Landslide Mitigation Installed
During construction of a new highway alignment, extensive ground cracks were identified in an area of a partially completed embankment. The ground cracks affected a 3,000-foot portion of the new roadway and extended 1,300 feet downslope. Landslide Technology (LT) was retained on an emergency basis to provide geologic reconnaissance, exploration recommendations, technical assistance with data interpretation, review grading plans, and to develop conceptual mitigation measures. As part of our services, a test program was implemented to test the feasibility of horizontal drains for draining the slide mass. The test program revealed that horizontal drains would suffciently reduce groundwater pressures in the clayey foundation materials. The highway subgrade was reinforced to bridge slide cracks and possible differential movements. A buttress was constructed to control an upper nested slide.
Following the installation of over 29 miles of horizontal drains over a three year period, overall drawdown varied up to about 30 feet locally, with 5 to 20 feet
commonly occurring. This drawdown and accompanying grade and alignment changes were enough to stabilize the large complex landslide and allow the project to be completed. In winter 2010, the highway opened to traffic without issue.