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Design and maintenance of pavement drainage is critical to ensure the long service life of pavements. A minimum assumed coefficient of saturated hydraulic conductivity (Ksat) value of the base materials is used to design the aggregate base/subbase layer geometry (i.e., thickness, width and slop). However, ksat is often a single assumed value used during design and is not field verified. ksat is typically either measured on small volume of material in the lab or estimated by using empirical relationships. Both methods do not adequately capture the field variability. In this study, a gas permeability test (GPT) device that has been recently designed and fabricated at Iowa State University is used to evaluate the hydraulic conductivity of pavement base materials in the field and laboratory. Field studies were conducted on newly constructed base layers projects in IA, MI and PA. Field testing conducted in MI and PA involved capturing the spatial of fines content and ksat variability over a relatively small area (smaller than 10 m by 10m area). Field testing in Iowa involved evaluating the effect of construction operations for placement or granular base/subbase on fine content, ksat, density and stiffness (i.e., number of passes, compaction using vibration, and static compaction). Laboratory studies were conducted using various materials to validate the gas permeability test (GPT) measurements by conductivity conventional laboratory falling and constant head testing. The difference between in situ and laboratory data was compared to complete the design parameter derivations, and effects of the pavement performance. Results indicated that GPT is repeatable (ksat of COV ≤ 1%) on a series of repeatability tests conducted on a material and has a wide range of ksat values (0.1 to 820 cm/sec). CHAPTER

In situ Assessment of Support and Drainage for PCC Subbase