砂土层中盾构隧道局部破坏引发连续破坏的机理研究

盾构隧道由混凝土管片拼接而成,接缝部位薄弱,在建设和运营过程中存在大量风险。国内外发生过多起因隧道管片局部损坏演变为隧道大范围破损甚至连续坍塌并导致地表沉陷等灾害。通过对隧道管片接头的受力分析,建立了接头的极限承载力M-N包络图,作为管片接头的破坏准则。以隧道联络通道施工时,隧道腰部设置洞门作为隧道局部破坏的背景,利用离散元软件PFC,通过FISH语言二次开发研究了隧道腰部管片局部破坏引发的隧道连续破坏机理。研究表明,隧道腰部局部破坏引起土体进入隧道内从而引起隧道腰部外土体松动,并且松动区外围产生的土拱的拱脚支承于隧道顶部区域,这都导致隧道内力急剧增大,直至超过管片及接头的极限承载力,隧道局部破坏发生扩展。由于隧道环间螺栓的作用,破坏环过大的变形引起邻近环横向变形增大,进而引发邻近环的破坏,破坏沿纵向传递,隧道发生大范围连续破坏。最后,初步提出并对比分析了多种隧道防连续破坏措施。

Mechanism of progressive collapse induced by partial failure of shield tunnels in sandy soil

The shield tunnel is generally composed of concrete segments, and there are many risks during both construction and operation because of weak joint parts. Both in China and other countries, the disasters that partial failure of tunnel linings causes a successive failure and even large ground surface subsidence happens in tunneling engineering are not very rare. According to the analysis of joint stresses, an ultimate bearing capacity envelope is established to address the failure criteria for the joints under different internal force conditions, and the failure criteria for both concrete segments and joints are implemented in the discrete element software PFC by using the FISH language. The progressive failure mechanism of the tunnel linings induced by partial failure is discussed. The results show that the partial failure at the springline reduces the resistance of the soil, and the soil arch formed above loose soil area falls on the top of the tunnel, both resulting in a sharp increase in the internal forces of the tunnel, which exceed the ultimate bearing capacity envelope and then induce an extension of partial failure. The failure rings with large transverse deformation cause the adjacent rings to be damaged because of the bolts between the rings. Finally, preliminary prevention measures are proposed and analyzed.