Liquefaction Potential of Christchurch Silty Soil

Southwest Christchurch, New Zealand, with thick successions of thinly interbedded fine sand and silt swamp deposits, had no-to-marginal liquefaction ejecta in the 2010-2011 Canterbury earthquakes even though state-of-practice liquefaction assessment procedures indicated severe ground failure would occur. To understand reasons for this discrepancy, the first cyclic simple shear tests were performed on high-quality "undisturbed" specimens of Christchurch silty soil. An alternative Japanese Standard JIS A 1224:2009 Test Method was developed to evaluate the minimum and maximum void ratios of the cyclic test specimens and establish their relative densities. The cyclic test specimens of the same soil unit were then mixed and reconstituted for steady-state testing in a triaxial device. This paper presents the stress-strain relationships, cyclic resistance ratio curves, and steady-state lines for three silty soils. The silty soils exhibited cyclic mobility with limited strain potential in the cyclic simple shear tests. The same dilative tendencies of the soil at its current state and effective stress were confirmed by the steady-state test results.