水下隧道大跨分岔结构设计与围岩稳定分析

长沙市营盘路湘江隧道主线与匝道分岔段为大跨扁坦结构，最大开挖跨度达21m，与单洞4车道相当，应作为特殊节点进行设计。通过调研与分析，从最小覆盖层厚度、净空断面、结构型式、支护参数等多方面分别对分岔隧道的最优设计方案进行论证，并采用地层一结构力学模型予以验证。研究表明，隧道东汉大跨结构最小覆岩厚度可按不小于12m进行控制；通过优化下半断面矢跨比可进行抗水压衬砌的内轮廓断面设计；江底隧道的抗水压支护结构体系应包含内、外2个层次；初步设计方案合理，技术先进。研究成果对于大型越江交通隧道工程具有参考意义。

Analysis of Rock Wall Stability and Structure Design of Large -span Branch Section of Underwater Tunnel

The bifurcated section between main line and crossroad of Xiangjiang Tunnel on Yingpan Road of Changsha is a large -span shoulder pole structure with the maximum excavated span up to 21m equivalent to 4 lanes on single hole, and should be designed as a special node. Based on investigation, study and analysis, this paper demonstrates the optimal design schemes for the bifurcated tunnels from many aspects including the minimum thickness of covering layer, clearance section, structural types and supporting pa- rameters, etc. , and verifies them by means of stratum - structure mechanical model. The study shows that the minimum thickness of covering rock of eastern bifurcated large - span structure of tunnels can be controlled according to not less than 12m; the inner contour section of water pressure resistant lining can be designed by optimizing the rise to span ratio of lower section ; the water pressure resistant supporting structure system of lab tunnel should include internal and external layers; the preliminary design is reasonable in scheme and advanced in technology. The achievements of study present the significance of reference for largescale crossrive traffictunnel projects.