Case Study on Slope Stability for Composite Subgrade with River Sand and Efflorescent Mudstone Rock

To solve problems concerning insufficient subgrade filler in highway construction, the feasibility of river sand and efflorescent mudstone rock (EMR) to fill subgrade with steep slope were evaluated in this study. First, the fundamental physical, compacting, and mechanical characteristics of river sand and EMR were obtained through laboratory tests. Then combining both the river sand and EMR with various subgrade heights, a total of 24 varieties of composite subgrade plans were generated. The slope stability analyses of these subgrades were conducted by the use of strength reduction method based on FLAC3D. According to the results, it can be shown that the river sand and EMR materials can be utilized to fill subgrade together for their close optimum moisture contents. On the premise of less than 8 m of the subgrade height, the safety factors of river sand subgrades with 3-4 m slope protection width (SPW) and a composite subgrade with 3-m SPW can satisfy technical requirements. The river sand embankment with 3-m SPW may be the best scheme in terms of the vertical deformation, location of potential sliding surface, and economic cost.