All specimens were initially compacted at the optimal water content of 24% and the dry density of 1.55 g/cm 3. The relative density is 2.71, liquid limit is 58.5%, and plastic limit is 22.8%. Particles with the diameter less than 0.05 mm account for 85% of the total weight. The soils were ground and sieved to 2 mm. The expansive soils are collected from a channel slope in the location of South-to-North Water Transfer Project in Nanyang city, China (Longitude: 112.52, Latitude: 33.00). One kind of disturbance functions for soil disturbed state strength, D 1, may be defined using the MD values as The MD value represents the relative average density of the scanned sample section and the SD value represents the inhomogeneity of the density for the same section. There are two quantifiable values from CT images: mean or MD value and standard deviation or SD value. The X-ray computed tomography provides an insight into the soil structure to evaluate the evolution of pores or fractures using the image analysis. In the recent decade, CT had been widely used to evaluate the evolution of the internal structure of soil by several researchers including Oda et al. The CT technique was first used in soil science by Petrovic et al. It is well known that this CT-value, equal to the MD, is linearly related to material density. CT images are presented with a shaded gray for low CT-value and light gray for high CT-value through the black to white range. Thus, the CT value of air should be -1000 because the coefficient of absorption for air is zero. Where μ i is the coefficient of absorption at the scanning point, μ w is the coefficient of absorption for water. While, the disturbance function defined by the MD value has often been used to characterize a rock damage. Therefore, the disturbance function expressed in terms of the SD value is deemed more reasonable and appropriate in analyzing the soil disturbed state strength using the quantitative CT morphometry. However, the MD value and its defined disturbance function have no regularity with the macro-pore size. As with the shear strength, the SD value and its defined disturbance function have a similar correlation with the cross-sectional area of macro-pore. It is found that the shear strength of three disturbed samples with the same macro-pore size is close to each other. Two types of disturbance functions are investigated quantitatively by CT-triaxial testing using four samples with different macro-pore sizes (disturbed samples) and one sample without a macro-pore (undisturbed sample). Two different quantifiable values from X-ray computed tomography (CT) images are usually used to define the disturbance function for soil disturbed state strength: mean density ( MD value) and standard deviation ( SD value).
These phenomena greatly affect the strength of soil and the degradation of land. Soil is a porous, multiphase, and loose medium, which is prone to serious disturbance by the activity of biological livings, accompanied with cracks and macro pores.
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