Slopes are mainly naturally occurred deposits, so slope stability is highly affected by inherent uncertainty. In this paper, the influence of heterogeneity of undrained shear strength on the performance of a clay slope is investigated. A numerical procedure for a probabilistic slope stability analysis based on a Monte Carlo simulation that considers the spatial variability of the soil properties is presented to assess the influence of randomly distributed undrained shear strength and to compute reliability as a function of safety factor. In the proposed method, commercially available finite difference numerical code FLAC 5.0 is merged with random field theory. The results obtained in this study are useful to understand the effect of undrained shear strength variations in slope stability analysis under different slope conditions and material properties. Coefficient of variation and heterogeneity anisotropy of undrained shear strength were proven to have significant effect on the reliability of safety factor calculations. However, it is shown that anisotropy of the heterogeneity has a dual effect on reliability index depending on the level of safety factor adopted.

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In this study, a series of strain-controlled cyclic triaxial as well as bender element tests are carried out, so that the dynamic properties of mixtures of sand and expanded polystyrene (EPS) beads can be assessed under large and small-scale shear strains, respectively. The effect of various parameters such as shear strain amplitude, confining pressure (25 kPa, 50 kPa and 100 kPa) and EPS weight content (up to 2% by weight) on the small strain shear modulus, secant shear modulus and damping ratio is investigated. Laboratory results indicated that the values of shear velocity and shear modulus obtained from the bender element tests decrease with increasing EPS content. The results also revealed that the damping and shear modulus of the samples are highly dependent on the weight percentage of EPS, such that the increase in EPS content results in the increase of damping ratio up to 100% or even more under constant confining pressure. On the contrary, for all the values of confining pressure, the shear modulus of the mixture undergoes a significant reduction with increasing EPS content. Moreover, it is shown that the confining pressure has a important impact on both the soil damping ratio and shear modulus.

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