Study On Construction Mechanical Characteristics And Long-Term Stability Of Large Section Tunnels With Closely Spaced

In order to meet the demands of growing economic and transport development and to solve the outstanding problems caused by separated tunnels, such as inflexible expanding line, large land area, high slope etc, the closely spaced tunnels with large section as represented by three-lane highway tunnel would gradually increased. However, the application study on the closely spaced tunnels with large section are still at a preliminary stage. The systematic study on their mechanical characteristics during construction is fairly few. Their design theory and construction method has not yet ripe . So current research could not meet the needs of construction these construction projects. In this paper, according to three-lane tunnel of ChaoYangSi in Chongqing beltway highway around the northern section of N7, construction mechanical characteristics, the proximity construction impact reasonable distance explored and long-term stability would be studied by adopting the methods of numerical simulation and in-site test.Aim at the complex mechanical properties of the closely spaced tunnels with large section, their three-dimensional elastoplastic analysis were made with the practical engineering examples. the deformation rules during excavating the tunnel were obtained. The deformation and mechanical characteristics in supporting structure and the rock surrounding tunnel were evaluated by near degree of yield. The effect rules of the closely spaced tunnels with large section during excavating were discussed.In order to select the rational methods to excavating the closely spaced tunnels with large section, their deformation and mechanical characteristics in supporting structure and the rock surrounding tunnel were obtained in the different excavating methods. The results showed that the obvious method in the controlling the surface subsidence and reducing the impact of tunnel construction proximity should be the double-sides-wall excavation method, the second should be CRD excavation method, the following should be the benching tunneling construction method, the last should be the whole section excavation method. The approaching yield line in the rock surrounding tunnel would be butterfly-shaped by CRD excavation method, the benching tunneling construction method and the whole section excavation method. But the mechanical characteristics in the rock surrounding tunnel would be more symmetrical by the double-sides-wall excavation method . Based on the existing research results of closely spaced tunnels, their deformation and mechanical characteristics in supporting structure and the rock surrounding tunnel were obtained in the different distance between the two tunnels. The research results showed that the more reasonable distance between the two tunnels should be 1D～1.2D(D means the width of a noked tunnel). Their deformation and mechanical characteristics of the surrounding rock in the noked tunnels were obtained by the strength reduction method. This calculated results were the same as the foregoing results. A new reasonable distance of the closely spaced tunnels with large section was proposed.Taking the rheological role of the rock surrounding tunnel into account, the long-term stability anlasys for the closely spaced tunnels with large section were made in this paper. The results showed that the effect of the rheological role for the deformation of the rock surrounding tunnel would be larger in the former decade, would gradually reduce over time, and would be in basically stable up to 50 years, that the effect of the rheological role would mainly embody in the secondary lining, but the secondary lining would be far from the level of yield and damage.