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Reliability-based design of an anchor-support excavation

Osvaldo Ledesma, William Gibson and Alejo Sfriso
Monday, November 18, 2019
First presented: 
XVI Panamerican Conference on Soil Mechanics and Geotechnical Engineering
Published paper
The design of the support of a 10m-deep urban excavation in Argentina is presented. A conventional approach was employed for the base case, where a set of geotechnical parameters is selected based on “engineering judgment” and a support system based on concrete wall and anchors was selected for the excavation. To enhance the understanding of the problem, a reliability-based analysis was performed using Plaxis: numerical models were employed to compute factors of safety and displacements for a range of input parameters and a First Order Second Moment (FOSM) technique was used to evaluate the probability of reaching a limit state. A Python code was developed to integrate FOSM into numerical analysis, resulting in an automatic calculation of the probability of failure using Plaxis. The probability of failure was estimated between 0.2% to 2% for the ultimate limit state and less than 0.8% for the serviceability limit state.

Feature Author

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
Alejo Oscar Sfriso

Alejo O. Sfriso is a Principal Engineer with 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. In addition to his activity at SRK, he is the Director of AOSA - Geotechnical Laboratory, Professor of Soil Mechanics and Geology of the University of Buenos Aires, Vice President for South America of the International Society of Soil Mechanics and Geotechnical Engineering for the period 2017 - 2021, former Professor of Geotechnics at the National University of La Plata and former President of the Argentinean Society of Geotechnical Engineering.

Principal Consultant
PhD, Civil Engineer
SRK Buenos Aires
SRK Africa