FEATURE ARTICLE Alberta Makes Peace with Highway Landslides Two-lane Highway 744, known locally as Judah Hill Road, traverses along the southwest face of a hogback ridge separating the Peace River and Heart River valleys. Since it was built in 1984, active landslides have plagued this ill-fated, 2.5 km (1.5 mi) stretch of highway that rests above the town of Peace River about 500 km (310 mi) northwest of the city of Edmon- ton in Alberta, Canada. Keeping this road open is a serious challenge. Government of Alberta Ministry of Transportation (Alberta Transportation) managed and remediated 15 landslides grouped into eight areas along the ridge. These stabilization efforts included the use of realignments, timber pile retaining walls, mixed lime and gravel columns, anchored cast-in-place concrete retaining walls, geotextiles, surface drainage diversions, pumping drains, earthworks, lightweight fill, and temporary portable bridges to span failed areas. The most recent landslide, Sunshine Slide, first visibly impacted a 120 m (394 ft) section of Judah Hill Road on May 3, 2013, when highway maintenance workers noticed transverse diagonal cracks in the asphalt. Both lanes of the highway con- tinued to rapidly deteriorate, developing open horizontal gaps up to 250 mm (9.8 in) wide, vertical drops up to 300 mm (11.8 in) deep and the protrusion of previously installed large stone columns upwards through the existing pavement structure. Alberta Transportation closed the road due to safety concerns on May 17. By May 21, large sections of the highway had completely collapsed due to the shifting earth underneath the roadbed. Even though it is in a relatively remote area, Judah Hill Road acts as a vital lifeline to the town of Peace River for the thousand cars that pass along it per day. Therefore, Alberta Transportation decided that permanently closing the highway or building an alternate highway outside the landslide area weren’t viable options. Instead, Alberta Transportation moved quickly to provide a temporary fix so at least one lane could be reopened to traffic. Geotechnical engineers determined the landslide failure plane and remediation plan. Within two weeks, emergency grading work was performed and a steel pipe was installed to divert highway surface water runoff past the landslide area. Sunshine slide caused large sections of Judah Hill Road to collapse (courtesy of Alberta Transportation) As a long-term solution, tied-back tangent pile walls were selected as the best remediation method to stabilize the landslide mass and anchor the remaining strata. Two tied-back walls were constructed about 300 m (984 ft) apart from each other just below the damaged sections of highway. Both walls were installed by Doublestar Drilling using Soilmec SM-14, SM-20 and SR-30 rigs. Once the walls were complete, three layers of expanded polystyrene geofoam blocks were used as backfill to reconstruct the highway embankment and reduce the soil pressure on the walls. Challenges and Solutions Performing stabilization work on a sloping hillside within an active slide area and with limited access was extremely challenging. The landslide had the potential to continue to move downslope. Furthermore, this demanding work occurred during an abnormally cold Alberta winter at temperatures as low as -30 degrees Celsius (-22 degrees Fahrenheit). Safety was a great concern for the people and equipment. AUTHORS Tyler Wilbur, Doublestar Drilling, and Craig Berninger, Champion Equipment Sales and Soilmec North America DEEP FOUNDATIONS • JULY/AUG 2015 • 89
