Giovanni B. Crosta

Professor (Università degli Studi di Milano, Italy)

Editor in Chief of Engineering Geology (2005 – 2013)

报告主题：Comprehensive study of a rapid moving rock slide: the Mt de la Saxe landslide

报告时间：2013/5/3(周五)上午10:45 – 12:00

报告地点：岩土楼201

Prof. Crosta’s main research interest is in landslide mapping, hazard and risk analysis, slope stability and monitoring, soil and rock mechanics. His main research topics are: deep seated slope deformations; slope hydrology; rock avalanche and debris flow analysis and modeling; use of rain fall records and monitoring data for setting up failure thresholds in Early Warning Systems; development of methods for quantitative hazard and risk assessment. He teaches courses in Engineering geology, Hydrogeology, Slope stability and applied geomorphology, numerical modeling.
 

报告摘要：
Rockslides in alpine areas can reach large volumes and, owing to their position along slopes, can either undergo large and rapid evolution originating large rock avalanches or can decelerate and stabilize. As a consequence, in particular when located within large deep seated deformations, this type of instability requires accurate observation and monitoring. In this presentation, the case study of the La Saxe rockslide (ca 8*106 m3), located within a deep seated deformation, undergoing a major phase of acceleration in the last decade and exposing the valley bottom to a high risk, is discussed. To reach a more complete understanding of the process, in the last 3 years, an intense investigation program has been developed.  Boreholes have been drilled, logged, and instrumented (open pipe piezometers, borehole wire extensometers and inclinometric casings) to assess the landslide volume, the rate of displacement at depth, and the water pressure. Displacement monitoring has been undertaken with optical targets, a GPS network, a ground-based interferometer, and four differential multi-parametric borehole probes. A clear seasonal acceleration is observed related to snow melting periods. Deep displacements are clearly localized at specific depths. GB-InSAR ground surface monitoring data are acquired, extracted and analysed to understand rockslide behavior and to zone it in areas with different behaviour. Subsurface displacement monitoring allows to stress the sensitivity of the rock slide to snow melt and the type of displacements. Groundwater flow and stress – strain modeling are performed to understand slope hydrogeological conditions and to test possible future scenarios. The analysis of the piezometric and snowmelt data and the calibration of a 1D block model allows the forecast of the expected displacements. To this purpose, a 1D pseudo-dynamic visco-plastic approach, based on Perzyna's theory, has been conceived. The viscous nucleus has been assumed to be bi-linear: in one case, irreversible deformations develop uniquely for positive yield function values; in a more general case, visco-plastic deformations develop even for negative values. The model has been calibrated and subsequently validated on a long temporal series of monitoring data and it seems reliable for simulating the in situ data.