Landslide hazard evaluation by means of several monitoring techniques, including an acoustic emission sensor

At Passo della Morte in the Italian Eastern Alps a geomorphological survey has identified potential instability of the valley side slope that could result in a debris/rock avalanche, which would threaten the Tagliamento River. A nationally important road passes through a tunnel 130 m long behind the potentially unstable slope. The stratum comprises a sequence of Limestone layers, dipping in the slope direction towards the river. Although currently there is no clear evidence of movement, the geological setting indicates a predisposition to instability that could involve a large landslide and extremely fast deformations can be foreseen. To appraise the physical characteristics of the rock mass and to provide an early warning of instability, monitoring instrumentation has been installed and monitored since late 2010. Extensometers, MEMS, TDR cables, a ver-tical inclinometer, a seismic station to monitor Limestone rock mass deformation generated micro-tremors and an acoustic emission (AE) monitoring system have been installed. The instruments are connected to real-time recording and transmitting units. The paper describes the geological setting and associated potential modes of instability. It details the design of the instrument installations and presents results obtained to date. In particular, the novel acoustic emission monitoring approach is described including sensor design, method of operation and comparison of the measured AE response with the deformation measurements and detected micro-tremor trends. Initial results indicate a strong response of the acoustic sensors to rainfall events. No sig-nificant rock mass deformations have been detected at depth within the slope to date, although a surface ex-tensometer has shown widening of a bedding tension crack. Upgrading of the instrumentation system is ongo-ing and it is planned to continue monitoring for the foreseeable future.