Rock Mapping, Characterization, and Stabilization in the Anton Anderson Memorial Tunnel, Whittier, Alaska

摘要

The Anton Anderson Memorial Tunnel was originally constructed in 1943 as a single-track railroad tunnel. The 4-km long, 5-m wide by 6.5-m high tunnel was excavated in metasedimentary rocks and mostly unsupported for 56 years. Modifications to the tunnel to allow dual rail and highway use were completed in 2000. The crown was raised, scaling performed, and crown support installed, consisting of chain-link mesh anchored with split sets and dowels. An isolated instance of rock instability in October 2016 resulted in a tunnel closure and installation of emergency stabilization measures, consisting of rock bolts and wire mesh. In response to the event, mapping and stability assessment was performed at several locations throughout the tunnel. Rock mapping, scanline surveys, and LiDAR data evaluation were used as the basis for rock mass classification, characterization of rock structure, wedge modeling, and subsequent stabilization design. Improvements consisting of rock bolts and shotcrete for portions of the tunnel are currently under design. Software facilitated the use of LiDAR data to efficiently assess rock structure throughout the tunnel and supplement field measurements. Empirical rock mass classification and tunnel support systems were compared in the context of existing tunnel support and modeling of future support requirements.