Study On The Structure Of Long-Life Tunnel Road Surface

Pavement engineering,as an important part of infrastructure construction,plays a huge role in promoting China’s economic development and the improvement of comprehensive national strength.The highway tunnel is favored because it has many advantages such as improving the line standard and shortening the mileage.By the end of 2019,the total mileage of road tunnels had increased from 0.133%to 0.378%in the past decade,and more than 19,067 road tunnels had been built.Highway tunnel is a semi-closed tubular space structure,with great differences in temperature,humidity and other environmental characteristics.It is also located in the throat of highway engineering.With the serious channelized traffic and frequent emergency braking,the structural mechanical response characteristics and the evolution law of functional performance are different from that of ordinary pavement.To meet operating comfort,security,fast,durable and economic requirements,need reasonable materials,structure combination and the thickness of the design,make the superior structure of the tunnel pavement performance and functionality,and the traditional tunnel of modified asphalt cement pavement under special load and environmental spalling,pit slot,and poor durability problems to be solved,Therefore,it is urgent to construct a new high-performance long life tunnel surface structure.In response to the national strategy of "transportation power",it practices the important strategic policy of "improving quality and efficiency and transforming".Based on the overseas research on long-life pavement materials under heavy load,the selection and indoor verification of long-life tunnel surface materials are carried out,and epoxy asphalt is determined as the surface wear functional layer.Using finite element analysis software Abaqus mechanical response characteristics of typical structure,and combined with the feature of tunnel pavement diseases and functionally gradient composite pavement design principle,proposed at the beginning of the long life span tunnel road table structure,to study and formulate structure under different mechanical parameters and load conditions,interlayer contact state and dowel bar performance evolution,different supporting conditions and mechanical properties;According to the"bridge principle",the life prediction and economic analysis of the structure prove that the epoxy asphalt pavement structure has excellent durability and good economic benefits.The main conclusions are as follows:(1)Through material selection and indoor test,the dynamic stability of epoxy asphalt mixture is up to 16,242 times/mm,the residual stability ratio is 91.7%,and the freezing-thawing splitting tensile strength ratio is 90.2%;At low temperature,the maximum flexure strength is 6.9MPa,the maximum flexure strain is 2800με,the friction coefficient is 74.5BPN,the seepage coefficient is more than 5253ml/min,and based on the successful application of epoxy asphalt materials in the San Mateo Bridge and the Second Nanjing Yangtze River Bridge,the special research on open-graded epoxy asphalt mixture in New Zealand has an estimated life span of 144 years,so epoxy asphalt can be used as an excellent long-Life time tunnel road surface material.(2)Through the mechanical response analysis of the epoxy asphalt tunnel pavement structure,the main control indicators are flexural tensile stress,flexural tensile strain,maximum vertical shear stress and transverse shear stress;when only the vertical load acts,the limit response value of each direction index All appear at the bottom of the layer;when the horizontal load acts,the maximum horizontal shear stress appears on the road surface.And the most unfavorable load position is the eccentric load;when only the vertical load acts,it is the position where the upper edge of the tire and the lower edge of the condensation joint overlap,and when the horizontal load acts,it is the overlapping position between the lower edge of the tire and the raw edge of the shrinkage joint;the load increases from the standard axle load To overload,and then to the emergency braking coupling,the tensile stress increases by 81.3%and 18.8,the tensile strain increases by 83.7%and 16.5%,and the shear stress increases by 79.4%and 81.6%,respectively.The fatigue resistance and crack resistance of the structure have the most significant effect,and the horizontal load has a significant effect on the shear flow deformation resistance of the structure.(3)The sensitivity analysis of fatigue characteristics of epoxy asphalt structure to parameters shows that the modulus of epoxy asphalt layer>thickness of epoxy asphalt layer>thickness of stress absorbing layer>modulus of stress absorbing layer.Single layer and double layer epoxy asphalt have good low temperature crack resistance.The fatigue resistance of the two-layer epoxy structure(thickness≥4cm)is better than that of the single-layer epoxy structure(thickness<4cm),and the shear resistance of the single-layer epoxy structure is better than that of the two-layer epoxy asphalt structure.The main control indexes are maximum longitudinal tensile stress,maximum longitudinal tensile strain and maximum transverse shear stress.The single-layer epoxy structure is suitable for different load conditions and has excellent cracking resistance,fatigue resistance and interlayer shear resistance.Double layer epoxy structure is suitable for overloading and channelized traffic section.The single-layer epoxy structure is more suitable for special load conditions.(4)The influence analysis of the modulus of stress absorbing layer of epoxy+stress absorbing layer(modified asphalt)structure shows that the cracking and fatigue resistance of epoxy+modified asphalt structure is better than that of epoxy+stress absorbing layer.The latter structure is suitable for the section with standard axle load and has excellent cracking resistance,fatigue resistance and interlayer shear resistance.It is not suitable for the section with heavy load and frequent emergency braking,turning and long longitudinal slope.The former structure is suitable for channelized traffic overload and frequent emergency braking sections.When the force transfer rod is set,the former structure is suitable for the section under vertical load only,while the latter structure is more suitable for overload or special load conditions,which can effectively play the energy dissipation performance of the stress absorption layer and improve the structural performance.(5)The performance evolution law of the proposed structure with different loading conditions and interlayer bond state shows that the interlayer contact state has significant influence on the longitudinal tensile stress,longitudinal tensile strain,vertical shear stress and transverse shear stress indexes of the structure;It has significant influence on the longitudinal tensile stress,transverse tensile stress(standard axial load),longitudinal tensile strain and transverse shear stress(horizontal load)of epoxy+stress absorbing layer structure.The mechanical response decreases with the increase of interlayer contact state,and the reduction increases with the increase of load condition.(6)The research on the influence of floor support on epoxy asphalt structure shows that the control indexes of floor clearance are longitudinal tensile stress,longitudinal tensile strain,transverse tensile strain and maximum vertical shear stress.The impact of floor clearance Angle on structural performance is the most significant,and it decreases with the increase of the depth of floor clearance.With the increase of the longitudinal size of the void surface,the mechanical response value generally increases,indicating that the longer the longitudinal size of the void surface,the more significant the influence on the structural performance.(7)According to the economic analysis,the recommended order is single-layer epoxy structure,epoxy asphalt+stress absorbing layer,epoxy asphalt+modified asphalt,and double-layer epoxy structure of typical structure;it shows that the epoxy asphalt tunnel pavement structure is in 30 It has good economic benefits during the year.