Abstract：
Considering that underwater tunnels are important river-crossing passages in urban areas at present, and using the construction of the Yingpan road tunnel in Changsha city as an example, some innovative design and construction methods are discussed for urban underwater bored tunnels. A method for determining minimum overburden is put forward based on the consideration of engineering control measures and analysis of the problems with existing methods, by which the minimum overburden is determined to be 11.5 m (more than 5 meters shallower than under existing methods in China and abroad) and the tunnel length is reduced by nearly 400 m accordingly. The water seepage during tunnel operation could be reduced by adopting a “blocking-based limited drainage” principle and adjusting grouting-ring thickness and relevant reinforcement parameters. A shallow-buried large-section underwater tunnel with a depth/span ratio of 0.46 and excavation area of 376 m2 is completed successfully using advance full-face pre-reinforcement, a double-layer primary support, a reasonable excavation section division, and proper construction arrangements.
2016, Vol. 53 