SOME RESERVATIONS ON THE USE OF SHOTCRETE.

The world-wide increase in the use of shotcrete for lining tunnels over the last decade has in many ways caused a small revolution in the tunneling industry. Primarily it has led to an increase in the speed of tunneling, but in most cases it has also reduced the costs of producing a safe tunnel. The lists of reservations to its use, or the descriptions of unfavorable conditions for shotcrete, are steadily decreasing. The main exceptions to its use are in plastic clays and quicksands, and the article discusses problems related to the interaction of shotcrete and swelling clay, sealing clay seams, water, frost and smooth planes. Refs.