Study On Instability Mechanism Of Root Loess Slope In Seasonal Frozen Soil Area

As the traffic construction in the central and western regions of China welcomes new opportunities,and the local government of Qingyang City in Gansu Province pays more and more attention to the ditches and soil and water conservation in the Dongzhi tableland,plant slope protection is the most common engineering measure in the traffic construction and ditches and tableland conservation in China.However,these regions are situated in the seasonal permafrost region,and the soil of the slope containing vegetation experiences freezing in winter and thawing in spring.Under the strengthening of herb roots and freeze-thaw damage,its engineering characteristics will change,causing uncertainty to the stability of the slope.This paper,researching the loess in Dongzhi tableland Qingyang Country,Gansu Province,through field survey and a series of laboratory test,freez-thawing is studied under the action of the strength of the root of the loess and the influence factors of infiltration characteristics,and calculates the Dong Zhi tableland area not frozen soil water content curve and heat conduction coefficient,on the basis of experimental data was carried out on the slope stability analysis,the main draw the following conclusion:1.Through the direct shear test,the factors of the strength of loess containing roots under freeze-thaw action were studied.It was found that the increase of the number of cycles reduced the shear strength and cohesion of the samples,while the inner friction Angle turn greater,and the value was less than 1.26°.The increase of moisture content will reduce the inner friction Angle and cohesion of the sample,and the sample with high moisture content needs fewer cycles to reduce to the minimum strength under the action of freeze-thaw.With the increase of the root content,the cohesion and shear strength of the sample can be improved,but the internal friction Angle cannot be increased.The more the number of freeze-thaw cycles,the worse the reinforcement effect of the root is.At the same time,the strength of the sample with high root content is more likely to deteriorate under the action of freeze-thaw.2.Through triaxial permeability test,the influence of root content and number of freezethaw cycles on the permeability coefficient of loess was studied.It was found that the higher the root content was,the higher the permeability coefficient was,and the sample containing root underwent 5 freeze-thaw cycles had the largest improvement rate of permeability coefficient.After ten loops of freeze-thaw,the osmosis ratio of the sample keeps increasing and then remain unchanged.when frequency of freeze-thaw loops is same,the higher the root content is,the greater the permeability coefficient is.3.The effects of root content,water content and cooling mode on temperature and unfrozen water content of the sample were measured by TDR,and it was found that root content had no effect on the temperature of the sample.The moisture content has influence on the freezing temperature of water in soil.When the ambient temperature drops sharply,the duration of the undercooling stage of the sample with high moisture content is shorter,and the duration of the constant temperature stage is longer.When the ambient temperature gradually decreases,the unfrozen water content curve shows obvious lag phenomenon,and the heat exchange coefficient of soil is calculated by the unfrozen water content curve.4.Using GEO-STUDIO to simulate the temperature and seepage changes of the slope in some cases,and evaluated slope stability based on this,it is found that the vegetation and freezethaw action affect the formation of shallow landslide by changing the strength of the soil,and promote the formation of deep landslide by changing the permeability characteristics of the slope.