Use of block theory in the Elk Creek Tunnel Project

As part of the Elk Creek Tunnel Project, a highway tunnel will be constructed near Elkton, Oregon. The wide-span tunnel will be driven using drill-and-blast methods through diverse geologic materials including talus deposits, siltstone/shale, and sandstone. For the sections through siltstone/shale and sandstone, block theory was used to identify removable blocks around the tunnel opening and to analyze the stability of these blocks. The stabilization system was designed to resist movement of any key blocks. Furthermore, block theory was used to generate configurations of joint traces delimiting removable blocks as seen on the tunnel roof and sidewalls. These joint trace maps will be used during construction to allow early detection of potentially unstable rock blocks and timely installation of any additional stabilization for these blocks.