Abstract:

Geological nonuniformity and large boulder have been the key influence factors for shield tunneling in gravel layers. Gravel layer has also been recognized as one of the difficult grounds due to its complicated problems during excavation. Unfortunately, lacking in experience for shield tunneling in such ground leads frequently to incapability of treating the geological characteristics properly and boring work as well. The case studied is Taiwan Power Company Hsichu Industrial Park Extra High Voltage Transmission Line Underground Cable Tunnel Project, which is located in Huko Township of Hsinchu County, with a total length of 8.4 km. The designed route passes through a gravel layer, with boulder content up to 50~80%. This article compiled and described the problems encountered during excavation phase, such as serious wear and tear of disc and cutter, repair and modification of disc, wear survey, excavation management system, adjustment of polymer to lubricate the soil, etc.

Key words: gravel layer, shield tunnel, cutter disc