Evaluation of Pavement Slab Rocking and Pumping with Elevation Profile Data

Abstract

A method is presented for estimating the amount of slab rocking and the amount of earth moved beneath a jointed concrete pavement as a result of slab rocking. The estimates are obtained with data from noncontact rapidly traveling profilers that collect surface elevation profiles along roadways at normal driving speeds without lane closure or traffic control costs. With profile data from FHWA Long-Term Pavement Performance (LTPP) General Pavement Study 3 (GPS-3) test sites, examples are provided to show how the apparent slab rocking and pumping volumes develop over time for most GPS-3 test sections that have shown significant faulting. The calculated pumping volume rate per equivalent single-axle load (ESAL) is shown to be relatively constant over time at these LTPP test sites. A preliminary linear regression predictive model for pumping rate per ESAL as a function of pavement design parameters is provided based on the test group of faulting GPS-3 pavements. This study indicates that pumping rate can be reduced with thicker and longer slabs and thicker layers of erosion-resistant base and subbase overlying erosion-susceptible subgrades. Slab lengths less than 15 ft (4.57 m) long appear noticeably more susceptible to rocking and pumping. Sites with high pumping rates typically have a combination of unusually large slabs locked in upward curvature and erosion-susceptible cross-section designs.