Geomechanics of Failures. Advanced Topics

Geotechnical failures, specially the catastrophic ones, are a stimulus to improve current understanding of phenomena and procedures and tools for analysis and prediction.

This unconventional approach to geomechanics is the essence of this book. In general, soil mechanics and geotechnical textbooks describe first the concepts and theoretical developments and then apply them to interpret or solve a particular applications. This book follows a different course. The case (a failure) is first described and then an explanation is sought. This requires a set of steps which can be summarized as follows: Identify the nature of the problem, develop a dedicated and specific formulation of the case, based on established basic concepts. In general, no single existing theory or procedure is available to solve the case at hand, provide a solution within an acceptable degree of complexity, extract the fundamental aspects of the problem and highlight its relevance.

The cases selected have been grouped into three main topics: Landslides, Embankments and Dams and Dynamics of Failures. Cases selected (Vaiont, Aznalcóllar, Brattas-St. Moritz) are unique and illustrate a number of relevant and to some extent controversial issues which are of wide interest, without claiming exhaustive treatment of the subject.

The book teaches how to build the necessary models to understand the failures. Well established soil mechanics concepts are the necessary background. But the cases analyzed require in general a step ahead which is specific for the case analyzed. Balance and equilibrium equations are often required as a starting point. They are formulated at different scales, which are selected having in mind the abstract representation of each case.

Various chapters illustrate also the coupled nature (flow-deformation-temperature) of geotechnical problems and the need to properly address these complexities in some cases. In fact, temperature effects, a subject often neglected in conventional analyses, are necessary to explain some catastrophic landslides (Vaiont). In some of the chapters, specific calculation tools, included in well known and widely available programs (Excel, Maple…) have been used. Details of the ad hoc programs developed have also been included in Appendices to help the readers to follow the details of the calculation.

Finite element methods have not been used. In the landslides analyzed (Vaiont and Brattas-St. Moritz) currently available commercial programs are of limited utility. In the remaining cases the analysis performed provides a sufficient insight and interpretation of field behaviour.

Chapters include also a short description of the changes in the original design and the mitigation measures which could have prevented the failure. Also, a summary section of lessons learned is provided in all chapters. Finally, selected topics and more advanced reading are suggested.

This book is associated with a Master/Doctorate course being offered at the Department of Geotechnical Engineering and Geosciences of UPC, Barcelona. Potential readers therefore include Graduate and Master students, faculty and professionals in the fields of Civil and Geotechnical Engineering.

Chapter 1 A Constrained Creeping Landslide: Brattas-St. Moritz Landslide, Switzerland; 1.1 Case Description; 1.1.1 Geometry, geology and displacements; 1.1.2 The teaning tower of St Moritz; 1.1.3 Chesa Corviglia; 1.1.4 The problem; 1.1.5 Long term stability and displacements; 1.2 The Theory; 1.2.1 Model assumptions; 1.2.2 Curve Fitting of Slope Displacements; 1.2.3 The Inverse Analysis Procedure; 1.2.4 The Safety Factor; 1.2.5 The Long Term Displacements; 1.2.6 The Time to Failure; 1.2.7 Summary; 1.3 Analysis of the Landslide ; 1.3.1 Geodetic measurements; 1.3.2 Simplified model ; 1.3.3 The safety factor ; 1.3.4 The long term displacements; 1.3.5 Discussion; 1.4 Analysis of the Leaning Tower; 1.4.1 Dilatometer Tests; 1.4.2 Leaning Instability; 1.4.3 Bearing Capacity ; 1.4.4 Discussion; 1.5 Mitigation Measures; 1.5.1 Stabilization of the leaning tower of St Moritz; 1.5.2 Stabilization of Chesa Corviglia; 1.5.3 Special Regulations for New Construction; 1.5.4 Defining Landslide Boundaries Using Fiberoptics ; 1.5.5 Monitoring of the earth pressure at the landslide bottom; 1.6 Lessons Learned; 1.6.1 Stability of Constrained Creeping Landslides; 1.6.2 Inverse Analysis; 1.6.3 Landslide Monitoring; 1.6.4 Stabilization of Structures ; 1.6.5 Environmental Factors and Landslide Stabilization; References; Chapter 2 Catastrophic Slide: Vaiont Landslide, Italy; 2.1 The landslide; 2.2 Geological setting; 2.3 The sliding surface; 2.4 Monitoring data before the slide; 2.5 Water pressures and rainfall; 2.6 A simple stability model; 2.6.1 Kinematics of the slide; 2.6.2 Two block model ; 2.6.3 Two interacting wedges; 2.6.4 Static equilibrium at failure; 2.6.5 Safety factors; 2.6.6 Landslide run out ; 2.7 Discussion; 2.8 Mitigation Measures; 2.9 Lessons Learned; 2.9.1 Slide reactivation ; 2.9.2 Impoundment of slide toe ; 2.9.3 Interpretation of field data ; 2.9.4 Computational procedures ; 2.9.5 Could it have been avoided?; Appendix 2.1 Safety Factor Fr. Solution of equation(2.30) ; Appendix 2.2 Global Safety Factor F; References; Chapter 3 Collapse of Compacted Soil: Girona Road Embankments, Spain; 3.1 Case Description ; 3.1.1 Questions asked; 3.1.2 Soil properties; 3.2 Collapse in practice; 3.2.1 Collapse of natural and compacted soils; 3.2.2 Rockfill collapse ; 3.3 Description of collapse and its modeling; 3.3.1 Effective stress; 3.3.2 Isotropic yielding of unsaturated soils; 3.3.3 Developing a simple model for collapse calculations; 3.3.4 Calculating loading and wetting strains; 3.3.5 Flow and collapse modelling; 3.4 Modelling the collapse of Girona road embankments ; 3.5 Results; 3.5.1 Discussion; 3.6 Mitigation Measures; 3.7 Lessons Learned; 3.7.1 Compaction on the dry side; 3.7.2 Natural collapsible soils; 3.7.3 Suction and stress variables; 3.7.4 The nature of collapse; 3.7.5 Capillary rise; 3.7.6 Modelling collapse; 3.7.7 Coupled flow-deformation; 3.7.8 Predicting the future behaviour of embankments; 3.8 Advanced Topics ; Appendix 3.1. Solving the coupled flow-deformation equation of the collapsing embankment; References; Chapter 4 Earth Dam Sliding Failure: Aznalcóllar Dam, Spain; 4.1 The Failure; 4.2 Geotechnical Properties of Tailings and Foundation Clay; 4.3 Water Pressures and Stresses in the Foundation; 5.3.1 A simple calculation model and its implications; 4.4 Limit Equilibrium Analysis; 5.4.1 Backanalysis of failure; 5.4.2 Undrained analysis; 5.4.3 Three dimensional effects. The role of bedding planes; 4.5 Discussion; 4.6 Mitigation Measures; 4.7 Lessons Learned ; 5.7.1 Soft clay rocks, hard clay soils; 5.7.2 Embankment loading; 5.7.3 Brittleness and progressive failure; 5.7.4 Bedding planes, discontinuities and tectonics; 5.7.5 Operating strength; 5.7.6 Construction procedure; 5.7.7 Pore pressures; 5.7.8 Undrained vs drained analysis; 4.8 Advanced Topics ; References; Chapter 5 Thermo-Hydro-Mechanics of a Rapid Slide: Vaiont Landslide, Italy; 5.1 Introduction; 5.1.1 A cheap laboratory heating experiment; 5.1.2 An

