Road Stabilization, Reconstruction, and Maintenance with a Combined Mechanically Stabilized Earth and Secant Pile Wall: Zion National Park, Utah

Abstract

A 1995 landslide diverted the North Fork of the Virgin River in Zion National Park, Utah, causing complete erosion of 180 m (590 ft) of the Valley Floor Highway, the park’s main access road. Buried utilities were damaged and 450 people were left stranded. Road reconstruction and maintenance have been ongoing in many phases since 1995 and have proved to be difficult because of environmental and physical constraints imposed by the river and by steep slopes of recent and historic landslide debris on both sides of the valley. In an effort to limit disturbance to the landslide slope while maintaining a two-lane access road adjacent to the river, a compound retaining wall was designed and constructed through the narrow reach of the valley. The lower part of the wall consists of cantilevered secant piles, providing 3.6 m (12 ft) of scour protection, and the upper part of the wall is a mechanically stabilized earth wall. Intermittently spaced foundation piles reduce the lateral loads on the secant piles, making cantilever support practical.