Effects of OCR on monotonic and cyclic behavior of reconstituted Shanghai silty clay

Abstract

Recently traffic induced geotechnical problems have been receiving increasing attention. Yet the silty clay from the third layer of Shanghai, which is within the main influence depth of traffic loading and overconsolidated, had not been sufficiently studied. A series of monotonic and cyclic undrained triaxial tests were thus carried out on reconstituted Shanghai silty clay with various overconsolidation ratios (OCRs). The silty clay specimens showed phase transformation behavior, which was characterized by stages of initial contraction, temporary phase transformation and later dilation. Such behavior could be termed as a transitional mode between the behavior seen for typical clays and that for sands. The dilation behavior in the later stage was shown more significant for overconsolidated specimens. Six different failure criteria were employed to study the friction angle. There was no observable effect of OCR on the friction angle for this silty clay as if it was a granular material. The undrained shear strength could be normalized with only a small deviation. The normalized shear strength increased with OCR and it behaved more as typical silts than clays at high OCRs. The development of permanent strain under cyclic loading was shown to depend significantly on the cyclic stress ratio and OCR. A higher OCR resulted in smaller permanent and resilient strains, and the decrease of the permanent strain with OCR was remarkable for lightly overconsolidated specimens. Such effect of OCR would be more significant in real soil condition where the soil is at least partially drained.