This paper reports results of in-situ tests and undrained cyclic shear tests on high-quality undisturbedsamples obtained by the in-situ freezing method at three sites where foundation soils had been improvedwith the sand compaction pile. The relationship between liquefaction resistances and N-value, which wasestablished based mainly on the field evidences of earthquake-induced liquefaction of natural soil depositsand reclaimed lands, compared quite well with that obtained from tests on fully saturated improved sandspecimens. Degree of saturation of the frozen sample was revealed to be considerably low, in the rangebetween about 70 and 90 %. This fact indicates that the liquefaction resistances of improved sands aresignificantly higher than those obtained from the relationship which is available only for fully saturatedsoils. Undrained cyclic shear tests were also carried out on unsaturated specimens and effects ofdesaturating sand on undrained cyclic shear strength and deformation characteristics were studied.
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