Abstract
The total ultimate resistance (or bearing capacity) of driven piles considering setup effects is composed of initial ultimate resistance and setup resistance, and the setup effects of driven piles are mainly reflected by the setup resistance. In literature, a logarithmic empirical formula is generally used to quantify the setup effects of driven piles. This paper proposes an increase factor (Msetup) to modify the resistance factor and factor of safety calculation formula in accordance with the load and resistance factor design (LFRD) principle; here, the increase factor is defined as the ratio of the setup resistance (Rsetup) to the initial ultimate resistance (R0) of driven piles. Meanwhile, the correlation between R0 and Rsetup is fully considered in the resistance factor and factor of safety calculation. Finally, the influence of four key parameters (ratio of dead load to live load ρ = QD/QL, target reliability index βT, Msetup, correlation coefficient between R0 and Rsetup, ρR0,Rsetup) on the resistance factor and factor of safety are analyzed. Parametric research shows that ρ has basically no effect on the resistance factor, which can be taken as a constant in further research, and ρ has a significant influence on the factor of safety. The value of Msetup has almost no effect on the resistance factor and factor of safety. However, βT and ρR0,Rsetup have a significant influence on the resistance factor and factor of safety, so the value selection of βT and ρR0,Rsetup are crucial for reliability-based design of driven piles. Through this study, it is concluded that considering setup effects in reliability-based design of driven piles will greatly improve the prediction for design capacity.
Highlights
During the process of pile installation, the excess pore pressure generated dissipates over time, and the effective stress in the soil will increase, which is the main reason for the increase in the total ultimate resistance of driven piles after installation with time [1,2]
Bian et al [23] put forward a methodology to separately calculate the resistance factors for ultimate base and shaft resistance for reliability-based design of driven piles considering setup effects based on the load and resistance factor design (LRFD) principle
This indicates that the negative correlation between R0 and Rsetup has a significant influence on the resistance factor of driven piles, while the positive correlation between R0 and Rsetup has a slight influence on the resistance factor of driven piles
Summary
During the process of pile installation, the excess pore pressure generated dissipates over time, and the effective stress in the soil will increase, which is the main reason for the increase in the total ultimate resistance of driven piles after installation with time [1,2]. LRFD is a more advanced design method than the existing allowable stress design (ASD) [17], and many countries and regions, such as the United States, Canada, China mainland, Japan, Korea, Singapore, Europe, and Hong Kong, have replaced ASD with LRFD Against this background, many researchers calculated the resistance factor and factor of safety for driven piles considering the setup effects based on the LRFD method. Bian et al [23] put forward a methodology to separately calculate the resistance factors for ultimate base and shaft resistance for reliability-based design of driven piles considering setup effects based on the LRFD principle.
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