Numerical modeling for the umbrella arch application at the shaft and tunnel intersection

Abstract

In order to finish urban shallow tunnels (driven by NATM) projects as scheduled shafts should be sunk at certain intervals to form new excavation faces. Entering the tunnel from nearby shafts in addition to the tunnel axis to create new excavation faces is time consuming and costly. For this reason, to form new excavation faces directly from the shafts sunk in tunnel axis seems more economical. However, the greatest problem in such a study appears to be the stability. The stress accumulations at tunnel-shaft intersection areas contain hazard from the aspect of stability. Although it is not likely to face serious stability problems in strong rocks, this situation is potentially prone to reaching to dangerous levels especially in weak rocks. In this study, the stability at the shafts sunk in the tunnel axis and the intersection points of Goztepe station as part of the 2nd stage of Izmir Metro, was analyzed by numerical modeling. The accuracy of the numerical modeling results was later verified comparing with the results of in-situ surveys and measurements. During the study, shaft-tunnel intersection areas have been consolidated by umbrella arch method. The main reason for this strengthening was the obvious difference in the sizes of the shaft and the tunnel i.e., shaft crossectional area was smaller than that of tunnel. Therefore, stability of tunnel-shaft intersection area was designed accounting that the whole load of the shaft was to be carried by the tunnel support and the ground itself. © ISRM International Symposium on Rock Mechanics, SINOROCK 2009.