Study On Mechanism Of Freezing And Thawing Hazard In Loess Area

The surface layer,in the loess area,is frozen in winter,and will be thawing in spring,even frozen at night and thawing during day,under the influence of environment temperature.The engineering properties of loess are change by freezing and thawing,which made it difficult to the construction and maintaince in loess area,for example,during the end of winter and the beginning of spring,problems induced by freezing and thawing are common phenomena,such as thaw slumping and peeling.In this paper,structure mechanical properties,the changes of temperature field,moisture field and surface displacement of slope,and slope stability of loess were studied to reveal the mechanism of loess slope disaster during freezing and thawing.The microstructure,surface feature and strength characteristics of undisturbed and remolded loess during freezing and thawing were studied in laboratory.Test results reveal that changes obviously in the microstructure of loess that the loess skeleton particles themselves and cohesiveness between adjacent particles can be observed during freezing and thawing.There is a great difference between the surface feature of undisturbed and remolded loess sample after freezing and thawing,relating to initial conditions.The cohesion of undisturbed and remolded loess all decreases exponentially with freezing and thawing times increasing,and that the gap that the cohesion of undisturbed loess is always greater than that of remolded loess in the same condition would get to close as increasing cycles.The internal friction angle has no obvious variation during the whole freezing and thawing process.The freezing and thawing damage coefficient of undisturbed loess is larger than that of remolded loess.According to a model test and the numerical simulation method of finite element,the changes of moisture field,and surface displacement of loess slope,subjected to freezing and thawing cycle,were studied.The results show that the temperature field and moisture field of loess slope were redistribute periodically caused by ambient temperature,and have strong relevance.The surface displacement of the slope also showed periodic fluctuation as ambient temperature,and the residual displacement increases due to frost heave and thaw settlement.There are flake shaped erosions and cracks in the surface of loess slope caused by intense variation of temperature causes.The finite element shear strength reduction method was used,to combine the test data of the undisturbed loess subjected to freezing and thawing cycles,for stability analysis under various factors.Results show that the safety factor of loess slope also exponentially decreases with freez-thaw increasing,also effected obviously by the geometric shape and initial conditions;the migration and gathering of water towards freezing front as well as the deterioration of shear strength are primary factors affecting slope instability during freezing and thawing.