Comprehensive test method for water retention, expansion and contraction and cracking of soil under dry-wet cycles

Abstract

The present invention provides a comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking properties under dry-wet cycles. The test method comprises: compacting the soil at an optimal water content to obtain two ring knife samples; placing the ring knife samples in a vacuum saturation cylinder for saturation, and then performing dry-wet cycles using natural air drying and dehumidification and bidirectional water film migration humidification, respectively. During the dehumidification process of the ring knife samples, a first data group and a first crack data group are obtained; during the humidification process of the ring knife samples, a second data group and a second crack group data are obtained; similarly, the two ring knife samples are subjected to repeated dehumidification and humidification steps, respectively, to complete at least N dry-wet cycles; based on the experimental results obtained from N dry-wet cycles, the water holding capacity, swelling and shrinkage, and cracking properties of the soil under the action of dry-wet cycles are obtained. Using the test method provided by the present invention, the water holding capacity, swelling and shrinkage, and cracking properties of the soil under the action of dry-wet cycles can be obtained simultaneously, and based on the same ring knife samples, the errors caused by different sample preparations can be avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a comprehensive test method for soil water retention, swelling and shrinkage, and cracking properties under dry-wet cycles. Background Art

[0002] At present, the existing technology for measuring the three engineering properties of soil swelling and shrinkage, cracks and water holding capacity is to measure them separately, that is, different soil samples are used to measure swelling and shrinkage, cracks and water holding capacity. Among them, water holding capacity refers to the relationship between soil suction and mass water content, which is generally characterized by soil-water characteristic curve. The current methods for measuring soil-water characteristic curve include axis translation technology, saturated salt solution vapor balance method, cold mirror dew point method, etc. The use cost of the above methods is very high and the operation is complicated; swelling and shrinkage refers to the swelling and shrinkage characteristics of soil volume. The existing technology mainly uses consolidation experiments to study soil swelling and shrinkage, which has the disadvantages of complex operation and long time consumption; cracks refer to the cracks on the surface of the soil when the tensile stress of the soil exceeds the tensile strength. The current existing technology uses tray sample preparation, puts it in an oven to reduce the water content, and obtains the crack index by taking pictures and crack processing software. Using different samples for separate testing ignores the inherent relationship between soil expansion and contraction, fissures and water holding capacity. For example, soil shrinkage can cause cracks to develop and water holding capacity to decrease. It may also cause errors due to different sample preparation. Therefore, it is necessary to conduct a comprehensive test on the three engineering properties of soil expansion and contraction, fissures and water holding capacity to improve the accuracy of the test. Summary of the invention

[0003] The purpose of the present invention is to provide a comprehensive test method for measuring the water holding capacity, swelling and shrinkage, and cracking of the same ring knife sample under the action of dry-wet cycles, thereby avoiding the errors caused by different sample preparations. At the same time, it can also provide a reference for whether the deformation and cracking of dam projects are stable under the rise and fall of reservoir water levels, as well as the service performance and safety assessment of dam projects.

[0004] To achieve the above object, the present invention provides a comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles, the test method comprising the following steps:

[0005] Step (1), compacting the soil at an optimum moisture content to obtain two ring cutter samples reaching a maximum dry density, wherein the ring cutter samples include a ring cutter and a soil sample filled in the ring cutter, wherein the soil sample is obtained by mixing dry soil prepared by a drying method with water, wherein the ratio of the mass of water in the soil sample to the mass of dry soil is the optimum moisture content corresponding to the dry soil;

[0006] Step (2), placing the two ring knife samples into a vacuum saturation cylinder for humidification respectively, to obtain two ring knife samples with saturated mass water content;

[0007] Step (3), placing the two ring knife samples that have been humidified in an indoor constant temperature environment for natural air drying and dehumidification, until the mass moisture content of the soil sample is reduced to the minimum mass moisture content, and obtaining a first data group and a first crack data group during the natural air drying and dehumidification of the ring knife samples, wherein the first data group includes the suction, porosity and saturation corresponding to the soil sample at multiple different target mass moisture contents, and the first crack data group includes the crack data corresponding to the soil sample at the multiple different target mass moisture contents;

[0008] Step (4), respectively performing bidirectional water film humidification on the two ring knife samples that reach the minimum mass water content in step (3) until the water stays on the surface of the soil sample and no longer penetrates into the interior of the soil sample, and during the ring knife sample humidification process, obtaining a second data group and a second crack data group, the second data group including the suction, porosity and saturation corresponding to the soil sample at the multiple different target mass water contents, and the second crack data group including the crack data corresponding to the soil sample at the multiple different target mass water contents;

[0009] Step (5), for the same two ring knife samples, repeat steps (3) and (4) multiple times in sequence, complete N dry-wet cycles, and obtain N first data groups, N second data groups, N first crack data groups, and N second crack data groups, wherein N is a positive integer greater than or equal to 5;

[0010] Step (6), based on the N first data groups and the N second data groups obtained from the N dry-wet cycles, obtain the water holding capacity and swelling and shrinkage of the soil under the action of the dry-wet cycles, and based on the N first crack data groups and the N second crack data groups, obtain the crack properties of the soil under the action of the dry-wet cycles.

[0011] In a specific implementation, the step of obtaining the suction of a soil sample corresponding to each target mass water content includes:

[0012] Two of the ring knife samples, two layers of first filter paper and one layer of second filter paper are loaded to obtain a test sample. Along the height direction of the test sample, the test sample includes a ring knife sample, a layer of first filter paper, a layer of second filter paper, another layer of first filter paper and another ring knife sample. The first filter paper is used to protect the second filter paper from directly contacting the soil sample. The second filter paper is used to measure suction. The first filter paper and the second filter paper are both Whitman No.42 filter papers. The diameter of the first filter paper is smaller than the diameter of the ring knife and larger than the diameter of the second filter paper.

[0013] Wrapping the test sample with plastic wrap, and placing it in the sealed box to conduct a balance test;

[0014] After the balance test is completed, obtaining a first mass of the wet second filter paper;

[0015] drying the second filter paper, and obtaining a second mass of the dried second filter paper;

[0016] calculating the water content of the second filter paper based on the first mass and the second mass of the second filter paper;

[0017] Based on the water content of the second filter paper, the suction of the second filter paper at equilibrium is calculated, and the suction of the soil sample is the same as the suction of the second filter paper.

