Study On The Thermal Characteristics And Mechanical Properties Of Seasonal Snow In Northeast China

Snow is an important natural resource,which is widely distributed.As a special underlying surface,the thermodynamic properties of snow is very important for the impact on the surrounding environment.With the continuous change of global climate,snow disasters occur frequently.At the same time,the increasing demand for snow related engineering requires the theoretical support of the basic physical and mechanical properties of snow.In order to solve these problems,this paper carried out related research on natural snow in Harbin,Heilongjiang Province,to explore the thermal and mechanical properties of seasonal snow in Northeast China.Analyze the changing laws and influencing factors of snow temperature,thermal conductivity and uniaxial compression properties.I hope this paper can provide reference and help to solve the problems related to snow.The main contents and conclusions of this article are as follows:(1)Through the observation of the crystal structure of natural snow,it is found that the snow crystals in Harbin area mainly present complex dendrite structure,accompanied by a large number of tiny,irregularly shaped snow particles with incompletely developed crystal structure.While observing the crystal structure of snow under the metamorphism,it is found that the metamorphism starts from the landing of snow,which promotes the fusion of snow crystals and forms the connected bonds.This is the fundamental factors for the change of the basic physical and mechanical properties of snow.(2)Based on the snow temperature data under different densities(0.30g/cm~3?0.35 g/cm~3?0.40g/cm~3?0.45 g/cm~3)of natural snow,analyze the variation characteristics of snow temperature.At the same time,analyze the variation law of the thermal conductivity of snow at different temperatures(-5°C?-10°C?-15°C?-20°C?-25°C)and densities(0.35 g/cm~3?0.40 g/cm~3?0.45 g/cm~3?0.50 g/cm~3?0.55 g/cm~3?0.60 g/cm~3).The results show that:The thermal conductivity of snow increases with the increase of density,and there is a good index correlation between them;The response of the thermal conductivity of snow to temperature shows obvious difference under different densities.In the density range of 0.40 g/cm~3?0.45 g/cm~3,the thermal conductivity increases with the increase of temperature;In the density range of 0.50 g/cm~3?0.60 g/cm~3,the correlation between the thermal conductivity and temperature is weak;During the temperature observation period,snow cover temperature was consistent with the change trend of air temperature,and both were less than 0?.In different periods of the day,the snow layer on the surface will appear the cold and warm center,and the temperature of the shallow 0?20cm snow layer will change dramatically.The variation range of snow layer temperature gradually decreases with the increase of snow depth,there is a good negative index correlation between amplitude of snow temperature and snow depth.The time of reaching the extreme value of deep snow temperature is slightly lagged behind that of surface snow layer.In the same depth of snow layer,the temperature decreases with the increase of density.(3)Uniaxial compression tests were carried out on natural snow at different temperatures(-5oC,-10oC,-15oC,and-25oC),loading rates(1?300 mm/min)and densities(0.35 g/cm~3,0.40 g/cm~3,0.45 g/cm~3,0.50 g/cm~3,0.55 g/cm~3,and 0.60 g/cm~3).The results show that plastic deformation transitions to brittle failure in snow with an increase in the loading rate.The critical loading rate between the two deformation modes is within the range of 10?30 mm/min;with increasing loading rate,the uniaxial compressive strength first increases and then decreases.The loading rate corresponding to the ultimate compressive strength is between 10 mm/min and 30 mm/min.The uniaxial compressive strength increases with increasing density,and there is a good linear relationship between the ultimate uniaxial compressive strength and density.The ultimate compressive strength achieved in these tests is 1.68 MPa.Additionally,the uniaxial compressive strength of snow increases with decreasing temperature,and the relationship is especially obvious at low loading rates and high densities.The loading rate and density are the key factors affecting the uniaxial compressive strength of snow;Snow metamorphism and aging also affect the compressive strength of snow.After 90 days of metamorphism,the strength of samples of 0.5g/cm3and 0.45g/cm3 decreased by 45.1%and 49.3%respectively;Through observing the structure of the compressed snow crystal,it was found that the change of the connected bonds between the snow crystals was the fundamental reason for the change of the mechanical properties of snow.