Study On The Mechanism Of Loess Landslide In The Seasonal Frozen Soil Area

The slope of the Northwest Loess Plateau is affected by freezing and thawing,which causes frequent loess landslides and serious ecological and life and property losses,therefore,it is of great theoretical significance and application value to study the mechanism of seasonal freeze-thaw induced loess landslides.Based on the National Natural Science Foundation Project "loess hydraulic erosion and landslide mutual feed mechanism and risk early warning",in Dongzhiyuan area,Qingyang,Gansu Province,a large number of field research has been carried out,and a series of laboratory tests have been carried out to systematically study the mechanism of loess landslide in freezing-thawing period.The main research contents and results are as follows:1.Through the laboratory test,the change law of soil permeability,water holding capacity and water holding capacity under the action of freeze-thaw is studied,and the influence of freeze-thaw times on the soil water physical properties is quantitatively analyzed,thus the mathematical model of the change of permeability coefficient under the action of freeze-thaw is constructed,which provides support for the determination of water physical parameters in seasonal frozen soil area2.The freezing temperature of soil was analyzed through the test of the relationship between the content of unfrozen water and temperature in the indoor soil samples,and the process of freezing temperature change was divided into five stages,and the different freezing temperature caused by different moisture content was explained;The change rule of unfrozen water content in soil under the action of freezing-thawing was studied,and it was found that the characteristic curves of melting and freezing had obvious hysteresis,and the mathematical model of unfrozen water content changing with temperature in freezing-thawing process was constructed.According to the unfrozen water content of soil at different temperatures,the corresponding specific heat and thermal conductivity were estimated,which provided support for the determination of the calculation parameters of temperature field of seasonal frozen soil slope.3.Through direct shear tests on undisturbed soil samples with different soaking lengths,the variation rules of peak strength and residual strength of samples with different soaking lengths were studied.The change rule of shear strength index with soaking time was studied,and the mathematical model of peak cohesion with soaking time was obtained,and the softening mechanism of soaking was analyzed to provide support for slope stability analysis.4.The samples containing freeze-thaw interface were prepared,and the changes of mechanical properties of the samples with different water content and those containing interface under the action of freeze-thaw cycle were studied by direct shear test in the laboratory.The attenuation coefficients λc and λφ of the shear strength indexes were defined,and the mathematical model of the attenuation coefficients of the shear strength indexes changing with the number of freezing-thawing times was constructed based on the test data,which provided support for the analysis of the stability of seasonal frozen soil.5.Based on the experimental data of laboratory tests,geo-studio software was used to construct the evolution model of slope temperature field and groundwater seepage field in the freezing-thawing process,and the stability analysis was carried out to further reveal the mechanism of slope instability under the effect of freezing-thawing:Frozen stagnant water leads to deep water destruction,which leads to overall instability;The freezing-thawing cycle reduces the strength of surface soil and causes shallow landslides;In the melting stage,the freezing-thawing interface becomes the water-barrier layer,and the upper layer of the meltwater flows along the slope of the freezing-thawing interface,which then leads to the down-layer landslide sliding along the freezing-thawing interface.