| Up to now,more and more airports have been built on frozen soil.Because of the frozen thaw cycle,a large number of diseases appeared in the airport runway in frozen soil area in a short time,which affected the normal use of the airport.This paper relied on runway project of an airport in Xinjiang,and made statistics on the damage forms of runway surface,analyzed the causes of frost heaving,and then proposed the methods to solve diseases,and provided reference for the design and evaluation standards of airport runway in frozen soil area in the later period.Through the understanding of the current research situation,it was found that the evaluation indexes of airport runway in frozen soil area were mainly two aspects: one was the deformation characteristics of pavement structure,the other was the deformation characteristics of runway foundation.In this paper,through the establishment of HWD test model,the deflection data under different working conditions were obtained,and the "improved deflection basin area index method" was put forward.Verified by the engineering measured data,it had high back-calculation accuracy and efficiency,and can be used as a method for the performance evaluation of airport pavement structure.The finite element simulation was carried out for the runway foundation of the composite geomembrane airport,and the influence of the composite geomembrane on the deformation characteristics of the foundation was compared,and the best location was found out,which provides the basis for runway reinforced foundation design.The main contents and conclusions are as follows:(1)The main causes of airport runway diseases in frozen soil area are as follows:first,in the design stage of pavement structure,the actual size of the modulus of subgrade reaction and the elastic modulus of pavement panel was not fully considered,and the area with bad foundation conditions was not strengthened and the thickness of pavement panel was small.The second is that the subgrade contains groundwater and there is the source of environmental water.The cycle of freezing thaw caused the cycle of frozen layer to change in uplift and looseness.(2)The finite element model of HWD airport pavement test was established.The simulation results show that when the pavement was too thick or too thin,the deviation between the simulated value and the analytical value at a certain measuring point would gradually increase with the increase of the modulus of subgrade reaction.Therefore,it was suggested that the appropriate plate thickness for the back-calculation of pavement structural parameters is 0.24-0.4 m.(3)The paper analyzed the systematic error of the existing area index method of the deflection basin,and obtained two measures to effectively improve the back-calculation of the structural parameters of the pavement: one was the arrangement scheme of remote sensor and local encryption at the front end;the other was to replace the deflection value of the specified measuring point in the formula of the area index of the basin by using the average value of all deflection values of the measuring points,and considered the deflection information of all measuring points to reduce the influence for the back-calculation results.According to the measures obtained,based on the fitting analysis of the deflection database,"improved deflection basin area index method" was proposed.The error calculation and comparison between the method and the three existing methods were made by using the measured deflection data of runway project of an airport in Xinjiang.It was found that the back-calculation accuracy of the method proposed in this paper was higher than that of the three,and the back-calculation efficiency was higher,It provided a new way for the back-calculation of pavement parameters and pavement evaluation in practical engineering.(4)According to the engineering situation of runway project of an airport in Xinjiang,the airport runway foundation model in frozen soil area was established.Based on the theoretical analysis of Winkler elastic foundation beam model,it could be concluded that the vertical stress reached the maximum at two points of landing.At the midpoint,the stress direction of the left and right points was opposite and the stress was offset,so the stress value was low,and the two small abrupt outside the load action point were caused by the soil restraint stress produced by the compression of the soil due to the load action.The vertical displacement reached the maximum value at the middle point of two loads.Because the distance between the wheels was close,the instantaneous impact on the pavement maked the stress superposition at the midpoint,and the vertical displacement was larger.(5)The model of runway foundation with composite geomembrane was established.Compared with the foundation stress and vertical deformation under ordinary foundation,it could be found that the ground stress and vertical displacement of the ground in frozen soil area with composite geomembrane were significantly reduced under the impact load of aircraft,thus protecting the pavement surface from damage and prolonging the pavement life.According to the model of composite geomembrane foundation,the influence of composite geomembrane on vertical displacement of foundation under different laying depth was studied.The optimum buried depth of composite geomembrane was determined to be 1.1 m,and the application of multi measures was taken in combination with the actual engineering situation. |
PDF Full Text Request