Over 71,000 miles (i.e., over 75%) of county roads in Iowa are granular (unpaved) roads. According to a recent estimate, Iowa’s county road departments spend over $145 million annually on maintenance costs, which predominantly include over $35 million for blading and over $110 million for resurfacing. In addition, a wide range in granular material quality, supply, and price available in different regions of the state results in significant differences in the level-of-service. Therefore, Iowa county engineers have a specific set of criteria based on their own experiences when designing and managing granular roads. Considering the lack of granular road structural design standards to meet Iowa county engineers’ requirements for current granular road management practices, significant research is needed to develop a comprehensive but practical structural design tool for cost-effective design and construction of local granular road systems in Iowa. The primary objective of this study is to meet such research needs. 

The Midwest region of the United States, including Minnesota, has been experiencing an increase in the number of heavy precipitation events. Historical precipitation data confirmed an increasing trend of heavy precipitation in Minnesota in the 21st century. This study focused on assessing the impact of heavy-precipitation events on moisture levels and stiffness of pavement foundation layers at the MnROAD facility. A two-step approach was adopted for predicting changes in saturation and for estimating corresponding resilient modulus values using the resilient modulus prediction equation employed in AASHTOWare Pavement Mechanistic-Empirical (ME) design. PLAXIS 3D, a finite element analysis tool, was used to simulate the movement of moisture within the pavement layer under varying heavy rainfall scenarios. Multiple linear regression models were developed from rainfall simulation data of the PLAXIS 3D model to predict base layer saturation based on rainfall characteristics and hydraulic conductivity of the material. ArcGIS Pro was then used to develop a framework to generate a preliminary vulnerability map showing changes in the resilient modulus of the pavement base layer from rain events.