| In recent years,with the development of major engineering practice in cold regions of China,especially the high-speed railway(including the construction of fast passenger dedicated line),expansive soils that occur in many parts with special poor engineering properties and have been found successively in the alpine deep seasonally frozen regions(eg.Harbin and Yanji,ect).The example of instability of expansive soil in cold region shows that freeze-thaw cycle is one of the most direct reasons that seriously affects the stability of expansive soil slope and induces landslide.In addition,because the deep residual expansive soil newly encountered in the construction of high-speed railway in the alpine deep seasonally frozen region of China was firstly discovered,there is no direct research work on this key scientific problem at home and abroad.As a result,there is a lack of reliable theoretical basis and feasible technical methods for the deformation analysis,earth pressure calculation,supporting structure design,stability evaluation,and landslide prevention and control for the expansive soil slope in the alpine deep seasonally frozen region.Therefore,"unreasonable design and experiential construction" is bound to become the mainstream of the current construction of cutting slope under such complex site conditions,which will definitely bring great engineering and safety risks to the development of high-speed railway construction.In view of this,the cutting expansive soil slope at Yanji section along the Jilin-Tumen-Hunchun high speed railway was taken as a research object.Laboratory tests on the microstructure and macroscopic mechanical properties of expansive soil under the effect of freeze-thaw cycles were conducted.Based on these experiments results show the evolution laws of microstructure and macroscopic mechanical properties of expansive soil under the effect of freeze-thaw cycles.An elastoplastic constitutive model of expansive soil exposed to freeze-thaw cycles,which could reflect the coupling relationship between volume strain and shear strain cross influence with p and q was proposed.With the aid of ABAQUS numerical finite element software,the UMAT subroutine of the double yield surface elastoplastic constitutive model of expansive soil was developed,which was based on the generalized plasticity theory.This elastoplastic constitutive model was applied to the three-dimensional numerical model of cutting expansive soil slope and sheet pile wall system.The main factors affecting the stability of expansive soil slope and the deformation characteristics under the effect of freeze-thaw cycles were revealed.Main content,method,and results are as follow:Firstly,mercury intrusion porosimetry(MIP),X-ray computerized tomography(X-ray CT),and consolidated-drained(CD)triaxial tests were conducted for the expansive soil at the Yanji section along the Jilin-Tumen-Hunchun high-speed railway under the effect of freeze-thaw cycles.These experiments results show the evolution laws of microstructure and macroscopic mechanical properties of expansive soil under the effect of freeze-thaw cycles.The microstructural analysis results reveal that the effect of freeze-thaw cycles is concentrated in pores size of 5～100μm.Moreover,based on the CT values,mathematical expression of macroscopic mechanical property degradation of expansive soil induced by micro-damage under the effect of freeze-thaw cycles was proposed.Then,based on the experiment results of microstructure and macroscopic mechanical properties of expansive soil exposed to freeze-thaw cycles,the volume yield surface and shear yield surface of saturated expansive soil were derived,which is on the basis of model framework proposed by Yin Zongze and the generalized plasticity theory.This elastoplastic constitutive model of expansive soil exposed to freeze-thaw cycles could reflect the coupling relationship between volume strain and shear strain cross influence with p and q.The constitutive model is verified by comparing with the results of triaxial test of expansive soil.With the aid of ABAQUS numerical finite element software,the UMAT subroutine of the double yield surface elastoplastic constitutive model of expansive soil was developed,which was based on the generalized plasticity theory.The validity and reliability of the UMAT subroutine were verified by comparing the experimental results with the numerical prediction.Thirdly,based on the elastoplastic constitutive model of expansive soil exposed to freeze-thaw cycles in Chapter 3,a three-dimensional numerical model of expansive soil slope and sheet pile wall system was established.The reliability of this numerical model was verified.Furthermore,a temperature field model of soil slope was established and the temperature field variations after excavation of 5years were studied.Based on maximum freezing depth,the deformation characteristics of expansive soil slope without snow cover were investigated.Moreover,considering the influence of freeze-thaw cracks,the deformation characteristics of expansive soil slope under extreme freezing-thawing of snow cover in spring thaw period was revealed with the aid of the model of snowmelt infiltration in Chapter 5.Finally,based on saturated unsaturated seepage theory,a three-dimensional numerical model of expansive soil slope-pile wall system under the condition of snow melt infiltration in spring was established.The general rules of slope collapse triggered by various thicknesses of snow cover,temperature change,and temperature difference between day and night was analyzed.The seepage fiel d and stability of expansive soil slope during snowmelt were simulated.Moreover,in view of the expansive soil slope in Binxi of Harbin-Jiamusi high-speed railway,the field monitoring was carried out to investigate the deformation development and evolution characteristics of soil slope under the condition of ’one freeze-thaw cycle’.On this basis,combined with the typical failure examples of expansive soil slope in cold region,the slope failure mechanism of expansive soil slope was illuminated in detail. |
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