Palestrante Confirmado – COBRAMSEG
Prof. Eduardo Alonso
Palestra: Triggering and motion of landslides
His main research interests have focused on stochastic analysis of soil heterogeneity, unsaturated soil mechanics, rockfill mechanics, coupled thermos-hydro-mechanical analysis and some chemo-mechanical interactions.
He has maintained over the years a special interest in landslide phenomena, a fascinating subject which receives attention in engineering geology, rock mechanics and soil mechanics. Recently he has contributed to the development of new computational techniques, the Material Point Method in particular, capable of addressing the static and dynamic aspects of landslide instability.
He has lectured in many countries and he has also acted as a consultant in a variety of geotechnical engineering projects in several countries. He is member of the Royal Academy of Engineering of Spain and he is the immediate past editor of ICE journal Géotechnique. Past honorary talks include Coulomb, Buchanan, Sowers, Croce, Heim, Kezdi, Rocha, BGA Touring, Rankine and Leonards lectures.
Resumo da Palestra
At the other extreme of landslide mobility, slow creeping motions are often found in natural and man-made environments. A relevant question is their evolution in time and the risk for a sudden acceleration. This question will be addressed for some sliding mechanisms.
Generalization to arbitrary geometries will be done by means of a calculation procedure, the Material Point Method, which was formulated for a three-phase granular medium. This computational tool, in the domain of continuum mechanics, provides also the opportunity of examining the transition from static impending failure to the subsequent dynamic motion. The material point formulation was adapted to incorporate thermal water pressurization in shearing surfaces generated by strain localization. The implication of this phenomenon, which enhances landslide mobility, will be discussed.
The lecture closes with a critical examination of the advances described and the prospects for improvements in predicting landslide mobility.
Limited heights of vertical cliffs and mountain walls linked to fracturing in deep tunnels – Q-slope application if jointed slopes
Nick Barton was born in England in 1944. He was educated in the University of London from 1963 to 1970: with B.Sc.(hons) in civil engineering from King’s College, and a Ph.D. in rock slope stability from Imperial College. He worked in NGI, Oslo from 1971-1980, and from 1984-2000, when he was a division director for 5 years and Technical Advisor for 10 years. From 1981-1984 he was manager of Geomechanics at TerraTek in Utah, USA. He was a visiting professor in the University of Luleå in Sweden, and in São Paulo Polytechnic University in Brazil in the nineteen-nineties. In 2000 he established the international consultancy Nick Barton & Associates in Norway. He is author and co-author of 310 papers, and has written two books. The first in 2000 was to develop the QTBM prognosis, the other in 2006 was to link rock quality and seismic attributes of rock masses at all scales. In 1973 he developed the Barton shear strength criterion linking joint roughness JRC and joint wall strength JCS, subsequently incorporating the gravity tilt test for calculating JRC. He is co-developer of the Barton-Bandis criterion for modelling coupled rock joint behaviour, published in 1982. In 1974 he developed the Q-system for characterizing rock masses and for selecting single-shell tunnel and cavern support. This was updated in 1993 with Grimstad to incorporate S(fr). He has consulted on several hundred rock engineering projects in 38 countries during the last 45 years, involving hydropower and metro tunnels and caverns, large dams, nuclear waste research, rock stress measurement, and jointed reservoir behaviour. He has ten international awards, including the ISRM 6th Müller Lecture in 2011. He is an honorary doctor of University of Cordoba, Argentina, and a Fellow of ISRM.
Resumo da Palestra
Intact brittle rock can fail in tension even when all principal stresses are compressive. This is due to lateral expansion and extension strain when near to a free surface, caused by Poisson’s ratio. Exceeding tensile strength due to stress anisotropy and Poisson’s ratio are the fracture-initiating conditions around deep tunnels, not the increasing mobilization of compressive strength, commonly beyond 0.4 x UCS. In a related discovery, the limiting height of vertical cliffs and near-vertical mountain walls can also be explained using extension strain theory. The range of limiting heights of approximately 20m for cliffs in porous tuff to record 1,300m high mountain walls in granite are thereby explained. Tensile strength is the weakest link behind cliffs and ultra-steep mountain walls. Sheeting joints can also be explained by extension strain theory. Maximum shear strength is the weakest link when stress levels are ultra-high, or when there is jointing and maximum slope angles is the issue. Here one can use Q-slope. The world’s highest mountains are limited to 8 to 9km. This is due to non-linear critical state rock mechanics. It is not due to UCS.