A Critical State Evaluation of Fines Effect on Liquefaction Potential

Published results from laboratory tests show that an increase in the percentage of fines generally leads to a reduction of the cyclic liquefaction resistance of a sand, while empirical correlations from in-situ tests consider the presence of fines as beneficial. In order to study this seemingly not univocal effect of tines content, this paper involves the integrated framework of Critical State Soil Mechanics. For this purpose, firstly the effect of tines on the location of the Critical State Line (CSL) is studied through statistical analysis of a large data set of triaxial element tests. Results show that fines affect the CSL location in the (e-lnp) space, but not its slope in (p-q) space. In particular, an increase of fines content practically leads to a clockwise rotation of the CSL in (e-lnp) space. Introducing this finding as a mere change in parameter values of an appropriate Critical State constitutive model, simulations of cyclic undrained triaxial tests were performed. These simulations show that the presence of fines is beneficial at relatively small effective stresses, i.e. the stresses prevailing at liquefiable layers in-situ. Furthermore, these simulations show that the effect is reversed at relatively large effective stresses, i.e. the stresses usually considered in laboratory tests

Improved Methodology for Estimating Seismic Coefficients for the Pseudo-Static Stability Analysis of Earth Dams

This paper presents an improved methodology for estimating seismic coefficients for the pseudo-static stability analysis of earth dams, which is based on a statistical analysis of input data and results for 112 potential failure surfaces, as estimated from 28 two dimensional seismic response analyses for eight (8) different zoned earth dams and high embankments. The new methodology employs design diagrams and equations and estimates the maximum and the effective seismic coefficients as a function of: (a) the peak ground acceleration at the free-field surface of the foundation soil, (b) the predominant period of the seismic excitation, (c) the eigenperiod of the earth dam, (d) the dam foundation conditions, and (e) the dimensionless ratio z/H of the maximum depth z of the failure surface over the height H of the earth dam. The proposed methodology offers accuracy and consistency with a standard deviation of the relative error in the estimation of the seismic coefficients in the order of ±24

Liquefaction performance of shallow foundations in presence of a soil crust

Liquefiable soils are currently categorized by all seismic codes as extreme ground conditions where, following a positive identification of this hazard, the construction of surface foundations is essentially allowed only after proper treatment soil. This article examines to what extent this situation may change in presence of a non-liquefiable soil crust, between the foundation and the liquefiable soil. Means are provided for analytical evaluation of the degraded bearing capacity and the associated seismic settlements for the specific case of strip foundations on a cohesive (clay) crust. Furthermore, the conditions are explored which ensure a viable performancebased design, and the issue of a critical soil crust thickness, beyond which liquefaction effects are minimal, is addressed. © 2007 Springer

Analysis of fault rupture propagation through uniform soil cover

This paper presents results from numerical simulations of the propagation of an active dip-slip fault rupture through a uniform soil layer covering the rigid bedrock. Following verification of the numerical methodology against field evidence, a parametric study is performed for loose and dense sand, for normally consolidated and overconsolidated clay, as well as for different fault dip angles (normal and reverse faults) and for different thicknesses of the soil cover. The soil is modeled as an elasto-plastic, strain-softening material that obeys the Mohr-Coulomb failure criterion. The study aims at establishing criteria for the approximate depiction of the location and the width of the zone with significant ground surface distortion, where the differential ground displacements induced by the fault rupture may threaten the integrity of man-mad structures. (c) 2009 Elsevier Ltd. All rights reserved