Study On Fission Mechanism Of Asphalt Mixture Under Unsaturated Seepage State

The rupture and loose damage of asphalt pavement has always been one of the main diseases affecting the service life of pavement,especially in the early stage of pavement opening.Studies have shown that the combined effect of water inside the pavement and driving load is the main cause of such diseases.However,the current research on hydraulic coupling is mostly based on the dynamic response of saturated pavement,without considering that the pavement is mostly in unsaturated state.Therefore,it is an important part of the study of loose and fission principle to clarify the mechanical response law under unsaturated seepage state,which can more truly reflect the stress state of pavement structure.In this paper,the asphalt mixture SMA-13,AC-13,OGFC-13 and unsaturated asphalt pavement are taken as the research objects.The relationship between porosity,permeability coefficient and water pressure of asphalt mixture is studied by improving the variable head pressure permeameter,which provides hydraulic parameters for numerical simulation.The finite element model of unsaturated and saturated asphalt pavement is established,and the mechanical response law of different asphalt pavement under different influencing factors is discussed.The main research contents and conclusions of this paper are as follows :(1)The relationship between porosity and permeability coefficient of asphalt mixture is explored by improving variable head pressure permeameter.The results show that there is an exponential relationship between porosity and permeability coefficient,that is,with the increase of porosity,the permeability coefficient increases,and the porosity can be used to evaluate the permeability of asphalt mixture.(2)By analyzing the permeability and water stability of asphalt mixture after hydrodynamic pressure,the results show that the permeability coefficient increases with the increase of hydrodynamic pressure and action time.The water stability of asphalt mixture under the action of dynamic water was evaluated by immersion Marshall test and freeze-thaw splitting test,and its index showed a downward trend.(3)The three-dimensional model of unsaturated and saturated asphalt pavement was established by ABAQUS finite element software to simulate the mechanical response of pavement under traffic load.The results show that under the action of traffic load,the pore water pressure and transverse stress of unsaturated asphalt pavement are less than those of saturated asphalt pavement,and the vertical displacement and vertical stress are greater than those of saturated asphalt pavement,which can predict that the asphalt pavement is prone to cracking and loosening under unsaturated condition.(4)By applying different driving loads,driving speeds and permeability coefficients of the upper layer,the influence of the three on the distribution of pore water pressure in unsaturated asphalt pavement is explored.The grey correlation analysis is carried out by using the results of orthogonal test to further clarify the influence of peak load,vehicle speed and permeability coefficient on pore water pressure.The results show that when the load of unsaturated asphalt pavement is greater,the pore water pressure is greater.When the speed is faster,the pore water pressure is greater,and the positive peak time is faster.When the permeability coefficient of the upper layer of asphalt pavement is smaller,the pore water pressure is greater.Under the influence of heavy load,fast driving and low permeability,the pavement is greatly affected by water,which easily leads to the occurrence of pavement looseness and cracking.Based on the grey correlation analysis,it is found that the pore water pressure inside the unsaturated pavement is greatly affected by the permeability coefficient,followed by the peak load,and the least affected is the driving speed.