Equivalent Design Strengths for Spatially Variable Cement-Treated Soil Slope

Deep soil mixing and jet grouting are in situ ground improvement techniques that are often used to enhance the stability of soft soil slopes for excavation and waterway projects. Although researchers have reported spatial variability in cement-treated ground, the literature on the influence of spatial variability on the stability of treated soil slopes is limited. In this study, the stability of a cement-treated soil slope is analyzed through two-dimensional random finite-element analysis, taking into consideration spatial variabilities in strength and unit weight of a cement-treated soil mass. Spatial parameters such as the mean strength mu qu, coefficient of variation COV, horizontal scale of fluctuation SOFh, and vertical scale of fluctuation SOFv are varied, and the equivalent design strengths and strength reduction factors are calculated. Furthermore, strength reduction factors for isotropic (SOFh/SOFv = 1) and anisotropic (SOFh/SOFv = 7.5) spatially correlated random fields are calculated. The results show that an increasing value of SOFh has a worsening effect on stability up to a particular value, that is, approximately 2.0 times the slope width B, beyond which the influence does not appear to be significant. A strong logarithmic relationship between the SOFh/B ratio and the computed strength reduction factors is observed. Finally, a modified equation for the strength reduction factor is proposed; in this equation, the effect of the scale of fluctuation is considered by introducing an influence factor RSOF. For SOFh/B ratios ranging from 0.02 to 0.7, RSOF varies from 1.0 to approximately 2.0, indicating a significant effect of the scale of fluctuation. However, for SOFh/SOFv ranging from 1 to 7.5, RSOF varies slightly.