Experimental Study On Saturated- Unsaturated Hydraulic Characteristics Of A Single Random Crack

The current studies on landslide are usually based on the continuum assumptions and ignoring the existence of cracks. The presence of cracks can provide preferential channels for rainfall, can generate an extra slope sliding force and become parts of the slip surface. Therefore, it is necessary to investigate the characteristics and the hydraulic properties of the crack. Soil samples are prepared in laboratory and the cracks formed during drying-wetting cycles. Then the crack aperture and the number of cracks are qualitatively and quantitatively analyzed. Finally the soil-water characteristic curves and the coefficient of permeability for a single crack are obtained using lab tests.The main contents are as the following:(Ⅰ) According to the nature of the soil as well as the practical engineering conditions, the soil samples are prepared by mixing different proportions of montmorillonite with the kaolin soil. Then some physical properties of the soil are determined according to the standard soil test methods. The crack development is observed after compacted, and then the mean, standard deviation and correlation distance are analyzed. The influences of water content, different montmorillonite proportions, the number of drying-wetting cycles and the size of the soil sample are analyzed.(Ⅱ) A device is developed to obtain the soil-water characteristic curves for a single crack. Then the device is used to measure the soil water characteristic curve of a man-made random crack. The random crack is used to simulate natural crack and it has a certain average width, standard deviation and correlation coefficient. The test results shown that the single crack would lose most of water and reach a residual water content under very low suctions. Then the soil-water characteristic curves are measured for the cracks with different mean aperture values. Result show that with the increase of crack aperture, its air entry value decreases and the residual water content dropped.(Ⅲ) A device for measuring the saturated coefficient of permeability is developed for a single crack. The saturated coefficient of permeability of the man-made crack is determined using the device. The test results show that the saturated coefficients of permeability for a single crack increase with the increasing of the aperture of the crack. The saturated coefficients of permeability increase linearly with the increasing of the hydraulic gradient, which indicate that the Cubic Law can be applied to describe the flow in a single random crack.