Experimental Study On Physical And Mechanical Characteristics Of Cohesive Foundation Soil For Zhanghu And Jihun Passenger Dedicated Railway

The foundation, the basis of railway embankment, and mainly composed of graval soil, gravel, rock, silt and cohesive soil.There are a great deal of sticky foundation soil in Zhanghu and Jihun railway passenger line,engineering properties of which should is tested to make sure if it can meet requirements of bearing capacity,deformation and stability,and provide a basis for the design of foundation reinforcement. This paper adopts indoor basic physical and mechanical properties experiments to test the two types of foundation soil,including their basic physical index,such as liquid-plastic limit,particle density,particle size distribution, moisture content,density and compaction, etc,and mechanical behavior,such as consolidation, shear and permeable.The main achievements and contributions are as follows:(1) Make indoor basic physical index tests about the two foundation soil like water ratio limit,particle density, grain size analysis,moisture content,density and compaction Based on the standard for classification of soils,the foundation soil of Zhanghu railway is defined as silty clay within the scope of the test soil depth,while the foundation soil of Zhanghu railway is defined as silty clay,silt,clay from top to down. The particle size of two sorts of foundation soil are mainly concentrated in below0.075mm,which takes up about75%.Soil optimum moisture content and maximum dry density are obtained by Z2heavy compaction test. According to the dry density of the foundation soil,Compacting factors of the two foundation soils both are about0.9.(2) The standardized consolidation test method is adopted to test the two kinds of foundation soil compression modulus,consolidation coefficient,permeability coefficient, preconsolidation pressure and elasticoplastic deformation,analyze the influence of preconsolidation pressure and consolidation coefficient by using different calculation methods,and permeability coefficient are calculated by using different testing methods..Both foundation soils all belong to medium compressible soil which have similar compressibility. With the increasing of consolidation pressure, compression modulus increases, coefficient of consolidation and coefficient of permeability both decrease,both present obvious non-linear rules.Based on the Casagrande method,a new method of determining preconsolidation pressure is put forward,which adopts polynomial to fit e-lgp curve and add testing points at the line segment of curve’s end artificially to control straight line of curve’s end. preconsolidation pressure of the two foundation soil is calculated with this method..By contrast with the foundation soil of Jihun railway,Zhanghu railway has a higher value in preconsolidation pressure.relative error of calculating preconsolidation pressure value by "f’ method and Casagrande method is19.2%.Calculating consolidation coefficient of two specimens of Zhanghu railway under400kpa by five kinds of common calculation methods shows that the different calculation methods of coefficient of consolidation basic equal.The compression-resilience tests show that the two foundation soils enjoy almost the same elastic deformation under the same stress path,as for plastic deformation,the foundation soil of Jihun railway is more big.variable head permeability test and consolidation tests have measured that the same soil has similar percolation coefficient.The permeability coefficient of two kinds of foundation soil is about i x10-7～10-8cm/s (i=1～10), both belong to one whose permeability is not strong at all.(3) In the direct shear tests,consolidated quick direct shear test method is adopted to test shear strength parameters of two kinds of foundation soil.With the increase of vertical pressure,the stress-strain curves of zhanghu railway foundation soil develop from softening to hardening,and Jihun railway foundation soil all have a tendency to harden. When the vertical pressure is small,with the beginning of the shear deformation,specimens begin to show Shrinkage deformation,subsequently dilatancy deformation.when the vertical pressure is higher, with the development of shear deformation,the soil has been characterized by shear deformation,vertical pressure is higher, the soil Shrinkage is the more obvious. Moisture content of Jihun railway foundation soil increases,cohesion and internal friction angle of the sample both decrease,and decreasing amplitude of the cohesion is greater.