Evaluation of reliability index and safety factors for pile load capacity estimation using CPT results

The reliability index is an important reliability parameter that is necessary for the development of reliability-based geotechnical design. Both the factor of safety (FS) and the reliability index (β) represent safety margin of structures against either failure or limit state. In this study, the reliability index is analyzed and evaluated in reference to the factor of safety currently adopted in working stress design for pile foundation. Evaluation of the reliability index focuses on CPT-based pile resistance method. Various load-settlement criteria including the 0.1B, Chin, De Beer, and Davisson's methods were adopted to determine pile load capacity from pile load test results. As a CPT-based pile load capacity estimation method, LCPC method was adopted. Using load-settlement curves and CPT results obtained from literature, FOSM analysis was performed for the determination of the reliability index. Based on FOSM analysis, safety margin given by current factor of safety used for the allowable and ultimate condition of pile load capacity are evaluated and compared with values of the reliability index for each load-settlement criterion.