Effects of heterogeneities of soils on the stability of slopes

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The purpose of this study was to investigate the effects of soil heterogeneities such as surface crusts, cracks, traffic pans, hard pans, macropores due to activities of plant and soil animals and artificial soil cuttings and bankings on the stability of slopes. The following three conclusions were obtained :1. REFRACTION OF FLOW OF WATER IN LAYERED SOILSIt is well known that stream lines in saturated layered soils refract at the interface between two media having different hydraulic properties, but the behaviour of stream lines in layered unsaturated soils were vague. This study clarified the physical properties of refraction of water flow in unsaturated soils theoretically and experimentally. The visualization technique was developed to verify the refraction law in saturated and unsaturated layered soils.2. PREFERENTIAL FLOW IN HETEROGENEOUS SOILSPreferential flows were classified into bypassing flow, fingering flow and funneled flow. The physical properties of funneled flow were investigated experimentally by using 8 mm video camera, semiconductor pressure transducers and a dye and the qualitative and quantitative relation between the funneled flow and fingering flow was clarified. Saturated flow model and unsaturated flow model were applied to analyse the funneled flow.3. THE RELATION BETWEEN HETEROGENEITY AND STABILITY OF SLOPESThe effects of surface crust on flow of water and stability of slopes were investigated experimentally. The effect of preferential flow on the stability of a model slope was also investigated experimentally. Further investigations are required to make clear the theoretical aspects of the effects of soil heterogeneities and preferential flows on the stability of slopes.