Assessment of Partial Safety Factors for Limit States Design of Foundations

While limit states design (LSD) is currently the standard structural design practice, it is relatively new in the geotechnical design. Adoption of LSD far geotechnical design is an international trend. In the present study, various LSD codes from the United States, Canada, and Europe were reviewed. A simple first-order-second-moment (FOSM) reliability analysis was performed to determine theoretically the ranges of load and resistance factor values for representative loads and foundation bearing capacity, respectively. In order for foundation design to be consistent with current structural design practice, it would be desirable to use the same loads, load factors and load combinations. The values of load factor, obtained from the FOSM analysis, were found to be generally consistent with those given in the codes, whereas the values of resistance factor indicated overall lower ranges due to high values of coefficient of variation used in the analysis. Since the degree of uncertainties included in bearing capacity of foundations varies with the methods used to estimate the bearing capacity, different values of resistance factor should be used fur different methods. For the purpose, continuous efforts are needed to be made first to accurately identify and quantify the uncertainties in the methods.