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季刊土と基礎 = Soil mechanics and foundation engineering

Using controlled liquefaction, a seismic isolation technique is introduced by which a large area with dozens of structures can be seismically isolated. The proposed Large Scale Seismic Isolation (LSSI) is in many ways similar to conventional base isolations. The required bearing is provided by a fully undrained pre-saturated liquefiable layer which has substantial vertical stiffness/capacity and minimal lateral stiffness. Moreover, required energy dissipation would be provided through material damping and Biot flow-induced damping within the liquefied layer. LSSI consists of a thick nonliquefiable crust layer and an underlying engineered pre-saturated liquefiable layer bounded by two impermeable thin clay layers. The liquefiable layer should be designed to trigger liquefaction as soon as possible within the early seconds of a design level seismic event. Adopting the energy-based GMP liquefaction theory, optimum gradation of the liquefiable layer is also investigated. It turned out that LSSI would effectively reduce acceleration response spectrum within short to medium periods. Contribution of the proposed LSSI is more pronounced in the case of stronger ground motions such as near field events as well as ground motions with longer return periods.

Large-scale seismic isolation through regulated liquefaction: a feasibility study

Generally seismic isolation is achieved by supporting the structure on laminated rubber bearings, friction pendulum bearings, roller bearings etc. Very little work has been performed using soil as a base isolation media. Experiments and analytical work has been performed on a structural model with raft footing and found encouraging results. Details of this work are presented in this paper.

S. J. Patil

Papers

Natural Seismic Base Isolation of Structures Having Raft Foundations