Abstract: To reduce the safety risk of the largespan section and the ultrasmall cleardistance section of the bifurcated tunnel, and to meet the schedule requirements, the method of replacing the middle rock pillar by smallclear span section and the optimizing the doublearch to side tunnel and enlargement and shotcrete is adopted according to the bad tunnel geological conditions, complex surrounding environment and high sensitivity of a bifurcated municipal tunnel. And then the side pilots of bifurcated largespan section are enlarged to original size of 2lane crosssection, the middle pilot is reduced in sequence, and the coherent construction of the pilots on both sides can be optimized into the integrated doubleside piloting method. By adopting the method mentioned above, the optimization of the construction method of the longspan section and the ultrasmall cleardistance section can be realized, the construction risk can be effectively controlled, and rapid construction can be achieved.

Key words: bifurcated tunnel, large span section, small clearance section, grouting reinforcement