Study On Failure Mechanism And Disposal Method Of Cement Pavement Slab Joint Under Heavy Load Traffic

The heavy load road is called "heavy load road" abroad,which refers to all the intercontinental roads and the road [1] with an average daily traffic volume of more than 20000 or more than 1000 of the daily 18 kip equivalent standard axis.The main characteristics of heavy load pavement are as follows:(1)the load of axle load is more frequent;(2)the axle load is more and more heavy;(3)the contact stress between the tire and the pavement is increased significantly,and the spatial distribution is not uniform [2].However,there is no clear definition of heavy duty pavement.There is no special code for heavy haul pavement design in China.A large number of investigations found that the early damage of heavy haul cement concrete pavement is frequent,and joint failure is one of the main diseases.The joint failure,such as wrong platform,mud pump,plate angle fracture and joint fracture,will affect the driving comfort,which will lead to the fracture of the pavement,reduce the service life of the road,and endanger the safety of the road.This paper analyzes the traffic characteristics of heavy-duty cement pavement,and designs four kinds of pavement structure according to the different axle load spectrum,and establishes the three-dimensional finite element model.This paper analyzes the development process of three types of failure modes between layers which leads to the failure of heavy load cement pavement,and studies the mechanism of joint failure caused by heavy load and the disposal method of joint.The main contents are as follows:(1)Through consulting the documents,the difference between the heavy load pavement and the ordinary axle load pavement is analyzed and summarized,and the fatigue equation and the axle load conversion formula of the heavy load pavement are discussed.The axle load spectrum of different truck proportions is established,and four kinds of pavement structures with different axle loads are analyzed.It is considered that the pavement design method based on fatigue stress is suitable for heavy load cement pavement,and the damage of heavy load cement pavement is not caused by simple design control index.It is necessary to further analyze the evolution process and mechanism of heavy load cement pavement failure under high load stress state.(2)The finite element model of a four side free heavy load cement pavement is established,and the reliability of the finite element solution and the influence of different axle load on the design parameters of heavy load cement pavement are analyzed.It is considered that the bending stress of the floor plate bottom and the base plate bottom under heavy axle load is much larger than that of the ordinary shaft.The change of axle load has the greatest influence on the load stress of the heavy load cement pavement,and the minimum effect on the load fatigue stress.(3)The influence of the transmission rod and positive and negative temperature gradient on the load transfer capacity of the boom and the heavy haul cement pavement are analyzed.It is considered that increasing the diameter of the transmission rod can not improve the load transfer coefficient,and the encrypt bar can reduce the deflection of the loaded plate to a certain extent,but it is not obvious to increase the load transfer coefficient;the vertical deflection should be avoided when the force pole is installed,and the test will be carried out to ensure the position of the force bar in the concrete;the positive temperature gradient leads to a positive temperature gradient.The rise of the road panel is easy to cause the uneven support and void of the laminates on the base of the base plate;the negative temperature gradient causes the road face to be concave down,which is easy to cause the fragmentation of the plate angle.(4)The influence of interlayer bonding degree on heavy load cement pavement is analyzed,and the development process of joint failure is analyzed from four stages of pavement slotting,interlayer support weakening,plate bottom empty and complete crack at the base.It is considered that the three failure modes between layers are the important reasons for the joint failure of heavy-duty cement pavement.The first and third types of failure forms lead to inhomogeneous support between layers and the bottom of the plate,which cause the fracture of the plate angle and the fracture of the joint.The second forms of failure cause the complete cracking of the base,resulting in the rapid deterioration of the pavement support and the occurrence of the diseases such as the wrong platform and the slime.(5)The damage types of slime,dislocation,joint fracture and plate angle fracture caused by heavy traffic load are analyzed and the corresponding suggestions are put forward:(1)In the early stage of road design,the investigation of axle load spectrum should be paid attention to and the rational design of axle load should be determined;(2)The design of the internal drainage of the pavement,the special design of the joint and the force transmission rod;(3)Setting the isolation layer to improve the interlayer bonding state;(4)To strengthen the preventive maintenance of the pavement,evaluate the pavement performance scientifically,and keep the maintenance and maintenance of the pavement in time and properly.