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在软岩地层中开挖大跨度引水隧洞,围岩自稳能力差,如何保证围岩稳定,进行安全施工是最突出的问题。通过现场踏勘调研,根据引水隧洞的工程地质条件,建立三维模型,基于卸荷岩体力学理论与方法,对开挖后的围岩稳定性进行了详细计算分析。计算结果表明,考虑开挖过程中的动态卸荷效应后,围岩产生了较大的变形,但主要集中在断层和隧洞相交的局部位置附近,洞轴线剖面其它位置的拱顶沉降大约在10 mm左右,隧洞周边位移相对值在规范允许范围之内,没有大范围失稳趋势。断层、不整合接触带位置附近的卸荷效应影响尤为明显,出现了明显的塑性区,产生了局部变形和应力集中,应该引起足够的重视,在开挖的过程中要及时或超前支护。最后,根据计算分析结果,提出了一些切实可行的施工方法建议措施。研究成果为引水隧洞的设计和施工支护提供了重要的参考。
In soft rock strata excavation of long-span diversion tunnel, the surrounding rock self-stabilization ability is poor, how to ensure the stability of the surrounding rock, the safe construction is the most prominent issue. Through on-site investigation and investigation, according to the engineering geological conditions of the diversion tunnel, a three-dimensional model is established. Based on the mechanics theory and method of unloading rock mass, the stability of the surrounding rock after excavation is calculated and analyzed in detail. The calculation results show that, considering the dynamic unloading effect in the excavation process, the surrounding rock has a large deformation, but mainly concentrated near the local location where the fault intersects with the tunnel. The vault settlement at other locations along the axis of the tunnel is about 10 mm, the relative displacements around the tunnel are within the allowable range of the norms and there is no trend of large-scale instability. The effect of unloading effect near the location of fault and unconformity contact zone is especially obvious. The obvious plastic zone appears, which has caused the local deformation and stress concentration. It should pay enough attention and should be timely or advanced support during the excavation. Finally, according to the result of calculation and analysis, some feasible measures for construction method are put forward. The research results provide an important reference for the design and construction support of the diversion tunnel.