Research Of Fatigue Crack Propagation Of Cement Concrete Pavement Under The Effect Of Vehicle Impact Load

The cement concrete pavement due to the lack of timely maintenance under construction,and the loads undergoing and the context after coming into service,results in the generation of initiation cracks on pavement structure.The study shows that overspeed is the main factor causing traffic accidents;therefore,it is necessary to set up the deceleration strip,restricting the driving speed on the road where the potential safety hazard exists.When the vehicles get through the deceleration strip at a certain speed,the vehicle bumping would occur,which will cause the extension of pavement cracks and,worse,shorten the service life of the cement concrete pavement structure.In this paper,the Abaqus program is used to establish the three-dimensional model of cement concrete pavement with initial fracture under the vehicle impact load,in which the influence of vehicle impact load on the cement concrete pavement structure with initial fracture is studied,where the specific relational expression that provides a more reasonable setting of deceleration strip on the cement concrete pavement with initial fractures has been suggested,and which has verified that the applicability of the proposed expression in the road section with catch-basin and offered a brand new idea for the setting of deceleration strip with initial cracks.Later on,the vehicle impact load is equivalent to the peak load by the use of impulse theorem and the load curve that changes over time is simplified,which,further,models the fatigue crack propagation of the cement concrete pavement under the vehicle impact load.The main work is as follows:1?The formation of discontinuous unit displacement field of the extended finite element method has been successfully deduced.The addition of discontinuous items made the product of the displacement of element nodes and the shape function possible to represent the discontinuous characteristics of the element.Neglecting the interaction of the structure layers despite of the fact that the cement concrete pavement mainly bears flexural-tensile stress,the XFEM model is used to establish the simplified cement concrete pavement model in the Abaqus software,analyzing the strained condition of pavement crack under tensile stress at both ends of the pavement.The results are in accordance with the actual situation and the accuracy meets the engineering requirements.2?According to the "Code for Design of Urban Road Engineering",the cement concrete pavement model with initial fracture is established,analyzing the cracks with different initial length(depth)and the responses of the cracks at the different positions under vehicle impact load.The results show that when the distance between the positions of the vehicle impact load and the crack is less than 0.2 m,the stress concentration being obvious in the front edge of the crack.When the distance between the position of the vehicle impact load and the crack is more than 0.5 m,the influence of the vehicle impact load on the cracks of pavement is small,in a low stress state near the crack,which is regarded as the basis for setting up the deceleration strip.Based on the given conditions,the proposed relational expression can be represented as:L*=L+v×0.1313.The influence of the catch-basin on the pavement structure is analyzed to verify the applicability of the road sections with inlets for storm water,showing that the influence of the inlets on the proposed relational expression is negligible.3?Establishing the fatigue crack propagation model of the cement concrete pavement under the effect of vehicle impact load.To analyze fatigue crack propagation,the vehicle impact is equivalent to the peak load by the use of impulse theorem,and the load curve that changes over time is simplified,which makes it convenient to apply the fatigue analysis module of Abaqus program.The research results show that when the fatigue crack propagation occurs,it,at the beginning,expands along the pavements' surface and then along the thickness of the pavement.Under the loads at the most unfavorable position,the crack penetrating along the thickness of the pavement extends around the zone of action,leading to the block failure of pavement.The vehicles impact load has a little effect on the fatigue crack propagation of the pavement's cracks when the distance between the position of the vehicle impact load and the crack is more than 0.5m,which verifies the applicability and reliability of the set site proposed of the deceleration strip.