Towards rockfall forecasting through observing deformations and listening to microseismic emissions

Abstract

Abstract. Reliable forecasting of rockfall is a challenging task, mainly because of the lack of clearly noticeable forerunners as well as due to the geological and geo-mechanical complexity of the rock movements involved. Conventional investigation devices still present some drawbacks, since most measurements are generally carried out at isolated locations as well as on the surface only. Novel remote-sensing monitoring instruments, such as Terrestrial Laser Scanning (TLS) and Ground-Based Interferometric Synthetic Aperture Radars (GB-InSAR), are capable of inspecting an unstable slope with a high spatial and temporal frequency. But they still rely on measurements of the failure surface, from which displacement or velocity are measured. On the contrary, acoustic emission/microseismic monitoring may provide a deeper insight of stress and strain conditions within the subsurface rock mass. In fact, the capability to detect microseismic events originating within an unstable rock mass is a key element in locating growing cracks and, as a consequence, in understanding the slide kinematics and triggering mechanisms of future collapses. Thus, a monitoring approach based on the combination of classical methodologies, remote sensing techniques and microseismic investigations would be a promising research field. In the present paper we discuss the technologies and we illustrate some experiments conducted in the framework of a project whose final goal is the installation of an integrated monitoring and alerting system on a rockface nearby Lecco (Italy). In particular, we present a review of performances and applications of remote sensing devices and some results concerning a terrestrial laser scanner preliminary campaign. Then, we report findings regardCorrespondence to: L. Longoni (laura.longoni@polimi.it) ing amplitude, frequency content and rate of signals recorded during an in situ test carried out to evaluate the performance of three different microseismic transducers.

Remote Sensing for Landslide Investigations: An Overview of Recent Achievements and Perspectives

“…In other cases, the instrument is placed only for a limited period to cope with emergency situations [199]. Other authors have investigated the integration of GBSAR to other sensors (e.g., with TLS, see [200]) to gather observation on both surface and subsurface [201].…”

“…According to Abellán et al [215], only a few research works used TLS to study precursory signs in the period prior to the final collapse. These mainly entail the detection of some precursory rock fall events [228,229], the measurement of pre-failure deformation [218], or the observation of micro-seismic events [119,201,230]. In fact, increase of fragmental rock fall activity might be a precursory signal of major events (see, e.g., [228]), while decrease might be a sign of stabilization [229].…”

A custom acoustic emission monitoring system for harsh environments: application to freezing-induced damage in alpine rock walls

“…In the context of rock fall hazard surveillance, for example, the AE technique was reported to have the highest potential for subsurface monitoring compared to other existing methods (Arosio et al, 2009). The requirements of such an application are already fulfilled by our measurement system; a network of spatially distributed AE-nodes could be used to monitor the critical or unstable positions of the rock wall, providing reliable data in near real-time.…”

Analysis of microseismic signals and temperature recordings for rock slope stability investigations in high mountain areas

“…As a result, a better comprehension of the failure process and of the precursory patterns leading to collapse is nowadays made possible (e.g., Senfaute et al, 2003;Amitrano et al, 2005;Shiotani et al, 2006). Many efforts have consequently been devoted to the development of reliable rock slope monitoring systems based on this approach (Senfaute et al, 2009;Arosio et al, 2009;Levy et al, 2011).…”