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The dynamic behavior of saturated sands has been sufficiently studied from different points of view, but in laboratory tests only the stress conditions, prior to dynamic stress, are reproduced at the level of the surface; that is, for conditions of zero static shear stresses ( τo ). For this reason, the main objective of this research is to reveal the influence that static shear stresses ( τo ) have on the response of the dynamically saturated sands. The experimental phase included: identification and classification tests and six monotonic simple shear tests and 17 cyclic simple shear tests with different combinations of monotonic ( τo ) and cyclic shear stresses ( τc ) and in undrained conditions. The tested samples were extracted from the ‘La Bocana Norte’ sector of the Port of Barcelona–Spain. The samples were taken at depths between 31 m and 55 m, with a corresponding effective vertical stress ( σ ’ ov ) between 290 kPa and 421 kPa, respectively. Based on the results of the tests, a detailed analysis was carried out on the influence of the combination of monotonic ( τo ) and cyclic ( τc ) shear stresses on the variation of the dynamic shear modulus ( G ). Specifically: in the stress–strain behavior, the development of both permanent ( γp ) and cyclic ( γc ) shear strain and the reduction of the effective stresses ( σ ′ v ) as a consequence of the generation of pore water pressure ( u ). The results of the laboratory tests generally show that: (a) the combination of  τo  and  τc  controls the stress–strain behavior, the degradation of the cyclic shear modulus, the development of permanent and cyclic shear strain, the generation of pore water pressures and the liquefaction risk, (b) in the monotonic case, an empirical function was established to evaluate the internal friction angle ( ϕ ') as a function of the shear strain ( γm ) (mobilized friction angle), (c) in the combined case of monotonic and cyclical stress, it was possible to establish an empirical function among the  G / σ ′ ov  ratio, the cyclic strain ( γc ) and the number of cycles ( N ) and among the  σ ′ v / σ ′ ov  ratio, the cyclic strain ( γc ) and the number of cycles ( N ), (d) based on empirical functions, a simple methodology can be proposed to assess liquefaction risk and (e) it is not always true that the liquefaction phenomenon occurs when the effective vertical stress ( σ ’ v ) is reduced to zero. Depending on the cyclic stress ratio ( τc / σ ’ ov ) liquefaction can occur in the first cycle with a reduction in vertical effective stress of just 70%.

Behavior of saturated micaceous silty sand subjected to a combination of static and cyclic load using simple shear tests