Authors have constructed sewerage project DTSS (Deep Tunnel Sewerage System) in Singapore. For the maintenance of face and bulkhead of TBM, the space in the front of the machine needed to be established. The object ground is composed of marine clay, silty sand, sandy silt with N values from 0 to 10 indicating very weak ground. The soil improvement was indispensable in order for safe working conditions underground. It was decided that the ground improvement by chemical and jet grouting was not feasible from the results of laboratory tests. Although authors noticed that the freezing method adopted in the joint of Tokyo Trans Bay Tunnel, the average annual temperature in Singapore is higher than that of Tokyo at above 25°C, giving rise to thermal problems, such as frost temperature and pitch of lance. This paper describes the design and application of the freezing method under the high temperature condition.
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