Abstract: The uplift piles in soft rock with shallow overburden are common in the design of tower foundation of transmission line projects in western China, but there are relatively few studies on the uplift piles at present. The choice of pile side friction resistance value in soft rock in current codes needs to be improved. In this study, field tests in the south side of the Qingjiang river in Guangyuan City were conducted to investigate the bearing performance of 5 uplift piles. By analyzing the Q-s curve, the axial force distribution of pile shaft and the exertion of pile side friction, the standard values of pile side ultimate friction of severely weathered sandstone and weathered sandstone were obtained. The relationship between the average ultimate friction resistance and the uniaxial compressive strength (UCS) of the soft sandstone was obtained as well. A formula to predict the ultimate bearing capacity of an uplift pile was also proposed. In addition, comparison was made between the field test measurements and the value calculated using the existing standards. Our study found an exponential relation between the average side resistance of piles and the UCS of soft sandstone. The standard values of the ultimate side friction found in heavily and medium weathered sandstones were 472 kPa and 1,027 kPa, respectively. This finding provides an engineering reference for future projects.

Key words: uplift bearing behavior, field test, ultimate side resistance, the UCS of rock, existing standards