Effect of diameter on the behavior of laterally loaded piles in weakly cemented sand

Integral pile shaft-columns have been increasingly used for bridge foundations in California because of the economical construction of large diameter Cast-In-Drilled-Hole (CIDH) piles. The current design method of piles against lateral loading involves the use of Winkler's spring concept with the standard nonlinear p-y curves. However, the accuracy of using these p-y curves for large pile diameters is questionable because they were developed based on relatively small pile diameters. This research study focused on an evaluation of the pile diameter effect on p-y curves through analytical and experimental programs. Furthermore, an assessment of inelastic performance of CIDH piles under cyclic loading was conducted.; Instrumented CIDH piles with diameters ranging from 0.4 m to 1.2 m were installed in dense weakly cemented sand, and both vibration tests and lateral load tests were carried out. Data from the tests for each pile diameter were used to back-calculate p-y curves. It was found that the pile diameter has insignificant effect on the p-y curves at the displacement level below the ultimate soil resistance. Beyond this range, the ultimate soil resistance increases as the pile diameter increases. Based on the characteristics of back-calculated p-y curves, a methodology to develop p-y curves for weakly cemented sand is proposed.; In contrast, analyses of the Treasure Island case history in loose sand show that the stiffness of the p-y curves increases with the pile diameter. The pile diameter effect therefore appears to depend upon the soil relative density, that is, increasing the soil relative density decreases the pile diameter effect.; Using the standard p-y curves currently available in the literature underestimates the soil resistance in weakly cemented sand for small diameter piles, but tends to overestimate the soil resistance to large diameter piles. Therefore, the use of these standard p-y curves for large diameter piles in weakly cemented sand should be used with caution.; Finally, results from the cyclic lateral pile load tests show that even low to medium levels of transverse reinforcement (0.6%) can provide adequate seismic performance due to the effect of soil confinement retarding the concrete spalling.