2 results for Anastasopoulos, I

  • Normal Fault Rupture Interaction with Strip Foundations

    Anastasopoulos, I; Gazetas, C; Bransby, MF; Davies, Michael; El Nahas, A (2009)

    Journal article
    The University of Auckland Library

    Observations after earthquakes where surface fault ruptures crossed engineering facilities reveal that some structures survived the rupture almost unscathed. In some cases, the rupture path appears to divert, “avoiding” the structure. Such observations point to an interaction between the propagating rupture, the soil, and the foundation. This paper i develops a two-step nonlinear finite-element methodology to study rupture propagation and its interaction with strip foundations; ii provides validation through successful Class “A” predictions of centrifuge model tests; and iii conducts a parameter study on the interaction of strip foundations with normal fault ruptures. It is shown that a heavily loaded foundation can substantially divert the rupture path, which may avoid outcropping underneath the foundation. The latter undergoes rigid body rotation, often detaching from the soil. Its distress arises mainly from the ensuing loss of support that takes place either at the edges or around its center. The average pressure q on the foundation largely dictates the width of such unsupported spans. Increasing q decreases the unsupported width, reducing foundation distress. The role of q is dual: 1 it compresses the soil, “flattening” fault-induced surface “anomalies”; and 2 it changes the stress field underneath the foundation, facilitating rupture diversion. However, even if the rupture is diverted, the foundation may undergo significant stressing, depending on its position relative to the fault outcrop.

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  • Fault rupture propagation through sand: Finite-element analysis and validation through centrifuge experiments

    Anastasopoulos, I; Gazetas, G; Bransby, MF; Davies, Michael; El Nahas, A (2007-08-01)

    Journal article
    The University of Auckland Library

    The three notorious earthquakes of 1999 in Turkey (Kocaeli and Duzce) and Taiwan (Chi-Chi), having offered numerous examples of surface fault rupturing underneath civil engineering structures, prompted increased interest in the subject. This paper develops a nonlinear finite-clement methodology to study dip-slip ("normal" and "reverse") fault rupture propagation through sand. The procedure is verified through successful Class A predictions of four centrifuge model tests. The validated methodology is then utilized in a parametric study of fault rupture propagation through sand. Emphasis is given to results of engineering significance, such as: (1) the location of fault outcropping; (2) the vertical displacement profile of the ground surface; and (3) the minimum fault offset at bedrock necessary for the rupture to reach the ground surface. The analysis shows that dip-slip faults refract at the soil-rock interface, initially increasing in dip. Normal faults may keep increasing their dip as they approach the ground surface, as a function of the peak friction angle rho(p) and the angle of dilation psi(p). In contrast, reverse faults tend to decrease in dip, as they emerge on the ground surface. For small values of the base fault offset, h, relative to the soil thickness, H, a dip-slip rupture cannot propagate all the way to the surface. The h/H ratio required for outcropping is an increasing function of soil "ductility." Reverse faults require significantly higher h/H to outcrop, compared to normal faults. When the rupture outcrops, the height of the fault scrap, s, also depends on soil ductility.

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