Abstract
Abstract Closely spaced twin tunnels were excavated vertically beneath an adjacent subway station in service in Beijing, China. Because of restrictions on the settlements of the existing subway station in the area, a special protection methodology was adopted, and an analysis was performed using real-time monitoring data to investigate the response of the overlying subway station to twin tunnelling and surface settlement characteristics. The results indicated that advanced grouting realizes regional integral uplifts within the range of a reinforced area. The lifting work with jacks is critical to restraining the trend of settlements. The final settlement trough of the columns displays a double-trough “W” shape that is induced by nonuniform lifting loads, and the total ground surface settlement profile displays an asymmetric single-trough “U” shape. The moment when temporary inverts and middle diaphragms are demolished is important, as it causes potential excessive settlements. With monitoring, this tunnel engineering was completed without interrupting the subway traffic, and the safety of the operating subway station and ground surfaces was successfully guaranteed. This is a valuable project case for establishing criteria to guide the construction of closely spaced twin tunnels in similar conditions.
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