Recent progress in the understanding of some fundamental issues associated with deep seated landslides from massive rock slope failure, i.e., slow to extremely slow moving massive natural rock slopes characterized by failures deformation which occurs at great depth, is addressed in this lecture. The Beauregard Landslide located in northwestern Italy in the Aosta Valley (Dora di Valgrisenche river) forms the reference case study. The interest stems from the presence, at the toe of this extremely slow moving landslide, of a concrete arch gravity dam which is being continuously loaded and has caused some closure of the arch with deformation and cracking developing on the downstream side. The discussion is on advanced laboratory testing of rock samples taken at depth along the basal sliding surface of the landslide, slope monitoring by state of the art approaches such as ground based interferometric synthetic aperture radar (InSAR), and numerical modelling developed and calibrated to simulate the behaviour patterns observed through monitoring. It is shown how these studies have contributed to the understanding of the underlying mechanisms and behaviour of deep-seated landslides. The aim is to gain the necessary confidence in predicting the likely development scenarios, assessing risk, and finding possible preventive/remedial measures.
Deep-seated landslides from massive rock slope failure (MRSF) are slow to extremely slow moving massive natural slopes characterized by failures deformation which occurs at great depth in excess of 100 m and up to 250–300 m [1], [2]. In cases such deformation takes place along a basal sliding surface which is described as a zone of sheared and cataclastic rock, locally reduced to a soil-like material with silt and clay. Deep-seated landslides are also known as deep-seated gravitational slope deformations (DSGSD), which occur on high relief energy hill-slopes, with size comparable to the whole slope, and with displacements relatively small in comparison to the slope itself. DSGSD exhibit on the ground surface typical morphologic and structural features such as double ridges, ridge depressions, scarps and counterscarps, trenches, and open cracks, etc. [3]. Triggering and causal mechanisms of these landslides include post-glacial slope unloading and changes in ground water flow, regional tectonic stresses, earthquake ground shaking, fluvial erosion at the toe, etc. The importance of deep-seated landslides is that they occur in many parts of the world, are considered to be a major geological hazard, and impact very significantly on infrastructures and on society [4]. It is to recognized that many aspects of deep-seated landslides are poorly understood and need be investigated in order to gain the necessary confidence for anticipating and predicting their behaviour, assess the risk, and find possible preventive/remedial measures. This is indeed due to the many complexities of the phenomena involved which encompass the understanding of the underlying mechanisms, the initial and post failure behaviour, and the different secondary processes resulting from instability [2]. In this lecture we will be principally concerned with the understanding of the underlying mechanisms and initial behaviour of deep-seated landslides.
