Density and stress history affect the strength and stiffness properties of sands. Due to the difficulties in acquiring undisturbed sand samples, the sampled sand is reconstituted to the in-situ density for laboratory testing. A laboratory testing practice is to model pre-storm design load events and likely even out stress concentrations from reconstitution, so called preshear, by applying a number of cycles of a fixed stress amplitude before shearing a triaxial specimen to failure or applying cyclic loading representing storm events. The purpose of this study is to identify the effects of cyclic preshear on shear strength and stress-strain characteristics of triaxially tested specimens. This is achieved by performing triaxial tests on dense/ medium dense and very dense specimens prepared with different cyclic stress amplitudes, and consolidation pressures. Several tests with similar conditions were conducted to study the repeatability of the tests and to enhance the confidence of interpretations. The effect of preshear on the maximum shear modulus and monotonic strength of the specimens appears to be insignificant. However, preshear improved the small/ intermediate strain stiffness and hence the stiffness degradation characteristics of the soil. With increasing cyclic stress amplitude, the axial strain corresponding to the onset of stiffness degradation increased.
Amin Rismanchian, Anders H. Augustesen, Lone Krogh, Tim Carrington and Nanna V. Thomsen
Keywords: Triaxial testing, preshearing, reconstitution, sand, stress-strain, repeatability
Publisher: DFI