First application of the finite strip method for backcalculation of rigid pavement properties from traffic speed deflectometer measurements

The traffic speed deflectometer (TSD) is a traffic speed deflection device (TSDD) that uses Doppler lasers to evaluate pavement structural capacity at traffic speed. This paper presents the first application of the finite strip method (FSM) for backcalculating rigid pavement properties from TSD measurements, fully leveraging the capabilities of this technology. The forward analysis accounts for slab connectivity, full-axle truck loading, and potential loss of slab support. The proposed approach was verified using closed-form solutions and the finite element method, with differences in maximum deflection and bending moment as small as 0.03%. Similarly, cases without closed-form solutions were modeled and compared with results from the finite element software Abaqus. The verified model was used to study load transfer efficiency (LTE) in rigid pavements. The method was applied to field TSD measurements on low-volume concrete pavements at MnROAD to backcalculate the elastic modulus and modulus of subgrade reaction and to obtain LTE. Differences between backcalculated and measured elastic modulus ranged from 3.7% to 12.6%, and LTE compared favorably with estimates from the falling weight deflectometer. The proposed FSM-based approach provides accurate and efficient evaluation of rigid pavement properties at traffic speed, offering a practical tool for large-scale pavement assessment without traffic disruption.