中文摘要：

在应考虑黏聚力作用的场合下，DDA法按强度折减技术或其它方法给出的安全系数比传统分析方法如极限平衡法明显偏低。即使采用改变块体划分方式、提高内力场分析精度、增加接触点等方法，也均不能提高安全系数。通过分析DDA接触模型发现，造成这一结果的根本原因在于DDA在处理界面黏聚力c时采用了与传统分析方法刚塑性模型完全不同的方式。刚塑性模型认为c是常数。而DDA认为一旦界面发生过滑移后c便为零，而是否滑移的判断完全依赖于接触力计算的准确性，接触力不准确导致发生滑移的不正确判断，使得c被不合理地消除，而DDA法采用的罚法接触处理以及动力迭代模式是很难保证准确获取接触力的。为此尝试为DDA法引入刚塑性模型，补偿接触点在滑面上的黏聚力作用，数值实验表明可明显提高DDA安全系数值，而与传统方法有较好的可比性，该建议措施对于DDA正确地进行边坡稳定性安全系数评估是有意义的。

英文摘要：

When cohesion needs to be considered in many cases, the factor of safety by the DDA using the strength reduction techniques is considerably underestimated compared with the traditional numerical methods such as the limit equilibrium methods. Some suggestions to improve the solutions are proved to be useless by numerical tests, such as changing the way of meshing blocks, improving the solution of block stress fields by alternative approximation techniques and raising the number of contact points on the boundaries. Through investigating the DDA contact model, it is found that the possible reason for the above phenomenon may be that the DDA deals with cohesion in a way quite different from the rigid plastic model adopted by the traditional limit equilibrium methods. The rigid plastic model regards cohesion as a constant, while the DDA takes the cohesion as zero once the slipping between the blocks boundaries occurs. But judging the occurrence of the slipping fully depends on the accuracy of normal and shear contact forces. If the contact forces are inaccurately evaluated, a falsely judged slipping state leads to the corresponding cohesion to be improperly eliminated. But the penalty method by the DDA for the contact analysis and the dynamic iteration computation are very hard to ensure the exact solution of contact forces. Based on this point, the rigid plastic model is used by the DDA to compensate for possible wrong loss of cohesion. Numerical tests prove the values of the factor of safety can be obviously raised, and they are even comparable with those by the traditional methods. This proves the suggestion of applying the rigid plastic model into the DDA is of significance while evaluating the slope stability factor of safety.