Factor of safety by the strength-reduction technique applied to the Hoek–Brown model

Osvaldo Ledesma, Iñaki García Mendive and Alejo Sfriso
Wednesday, November 9, 2016
First presented: 
ENIEF 2016.
Published paper
This paper describes the implementation of the Hoek–Brown model as a perfect elastoplasticity model in a finite element code. The yield function is a standard Mohr–Coulomb surface incorporating a stress-dependent friction angle which accomplishes an exact reproduction of the Hoek- Brown strength envelope for all stress states. The formulation of the model is performed in such a way as to allow for a direct implementation of the shear strength-reduction technique in order to calculate the factor of safety of boundary-value problems. The efficiency of the numerical algorithm is discussed, with emphasis in the effect of the numerical implementation of three dilatancy models: deviatoric associativity, full non-associativity employing a Mohr–Coulomb shaped plastic potential and radial return. A comparison is presented between the results obtained for slope stability analyses using limit equilibrium methods and the built-in Hoek–Brown model available in Plaxis. Finally, the application of the model to an excavation for an underground mine in Uruguay is presented and discussed.


Feature Author

Alejo Oscar Sfriso

Alejo Sfriso has 25 years of experience in geotechnical engineering for infrastructure and mining works. He is an expert in the application of numerical methods for geotechnical design and analysis. Alejo belongs to twelve professional associations, including ISSMGE, IAEG, ISRM, IGS, ICOLD, IACMAG, ITA, ASCE and its corresponding chapters in Argentina. He was member of the Executive Committee of the Argentinean Society for Geotechnical Engineering in the period 1997 - 2015, being the President of the Society (2011-2015). Alejo serves as Professor at the University of Buenos Aires since 1989 and at the University of La Plata between 1996 and 2015, in the subjects of Soil Mechanics, Rock Mechanics and Foundations. He also serves as jury member for faculty positions and theses, reviewer of journals, member of advisory committees, conference organizing committees, and departmental councils at the Faculty of Engineering of University of Buenos Aires, among others.

Principal Consultant
PhD, Civil Engineer
SRK Buenos Aires
Osvaldo Ledesma

Osvaldo Nicolás Ledesma is a Senior Consultant at SRK´s Buenos Aires office, with experience in the design of foundations, excavations, tunnels, embankments and retaining structures for infrastructure and mining projects in Argentina, Peru, Paraguay, Uruguay, Canada and Papua New Guinea.  He has advanced knowledge of numerical methods for geotechnical structure design as well as experience in geotechnical field and laboratory testing. Osvaldo is currently pursuing a PhD in numerical modelling of soils in unsaturated conditions and serves as Assistant Professor of Soil Mechanics and Geology at the University of Buenos Aires.

Senior Consultant
Geotechnical Engineer
SRK Buenos Aires
Iñaki García Mendive

Iñaki García Mendive is a geotechnical engineer in SRK’s Buenos Aires office. His specialization focuses on the characterization of rock masses, application of empirical and numerical methods for design and validation in open pit and underground operations. He has experience in the design of geotechnical projects including foundations, anchor systems, embankments, slopes and excavations (OP and UG). He has participated in investigation projects at the Soil Mechanics Laboratory of the University of Buenos Aires. He collaborated as teaching assistant in the course of Strength of Materials.

Geotechnical Engineer
SRK Buenos Aires
SRK Turkey