Research On The Influencing Factors Of Freeway Subgrade Frost Damage In Seasonally Frozen Ground Region

With the development of national economy, highway traffic is playing a more and more important role, which is the basis of the economic development in a society. However, There are many factors which have impacts on the stability of the subgrade , while the basic ones are the intensity and the stability of the subgrade. To the freeway of the seasonally frozen ground, it is a serious problem that the seasonally frost damage always makes the highway construction in North China difficult. Because, the freeway, which is built in seasonal frozen regions, often can't bring the convenience and high speed into play because of the roadbed frost damage, such as road surface fissure, thawing settlement track, bulge, frost boiling, etc. Furthermore, it will affect traveled vehicle and do harm to the people's life and property. Study the fundamental principle of freeway roadbed frost damage and exploring the regularity that it take place and develop are becoming more and more important .The research can guide the roadbed freeze resistance design, construction and maintenance of the frost damage road. According to three years field frost damage drilling investigation , in-situ observation and a lot of laboratory freezing and thawing and water translocation simulation experiments , adopting concluding , regression and other methods ,this dissertation analyzed the influencing factors of the freeway roadbed frost damage .The text mainly consists of five chapters .The present status of roadbed frost damage study and some basic work for this dissertation were introduced in the first chapter.The second chapter was research on the influencing factors of freeway subgrade frost damage. Firstly, it discusses mechanics of frost damage and introduces the damaged formats of freeway subgrade frost damage, which contain mainly transverse flexible deformation and lengthways long fissure that led by the frost heave and settlement and bulge that induced by the highway frost boiling. Secondly, it analyses the influence of water, soil, temperature and subgrade trait factors on frost damage of soil, establishes linear regression curve and equation of the water content and frozen-heave factor, thaw subsidence coefficient of the classical soil, which can get the conclusion that frozen-heave factor and thaw subsidence coefficient will intensify with increasing of the water content,and it analysis the influene of soil to the frost heave susceptibility by the component of grain size and plasticity of soil,gets conclusion that, in some condition, the frost heave susceptibility will reduce when the grain changes small, the specific area changes big and plasticity intensifies.Moreover, it analyzes the effect of temperature and feature of subgrade, when there's enough water content, the lower temperature is, the bigger frost heave coefficient is; the frost heave coefficient will reduce when the amount of fill of subgrade increases. At last, elaborates the regularity of subgrade frost heave, the freezing heave course is divieded into four types, which are slow increasing type, freezing shrink-freezing heave type, zero freezing heave and freezing shrink; gives the distribution of frost heave alone frost depth, obtains that some parts of total frost heave located the base of the biggest frost depth, which is about 15% under the biggest frost depth.The third chapter is the study on the water redistribution of roadbed. According to above analyses, the water redistribution is the fundamental problems of subgrade frost damage. In the first section, by research on the water redistribution, in the closed freezing system, the water content of the freezing layer increases, but in some depth under the freezing layer, the water content decrease. In the second section, it analyzes the influencing factor of the water redistribution, and gets some conclusions that the greater water content, the shallower groundwater lever and the lower temperature will accelerate the water moving. The last section points out that the intensity of the water redistribution has positive correlativity with the roadbed frost heave.The fourth chapter focuses on the relationship of the rising height of capillary water and frost heave. At first, it elaborates the mechanism of the rising height of capillary water and the thinking of research with the relationship of frost heave. Secondly, analyzes and compares the distributed situation of the water content alone the height in a capillary belt. Moreover, integrates the data of research on the distribution of capillary water alone the height and the regularity ofη- w that revealed by frost heave test of indoors, and then get the effective frost damage height.The fifth chapter is the conclusion of this paper. Through the study of the above, can obtain regularly understanding of phenomenon of the subgrade frost damage, and also accumulate some experiences the advancing research in the future.