to maximize the dynamic change process of crack enlargement; when the mass change of the sample is less than 0.5% after three consecutive weighings, the drying process is considered to be over, the crack development is stable, and the first humidification test is started.

[0106] For the samples after drying and dehydration, the first humidification test was carried out, and the humidification method of "spraying water on the sample surface" was adopted, that is, a pressure spraying pot was used to evenly spray water to the entire rock and soil surface. According to the local erosive rainfall intensity, the maximum rainfall intensity was 30min, that is, 15.0mm / h, the rainfall was 15mm, and the sample device area was 30cm×30cm. The water spraying volume was 1350ml and the spraying time was 60min. During the water spraying process, it was ensured that the soil structure was not damaged and no water accumulation was generated. After the water spraying was completed, the bottom was weighed when there was no dripping, and photos were taken to record and observe the changes in the cracks until the shrinkage cracks at the rock-soil interface were completely closed. The humidification test was ended and the next round of drying test began.

[0107] 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.

[0108] Step 5: Image processing and data extraction

[0109] According to the method of the present invention, the total length, average width and surface crack rate of the rock-soil interface shrinkage cracks 11, the length and average width of the soil surface shrinkage cracks 12 and other development indicators are extracted by digital image processing technology for the obtained rock-soil interface shrinkage cracks pictures. The processing steps are: cutting out the area in the center of the sample as the processing object (such as 25cm×25cm) to eliminate the boundary influence of the edge of the container, and then processing and analyzing it through image preprocessing, crack identification and quantification, etc., and extracting or calculating the development characteristics and related parameters of the rock-soil interface shrinkage cracks in the process of appearance, development, stability and closure through relevant software: ① Crack development characteristics: crack area, length, width, surface crack rate, etc.; ② Related parameters: soil moisture content at different times of crack appearance, development, stability, closure, etc. (calculated according to the above weighing data).

[0110] Embodiment 3: A device and method for studying shrinkage cracks at the rock-soil interface in a rocky desertification region, comprising the following steps:

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

[0112] According to the method of the present invention, a plexiglass container 1 with a side length of 30 cm×30 cm×30 cm is designed, and an plexiglass 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 at the bottom of the container for drainage, and the density meets the requirement of smooth water inlet and outlet; at the same time, quartz sand (50 mesh) with a thickness of about 1 cm is laid at the bottom of the device to ensure smooth water inlet and outlet and good hydraulic contact with the soil.

[0113] Step 2: Prepare soil 4 and rock 2

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

[0115] Step 3: Prepare the specimen with developed shrinkage cracks at the rock-soil interface

[0116] According to the method of the present invention, the rock mass 2 with the 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 sideways, and the soil 4 and the rock mass 2 are filled in according to the principle that each of them occupies about half; when filling the soil, the original bulk density (1.10g / cm 3) are filled into the container in layers until they are level with the surface. At this time, the rock and soil each occupy about 50% of the container surface. The weights of the plexiglass container 1, the rock mass 2 and the filled soil 4 are weighed and recorded respectively. The soil layer thickness is divided into three levels: 10, 20 and 30 cm. The rock surface geometry of the rock-soil contact surface is designed to be concave, and the rock surface inclination is designed to be 90°. Each treatment is repeated more than 3 times.

[0117] Step 4: Wetting test and drying test of the specimen with shrinkage crack development at the rock-soil interface

[0118] According to the method of the present invention, based on the rock-soil interface shrinkage crack development sample prepared above, an indoor dry-wet cycle test is carried out, and the specific steps are as follows:

[0119] For the above samples, initial humidification is started, and the initial humidification method of "water absorption from the bottom of the soil layer to the soil surface" is adopted, that is, the rock-soil interface shrinkage crack sample is placed in a water holding device with a water level flush with the quartz sand 5. The water holding device is replaced by a larger inflatable fish pond. The water is gradually absorbed by the soil 4. At this time, the water holding device should continuously replenish water 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 holding device to be flush with the fill surface to make the soil sample completely saturated. At this point, the humidification process is completed.

[0120] For the humidified sample, the first drying water loss test was carried out, using the "drainage at the bottom of the soil layer + evaporation on the soil surface" water loss method, that is, the water storage device was drained, and the sample was placed in a well-ventilated greenhouse for a dry-wet cycle test, and the temperature was controlled at 24°C to 32°C (the average daily maximum temperature in this area from May to September). At this time, the moisture in the sample can be discharged from the test device through leakage and quartz sand 5, and can also be discharged from the test device through water vapor evaporation through the soil surface. The initial state of the sample is recorded when drainage begins. After that, as the water loss process continues, the contact position between the soil surface and the rock will develop into a rock-soil interface shrinkage crack 11. Starting from the initial state, photographs are taken continuously at intervals of 8 hours to record the surface morphology of the sample, and a soft ruler is used to measure and record the development of the crack depth on the outer wall, while the weight change of the weighing device is measured; when shrinkage cracks appear at the rock-soil interface, the interval between photographing and weighing is shortened to 4 hours to maximize the dynamic change process of crack enlargement; when the mass change of the sample is less than 0.5% after three consecutive weighings, the drying process is considered to be over, the crack development is stable, and the first humidification test is started.

[0121] For the samples after drying and dehydration, the first humidification test was carried out, and the humidification method of "spraying water on the sample surface" was adopted, that is, a pressure spraying pot was used to evenly spray water to the entire rock and soil surface. According to the local erosive rainfall intensity, the maximum rainfall intensity was 30min, that is, 15.0mm / h, the rainfall was 15mm, and the sample device area was 30cm×30cm. The water spraying volume was 1350ml and the spraying time was 60min. During the water spraying process, it was ensured that the soil structure was not damaged and no water accumulation was generated. After the water spraying was completed, the bottom was weighed when there was no dripping, and photos were taken to record and observe the changes in the cracks until the shrinkage cracks at the rock-soil interface were completely closed. The humidification test was ended and the next round of drying test began.

[0122] 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.

[0123] Step 5: Image processing and data extraction

[0124] According to the method of the present invention, the total length, average width and surface crack rate of the rock-soil interface shrinkage cracks 11, the length and average width of the soil surface shrinkage cracks 12 and other development indicators are extracted by digital image processing technology for the obtained rock-soil interface shrinkage cracks pictures. The processing steps are: cutting out the area in the center of the sample as the processing object (such as 25cm×25cm) to eliminate the boundary influence of the edge of the container, and then processing and analyzing it through image preprocessing, crack identification and quantification, etc., and extracting or calculating the development characteristics and related parameters of the rock-soil interface shrinkage cracks in the process of appearance, development, stability and closure through relevant software: ① Crack development characteristics: crack area, length, width, surface crack rate, etc.; ② Related parameters: soil moisture content at different times of crack appearance, development, stability, closure, etc. (calculated according to the above weighing data).

[0125] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0126] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

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) being located outside the test container; Filling the empty area of ​​the test container with soil (4) to form a test sample; The test sample is subjected to any number of dry-wet cycles, the crack development process is recorded, and the change in 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), wherein the bottom of the organic glass container (1) is provided with organic glass container bottom holes (9) arranged in a matrix, and the bottom of the organic glass container (1) is paved with quartz sand (5).

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: Placing the test sample 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 containing device; After the surface of the soil (4) is moistened, the water level in the water storage device 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 finished.

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: Calculating the amount of water sprayed, and evenly spraying the water onto the surface of the rock mass (2) and the soil (4); After the water spraying is finished, 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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