Incorporating Site Variability into LRFD Design of Pile Foundation

This paper focused on evaluating the effect of variations in geotechnical properties on the design of deep foundations. The coefficients of variation of undrained shear strength and friction angle (COV_Su, COV_ϕ) and the effect of sampling location on the deep foundation resistance factor were investigated. For the cohesive soil condition, analysis was done in the Red River site in Louisiana, where the weighted average undrained shear strength (S_u) and the COV_Su range from 54.89 kPa to 105.39 kPa, and from 7% to 48%, respectively. For the cohesionless soil condition, analysis was done for the weighted average friction angle (ϕ) of 30°, and for the COV_ϕ range from 0% to 50%. For the mixed soil layers, analysis was performed in Metairie site, where the S_u, ϕ, COV_Su, and COV_ϕ are 23 kPa, 39°, 27%, and 35%, respectively. The results showed that the resistance factor of deep foundation, ϕ_df, decreases with increasing the COV_Su and the COV_ϕ, and with increasing the distance of borehole from the pile foundation. In the site with multiple boreholes, the effect of sampling location on the resistance factor of deep foundations was investigated, and the resistance factor was calculated using the inverse distance weight (IDW) method.