针对软弱地基上的高速公路填方路堤稳定性问题，利用整体圆弧法稳定性分析原理，推导了同时考虑滑动面上黏聚力 和内摩擦角 联合作用的平衡方程；并将滑面上内摩擦角 在滑面切向方向上的作用等效为黏聚力作用，提出在此条件下的等效黏聚力概念；进而利用平衡方程和等效黏聚力讨论了合理反压护道宽度和高度的确定方法。以某高速公路反压护道工程为背景，进行了护道断面尺寸的设计计算和分析，并将安全系数和滑体特征与规范推荐方法进行了对比分析。结果表明：相对只考虑黏聚力的计算结果，综合考虑黏聚力 和内摩擦角 联合作用的分析方法更接近大部分软弱地基内摩擦角非零的工程实际条件，且在获得相同安全系数时具有更优的断面尺寸（节约用地和土方量）；该方法与规范推荐方法计算的安全系数有紧密的联系，其值取1.05时与规范容许值较为吻合；该方法能避免设计中依靠经验反复试算确定护道尺寸的盲目性，可减少设计工作量。

To investigate the stability of the expressway embankment on soft ground, the whole arc method is used to deduce a limit equilibrium equation with coupling variables of internal friction angle and cohesion .The effect of internal friction angle on the tangential direction of slip surface is then assumed equivalent to cohesion effect, and the concept of equivalent cohesion is proposed. Based on the limit equilibrium equation and the equivalent cohesion, a procedure to calculate the optimal section size of loading berm is developed. The proposed procedure is used to design the section size of the loading berm and to determine the safety factor for a expressway embankment, and the calculated results are compared with the method from the code. The results show that because the combining effect of internal friction angle and cohesion is considered, the proposed procedure has a greater advantage in acquiring the optimal section size of loading berm than the method recommended by the code, in which only cohesion is considered. The safety factor calculated by the proposed method is 1.05, which agrees well with the results obtained with the method from the code. The proposed method can avoid the shortcomings of traditional methods that require experience in determining the size of berm.