An acoustic emission slope displacement rate sensor: Comparisons with established instrumentation

An acoustic emission slope displacement rate sensor: Comparisons with established instrumentatio

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

An acoustic emission slope displacement rate sensor — case studies

Research over a period of 20 years has resulted in development of a battery operated unitary acoustic emission (AE) sensor which, when used with a standard active waveguide installation, can quantify soil slope displacement rates continuously and in near real‐time. The active waveguide is installed in a borehole through existing or anticipated shear zones, and comprises a steel tube with granular soil surround. The AE sensor is located at ground level and with the waveguide is encased in a cover. Deformation of the slope strains the granular backfill, which generates AE through rearrangement of the particles. The AE propagate as stress waves along the steel tube to the ground surface where they are detected and quantified by the sensor, which is used to provide alert text messages if pre‐determined thresholds are exceeded. The use of a reproducible waveguide allows standard interpretation of the generated AE to provide information on soil slope displacement rates, and the granular soil backfill generates measureable AE when the system is installed in slopes formed in ‘quiet’ fine grained soils. The approach monitors AE at high frequencies to exclude environmental background noise and hence ensure that false alarms are not generated. In rock slopes, the grouted waveguide is passive, with measured AE generated by rock deformation mechanisms. The sensors have been deployed on multiple sites in the UK and in Italy, Austria and Canada. At all sites performance of the AE sensors has been compared with traditional deformation monitoring instrumentation including ShapeAccelArray, inclinometer, extensometer and time‐domain reflectometry. Measurements from these field studies have demonstrated that generated AE are proportional to slope displacement rates. This paper outlines the AE measurement and the interpretation techniques developed, and presents field comparisons of measured AE trends and slope displacement rates obtained from extended trials at several sites. It is concluded that the AE technique can be used as a reliable early warning system for soil slope instability. Applications in rock slopes are promising but further work is required to link detected AE to rock deformation mechanisms and hence to derive thresholds as a basis for early warnings