Response of normally consolidated kaolin clay under irregular cyclic loading and comparison with predictions from the accumulation procedure

Abstract

The accumulation procedure on contour diagrams of shear strain is used in geotechnical design to account for the effect of cyclic loading on offshore foundations. In this paper, contour diagrams of maximum shear strain are presented based on a series of stress-controlled, symmetrical and non-symmetrical, cyclic direct simple shear tests on normally consolidated kaolin clay that can be used to re-examine the extensive database of model testing in kaolin clay. It is shown that the failure under non-symmetrical cyclic loading can be defined at a higher maximum shear strain than under symmetrical loading, offering potential opportunities for reducing foundation sizes for structures that are less sensitive to displacement. Staged tests with parcels of uniform amplitudes have been also performed to compare the measured shear strains with the values predicted by the accumulation procedure. It is shown that the accumulation procedure predicts the strain measured in the symmetrical staged tests well but overpredicts shear strains measured in the non-symmetrical staged tests. KeywordsCyclic loading; normally consolidated clay; direct simple shear test List of notation a fitting parameter for contour diagram of γmax b fitting parameter for contour diagram of γmax c fitting parameter for contour diagram of γmax CSR cyclic stress ratio DSS direct simple shear e0 void ratio (as extruded) f frequency Gcyc cyclic shear modulus Gs specific gravity Published in Géotechnique https://doi.

Vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay

“…γ max = 25% -also shown on Figure 10 and defined in the same way as failure for the model tests reported here, i.e. at the point where the change in γmax per cycle increases rapidly (Zografou et al 2018a). The findings indicate that instability failure of the foundation under tension occurred at a common strain level irrespective of loading history, although the strain level is not immediately comparable to that defining failure at the element level in the DSS tests.…”

“…The normalised shear stress and number of cycles at failure are also plotted on the contour diagram on Figure 10 for the centrifuge test with low-level cyclic loading followed by a consolidation period and a parcel of cyclic loading of high magnitude [LOW_CONS_HIGH] (q V,max/qV,ult = -0.95 and N = 41). It is noted that the first parcel with qV,max/qV,ult = -0.36 (-0.10 ± 0.30) and N = 1080 plots near the horizontal contour of 1% and is not considered in the accumulation procedure (Zografou et al 2018a, Zografou et al 2018b. As shown in Figure 9 and discussed above, T-bar tests through the foundation footprint in the cyclic test with the same sequence until the end of consolidation period [LOW_CONS indicated that the increase in s u is between 20%, close to the centre of the foundation and up to 70% close to the edges of the foundation.…”

Responses of frozen, fine-grained soils due to multiple packets of cyclic stress with variable amplitude and an empirical prediction model

“…Additionally, in the case of cyclic loading induced by wind or waves, the amplitude fluctuates. Under these conditions, various combinations of loading magnitudes and sequences are applied to the soils and the sequences of cyclic loading will affect the response of soils significantly (Kaggwa et al 1991;Zografou et al 2019). However, the relevant studies concerning this topic on frozen soils have been relatively limited and the effect is still unclear at present.…”

“…Compared with frozen soils, more research has been carried out on the cyclic and accumulated behaviour of unfrozen soils under cyclic stress with varying magnitudes over a range of cycles. The experimental data indicates that the sequences of cyclic stress package or the cyclic stress history affect the accumulated and cyclic behaviours significantly (Kaggwa et al 1991;Zografou et al 2019).…”

“…The starting cycle is first determined as the number of cycles with the same amount of accumulated strain induced by prior cyclic stress in this curve. Then, the incremental accumulated strain induced by this parcel of cyclic stress can be obtained from the curve after the starting cycle (Zografou et al 2019). In fact, the hardening effect induced by the prior cyclic loading is considered in this method.…”