Study On Seepage Stability Of Railway Subgrade Filled With Volcanic Cinder Mixed Soil-Gravel Sand

About the studies on coarse-grained soil of Railway subgrade at present, they are mainly focus on compaction characteristics, shear strength, characteristics of deformation and strength in the static and dynamic load process. However, the seepage characteristic of coarse-grained soil filler has been rarely studied, which revelent standards also dosen’t indicate clear design-requirements for. With the water flowing, the seepage force would apply on the coarse-grained soil filler, whose soil structure and physico-mechanical properties may be changed. Thus, coarse-grained soil filler’s seepage stability ought to earn widespread attention and become an important element to evalute its mechanical property.Based on volcanic cinder mixed soil-gravel sand filler’s seepage deformation test, its seepage stability property is researched. By the seepage deformation test on volcanic cinder mixed soil-gravel sand with different volume blending ratio and dry density, the seepage failure type and the critical hydraulic gradient value are changed and the rule is also comfirmed. Based on Poiseuille’s laminar flow and Kozeny-Carman hydraulic radius theory, a framework-pore model is proposed, by which a method to distinguish seepage failure type is developed. Base on field and laboratory infiltration test, the permeability coefficient of surface layer of subgrade, which is filled with volcanic cinder mixed soil-gravel sand, is measured. What’s more, the surface layer of subgrade’s hydraulic gradient value is analyzed with rainwater infiltration.(1) Seepage deformation test study on volcanic cinder mixed soil-gravel sandAim at understanding volcanic cinder mixed soil-gravel sand’s seepage stability, a serious of Seepage deformation experiment,which has different volume blending ratio(2:l and 3:1) and dry density, is conducted. Test results show that for the same volume blending ratio, the permeability coefficient of volcanic cinder mixed soil-gravel sand decrease along with the increased dry density. As the improvement of dense degree, the seepage failure type change from piping to soil flow. In addition, dry density seldom influences piping’s critical hydraulic gradient value,so does not soil flow. Still the difference in fines content makes volcanic cinder mixed soil-gravel sand which has 2:1 volume blending ratio become more stable than the one which has 3:1 volume blending ratio when undertaken seepage pressure. Through the text results, a conclusion can be drawn that dry density makes the particle constrain increased and has an effect on volcanic cinder mixed soil-gravel sand’s soil structure, that skeleton-pore structure change into skeleton-dense structure.(2) The method to distinguish seepage failure type about coarse-grained soil fillerBased on Poiseuille’s laminar flow and Kozeny-Carman hydraulic radius theory, the pore between skeleton is supposed as a bunch of parallel capillary tubes. Defining the maximum diameter of fines which skeleton capillary tubes allows pass through is called loss-diameter d.One situation that d> d3 is piping and another d≤d3 is soil flow. Moreover, using this method to analyze the seepage failure of volcanic cinder mixed soil-gravel sand whose volume blending ratio is 2:1 and 3:1, comparing Kondratchev’s and Liu Jie’s method, a conclusion has been taken that this skeleton capillary tubes which based on Poiseuille’s laminar flow and Kozeny-Carman hydraulic radius theory can accurately distinguish volcanic cinder mixed soil-gravel sand’s seepage failure type.(3) Infiltration test on surface layer of subgrade filled with volcanic cinder mixed soil-gravel sandBased on field single-loop infiltration test, the permeability coefficient of surface layer of subgrade is measured,whose permeability rank is evaluated, too. Applying the principle about infiltration test and conducting laboratory infiltration test, surface layer of subgrade’s hydraulic gradient value ir= 1 when the rainwater permeate into it. What’s more, there is a field survey of erosion about surface layer of subgrade after a rainy season. This survey show that there is no erosion on the surface surface layer of subgrade and the volcanic cinder mixed soil-gravel sand subgrade has a favorable seepage stability when it is raining.