Lateral response of pile-cap foundation systems and seat-type bridge abutments in dry sand

A centrifuge model study of lateral response of pile-cap foundations and seat-type bridge abutments is presented. A total of thirteen models were tested, all in dense dry Nevada sand of 75% relative density. Ten of these centrifuge tests were performed at a centrifugal acceleration of 30-g on models of the cap, single pile, and pile-cap system in this dense dry sand. These tests approximately modeled a prototype reinforced concrete square, 1.14 m x 1.14 m by 0.84 m high cap and a typical 40-cm diameter Cast-In-Drilled-Hole (CIDH) pile in dense dry sand. Lateral secant stiffness and material damping ratio at various displacement amplitudes, and the ultimate lateral capacity of the foundation were measured. The objective of these tests was to study the relative contributions of a single pile and of an embedded cap to the total lateral response of the pile-cap system; as well as the contributions of the base, shearing sides, and active/passive sides of the cap to the response of the cap. Three-dimensional static nonlinear finite element analyses were used to predict the measured lateral load-displacement curves of centrifuge tests on cap-alone. Parametric studies were then performed to study the influence of the value and distribution of the soil shear modulus and of the cap/footing geometry on the nonlinear lateral response of the footing. Three centrifuge tests at centrifugal accelerations ranging between 50 and 100 g were performed on a model of seat-type abutments in dense dry sand, simulating prototype bridge abutments of various dimensions including a typical California abutment geometry. The measured secant stiffnesses and the measured ultimate lateral capacities are compared with standard design procedures.