Construction Example for Tunnelling Under and Adjacent to Complexity Condition in Weathered Rock

ABSTRACT: In South Korea, wide spreaded weathered rock has many problems during construction excavation of tunnelling. Especially, construction of new excavations adjacent to and below parts of Existent buildings or footings of bridges has often caused very serious problems. In Pusan, Korea Telecom communication tunnel(D=3.3m) was successfully completed during the 1999 summer using NATM, without damage to the existing footings of high level road or disruption to the proceedings of subway construction on the very weak rock(weathered rock). Monitoring of construction activities was focused throughout on ensuring damages to the adjacent footings of over bridge and existing buildings and subway construction by (i) strict methods of excavation control and (ii) pre-monitoring which are layered settlement gauges and inclinometers for all main points of the site and (iii) monitoring in the tunnel with very sensitive 3-D displacement gauges. All areas where possible excavation-related displacements could compromise the stability of the existing footings of high level road or heavy buildings and subway were monitored with a comprehensive arrangement of instrumentation, positioned on the basis of extensive FLAC(2D) modeling undertaken to optimize excavation geometry and reinforcement layouts. We also have related the results of real gauge reading values versus simulation data by FLAC.