A calculation method of soil shrinkage characteristic curve based on digital image processing

Abstract

The present invention discloses a soil shrinkage characteristic curve calculation method based on digital image processing, including sample preparation, vacuum saturation of the sample, sample dehumidification test, and relevant data in the sample dehumidification process calculated by mass change data and digital image, and finally analyzing the data, drawing the change curves of void ratio, porosity, and volume strain with saturation, and giving the evolution law of void ratio and shrinkage with soil-water ratio. Based on digital image processing technology, the present invention uses software ImageJ to screen image boundaries and perform binarization processing, calculates the pixel value of the sample image, and then obtains the sample size by calibrating the known size image; combined with volume change data, soil moisture content, void ratio, saturation and other indicators are obtained by calculating mass change data, and then quantitatively describes the change law of void ratio with water content or soil-water ratio. The calculation method of the present invention has important scientific significance and engineering value for studying soil drying shrinkage.

Description

Technical Field

[0001] The invention relates to the field of geotechnical test calculation, and in particular to a method for calculating a shrinkage deformation characteristic curve of a soil drying process based on digital image processing. Background Art

[0002] The content of hydrophilic clay minerals in soil has a significant impact on its mechanical properties. A large amount of clay mineral components will cause the soil to shrink and deform significantly during the drying process, which in turn affects its engineering properties. For example, expansive soil, which is used as a barrier material for landfills, has a high clay content. Due to changes in environmental conditions, the water content of the soil decreases, causing the soil to shrink and deform, and even crack, reducing its barrier effect on landfill waste; clay soil used as a buffer filling material for geological storage of nuclear waste, under the action of radiant heat, the soil undergoes a heating, dehumidification and drying process, presenting an unsaturated state, with low water content and high suction, which leads to changes in the mechanical properties of the soil, posing a threat to the long-term stable storage of nuclear waste.

[0003] In addition to quantitatively analyzing the shrinkage and deformation properties of soil, the shrinkage characteristic curve is also closely related to the water holding characteristics of soil. In characterizing the mechanical behaviors such as soil deformation caused by changes in water content, the shrinkage characteristic curve is equally important as the soil-water characteristic curve. Therefore, how to accurately characterize the shrinkage and deformation characteristics of soil and quantitatively describe the evolution of soil deformation with water content or soil-water ratio is a useful exploration for analyzing the mechanical mechanism of shrinkage deformation. Summary of the invention

[0004] The purpose of the present invention is to provide a soil shrinkage characteristic curve calculation method based on digital image processing technology, which can effectively improve the quantitative characterization accuracy of the evolution of soil porosity with soil-water ratio or moisture content, and provide an effective means for studying the mechanism of soil drying shrinkage.

[0005] The present invention provides a soil shrinkage characteristic curve calculation method based on digital image processing, the steps are as follows:

[0006] (1) Sample preparation and determination of initial soil moisture content ω 0, given dry density ρ d , calculate the actual mass of the sample at the initial moisture content m ss ;

[0007] Compact the sample and calculate the mass of the compacted sample based on the ring cutter size m s and initial volume V 0, where m s =(1+0.01× ω 0)× ρ d× V 0, V 0 Calculated based on the inner diameter and thickness of the ring cutter;

[0008] Weigh and record the mass of the ring cutter m h , calibrate the quality of the sample plate m b Total mass of the cutter ring and compacted specimen m h+s , considering the loss of soil particles during the sample preparation process, the actual mass of the sample at the initial moisture content is m ss is the total mass of the cutter ring and compacted sample m h+s Ring knife quality m h The difference, that is m ss = m h+s - m h ;

[0009] (2) After the sample is prepared, vacuum and saturate it. After the sample is fully saturated, weigh and record the total mass of the ring knife and the sample. m h+sa ;

