Model Testing on the Effects of Section Geometry and Stiffness on the Cyclic Lateral Behavior of Piles in Loose Sand

Abstract

In this study, two-way cyclic lateral loading tests with constant displacement amplitude are performed to investigate the effect of cross section geometry and modulus of elasticity on the behavior of model piles in sand. Various laboratory pile models were tested in a metal test tank equipped with various facilities including cyclic lateral loading system, devices to measure displacement and pressure along the pile, an inverter to adjust or change loading frequency, sand raining system, etc. Different cross section geometries, including square and circular shapes, were used for piles made of polyethylene and polyurethane. A loading frequency of 0.29 Hz and a total number of 145 loading cycles were used for all the tests. Results revealed that in constant displacement amplitude tests, both lateral load resistance of the pile head and stiffness of the pile–soil system increase with an increase in the number of loading cycles; however, the rate of increase gradually decreases. It is shown that these variations may be formulated using a logarithmic relationship, which includes a degradation parameter reflecting rate of these changes. For tests with different pile cross section shapes, dimensions, and moduli of elasticity, the degradation parameter varied from 0.08 to 0.18. The pile head load and stiffness of the pile–soil system at the end of the 145th cycle varied from 1.4 to 1.85 times those of the first cycle for different section shapes, dimensions, and moduli of elasticity.