移动交通荷载下公路软土地基的沉降计算

Predicting settlement of road on soft subsoil induced by moving traffic load

交通荷载是一种移动的重复作用荷载,在地基中产生的附加动应力的路径和大小与移动速度密切相关,目前的简化算法中忽略了移动速度的影响。通过数值积分算法得到了交通荷载在地基中引起的附加动应力,探讨了移动荷载下地基中应力路径特点及其与荷载移动速度的关系,提出在拟静力计算的地基附加应力结果上乘以荷载速度效应的放大系数的简化近似方法,给出了便于工程应用的放大系数的实用图表。根据移动荷载在地基中产生的附加动应力路径的特点,提出了一个适用于循环心形应力路径的饱和软土残余变形的经验模型,通过对已有试验成果的模拟,初步验证了所提模型的有效性。在此基础上,建议了一种考虑荷载移动速度影响的路基沉降实用算法。以Saga机场高速公路的沉降计算为例,初步探讨了不同车速比下的公路沉降发展的特点和规律。

The acting position of traffic load moves on road surface with certain velocity. The induced stresses in subsoil imposed by traffic load depend on the moving velocity of load, whereas the simplified procedures nowadays used for induced stresses calculation by traffic load have ignored this velocity effect. The paper studies the long-term settlement of road on soft subsoil with emphasis on the velocity effect of moving traffic load. The numerical integration method is employed to get the induced stresses in the elastic half-space by a surficial moving point load with uniform velocity. By analyzing the characteristics of the induced stresses, a practical procedure is proposed for calculating traffic-load-induced stresses in road subsoil, which combines the results of commonly-used pseudo method with two amplification coefficients accounting for velocity effect. In the other aspect, an empirical model is proposed for quantifying the accumulation of residual strain during the long-term repeated cycles of heart-shaped stress paths, a typical stress path-induced by surficial moving load. The proposed empirical model is validated by the simulated test results. Once the induced stresses and residual strain of the subsoil can be calculated, the road settlement prediction is straightforward following the layer-wise summation procedure. The Saga airport road is taken as an example to analyze the influence of vehicle moving speed on long-term settlements.