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

Alpine landslide risk scenario: run-out modelling using a 3D approach

Rockslides of considerable volume developing on the flanks of narrow alpine valleys represent a significant hazard for the potential of river damming and consequent sudden discharge of water. A limestone rock mass of about 650,000 m3 endangers a portion of the upper course of Tagliamento River valley in north-eastern Italy. This section of the valley is prone to detachment of rock landslides due to its structural setting and it has a history of landslide damming: in the literature two huge events are widely documented and a third event is identified and described in this paper. The ancient detachment crown and the corresponding deposit can be observed in the portion of slope adjacent to the unstable rock mass. This paper deals with the run-out model of the unstable rock mass using a Smoothed Particles Hydrodynamics (SPH) model implemented in the DAN3D code. In order to select the appropriate material parameters, the ancient rockslide was back-analysed. Subsequently, the parameters were applied to the present unstable portion of the slope to determine the location and dimensions of the deposit that could be formed. It is demonstrated that the deposit has the potential to create a natural dam across the Tagliamento River that would form a 500,000 m3 lake. Although the lake will have limited dimensions, this would represent a very high risk for the downstream villages and infrastructures in case of a sudden collapse of the natural dam

Strategies for rock slope failure early warning using acoustic emission monitoring

Research over the last two decades has led to development of a system for soil slopes monitoring based on the concept of measuring Acoustic Emission (AE). A feature of the system is the use of waveguides installed within unstable soil slopes. It has been demonstrated that the AE measured through this technique are proportional to soil displacement rate. Attention has now been focused on the prospect of using the system within rock materials. The different nature of the slope material to be monitored and its setting means that different acoustic trends are measured, and development of new approaches for their interpretation are required. A total of six sensors have been installed in two pilot sites, firstly in Italy, for monitoring of a stratified limestone slope which can threaten a nationally important road, and secondly in Austria, for monitoring of a conglomerate slope that can endanger a section of the local railway. In this paper an outline of the two trial sites is given and AE data collected are compared with other physical measurements (i.e. rainfall and temperature) and traditional geotechnical instrumentation, to give an overview of recurring AE trends. These include clear AE signatures generated by stress changes linked to increased ground water levels and high energy events generated by freeze-thaw of the rock mass