Study On Design Indexes Of Semi-rigid Baseasphalt Pavement In Zhejiang Highway Tunnel

China has become one of the countries with the largest number of tunnels in the world.At present,there are still no design specification or guides to guide people in the structural design of tunnel pavements.Only road asphalt pavement design specification or urban road design specifications can be applied.There are many studies on semi-rigid base asphalt pavement in soil base sections,but there are few studies on semi-rigid base asphalt pavements in tunnels.The paper analyzes the mechanical response and fatigue life of the semi-rigid base layer without transverse cracks and transverse penetrating cracks and the pavement structure under the action of symmetric load and partial load.The ABAQUS software is used to establish three-dimensional finite element model of semi-rigid base asphalt pavement with the transverse cracks in the base layer.;under the condition of partial load,the mechanical response of the pavement structure and the sensitivity order of the influencing factors are analyzed under vertical load and the combined action of horizontal load and vertical load.Compare with the mechanical response of the semi-rigid base asphalt pavement in the tunnel and the soil base sections,consider the?Specifications for Design of Highway Asphalt Pavement??JTG D50-2017?at the same time,proposed the asphalt pavement control index of the semi-rigid base layer?predetermined through crack?in the tunnel.The main conclusion of this paper are as follows:?1?The internal tensile strain of the asphalt layer is proposed as the fatigue failure control index,and the mechanical response is the tensile strain along the driving direction;the permanent deformation index of the asphalt mixture layer recommended by the Specifications is maintained,and the mechanical response is the vertical compressive stress;The internal shear stress is the shear failure control index,and its mechanical response is shear stress;the bottom layer tensile stress is not controlled.?2?The most unfavorable lateral position of the strain along the driving direction should be taken from point A below the tire,and should not be taken as the bottom of the asphalt layer in the vertical direction,but should be determined according to the specific structure combination.Sensitivity order of influencing factors of tensile strain maximum and depth position along the driving direction:asphalt layer thickness>asphalt layer modulus>base layer modulus?base layer thickness.?3?Under vertical load,the vertical position of the maximum shear stress S12 and S23 is located in the surface layer rather than the bottom of the layer,and the lateral position is at the edge of the tire.The maximum value of shear stress S23 is located at the top of the surface layer under the action of horizontal load and vertical load.The maximum value of shear stress S12 is located in the surface layer.Sensitivity order of influencing factors of shear stress:asphalt layer thickness>base layer modulus?asphalt layer modulus>Base layer thickness.?4?The shear stress intensity factor(K_II)of each structure under vertical load is greater than the open type stress intensity factor?KI?;and the open type stress intensity of each structure under the combined action of horizontal load and vertical load The factor?K_I?is greater than the shear stress intensity factor(K_II).?5?Since the maximum tensile strain in the asphalt layer is significantly larger than the bottom tensile strain of the asphalt layer,the fatigue life in the asphalt layer is much smaller than the fatigue life of the asphalt layer.Sensitivity ordering factors of fatigue cracking life of asphalt layer bottom layer:base layer modulus>surface layer modulus?surface layer thickness>base layer thickness.In the calculated value range,the larger the base layer modulus,the thicker the base layer thickness and the smaller the asphalt surface layer modulus,the more favorable the fatigue cracking life of the asphalt surface layer.?6?Based on the principle of BP neural network,the relationship model between control index and structural parameters and material parameters was established by using MATLAB software.