Case study of control technology of structural settlements due to tunnelling beneath a subway station

The case study of closely spaced twin tunnels excavated vertically beneath the adjacent Chaoyangmen station in Beijing, China is introduced. The existing subway station is part of the Beijing subway Line 2. The new rectangular twin tunnels, running from Chaoyangmen station to Dongdaqiao station, are part of Beijing subway Line 6. The numerical simulation analysis using FLAC^3D is conducted to analyze the structural settlement of the subway station due to the construction of the adjacent twin tunnels excavated by using the shallow tunnelling method. The control scheme of the structural settlement of the subway station is proposed. In addition, more attentions are focused on the analysis and safety evaluation on the structural settlement based on the monitoring data. The main conclusions are as follows: the section of the subway station between twin movement joints near the twin tunnels is the key zone for settlement control. Some required measures are adopted during the construction of twin tunnels beneath the adjacent subway station. It’s found that the backfill grouting behind the primary lining of tunnel reduces the structural settlement of the subway station to some extent, and lifting by hydraulic jacks is the key part in the settlement control. Moreover, there is obvious structural settlement of the subway station at the early stage of construction. According to the monitoring data, the loadings of lifting jacks are adjusted, and the quality of grouting reinforcement is strengthened in time to ensure the structural safety of the subway station during construction. The research results can provide reference for similar projects of new subway tunnels excavated beneath adjacent existing underground structures in urban areas.