Selecting Rock Bolt Locations
As part of a construction project to improve a 6.2-kilometer long section of Montana State Highway 200, east of Thompson Falls, Montana, highway realignment and improvement of rockfall catchment areas required five major rock cuts. Four of the cuts were designed to be cut at 0.25H:1V and the fifth at a 0.5H:1V slope angles.
However, due to the geologic structure, the Montana Department of Transportation (MDT) realized that the five slopes would require rock bolt and rock dowel reinforcements to reduce the likelihood of large scale rockfall events. MDT retained Landslide Technology (LT) to provide technical support for these slope reinforcements. LT provided three months of full-time on-site construction support services, including identification of rock bolt and dowel locations, bar lengths and orientations, and guiding and documenting rock bolt installation and acceptance testing.
The bolts and dowels were completed while the rock cut was being constructed in stages, increasing the production of the bolting crew and allowing the use of a large and efficient rock drill. Bolts were 1-inch diameter steel bars up to 30 feet long anchored with polyester resin cartridges. Each bolt was tested for compliance. In total, 127 rock bolts and 50 dowels were installed, with LT documenting location, length, and orientation information for each installation.