[0010] After weighing, remove the sample from the ring cutter, place it on a calibrated sample plate of known size, and weigh the total mass of the sample plate and the saturated sample. m b+sa , image acquisition, and binarization processing by software ImageJ to obtain digital images of the area and height of the sample and the calibration sample plate, and calculate the volume of the sample after saturation V sa ,Right now V sa = H sa × A sa , H sa = P sh ×H b / P bh , A sa = P sA ×A b / P bA ,in, H sa To calculate the saturated sample height, P shH is the pixel for calibrating the sample plate height. b To calibrate the actual height of the sample plate, P bh is the saturated sample height pixel, A sa To calculate the saturated sample area, P sA A is the pixel of the calibration sample area. b To calibrate the actual area of ​​the sample plate, P bA is the saturated sample area pixel;

[0011] (3) Sample dehumidification test: place the sample plate and the sample in a moisturizing container with a given relative humidity, and collect the total mass data of the sample plate and the sample at regular intervals. m i , i ≥1, i The number of times is indicated, and the area and height images are collected until the mass change of the sample soil under the relative humidity condition within 48 hours is less than 0.01g;

[0012] The sample dehumidification test is performed by repeating step (3) in moisturizing containers with different relative humidity, wherein when the relative humidity is greater than 85%, data is collected every 4 hours, and when the relative humidity is less than 85%, data is collected every 8 hours;

[0013] (4) Calculate relevant data during the dehumidification process of the sample through mass change data and digital images;

[0014] According to the initial volume V 0. Initial moisture content ω 0. Sample mass at initial moisture content m ss , calculate the initial dry density of the actual soil sample ρ d0 = m ss / (1+0.01× ω 0) / V 0;

[0015] According to the initial dry density of the actual soil sample ρ d0 Soil particle density G s , calculate the actual initial porosity of the sample n 0 and initial porosity ratio e 0, that is n 0=1- ρ d0 / G s , e 0= n0 / (1- n 0);

[0016] According to the saturated volume of soil V sa and initial porosity ratio e 0, calculate the volume of sample soil particles V s = V sa / (1+ e 0);

[0017] According to the volume of soil particles V s and initial porosity ratio e 0, calculate the pore volume of the sample V V = V s × e 0;

[0018] According to the initial moisture content ω 0. Soil particle specific gravity G s , initial porosity ratio e 0, calculate the initial saturation of the sample

[0019] S r0 = ω 0× G s / e 0;

[0020] According to the total mass of the sample plate and the saturated sample m b+sa And the total mass of the sample plate and dehydrated sample currently recorded m i , calculate the mass of the remaining water in the current sample m wi = m b+sa - m i ;

[0021] Calculate the current sample volume based on the dehydrated sample digital image V i , i ≥1, i Indicates the number of times;

[0022] According to the current sample volume V i Soil particle volume V s , calculate the current sample porosity e i= ( V i -V s ) / V s And the current sample porosity n i = ( V i -V s ) / V i , i ≥1, i Indicates the number of times;

[0023] Assuming the density of water is ρ w =1g / cm 3 , so the mass of the remaining water in the current sample is m wi The current residual pore water volume V wi , according to the current residual pore water volume V wi Soil particle volume V s , calculate the current sample soil-water ratio R=V wi / V s , i ≥1, i Indicates the number of times;

[0024] According to the quality of the remaining water in the current sample m wi , Current sample volume V i Soil particle volume V s , calculate the current saturation of the sample S ri = m wi / ( V i -V s )×100%, i ≥1, i Indicates the number of times;

[0025] (5) Based on the data from step (4), a comparative analysis is conducted to plot the variation curves of void ratio, porosity, volume strain, etc. with saturation, and the evolution law of void ratio and shrinkage rate with soil-water ratio is given.

