Evaluating stability of anisotropically deposited soil slopes

Natural soils often exhibit an anisotropic fabric pattern as a result of soil deposition, weathering or filling. This study aims to investigate the effects of spatially variable anisotropic soil fabric in a slope on its safety factor and failure mechanisms, and to identify the critical fabric orientation that is most unfavorable to the slope stability. The strength properties of colluvium (i.e., cohesion and friction angle) are modeled as random fields under two conditions (i.e., independent and negatively correlated). The study reveals that there exists a critical fabric orientation at 30 degrees at which the mean factor of safety is the lowest and the probability of failure is the highest. The negative cross-correlation between soil shear strength properties leads to a significantly lower probability of failure, compared to the independent case. The highest proportion of deep failure mechanism is also identified at the same fabric orientation of 30 degrees. The identified critical fabric orientation is gentler than the slope inclination. This study suggests that the conventional understanding that stratification parallel to the slope surface appears to be the most unfavorable condition leading to the lowest safety level does not hold for spatially varying soils.