Numerical modeling of centrifuge cyclic lateral pile load experiments

To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussées. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on re...     

Slab foundation subjected to thrust faulting in dry sand: Parametric analysis and simplified design method

Motivated by recent case histories of faulting-induced damage to structures (Chi-Chi, 1999; Wenchuan 2008), this paper applies a thoroughly validated finite element analysis methodology to study the response of slab foundations subjected to thrust faulting. A parametric study is conducted, investigating the effect of key response parameters. It is shown that the stressing of the foundation, and consequently of the superstructure, stems mainly from loss of support. Depending on the geometry, loss of support takes place either under the edges or under the middle of the foundation, generating hogging or sagging deformation, respectively. Increasing the weight of the structure and/or decreasing soil stiffness leads to less stressing of the foundation. Surprisingly, even when the fault rupture emerges beyond the structure, completely avoiding the foundation, substantial foundation distress may still be generated. Exploiting the results of the parametric study, a simplified design method is developed, calling for conventional static analysis of a slab on Winkler supports, “simulating” the fault rupture by removing Winkler springs from equivalent area(s) of loss of support. The latter can be estimated with the help of design charts, further facilitating its use in practice. The proposed simplified method should not be viewed as a general design tool, but as a first idea of a practical solution to the investigated problem.     

Vibrational characteristics of soil deposits with variable wave velocity

The paper studies certain dynamic characteristics of soil deposits with wave velocities increasing with depth according to (1 + μz)^m, where m = 1, 2/3, 1/2, 1/4 and 0. Analytical solutions are presented for the fundamental periods, mode shapes and amplification functions due to vertically propagating shear waves and the effects of type (m) and rate (μ) of heterogeneity are systematically investigated. The analytical–numerical techniques are used to study the attenuation with depth in a deposit of the vertical and horizontal displacements due to travelling of Rayleigh waves. Differences attributed to different heterogeneities are discussed in connection with the machine isolation problem and the steady-state vibration technique for soil exploration. Finally, the dependence on soil heterogeneity of the time–distance response curves, obtained during seismic refraction surveys, is graphically illustrated.