Fatigue behavior of static drill rooted piles under dynamic loading in Shanghai regional railway engineering

With the rapid development of Shanghai's regional railway system, as a new pile foundation technology Static Drill Rooted Piles (SDRP) have been widely applied in related projects. Due to the high-frequency, low-amplitude, and long-term characteristics of regional railway traffic loads, research on the fatigue behavior of SDRP is of great significance for ensuring long-term operational safety. This study is based on field tests from a Shanghai regional railway project, where an axisymmetric numerical model of SDRP is established and validated through field pull-out test data. The local stress-strain method combined with a bilinear unified S-N curve is employed to analyze the fatigue life and mechanical response characteristics of SDRP under cyclic train loading. The results show that within the axle load range of 14~17 tons, cycles to failure N of SDRP exceeds 10³⁰, far surpassing the 100-year design service life requirement. The maximum stress in the pile is concentrated at the connection between the upper pipe pile and the lower rooted pile, with stress levels well below the failure stress under 17-ton axle load. In the frequency range of 50~150 Hz, the dynamic load frequency has negligible influence on pile head displacement, with variations of less than 0.5 mm. These findings provide a theoretical basis for the design and application of SDRP in Shanghai regional railway projects.