In Scandinavian traffic tunnels soft drains covered with shotcrete are often installed to lead away un-wanted water, giving little resistance to shotcrete shrinkage, which may cause severe cracking. Mapping of shrinkage cracks was done in situ, followed by analyses focused on stresses due to drying shrinkage and various time of waiting between turns of spraying, with or without water curing. The effect of dilatation joints has also been investigated. A recently developed laboratory test set-up with shotcrete on instrumented granite slabs represent shrinkage of shotcrete on soft drains. The test results indicate that addition of glass fibres could reduce the cracking problem.
QC 20160318