Experimental Study On Anisotropy Of Permeability And Mechanical Properties Of Remolded Silt In Yellow River Flooding Area

Soil is a kind of three-phase complex.The arrangement and combination of soil particles and the force between soil particles and each phase lead to different structures of soil.It is because of the existence of this structure that makes the soil show anisotropy.The remolded soil samples with different preparation methods will also form different structures,so the remolded soil prepared by different methods will show different forms of anisotropy.In addition,different regions,the same soil,due to its formation and particle composition is different,will also affect the properties of soil.Silt soil in the Yellow River basin is a typical silt formed by repeated erosion and deposition of sediment.Since the formation mode of this kind of silt is different from that of silt in other regions and the particle size is relatively concentrated,the mechanical properties and permeability characteristics of this kind of silt will be different from those of silt in other regions,and the anisotropy of soil will also be different.In addition,silt is also commonly used as filling material in these areas.Due to different backfill processes,backfill silt will also show different anisotropy.Based on this,two methods of static pressure and compaction are used to reshape the silt in the Yellow River flood area.The permeability,compression and mechanical properties of the specimens in different sampling directions were studied by indoor permeability test,compression test,consolidation quick shear test and triaxial consolidation undrained test.According to the test results,the influence of sample preparation method and dry density on the permeability characteristics and mechanical properties of remolded silt in the Yellow River flood area is analyzed,and the following conclusions are obtained :(1)The results of variable head permeability test show that the two remolded silts show anisotropy,and the permeability in the vertical direction is the strongest,and the permeability in the horizontal direction is the weakest.But the permeability anisotropy of compaction remolded sample is more obvious than that of static pressure remolded sample.When the dry density of the sample is the same,the permeability of the remolded soil sample by static pressure method is stronger than that by compaction method.With the increase of dry density,the permeability of the two remolded soils gradually decreases.In addition,dry density has a significant effect on the permeability anisotropy of compacted remolded silt,but has no significant effect on the permeability anisotropy of static pressure remolded silt.(2)The compression anisotropy of two kinds of remolded silt was studied by indoor compression test.The results show that both compaction method and static pressure method can make the remolded soil compressive anisotropy.Dry density has no significant effect on the compressive anisotropy of the two remolded silts,that is,the increase of dry density cannot weaken the compressive anisotropy of remolded silt,but the increase of dry density can reduce the compressibility of remolded silt.In addition,under the same conditions,the compaction sample has low compressibility.(3)Consolidation quick shear tests show that the shear strength of the two remolded soil sample is anisotropic.From the sampling point of view,for two kinds of remolded silt,the shear strength of the sample cut along the vertical direction is the largest,but due to the different sampling methods,the corresponding direction of the minimum shear strength is different.In addition,the sample preparation method has a great influence on the anisotropy of cohesion.With the increase of dry density,the shear strength of remolded soil samples increases,and the anisotropy of soil cohesion is more obvious,but the change of dry density has no significant effect on the anisotropy of internal friction angle.(4)Triaxial consolidated undrained shear test of compacted remolded silt shows that the relationship between shear strength and sampling angle is similar to the consolidated fast shear test,that is,the anisotropy is mainly reflected in the cohesion,and the cohesion of the sample cut along the vertical direction is the largest,and the sample cut along the horizontal direction is the smallest.The peak value of deviatoric stress increases with the increase of dry density and confining pressure,and the cohesion and internal friction angle also increase,but the strength anisotropy of soil decreases.In addition,the effective cohesive force is less than the cohesive force expressed by the total stress,but there is little difference in the internal friction angle between the two expressions.In addition,it can be seen from the variation curve of pore water pressure that the peak value of pore water pressure increases with the increase of confining pressure,and the peak time of pore water pressure is earlier than that of deviatoric stress.