Improved Prediction of Permeability Rates and Performance for Green Infrastructure Using Standard Penetration Testing

The push to incorporate green infrastructure (GI) practices in large metropolitan areas has become a major component of many city vision plans. Due to the need to capture and minimize runoff resulting from continued development, organizations such as the Philadelphia Water Department and New York City Department of Environmental Protection (NYCDEP) have been conducting geotechnical investigations at parks, schools, crosswalks, and alongside public roads to repurpose paved and impervious surfaces for improved stormwater management. In general, as part of each city’s green infrastructure program, a geotechnical investigation consisting of soil borings, field permeability, and laboratory index property testing is performed at prospective locations. In many cases, the approval to implement GI at a location is based on adequate field permeability as well as minimal fines content. Based on observation of hundreds of field-permeability tests conducted by our firm, however, it was noticed in many cases that, although there was a percent finer exceeding the prescribed criteria, the in situ field permeability test indicated a level of performance with passing permeability. As both city programs are based on these two acceptance criteria, it is the intent of this paper to use the data collected to-date to help identify that additional qualifiers should be considered to understand the behavior of the soil and long-term performance of GI features. This paper presents research behind an attempt to prepare a refined predictor of permeability and acceptance criteria for regulatory agencies rather current model of only evaluating fine-grained fraction of soil.