Offshore wind turbines are subjected to more significant wave and wind environmental loads at extreme weather conditions, making subsoil experience various loading stages with different amplitudes. To investigate the coupling effect of both cyclic shear stress ratio (CSR) and stage amplitude ratio (Ar) between normal and extreme weather conditions, a series of bi-directional simple shear tests with five different Ar and three CSR values were conducted on marine sand using the variable-direction dynamic cyclic simple shear (VDDCSS) apparatus. In the tests, soil samples were compacted under vertical stress and then sheared in undrained conditions by applying two shear stresses acting in different horizontal directions. Test results indicated that the cyclic strain, pore water pressure ratio, and cyclic strength were significantly determined by the value of stage amplitude ratios and the CSRs: at the same CSR, cyclic strains, and pore water pressure increased while cyclic strength decreased with the Ar. Comparing the test data between various cyclic stress ratios found that the CSRs can accelerate shear strains, pore pressure accumulation, and cyclic strength attenuation.

Soil instability and potential failure under principal stress rotation require greater attention than ever before due to increased operation of heavier and longer high-speed trains. This study focuses on the interplay between cyclic vertical stress and torsional shear stress on the failure condition of a low-plasticity subgrade soil, facilitated by a hollow cylinder apparatus. Combined vertical and torsional loading significantly influences strain response, with increasing torsional stress leading to higher strain accumulation. Moreover, the data indicate that an increase in torsional shear stress is generally accompanied by a swift rise in the EPWP and a corresponding decrease in the soil stiffness. In view of this, a novel parameter, the overall stiffness degradation index (delta o) that simultaneously captures both the vertical and torsional shear effects under principal stress rotation is proposed as an early indicator of instability. In addition, a normalised torsional stress ratio (NTSR), which is the ratio of the amplitude of torsional shear stress to the confining pressure, is introduced to assess the impact of torsional shear stress. Whereby, higher NTSR values correlate with premature inception of failure. These experimental results provide new insights for a better understanding of soil instability under simulated railway loading.

The soft clay under the road ground will suffer cyclic torsional shear stress encountered traffic load in addition to axial stress, which will cause further deformation of clay. To investigate the effect of torsional shear stress on the cumulative axial strain of clay, a series of undrained tests under cardioid stress path were performed on K0 consolidated undisturbed samples by using a hollow cylinder apparatus (HCA). The effect of vertical cyclic stress ratio (VCSR) and shear stress ratio (eta) on the deformation and degradation characteristics of clay was investigated. The results indicate that there is inconsistency between the strain path and stress path. The increase in eta further accelerates the accumulation of axial strain, which resulted from the degradation of clay induced by torsional shear stress. Considering the VCSR and eta, a calculation method of degradation index was developed. Furthermore, a cumulative axial strain prediction model of clay under the cardioid stress path was established considering the degradation. This model addresses the limitation of traditional prediction models by considering the impact of torsional shear stress on cumulative axial strain.

Mining Exploration, excavation, and construction are considered as mining activities which are recently growing dramatically. Therefore, utilizing the mining wastes with the least environmental damage is a significant concern. Tailings dams are one of the conventional solutions that store the extracted hazardous substances safely for water resources management and environmental protection. This reseach deals with the effects of monotonic and seismic loadings on silt-sized copper wastes existed in a tailings dam at Northwest Iran as a case study. Various values of initial static shear stress are performed using an automated cyclic triaxial system. Monotonic undrained compressive tests were performed with a relatively constant density and considering three values of 50, 100, and 150 kPa for mean effective stress. Depending on the first density of samples, applying a mean effective confining pressure of 100 kPa, increased the initial densities by 25 to 30% as compared to the initial condition.Moreover, the effect of initial shear stress ratio with three values of 0, 0.2, and 0.4 was evaluated. No peak point was observed for samples under alpha = 0, whereas, samples with alpha = 0.4 encountered a peak point before reaching to the phase transformation point. The results of cyclic experiments were used to evaluate capacity energy and residual pore pressure based on the strain energy approach. Cyclic tests on the samples were performed considering the shear amplitude of 0.75% and frequency of 0.3 Hz. It is shown that the most energy dissipation occurs at the first cycle possessing the highest stiffness. For alpha = 0, energy density increased from 474 J/m(3) to 1147.4 J/m(3); however, a more intense increase was measured from 682 J/m(3) to 5839 J/m(3) when alpha = 0.4. It is also found that applying initial shear stress has a pretty considerable influence on monotonic strength and the liquefaction resistance of silts. The increase of alpha from 0 to 0.4 yielded a linear increase in the shear strength of samples in the range of 20 kPa to 70 kPa. The results of this paper were then validated accurately through some previous studies.