Study on the election of construction schemes for the entrance segment of tunnel with unsymmetrical loading through large-span thin-dover

Jiulian-mountain tunnel is an very important project for a section of Longyang Jiangxi in Da-guang highway. Because Jiulian-montain tunnel has a series of geological problems, like shallow-depth, bias-pressure, big-span,water-rich, rock burst and so on, which is a typical long - wide highway tunnel grew up under complex conditions, construction of the entrance segment is extremely difficult and slow in progress. In order to efficiently accomplish the construction of tunnel on time, it is necessory to elect rational construction scheme of the entrance segment. The numerical simulation for three construction methods,which are benching tunneling method, method of core-keeping cut in stages and CD method, are carried out by means of Three-dimensional fast lagrangian analysis of continua method(FLAC(3D)) in this paper. Based on the result of the numerical simulation analysis and contrast, some conclusions and suggestions are proposed, some gist are offered in order to choose the construction method rationally,and arrange the construction order scientifically, and control the construction pace optimally, and reduce the harm of the construction