Stefano Utili   Dipl(Eng) MSc PhD CEng MICE

Associate Professor (University of Warwick, United Kingdom)

报告主题：The use of the limit analysis upper bound method to gather new findings on the stability of slopes

报告时间：2013.5.3(周五) 上午9:30 – 10:45

报告地点：岩土楼201

Dr. Stefano Utili is currently Associate Professor of geotechnical engineering in the School of Engineering at the University of Warwick, United Kingdom. From 2008 to 2011 he was Lecturer (Assistant Professor) at the University of Oxford, Department of Engineering Science. From 2006 to 2008 he was Post-doctoral research Fellow at Strathclyde University (Glasgow, UK). From 2004 to 2006, he worked in the industry which allowed him to become a Chartered full member of the ICE (Institution of Civil Engineering). He is visiting Professor at Politecnico di Milano (Milano, Italy). His main research interests are: modelling of lunar soil, interaction soil-pipeline, modelling of landslides and debris flows in terrestrial and Martian environments, the extension of the DEM to non-spherical particles, optimisation of shot peening parameters. Currently, he is supervising a group of 8 PhD students. (Personal website: http://www2.warwick.ac.uk/fac/sci/eng/staff/su/ )

报告摘要：The presentation is about recent findings on the influence of cracks on the stability of slopes. The stability of homogeneous slopes with cracks is investigated by the kinematic method of limit analysis, providing rigorous upper bounds to the true collapse values for any value of engineering interest (i.e. slope inclination, depth and location of tension cracks). Previous stability analyses of slopes with cracks are based mainly on limit equilibrium methods, which are not rigorous, and are limited in their capacity for analysis, since they usually require the designer to assume a crack depth and location in the slope. Conversely, numerical methods (e.g. finite-element method) struggle to deal with the presence of tension cracks in the slope, because of the discontinuities introduced in both the static and kinematic field by the presence of such cracks. In this presentation, solutions are provided in a general form considering cases of both dry and water-filled cracks.
Critical failure mechanisms will be illustrated for: i) cracks of known depth but unspecified location, ii) cracks of known location but unknown depth, and iii) cracks of unspecified location and depth. The upper bounds are achieved by assuming a rigid rotational mechanism (logarithmic spiral failure line). It is also shown that the results provide a significant improvement on the currently available upper bounds based on planar failure mechanisms, providing a reduction in the stability factor of up to 85%. Implications for the design of slopes will be explored. An example of application of the limit analysis method is provided concerning the stability of the walls in Valles Marineris in Mars. Using limit analysis the range of cohesion and friction angle values associated to realistic failure geometries were explored and predictions compared with the more classical Culmann's translational failure model. The analysis is based both on synthetic, simplified slope profiles, and on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles, the estimated failure surface geometry and ridge crest retreat. This offers a link between rock mass properties, slope geometry and volume of the observed failure, represented in dimensionless charts. The role of groundwater flow and seismic action on the decrease of slope stability is also estimated. Pseudo-static seismic analyses provide another set of dimensionless charts and show that low seismicity events induced by meteoroids impacts, compatible with the size of craters, could be a cause for some of the observed landslides, if poor rock properties for VM are assumed. Analyses suggest that rock mass properties are more similar to their earth equivalents with respect to what has been previously supposed.