[0018] In a specific embodiment, the calculation formula of the suction of the second filter paper is:

[0019]

[0020] in, is the suction force of the second filter paper at equilibrium, ω f is the moisture content of the second filter paper.

[0021] In a specific implementation, the step of obtaining the porosity ratio of the soil sample corresponding to each target mass water content includes:

[0022] Respectively obtain multiple diameters and multiple height values ​​corresponding to multiple different angles of two current soil samples, and calculate the average diameter and average height of each current soil sample, wherein the current soil sample is a soil sample obtained after completing a balance test at a target mass moisture content;

[0023] Obtaining the arithmetic mean of the average diameters of the two current soil samples and the arithmetic mean of the average heights of the two current soil samples, and using them as the current diameter and current height of the soil sample at the target mass water content;

[0024] Based on the current diameter and the current height of the soil sample, calculate the current volume of the soil sample;

[0025] Based on the current volume of the soil sample and the initial volume of the soil sample, the porosity ratio of the soil sample at the target mass water content is obtained.

[0026] In a specific embodiment, a method for obtaining the saturation of a soil sample corresponding to each target mass water content includes: obtaining the saturation of the soil sample based on the target mass water content, the porosity, and a saturation calculation formula, wherein the saturation calculation formula is:

[0027] Among them, S ris the saturation of the soil sample, ω is the target mass water content of the soil sample, e is the porosity of the soil sample, G s It is the weight of soil particles.

[0028] In a specific implementation, the step of acquiring crack data of a soil sample corresponding to each target mass water content includes:

[0029] Acquire an original RGB image including a current soil sample, wherein the original RGB image includes a plurality of cracks, and the current soil sample is a soil sample obtained after a balance test of a soil sample at a target mass water content;

[0030] Gray-scaling and cropping the original RGB image to obtain a processed image of a preset size;

[0031] Importing the processed image into image analysis software for analysis and processing to obtain parameter information of each crack, wherein the parameter information includes at least the crack area and the crack length;

[0032] Based on the parameter information of each crack, the crack data of the current soil sample is obtained, and the crack data at least includes a surface crack ratio and an average crack width. The surface crack ratio is the ratio of the sum of the areas of multiple cracks to the bottom area of ​​the ring knife, and the average crack width is the ratio of the sum of the areas of multiple cracks to the sum of the lengths of multiple cracks.

[0033] In a specific embodiment, the step (2) further comprises determining the multiple different target mass moisture contents based on the ring knife sample with saturated mass moisture content, specifically:

[0034] Obtaining the mass of the ring cutter sample with saturated water content, and calculating the saturated mass water content, wherein the saturation value corresponding to the saturated mass water content is 100%;

[0035] Divide the saturation of 100 units to obtain M saturation values, where M is a positive integer and 10≤M≤20;

[0036] Based on a preset formula, M mass water contents corresponding to the M saturation values ​​are obtained, and the M mass water contents are the multiple different target mass water contents.

[0037] In a specific implementation, the preset formula includes:

[0038] w=(S r ×e) / G s ;

[0039] Where w is the mass water content of the soil sample, S r is the saturation of the soil sample, e is the porosity of the soil sample, Gs is the weight of soil particles;

[0040] The calculation formula of the porosity ratio e of the soil sample is:

[0041] Among them, ρ ω is the water density, ρ d Is the dry density.

[0042] In a specific embodiment, it is characterized in that the first data group and the second data group both include suction data, porosity data and saturation data of the same quantity as the target mass water content, the first fracture data group and the second fracture data group both include surface fracture ratio and average fracture width of the same quantity as the target mass water content, and the step (5) includes:

[0043] Taking multiple suctions obtained from the same dehumidification or the same humidification as the horizontal coordinates, and multiple target mass water contents, multiple saturations, and multiple porosity ratios corresponding to the multiple suctions as the vertical coordinates, 2N suction-mass water content curves, 2N suction-saturation curves, and 2N suction-porosity ratio curves are formed;

[0044] Compare 2N suction-mass water content curves and 2N suction-saturation curves to obtain the water holding capacity of soil under the action of dry-wet cycles;

[0045] Compare 2N suction-void ratio curves to obtain the expansion and contraction of soil under the action of dry-wet cycles;

[0046] Based on the changes in the surface crack rate and the average crack width with the number of dry-wet cycles at the same target mass moisture content, and / or the changes in the surface crack rate and the average crack width with the multiple target mass moisture contents during the same dehumidification or the same humidification, the crack properties of the soil under the action of dry-wet cycles are obtained.

[0047] In a specific implementation, the soil sample may be one of red soil, clay soil, and loess.

[0048] The beneficial effects of the present invention include at least:

[0049] 1. The present invention provides a comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles, the test method comprising: compacting the soil at an optimal moisture content to obtain two ring knife samples with maximum dry density; placing the ring knife samples in a vacuum saturation cylinder for humidification to obtain two ring knife samples with saturated mass moisture content; placing the two ring knife samples with saturated mass moisture content in an indoor constant temperature environment for natural air drying and dehumidification until the mass moisture content of the soil samples is reduced to the minimum mass moisture content, and obtaining a first data group and a first data group during the dehumidification process of the ring knife samples. Crack group data; two ring knife samples that have reached the minimum mass water content are subjected to bidirectional water film humidification, and during the humidification process of the ring knife samples, a second data group and a second crack data group are obtained; similarly, the two ring knife samples repeat the dehumidification and humidification process N times, respectively, to complete N dry-wet cycles, where N is a positive integer greater than or equal to 5; based on the N first data groups and N second data groups obtained from the N dry-wet cycles, the water holding capacity and swelling and shrinkage of the soil under the action of the dry-wet cycle are obtained, and based on the N first crack data groups and N second crack data groups, the cracks of the soil under the action of the dry-wet cycle are obtained. In this way, the test method provided by the present invention uses the same two ring knife samples when measuring the water holding capacity, swelling and shrinkage, and cracks of the soil under the action of the dry-wet cycle, which simplifies the soil sample preparation operation and avoids the error caused by sample preparation; at the same time, the test method provided by the present invention establishes the correlation between the three engineering properties of soil water holding capacity, swelling and shrinkage, and cracks, and can provide more accurate and more complete evaluation data for the service performance and safety evaluation of geotechnical related engineering.

