Comparison of two different primary support structures in Thirra tunnel, R. Albania in weak rock conditions

摘要

Tunnel Thirra-Kalimash by the design is constructed as two bored tubes, South tube and North tube. The length of the South tube is 5470 m and of the North tube is 5480 m. According to the geotechnical conditions the North side of the tube is in serpen-tinized dunitite, the South side is entirely in the gabbro. In the middle part of the rock formation where the tunnel has to be excavated a formation of piroksenite is expected. Accordinng to resticted geotechnical investigations a broad presumed fault zone is expected in the piroksenite rock formation. With the start of the works rock mass conditions were not fully defined. Due to the geological overbuden in the middle of tunnel, huge convergences are occured which result in collapse of middle part of South tube. A new design for this part of South and North tube has been developed on base of NATAM methodology in tunnel excavation. This approach results in excellent prevention of convergences and enable efective finishing of tunnel excavation and finishing works.