Minimising the kinematic loading demand on bridge piers from laterally spreading crustal layers

During earthquake-induced lateral spreading, large kinematic loads can be exerted on bridge piers and pile caps which pass through the soil. This is particularly true when cohesive crustal layers are found at the ground surface, overlying liquefiable material. In these circumstances, the relative impermeability of the crust can lead to the formation of a water film at the interface with the liquefiable soil, resulting in large down-slope movements of the crust. As this surficial layer does not soften substantially, large kinematic loads can be applied to structural elements passing through the soil. This paper investigates the effect of pier design, specifically whether separated piers or a single monolithic pier are used, on the kinematic demand which is placed on bridge from the spreading crust. Small-scale model testing data is presented, in which a modified direct shear box was used to simulate the spreading of cohesive material past
structural inclusion. For a given cross-sectional area or second moment of area (i.e. bending stiffness for a given material) required of the pier(s), which will typically be dictated based on structural considerations, the optimal design will be sought which minimizes the kinematic demand. This offers a straightforward
way of optimizing the basic seismic resilience of a structure at no extra cost and may obviate the need for further active remedial measures.