[0026] The present invention is based on digital image processing technology. By processing digital images and mass data collected by a high-precision camera, the image boundary is screened and binarized through the software ImageJ, the pixel value of the sample image can be calculated, and then the sample size is obtained by calibrating the image of known size; combined with the volume change data, the soil moisture content, porosity, saturation and other indicators are obtained by calculating the mass change data, and then the change law of the porosity with the water content or the soil-water ratio is quantitatively described, which is of great significance for characterizing the shrinkage and deformation characteristics of the sample and the soil classification method, and has important scientific significance and engineering value for studying the drying shrinkage of soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the soil shrinkage characteristic curve calculation method based on digital image processing of the present invention;

[0028] Figure 2 is a graph showing the relationship between the sample volume strain and the sample saturation calculated based on the mass change and volume change of the embodiment;

[0029] Figure 3 is a graph showing the relationship between the porosity ratio and the saturation of the sample of the embodiment;

[0030] Figure 4 is a graph showing the relationship between the porosity and saturation of the sample in the embodiment;

[0031] Figure 5 is a graph showing the relationship between the void ratio and the volumetric water content of an embodiment;

[0032] Figure 6 is a graph showing the relationship between porosity and volumetric water content in an embodiment;

[0033] Figure 7 The shrinkage characteristic curve and shrinkage rate curve characterized by the void ratio and soil-water ratio of the silt in the embodiment;

[0034] Figure 8 It is a shrinkage characteristic curve and a shrinkage rate curve characterized by the void ratio and soil-water ratio of clay soil in the embodiment. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to the accompanying drawings and embodiments, but is not intended to limit the present invention:

[0036] Example 1

[0037] Reference Figure 1 , a soil shrinkage characteristic curve calculation method based on digital image processing, taking powdery soil as an example, the calculation method steps are as follows:

[0038] (1) Sample preparation, testing the initial moisture content of powdered soil samples ω 0, given dry density ρ d , calculate the actual mass of the sample at the initial moisture content m ss ;

[0039] Compact the sample and calculate the mass of the compacted sample based on the ring cutter size m s and initial volume V 0 ,in, m s =(1+0.01× ω 0)× ρ d × V 0, V 0 Calculated based on the inner diameter and thickness of the ring cutter;

[0040] Weigh and record the mass of the ring cutter m h , calibrate the quality of the sample plate m b Total mass of the cutter ring and compacted specimen m h+s , considering the loss of soil particles during the sample preparation process, the actual mass of the sample at the initial moisture content is m ss is the total mass of the cutter ring and compacted sample m h+s Ring knife quality m h The difference, that is m ss = m h+s - m h ;

[0041] (2) After the sample is prepared, vacuum and saturate it. After the sample is fully saturated, weigh and record the total mass of the ring knife and the saturated sample. m h+sa ;

[0042] After weighing, remove the sample from the ring cutter, place it on a calibrated sample plate of known size, and weigh the total mass of the sample plate and the saturated sample. m b+sa , image acquisition is performed, and the acquired images are binarized by using the software ImageJ to obtain the digital images of the area and height of the sample and the calibration sample plate, and the volume of the sample after saturation is calculated. Vsa ;

[0043] In this embodiment, open the software ImageJ, click Open→select the image, click Process→Find Edges to automatically obtain the image boundary, click Process→Binary→Make Binary to binarize the sample, select the magic wand to pick the sample boundary, click Analyze→Measure to obtain the area or height pixels of the sample, and calculate the sample height or area according to the corresponding pixels and geometric dimensions of the calibration sample plate of known size;

[0044] Calculate the volume of the sample after saturation V sa ,Right now V sa = H sa × A sa , H sa = P sh ×H b / P bh , A sa = P sA ×A b / P bA ,in, P sh H is the pixel for calibrating the sample plate height. b To calibrate the actual height of the sample plate, P bh is the saturated sample height pixel, P sA A is the pixel of the calibration sample area. b To calibrate the actual area of ​​the sample plate, P bA is the saturated sample area pixel, A sa To calculate the saturated sample area, H sa To calculate the height of the saturated sample;

[0045] (3) Sample dehumidification test: place the sample plate and the sample in a moisturizing container with a given relative humidity, and record the total mass data of the sample plate and the sample at regular intervals. m i ( i ≥1), i The number of times is indicated, and the area and height images are collected until the mass change of the sample soil under the relative humidity condition within 48 hours is less than 0.01g;

[0046] Repeat step (3) in the moisturizing containers with different relative humidity. When the relative humidity is greater than 85%, the data collection frequency is appropriately increased to collect data once every 4 hours. When the relative humidity is less than 85%, the data is collected once every 8 hours.

