TEST RESEARCH ON MECHANISM OF FREEZING AND THAWING CYCLE RESULTING IN LOESS SLOPE SPALLING HAZARDS IN LUOCHUAN

The freezing and thawing cycle results in spalling hazards in loess slope in Luochuan.For comparison,the samples of loess suffering from spalling hazards in Luochuan and those not spalling have been collected respectively.In order to simulate the freezing and thawing process of the natural loess slopes,the test on the freezing and thawing cycle is carried out in the open conditions without any water being replenished,which is to observe the change of the properties of soil samples on the surface as well as its height,dry density,water content,cohesion and internal frictional angle under the function of freezing and thawing cycle.The test results indicate that in the first few cycles,the samples collected from Luochuan have slight increase in volume and water content.The soil structure is destroyed by the icy freezing expansive force in the process,which cannot be recovered in the thawing process.The soil strength is weakened by repeated freezing and thawing processes.After about ten cycles of freezing and thawing,the physico-mechanical condition of soil tends to be stable.While in the thawing process,the interface of water and ice has the softening function of water and the facilitating effect.If there is very good exposed surface,the spalling hazards in loess slopes may easily occur along this interface between water and ice;the negative pore water pressure may occur at the frozen edge in the process of freezing of soil samples.The soil density increases,while the volume decreases,and the soil strength is enhanced;in the process of thawing,the effective stress reduces;the total stress remains unchanged;the thawing volume is larger than the frost heaving amount.The cohesion of soil is slightly enhanced;therefore,it is not likely to have spalling hazards.