The driving of three tunnels in loose cohesionless soils at warrington has enabled ground deformations during bentonite tunnelling to be monitored for a second time in great britain and enabled them to be compared with the settlements occurring when tunnels were driven in compressed air or in chemically stabilised ground. Depending on the degree of ground stabilisation and on the tunnelling technique the amount of ground lost during tunnelling varied from 0.3 to 7.1 per cent of the excavated tunnel volume; settlements at the ground surface varied from 1.3 to 42.2 mm. It is concluded that the bentonite is likely to provide more effective ground support than compressed air in cohesionless soil and while chemical treatment was more effective than either, the possibility of some additional settlement during the injection process had to be considered. (Author/publisher)
Abstract