Undercutting construction technology of a municipal tunnel beneath existing railways in Hangzhou

Undercutting construction technology of a shallow-buried tunnel in water-bearing layer of sandy silt was introduced.By taking some assisting construction measures such as advanced forepoling reinforcement,full-sectional grouting and CRD construction method,the passing of tunnel beneath the existing trunk railways and the construction safety of closely-spaced large-span twin tunnels were guaranteed.