Hydrological Behavior of an Infiltration Induced Landslide in Colorado, USA

Infiltration-induced landslides are common geological hazards in the world. When they occur along highways they threaten public safety and private property, block highway traffic, and damage transportation infrastructure. Since the hydrology of the site affects the effective stress distribution and consequently the stability of the slope, monitoring the dynamic changes in pore water due to climatic changes is important. This work presents the study of the hydrological behavior of an active landslide on an embankment on Interstate-70 west of the Eisenhower/Johnson Memorial Tunnels in Summit County, Colorado; where seasonal movement of more than 1.5 m has been recorded during the past decades. At this site, the failure surface was identified to be within the range of groundwater table locations. Information from previous reports on the site was combined with data obtained from three additional boreholes to generate a soil profile. Three piezometers were installed near the crest and toe of the landslide and monitored hourly for over four years. A unique hydrological behavior was observed; the groundwater level beneath the westbound shoulder of I-70 changes twice as much as the groundwater level beneath the eastbound shoulder, with the two locations being only 30 m apart. A conceptual model that captures the principal mechanisms at the site is proposed. Observations of the seasonal embankment movement are related to the location of groundwater table, and confirmed with slope stability analysis using an extended modified Bishop’s method that accounts for suction stress in unsaturated soils.