Construction of two short tunnels using artificial ground freezing

As part of a pipeline upgrading scheme, a short length of new tunnel was required between two existing shafts each lying close to a water course - a river estuary and a sea-going canal. Horizontal freeze tubes were drilled into place toward each old shaft from a new larger diameter shaft sunk at the mid point. Following refrigeration by an ammonia-brine system the tunnels were advanced by hand excavation and lined with bolted concrete segments. The freeze tube drilling toward the canal shaft encountered a consistent timber obstruction just short of their intended length. The method of drilling and placing horizontal freeze-tubes below the ground water table in alluvial soils, with a minimum of ground disturbance and loss is described.