Bored tunnelling – NATM tunnelling

Twenty-three papers were submitted for this session and tunnel excavation stability was the topic most dealt with, several case histories being presented to illustrate construction details and sequences adopted either to ensure stability or as collapse remedial measures. Groundwater control was a key topic in many papers, use of compressed air being one of the techniques employed. Several ground improvement schemes using jet grouting, impregnation grouting, and one compensation grouting trial are described. Use of ground anchors in weak rocks was reported as permitting much lighter sprayed concrete linings, and inducing smaller settlements than for a support based exclusively on heavier linings. Some cut&cover tunnels are also reported, including a case history involving a building collapse.