Dynamic Analysis And Backcalculation Based-FWD Geometric Parameters

With the improvement of the domestic road network,the accompanying problems such as road maintenance and inspection have become increasingly prominent.Objective and accurate evaluation of the structural strength of the pavement has guiding significance for road maintenance.The road structure is usually evaluated by the geometrical characteristics of the deflection basin and the direct inversion of the road surface modulus by means of the deflection basin value.However,the geometric characteristics of the curved basin can only control the strength of the pavement structure macroscopically,and the accuracy of directly inverting the pavement modulus through the deflection basin value is often unsatisfactory.Therefore,based on the above two aspects,this paper makes a deeper study on the evaluation of pavement strength.Firstly,this paper based on ABAQUS finite element analysis software,a three-dimensional numerical model of semi-rigid base asphalt pavement structure is established.The geometrical index of the deflection basin is studied and analyzed,and the geometric characteristics of the deflection basin and the modulus of the structural layer are further explored.Relationship.Secondly,according to the prediction ability of BP neural network,the neural network inverse calculation model is constructed based on the parameters of the deflection basin.Then,in order to eliminate the influence of the thickness factors of each structural layer,the more accurate mapping relationship between the deflection basin and the modulus of each structural layer is constructed,and the gray correlation analysis between the structural layer parameters and the deflection basin data is carried out by means of the grey correlation theory.The correlation matrix is obtained,and the correction coefficients of each measurement point corresponding to the inversion of the modulus of each structural layer are obtained.Finally,by comparing the theoretical and measured values of the deflection basin data,it is verified that the accuracy of the modified modulus inverse calculation has been greatly improved,which provides a reliable theoretical basis for evaluating the strength of the pavement structure.The main research conclusions of this paper are as follows:（1）Study on the geometric characteristics of the deflection basin:By analyzing the regularity of the curve of the deflection basin as the structure layer parameters change,it is found that the deflection performance within the range of 0～20 cm from the center of the drop hammer has the closest relationship with the surface layer modulus;The deflection performance within the range of 20～60 cm from the center of the drop weight is most closely related to the modulus of the base;the deflection performance farthest from the load center is most closely related to the modulus of the soil foundation.By analyzing the geometric parameters of the deflection basin,it is found that the area index A₃ can more accurately reflect the pavement structural strength;there is a highly linear correlation between the curvature radius at 0.15 m from the load center and the modulus and thickness of the surface layer.（2）Research on back calculation of structural layer modulus:By analyzing the gray correlation between the deflection value of each measurement point and the structural parameters,it is found that the correlation between the deflection basin curve and the soil base modulus increases with the distance of the measurement points The increase means that the deflection value at the farthest point of measurement is closely related to the soil modulus.The structural layer modulus inverse calculation directly through the deflection value has a large error.Therefore,the gray correlation correction coefficient is introduced to modify the model.After the correction,the accuracy of the inverse calculation of the structural layer modulus is improved,and the structural layer modulus is The calculation accuracy is ranked from high to low in order of surface modulus>soil modulus>basic modulus,and all three have met the engineering accuracy requirements.