Ground freezing and spray concrete lining in the reconstruction of a collapsed tunnel

During the construction of 14 ft diameter flow transfer tunnel for Yorkshire Water in Kingston upon Hull, UK, a 350 ft length of completed tunnel collapsed within a few days of construction. The tunnel was constructed using a full face Earth Pressure Balance (TBM) and a segmental concrete lining in alluvial and glacial soils with a high water pressure. Artificial Ground Freeze with Liquid Nitrogen as the freeze medium was used to stabilize the ground to permit the reconstruction of the tunnel along its original alignment. Excavation and reconstruction was carried out within the frozen ground using sequential excavation techniques and sprayed concrete primary and secondary lining. This paper describes the design of the Artificial Ground Freeze, the reconstruction of the tunnel and a description of the lessons attained from constructing a major civil engineering structure in frozen ground. Details on the extensive monitoring system and safety measures implemented are also given.