Geological, geophysical and geotechnical investigations into the internal structure and kinematics of an unstable, complex sliding mass in crystalline rock

摘要

Slope instabilities in massive crystalline rock are controlled by the internal structure of the rock mass which can be very complex. To understand the processes controlling the instability, it is necessary to identify the active discontinuities which govern the internal deformation, and to describe the kinematics of the unstable rock mass. In this paper we present results of a detailed analysis of the active features within an unstable gneissic rock mass of several million cubic meters volume from the Swiss Alps. The 3-D distribution of discontinuities within the rock mass was assessed using surface mapping and optical televiewer logs run in three boreholes drilled to depths of between 50 and 120 m. The subset of active fractures was identified from various types of surface displacement measurements and from surveys of inclinometer/extensometer casing installed in the boreholes. The active discontinuities were found to correspond to the major fractures which belong to an extensive network. Radar reflection profiles run in the boreholes showed that these active fractures extended significant distances from the borehole, in one case at least 49 m. Active fractures were found to be better reflectors of radar signals than inactive ones. The integration of all results was used to build a kinematic model describing the ongoing internal deformation of the rock mass.