ABSTRACT:
Slope deformation of deep-seated rock slides in crystalline rock is often characterized by phases of acceleration and deceleration. In some cases, these phases of low and high activity show a velocity difference of three orders of magnitude. Such slopes appear to present a hazard to inhabitants and infrastructure in the valleys below, but much uncertainty exists as to the nature of the observed episodic behavior and eventual deceleration and selfstabilization of the moving mass following periods of high acceleration, and whether such behavior will continue into the future or whether the potential for a brittle-type, rapid catastrophic failure exists. This paper presents two case studies from the Austrian Alps where the time-dependent/episodic behavior of two well monitored rockslides is analyzed, and the possible mechanisms contributing to their ability to re-stabilize are discussed.
1 INTRODUCTION
Deep-seated rockslides located in Northern Tyrol (Austria) were investigated to study their kinematics and deformation behavior. Generally, rockslides are characterized by deformation along one or several shear zones where most of the measured total slope displacement localizes. Such shear zones contain fault breccias or gouges i.e. material that is newly formed through cataclasis and fragmentation of the rock during deformation and shearing, and which possesses soil-like mechanical properties. In some cases, rockslide rupture surfaces have been observed to form through the reactivation of favorably orientated pre-existing brittle fault zones of tectonic origin. The tectonically formed fault breccias or gouges in these cases act to fully or partly reduce the shear strength along the sliding zone. Less frequently, case studies have been presented where a heavily fractured rock slab has slid onto glacial deposits located on the lower half of the slope, suggesting slip magnitudes of several hundred meters (Brückl et al. 2004, Tentschert 1998, Lauffer et al. 1967).
