All cut slopes gradually deteriorate for a long time after excavation. Anticipating the change in the rock mass before cut slope is essential in terms of safety maintenance. However, it is unusual to verify the prior evaluation and estimation excepting cases where problems occurred. Therefore, the precise prediction of the deterioration before a serious accident is one of the main subjects for geotechnical engineers. This paper describes the process and results of the research concerning deterioration analyses of the rock slope site, based on the discontinuity survey.
The study area is located in the mountainous district of the northeast Hokkaido, Japan, which is mostly composed of Pliocene welded tuff categorized as medium-hard rock in geotechnical engineering. Our investigation site is a rock slope where jointed bedrock of the welded tuff exposes to a roadside. The rock slope had been in danger due to opening of discontinuities and overhanging rocks, therefore, it was excavated up to 70m high for the stabilization in 1998.
For the purpose of this study, borehole drilling and borehole scanning at two locations (upper and lower slope) were carried out in 2004 and 2012. Measured dip and dip direction data of discontinuities have been plotted on stereographic projections to analyze kinematically the changes of the rock slope.
As a result, almost no change has been identified in case of the upper slope, while significant changes have been observed in the lower slope case of 2012 due to the shear strength increased by the excavation.
