Passive Earth Pressure Mobilization during Cyclic Loading

The passive resistance measured in a series of full-scale tests on a pile cap is compared with existing theories. Four different soils were selected as backfill in front of the pile cap and the load-deflection relationships under cyclic loading were investigated. The log spiral theory provided the best agreement with the measured passive resistance. The Rankine theory significantly underestimated the passive force, while the Coulomb theory generally overestimated the resistance. The displacement necessary to mobilize the maximum passive force was compared with previous model and full-scale tests and ranged from 3.0 to 5.2% of the cap height. A hyperbolic model provided the best agreement with the measured backbone passive resistance curve compared with recommendations given by Caltrans and the U.S. Navy. However, this model overestimated the passive resistance for cyclic loading conditions due to the formation of a gap between the pile cap and backfill soil and backfill stiffness reduction. Based on the test results, the cyclic-hyperbolic model is developed to define load-deflection relationships for both virgin and cyclic loading conditions with the presence of a gap.