Jet-grouting and other ground treatment can occasionally give rise to unexpected consequences. This paper describes a case study in which an annulus of jet-grout was formed in advance of tunnelling works in soft marine clay. When the tunnels were excavated inside the annulus, some six to twelve months after grouting, it was found that the ground temperature was 15°C higher than the ambient temperature, and ammonia gas pervaded the tunnel. Compressed air working was mandatory and vorking conditions within the tunnel became very unpleasant. The mechanisms of heat generation and dissipation and the generation of ammonia are discussed.
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