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This paper aims to investigate the effects of cyclic shear amplitudes and loading sequences on a soil–structure interface using direct shear tests under a large number of loading cycles. A series of cyclic direct shear tests were performed on a granular soil-rough interface under the constant normal load (CNL) condition. Initially, monotonic interface direct shear tests were carried out as benchmarks to specify test boundaries and proper ranges of assigned cyclic amplitudes. Dry standard Fontainebleau sand in dense and loose conditions and a modified rough surface material were utilized to represent a soil-rough structure interface. A series of CNL cyclic interface direct shear tests was then conducted by varying the applied cyclic shear stress amplitudes and the cyclic loading sequence (small-to-large and large-to-small patterns) with a large number of testing cycles (104). Immediately after the cyclic shear tests were completed, monotonic interface direct shear tests were again performed to examine the post-cyclic behaviour of the soil-rough interface. Test results yielded that the applied cyclic shear stress amplitudes did affect the soil-rough interface by inducing a gradual contraction and an expansion in shear displacement accumulation. The maximum stress ratio could notably influence the volumetric behaviour and shear displacements. The accumulation of mean cyclic displacements was independent of the change in cyclic shear stress amplitudes between two consecutive cyclic loading sequences. The post-cyclic behaviour showed that changing the shear stress cycles between two consecutive packages did not influence the peak stress ratio. [ABSTRACT FROM AUTHOR]

The development and construction of offshore wind farms requires the correct estimation of the friction that can be mobilised at the rock/grout interface. In conventional studies, the shear behaviour of a joint is usually investigated with laboratory tests under constant normal load/stress (CNL), however, in engineering practice, direct shear testing under constant normal stiffness (CNS) has been proved to be more realistic in the assessment of the development of the side shear resistance in rock grouted pile design. In this work, an extensive experimental campaign on the shear response of a weak carbonate rock (limestone) interface with grout is presented, in the frame of offshore wind turbines. First, basic mechanical testing is performed on the two interface materials in order to evaluate their mechanical properties. The output of these tests reveals not only the contrasting properties of the two interacting materials, but also the decreased response of the limestone in the presence of water. A series of monotonic shear tests (both under CNL and CNS conditions) on wet rough limestone/grout interfaces reveal the high impact of adhesion between the two materials to the mechanical response. Based on the monotonic results, a number of CNS shear tests under cyclic loading takes place, where different failure modes are observed dilatant and contractant response. The variability of the failure mode is strongly related not only to the adhesion created with the cast grout, but also to the limestone's micro-structural heterogeneity that manifests already after consolidation. The post-shear morphological state of the interface is analysed, while the variability of the failure surface and the presence of water gouge creation do not allow a clear correlation of the morphologfy to the mechanical response. Overall, the response of this type of weak rock interface where the properties of the grout are significantly higher, is governed by the behaviour of the rock. [ABSTRACT FROM AUTHOR]

The accumulation of irreversible deformations of the soil of foundation, under cyclic loading, becomes important if the number of cycles is very high. Hence appears the importance of predicting cyclical deformations after many cycles. This paper presents a simple explicit model for modeling the cyclical behavior of sands in drained condition. This approach consists in proposing of a formulation to estimate the accumulated irreversible strain, based on an analogy between Soft Soil Creep Model and the pseudo cyclic creep, in such a way to define an equivalence between cyclical parameters and parameters of the used model. The last section is devoted to the parametric study of the proposed formulation. We are essentially interested in the influence of the cyclic parameters on the evolution of the accumulated irreversible strain. [ABSTRACT FROM AUTHOR]