Abstract
Transparent porous media combined with digital image processing technology can be used to quantify the saturation of local fluids. In this regard, the calibration relationship between the pixel intensity of the image and the saturation of the wetting liquid is the crucial premise for whether this technique can be promoted and applied, and it is also a bottleneck that limits whether this technique can be rapidly and extensively developed. However, owing to gravity‐driven effects, wetting liquid in a residual state usually exhibits an irregular boundary caused by the phenomenon of saturation overshoot, which makes it very difficult to use the previous overflow method to obtain the data pair of saturation‐pixel intensity accurately. To this end, we have made some improvements to the specific testing method for wetting liquid saturation in the residual state and proposed a local centrifugal sampling method, which considerably improved the accuracy of this method. The results show that the relationship between the pixel intensity and saturation of the transparent soil obtained through this method is generally consistent with the regularity of the previous calibration method but shows better correlation. The results of this study will drive further potential application of transparent soil in the flow of partially saturated porous media.
Highlights
Soil water content is a key variable in understanding the hydraulic behavior and hydrological processes of unsaturated soils in seepage areas [1,2,3]
Transparent soil consisting of refractive index- (RI-) matched solid particles and pore fluids has become a powerful tool for investigating many geotechnical and global environmental engineering problems [9,10,11,12]
Centrifugation was carried out to obtain the oil-sand mass ratio w of the samples to determine the degree of saturation. is operation relieves the otherwise strict condition that the initial water content must be at 100% saturation when employing the conventional overflow method and overcomes the difficulty that the residual moisture content cannot be quantified due to the nonuniformity of boundary conditions in the seepage process
Summary
Soil water content is a key variable in understanding the hydraulic behavior and hydrological processes of unsaturated soils in seepage areas [1,2,3]. Erefore, the disturbance of sample digging has no influence on the calculation of the void ratio In essence, this method is used to measure local water content, similar to a moisture sensor, but more efficient as it obtains the average water content in an entire area, not just for a single point, which is more suitable for this test condition. E operation is to subtract the average pixel intensity value obtained in the previous step from the background, which is a systematic coordination processing between the pictures based on the black and white reference dots. Camera settings were carefully selected to ensure that the images of black and white reference dots are not pixel intensities of 0 or 255, respectively, (not pure black or white) to ensure that the intensity values measured near these extremes are not truncated [23]
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