Numerical modelling of toe buckling deformation in Haast Schist, Central Otago, New Zealand

Toe buckling deformation is an outward expression of strain which develops near the base of a slope in response to induced gravitational and tectonic stresses acting on a rock mass and can lead to kinematic slope instability. This deformation mechanism is considered responsible for anomalously oversteepened foliations identified underlying three deep-seated landslides within schist bedrock of Cromwell Gorge, Central Otago, New Zealand. Spatial and temporal complexities of schist behaviour in response to stress regimes were numerically modelled using Finite Element Methods based on site-specific field (slope and tunnel mapping, borehole logging) and laboratory (UCS, triaxial, indirect-tensile, point load, shear box) testing data. Sequential unloading was incorporated in the model to simulate the evolution of Cromwell Gorge from a low relief surface (Otago Peneplain) to present day topography (1400 m deep). Sensitivity analyses reveal that specific combinations of high locked-in tectonic stresses, foliation stiffness and orientation contributed to the development of flexural toe buckling at the base of Cromwell Gorge.