Experimental Study On Freezing-thawing Damage Of Channel Soil Slope In Seasonal Freezing Area

In this paper,taking the canal base soil in Harbin Xin Ren irrigated area as the test material,based on the actual temperature data of three years in Harbin area in 2010~2012,the similarity ratio of freezing index(C_I)is 1:135 and the correction coefficient K of the laboratory is 1.13.The freezing and thawing cycle of different initial state specimens is carried out by the 0~11 freezing and thawing cycle.freezing and thawing process adopts Unidirectional freezing,bi-directional melting of natural freezing and thawing,the sample after a predetermined freeze-thaw cycles,remove the sample determination of its physical and mechanical indicators,get the following conclusion:With the increase of freeze-thaw cycle,soil physical property damage rule is:The coefficient of permeability of unsaturated sample under a closed system,but the overall rate gradually reduced,the increased permeability coefficient values in about 7 times tend to be stable,and in the same under freeze-thaw cycles,the permeability coefficient increases with the increase of dry density and moisture content.The thermal conductivity of unsaturated samples decreases linearly in the closed system.Under the condition of the same freeze-thaw cycle coefficient,the thermal conductivity increases with the increase of dry density and moisture content.Under the closed system,the saturated sample is reduced exponentially.The modified Chung and Horton models are used to predict the numerical value of the thermal conductivity under different freezing and thawing cycles.The difference between predicted value and real value is small.The difference between predicted and actual values under different freezing thawing cycles is 5.15%,2.89%,2.21%,0.52%,0.31%,0.55%,0.33%.For the sample in an open system,the thermal conductivity increased significantly after the first freeze-thaw.After the unsaturated samples were freeze-thawed in the closed system,the vertical moisture content was redistributed due to the formation of the frozen front.Combined with different initial moisture content,the upper sample moisture content is reduced,in the central sample 10 cm inside certain limits,sample moisture content increases,and in the lower part of the rest,sample moisture content is also reduced.After repeated freezing-thawing of saturated samples and open samples in closed system,the average dry density decreased and the average porosity increased.With the increase of the number of freeze-thaw cycles,the physical properties of the soil are as follows:The cohesive force of the specimen is gradually reduced,regardless of the initial state of the specimen and the supply of the external source of water in the freezing thawing process.When the freezing and thawing cycles at the same time,the cohesion of soil increases with the moisture content and lower,with the increase of dry density and the rise,under different dry density and moisture content,soil cohesion and internal damage relations for index form of freeze-thaw cycles.The damage coefficient Kc and freeze-thaw times of saturated samples in the closed system showed exponential changes,while the damage coefficient Kc and freeze-thaw times of samples in the open system were approximately linear.The internal friction Angle of unsaturated samples increases gradually under the closed system,but the rate of increase in each freeze-thaw cycle is not consistent and there is no obvious rule to follow.However,for samples with the same number of freeze-thaw cycles,the internal friction Angle is significantly affected by dry density and moisture content,and its value is proportional to dry density and inversely proportional to moisture content.The relationship between the friction angle damage coefficient K?and the number of freeze-thaw cycles under the closed system can be expressed as a logarithmic function,while the relationship between the damage coefficient K?and the number of freeze-thaw cycles in the open system is linear.The elastic modulus of unsaturated specimens in the closed system showed a decreasing trend.When the number of freezing and thawing cycles is fixed,the modulus of elasticity is also affected by dry density and moisture content,which increases with the increase of dry density and decreases with the increase of water content.When the confining pressure is 100 kPa,the cracking damage of the elastic modulus is greater than that of the first freeze thaw.For the specimens with the same initial state and the same freeze-thaw cycles,the elastic modulus increases with the increase of confining pressure.In the closed system,the average dry density and the average porosity of the two are consistent.With the freezing and thawing cycle,the average dry density decreases and the average porosity increases.The physical and mechanical properties of the saturated samples under the closed system are analyzed by the grey correlation analysis and the related physical and mechanical indexes determined by the test.It is found that the freezing thawing is the external cause of the change of the soil properties,while the average porosity is the internal cause.The change of soil properties is essentially the result of internal and external factors.The influence of physical properties on mechanical properties is as follows:average porosity,average dry density,permeability coefficient and thermal conductivity.