The Amount of Sand Required to Transform Roadside Compacted Soil into Sustainable Stormwater Treatment Solutions

Required compaction of roadside soil, the largest built environment in space-constrained urban areas, lowers its infiltration capacity and makes it impractical for stormwater treatment. However, roadside soil can be turned into sustainable stormwater solutions by adding a bulking agent, such as sand, that could infiltrate stormwater and recharge groundwater. Yet, the quantity of sand needed for different hydrologic soil groups is unknown. Measuring the hydraulic conductivity of compacted soils mixed with different amounts (50%–90% by volume) of sand, we estimated that 70%–85% sand was needed to achieve a threshold infiltration capacity of $127–254\mathrm{mm}{\mathrm{h}}^{-1}$ irrespective of soil type. We developed an empirical equation that could predict the hydraulic conductivity of compacted soil and sand mixture based on their effective grain size ($D_{10}$). The results inform the urban planner to transform the road infrastructure from a source of water pollution to a network of stormwater treatment solutions.