Lateral Spreading Forces on Bridge Piers and Pile Caps in Laterally Spreading Soil: Effect of Angle of Incidence

摘要

In this paper, the kinematic forces which may be applied to bridge piers or pile caps from laterally spreading surficial cohesive soil layers (nonliquefied crusts) through which they pass are considered. Such forces often represent the largest load component acting on a structure and/or foundation during liquefaction-induced lateral spreading. Both circular and square structural inclusions are considered, and particular attention is paid to the orientation of the inclusion to the direction of spreading, here defined as the angle of incidence (θ). Experimental modeling was conducted using a modified direct shearbox to simulate the spreading of kaolin past structural inclusions at various θ. Load-displacement data and particle image velocimetry analysis revealed that the ultimate load for both square and circular cases may be determined using a wedge-based upper-bound plasticity analysis. For circular sections, this ultimate load is independent of 8 due to radial symmetry. The ultimate load on square sections was found to depend more significantly on θ and a simple analytical method is presented to account for this. The method suggests that the ultimate loads acting on square bridge piers or pile caps will be a maximum when the spreading soil impinges on the corners of the inclusion, at which time the ultimate load will be 19-26% larger (depending on the soil-structure interface roughness) than for spreading impinging on the edge of the inclusion. Experimental tests suggested a value of 22%. Finally, the tests support previous results suggesting that when the underlying soil is unable to carry redistributed shear stress (i.e., when it is liquefied) load-displacement curves in the crustal layers are less stiff than for typical retaining structures under static conditions. The displacement at soil yield was found to be between 20-30% of the height of the inclusion in the layer, and also depends on 9 in the case of square inclusions.