Yang-Hoo Park and Kook-Hwan Cho
International Journal of Railway, vol. 9, no. 1, pp.21-26, 2016

Abstract : When excavation under existing structure is planned for a new construction project, the underpinning method is one ofthe most applicable construction methods. This study introduces a new modified underpinning method which is appliedto construct a new subway line in Seoul Metropolitan. The new subway line was designed to pass underneath the exist-ing subway line. Existing subway line carries about 2 million passengers daily, which is 33% of total passengers usingsubway in Seoul, and is the only circulation line in Seoul. Subway trains are passing 540 times through this section in aday. By applying a new underpinning method, the subway box structure of line is exposed 54m in the air supported bybearing piles. The proposed method was carefully monitored using heavy instrumentation system during construction.This study proposed and verified the application of the modified underpinning method, which can reduce constructionperiod by 1.5 times and the construction cost by 1.2 times comparing with conventional method. The importance of con-sidering construction sequence is investigated and verified by analyzed data non-considering construction sequence. Theunexpected heaving which can bring up a dangerous situation for train running stability were measured, so this studyshows that the upward movement has to be analyzed in designing process. As the use of underground space increases,the proposed method can be a good example of underground development.

Keyword : New Modified Underpinning Method, Stability, Safety, Excavation