22nd European Young Geotechnical Engineers Conference (EYGEC)

Gothenburg (Suecia), 26-29 de agosto de 2012

1.- «Backanalysis in tunnels using different minimization algorithms»

Autores: C. de Santos, A. Ledesma, A. Gens

Keywords: Backanalysis, Genetic Algorithm, Tunnel

Resumen: The paper describes a procedure to perform backanalysis of tunnel excavation problems in an automatic manner. The measured displacements are compared with the calculated ones obtained from a Finite
Element Analysis, forming the objective function. The parameters that best represent the measured data are those that minimize the objective function and a suitable minimization algorithm is required.
In this paper a genetic algorithm and a gradient based method are described. The Finite Element code Plaxis has been used as a tool for the direct analysis.The parameters to identify are the coefficient of lateral earth pressure (K0) and the reference Young’s modulus for unloading and reloading (Eur ref), to the reference pressure (pref). The «Hardening soil model» from Plaxis has been the constitutive model selected to simulate the soil behavior. The geometry considered is a synthetic case involving the excavation of a circular tunnel. The paper shows the advantages and disadvantages of each optimization algorithm in the context of this tunnel excavation problem.

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1.- «Influence of gravel density in clay reinforced with stone columns. Laboratory study»

Autores: M. Miranda

Keywords: Stone column, settlement reduction, unit cell, stress concentration factor, area replacement ratio

Resumen: Small scale tests were performed in the laboratory to study the influence of the density of columns in the deformation and radial consolidation around end-bearing columns installed in soft soils. For this purpose, the behavior of a horizontal slice of a representative unit cell formed by the column and the surrounding soil was analyzed. Two column densities were tested, with a relative density of Dr =100% [1] and Dr=30%. Gravel was used for the central column and kaolin clay for the natural soil. Some interesting results are the vertical strain reduction of approximately 15% for columns with Dr =30% and 25% for columns with 100%, and the stress concentration factor between 4 and 15 for Dr=100% and 3-7 for Dr =30%. The experimental results have been compared with some of the theoretical solutions more used in the study of stone columns behavior.

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