[0050] Second, the present invention uses the filter paper method to measure the suction of the soil sample, uses the measurement data of the vernier caliper and the volume calculation formula to obtain the porosity of the soil sample, uses the porosity, target mass water content, and the saturation calculation formula to obtain the saturation, and establishes the suction-mass water content curve, suction-saturation curve, and suction-porosity curve corresponding to each dehumidification and each humidification to analyze the water holding capacity and swelling and shrinkage of the soil. At the same time, the original image including the cracks is accurately processed and quantitatively analyzed by image analysis software to obtain the crack data of the soil sample, and further analyzes the surface crack rate and the average crack width under the same mass water content. The relationship between the degree and the number of dry-wet cycles and the relationship between the surface crack rate and the average crack width and multiple target mass moisture contents in the same dehumidification or the same humidification, so as to obtain the soil crack properties; the measurement methods use the same ring knife sample and the measurement methods are related to each other. The present invention creatively combines the filter paper method + vernier caliper measurement method + balance measurement method + image analysis software to comprehensively measure the water holding capacity, swelling and shrinkage and crack properties of the soil sample and establish the relationship between the three properties, thereby improving work efficiency and providing a reference for whether the deformation-cracking of the dam project has reached stability under the rise and fall of the reservoir water level, as well as the service performance and safety evaluation of geotechnical related projects.

[0051] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic flow chart of the steps of a comprehensive test method for soil water holding capacity, expansion and contraction, and cracking properties under dry-wet cycles provided by an embodiment of the present invention;

[0053] Figure 2 A schematic diagram of the structure of a test specimen and a sealing box in a balance test provided by an embodiment of the present invention;

[0054] Figure 3 A curve diagram showing the relationship between suction and target mass water content of Jiangxi red soil under dry-wet cycle provided by one embodiment of the present invention;

[0055] Figure 4 A curve diagram showing the relationship between suction and saturation of Jiangxi red soil under dry-wet cycles provided by one embodiment of the present invention;

[0056] Figure 5 A curve diagram showing the relationship between suction and porosity of Jiangxi red soil under dry-wet cycles provided by one embodiment of the present invention;

[0057] Figure 6 A graph showing the relationship between the surface crack rate and the average crack width and the number of dry-wet cycles of Jiangxi red soil at the optimal moisture content (dehumidification path) provided in one embodiment of the present invention;

[0058] Figure 7 A graph showing the relationship between the surface crack rate and the average crack width and the number of dry-wet cycles of Jiangxi red soil at the optimal moisture content (humidification path) provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0059] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0060] Please refer to Figure 1 and Figure 2 The present invention provides a comprehensive test method for soil water retention, swelling and cracking under dry-wet cycles. The soil water retention, swelling and cracking are tested using the same ring knife specimen, which can avoid the errors caused by different sample preparations and provide a reference for whether the deformation and cracking of dam projects are stable under the rise and fall of reservoir water levels, as well as the service performance and safety evaluation of geotechnical related projects.

[0061] In the present invention, the test equipment used in the test method includes a stacked saturator, a vacuum saturation cylinder, an oven, a tray, a ring knife, Whitman No.42 filter paper, a permeable stone, a plastic wrap, a sealing box, a dryer, a spray pot, tweezers, a digital display vernier caliper, an ordinary electronic balance, an electronic balance (accuracy 0.0001g), a camera and CIAS image analysis software, etc.

[0062] The test method comprises the following steps:

[0063] Step S10, compacting the soil at the optimum moisture content to obtain two ring knife samples reaching the maximum dry density, wherein the ring knife samples include a ring knife and a soil sample filled in the ring knife, and the soil sample is obtained by mixing dry soil and water prepared by a drying method, wherein the ratio of the mass of water in the soil sample to the mass of dry soil is the optimum moisture content corresponding to the dry soil.

[0064] Optionally, the soil sample may be one of red soil, clay soil and loess.

[0065] In the present invention, the soil sample is red soil from Jiangxi Province. Red soil exists in large quantities in Jiangxi Province, accounting for 70% of the province's soil area, and is widely used as filling material for dam projects. Due to the rise and fall of reservoir water levels, the volume of the dam red soil expands and contracts, cracks develop, and the water holding properties deteriorate. These engineering properties of red soil have a serious impact on the normal service performance and safety status assessment of red soil-related projects.

[0066] In the present invention, two ring knife samples are obtained by using the compression method, and the steps of obtaining each of the ring knife samples include:

[0067] (1) Dry soil is prepared by drying method.

[0068] The drying method specifically includes drying the test soil in an oven at 105° C. for at least 12 hours to obtain dry soil.

[0069] (2) Use the calculation formula for dry soil mass and the calculation formula for water mass to determine the mass of dry soil and water required.

[0070] Specifically:

[0071] The formula for calculating the required dry soil mass is: m s =ρ d ×V.

[0072] Among them, m s is the dry soil mass, ρ d is the dry density, and V is the volume of the cutter ring.

[0073] In the present invention, the size of the ring cutter is Φ61.8mm×H20mm, and its volume is 60cm 3, its mass is 43g.

[0074] ρ d Take the maximum dry density ρ dmax , ρ dmax =1.668g / m 3 .

[0075] Using the calculation formula for dry soil mass, it is calculated that the required dry soil mass is 100.1 grams.

[0076] The required water quality is calculated as:

[0077] m w =m s ×ω

[0078] Among them, m w is the water quality, ω is the optimal water content.

[0079] Preferably, the optimum moisture content is determined by a compaction test.

[0080] In the present invention, the optimum water content of red soil is 18.3% as measured by compaction test.

[0081] Using the water mass calculation formula, it was calculated that the mass of water required for 100.1 g of dry red soil is 18.3 g.

