Lateral Stiffness and Bending Moment Changes along Piles Having Different Sections in Loose Sand Subjected to Cyclic Lateral Loading

Two-way cyclic lateral loading tests with constant displacement amplitude were performed on model piles in the sand to investigate the effects of cross-section geometry and modulus of elasticity on their behavior. The tested model pile sections included one square and three circular shapes and were made of polyethylene and polyurethane materials. The frequency of the cyclic loading was 0.29 Hz and the total number of loading cycles was 145 for all the tests. The model piles were tested in a metal test tank equipped with various facilities including a cyclic lateral loading system, devices to measure displacement and pressure along with the pile, an inverter to adjust or change loading frequency, a sand raining system, etc. Test results indicated that, from a global point of view, the soil modulus of lateral subgrade reaction and maximum moment developed in the pile increases with the number of loading cycles; however, the rate of increase gradually decreases. These variations may be formulated using a logarithmic relationship which includes a degradation parameter that reflects the rate of the mentioned decrease. It was also concluded that the cyclic effects are more significant for the lateral load resistance and stiffness than for the moment. The maximum moment at the 145th cycle for piles with various section geometries and elasticity moduli varied from 1.10 to 1.18 times the value obtained in the first cycle. Depending on the section shape and dimension, cyclic loading can increase the lateral stiffness of the soil at depths shallower than about 6.2 to 9.3 times the pile diameter.