浅覆盖层软质岩中抗拔桩承载特性现场试验研究

我国西部地区的电力工程正日益增加，浅覆盖层软质岩中抗拔桩在输电线路工程的杆塔基础设计中极为常见，而目前对此的相关研究相对较少，现行规范对软质岩层的桩侧摩阻力取值也有待完善。在广元市清江河南侧采用现场试验的方法研究了5根抗拔桩的承载特性，整理分析了Q-s关系曲线、桩身轴力分布和桩侧摩阻力发挥情况，得到了强风化砂岩和中风化砂岩的桩侧极限摩阻力标准值。拟合出软质砂岩的平均桩侧极限摩阻力与岩石单轴抗压强度之间的关系，进一步总结出抗拔桩极限承载力的预测公式，并将现行规范计算结果与现场试验测试结果作对比分析。结果表明，软质砂岩的平均桩侧极限摩阻力与岩石单轴抗压强度可用指数函数形式表示；强风化砂岩、中风化砂岩的桩侧极限摩阻力标准值分别为472、1 027 kPa，可为实际工程提供参考依据。

Field tests on bearing behaviors of uplift piles in soft rock with shallow overburden

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.