Lab Study On Permanent Deformation Of Subgrade Soil Induced By Long-term Operation Of Upgrading-speed Railway

The subgrade beds of existing lines were designed and constructed by previous standards and its status deteriorated after a long-term operation due to a low level of fillings and compaction. Nowadays the railway trains have widely increased speed several times. With the train's higher speed, larger amount of passenger and freight, an increase in dynamic load's amplitude, frequency and cyclic number brought a larger cumulative plastic deformation and worse subgrade status. Thus it influenced the schedule of upgrading-speed.The foundation under rail tracks guarantees the high regularity and stability for upgrading-speed railway. And as the direct support, the subgrade bed must have high strength and rigidity, as well as good stability and durability. Taking Huning Railway Line as engineering background, this paper studied the deformation behavior of subgrade bed soil induced by both train load and sinusoidal load through dynamic triaxial tests. Based on the rest results, the nonlinear and hysteresis deformation behavior of bed soil can be represented by dynamic stress-strain hysteresis loops and backbone curves. And cumulative deformation can be represented by the relationship between permanent deformation and cyclic number. The elementary formula to predict permanent deformation was discussed, and the internal and external influencing factors were analyzed including compaction coefficient, water content, cell pressure, dynamic stress wave, amplitude, frequency, cyclic number, etc. The equivalent sinusoidal load of upgrading-speed railway load was proposed through loading a series of sinusoidal load of various amplitudes and forms. Namely, the reduction coefficient value of equivalent sinusoidal load was advised when one half-sinusoidal wave represents one bogie.The permanent deformation behavior of subgrade bed soil was analyzed and the estimation relationship between the permanent deformation and train load was proposed in an elementary level. The research on deformation behavior of subgrade bed soil induced by train load will contribute to the subgrade reconstruction and conservation of existing line.