平面应变条件下的极限土压力

 针对朗肯土压力理论计算结果与实测结果往往出现偏差，且在很多工况下偏于保守的不足，基于平面应变条件下考虑中主应力影响的强度准则，提出新的土压力计算方法。平面应变方向上的主应力在极限平衡条件下为中主应力，在刚塑性假定的基础上通过静止土压力系数确定，结合强度准则得到大主应力与小主应力之间的关系，进而求得土压力系数。该方法的优点在于：一方面理论严密，结论简单，便于应用，通过简单的计算即可得到分析结果；另一方面分析结果不仅能充分发挥材料的强度潜能，产生一定的经济效益，并且对于实际工程分析结果仍然是偏于安全的。理论分析结果表明，朗肯土压力理论的计算误差随着土的摩擦角的增大而增大。通过与试验结果的比较表明，该土压力计算方法更接近实测数据，从而可更好地指导挡土结构的设计计算。

LIMIT EARTH PRESSURE UNDER PLANE STRAIN CONDITION

Based on the strength criterion under plane strain condition and Rankine¢s theory，a simplified method for determination of limit earth pressure is proposed. The principal stress in the plane strain direction，which can be determined under the rigidity-plasticity assumption using static earth pressure coefficient，is the intermediate principal stress under the limit equilibrium condition. The relationship between major and minor principal stresses is obtained based on the strength criterion. Then the earth pressure coefficient can be determined. Although the proposed method is as simple as that of the Rankine¢s theory，it can obtain more reasonable calculation results，and accordingly improve the design methodology yielding output more economically. The results also show that the difference between the proposed method and the Rankine¢s theory is enlarged along with the increase of the friction angle of the material. The validity of this method is confirmed by observed data from the practical foundation engineering. Compared with the Rankine¢s theory，the proposed method can be more rationally used in soil-retaining structure designing.