关于FHWA的加筋土挡墙设计指南对比分析

为了对比分析FHWA-NHI-00-043和FHWA-NHI-10-024这2个版本的异同, 从而深入理解FHWA有关加筋土挡墙设计方法的发展方向与趋势, 通过算例较为细致地对比分析了二者设计方法的不同之处, 包括抗滑移验算、基底合力偏心距验算、侧向土压力K_r计算和拉拔稳定性验算等。分析结果表明:基于极限平衡理论的设计方法比较保守, 并且与挡墙实际工作状态相差较远, 而荷载与抗力系数法较为经济安全, 且符合挡墙实际工作状态;荷载与抗力系数法的设计理念和极限状态法相关。美国的加筋土挡墙设计方法正在逐步向极限状态法发展。

Comparative Analysis on FHWA Design Guidelines for Reinforced Earth Retaining Wall

The current design guide FHWA-NHI-10-024 (Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes) is based on the LRFD (Load and Resistance Factor) concept, and the previous version FHWA-NHI-00-043 (Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines) is based on the limit equilibrium theory. In this paper, a detailed comparative analysis on the differences between the two design methods is presented by computations in terms of slip resistance, base resultant force eccentricity, lateral earth pressure K_r and pull-out stability. By computation examples, the development trend of FHWA design methods for reinforced earth retaining wall is obtained. Result shows that the limit-equilibrium-based method is conventional and differs greatly from the actual working condition of retaining wall; while the LRFD-based method is economical and safe, and is in consistency with the actual working condition. The design concept of LRFD is related with limit state method, which indicates that the design method for reinforced retaining wall is developing towards limit state method.