Discussion on underground excavations and slope stability

DR W. H. WARD, Consulting Engineer

The construction of the road tunnel at Lewes, Sussex, and the nature of the chalk at the site has been described in several papers and illustrated in two presentations to the symposium, but no one has reported on its performance. I first visited the tunnel shortly after it had been opened, in 1979, during the European Soil Mechanics Conference at Brighton. I saw it again in September 1989 and my observations led me to believe that it would prove to be a most instructive case record of long-term tunnel deformation in an open-jointed chalk mass forming a cliff. Its performance should be recognized when considering the design of future tunnels to be built in similar situations. The tunnel is well worth a short visit: moreover good exposures of the chalk may be seen adjacent to the south portal where there is a convenient parking space.