Study On Mechanical Properties Of Silty Soil In Seasonal Frozen Soil Region

With the acceleration of urbanization,the number of motor vehic les has increased rapidly,subway plays an important role in alleviating urban traffic pressure.In 1969,the first subway in China was built and put into use in Beijing.Up to now,more than 30 cities in China have built or are building subway.The subway project has gradually turned to cold areas,such as Baotou,Inner Mongolia.which is belong to seasonally frozen area.In order to ensure the stability and safety of the project,it is necessary to confirm and evaluate its physical and mechanical properties under different environmental and human factors.The soil properties become more complex because of the special environment in this area.In order to make the research results universal,three kinds of soil samples with water content subjected to different times of freeze-thaw cycles,then the static and dynamic triaxial tests were carried out to obtain the relationship between stress-strain curves.It provides a basis for studying the change law of mechanical properties of soil in seasonal frozen soil area.The main contents and results are as follow:(1)test the physical properties of the soil samples retrieved.The basic physical indexes of the soil samples were measured,including natural moisture content,density,optimum moisture content,liquid plastic limit index,and soil particle analysis test showed that the soil sample is silty soils.The silty soils remolded soil samples with different moisture contents were prepared.(2)triaxial compression test on silty soils of different moisture content.Three kinds of remolded soil samples with different moisture content were subjected to 0,1,3,5,7,9 and 11 freeze-thaw cycles to carry out triaxial compression tests under different confining pressures.The stress-strain curves and static parameters of three kinds of water-bearing soils under different freeze-thaw cycles and confining pressures were obtained.The results show that: the stress-strain curves change from strain softening to strain hardening with water content,and the softening becomes more obvious with the decrease of confining pressure,and the stress-strain curves of unfrozen-thawed soils change from softening to hardening with the increase of freeze-thaw cycles;The static elastic modulus,failure strength and shear strength of silty soil are proportional to the confining pressure and the maximum at the optimum moisture content;the freeze-thaw cycles weakens the static elastic modulus,failure strength and shear strength.After significant analysis,it is found that freeze-thaw cycle,confining pressure and moisture content have great influence on elastic modulus.(3)Dynamic triaxial test on silty soils of different moisture content.Three kinds of remolded soil samples with different moisture content were subjected to 0,1,3,5,7,9 and 11 freeze-thaw cycles to carry out dynamic triaxial tests under different confining pressures and load amplitudes.The British GDS dynamic triaxial tester was used to simulate the train cyclic load.The kinetic parameters of three kinds of water content soil under different freeze-thaw cycles and different confining pressures were obtained.The results show that: the dynamic elastic modulus and dynamic shear modulus decrease with the increase of freeze-thaw cycles,the dynamic elastic modulus of the unfrozen soil samples is the highest,and tends to be stable after 9 freeze-thaw cycles,it increases with the increase of confining pressure and decreases with the increase of amplitude,and the maximum at the optimum moisture content;The dynamic ratio of Poisson's is directly proportional to moisture content,amplitude and confining pressure,and has no obvious law with the number of freeze-thaw cycles,but the ratio of Poisson's ratio of unfrozen soil is obviously lower than that of frozen soil;the damping ra tio is directly proportional to the number of freeze-thaw cycles,moisture content and amplitude,and inversely proportional to confining pressure.(4)establish static and dynamic modulus transformation theory.The dynamic elastic modulus is deduced from the simple and easy-to-measure static elastic modulus by nonlinear fitting of the measured static and dynamic elastic modulus,which can provide fast and accurate dynamic elastic modulus for engineering.