[0047] (4) Calculate relevant data during the dehumidification process of the sample through mass change data and digital images;

[0048] According to the initial volume V 0. Initial moisture content ω 0. Sample mass at initial moisture content m ss , calculate the initial dry density of the actual soil sample ρ d0 = m ss / (1+0.01× ω 0) / V 0;

[0049] According to the initial dry density of the actual soil sample ρ d0 Soil particle density G s , calculate the actual initial porosity of the sample n 0 and initial porosity ratio e 0, that is n 0=1- ρ d0 / G s , e 0= n 0 / (1- n 0);

[0050] According to the saturated volume of soil V sa and initial porosity ratio e 0, calculate the volume of sample soil particles V s = V sa / (1+ e 0);

[0051] According to the volume of soil particles V s and initial porosity ratio e 0, calculate the pore volume of the sample V V = V s × e 0;

[0052] According to the initial moisture content ω 0. Soil particle specific gravity Gs , initial porosity ratio e 0, calculate the initial saturation of the sample S r0 = ω 0× G s / e 0;

[0053] According to the total mass of the sample plate and the saturated sample m b+sa And the total mass of the sample plate and dehydrated sample currently recorded m i ( i ≥1) i Indicates the number of times and calculates the mass of the remaining water in the current sample m wi = m b+sa - m i ( i ≥1), i Indicates the number of times;

[0054] Calculate the current sample volume based on the dehydrated sample digital image V i ( i ≥1), i Indicates the number of times;

[0055] According to the current sample volume V i ( i ≥1) and soil particle volume V s , calculate the current sample porosity e i = ( V i -V s ) / V s ( i ≥1) and the current sample porosity n i = ( V i -V s ) / V i ( i ≥1), i Indicates the number of times;

[0056] Assuming the density of water is ρ w =1 g / cm 3, so the mass of the remaining water in the current sample is m wi ( i ≥1) is the current remaining pore water volume V wi ( i ≥1), based on the current remaining pore water volume V wi ( i ≥1) and soil particle volume V s , calculate the current sample soil-water ratio R=V wi / V s ( i ≥1), i Indicates the number of times;

[0057] According to the quality of the remaining water in the current sample m wi ( i ≥1) Current sample volume V i ( i ≥1) and soil particle volume V s , calculate the current saturation of the sample S ri = m wi / ( V i -V s )×100%( i ≥1), i Indicates the number of times;

[0058] (5) Based on the data from step (4), a comparative analysis is conducted to plot the variation curves of void ratio, porosity, and volume strain with saturation. The evolution law of void ratio and shrinkage rate with soil-water ratio is given as follows: the shrinkage process of silt is divided into three stages, namely proportional shrinkage, residual shrinkage, and zero shrinkage. When the soil-water ratio is less than 0.5, the shrinkage rate of silt tends to zero.

[0059] Example 2

[0060] Using the method of Example 1, taking clay as an example, soil shrinkage characteristic curve calculation based on digital image processing is performed. Figure 8, the shrinkage characteristic curve of the void ratio and shrinkage rate of clay samples changing with the soil-water ratio. The shrinkage process of clay is divided into three stages, namely proportional shrinkage, residual shrinkage and non-zero shrinkage stage. Unlike silt, clay has an obvious non-zero shrinkage stage, and the shrinkage rate in the residual shrinkage stage is higher. When the soil-water ratio is less than 0.1, the shrinkage rate of clay still increases.

[0061] Reference Figure 2 ,The example sample volume strain changes with saturation ,shows that the volume strain of the example is 16.5%, the maximum volume strain of the clay is 4.6%.

