Recently, the concept of performance based design has become popular for many types of structures, including port facilities under seismic loading. For the case of pile-supported wharves, the level of performance is generally estimated using the displacement capacity of the structure. Therefore, understanding soil-pile interaction is one of the most critical factors for estimating performance. One of the biggest challenges on the displacement estimation is defining the soil parameters. However, only limited information is available in the literature on the behavior of laterally loaded piles in the large-diameter rockfill typically used in port dike construction, where the particle size approaches the pile diameter.;In light of this, a series of full-scale lateral load tests on piles in the rockfill were conducted in order to obtain a better understanding of the performance of the wharf deck-pile-soil system against lateral loading, and reaction mechanism in rockfill. All the tests were conducted successfully, and large amount of useful data and some important observations were obtained during and after the tests.;Following the experiments, numerical analyses were conducted with a set of soil dependant stiffness curves (i.e. p-y curves) currently used for design practice. These results were compared with the test results in order to assess the validity of the current design approach. It was concluded that those p-y curves could provide reasonable rotation and deflection profiles along the test piles, but gave considerably underestimated ultimate lateral resistance of the pile-soil system. In order to find possible reasons for this, the observations during and after the tests were carefully reviewed. Based on the review, it was found that the lateral reaction from the rockfill under low confinement plays a very important role. Considering particulate mechanism in the rockfill, a reasonable hypothesis was developed; i.e. the lateral reaction from the rockfill is a combination of reactions due to both friction and interlocking between large rock particles. Based on this hypothesis, backcalculation of the p-y curves was carried out comparing the experimental and numerical results, and it was concluded that addition of the interlocking concept to the p-y curves used in the current design methodology significantly improved performance.
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