Stability analysis of subway box structure supported by modified underpinning method

摘要

When excavation under existing structure is planned for a new construction project, the underpinning method is one of the most applicable construction methods. This study introduces a new modified underpinning method which is applied to construct a new subway #9 line in Seoul Metropolitan in South Korea. The new subway line #9 was designed to pass underneath the existing subway line #2. Subway line #2 carries about 2 million passengers daily, which is 33% of total passengers using subway in Seoul, and is the only circulation line in Seoul. Subway trains are passing 540 times through this section in a day. By applying a new underpinning method, the subway box structure of line #2 is exposed 54 m in the air supported by bearing piles. The proposed method was carefully monitored using heavy instrumentation system during construction.