Study On Mechanism Of Subgrade Thawing And Countermeasrue Against Pavement Structure Distress In Permafrost Region

With the development of highway construction in permafrost region, heat equilibrium of permafrost is destroyed, which causes more engineering problems and much pavement premature failure. The formation and growing of pavement distress request more focus on mechanism of subgrade thawing settlement, forcasting of thawing settlement, analyzing of pavement structure and countermeasure against distress. The forementioned problems are researched based on pavement distress investigation in this paper.The heat equilibrium of original subgrad is destroyed for global climate becoming warmer and reconstruction of highway. In order to explore mechanism of subgrade thawing settlement, using determinism axiom, local action axiom, equipresence axiom and combining conservation of mass, conservation of momentum, conversation of energy, entropy unequality and volume fracton condition, mixture theory of permafrost thawing is deduced. In deducing process, permafrost is regarded as porous media which is composed of soil partical, ice and fluid matter (including unfrozen water and air).Permafrost subgrade thawing process is correlative with environment, subgrade and pavement structure and material thermal parameter. Temperature and settlement of soil model in frozing and thawiong process are tested by laboratory test. Then FEM model is established which has the same dimension, the same thermal parameter and the same boundary condition with test model, the temperature of FEM model in frozing and thawing process are calculated. Calculated results show it's satisfied with test results.Permafrost interior heat accumulation causes mechanical performance reducing and which leads to thawing settlement. The thawing settlement of permafrost is simulated by FEM in the paper. In simulating process, simulated temperature results in previous step is input to settlement simulating model as field variables, physical and mechanical parameters are defined as function of temperature, then uning soil consolidation theory the simulation is put into practice. Comparing calculated and test results, it's approved that the simulating method is feasible and credible.Intrinsic law of subgrade deformation in permafrost region is researched based on field test data of Qinghai-Tibet highway subgrade deformation. The test data is constructed to multidimensional space using phase space reconstruction theory, independent variabl, function and sample number are defined in the multidimential space, then data regression is implemented by partial least square regression, regression precision is scaled by given index. Through the entire procedure the forecasting model of subgrade deformation is constructed.For especial geographical and climatic conditions, pavement distress in permafrost region is more severe and complicated than that in other region. The distress is exterior reflection of asymmetrical settlement and mechanical performance reducing of pavement material. In the paper, the displacement and stress of pavement structure under different subgrade thawing depth are analyzed by ABAQUS software. Comparing analyzed results, the optimum pavement structure suited to permafrost region is brought forward. At the same time, the countermeasures against pavement structure distress are designed by contraposing reviewed pavement distress traits in permafrost region.