U型碾压混凝土薄、高拱坝在国内外尚不多见,其中湖北省青龙拱坝因地形条件的独特尤为特殊,应力分布规律较常规V型拱坝有根本性差异,即在距坝底1/4坝高的下游坝面拱冠处出现较大面积的拉应力区,因此对青龙U型薄拱坝破坏机制及安全度的探讨非常必要。基于带拉破坏Drucker-Prager准则,利用强度储备系数法和超载法,分别对青龙拱坝的极限承载能力进行弹塑性有限元分析;运用位移突变法、塑性区贯通及收敛性等破坏判据,探讨其破坏机制,评价其整体安全度。结果表明:选用分析承载能力的方法不同,则青龙U型薄拱坝在极限承载过程中上、下游坝面破坏形态不同,但坝体最终的破坏形态基本一致;总结了其渐进破坏模式特点,并指出其在极限承载过程中由于应力的自行调整,拉应力减小或消失,满足稳定安全要求。

U-shaped thin and high arch dam is rarely seen all over the world. Qinglong arch dam in Hubei province is especially significant on account of its special terrain conditions. It is an RCC thin arch dam constructed in particular U-shaped river valley. The stress distribution of Qinglong arch dam is significantly different from that of conventional V-shaped dam. A large tensile stress area was found in the downstream arch crown which is 1/4 dam height from the bottom of dam. In view of this, discussions on the failure mechanism and safety of the dam are imperative. On the basis of the Drucker-Prager criterion, the ultimate bearing process of Qinglong arch dam is calculated and analyzed by using strength accumulation coefficient and overloading coefficient. Furthermore, by recording the abrupt change of dam displacement and observing the connected plastic zones and the convergence in the evolutionary process, the failure mechanisms of Qinglong arch dam is discussed and the safety degree is evaluated. Results suggest that different simulation methods lead to different destruction modes of dam in the upstream and downstream. But the final destruction patterns are consistent in general. As the stress of Qinglong arch dam in the ultimate bearing process adjusts itself, the tension stress decreases or disappears, and the safety of dam meets stability requirements. In addition, the characteristics of progressive failure mode of the dam are summarized. The research results offer important reference for similar projects.