Long-Lasting Gravel Roads: Case Study from the United States

Abstract

Gravel surfacing is commonly used on low-volume roads in rural areas of the United States to form farm-to-market networks that contain more than a million miles of unpaved roads. Some of these roads carry appreciable amounts of trucks and farm machinery. Some of these roads, if properly designed and constructed, can last a long time. One such road is in Hand County, South Dakota. This road was constructed in 1963 and has never been rehabilitated or reconstructed since its construction, and it has shown excellent performance for more than 37 years. This road normally carries less than 200 vehicles per day, but significant numbers of heavy trucks use the road. This exceptional performance led to an investigation of the reasons why that road lasted as long as it did without major maintenance or rehabilitation. Although this type of road construction is common in other nations, under different names, the practice of constructing this type of road in the United States was done without documented specifications. The main objectives of the study were to determine all factors that contributed to the longevity and the remarkable performance of this road through field and laboratory investigations. Field investigations with a dynamic cone penetrometer (DCP) revealed that both the quality and the quantity of aggregate base were more than adequate. Although the subgrade soil was classified as A6 according to AASHTO soil specifications, it provided good support according to DCP data. Tests of the flatness and elongation of the coarse aggregate and the angularity of the fine aggregate also revealed satisfactory results. Gradation tests also revealed compliance with specifications.