Study On Unsaturated Shear Mechanical Properties And Micro-mechanism Of Site Silt

Most of the earthen sites in Central Plains are rammed with silt,but silt is often unsaturated,highly sensitive to water.The deterioration effect of its strength often leads to cracks and collapses in the earthen sites.Therefore,it is of great significance to study the mechanical properties and micro-evolution mechanism of the soil under different water content.In this study,the silt of Zhengzhou Site is taken as the research object,making samples by adding water and drying methods,through direct shear test,constant water content triaxial shear test and scanning electron microscope test,the mechanical properties and micro-evolution mechanism of silt under different water content are discussed by combining macro-and micro-methods,and the dialectical relationship between macro-unsaturated mechanical properties and micro-structure is analyzed.It provides a theoretical basis for the tamping and protection of silt at the site.The following conclusions are obtained from the study:(1)Samples with different water content were prepared by adding water and drying methods respectively,and the variation laws of mechanical properties of silt on single shear plane was studied by direct shear test.The results show that the variation laws of shear strength and shear strength indexes of samples with different moisture content are quite different under the conditions of adding water and drying methods.(2)The triaxial shear test with constant water content explores the failure modes and mechanical properties of soils under complex stress state in multi-angle loading.The results show that the failure modes of silt samples with different water content are quite different.The failure modes of silt samples including single local shear failure,single shear plane failure and swelling failure under water addition method,while those of drying method include splitting failure,single local shear failure,single shear plane failure,"X" cross shear failure,multiple parallel shear failure and swelling failure.The variation of strength and parameters with water content under triaxial shear test and direct shear test is quite different.It seems that there is a contradiction between the experimental rules obtained by the same way of water content formulation,which better illustrates the different shear properties of silt under single shear stress state and complex shear stress state.(3)Under water addition method,quantitative analysis by Image-Pro Plus(IPP)image analysis software shows that the average equivalent diameter and porosity of pores decrease first and then increase with the increase of water content,and the trend of shear strength is negatively correlated with its change law.The average equivalent diameter and porosity of pores under drying method showed a more uniform increasing trend with the increase of water content.There are some differences in the distribution law of pore orientation frequency,the pore angle distribution is more uniform at low water content,and the pore angle distribution shows the characteristics of dominant interval under high water content.It can be seen that the content of water have a significant influence on the size,distribution and shape of pore,and the change of pore leads to the change of macroscopic mechanical properties of soil.(4)The strength variation of soil samples prepared by two methods of adding water and drying is quite different.Sampling method results in a great difference in pore distribution in the sample,which leads to a change in the gravitational force between particles in the sample,thus changing the structure of the sample,resulting in a different law of change in soil strength.The variation of strength and parameters with water content under triaxial shear test and direct shear test is quite different.It can be inferred that the occurrence state and content of water in soil sample have a great influence on its mechanical properties.