Road Location and Construction Practices: Effects on Landslide Frequency and Size in the Oregon Coast Range

Abstract

Abstract The effects of road location and construction practices on landslide frequency and size were studied in a 300,000-ac area of the Oregon Coast Range. Roads were divided into two groups. Roads in Group I had been built using a combination of steep road grades and full-bench, endhaul construction to minimize slide risk. Group II roads were built using location and construction practices typical of the late 1960s and early 1970s. Using steep road grades to maintain ridgetop locations and full-bench end-haul construction did reduce landslide frequency and size on Group I, as compared to Group II, roads. The marginal cost of reducing slide volumes/road-mile from the volumes found on Group II roads to the volumes found on Group I roads was six times greater in more plastic than in less plastic soils when roads crossed slopes of equal steepness. When roads crossed slopes with a sideslope steeper than 50%, the estimated cost of reducing the volume/road-mile of slide from Group II to Group I levels ranged from $81/yd³ ($154/ac) to over $12,000/yd³ ($3675/ac), depending on landtype, sideslope, and endhaul distance. West. J. Appl. For. 2(4):119-124, October 1987.