黄土地基掏挖扩底基础抗拔试验研究

随着西部电网建设的发展，越来越多的架空输电线路需经过黄土地区。输电线路杆塔基础抗拔能力通常是其设计控制条件。掏挖扩底基础因具有较好的抗拔承载性能而在黄土地区输电线路工程中得到广泛应用。根据甘肃黄土地区2个试验场地12个掏挖扩底基础实测上拔荷载位-移曲线，分别采用Chin双曲线模型以及初始直线斜率法、双直线交点法和L1-L2方法确定了基础抗拔极限承载力及其对应位移，得到了抗拔基础归一化荷载-位移曲线，采用归一化荷载-位移双曲线模型对试验结果进行拟合，给出了不同保证概率下基础荷载-位移预测曲线。结果表明：初始直线斜率法得到的承载力最小，双直线交点法次之，Chin数学模型法最大，宜采用L1-L2方法确定黄土地基掏挖扩底基础抗拔承载性能；荷载-位移曲线归一化处理可显著减小实测荷载-位移曲线的离散性，按双曲线拟合参数a、b均值确定的归一化荷载-位移曲线代表了试验平均值，而试验荷载-位移曲线刚度远大于95％保证概率的预测曲线。

Experimental investigation on uplift behavior of belled piers in loess

In recent years, the construction of electricity transmission systems that span from west to east China has been planned. Thus, the construction of foundations for overhead transmission towers is inevitable. Uplift loading often controls the design of transmission tower foundations. Belled piers have been used in loess area to satisfy the requirements for uplift resistance. At two places in Gansu province, twelve full-scale tests were carried out to investigate the uplift behavior of belled piers in loess. Based on the measured load-displacement curves, the ultimate bearing capacities and displacements were interpreted using the Chin hyperbolic model, the slope tangent, double line intersection and L1-L2 methods. A mean normalized load-displacement curve was obtained based on the statistical data of measured results. By fitting measured load-displacement data using a normalized hyperbolic model, normalized hyperbolic load-displacement curves were suggested at different confidence levels. The results show that the slope tangent and Chin methods represent the lower and upper bounds, respectively. The L1-L2 method is appropriate for interpreting the failure bearing capacity. Normalizing the measured load-displacement curves reduces the scatter in the curves. The mean curve more closely represents the actual test data. However, the field tests show a substantially stiffer load-displacement response than the curve at the 95% confidence limit.