The Dynamic Characteristics Of Expansive Soil And Dynamic Behaviors Of Subgrade Under The Bidirectional Cyclic Loading

Based on a case study of roadbed soil obtained from Jingmen, Hubei province, remolded expensive soil was researched systematically, according to the indoor experiment and theoretical analysis, about its characteristics of dynamic strength and deformation under both unidirectional and bidirectional cyclic loading. The dynamic response of the high-way railway subgrade was carried out by numerical simulation.Firstly, through the experiment of unidirectional and bidirectional dynamic triaxial test, which is homology phase, of remolded expensive soil, main experiment curve, presetting hyperbolic form, as well as the relation of dynamic modulus and dynamic strain were achieved. With the increasing dynamic strain, cell pressure and water content, the dynamic modulus reduce; with the vertical dynamic stress increasing, dynamic deformation reduce, and the dynamic modulus attenuates fast; The damping ratio of whole strain is calculated, according to the equation of equivalent damping ratio, with the increasing vertical dynamic stress and water content, the damping ratio raises. However, the frequency affection to dynamic response is subtle.Secondly, a discussion on the characteristic of dynamic strength of remolded expensive soil together with fitting formulas to dynamic stress and vibration times under different cell pressure were presented basing on the research of dynamic behavior, the results show dynamic strength of remolded expensive soil raised much compared to natural expansive soil.Thirdly, theoretical analysis for stress state of remolded expensive soil was taken under bidirectional cyclic loading with distinct phases. Paper give two parameterσ45°max,τ45°max, which maximizing when phase difference equal to 0°or 180°. A formula for calculating dynamic deformation under bidirectional cyclic loading was put forward using linear elastic model, thus, relationships between dynamic stress and dynamic deformation depending on phase difference can be achieved.Finally, the transient dynamic analysis of a track-subgrade three-dimensional finite element model was done by using ANSYS. The conclusion showed broad distinction of dynamic response between bidirectional cyclic loading and the unidirectional cyclic loading condition. Rail and subgrade stress history curves were extracted. To a certain layer of the subgrade and the foundation, dynamic Responses diffuse with the depth and also get the diffuse with the landscape orientation. Results show the vertical dynamic deformation linearly attenuate with depth, but vertical dynamic stress decaycurve is nonlinear, both increase with higher velocity.