[0082] (3) According to the mass of dry soil and the mass of water determined in step (2), the required dry soil and water are weighed, and the dry soil and water are evenly mixed to obtain wet soil, and the wet soil is sealed and stored for 24 hours to allow the dry soil and water to fully blend, thereby obtaining a soil sample.

[0083] (4) Pour the soil sample into the sample press of the ring knife, smooth the surface of the soil sample, and press the soil sample tightly through a piston with static pressure to obtain the ring knife sample.

[0084] Step S20, placing the two ring knife samples into a vacuum saturation cylinder respectively for humidification to obtain ring knife samples with saturated mass water content.

[0085] Preferably, the step S20 also includes determining the multiple different target mass moisture contents based on the ring knife sample with a saturated mass moisture content, specifically: (a) obtaining the mass of the ring knife sample with a saturated mass moisture content, and calculating the saturated mass moisture content, wherein the saturation value corresponding to the saturated mass moisture content is 100%.

[0086] In this embodiment, after saturation in the saturation cylinder, the mass of the ring knife sample with saturated mass water content is weighed by an electronic balance and is 165.8 g, that is, the mass of the soil sample is 165.8-43 (ring knife mass) = 122.8 g.

[0087] Saturated mass water content = (mass of soil sample - mass of dry soil) / mass of dry soil = (122.8-100.1) / 100.1 = 22.7%.

[0088] (b) Divide the saturation of 100 units to obtain M saturation values, where M is a positive integer and 10≤M≤20.

[0089] It can be understood that the number of saturation values ​​is the same as the number of target mass water contents.

[0090] In this embodiment, M is 12, and M saturation values ​​S r They are 100%, 95%, 90%, 81%, 70%, 60%, 50%, 40%, 30%, 20%, 10% and 6% respectively.

[0091] In other embodiments, other saturation data such as 85%, 75%, 65%, 58% and the like may also be used. In the present invention, when performing saturation division, the difference between every two adjacent saturations is as close as possible.

[0092] (c) obtaining M mass water contents corresponding one-to-one to the M saturation values, wherein the M mass water contents are the multiple different target mass water contents.

[0093] The calculation formula of mass water content w is: w = (S r ×e) / G s .

[0094] Among them, S r is the saturation of the soil sample, e is the porosity of the soil sample, G s It is the weight of soil particles.

[0095] The calculation formula of the porosity ratio e of soil samples is:

[0096] Among them, soil particle weight G s Take 2.69, ρ ω For watertightness, take 1.0g / cm 3 , dry density ρ d Take 1.668g / cm 3 .

[0097] For ease of understanding, for example, when the saturation value is 70%, the corresponding mass water content = [(2.69 / 1.668-1)×0.7] / 2.669 = 15.9%.

[0098] In the present invention, the M saturation values ​​and the M mass water contents corresponding thereto are shown in Table 1.

[0099] Table 1 Correspondence table of different saturation and mass water content

[0100]

[0101]

[0102] Step S30, placing the two ring knife samples that have been humidified in an indoor constant temperature environment for natural air drying and dehumidification, until the mass moisture content of the soil sample drops to the minimum mass moisture content, and obtaining a first data group and a first crack data group during the natural air drying and dehumidification process of the ring knife samples, the first data group including the suction, porosity and saturation corresponding to the soil sample at the multiple different target mass moisture contents, and the first crack data group including the crack data corresponding to the soil sample at the multiple different target mass moisture contents.

[0103] It should be noted that in the first dehumidification process, the ring knife sample that has been humidified is the ring knife sample obtained by saturation of the vacuum saturation cylinder in step S20, and in the other dehumidification processes, the ring knife sample that has been humidified is the ring knife sample obtained by bidirectional water film humidification in step S40.

[0104] Preferably, the number of the multiple different target mass moisture contents is 10-20.

[0105] In the present invention, the number of the multiple different target mass water contents is 12. Preferably, the step of obtaining the suction of the soil sample corresponding to each target mass water content includes:

[0106] (1) Two of the ring knife samples 101, two layers of first filter paper 102 and one layer of second filter paper 103 are loaded to obtain a test sample 100. Along the height direction of the test sample 100, the test sample 100 includes a ring knife sample 101, a first filter paper 102, a second filter paper 103, another first filter paper 102 and another ring knife sample 101 stacked in sequence. The first filter paper 102 is used to protect the second filter paper 103 from directly contacting the soil sample. The second filter paper is used to measure suction. The first filter paper 102 and the second filter paper 103 are both Whitman No.42 filter papers. The diameter of the first filter paper 102 is smaller than the diameter of the ring knife and larger than the diameter of the second filter paper 103.

[0107] In this embodiment, the diameter of the ring knife is 61.8 mm, the diameter of the first filter paper 102 is 59 mm, and the diameter of the second filter paper 103 is 55 mm.

[0108] In the present invention, the central axis of the ring knife, the central axis of the first filter paper 102 and the central axis of the second filter paper 103 are located on the same straight line.

[0109] (2) The test sample 100 is wrapped with a plastic wrap 200 and placed in a sealed box 300 for a balance test.

[0110] The structural diagram of the test sample 100 placed in the sealing box 300 is shown in Figure 2 .

[0111] In the present invention, the test sample 100 is wrapped with three layers of plastic wrap, and then placed in a sealed box and sealed to enter the second filter paper moisture content balance period, and the balance time is 9 days.

[0112] In the present invention, the equilibrium time refers to the conclusion of the American Society for Testing and Materials (ASTM).

[0113] Optionally, the equilibrium time may be determined through multiple experiments, that is, experiments with various equilibrium times such as 5 days, 7 days, 9 days, 11 days, etc. may be conducted to determine the appropriate equilibrium time.

[0114] (3) After the equilibrium test is completed, a equilibrium sample is obtained, and a first mass of the wet second filter paper is acquired.

[0115] The balance sample comprises a ring cutter and a balance soil sample.

[0116] After the balance test, that is, after the balance time of 9 days, the second filter paper was quickly taken out with tweezers, put into an electronic balance with an accuracy of 0.0001 g for weighing, and the first mass of the wet second filter paper was recorded.

[0117] (4) Drying the second filter paper and obtaining a second mass of the second filter paper after drying.

