Research On Seepage-drainage Geogrid Roadbed Of Changes With Moisture And Heat By Freeze-thaw Action

More than half of China’s land area is covered by seasonal frozen soil.In addition,the frost heaving and thaw collapse of soil have great influence on the stability of subgrade in seasonal frozen soil area,which is affected by moisture in the soil.Due to the global warming,the permafrost regions is decreasing that leads the seasonal frozen soil areas expanding and moving to high latitudes.The strength,stability and durability of subgrade will be seriously affected by Freezing-thawing in seasonal frozen soil area and thawing of permafrost under subgrade.For the problem of the excessive moisture content in the subgrade soil in seasonal frozen soil area,Seepage Drainage Geogrid(SDG)has been developed by Institute of Cold Regions Science and Engineering Northeast Forestry University.lt is base on the design ideas of Insulation subgrade,ventilation subgrade structure,plastic drainage board,geogrid,soil composite principle.SDG Combined with the subgrade soil that can play a positive role in hydrothermal stability of subgrade soil reducing the moisture content of subgrade soil and improving the stability of subgrade in seasonal frozen soil area.This paper is base on the Laboratory research on small size to know changing rule of soil temperature and moisture content,then the freeze-thaw cycle experiment was carried out with its full scale model of SDG subgrade.According to the changing rule of soil temperature and moisture content of SDG subgrade obtained from previous experiments,laboratory experiments of other research contents were carried out:1.Under the action of freezing-thawing,the reasonable SDG subgrade structure form is built2.To optimize the soil material of SDG subgrade;3.Synergistic influence of grid configuration and scale effect on heat transfer field;4.Establish the mathematical model of soil water-heat coupling with interface constraints.The research results show that:1.After laying SGD,the response speed of surrounding soil to external temperature change is significantly changed;When the external temperature drops to negative temperature,it can prevent the one-way accumulation of water migration at the bottom,and thus slow down and prevents the formation of ice lenses.When the external temperature rises to positive temperature,the moisture content of surrounding soil can be significantly reduced.It is an effective way to improve the efficiency of SGD to increase the configuration size and laying layer number of seepage and drainage geogrid,increase the aperture of the pipe wall of the grid and reduce the pore space.2.The drainage mechanism of osmotic drainage geogrid verifies the theory of membrane water transfer.The mechanism of thermal control and drainage effect of particles on soil,water and air as the leading factor of the energy transfer medium,under the condition of the outside air temperature change,the energy transfer between the material and exchange,thus causes the internal temperature and moisture changes of soil,which makes the soil temperature field and moisture field redistribution,the redistribution reduce physical subgrade soil caused by water freezing injury;3.By simulating the model experiment process through the finite element software COMSOL Multiphysics,the overall variation law and distribution of temperature and moisture of the infiltration and drainage grid soil under freeze-thaw conditions are obtained,which is the same as the conclusion of the experiment.After optimizing the soil material of the model test piece,the use of high thermal conductivity or large porosity filler can improve the cooling and drainage properties of the osmotic drainage grid under the same conditions.