LAUSR

Abstract This paper presents a three-dimensional trench stability analysis in non-uniform undrained clay adopting the kinematic approach of limit analysis. Rather than assuming a classic curved cylinder (“torus”) shape, the failure surface of the proposed rotational mechanism is formulated by a spatial discretization technique in order to accommodate the non-uniformity profile of soil’s undrained shear strength in a multi-layered ground as well as better adaptation to typical trench geometries in practice. The present study agrees well with the traditional torus rotational mechanism in terms of the normalized trench stability number in uniform clay when trench length to depth ratio is greater than 0.6, while significant improvement to the previous solution is achieved for shorter trench panels. A linear variation pattern between trench stability number and soil shear strength gradient is found for non-uniform soil profiles, in particular for shorter trenches. A simplified method is thereafter introduced for preliminary trench stability evaluation in non-uniform clay profiles. For trenches in two-layered clay, a more notable change in trench safety factor with layer thickness ratio is observed when the top layer is weaker than the bottom layer.