Experimental Study On The Influence Of Water Content And Cold End Temperature On Frost Heaving Characteristics Of The Graded Crushed Stone Filler In The Surface Layer Of The Grade Bed

Railway construction planning is a very important part in the national comprehensive three-dimensional transportation network layout planning,in which the high-speed railway is 70,000 kilometers,forming a high-speed railway network with "eight vertical and eight horizontal" high-speed railway main passages as the skeleton and regional high-speed railways connecting.With the rapid development of China’s high-speed railway construction,more and more high-speed railways are traveling in cold regions with seasonal frozen soil.In seasonal frozen soil areas,the subgrade of high-speed railway will appear frost heaving and thawing settlement with the change of seasons,which is easy to produce uneven frost heaving and thawing settlement.The frost heaving deformation of bed surface graded crushed stone filler is one of the important sources of subgrade frost heaving deformation,which affects the smoothness of track structure and the safety of train operation.Therefore,it is very important to reduce the displacement of subgrade frost heaving deformation during subgrade operation.Based on the research background of high-speed railway subgrade in seasonal frozen soil area,this paper analyzes the influencing factors of subgrade frost heaving,and chooses graded crushed stone in bed surface as the research object.The basic physical properties and frost heaving characteristics of graded crushed stone filler are studied through indoor tests.The main research work and conclusions include:(1)The maximum dry density and permeability coefficient of the filler are measured by the basic physical properties test,and the freezing temperature of the sample is measured by the freezing temperature test,which provides a basis for the subsequent freezing test.(2)Under a certain cold end temperature condition,through the large model unidirectional frost heaving test of graded crushed stone subgrade filler under two conditions of different water content and different immersion height,the change process of temperature field,freezing depth,freezing rate,frost heaving deformation and frost heaving rate of graded crushed stone sample with time is obtained.The results show that the higher the water content in the filler,the smaller the freezing depth,but the greater the frost heave deformation.When the filler is completely soaked in water,the frost heave rate is the highest,reaching 0.9%;The frost heaving rate under open immersion condition increases with the increase of immersion height,and the maximum is 1.06 %.In the rapid growth stage,the proportion of closed system and open system to all frost heave displacement is 70 %-80 % and 60 %-70 %,respectively.(3)Through the large model unidirectional frost heaving test of graded crushed stone subgrade filler under different cold end temperature conditions,the test results of graded crushed stone samples are analyzed.The results show that the freezing depth increases linearly with the decrease of cold end temperature,and the frost heaving rate has a maximum point with the decrease of cold end temperature.When the cold end temperature is-15 ℃,the frost heaving rate reaches 0.33 %.(4)After the freezing test,the samples are divided into frozen area and unfrozen area,and the temperature gradient in frozen area is greater than that in unfrozen area.The temperature gradient in the frozen area of the sample increases with the increase of water content.