Experimental Study On Static And Dynamic Behavior Of Coarse-grained Soil From High-speed Railway Subgrade In Cold Regions

The mechanical properties of the fillings directly affect the strength,deformation and stability of the subgrade.The coarse soil has been widely used in the construction of railway subgrade because of its excellent engineering characteristics.With the construction of High-speed railway in cold regions,the research of the strength properties and deformation characteristics of the frozen or unfrozen coarse-grained soil under static or dynamic loads should be emphasized.Therefore,with the fund of the National Natural Science Fund(Study on hydrothermal stability and deformation control of High-speed railway Graded crushed rock in cold region-No.51378057)and(Study on deformation mechanism and long term stability of crushed stone embankment in Permafrost Regions-No.41371081),this paper has conducted the basic physical properties tests,large-scale direct shear tests and dynamic direct shear tests for coarse-grained soil of a High-speed railway in cold regions,how the vertical pressure,moisture content,temperature,compaction and other factors may influence the strength properties and deformation characteristics of coarse-grained soil are analyzed,to provide scientific basis for permafrost area of High-speed railway construction design and safety evaluation.The main contents and conclusions are as follows:(1)The coarse-grained soil from the bottom layer of the High-speed railway subgrade in cold regions are obtained.According to the Code for design on subgrade of railway,the filling can be classified as gravel sand with good grading,which is the group A soil.Besides,optimum moisture content and the maximum dry density have been obtained.(2)With the large scale direct shear apparatus for coarse-grained soil and dynamic direct shear system for frozen soil which designed by the Frozen Soil Laboratory of Beijing Jiaotong University,large-scale direct shear tests and dynamic direct shear tests have been conducted for the frozen or unfrozen coarse-grained soil with different moisture content,temperature,compaction and vertical pressure.(3)The stress-strain characteristics and strength characteristics of coarse-grained soil under static stress are studied.It is found that the shear shear displacement curves of the coarse-grained soil are strain-softening type at lower vertical pressures,and become the strain-hardening type with the increasing of vertical pressure.The strength characteristics of coarse-grained soil in frozen and unfrozen states also have been compared.The results show that the shear strength increases with the increase of vertical pressure.With the increase of moisture content,the shear strength of coarse-grained soil in the frozen state increases significantly,but decreases in the unfrozen state.In addition,in the range of the test moisture content,the C value of the coarse-grained soil in the frozen state is larger than in the unfrozen state,but the value of the internal friction angle is smaller than in the unfrozen state.(4)The strength properties and deformation characteristics of coarse-grained soil under cyclic loading are studied.It is found that there are significant differences in the failure patterns of coarse-grained soil in unfrozen and frozen conditions.The strength characteristics of coarse-grained soil in frozen and unfrozen states have been compared,the results show that the dynamic strength increases with the increasing of the vertical pressure or the degree of compaction,decreases with the increasing of the vibration times,and the dynamic strength in frozen state is much larger than in unfrozen state.In addition,the cumulative deformation of the coarse-grained soil increase with the increasing of the dynamic load amplitude or the vibration times,but decreases with the increasing of the vertical pressure.