Experimental Study On Mechanical Properties Of Silty Soil Under Plane Strain In Zhengzhou Area

With the continuous development of social economy,more and more large-scale projects related to people’s livelihood rush out,such as high-speed railways,high-rise buildings,expressways,urban subways,residential buildings,etc.In these projects,high fill subgrade,tunnel excavation,foundation pit excavation support,slope support and other projects will be involved.This kind of engineering can be regarded as vertical loading and unloading problem under plane strain condition.The results show that the stress path has great influence on the stress-strain relationship of soil,and different stress paths have obvious difference on the deformation strength of soil.In most cases,the soil parameters and constitutive model are determined by a single stress path test,which is designed and calculated in practical engineering.In this way,the design basis of the project deviates from the actual soil parameters,and the potential risks are different.Therefore,it is of great significance to carry out vertical loading and unloading tests under different stress paths.In this paper,a plane strain test is carried out by using a plane strain gauge developed by ourselves.The influences of different stress paths,consolidation stresses and stress loading ratios on stress-strain relationship,lateral strain and deviatoric stress are studied,and the strength and deformation parameters of soil are obtained.According to the test results and numerical simulation,the influencing factors of subgrade settlement are explored.The research content and conclusions of this paper are as follows:1.The deformation and strength characteristics of silt samples under different stress path tests are compared.The results show that the trend of deviatoric stress,lateral strain and vertical strain is the same under four different stress path tests.The initial dry density has great influence on the stress-strain relationship of silty soil.Under different stress paths,the increase amplitude of vertical strain and lateral strain decreases with the increase of dry density,and they are negatively correlated.The initial water content has no significant effect on the stress-strain.2.The influence of consolidation stress on specimen deformation and strength is studied.Under different consolidation stresses,the deviatorial-stress-strain curves of silty soil show a hardening type.The tangent modulus of the curve increases with the increase of consolidation stress,and the deviatoric stress increases with the increase of consolidation stress in shear failure.With the increase of consolidation stress,the deviatoric stress and vertical strain of silty soil increase,but the range of change is small.When the pore water pressure reaches a certain level,the soil sample will produce plastic flow and dilatancy deformation,and the ultimate vertical strain will gradually increase.The failure principal stress line of specimens with different dry densities is the same under loading path.3.The influence of loading ratio on specimen deformation is studied.Under different loading ratios（Δσ₃/Δσ₁）,the deviatoric stress-strain curves of silty soils are all hardening curves.With the increase of the loading proportion,the slope of the stress-strain curve increases,and the failure deviator stress of the sample increases.With the increase of loading proportion,the deviatoric stress value and vertical strain of silt increase in the failure process.The failure deviator stress（σ₁-σ₃）_fincreases linearly with the increase of the loading ratio,and the curves of different dry densities are basically parallel.4.Factors affecting subgrade settlement are analyzed through numerical simulation.In the fill subgrade,the settlement of subgrade increases linearly with the increase of fill height.The influence of the ratio of slope to height of subgrade on the settlement of subgrade increases linearly,and the influence of settlement deformation is relatively small.Among the different filling materials,the settlement deformation of polystyrene foam is the smallest.For the same material,the degree of compactness has obvious influence on the settlement deformation,so the appropriate degree of compactness should be selected.