Research On Performance Evaluation Of Pavement Structure Of Existing Highway Based On Dynamic Deflection Backcalculation

The accurate evaluation of the structural performance of the old road and the reasonable treating and utilizing strategy play an important role in keeping the service life of the existing roads during the highway R&E(Reconstruction and Expansion)projects and the scientific use of highway construction funds.At present,there are many shortcomings in the structural performance evaluation of existing highway.Taking Jiangsu Province as an example,the main manifestations are the low efficiency of destructive detection,the lack of discrimination of structural performance indicators,and the large errors in old road treatment and utilization strategy based on single apparent disease indicators.Therefore,it is necessary to further study non-destructive testing indicators to develop appropriate performance evaluation indicators for old road structures.As the most representative pavement structural performance evaluation index,the direct use of the deflection basin to construct evaluation indexes is limited by field test conditions and differences in pavement structure types,leading to difficulties in forming a common standard.Backcalculation can provide input parameters for multi-indexes analysis of pavement modeling and make it applicable to different working conditions.Therefore,in this paper,based on the investigation of the evaluation methods of road deflection structure performance at home and abroad,in order to solve the problems of insufficient utilization of dynamic information and incomplete study of viscoelastic material properties of asphalt mixtures in the current backcalculation.(1)The dynamic modulus of each structural layer of the existing pavement is obtained through the dynamic modulus test of the composite structure in layers,and the test parameters are transformed into viscoelastic parameters and time-temperature equivalent parameters based on the generalized Maxwell model of asphalt mixture.(2)Establish a numerical model of the kinetic viscoelastic temperature field coupled analysis pavement finite element,and conduct a comparative study of different analysis conditions and working conditions.(3)The BP neural network backcalculation model is built,and the road surface temperature and the differential area of the deflection time curve are added as additional feature vectors in the backcalculation input parameters to further consider the dynamic effect of FWD and the effect of temperature-viscoelastic coupling on the response of deflection.(4)The pavement structural performance is evaluated with the help of the backcalculation modulus based on the actual measured section at the site of a highway reconstruction and expansion project in Jiangsu Province.The main conclusions include:(1)The kinetic viscoelastic-temperature field coupled analytical pavement numerical model can simulate the mechanical response of the pavement structure under complex temperature conditions in the field,and the load center deflection is more sensitive to temperature when considering the coupling effect of temperature boundary conditions and viscoelastic material properties of asphalt mixture.(3)The BP neural network backcalculation model with the kinetic viscoelastic-temperature field coupled analysis pavement numerical model as the positive calculation,and the introduction of the differential area A1 of the bending and settlement time curve and the road surface temperature T can better consider the dynamic effect of the FWD and the viscous-temperature material properties of the asphalt mixture.The average coefficient of variation between the real modulus of the test set and the predicted modulus of the backcalculated model does not exceed 12%,which has good backcalculation accuracy;the correlation between the theoretical deflection calculated by the backcalculated modulus and the actual measured deflection in the field reaches 0.95,and the coefficient of variation is 8%,which means the backcalculation model can effectively restore the actual pavement mechanical response.(4)The improved existing pavement structure performance calculation method based on the backcalulation modulus shows that the fatigue cracking life of asphalt layer and semi-rigid layer and the vertical compressive strain on the top surface of the roadbed of the measured section of a highway reconstruction and expansion project in Jiangsu Province meet the design requirements,and the measured section only needs key disease repair and functional repair when the old road is rehabilitated and expanded,and no structural reinforcement is needed.