Rock Slope Stability of the Cretaceous Izumi Group

The Upper Cretaceous Izumi Group in the vicinity of Naruto Strait, consists mainlyof sandstone and shalealternation and shows the monoclinic geologic structure. Well stratified bedding plane forms a distinct geologicdiscontinuous plane, developing cross joints nearly perpendicular to the bedding plane.The authors studied both a theoretical simple slope model by TERZAGHI and the actual conditions of manyroad cuts. Stability of stratified Izumi Group depends primarily on the bedding plane orientation with referenceto the slope. Further, slope stability is affected by continuous joints and small faults which is difficult topredict its presence before cutting.