LANDSLIDE STABILIZATION USING MICROPILES, WASHINGTON COUNTY, PENNSYLVANIA

The subject of this presentation is a 2,900-foot long portion of State Route 837 in Washington County, Pennsylvania. This section of two-lane highway has experienced chronic vertical and lateral displacements for several decades. Extensive, small-scale pavement repair and resurfacing was periodically required throughout the area. In 1999, a project was initiated to investigate the root causes of the pavement distress and develop long-term solutions to the problems. Literature studies confirmed that the roadway traverses an ancient landslide. Observation of surface features and review of previous monitoring efforts indicated that the colluvial mass was experiencing ongoing movements. Subsurface exploration and instrumentation programs were implemented to determine the mechanisms contributing to the slope movements and to delimit the landslide. The failure plane was isolated within a layer of colluvium near the top of bedrock. Coal mining records also show that nearby mine drainage discharges have likely been facilitating the landslide movements. Several remediation alternatives, ranging from traditional retaining walls to lateral drains, were evaluated with respect to economics and applicability to the site. Ultimately, micropiles were employed as soil reinforcement to provide long-term stabilization of the slope. Concurrent improvement of the site's drainage system was also performed to complement the soil reinforcement and increase the overall effectiveness of the stabilization scheme. Construction was completed in 2004. This presentation describes diagnosis of the landslide's origins and design of the remedial measures. An overview of the project's construction is also presented.