An Arc-Tangent Failure Surface for Stability Analysis of Karstic Red-Clay Slopes Under Dry-Wet Cycles

Stability analysis of residual red-clay slopes formed on karstified carbonate rocks challenges conventional analytical methods, such as the simplified Bishop method, that often mandate a presumed failure surface inside the slopes. The strength of residual red clay can be significantly affected by the dry-wet cycles in karstic regions, leading to shallow instability failure of a slope that does not follow a circular shape. Based on comprehensive field studies, this work proposes a new failure surface composed of a circular-arc at the slope toe and a linear tangent segment of the arc along the slope for analyzing the stability of karstic red-clay slopes that experience dry-wet cycles. Key factors that affect the ultimate failure mode of a slope, including the growth of fissure depth, increase in fissure water pressure, and attenuation of soil strength, are properly evaluated, and the proposed arc-tangent sliding surface shows improved prediction of the failure of red-clay slopes as tested on a field slope. The method developed is useful for designing waterproof and moisture-preserving measures for red-clay slopes, such as turfing the slope surfaces.