Discs and boulders

摘要

Ground characterised by hard boulders embedded in a soft matrix represents one of the most challenging conditions for TBMs, as the cutterhead must cope with the non-optimal conditions of cutting hard blocks while simultaneously excavating through soil-like material. Dowden and Robinson and Hunt & Mazhar summarise several case histories relating to this problem and provide guidance with respect to site investigations and baselining strategies. Some rock types constituting boulder laden ground include:rn1. Sedimentary rocks - cemented alluvial channel deposits, colluvium/talus, landslide debris, and glacial till rn2. Igneous rocks - agglomerates, lahars, and pyroclastic deposits.