Effect of soil permeability on soil–structure and structure–soil–structure interaction of low-rise structures

Abstract

Earthquake-induced soil liquefaction can generate excessive damage to building structures due to significant reduction in soil effective stress. With increasing urbanisation and population growth, the performance of closely spaced buildings, such as those in towns and cities, is of greater concern where structure–soil–structure interaction (SSSI) may occur in conjunction with full or partial liquefaction. This study investigates the seismic performance of isolated and adjacent structures built on shallow foundations on soils of different permeability (i.e. with different amounts of drainage and therefore generating different amounts of excess pore water pressure) using a combination of dynamic centrifuge modelling and finite-element modelling. The results demonstrate that the reduction in free-field ground surface intensity measure (specifically, Housner intensity) due to increasing liquefaction can be correlated to an index which is the normalised integral of excess pore pressure ratio (ru) with depth. This index can express the amount of liquefaction uniquely, even when full liquefaction occurs to only partial depth, or where excess pore water pressures are increased but below the level of full liquefaction at all depths. This underlying correlation means that structural demand reduction (e.g. reduction in inter-storey drift ratio) with liquefaction (SSI effect) can be linked to either: (a) the ru–depth index; (b) the depth of the liquefaction front, which can be estimated from a liquefaction triggering analysis; or (c) the ground surface intensity amplification/attenuation in the free field from the results of one-dimensional free-field soil column analyses. Where there are adjacent structures, a strongly beneficial SSSI effect on co-seismic settlement and a detrimental effect on drift in non-liquefied soil, as observed in this and previous studies, reduced towards a null effect in both cases with increased liquefaction, with liquefaction appearing to isolate the structures from each other (at least for the configuration considered herein). This has also been linked to the amount of amplification/attenuation of surface ground motion in the free field (or amount of liquefaction) as a simple indicator of the likely importance of SSSI effects in liquefiable soil.