Study On Construction Scheme Of Tunnel Opening At Special Geometrical Place

With the rapid development of transportation system in China, construction of tunnels and underground structures is enormously increasing. Meanwhile, the geometrical and topographical conditions are more and more complicated. In the many problems of tunnel construction, the tunnel portal to be excavated becomes a key one due to the geological conditions and construction difficulties.In this thesis the problems in the tunnel portal construction of Taishangou Tunnel of Shibai Highway are studied. The collapse of the reasons and process before the reasonable measures are taken has been analyzed. Meanwhile, the reasonable measures aimed the complicated geometrical conditions at the tunnel portal have been taken.The contents are as follows.1. Based on the related references, the present methods of judgments and treatments for the slope stability at the tunnel portal are summarized.2. Aiming to the special geometrical conditions at Taishangou tunnel portal, the process and reasons of the collapse at portal has been analyzed. The emergency measures have been taken based on the site construction and this can avoid the further collapse.3. According to the collapse process and geological conditions at the tunnel portal, the construction scheme for the tunnel opening has been taken, i.e., combination of pile foundations and long pipe roof. The mechanics of the long pipe roof to treat the tunnel collapse is studied and a simple and effective mechanical model is proposed. The safety has been analyzed and the relative parameters have been calculated.4. The finite difference method software, FLAC3D, is used to analyze the treatment scheme at the portal. The stresses of the tunnel bracing and settlements of the ground surface have been calculated. Comparing the theoretical results and numerical simulation, the applicability of the treatment is demonstrated through the comparison of the results of numerical modeling and the site monitoring.5. The results of the article can be referred to other tunnels in the undergoing construction of highway, and in the similar situations of excavation of tunnel portals.