Eduardo E. Alonso, born in 1947, got his degree in Civil Engineeering (Ingeniero de Caminos, Canales y Puertos) in Madrid in June 1969. He got a PhD in Northwestern University in 1973. At present he is Professor of Geotechnical Engineering at the UPC in Barcelona. He is the author of more than 300 papers published in Proceedings of Conferences and learned journals. Professional activities include foundation problems, deep excavations, nuclear power plants, slope stability, breakwaters, earthdams, tunneling and underground waste disposal. Awards: Thomas Telford Medal (ICE) in 1994 and 2007; Crampton Prize (ICE) in 2006; J. Torán Prize in 1995; N. Monturiol medal in 2000; Second Coulomb lecturer in 2003 and Eleventh Buchanan Lecturer, Texas A&M in 2003; Tenth Sowers Lecturer, GeorgiaTech, Atlanta in 2005. He is member of the Royal Academy of Engineering of Spain since 1995 and member of the Royal Academy of Sciences and Art of Barcelona since 2007.

 

Núria M. Pinyol, born in 1978, got her degree in Civil Engineering (Ingeniero de Caminos, Canales y Puertos) in Barcelona in June 2004. At present she is a Researcher of the International Center for Numerical Methods in Engineering (CIMNE, Barcelona). She has worked on the development of constitutive models for bonded expansive soils and in the analysis and modeling of the geotechnical behaviour of earth and rockfill dams. One of her papers ("A review of Beliche dam") was awarded the Crampton Prize (ICE, UK) in 2006. Her main research interests are: behavior of unsaturated soils, expansive soils and rocks, hard soils and soft rocks, numerical analysis in Geomechanics, dams, slope stability and rapid slides.

Alexander M. Puzrin, born in 1965, studied Structural Engineering at Moscow Institute of Civil Engineers (1982-1987) and Applied Mathematics at Moscow State University (1990). He received his Ph.D. in Geotechnical Engineering from the Technion - Israel Institute of Technology in 1997, where he joined the faculty. In 2002 he became a faculty at the Georgia Institute of Technology (USA). He has been Professor of Geotechnical Engineering at the ETH Zurich since 2004. Prof. Puzrin has been involved as an expert in geotechnical projects in Russia, Israel and Switzerland. His expertise lies in progressive and catastrophic failure and constitutive modeling of geomaterials. He is the author of more than 60 papers. Awards: Technion Excellence in Teaching Award in 2001; ASCE (Student Chapter) Outstanding Faculty Award in 2003; ICE Bishop Medal in 2004.