不同强度准则下软岩巷道底板破坏安全性比较分析

长期以来，对地下硐室的稳定性评价一直缺乏一个合理的评判标准，传统有限元法无法计算出硐室的安全系数，仅凭应力、位移和塑性区大小很难确定硐室的安全度。为解决这一难题，吸收极限分析有限元方法的优点，开展基于强度折减技术的软岩巷道底板的安全系数求解。极限分析本质上是强度问题，强度准则的选取对求解结果影响很大，为此探讨不同强度准则参数之间的关系和经典D-P准则与扩展D-P准则之间的剪切安全系数的转换。考虑巷道底臌是由于两帮岩体产生压模效应而造成底板岩体出现的整体剪切破坏，通过不断折减岩体的抗剪强度参数，以底板特征点位移突变为破坏判据，求解底板的稳定安全系数及潜在破裂面，并比较不同强度准则下的求解结果。结果表明，安全系数的理论转换公式具有较高的计算精度；不同强度准则求解的安全系数关系为DP1准则＞M-C准则＞扩展D-P准则＞DP4准则＞DP2准则＞DPM-C准则＞DP3准则，即DP1准则是偏不安全的，其中DP2，DPM-C，DP3准则求解结果吻合较好；网格密度及剪胀角的选取对结果收敛影响很大。

SAFETY ANALYSIS FOR SOFT ROCK TUNNEL FLOOR DESTRUCTION BASED ON DIFFERENT YIELD CRITERIONS

For a long time，stability evaluation of underground tunnel is unreasonable and unscientific. Safety factor of cave cannot be got by classical finite element method and it is difficult to judge the stability of tunnel by the criterion of stress，displacements of tunnel perimeter or size of plastic zones of surrounding rocks. Therefore，strength reduction technique is conducted to solve the stability factor of tunnel floor. Ultimate analysis is essentially a strength problem，so different strength criterions would cause different results. In view of this，relationship of strength parameters of different yield criterions are put forward and conversion expressions of the shear safety factors between classical Drucker-Prager(D-P) criterion and extended D-P criterion were obtained based on plane strain assumption. Considering that floor heave is caused by the general shear failure by compression effect of rock mass of tunnel walls，stability safety factors and potential failure surface of soft rock tunnel floor were analyzed according to the damage criterion of displacement catastrophe based on strength reduction finite element method，and results were compared with respect to different yield criterions. The results show that，theory conversion methods of safety factors have higher accuracy. Relationship of safety factors solving by different criterions are DP1＞M-C＞generalized D-P＞DP2＞DP4＞DPM-C＞DP3，which shows result of DP1 is in unsafe side and the results of DP2，DPM-C，DP3 are in good agreement with each other. Grid density and dilatancy angle have great influence on the results convergence.