Permeability Of Loess Considering Pore Characteristics And Anisotropy

Loess has strong water sensitivity and its strength characteristics and deformation indexes are closely related to water content.The permeability of loess is the internal reason for the change of its water content.When the moisture content of loess increases,it will lead to a series of engineering diseases such as foundation settlement,ground subsidence and landslide.Therefore,it is of great significance to carry out research on the permeability of loess.The pore and structure characteristics of loess make the loess have significant osmotic anisotropy,which has significant influence on the water field of loess.Therefore,it is imperative to study the permeability characteristics of loess considering the pore characteristics,but there is still a lack of research in this field.In this paper,the pore characteristics of loess are considered and the main results are as follows:(1)The pore structures of soil samples with different orientations and different pore ratios were observed by scanning electron microscopy(SEM),and the characteristics of pore structures were analyzed and classified.The results show that the microscopic structure of soil samples with the same pore ratio under the microscope has its own characteristics.According to the proportion of the area calculated from different pore diameter ranges to the total pore area and the degree of pore concentration,the pores of unmodified loess can be classified into three categories,respectively: Small pores,medium pores and macropores.Small pores refer to the pores between the aggregates,and the pore diameter is concentrated below 1mm.Medium pore refers to fine root pore or capillary pore,pore diameter concentrated in 1～2mm;Macropores refer to coarse root pore pores,and the pore diameter is more than 2mm.According to the classification,the preliminary work is done for the next variable head test.(2)According to the classification of pore characteristics,the variable head permeability test was carried out on the soil samples.The saturated permeability coefficients of different pore ratios and different directions are included.At the same time,the change of the permeability process in saturated samples under different pore types is analyzed.The results show that the permeability coefficient in the two directions is positively correlated with the porosity ratio,and the permeability coefficient in the horizontal direction is different from that in the vertical direction for different pore types,and the anisotropy becomes more obvious with the increase of pore diameter in the soil sample.(3)Analyze the water field of loess foundation under trench seepage through numerical simulation calculation.The permeability coefficient of unsaturated loess is introduced into the test of trench seepage,and the influence of pore type on foundation is considered.The results show that the larger the pore ratio,the higher the pressure,the faster the water infiltration rate,the larger the saturation range,and the more obvious the anisotropy.The infiltration rate of small pores is slow,the saturation range is the smallest,and the anisotropy is not obvious.With the increase of pore diameter,the infiltration rate of large pores is fast,the saturation range is the largest,and the anisotropy is more obvious.(4)Through numerical simulation test,the finite element calculation model of slope rainfall infiltration model is built.Through the direct shear test,the strength anisotropy of the original loess and the remolded loess was studied,and the strength characteristics of different water content and different compaction were obtained,which prepared the foundation for the subsequent rainfall infiltration simulation of the slope.On the basis of defining the model parameters and boundary conditions,the effects of root pore and anisotropy were considered.The results show that with the increase of rainfall,the process of soil humidification is accelerated,the dead weight of soil increases rapidly,and the safety factor decreases gradually.The larger the pore diameter is,the lower the slope stability coefficient is.The pore diameter has a great influence on the stability of slope.