Mined tunnel excavation for DC Water's First Street Tunnel project in an urban residential neighborhood with complex ground conditions; required the utilization of ground improvement with ground freezing. A total of three connection tunnels (adits) of different size and geometry have been constructed between deep drop shafts and the main tunnel, which was excavated by Tunnel Boring Machine. This paper is focused on the adit design challenges and contractor's means and methods to successfully deliver this project. The application of vertical ground freezing required innovative construction sequencing, unique solutions to maintain the freeze during excavation, and deliberate equipment selection. Lessons learned from the design through construction are provided.
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