Research On Highway Subgrade Widening Scheme And Deformation Control In Seasonal Frozen Area

With the vigorous development of economy, the number of automobiles is also increasing, huge traffic volume has caused a big chanllenge for the existing highway network. But most of the highway built in the last century cannot withstand the increasing traffic volume, which lead to the poor road transportation efficiency. Subgrade widening with the advantages of covering a smaller area,costing less money,openning sooner has become the key measure to solve this problem. And the differential deformation control has been a problem in subgrade widening project, widening project in the seasonal frozen soil area should not only consider differential deformation between the new and old subgrade caused by the new filled subgrade soil, but also the further impact on the widening differential deformation caused by the seasonal freezing and thawing of the soil.This paper analyzed the widening subgrade deformation in seasonal frozen areas,considering the influence of water on the c and (p.The paper mainly includes the following aspects:Firstly, a calculation model of widening subgade unsteady temperature field is established based on temperature field control equation. According to the boundary conditions of temperature determined by the cyclic variation of temperature in seasonal frozen area and the variation of materials'thermal parameters in freezing area,melting area and transition area, a calculation model of widening subgade unsteady temperature field in seasonal frozen areas has been given.At the same time, the change of the temperature field of the subgrade before and after widening has been analyzed as well as the influence of widening time on the temperature of the subgrade.The conclusions includes:Under the same time, the temperature of subgrade after widening is greater than that before widening in the corresponding location.When calculating time is 10 years, the temperature of subgrade after widening becomes almost uniform with that before widening in the corresponding location.The later widening time,the more obvious effect on the the temperature of subgrade.Secondly, a calculation model of the change of water contents in soil in the process of freezing has been established based on Fick's first law which has been revised by the temperature gradient. Similarly a calculation model of the change of water contents in soil in the process of melting has been established based on Darcy's law which has been revised by the temperature gradient. Thus a calculation model of the change of water contents in soil after the action of one time freezing-thawing has been set up considering the comprehensive action of freezing-thawing.Finally, a deformation calculation model of widening subgrade in seasonal frozen area has been established based on the water contents in subgrade after one time freezing-thawing and the regression relation expressions between water contents and strength parameters of soils.The influence of widening mode,widening width, filled height, the number of geogrid layers, freezing-thawing cycles on the deformation of widening subgrade has been analyzed. Preliminary conclusions include:Bilateral widening mode is good for force equilibrium of subgrade, but the control of construction process is difficult;When the height of the subgrade increases to 6m, the increase amplitude of horizontal displacement of the new subgrade slope toe and under the new subgrade slope toe is bigger,which leads to the necessarity of special controling measures; Laying geogrid indistinctly decrease the vertical displacement of subgrade, but obviously decrease the horizontal displacement of the new subgrade slope toe and under the new subgrade slope toe; The vertical deformation of the subgrade increases with the increase of the number of freeze-thaw cycles, but the increase amplitude is not significant.