Numerical and Physical Modeling of Flexural Slip Phenomena and Potential for Fault Movement

121

Earthquake fault ruptures may emerge at the ground surface causing large differential movements. When fault ruptures emerge at or adjacent to the position of existing foundations, significant damage can be caused. However, the study of recent faulting events revealed that in some circumstances the fault-rupture emergence is deflected by the presence of buildings leaving the buildings intact. A centrifuge modelling study has been conducted to investigate how normal faults interact with strip foundations which run parallel to the strike direction. The study confirms that fault rupture may be deviated by the presence of the foundation so that the foundation is protected from the most serious differential movements. However, whilst the fault propagates to the soil surface the foundation has to withstand initial movements before the final fault rupture emergence mechanism is activated. The centrifuge results suggest that it is the bearing pressure of the foundation which causes the deviation of the fault rather than the kinematic restraint of the foundation. The interaction between the earthquake fault and the shallow foundation depends on the foundation bearing pressure, foundation width, soil depth and position of the fault relative to the foundation and these aspects should be considered in design. Results from the tests are used to validate a series of finite element analyses as reported in an accompanying paper.

Section: Free-field Conditions (Test 12)supporting

confidence: 55%

Section: Introductionmentioning

confidence: 96%

Centrifuge modelling of normal fault–foundation interaction

Bransby

Davies

Nahas

2008

121

“…Cole and Lade 1984;Bray 1990;Taniyama and Watanabe 2002) and numerical study (e.g. Roth et al 1982;Ramancharla and Meguro 2002). Other relevant studies include the investigation of the reverse trap door problem (e.g.…”

Section: Introductionmentioning

confidence: 99%

Centrifuge modelling of reverse fault–foundation interaction

Bransby

Davies

Nahas

et al. 2008

116

The propagation of reverse faults through soil to the ground surface has been observed to cause damage to surface infrastructure. However, the interaction between a fault propagating through a sand layer and a shallow foundation can be beneficial for heavily loaded foundations by causing deviation of the fault away from the foundation. This was studied in a series of centrifuge model tests in which reverse faults of dip angle 60 • (at bedrock level) were initiated through a sand layer, close to shallow foundations. The tests revealed subtle interaction between the fault and the shallow foundation so that the foundation and soil response depend on the foundation loading, position, breadth and flexibility. Heavily loaded rigid foundations appeared best able to deviate fault rupture away from the foundation but this deviation could be associated with significant foundation rotations. However, a lightly loaded foundation was unable to deviate a reverse fault and the fault emerged beneath the foundation. This led to gapping beneath the foundation as well as significant rotations and may cause severe structural distress. As well as providing insight into the mechanisms of behaviour, the data from the tests is used to validate finite element analyses in a separate article.

“…In contrast, Bray (1990) and Bray et al (1994 a,b) also utilising the FE method, but with a hyperbolic non-linear elastic constitutive law achieved satisfactory agreement with small-scale tests (Bray et al, 1993). Analyses performed by Roth et al (1981Roth et al ( , 1982, Loukidis (1999), and Erickson et al (2001) were also successful. They all applied the finite difference (FD) method with elastoplastic constitutive model, Mohr-Coulomb failure criterion, and strain softening.…”

Section: Fault Rupture Propagation In the Free-fieldmentioning

confidence: 98%

Foundation–structure systems over a rupturing normal fault: Part II. Analysis of the Kocaeli case histories

Anastasopoulos

Gazetas

2007

Motivated by the observed (successful and unsuccessful) performance of numerous structures on top of, or immediately next to a normal fault that ruptured during the Kocaeli 1999 earthquake, this paper: (i) develops a two-step finite element methodology to study the propagation of a fault rupture through soil and its interplay with the foundation-structure system, denoted hereafter "Fault Rupture-SoilFoundation-Structure Interaction" (FR-SFSI), (ii) provides validation of the developed methodology through successful Class "A" predictions of centrifuge model tests, and (iii) applies the centrifuge-validated methodology to study one-by-one the Kocaeli case histories of the first paper (Part I). It is shown that the presence of a structure on top of an outcropping fault may have a significant influence on the rupture path: with heavy structures founded on continuous and rigid foundations, the fault rupture diverts substantially and may avoid rupturing underneath the structure. The latter undergoes rigid body rotation, with its foundation sometimes loosing contact with the bearing soil, but in most cases retaining its structural integrity. In stark contrast, buildings on isolated footings and, perhaps surprisingly, piles exert a smaller diversion of the rupture which is thus likely to outcrop between the footings or pile caps; the latter may thus undergo devastating differential displacements. It is shown that structures in the vicinity of faults can be designed to survive significant dislocations. The "secret" of successful performance lies on the continuity, stiffness, and rigidity of the foundation.