Research On Construction Process Mechanics Of Closely Spaced Tunnels

The closely spaced tunnel is one of the feasible solutions for tunnel construction, which is an effective supplementary type for the separated tunnel. By using closely spaced tunnels, some outstanding problems caused by separated tunnels such as inflexible expanding line, large land area, high slope, and so on, can be solved more effectively. However, the application and study of the closely spaced tunnel are still at a preliminary stage. The systematic study on the mechanical response during construction is fairly few. In engineering practice, the guideline for design and construction is insufficient.In this dissertation, systematically and thoroughly study and evaluations were carried on the construction mechanics of the closely spaced tunnel, basing on the Pingnian tunnel of Luo-Fu expressway in Yunnan Province. The research methods include numerical simulation, similarity model test and in-situ monitoring measurement.Firstly, in order to obtain a better understanding of the Pingnian tunnel, a comprehensive geotechnical investigation was completed, which consisted of investigation of special topic, sampling, and laboratory test. All these make us renewed the understanding of geological condition of the tunnel, which is helpful for the later researches. Plane strain model tests were performed, which is guided by similarity theory. And the numerical simulations according to the tests by the FEM were also conducted to compare the results of the tests. By analyzing the results of the two methods, we can draw the characters of the stress distribution in surrounding rock, the movement of rock during the construction. The mechanism and performance of the interaction between two tunnels were understood more thoroughly.Secondly, using the large finite element software Msc.Marc, the 2D numerical simulations were conducted. The factors affecting on the construction mechanisms of the tunnels, including surrounding rock classification, construction methods, depth of tunnel, bias angle and the relative position of two tunnels, were analyzed. The laws of these factors affecting on the interaction and construction mechanics were achieved.3D elastic-plasticity analyses were performed to simulate all the construction procedures of the closely spaced tunnel The two key factors, including the distance between the two working faces and the bench length, were analyzed. The evolutions of stress and deformation in the rock and the lining with the longitudinal excavation during the construction were achieved. The interaction of the two tunnels and characteristic mechanical behavior of the surrounding rock and lining during longitudinal excavation were obtained.Then, the displacement evolutions of the lining and surrounding ground were presented by the functions, which was summarized by in-situ data. A stability critieria based on the ground pressure were summarized here also. The principles of monitoring were concluded for future project.Finally, the problems requiring further studies are discussed.