Field and Numerical Evaluation of Traffic Speed Surface Deflection Measurements to Estimate Load-induced Fatigue Response

Abstract

Abstract Traffic speed deflection devices (TSDDs) are actively used around the world in network level pavement management applications because of their relative merits over traditional deflection devices (e.g., FWD, Benkelman beam, etc.) in evaluating the pavement structural condition. Past researchers utilized several deflection indices based on FWD surface deflections to estimate critical responses such as load induced fatigue strains at the bottom of the asphalt concrete (AC) layer. However, the differences in loading configuration and viscoelastic material behavior under moving nature of the load of TSDDs may limit the use of the same indices from the FWD deflections to predict those critical responses. The two TSDDs: traffic speed deflectometer (TSD) and rolling weight deflectometer (RWD) were evaluated as a part of a FHWA study at the MnROAD facility in September 2013. Load-induced pavement response data were collected during field tests along with TSDD surface deflection measurements. 3D-Move program was chosen to undertake the analytical modeling since it can model moving load and accommodate the rate-dependent material properties (viscoelastic). A number of indices that are best related to fatigue strain were identified from 48 individual indices. The study verified the capability of TSDD surface deflection measurements to predict the critical fatigue strains at the network level. However, the prediction accuracy can be improved if response lag between the maximum load and the deflection is accounted in the TSD deflection computation algorithm. Evaluation of the RWD device with two surface deflection measurements reveals that both RWD sensors need to be positioned in front of the rear axle to have a better related index to fatigue strains.