[0118] The drying is specifically to place the filter paper in an oven at 105° C. for more than 6 hours, and then quickly measure the mass of the second filter paper after drying, and record the second mass of the second filter paper after drying.

[0119] (5) Calculating the water content of the second filter paper based on the first mass and the second mass of the second filter paper.

[0120] The water content of the second filter paper=(first mass-second mass) / second mass.

[0121] (6) Based on the water content of the second filter paper, the suction of the second filter paper at equilibrium is calculated, and the suction of the ring knife sample is the same as the suction of the second filter paper.

[0122] In the present invention, according to the rating curve of filter paper in ASTM, the suction of the second filter paper at equilibrium is calculated according to the following formula, specifically:

[0123]

[0124] in, is the suction force of the second filter paper at equilibrium, ω f is the moisture content of the second filter paper.

[0125] Preferably, the step of obtaining the porosity ratio of the soil sample corresponding to each target mass water content comprises:

[0126] Step (1), respectively obtaining multiple diameters and multiple height values ​​corresponding to multiple different angles of two current soil samples, and calculating the average diameter and average height of each of the current soil samples, wherein the current soil samples are soil samples at the target mass moisture content obtained after completing the equilibrium test.

[0127] In this step, firstly, the soil samples in the two ring knife samples that have completed the balance test are taken out respectively and named as current soil samples. Then, a digital display vernier caliper with an accuracy of 0.01 mm is used to test the two current soil samples from 5 angles respectively. Then, the arithmetic mean of the diameters of the 5 angles and the average heights of the 5 angles corresponding to each current soil sample are calculated to obtain the average diameter and average height of the two current soil samples.

[0128] It can be understood that the five angles are merely the angle data corresponding to this embodiment, and the number of different angles can also be 4, 6, 7, etc.

[0129] Step (2), obtaining the arithmetic mean of the average diameters of the two current soil samples and the arithmetic mean of the average heights of the two current soil samples, and using them as the current diameter and current height of the soil sample at the target mass moisture content.

[0130] For ease of understanding, an example is given. Assuming that the diameter of the first current soil sample is A1 and the height is B1, and the diameter of the second current soil sample is A2 and the height is B2, then the current diameter A = (A1+A2) / 2, and the current height B = (A1+A2) / 2.

[0131] Step (3), based on the current diameter and current height of the soil sample, calculate the current volume of the soil sample.

[0132] The soil sample is regarded as an ideal cylinder, and the volume of the soil sample is calculated using the volume formula of a cylinder.

[0133] Step (4), based on the current volume of the soil sample and the initial volume of the soil sample, obtaining the porosity of the soil sample at the target mass water content.

[0134]

[0135] Among them, V s is the initial volume of the soil sample, in cm 3 ;m s is the dry soil mass, ρ w is the density of water, take 1.0g / cm 3 , G s is the soil particle weight, which is taken as 2.69, and V1 is the current volume of the soil sample, in cm 3 , e′ is the porosity ratio of the soil sample.

[0136] Preferably, the step of obtaining the actual mass moisture content of the soil sample corresponding to each target mass moisture content comprises:

[0137] Step (1), weighing the masses of the two current soil samples respectively, and calculating the average mass of the two current soil samples.

[0138] The current soil sample is a soil sample at a target mass moisture content obtained after completing a balance test.

[0139] In this step, a common balance is used to weigh the masses of the two current soil samples respectively, and the arithmetic mean of the masses of the two current soil samples is calculated.

[0140] Step (2), based on the average mass of the two current soil samples and the mass of the dry soil in step (1), obtain the actual mass moisture content of the soil sample at the target mass moisture content.

[0141] The average mass of the two current soil samples is represented by the letter m. v express.

[0142] The actual mass water content = (m v -dry soil mass) / dry soil mass*100%.

[0143] It should be noted that in the present invention, there is no order of priority for measuring the volume of the current soil sample and weighing the weight of the current soil sample, that is, there is no order of priority for the steps of obtaining the actual mass moisture content of the soil sample corresponding to each target mass moisture content and the steps of obtaining the porosity of the soil sample corresponding to each target mass moisture content.

[0144] In the present invention, the actual mass moisture content is used to check whether the mass moisture content of the soil sample has changed after equilibrium. Specifically, the actual mass moisture content (the soil sample after equilibrium) is compared with the target mass moisture content to obtain a comparison result, and when the comparison result meets the preset conditions, the target mass moisture content is used as the calculation basis.

[0145] In the present invention, when the absolute value of the comparison result between the two is within the range of 0.1% to 0.3%, the preset condition is met.

[0146] In this embodiment, the actual mass water content and the target mass water content vary slightly (satisfying the preset conditions), and the calculation of saturation hereinafter is based on the target mass water content. Preferably, the method for obtaining the saturation of a soil sample corresponding to each target mass water content is specifically as follows: based on the target mass water content, the porosity, and the saturation calculation formula, the saturation of the soil sample is obtained.

[0147] The calculation formula of the saturation is:

[0148] Among them, Sr is the saturation of the soil sample, ω is the target mass water content of the soil sample, e is the porosity of the soil sample, G s It is the weight of soil particles.

[0149] In the present invention, the red soil G in Jiangxi Province s Take 2.69.

[0150] In the present invention, the minimum mass water content of the red soil in Jiangxi Province is 1.3%.

[0151] Step S40, respectively perform bidirectional water film humidification on the two ring knife samples that reach the minimum mass moisture content in step S30 until the moisture stays on the surface of the soil sample and no longer penetrates into the interior of the soil sample. During the ring knife sample humidification process, obtain a second data group and a second crack data group, the second data group includes the suction, porosity and saturation corresponding to the soil sample at multiple different target mass moisture contents, and the second crack data group includes the crack data corresponding to the soil sample at the multiple different target mass moisture contents.

[0152] The bidirectional water film humidification is specifically as follows: two geotextile filter papers, two permeable stones and a knife ring sample are arranged in a preset manner to obtain a knife ring sample to be humidified, and then water is added from the top of the knife ring sample to be humidified. The preset manner is specifically a permeable stone, a filter paper, a knife ring sample, another filter paper and another permeable stone stacked in sequence.

