| Most of China's loess distribute in seasonally frozen ground.When the external environment temperature change,the temperature field in the soil changes accordingly,so the soil at different depths undergoes different extent of freeze-thaw cycles.The temperature field changeing lead to significant moisture migration,which causes the soil at different depths to experience different degrees of humidification and dehumidification cycles.After experiencing many freeze-thaw cycles or humidification and dehumidification cycles,the microstructure of loess changes,and the macroscopic manifestation is that the shear strength parameters are attenuated,which may lead to engineering disasters.This article took remolded loess from a fill area in Yanan as the research object.Through laboratory experiments and theoretical analysis,explored the law of moisture migration in remolded loess under freezing conditions,analyzed the deterioration effect of freeze-thaw on shear strength of remolded loess.The main contents and achievementes of the paper are as follows:(1)Self-made moisture migration tester was used,kept compaction of the test soil as a certain value,considered the influencing factors such as initial moisture content and freezing temperature,three unidirectional freezing tests were conducted.The changing law of moisture field and temperature field in loess was obtained through experiments,a logarithmic function model for real-time freezing depth and freezing index was established,a power function model for the final freezing depth and negative temperature level was established and the law of the change of water content near the freezing front and the formation mechanism are revealed.(2)After freezed and thawed several times in the test tube,the ring-knife sample was taken at the typical depth to determine the shear strength parameters by direct shear test.By analyzing the parameters,the changing law of internal friction angle and cohesion of the remolded loess at different depths with the cycles were summarized,and the deterioration model of shear strength with freeze-thaw cycle was established.(3)The microscopic mechanism of deteriorating shear strength of remolded loess was obtained by an electronic scanning microscope and image digital processing software.With the accumulation of freeze-thaw cycles,the large pores in the soil gradually increased,the pore area ratio gradually increased,the effective bearing area decreased.Ttherefore,the shear resistance of soil decreased under the same conditions.(4)Based on the related theory of continuum damage mechanics,combined with the cohesion force decay rate R,degree of deterioration D,microscopic characteristics and macroscopic characteristics,the degree of soil degradation is divided into four categories.In addition,corresponding treatment measures were proposed for soils with different degrees of deterioration.(5)According to the previous experimental conclusions,a loess fill slope model was established,and slopes under various conditions were analyzed from multiple perspectives.Freeze-thaw has a certain influence on the slope.However,due to the limited depth of freezing,freeze-thaw effect is not enough to make the slope unstable,but effective reinforcement and protective measures are still needed to prevent disasters. |
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