Abstract:Alternating actions of excavation and unload have a very important influence on deformation and instability of high and steep bedding rock slopes with upper steep and lower gentle style, which are widely distributed i in China's western regions. Taken the high and steep bedding rock slopes belonging to Jianshan phosphorite mine, Yunnan phosphate group Co., Ltd as engineering background, model experiment had been conducted on the basis of similarity theory, alternating actions of excavation and unload effects on their deformation and instability were investigated. Research results showed that: deformation displacements of high and steep bedding rock slopes with upper steep and lower gentle style progressively becomes larger with depth of excavation gradually increasing. Its integral deformation laws are that upper slope moves downward, while lower part uplift to the free surface due to compression. At the same time, when the excavation is to a certain depth, many strike cracks can be developed into the slope, then they continuously extended to the slope body in pace with increasing excavation depth; during the whole process of excavation, potentially most dangerous slip surface of composite-style with plane and circular arc surface have be developed gradually into the slope, and deformation and instability characteristics of slip—bending—shear style have be shown; although the deformation of the slope is reduced, the trend of deformation and instability of slope is not changed, so the shallow unloading effect is not ideal, while deep unloading effect is very obvious and cracks in the slope almost completely eliminated. Research achievements play a reference guiding role for early warning and forecast and control design of high and steep bedding rock slopes.