Arching in granular soils: experimental observations of deformation mechanisms

Understanding soil arching is an important component of predicting soil behaviour in cases such as the progressive displacements above sinkholes and when predicting loads on buried structures, where the expected deformation mechanisms are used to predict the applied loads. Visual validation of these deformation mechanisms above a void at appropriate stress levels remains limited. Centrifuge tests on dense sand were conducted to allow visualisation of the deformation mechanisms and hence enable a more accurate prediction of the load–displacement curve. The results showed that at the point of maximum arching a triangular failure zone corresponding to the formation of an apparent active failure wedge forms with proposed angles of 45° − ϕ_p/2 to the vertical. If the soil height is large enough to allow the full formation of this initial wedge, the deformation mechanism progresses to a vertical prism. Otherwise, the soil collapses into the void. A modification of the classical arching theory is required to allow it to be used to more accurately predict the stresses at the point of maximum arching and in the ultimate state with large displacements.