Influence of Subgrade/Subbase Non-Uniformity on PCC Pavement Performance

Several reconstructed Portland Cement Concrete (PCC) pavement projects in Iowa were recently studied to evaluate the influence of subgrade/subbase non-uniformity on pavement performance. Crack surveys and field tests to evaluate the subgrade/subbase were conducted. Dynamic cone penetrometer, nuclear density gauge, GeoGauge vibration, and Clegg Impact Hammer tests were performed in a grid pattern (2.5 m x 2.5 m over an area of about 7.5 m wide by 30 m long) to develop a database of the subgrade/subbase engineering property values. Results of stiffness, moisture and density, strength, and soil classification were used to produce plots indicating spatial variability of a given property. Natural subgrade soils, fly ash stabilized subgrade, reclaimed hydrated fly ash subbase, and aggregate subbase were studied. The influence of spatial variability of subgrade/subbase was evaluated by modeling elastic properties of the pavement and subgrade using the ISLAB2000 finite element analysis program. Results show that non-uniform subgrade/subbase stiffness increases localized deflections and causes stress concentrations in the pavement, which lead to fatigue cracking and other types of pavement distresses.