Effect of soil amendments on the compaction characteristics, hydraulic conductivity, and tire sinkage potential of roadside soils

Abstract

State highway agencies (SHAs) are required to comply with the National Pollution Discharge Elimination Permit (NPDES), which requires that the majority stormwater runoff from highways infiltrate into the roadside and that agencies implement soil based best management practices (BMPs). Per this new permit, SHAs are to install soil based BMPs that can absorb the 85th percentile of a 24-hour stormwater event. The area used for this purpose is typically the road embankments/slopes located adjacent to the roadside, best known as Clear Recovery Zone (CRZ). The CRZ must be traversable and recoverable to meet roadside traffic safety standards. A major concern for SHAs is the uncertainty on how these BMPs will affect the safety of a vehicle should that vehicle leave the roadway and interact with the soft soils. Considering this concern, the study described in this paper has assessed the impact of soil amendments on the compaction characteristics, hydraulic conductivity, and sinkage potential of six native soils of the state of California. These six soils were amended with four of the most used BMPs by the California State of Transportation (Caltrans). The results showed the hydraulic conductivity drops when the percentage of organic matter increases in the soil. They also showed that soils with a soaked surface had much larger sinkage than soils with an intact surface, this sinkage potential increase at the soak condition is proportional to the soil’s clay content.