Analysis Using Finite Element Method For Cracking In Asphalt Pavement Under Traffic Load

With the growing of China's highway construction, the damage of asphalt pavement is more serious. The cracking is one of the main forms. As stress concentration exists around the crack tip, the traditional elastic layered theory had been unable to solve the problem of crack propagation.Fracture mechanics are applied to the finite element method (FEM) in this paper. A two-dimensional finite element model is established using the finite element software ABAQUS to analyze the asphalt pavement with crack and its overlay. By changing the forms of load, depth of crack, crack location, thickness and modulus of the surface layer, thickness and modulus of the overlay and modulus of the geogrid, we analyze the horizontal stress, vertical stresses, shear stresses around the crack, surface deflection and stress intensity factor in the pavement structure. We have the following conclusions:(1) Compared with other forms of load, offset load has the most unfavorable effect on the pavement with surface crack. Under offset load, the stresses around the crack tip and the surface deflection in the pavement with cracks have a great increase compared with that without cracks. With the increase of crack depth, the stresses, the stress intensity factor around the crack tip and the surface deflection increase in varying degrees.(2) For the pavement with cracks, increasing thickness of the surface layer is valid to reduce stresses at the crack tip, but when the thickness of the surface layer increases to a certain value, its effect on stresses is gradually reduced. The stresses and stress intensity factor at the crack tip increase with the increase of modulus of the surface layer, whereas the surface deflection decreases.(3) Repaving the old pavement with surface crack can make the stresses, the stress intensity at the crack tip and surface deflection decrease. As the thickness of the overlay increases, the stresses, stress intensity factor at the crack tip and the surface deflection decrease. Increasing the modulus of the overlay can effectively reduce stresses around the crack tip and surface deflection, but it can also make the stress intensity factor increase.(4) By adding geogrid between the old pavement and the overlay, we can make the stresses around the crack tip within the existing asphalt pavement decrease. But at the same time, the stress intensity factor at crack tip and the stresses in the G-AC layer increase. The reason is:because of the addition of the geogrid, a large part of stresses originally undertaken by the overlay are now undertaken by G-AC layer. Increasing the modulus of geogrid can reduce the stresses around the crack tip, but its effect is not obvious.