Experimental Study On Physical And Mechanical Characteristics Of Silty Clay For High-Speed Railway Subgrade Filler

Railway subgrade is an important part of the basis of track structure and is consist of debris material. The strength and stability of subgrade is affected by many factors as natural condition, the upper load, filling, so it is necessary to strictly control the filler to satisfy the demand of enough strength, stiffness, uniformity and long term stability. Fine soil has a widely spread in China and it is common to extensively use it to replace high quality filler as subgrade filler. So it has essentially meaning to research the physical and mechanical properties of fine soil filler. This paper makes an indoor soil test systematically on the silty clay with sand from Wuhan Wuhan-Guangzhou high-speed rail test section. The main work and conclusions are below:(1) Make routine soil tests like particle density and analysis, water content limits compaction, penetration and consolidation. The soil is defined as the silty clay with sand (CLS) based on the soil classification criteria. The size of the compaction tube and the stratified case has little influence on the compaction test results of samples under the condition of the same unit volume compaction work. Sample of 95% compaction belong to medium compaction soil. The compression of saturated soil is larger than under the condition of optimum moisture content. The sample's (92% and 95% compression) permeability coefficient is about i×10-/cm/s (i=1-10).the permeability decrease when the compaction increase.(2) Determine the shear strength of soil under different conditions though tests as direct shear test, consolidated undrained triaxial test (CU), consolidated-drained tria xial test (CD), shear tests with controlled net mean stress equaling constant and so on. The effective stress shear strength index of shear tests with controlled net mean stress equaling constant is smaller than that of consolidated undrained triaxial test (CU), and much smaller than that of consolidated-drained tria xial test (CD). The shear strength index of slow consolidation of direct shear test on the saturated specimen of 95% compression degree is mostly equal to that of consolidated-drained triaxial test (CD). The difference is not more than 3%. In the consolidated undrained triaxial test (CU), the stress-strain curves of soil transform from strain hardening to Strain softening. The shear strength rndex is strongly affected by the degree of compaction. The internal friction angle of soil varies a lot under different failure criteria. Thus the cohesion does not. In the static triaxial test, with the increase of the shear loading, in the first place the sample is in the elastic state, then produce axial plastic deformation. When the axial strain reaches some extent, the sample begins to appear lateral plastic deformation, then volume expansion, finally occurs shear failure until pore pressure drop. The lateral plastic deformation and volume expansion come out closely, their corresponding static deviator stress is about 60.5% of ultimate static strength.(3) In the process of static triaxial test, using random error correction method to correct the test curve that contain axial strain and using LVDT local displacement sensors to make axial strain test both can effectively eliminate the test error that sample end contact bring. The sample with LVDT local displacement sensors on it has a confinement effect that its strength can raise 5-10%.(4) Based on the discuss of three -triaxial test program:one-way compression vibration, one-way tension and compression vibration and bi-directional vibration load, compare influence on the dynamic properties of the sample by different vibration loading. In the one-way compression vibration triaxial test, saturated specimen of 95% compression degree mainly appears the state of vibration compaction and dilatancy damage. In the different sections that dynamic stress amplitude increases, the sample appear different state of lateral plastic deformation first, volume expansion first, pore pressure drop first. In the one-way tension and compression vibration and bi-directional vibration load test, in the main compression zone, the sample appears plastic deformation and compacted slowly and pore pressure become larger. Finally the soil becomes soft. In the failure stage, it appears obvious pore pressure fluctuations, axially deformation and dynamic stress attenuation. The dynamic strength and confining pressure of the saturated specimen of 95% compression degree basically abbeys the law of linear growth. In the one-way compression vibration and one-way tension and compression vibration tests, the vibration frequency has little influence on the dynamic strength of the sample.