Experimental Investagation On Permanent Deformation Of Ballastcoarse Grained Soil Induced By Cyclic Train Load

Passing trains action and cold regions periodic freeze-thaw action seriously influence to rail track performance; passing trains safe-operation directly depend on a track performance. Ballast gravel and coarse grained soil deformation behavior were studied by a lot of researchers, but in most cases, the materials testes separately without considering the interaction between them, either testing ballast gravel only or testing coarse grained soil only. This paper present research dynamic response mechanism and dynamic interaction between ballast gravel and coarse grained soil layers. Research perform in the laboratory, by applying to the sample dynamic load and freeze-thaw cycles, modeling passing trains cyclic load and climate influence. Physical model tests on a ballast gravel layer overlying a coarse grained soil layer were carried out under different conditions in terms of water content, loading amplitude, loading frequency and freeze-thaw cycles. The results obtained allow the following main conclusions to be drawn:(1) For obtain the experiment data, ballast gravel-coarse grained soil experiment model was designed and cyclic dynamic loading tests was performed.Ballast gravel-coarse grained soil interaction was studied by analyze computerized tomography scans and experiment data. It was observed, that ballast gravel-coarse grained soil penetration, ballast gravel-coarse grained soil third layer creation and mud pumping phenomena depend on sample water content, loading amplitude,loading frequency and coarse grained soil dry unit mass.(2) Ballast gravel-coarse grained soil plastic deformation consist of two phases. While the first phase(the first 2000 loading cycles), specimen plastic deformation increase significantly up to approximate 80% of the whole plastic deformation obtained by the experiment. During the second phase, specimen plastic deformation basically stable. Computerized tomography scans analize results showed, that the average thickness of ballast gravel-coarse grained soil interlayer is11.5mm, amount to 3.8% of the total height of the sample.(3) It was observed, that the ballast behavior depends on the coarse grained soil state, and specimen water content influence to the plastic deformation more than load application time. Specimen water content increase from the close tooptimum to saturated condition, specimen plastic deformation increase 6 times.Dynamic load amplitude increase from 105 k Pa to 155 k Pa, plastic deformation increase 30%, dynamic load amplitude increase from 155 k Pa to 205 k Pa, plastic deformation increase 40%. Specimen water content optimum, close to optimum or specimen after freeze-thaw action, specimen plastic deformation rise up with increase of loading frequency, but while specimen in the saturate state, 2Hz load frequency plastic deformation more than 4Hz.