Cost-Effective Landslide Mitigation: Harnessing the Power of Horizontal Drains in Glacier National Park-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the investigation and mitigation of a long-running landslide at Milepost 6.2 in Glacier National Park. The slide repeatedly damaged the road after its original construction, and earlier attempts to monitor movement were disrupted when instruments sheared. In 2015, investigators drilled five boreholes across two slide lobes and a less-disturbed area, collecting soil samples and installing inclinometers and nested vibrating-wire piezometers.<br /><br />Analysis identified a failure surface in a fine-grained zone within glacial till. Laboratory testing and field monitoring showed that slope stability was highly sensitive to groundwater conditions. Because groundwater levels upslope of the road were uncertain, the team used stability models to assess the relative benefit of drainage rather than predict absolute stability. The models indicated that drainage could improve the factor of safety by roughly 10–30%.<br /><br />Horizontal drains were installed in fall 2017. Post-construction monitoring recorded a 10–15-foot lowering of groundwater levels, accompanied by a dramatic decrease in slide movement. The project demonstrates that horizontal drains can provide cost-effective landslide mitigation, while emphasizing the importance of thorough site investigation, groundwater monitoring, and ongoing maintenance of the drains.

Keywords

landslide mitigation

Glacier National Park

Milepost 6.2

groundwater drainage

horizontal drains

slope stability

glacial till

boreholes

inclinometers

vibrating-wire piezometers