Tensile response and fracturing process in moderate and high plasticity clays

Sinkholes in clay soils can be considered as the collapse of a soil layer previously bridging a void. Here, flexural deformation in the clay drives the formation of tensile cracks from the lowest surface of the layer and the consequent soil collapse is from crack propagation. Considering a simplified model of the sinkhole geometry, this paper aims to describe the tensile and fracture behaviour of clay soils with different plasticity indices. Speswhite kaolin, London and Durham clays were tested using direct tensile and bending tests. Moderate and high plasticity clays showed a nonlinear fracture response with increasing moisture content, while low plasticity clays demonstrated a linear response. Bending tests confirmed the importance of the moisture content while the plasticity index confirmed the difference in ductile or fragile collapse for fracture propagation. To assess the results, Elasto-Plastic Fracture Mechanics (EPFM) theory was applied to clays with appropriate modifications. The analysis demonstrated that EPFM theory provides a good baseline for predicting tensile fracture behaviour in clay soils which can be extended in future research.