Study On Physical And Mechanical Properties Of Sliding Zone Soil Of Heifangtai Loess Landslide In Gansu Province

Loess is a special wind sediment with porous and weak cementation widely distributed in the northwest of China,and its mechanical properties will obviously show the characteristics of yield softening,disintegration and collapsibility when it meets with water.This characteristic of loess makes geological disasters occur frequently in the Loess Plateau area of China,and Heifangtai area of Gansu Province is one of the typical areas.Heifangtai has been reclaimed from an uninhabited plateau to farmland.Since 1968,many large-scale landslides have taken place,which have caused huge losses to the local people's economic development and safety of life and property.In this paper,the typical loess landslides in Heifangtai area are selected as the research objects.Based on the regional geological background and the reality of perennial irrigation,the disastrous effects of tectonic and geomorphological conditions and the physical and mechanical behavior of the soil in the sliding zone affected by different factors are preliminarily analyzed through field survey and laboratory tests.The main research contents and conclusions are as follows:?1?Triaxial creep tests were carried out on Q₃ loess in Heifangtai area under different water contents,different structures,different confining pressures,different dry densities,different wet and dry cycles.Generally speaking,soil strength is negatively correlated with water content,positively correlated with confining pressure and dry density.The structural strength difference between undisturbed loess and remolded loess is related to water content.The results of different dry-wet cycles show that soil strength decreases with the increase of cycles,but it is not absolutely linear.?2?Ring-shear tests were carried out on Q₃ loess in Heifangtai area under different water contents,different normal stresses,different shear rates,different salt concentrations,different shear modes.The shear strength of soils is negatively correlated with water content and positively correlated with normal stress.The effect of shear rate is mainly reflected in the high normal stress condition.The residual strength increases first and then decreases with the increase of shear rate.Salt content has opposite effects in different regions.The results of different shear modes show that the peak strength and residual strength of multi-stage shear mode are less than that of single-stage shear mode.?3?The microstructures of creep and ring shear specimens were studied by scanning electron microscopy.Under the influence of water,salinity and stress conditions,macro-deformation infiltrates into the change of micro-soil particle structure,and the rearrangement of soil particle structure reflects the change of soil sample strength.The interaction of the two factors affects the formation and development of landslides.