Speaker: Kyle Radach, Shannon & Wilson

Topic: Design and Construction of a Retaining Wall on the Miller Creek Landslide, I-70 West Vail Pass Auxiliary Lanes Project, Eagle County, Colorado

Abstract: In 2021, design work commenced on a $325 million project for the Colorado Department of Transportation to improve traffic flow and safety along a ten-mile stretch of Interstate 70 (I-70) from the Town of Vail to the summit of Vail Pass. Shannon & Wilson was retained to provide geotechnical recommendations and design for a retaining wall (designated Wall 1) located adjacent to the westbound I-70 lanes through the toe of the Miller Creek Landslide, a large landslide first investigated in the 1970s during original construction of I-70 that is estimated to be 0.5 miles wide and 0.75 miles long. Wall 1 is a 5-tiered soil nail wall with an overall length of 1,150 feet and a combined design height of 49 feet.

The main geotechnical challenge facing the design and construction of Wall 1 was the stability of the Miller Creek Landslide during and after construction. Slope stability and seepage analyses showed unacceptably low factors of safety for global stability at Wall 1 due to the high groundwater conditions and the excavation for the wall. Our analyses showed an acceptable factor of safety could be achieved by lowering the groundwater level up to 30 feet. To achieve this groundwater drawdown, 18 temporary horizontal drains were installed at the start of construction and 28 permanent drains installed near the end of construction to lower groundwater levels upslope of the wall, maintain acceptable factors of safety for Wall 1, and mitigate the destabilizing impacts of wall construction on the Miller Creek Landslide.

Dinner and non-alcoholic beverages provided. Social hour and dinner begin at 5:30, announcements and introductions at about 6:45, talk will begin at about 7 pm.