Layer modulus determination

Abstract

The US Federal Highway Administration (FHWA) sponsors and conducts research in truck size and weight (TS&W), pavement design and rehabilitation and highway cost allocation problem areas. As part of this overall effort, the Truck Pavement Interaction (TPI) research programme of the Pavement Performance Division at the Turner Fairbank Highway Research Center (TFHRC) in McLean, Virginia, has established a comprehensive research plan to investigate techniques for the true optimization of the highway infrastructure: optimization between pavement rehabilitation strengthening and the deployment of Friendly Vehicle Fleets intra North America. The main premise of the TPI programme is that only through the use of well validated and calibrated mechanistic pavement whole life prediction models can one achieve realistic solutions to these goals. Thus, a very first step toward achieving these goals is the validation and/or calibration of the layer theory models that will compose the basic mechanistic modelling tool set proposed for use by TPI. As part of this effort, TPI has participated in the conduct of controlled heavy vehicle rolling load tests to study pavement primary response and damage due to different vehicle loading and environmental conditions. Tests conducted to date include dynamic load tests on the FHWA test road located at TFHRC, tests on LTPPISPS–8 sections of the Ohio test road and ALF (accelerated load facility) tests at TFHRC. The work described herein is an attempt to investigate the best techniques for estimating layer moduli so that these techniques can be used, with reliability, for future work. Several modulus back calculation methods were implemented using falling weight deflectometer (FWD) surface deflection basins taken from the experiments conducted at ALF. Not completely satisfied with these methods, a new method incorporating soil mechanics principles coupled with the Boussinesq/Odemark method was developed using actual pavement layer deflections also taken from the ALF site. Basic differences among the methods are presented, calculated layer moduli using the new method are compared with moduli calculated by the other methods, and advantages and disadvantages of each are discussed.