STUDY ON DEFORMATION AND FAILURE MODES OF RED LAYER SLOPE IN ENSHI BASIN

The red beds is wide distributed in Enshi Basin with a large number of slopes or man-made high and steep slopes. Because of the specialities of the engineering geological properties, the deformation and failure of the slopes under the natural geological process and human engineering activities always cause casualties and property losses, which has greatly influences and restrictions on the construction of urban municipal engineering and road engineering. According to the field engineering geological investigation, drilling, field test (water pressure and infiltration test), sample collection and laboratory rock mass parameters test, the engineering geological property, hydraulic characteristics and slope deformation characteristics of red beds are investigated. The red beds in Enshi Basin can be divided into "hard sandstone" and "soft sandstone", the former ones are relatively impermeable layers composed by better consolidated silt-stone and sandstone with high strength, lower permeability; the latter ones are aquifer layer composed by poor consolidated sandstone with low strength, strong permeability. The scale of deformation and failure of slope is small, but the quantity is big and the harmfulness is heavy. This paper have researched on the deformation and failure mode of slopes from two aspects:the motion mode and influencing factors. According to the movement modes of the slope rock mass, the deformation and failure of the red bed slopes are divided into three kinds:the bedding rock landslide, the falling collapse, and the dumping collapse. Based on the deformation and failure influencing factors, the deformation and failure of the slopes also are divided into three kinds:soft and hard sandstone layers with different weathering functions, the disadvantageous combination of the bedding planes and the cutting structure planes, the artificial excavation disturbance. The characteristics and the processes of the various types of deformation and failure modes are analyzed, which has significant guiding and reference value for the prevention and control of the deformation and damage of the red bed slopes in Enshi Basin and areas of the same kind.