Seismic Stability of Unsupported Conical Excavation in Clayey Ground

Conical excavations without support are often made in some field projects, such as foundations for piers, oil and water tanks. The seismic stability of these excavations has been given least importance in the research field. The instability of these unsupported excavations might increase during a seismic event. Hence, a realistic estimation of the seismic stability of unsupported excavations is a prominent issue, especially for the perpetual purpose. In the present study, seismic stability number for unsupported excavations has been proposed using the finite element (FE) analyses. Due to symmetry in the geometry about the vertical axis, axisymmetric FE models have been developed using OptumG2 software based on the finite element limit analysis approach. The soil (clay, with isotropic and constant undrained shear strength property) has been modelled as a perfectly plastic Tresca material following an associated flow rule. Boundary conditions were considered as per the field conditions, and seismic loads were considered as pseudo-static force applied in terms of horizontal seismic coefficient, α_h. Adaptive meshing technique was adopted to predict the results reasonably closer to exact solutions. The seismic stability of these conical excavations is reported in terms of stability number. Moreover, the effects of depth of excavation, inclination angle, intensity of seismic loading, etc. on the seismic stability number are explored in detail. For deeper insights and influence of various affecting parameters, non-dimensional design charts are presented. Further, it has been observed that the considered parameters have significant effects on the seismic stability of conical excavations.