Study On Crack Expansion And Stiffness Coordination Of Asphalt Pavement Structure In Road-bridge Transition Section

The dividing line area between high-grade asphalt roads and bridges is generally set up as a bridge head deck as a road and bridge transition section,which destroys the overall stiffness coordination of the asphalt pavement structure,makes the asphalt pavement paved at the bridge head deck more likely to produce stress concentration diseases,in order to overcome the pavement stress concentration pavement cracking and other diseases at the bridge head deck,improve the service life of the pavement at the bridge head deck.In this study,through the single-factor structural stiffness change,the law of pavement cracks and fatigue life change of surface layer in the transition section of road and bridge is coordinated,the tensile stress of the transition section of road and bridge is coordinated by changing the stiffness of the pavement structure,and the multi-factor orthogonal test is designed to coordinate the surface shear stress to determine the combination of asphalt pavement structure at the bridge head deck,and a multi-factor fatigue life estimation model based on structural combination and mechanical control index is established,and the main research contents and conclusions are as follows:(1)Relying on the raw materials of the road and bridge transition section of the Gongzhou Road Project in Guigang City,Guangxi,the asphalt mixture AC-13,AC-20 and AC-25 grade design was carried out,and the optimal oil-to-stone ratios of AC-13,AC-20 and AC-25 were obtained by indoor tests of 4.8%,4.2% and 3.8%,respectively;The dynamic modulus is 8 853 MPa,10 894 MPa and 13 148 MPa,respectively.(2)Abaqus finite element was used to establish a three-dimensional five-layer system of road and bridge transition section pavement model,and the pavement crack growth law of road and bridge transition section under different stiffness differences of structural layers was studied,and the results showed that the stress strength factor KII increased with the increase of surface modulus,and decreased with the decrease of stiffness difference between surface layer and base layer,stiffness difference between surface layer and bridge head deck layer,and stiffness difference between surface layer and soil foundation.Stiffness coordination(reduction of stiffness difference)can effectively reduce the propagation speed of fatigue cracks.(3)According to the trabecular shear fatigue test,the values of the calculated parameters c and n of the Paris model were obtained by fitting regression,and the fatigue life law under the action of single factor under stiffness change was calculated and analyzed by the Paris model,and the results showed that the fatigue life of the surface layer decreased with the increase of surface modulus and axle load,and increased with the increase of surface thickness,base modulus,base thickness,layer modulus,layer thickness,soil modulus and vehicle speed,among which the significance of each influencing factor on the fatigue life of the surface layer was:surface thickness> vehicle speed> soil foundation modulus > Axle loading> layer thickness>base layer thickness> surface modulus> base layer modulus> laminate modulus.(4)According to the results of(3)analysis,the stiffness of the low tensile stress and surface shear stress of the bottom layer of the road is coordinated,and the estimated analysis is carried out from the structural combination and material,and the results show that the stiffness of the base layer should be 1 000 MPa.The stiffness of the bottom layer should be more than 3 times the stiffness of the base layer,the stiffness of the bridge head deck should not exceed 10 000 MPa,and the value range of the surface stiffness of the road and bridge transition section is 4274~7 269 MPa,the durability of the pavement layer of the road and bridge transition section is the best,and the fatigue life estimation model of asphalt surface layer at the bridge head deck with multi-factor structural combination and mechanical index is established.The research results can provide corresponding theoretical support for the rational design of asphalt pavement at the bridge head deck in China,and provide a new method for the essential treatment of bridgehead diseases in China.