In Situ Evaluation of Layer Stiffnesses of Airport Pavements by Crosshole Seismic Tests

Abstract

Many runways and taxiways in major international airports have been in service for 20 years or more. To manage this pavement system effectively, it is important to determine existing pavement conditions and to predict remaining service life. These two aspects are some of the challenges facing airport and highway engineers alike. By knowing the rate of change since the commissioning of the runway, one may be able to predict the remaining life of the pavement. Optimizing the useful life of the pavement is an effective way of managing the pavement and maximizing the benefit of the capital investment. To evaluate existing pavement conditions at the Dallas–Fort Worth (DFW) International Airport, a testing procedure was used that had been developed at The University of Texas at Austin using seismic waves. This procedure involves performing crosshole seismic tests with a system tailored to perform independent measurements in all layers of the pavement profile, that is, independent stiffness measurements in the surface, cement-treated base, and lime-stabilized subbase layers as well as the subgrade. The cross-hole procedure proved to be very effective for measurements of both runway and taxiway pavements. The test procedure, field equipment, and test results are presented herein. Issues considered in the study include how each layer stiffness has changed with more than 20 years of service at DFW; what is the relative stiffness change in each of the layers between trafficked and untrafficked areas; and how have the stiffnesses of the different layers beneath the joints changed relative to these same layers beneath the midslab areas.