A review of grouting techniques utilised for bored tunnelling with emphasis on the jet grouting method

Abstract

The relatively new jet grouting technique was utilised to treat soft marine countered during the driving of some MRT bored tunnels. This paper studies what is believed to be the largest scale jet grouting operation undertaken to date. This involved forming, with 4700 holes, a 1.5 m jet grouted annulus around a 1 km length of the 6 m diameter Contract 108 tunnels. Particular aspects highlighted are the associated problems of ground heave, high ground temperatures and ammonia encountered during tunnelling. Two other MRT tunnels were driven through similar soft ground conditions with open shields. The different combinations of free or compressed air with or without ground treatment (both chemical and jet grouting) are compared from the viewpoint of surface settlement and tunnelling conditions. Jet grouting proved to be effective in reducing surface settlement due to tunnelling and in improving tunnel progress rates. The extensive heave control trials conducted on C108 indicated that heave levels are, to some extent, controllable. However, considerations of location and programme bear a significant effect on jet grouting feasibility. Cost considerations, although also a significant factor, were beyond the scope of this paper.