隧道与前方大型溶洞应力集中叠加效应

在陆家寨岩溶隧道施工期间,曾预报并揭露大型溶洞,施工过程中接近溶腔段围岩变形较大且伴随围岩块体脱落,给隧道施工带来极大的安全隐患。基于深埋球形洞室的弹塑性二次应力分布,结合新奥法隧道施工理念,利用FLAC3D模拟隧道开挖接近并进入大型溶洞的过程。在自重应力场下分析不同大小的球形洞室周围应力场对隧道围岩变形的影响。结果表明:球形洞室会在周围形成中心半径为1. 5倍洞室半径的应力集中带;隧道开挖接近应力集中带时,将引起隧道前方应力集中区与溶洞应力集中带的叠加;随着隧道继续开挖,叠加效应在下一个进尺完成后失效;分布在隧道两侧围岩,该叠加再分散的过程会造成拱顶、拱肩的变形增大,影响隧道开挖的安全。研究为中国岩溶隧道的建设有重要的参考和借鉴价值。

Study on Stress Concentration Superposition Effect between Tunnel and Large Karst Cave

During the construction of Lujiazhai Karst Tunnel, large-scale karst caves are predicted and exposed. During the construction process, the surrounding rock near the karst cave section deformed greatly and accompanied by the falling off of surrounding rock blocks, which brought great potential safety hazards to the tunnel construction. Based on the elastic-plastic secondary stress distribution of deep-buried spherical caverns and the construction concept of NATM tunnel, FLAC3D is used to simulate the process of tunnel excavation approaching and entering large karst caverns. Analysis the influence of stress field around spherical caverns of different sizes on the deformation of tunnel surrounding rock under self-weight stress field. The results show that: A stress concentration zone with a center radius of 1.5 times that of the cavern will be formed around the spherical cavern. When the tunnel excavation approaches the stress concentration zone, the stress concentration zone in front of the tunnel and the stress concentration zone in the karst cavern will be superimposed. As the tunnel continues to excavate, the superposition effect will fail after the completion of the next footage and distribute in the surrounding rocks on both sides of the tunnel. The process of superposition and redistribution will increase the deformation of arch roof and shoulder, and affect the safety of tunnel excavation. This study has important reference value for the construction of Karst Tunnel in China.