Study of the Treatment Scheme for a Large, Dry Karst Cave in the Yangqiaoba Tunnel

Due to the restrictions of investigative techniques, construction and operation risks of tunnelling in a karst region may result in large karst caves. Based on the present conditions and supplementary investigation information concerning the large karst cave encountered during construction of the Yangqiaoba tunnel on the Fengjie-Wuxi expressway in Chongqing, construction schemes are put forward, including: bridge crossing,subgrade filling and open cut tunnel, backfilling and bored tunnel, and five realignment options. Through a comprehensive comparison regarding the geological conditions, construction risks, project cost and construction schedule, the realignment option with the least additional costs and shortest construction time was finally adopted,in which the alignment of the left tunnel tube would be skewed to the left in order to bypass the karst cave.During the construction period, no large caves have been encountered, therefore geological risks have been avoided, and construction safety, schedule, and cost savings have been ensured.