[0062] Reference Figure 3 , the variation trend of the porosity of the samples in the embodiment with the saturation is that with the decrease of the saturation, the porosity of clay and silt drops sharply when the saturation is greater than 95%, and then the porosity of clay gradually decreases with the saturation, and the porosity of silt gradually tends to be stable with the decrease of saturation.

[0063] Reference Figure 4 , the porosity of the samples in the embodiment changes with the saturation. As the saturation decreases, the porosity of clay and silt drops sharply when the saturation is greater than 95%, and then the porosity of clay gradually decreases with the saturation, and the porosity of silt gradually tends to be stable with the decrease of saturation.

[0064] Reference Figure 5 , the variation trend of the porosity of the samples in the embodiment with the volumetric moisture content, with the decrease of the volumetric moisture content, the porosity of clay and silt gradually decreases, when the volumetric moisture content is greater than 0.1, the porosity of clay decreases rapidly with the volumetric moisture content, when the volumetric moisture content is less than 0.1, it gradually tends to be stable, when the volumetric moisture content is greater than 0.4, the porosity of silt decreases rapidly with the volumetric moisture content, when the volumetric moisture content is less than 0.4, it gradually tends to be stable.

[0065] Reference Figure 6 The variation trend of porosity of the samples in the embodiment with volumetric water content is as follows: with the decrease of volumetric water content, the porosity of clay and silt gradually decreases; when the volumetric water content is greater than 0.1, the porosity of clay gradually decreases with volumetric water content, and tends to be stable when the volumetric water content is less than 0.1; when the volumetric water content is greater than 0.4, the porosity of silt gradually decreases with volumetric water content, and tends to be stable when the volumetric water content is less than 0.4.

[0066] Reference Figure 7, Example 1 shows the shrinkage characteristic curve of the void ratio and shrinkage rate of silt samples as the soil-water ratio changes. The shrinkage process of silt is divided into three stages, namely proportional shrinkage, residual shrinkage and zero shrinkage stage. When the soil-water ratio is less than 0.5, the shrinkage rate of silt tends to zero.