[0153] The water adding process between two adjacent target mass water contents is to add water according to a preset time interval, and the preset time interval may be 3 minutes, 5 minutes, 7 minutes, etc., which may be specifically determined based on experience.

[0154] The water adding treatment adopts water adding in a watering can.

[0155] For ease of understanding, this step is illustrated by an example. Assuming that multiple different target mass moisture contents are W1, W2, W3, etc., first, use a watering can to add water at preset intervals until the target mass moisture content is W2, and then perform a balance test on the ring knife specimen corresponding to the target mass moisture content W2, and then obtain the suction, porosity and saturation of the soil sample corresponding to the target mass moisture content W2; then use a watering can to add water at preset intervals until the target mass moisture content is W3, and then perform a balance test on the ring knife specimen corresponding to the target mass moisture content W3, and then obtain the suction, porosity and saturation of the soil sample corresponding to the target mass moisture content W3, and so on, until the suction, porosity and saturation of the soil samples corresponding to all target mass moisture contents are obtained.

[0156] It can be understood that the humidification process of the present invention is not continuous humidification until the soil sample reaches saturated mass water content.

[0157] In the present invention, during the bidirectional water film humidification, when the water stays on the surface of the ring knife sample and no longer penetrates into the inside of the ring knife sample, the humidification is stopped.

[0158] In this step, the steps for obtaining the suction value, porosity and saturation corresponding to the soil samples of the second data group at the multiple different target mass water contents are the same as those in step S30, and will not be repeated here.

[0159] In the present invention, step S30 corresponds to a dehumidification process, and multiple different target mass moisture contents are achieved in order from large to small. Step S40 corresponds to a humidification process, and multiple different target mass moisture contents are achieved in order from small to large.

[0160] Preferably, the step of acquiring crack data of a soil sample corresponding to each target mass water content comprises:

[0161] (1) Acquire an original RGB image including a current soil sample, wherein the original RGB image includes a plurality of cracks, and the current soil sample is a soil sample obtained after completing a balance test at a target mass water content.

[0162] In this step, the cracks generated on the surface of the current soil sample are photographed by a camera to obtain an original image including the cracks.

[0163] In actual operation, the camera captures the current soil sample including the ring cutter.

[0164] (2) Grayscale processing and cropping are performed on the original image to obtain a processed image of a preset shape.

[0165] In the present invention, Photoshop software is used to grayscale the original RGB image, and the grayscaled image is cropped to obtain a processed image of a preset size, wherein the preset shape is a square with a side length of 61.8 mm.

[0166] (3) Importing the processed image into image analysis software for analysis and processing to obtain parameter information of each crack, wherein the parameter information includes at least the crack area and the crack length.

[0167] In this embodiment, the image analysis software is CIAS image analysis software. In other embodiments, other image analysis software having the same functions as CIAS image analysis software may also be used.

[0168] In the present invention, the process of analyzing and processing using CIAS image analysis software is as follows:

[0169] Import the processed image into CIAS image analysis software, adjust the threshold value, click segment, and obtain a binary image; click edit binary image to remove noise, fully display the sample cracks, and obtain a denoised image; click the "Segmentation" module to divide the crack image area, obtain the pixels of the area corresponding to the sample ring knife area through the divided area, and establish a conversion relationship between pixel units and actual units; click the "Crack" module to analyze the crack parameters, then click "Auto analysis (Crack)", wait 10-30 seconds to obtain the central axis of the crack network, and then click "Crack property table" to pop up the crack geometry information table to obtain the parameter information of each crack, the parameter information at least includes parameters such as crack area, length, width, direction, etc., and the actual parameter information of the crack parameters can be obtained according to the conversion relationship between pixel units and actual units.

[0170] (4) Based on the parameter information of each of the cracks, the crack data of the current soil sample is obtained, and the crack data at least includes a surface crack ratio and an average crack width. The surface crack ratio is the ratio of the sum of the areas of the multiple cracks to the bottom area of ​​the ring knife, and the average crack width is the ratio of the sum of the areas of the multiple cracks to the sum of the lengths of the multiple cracks.

[0171] The fracture data group consists of fracture data under different target mass water contents.

[0172] It should be noted that if both current soil samples have cracks, photos are taken for both, and after taking the photos, Photoshop software and CIAS image analysis software are used respectively. That is, it can be understood that the crack data group obtained in each dehumidification and humidification process may include crack data of one current soil sample under different target mass moisture content, and may also include crack data of two current soil samples under different target mass moisture content.

[0173] In the present invention, the first crack data set and the second crack data set correspond to crack data obtained in the dehumidification and humidification processes, respectively. The dehumidification process is the crack generation process; the humidification process is the crack healing process, and only the ring knife samples whose cracks have not been completely healed during the humidification process are photographed.

[0174] Step S50, for the same two ring knife samples, repeat steps S30 and S40 multiple times in sequence, complete N dry-wet cycles, and obtain N first data groups, N second data groups, N first crack data groups and N second crack data groups, where N is a positive integer greater than or equal to 5.

[0175] It can be understood that each dry-wet cycle includes a dehumidification process and a humidification process.

[0176] In the present invention, N=5, that is, 5 dry-wet cycles are completed, represented by the first dehumidification, the first humidification; the second dehumidification, the second humidification; the third dehumidification, the third humidification; the fourth dehumidification, the fourth humidification; the fifth dehumidification, the fifth humidification.

[0177] Step S60, based on the N first data groups and the N second data groups obtained from the N dry-wet cycles, obtain the water holding capacity and swelling and shrinkage of the soil under the action of the dry-wet cycles, and based on the N first crack data groups and the N second crack data groups, obtain the crack properties of the soil under the action of the dry-wet cycles.

[0178] The first data group and the second data group both include the same number of suction data, porosity data and saturation data as the target mass water content; the first fracture data group and the second fracture data group both include the same number of surface fracture ratios and average fracture widths as the target mass water content.

[0179] It can be understood that if no cracks are generated during the current dehumidification process, the surface crack rate and the average crack width are both 0.

