Study On Engineering Characteristics Of Loess-Paleosol

Interbedding between loess and paleosol occurs in the loess stratum,so the engineering properties of loess and paleosol are of critical importance to the engineering design and disaster analysis in the loess area.Many results of research on the engineering properties of loess are available,but the systematic research into the engineering properties of paleosol is lacking;consequently,it is difficult to determine the differences in the engineering properties between loess and paleosol.Taking paleosol in the loess stratum as the subject of research,this paper focuses on the research into the substance composition,soil-water characteristic curve,shear strength and permeability characteristics,etc.of paleosol and compares it with loess having a conformable contact with it.Based on the conventional geotechnical laboratory test and the comparison of the indexes of physical properties between paleosol and loess having a comfortable contact,the result shows that loess-paleosol and loess described in this paper belong to silty clay.The silt content in paleosol is 9.3% less than that in loess,the clay content in paleosol is 9.8% more than that in loess,the content of quartz and albite in paleosol is less than that in loess,and the content of calcite,chlorite and clay minerals is higher than that in loess;the liquid limit and plastic limit of paleosol are slightly higher than those of loess,the plasticity index is slightly higher than that of loess,and the optimum moisture content and maximum dry density are more than those of loess.Based on the pressure plate test and the comparison of soil-water characteristic curves of paleosol and loess,the result shows that the hysteresis effect of soil is less than that of loess and the matric suction with the change rate of water content is less than that of loess;the slope of soil-water characteristic curve of soil and loess is reduced as the dry density increases,and for paleosol and loess with the same moisture content,the matric suction change of paleosol caused by a change in dry density is greater than that of loess;the matric suction of remolded soil specimens is greater than that of undisturbed soil specimens and the structural impact on the soil-water characteristic curve of loess is more obvious than that of paleosol when they have the same moisture content;the slope of soil-water characteristic curve of remolded paleosol and loess is decreased as the moisture content of specimens grows,and the higher the moisture content of specimens is,the smaller the difference of soil-water characteristic curves of paleosol and loess is;both van Genuchten equation and Fredlund-Xing equation can better fit the soil-water characteristic curves of paleosol and loess,and compared with van Genuchten equation,Fredlund-Xing equation has a better fitting effect,and based on the test results,the equations of soil-water characteristic curves of paleosol and loess are obtained through fitting and the differences between them is analyzed.Based on the unsaturated soil triaxial test and in view of the impact of density and matric suction,the experimental study is carried out for the shear strength characteristics of paleosol and loess.The stress-strain curves of paleosol and loess are hardening curves,and the higher the dry density is,the larger the slope of the curve is,the higher the shear strength is;both cohesion and internal friction angle of paleosol and loess increases as the dry density grows and the relationships among cohesion,internal friction angle and dry density are basically linear.The cohesion of paleosol is greater than that of loess and the internal friction angle is less than that of loess under the condition that their dry density and moisture content are identical.When the moisture content is identical,the change in cohesion of paleosol varying with the density is greater than that of loess and the change in internal friction angle is less than that of loess.The cohesion of paleosol and loess increases as the matric suction grows,the degree of change in cohesion of paleosol varying with the matric suction is less than that of loess,the change in matric suction has no impact on the internal friction angle,and the rate of increase in the shear strength of loess with the confining pressure is higher than that of paleosol.The permeability characteristics of paleosol and loess are researched on the basis of the triaxial tests of undisturbed soil specimens and remolded soil specimens.The permeability coefficient of paleosol is smaller than that of loess with the same density.The permeability coefficients of undisturbed and remolded paleosol and loess decrease as the dry density grows and the difference between them is reduced as the dry density increases.Under the condition that both dry density and initial moisture content are identical or similar,the permeability coefficients of undisturbed specimens of paleosol and loess are obviously higher than those of remolded specimens,and the lower the dry density is,the more obvious the structural impact is,and the structural impact on the permeability coefficient of loess is more significant than that of paleosol.The inferior quadrilateral element is used to establish a numerical computation model to address the seepage issue of loess foundation containing paleosol strata.The model is employed for numerical computation of the changes in moisture field in the foundation soil under different site conditions and infiltration conditions to get the law of water infiltration into the loess foundation containing paleosol strata.It is proposed when backfilling is required,paleosol may be backfilled and compacted to reduce water infiltration into foundation soil.