Evaluation of Deep Patch Landslide Mitigation Design Methodology

Abstract: FLH and its partners are responsible for thousands of miles of low-volume roads through steep mountainous terrain. Roads in mountainous terrain were often constructed by cutting into the uphill side of the road and casting the material onto the downhill side with little or no compaction, known as “cut and cast” construction. Over time, the soil materials settle and begin to creep down the slope, becoming an active, but relatively small scale and slow moving landslide under the roadway pavement. Stabilization of the pavement can require annual or even semiannual maintenance, and the traditional reconstruction method is an expensive process. A technique that has occasionally been utilized by the USFS and FLH to mitigate these small scale and slow moving landslides on low volume roads is the “deep patch”. A deep patch consists of subexcavating 1.5 to 6 feet below the surface and reconstructing a geosynthetic reinforced fill section over the landslide. Although the deep patch does not usually fully stabilize the landslide it has proven to be a very cost effective means of slowing the development and propagation of surface distress and settlement. The USFS has developed a simplified design method for the deep patch process, but actual field performance of deep patch sections has not been well documented. Through this project, WTI researchers will visit and collect data from deep patch construction sites, evaluate the performance of the deep patch process, and recommend improvements to current FLH and FS deep patch design and construction methods.

Sponsoring Organization: Federal Highway Administration - Federal Lands Highway Division

Completion Date: 3/31/2012

Additional Project Information: http://www.westerntransportationinstitute.org/research/4W3350.aspx

Reports: Report not available at this time