[0180] Step S60 specifically includes:

[0181] With multiple suctions obtained from the same dehumidification or the same humidification as the horizontal coordinates, and multiple target mass moisture contents, multiple saturations and multiple porosity ratios corresponding to the multiple suctions as the vertical coordinates, 2N suction-mass moisture content curves, 2N suction-saturation curves and 2N suction-porosity ratio curves are formed.

[0182] In the present invention, the correspondence between suction and target mass water content, the correspondence between suction and saturation, and the correspondence between suction and porosity ratio refer to values ​​obtained under the same target mass water content.

[0183] The 2N suction-mass moisture content curves and the 2N suction-saturation curves were compared to obtain the water holding capacity of the soil under the action of dry-wet cycles.

[0184] In this step, 2N suction-mass moisture content curves are compared to obtain a first analysis result; 2N suction-saturation curves are compared to obtain a second analysis result; based on the first analysis result and the second analysis result, the water holding capacity of the soil under the action of dry-wet cycles is obtained.

[0185] The 2N suction-void ratio curves were compared to obtain the swelling and shrinkage of soil under the action of drying and wetting cycles.

[0186] In this step, 2N suction-void ratio curves are compared to obtain a third analysis result, and based on the third analysis result, the expansion and contraction of the soil under the action of dry-wet cycles is obtained.

[0187] Based on the changes in the surface crack rate and the average crack width with the number of dry-wet cycles at the same target mass moisture content, and / or the changes in the surface crack rate and the average crack width with the multiple target mass moisture contents during the same dehumidification or the same humidification, the crack properties of the soil under the action of dry-wet cycles are obtained.

[0188] In the present invention, N=5, the number of the first data group and the number of the second data group are both 5. Since the number of target mass moisture contents is 12, the first data group corresponding to each dehumidification includes 12 suction data, 12 porosity data and 12 saturation data, and the second data group corresponding to each humidification also includes 12 suction value data, 12 porosity data and 12 saturation data.

[0189] Since the data in the first data group corresponding to the second dehumidification and the first dehumidification, the data in the first data group corresponding to the fourth dehumidification and the third dehumidification, the data in the second data group corresponding to the second humidification and the first humidification, and the data in the second data group corresponding to the fourth humidification and the third humidification are not significantly different. In order to intuitively reflect the data rules, the present invention uses the suction of the first dehumidification, the third dehumidification, the fifth dehumidification, the first humidification, the third humidification and the fifth humidification as the horizontal coordinates, and the target mass water content, porosity and saturation as the vertical coordinates to draw a curve graph, see Figures 3 to 5 ,in, Figure 3 This is the relationship curve between the suction and mass water content of Jiangxi red soil under the action of dry-wet cycle. Figure 4 This is the relationship curve between suction and saturation of Jiangxi red soil under the action of dry-wet cycle. Figure 5 This is a curve diagram showing the relationship between suction and porosity of Jiangxi red soil under the action of dry-wet cycles.

[0190] Taking the crack data obtained at the optimal water content as an example, the present invention uses the number of dry-wet cycles as the horizontal axis, and the surface crack rate and the average crack width as the vertical axis to draw a curve graph, see Figure 6 and Figure 7 , Figure 6 The graphs are the relationship between the surface crack rate and average crack width and the number of dry-wet cycles of Jiangxi red soil at the optimal moisture content (18.3%) (dehumidification path). Figure 7 This is a curve diagram showing the relationship between the surface crack rate and the average crack width and the number of dry-wet cycles of Jiangxi red soil at the optimal moisture content (18.3%) (humidification path).

[0191] In the present invention, the crack data under different mass water contents have the same changing pattern as the number of dry-wet cycles increases, so they are not listed one by one.

[0192] It should be noted that Figure 3 and Figure 4 It reflects the water holding capacity of the soil sample. Figure 5 It reflects the expansion and contraction of the soil sample. Figure 6 and Figure 7 It reflects the cracking properties of the soil sample.

[0193] from Figure 3 and Figure 4 It can be seen that with the increase in the number of cycles, the soil-water characteristic curve of the soil sample gradually moves downward and tends to be stable; at the same time, under the condition of the same suction, the dehumidification curve is higher than the moisture absorption curve, and there is an obvious hysteresis effect between the dehumidification and moisture absorption curves, and it gradually decreases until it stabilizes with the increase in the number of dry-wet cycles. Figure 5 It can be seen that with the increase in the number of dry-wet cycles, the void ratio gradually increases, that is, the volume of the soil sample gradually increases. Figure 6 and Figure 7 It can be seen that with the increase in the number of dry-wet cycles, the surface crack rate and the average crack width both increase during the dehumidification and humidification process, and gradually tend to stabilize.

