Dynamic Fluidization of Soils

Free‐field limit analysis of a homogeneous layer of dry soil excited by uniform horizontal and vertical acceleration components leads to simple equations describing various stages of inertial shear fluidization. Orientations of potential shear flow spread out from the initial slip planes developed at moderate acceleration ratios, less than 0.3, until the general fluidization state is reached, when a broad band of planes are mobilized throughout the layer. In these directions, the layer then behaves as a viscous fluid. For loose saturated soils, it is postulated that initial fluidization will initiate liquefaction, and therefore the free‐field solution for this neutral case may serve as a useful benchmark for estimating liquefaction trigger accelerations. All intermediate stages, both active and passive, from static conditions to general dynamic fluidization are expressed. The solution seems relatively insensitive to boundary conditions, since the free‐field lateral pressures derived do not differ significantly from the classic solution for dynamic active or passive pressures on sliding retaining walls. Finally, both initial and general fluidization of a dry sand layer are demonstrated by shaking table tests of a circular footing and a submerged buoyant box.