During the spring 2011, the approximately 40-foot-high roadway embankment experienced a slope failure. As a result, a 10-foot tall head scarp intersected the original roadway alignment and the slide appeared to be about 350 feet long. In 2012, an attempt was made to repair the landslide by mass excavation and reconstruction of the slope, along with installation of an underdrain system. After construction of this subgrade correction was complete, ongoing pavement distress has occurred that continues to be a maintenance and safety concern for NDDOT. As such, mitigation of the Highway 73 Landslide at RP 8.3 was a critical project to NDDOT in its role of being the transportation agency for the state. 

The landslide was mitigated using 13,947 linear feet of five foot-diameter drilled shafts arranged on a staggered pattern and installation of a deep one-pass drainage trench.

The drilled shafts were heavily reinforced to provide resistance to existing landslide forces and additional forces that may develop during movement of the ground surface on the downhill side of the drilled shafts. These drilled shafts were installed
through overburden and landslide materials and embedded in bedrock of the Sentinel Butte Formation. The installation of the drilled shafts presented several construction challenges and thorough inspection by experienced personnel were critical to making sure the drilled shafts were installed in accordance with the plans. These challenges included weak soil and bedrock conditions, a high groundwater table, and significant lengths.