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Recent major seismic events, such as the Chi-Chi (1999) and the Wenchuan (2008) earthquakes, have offered a variety of case histories on the performance of structures subjected to reverse faulting-induced deformation. A novel faulting mitigation method has recently been proposed, introducing a soft deformable wall barrier in order to divert the fault rupture away from the structure. This can be materialized by constructing a thick diaphragm-type soil bentonite wall (SBW) between the structure and the fault rupture path. The paper investigates the key parameters in designing such a SBW, aiming to mitigate the fault rupture hazard on shallow foundations. The paper employs a thoroughly validated finite element analysis methodology to explore the efficiency of a weak SBW barrier in protecting slab foundations from large tectonic deformation due to reverse faulting. A dimensional analysis is conducted in order to generalize the validity of the derived conclusions. The dimensionless formulation is then used to conduct a detailed parametric study, exploring the effect of SBW thickness w/H, depth HSBWl/H, and shear strength τsoil/τSBW, as well as the bedrock fault offset h/H, foundation surcharge load q/ρgB, and fault outcrop location s/B. It is shown that the wall thickness, depth, and shear strength should be designed on the basis of the magnitude of the bedrock fault offset, the location of the fault relative to the structure, and the shear strength of the soil. The efficiency of the weak barrier is improved using lower strength and stiffness material compared to the alluvium. A simplified preliminary design methodology is proposed, and presented in the form of a flowchart.

Abstract. As pipelines pass from large geographical regions Chi-Chi (1999) and Wenchuan (2008)

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Surface fault ruptures damage structures which are located at the intersecting zones of active faults. It is essential to consider the undesirable effects of surface fault ruptures when designing structures. Geotechnical measures such as reinforced soil foundations effectively mitigate the hazards related to surface faults. The present work conducted a series of tests on foundations reinforced with geosynthetics, including geogrids, geocells and geogrid-geocell layers. These tests simulated the behavior of 1.5 m-wide strip footings located in 6-m thick alluvium that had been displaced 60 cm. A total of 12 disparate tests in terms of the number and type of reinforcement were conducted at a scale factor of 10. Image analysis of the results indicated desirable behavior for reinforced soil foundations in terms of reduced angular distortion, uniform settlement and deviation of the fault path. For normal fault rupture, the angular distortion of foundations reinforced by one geogrid layer, one geocell layer, one geogrid-geocell layer or two or three geo-grid layers decreased by 60%, 30%, 70%, 80% and 80%, respectively. These results also revealed that an increase in the number of geogrid layers to more than two layers caused an insignificant decrease in angular distortion. The decrease in angular distortions observed for soil foundations reinforced by one geogrid layer, one geocell layer and one geogrid-geocell layer were 7%, 16% and 40%, respectively, for reverse faulting. The performance of a reinforced soil foundation subjected to normal faulting was more acceptable than that for reverse faulting.

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