Nonlinear stress-strain response of soft Chicago glacial clays

Abstract

This paper presents the results of extensive experimental works to analyze the stress-strain response of hand-cut block samples of soft Chicago glacial clays deposited in fresh water environments. The block samples were obtained from the excavation for the Block 37 project where top-down construction methods were employed. Specimens were instrumented with bender elements and local LVDTs. After recompression to the in situ stresses of the samples, drained and undrained stress probe tests were conducted. Propagation velocity of the specimens cut from the block samples measured by bender elements after recompression and creep agrees well with the seismic cone penetration tests. The shear, bulk and cross-coupling moduli are strongly dependent on strain level and stress probe direction. The coupled moduli relating shear and volumetric responses are not the same. The shear modulus degradation curve obtained from the specimen with the undrained stress probe was the same as that of the specimen with the drained stress probe. The soft Chicago glacial clays exhibit incrementally nonlinear responses at small strains.