Erosion Resistant Rock Shoulder

With the advent of climate change, weather patterns are becoming more unpredictable, and consequently, severe drought and flooding are unavoidable. For highway structures, this new weather pattern created new problems in the pavement system. Particularly during the Winter of 2019, extended heavy rains in Nebraska severely washed out roadbed materials in several different places, which is an unexpected challenge for engineers to mitigate. In addition, District Maintenance Operations reported that eroded and dislodged shoulder aggregate often struck the lawnmower blades and cause longer downtime. Techniques to evaluate erosion resistance of these materials are not well developed so far. Consequently, the improved design of erosion resistant aggregate and combinations of soil and aggregate are needed. An improved design would also reduce shoulder mower blade maintenance issues. The research project would start by conducting a thorough study of the erosion characteristics of current erosion resistant aggregate. NDOT currently utilizes the gradation of crushed rock surface course and soils. A properly compacted crushed rock surface course is believed to provide high bearing stress and erosion resistance (Junliang et al. 2017; USDA, 2017; US Army, 2020). However, materials with this gradation are not always readily available or perform as intended. The erosion resistance of these materials is not clearly quantified as well. This study combines dedicated testing methods and hydrodynamics analysis technique to test, evaluate and obtain the erosion resistant shouldering materials which outperform the current design recommendation so that, 1) Alternate gradation of crushed rock surface course that can be sourced in Nebraska are needed because the rocks satisfying the gradation requirement may not be available in certain circumstances. 2) Additional reinforcing techniques (such as adding binder materials to gravels) may be recommended to enhance the erosion resistance of the crushed rock surface course.