[0194] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A comprehensive test method for soil water holding capacity, expansion and contraction, and cracking under dry-wet cycles, characterized in that: The test method comprises the following steps: Step (1), compacting the soil at an optimum moisture content to obtain two ring cutter samples reaching a maximum dry density, wherein the ring cutter samples include a ring cutter and a soil sample filled in the ring cutter, wherein the soil sample is obtained by mixing dry soil prepared by a drying method with water, wherein the ratio of the mass of water in the soil sample to the mass of dry soil is the optimum moisture content corresponding to the dry soil; Step (2), placing the two ring knife samples into a vacuum saturation cylinder for humidification respectively, to obtain two ring knife samples with saturated mass water content; Step (3), placing the two ring knife samples that have been humidified in an indoor constant temperature environment for natural air drying and dehumidification, until the mass water content of the soil sample is reduced to the minimum mass water content, and obtaining a first data group and a first crack data group during the natural air drying and dehumidification of the ring knife samples, wherein the first data group includes the suction, porosity and saturation corresponding to the soil sample at multiple different target mass water contents, and the first crack data group includes the crack data corresponding to the soil sample at the multiple different target mass water contents; Step (4), respectively performing bidirectional water film humidification on the two ring knife samples that reach the minimum mass water content in step (3) until the water stays on the surface of the soil sample and no longer penetrates into the interior of the soil sample. During the ring knife sample humidification process, a second data group and a second crack data group are obtained, wherein the second data group includes the suction, porosity and saturation corresponding to the soil sample at the multiple different target mass water contents, and the second crack data group includes the crack data corresponding to the soil sample at the multiple different target mass water contents, wherein: The steps for obtaining the suction of the soil sample corresponding to each target mass water content include: Two of the ring knife samples, two layers of first filter paper and one layer of second filter paper are loaded to obtain a test sample. Along the height direction of the test sample, the test sample includes a ring knife sample, a layer of first filter paper, a layer of second filter paper, another layer of first filter paper and another ring knife sample. The first filter paper is used to protect the second filter paper from directly contacting the soil sample. The second filter paper is used to measure suction. The first filter paper and the second filter paper are both Whitman No.42 filter papers. The diameter of the first filter paper is smaller than the diameter of the ring knife and larger than the diameter of the second filter paper. Wrap the test sample with plastic wrap and place it in a sealed box for a balance test; After the balance test is completed, obtaining a first mass of the wet second filter paper; drying the second filter paper, and obtaining a second mass of the dried second filter paper; calculating the water content of the second filter paper based on the first mass and the second mass of the second filter paper; Based on the water content of the second filter paper, the suction of the second filter paper at equilibrium is calculated, and the suction of the soil sample is the same as the suction of the second filter paper; Step (5), for the same two ring knife samples, repeat steps (3) and (4) in sequence for multiple times, complete N dry-wet cycles, and obtain N first data groups, N second data groups, N first crack data groups, and N second crack data groups, wherein N is a positive integer greater than or equal to 5; Step (6), based on the N first data groups and the N second data groups obtained from the N dry-wet cycles, obtain the water holding capacity and swelling and shrinkage of the soil under the action of the dry-wet cycles, and based on the N first crack data groups and the N second crack data groups, obtain the crack properties of the soil under the action of the dry-wet cycles.

2. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 1 is characterized in that: The calculation formula of the suction force of the second filter paper is: ； in, is the suction force of the second filter paper at equilibrium, is the moisture content of the second filter paper.

3. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 1 is characterized in that: The steps for obtaining the porosity ratio of the soil sample corresponding to each target mass water content include: Respectively obtain multiple diameters and multiple height values ​​corresponding to multiple different angles of two current soil samples, and calculate the average diameter and average height of each current soil sample, wherein the current soil sample is a soil sample obtained after completing a balance test at a target mass moisture content; Obtaining the arithmetic mean of the average diameters of the two current soil samples and the arithmetic mean of the average heights of the two current soil samples, and using them as the current diameter and current height of the soil sample at the target mass water content; Based on the current diameter and the current height of the soil sample, calculate the current volume of the soil sample; Based on the current volume of the soil sample and the initial volume of the soil sample, the porosity ratio of the soil sample at the target mass water content is obtained.

4. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 3 is characterized in that: The method for obtaining the saturation of a soil sample corresponding to each target mass water content includes: obtaining the saturation of the soil sample based on the target mass water content, the porosity ratio, and a saturation calculation formula, wherein the saturation calculation formula is: ; Among them, S r is the saturation of the soil sample, is the target mass water content of the soil sample, e is the porosity ratio of the soil sample, G s It is the weight of soil particles.

5. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to any one of claims 2 to 4, characterized in that: The steps for obtaining crack data of soil samples corresponding to each target mass water content include: Acquire an original RGB image including a current soil sample, wherein the original RGB image includes a plurality of cracks, and the current soil sample is a soil sample obtained after a balance test of a soil sample at a target mass water content; Gray-scaling and cropping the original RGB image to obtain a processed image of a preset size; Importing the processed image into image analysis software for analysis and processing to obtain parameter information of each crack, wherein the parameter information includes at least the crack area and the crack length; Based on the parameter information of each crack, the crack data of the current soil sample is obtained, and the crack data at least includes a surface crack ratio and an average crack width. The surface crack ratio is the ratio of the sum of the areas of multiple cracks to the bottom area of ​​the ring knife, and the average crack width is the ratio of the sum of the areas of multiple cracks to the sum of the lengths of multiple cracks.

6. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 1 is characterized in that: The step (2) further includes determining the plurality of different target mass moisture contents based on the ring knife sample having a saturated mass moisture content, specifically: The mass of the ring cutter sample with saturated water content is obtained, and the saturated mass water content is calculated, wherein the saturation value corresponding to the saturated mass water content is 100%; Divide the saturation of 100 units to obtain M saturation values, where M is a positive integer and 10≤M≤20; Based on a preset formula, M mass water contents corresponding to the M saturation values ​​are obtained, and the M mass water contents are the multiple different target mass water contents.

7. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 6 is characterized in that: The preset formula includes: w=(S r ×e) / G s ; Where w is the mass water content of the soil sample, S r is the saturation of the soil sample, e is the porosity of the soil sample, G s is the weight of soil particles; The calculation formula of the porosity ratio e of the soil sample is: ; in, is the water density, Is the dry density.

8. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 1 is characterized in that: The first data group and the second data group both include suction data, porosity data and saturation data in the same quantity as the target mass water content, the first fracture data group and the second fracture data group both include surface fracture ratios and average fracture widths in the same quantity as the target mass water content, and the step (5) includes: Taking multiple suctions obtained from the same dehumidification or the same humidification as the horizontal coordinates, and multiple target mass water contents, multiple saturations, and multiple porosity ratios corresponding to the multiple suctions as the vertical coordinates, 2N suction-mass water content curves, 2N suction-saturation curves, and 2N suction-porosity ratio curves are formed; Compare 2N suction-mass water content curves and 2N suction-saturation curves to obtain the water holding capacity of soil under the action of dry-wet cycles; Compare 2N suction-void ratio curves to obtain the expansion and contraction of soil under the action of dry-wet cycles; Based on the changes in the surface crack rate and the average crack width with the number of dry-wet cycles at the same target mass moisture content, and / or the changes in the surface crack rate and the average crack width with the multiple target mass moisture contents during the same dehumidification or the same humidification, the crack properties of the soil under the action of dry-wet cycles are obtained.

9. The comprehensive test method for soil water holding capacity, swelling and shrinkage, and cracking under dry-wet cycles according to claim 1 is characterized in that: The soil sample is one of red soil, clay soil and loess.

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