Claims

1. A method for calculating soil shrinkage characteristic curve based on digital image processing, It is characterized in that The calculation steps are as follows: (1) Sample preparation and determination of initial soil moisture content ω 0 , given dry density ρ d , calculate the actual mass of the sample at the initial moisture content m ss ; Compact the sample and calculate the mass of the compacted sample based on the ring cutter size m s and initial volume V 0 ,in, m s =(1+0.01× ω 0 )× ρ d × V 0 , V 0 Calculated based on the inner diameter and thickness of the ring cutter; Weigh and record the mass of the ring cutter m h , calibrate the quality of the sample plate m b Total mass of the cutter ring and compacted specimen m h+s , considering the loss of soil particles during the sample preparation process, the actual mass of the sample at the initial moisture content is m ss is the total mass of the cutter ring and compacted sample m h+s Ring knife quality m h The difference, that is m ss = m h+s - m h ; (2) After the sample is prepared, vacuum and saturate it. After the sample is fully saturated, weigh and record the total mass of the ring knife and the sample. m h+sa ; After weighing, remove the sample from the ring cutter, place it on a calibrated sample plate of known size, and weigh the total mass of the sample plate and the saturated sample. m b+sa , image acquisition, and binarization processing by software ImageJ to obtain digital images of the area and height of the sample and the calibration sample plate, and calculate the volume of the sample after saturation V sa ,Right now V sa = H sa × A sa , H sa = P sh ×H b / P bh , A sa = P sA ×A b / P bA ,in, H sa To calculate the saturated sample height, P sh H is the pixel for calibrating the sample plate height. b To calibrate the actual height of the sample plate, P bh is the saturated sample height pixel, A sa To calculate the saturated sample area, P sA A is the pixel for calibrating the sample area. b To calibrate the actual area of ​​the sample plate, P bA is the saturated sample area pixel; (3) Sample dehumidification test: place the sample plate and the sample in a moisturizing container with a given relative humidity, and collect the total mass data of the sample plate and the sample at regular intervals. m i , i ≥1, i The number of times is indicated, and the area and height images are collected until the mass change of the sample soil under the relative humidity condition within 48 hours is less than 0.01g; (4) Calculate relevant data during the dehumidification process of the sample through mass change data and digital images; According to the initial volume V 0 , initial moisture content ω 0 , Sample mass at initial moisture content m ss , calculate the initial dry density of the actual soil sample ρ d0 = m ss / (1+0.01× ω 0 ) / V 0 ; According to the initial dry density of the actual soil sample ρ d0 Soil particle density G s , calculate the actual initial porosity of the sample n 0 The initial porosity ratio e 0 ,Right now n 0 =1- ρ d0 / G s , e 0 = n 0 / (1- n 0 ); According to the saturated volume of soil V sa and initial porosity ratio e 0 , calculate the volume of sample soil particles V s = V sa / (1+ e 0 ); According to the volume of soil particles V s and initial porosity ratio e 0 , calculate the pore volume of the sample V V = V s × e 0 ; According to the initial moisture content ω 0 Specific gravity of soil particles G s , initial porosity ratio e 0 , calculate the initial saturation of the sample S r0 = ω 0 × G s / e 0 ; According to the total mass of the sample plate and the saturated sample m b+sa And the total mass of the sample plate and dehydrated sample currently recorded m i , calculate the mass of remaining water in the current sample m wi = m b+sa - m i , i ≥1, i Indicates the number of times; Calculate the current sample volume based on the dehydrated sample digital image V i , i ≥1, i Indicates the number of times; According to the current sample volume V i Soil particle volume V s , calculate the current sample porosity e i = ( V i -V s ) / V s And the current sample porosity n i = ( V i -V s ) / V i , i ≥1, i Indicates the number of times; Assuming the density of water is ρ w =1 g / cm 3 , so the mass of the remaining water in the current sample is m wi The current remaining pore water volume V wi , according to the current residual pore water volume V wi Soil particle volume V s , calculate the current sample soil-water ratio R=V wi / V s , i ≥1, i Indicates the number of times; According to the quality of the remaining water in the current sample m wi , Current sample volume V i Soil particle volume V s , calculate the current saturation of the sample S ri = m wi / ( V i -V s )×100%, i ≥1, i Indicates the number of times; (5) Based on the data from step (4), a comparative analysis is conducted to plot the variation curves of void ratio, porosity, and volume strain with saturation, and the evolution law of void ratio and shrinkage rate with soil-water ratio is given.

2. The soil shrinkage characteristic curve calculation method based on digital image processing according to claim 1, Features: The sample dehumidification test of step (3) is repeated in moisturizing containers with different relative humidity, wherein when the relative humidity is greater than 85%, data is collected every 4 hours, and when the relative humidity is less than 85%, data is collected every 8 hours.

3. The soil shrinkage characteristic curve calculation method based on digital image processing according to any one of claims 1 to 2, Features: When the sample soil is pulverized soil, the evolution law of its porosity and shrinkage rate with the soil-water ratio is as follows: the shrinkage process of pulverized soil is divided into three stages, namely proportional shrinkage, residual shrinkage and zero shrinkage. When the soil-water ratio is less than 0.5, the shrinkage rate of pulverized soil tends to zero.

4. The soil shrinkage characteristic curve calculation method based on digital image processing according to any one of claims 1 to 2, Features: When the sample soil is clay, the evolution law of its porosity and shrinkage rate with soil-water ratio is as follows: the shrinkage process of clay is divided into three stages, namely proportional shrinkage, residual shrinkage and non-zero shrinkage. Unlike silt, clay has an obvious non-zero shrinkage stage, and the shrinkage rate in the residual shrinkage stage is higher. When the soil-water ratio is less than 0.1, the shrinkage rate of clay still increases.

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