Determination of Shaft and Base Resistance Factors for Drilled Shaft Embedded in Rock in Korea

Abstract

The Load Resistance Factor Design(LRFD) method was introduced about a decade ago and is being used increasingly in Korea in the geotechnical engineering field. The resistance factors suggested by AASHTO for drilled shafts also were introduced in Korea. However, since most bedrock conditions in Korea differ from those of the US in terms of weathering and strength, direct application of the AASHTO resistance factors for geotechnical design in Korea is thought to be inappropriate. Thus, appropriate resistance factors for the design of drilled shafts socketed into weathered rock in Korea were pursued in this study. Towards this aim, 22 cases of data for shaft resistance and 11 cases for base resistance were collected from the results of pile load tests performed at 13 different sites, and analyzed using a reliability-based approach wherein the target reliability index was set to 2.0. Obtained resistance factors ranged over 0.48~0.56 for the shaft resistance and 0.34~1.93 for the base resistance. When the target reliability was considered as 3.0, the resistance factors were evaluated as approximately one half of the shaft resistance and two thirds of the base resistance when the target reliability index was 2.0.