Recalibration of LRFD Resistance Factors for Driven Steel Piles at End of Drive Conditions in Alberta, Canada

Abstract

The geotechnical resistance factor (GRF) is an important parameter used as a part of the implementation of the load and resistance factor design (LRFD) method. This paper presents the improvement of the GRF used in the design procedure for axially loaded driven piles in Alberta, Canada. To obtain this goal, an extensive database of in situ pile load tests, including the results of 28 static load tests (SLT) and 623 pile driving analyzer (PDA) tests was collected from different locations in Alberta. Various known static analysis methods were used for the prediction of pile bearing capacity based on laboratory and in situ geotechnical tests. The GRFs for the static analysis methods were calibrated using a well-known probabilistic technique, called Monte Carlo simulation (MCS). Calibrated GRF values have been recommended for the design of pile bearing capacity based on the soil type, cohesive fine content along the pile length, different empirical methods, and geological region of Alberta. The results showed that regional calibration of GFR based on the local database resulted in higher values of resistance factors than those recommended in national codes, leading to a more accurate and cost-effective design procedure. In the recent decades, many countries have moved from the allowable strength design (ASD) method to the load and resistance factor design (LRFD) method. The LRFD method employs the geotechnical resistance factor (GRF) to design geotechnical structures such as pile foundations. As recommended by different design codes, regional recalibration of GRF based on local in situ pile tests can lead to being more reliable and removing unnecessary conservative assumptions during the pile design procedure. Using a comprehensive database, including 28 static load and 623 PDA tests carried out in Alberta, Canada, it is aimed to evaluate and calibrate the GRF of the LRFD method for the bearing capacity of driven steel piles based on site-specific geotechnical investigation reports and analytical approaches considering different static analysis methods in this study. Based on the results, the recommended GRFs in cohesive, mixed and cohesionless soils for β=2.33 are 0.58, 0.62, and 0.64, respectively. However, for β=3.00 the GRF values are 0.46, 0.49, and 0.49 for cohesive, mixed and cohesionless, respectively. The regionally recalibrated GRFs are higher than those recommended by CFEM, which may lead to reducing the number or length of piles required during the design process.