Underground excavations and slope stability

Few large tunnels have been constructed in chalkthis century: Dr Lionel Lake, in his keynotepaper, describes two road tunnels with a lengthless than 2 km at Dartford and Lewes. These, andthe storage caverns at South Killingholme apart,tunnelling in the chalk has been at smallerdiameters, usually for sewers. In the 19thcentury, however, a considerable amount oftunnelling was undertaken during the railwaybuilding era. It is interesting to reflect thatin excess of 150 km of tunnels are being

constructed for a modern descendant of that era the Channel Tunnel - mainly in the Lower Chalk,by the mid-1990s.

The clear message emerging from Dr Lake's keynoteaddress is that the two crucial issues fortunnelling in chalk are water and discontinuitiesor fissuring and the determination of thequantity of these at any particular locale. Thepaper on the gas storage caverns at SouthKillingholme highlights a third, the excavationprocess, and illustrates how misappraisal herecan have serious consequences.