Study On Dynamic Response In Pavement And Subgrade Of Airport In Mountainous Area Subjected To Aircraft Single-wheel Load

Construction of mountainous regional airport plays an important role in the strategy of West China development, which can also promote the development of local tourism industry, optimize the Aviation layout and coordinate development of the regional economy. It is necessary to construct mountainous regional airports for national defense security, maintenance of security and stability in border areas, and emergency service and disaster relief in China. Excavating-filling subgrade is one of the most important characteristic of airports in mountainous area.Subjected to moving aircraft load, dynamic stresses in the pavement and subgrade are uneven, leading to pavement uneven settlement after construction. This can be the key point of runway quality worsening factors. So it is important to study dynamic response in pavement and subgrade of airport in mountainous area subjected to moving aircraft load.Considering the longitudinally excavating-filling characteristic of airport subgrade, a semi-analytical Finite Element Method is proposed to analyze this dynamic response problem by Fourier Transform in the transverse direction of the runway. The corresponding finite element formulations are derived, and the finite element analysis program is coded. On this basis, to study dynamic response in pavement subjected to single-wheel load, the influence of the load speed, the pavement structure types, and different kind subgrades is analyzed respectively. Main conclusions include:(1) The influence on dynamic stresses in pavement and subgrade of the load speed, the pavement structure types, and different kind of subgrades is obvious. Subjected to single-wheel load, the pavement produces bending deformation. The vertical compressive stress is the major dynamic stress in subgrade soil. The the influential depth of additional stress in soil under rigid pavement structure is about 5m.(2) With the increase of load speed, dynamic stresses in pavement increase. But as a result of big pavement stiffness and high elastic-wave velocity, increase of dynamic stress amplitude is not obvious except for longitudinal stress.a) Longitudinal tensile stress zone existed in front of the load point in pavement. For the load speed of 80m/s, its amplitude can be 20% of the compressive stress amplitude under single-wheel load, which should be paid enough attention in the pavement structure design.b) Stress peaks in pavement structure of longitudinal and transversal direction is close, which are less influenced by load speed. The rigid pavement mainly depends on the bending strength of the cement concrete slab to bear the plane loads. Macadam Base bears much smaller tensile stress in longitudinal and transversal direction. The flexible pavement mainly depends on asphalt concrete slab to bear compressive stresses, Macadam Base upper layer bears tensile stress, underlayer is auxiliary tensile structure.c) The stress distribution effect of pavement slab is obvious. The peak value of vertical compressive stress on ground under flexible pavement is smaller than 1.8%of the static pressure under single-wheel load. For rigid pavement, this number is only 1.2%.d) Near excavating-filling interfaces, the dynamic stresses on the ground and in the pavement are both concentrated. The influence range of excavating-filling subgrade in the pavement is about 20 meters in longitudinal direction. The shear stress in pavement slab near the interface in front of load is approximately 1.15 times that of evenly filling subgrade. And the longitudinal stress concentration factor of pavement slab can be 350%.(3) Dynamic stress path of soil in homogeneous soil under low speed load is heart-shaped. Dynamic stress path of soil under pavement structure is tilted egg-shaped with an angle. With load moving speed increase, dynamic stress path counterclockwise, asymmetry about the x-axis become more obvious, and major axis of stress path in deeper soil become longer.a) With the increase of soil depth, the vertical dynamic stress amplitude decrease quickly, long to short axis ratio of stress path increase.b) The dynamic stress time history curves of soil near excavating-filling subgrade interface change significantly. Long to short axis ratio of stress path increase. Dynamic stress path of soil is tilted spindle-shaped.