Dynamic Backcalculation Of Layer Property And Performance Evaluation For Asphalt Pavement

The FWD(Falling Weight Deflectometer)is widely used as non-destructive evaluation technology.The layer properties backcalculation using the measured FWD data,is common routine for the pavement analysis and performance evaluation of in-service pavement.The forward analysis method is the main component of backcalculation process,hence the accuracy and objectivity of the simulation of the pavement behavior under FWD loading is the key point for the layer property backcalculation and performance assessment.The current backcalculation procedures are based on the layered elastic theory,which could not take into consideration that the viscoelastic property of asphalt concrete(AC)and the dynamic nature of FWD loading.The difference between the analysis mode and the actual pavement behavior will be inevitably transferred into the backcalculated layer properties,causing questionable evaluation of pavement performance using the computed pavement response from backcalculated layer property,as well as difficulty in quality assessment and the rehabilitation design of pavement.Due to the inadequate ability of current methods,the following researches were conducted in this dissertation:(1)The spectral element method(SEM)was used to perform the dynamic analysis of asphalt pavement under FWD loading,where the AC was treated as viscoelastic material characterized by the MHN(Modified Havriliak-Negami)model.The computed response from SEM was compared with those from FEM(Finite element method),which shows the accuracy of dynamic viscoelastic analysis for asphalt pavement using SEM.(2)The SEM was used as forward analysis engine to backcalculate the layer properties,including the viscoelastic properties of AC layers and elastic moduli of other layers.The backcalculated results could characterize the pavement behavior precisely.The response was computed using the backcalculated layer properties and then compared with the measured ones from the embedded sensors,the precision of backcalculated results was presented.(3)Aiming at typical pavement structures with flexible,semi-rigid and rigid base,the layer property was backcalculated using the proposed approach and traditional procedures,namely dynamic and static parameters,respectively.The variability and effectiveness of backcalculated approaches was compared.The comparison indicated that the backcalculated layer moduli from static approaches exhibited a modulus transferring phenomenon between layers,which pose a serious concern in the characterization of layer property.The dynamic backcalculation procedure could effectively avoid the modulus transferring as well as lead to a lower COV and higher reasonable percentage.The results from dynamic approach could characterize the pavement behavior more realistically.(4)The two sets backcalculated results obtained from dynamic and static approaches were employed to analyze pavement responses to moving vehicular loading using the LET and layered viscoelastic theory,respectively.The influence of backcalculated results on the pavement behavior was investigated.The results shows that the vehicle speed has a significant influence on the analyzed response.Only elastic modulus for each layer was backcalculated from static approach,which could not take account the effect of moving speed.The computed response could not objectively perform assessment for pavement performance.The dynamic approach could overcome the problem and lead to more effective routine for pavement assessment.(5)Finally,the reduction of layer moduli during the serve life was investigated.The backcalculation was conducted on the field measure FWD data at different years using the dynamic and static approaches.The results from elastic approach will exhibit modulus transferring phenomenon,which poses a serious concern on the explanation of moduli reduction.The dynamic approach could provide acceptable result for the assessment of modulus reduction.The backcalculated result was employed to compute the pavement response using the layered viscoelastic theory,the variety of pavement response was analyzed.Results indicated that the proposed pavement analysis approach based on dynamic backcalculation could provide the scientific explanation of layer modulus reduction and pavement response increase during the pavement serve life.The proposed approach could furnish effective routine for pavement distress mechanism as well as the reduction of performance.