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基床层是铁路路基的核心组成部分,一般为粗颗粒土,厚约2.5~3.0 m,长期直接承受行车荷载的反复作用,其在动载反复作用下的变形特性是评价路基工作性能的关键要素之一。为研究粗粒土在列车循环荷载作用下的应力-应变特性,开展了一系列应力控制的单向循环加载大型动三轴试验,模拟列车动载和路基粗粒料填筑实际情况,包括不同动应力幅值(模拟不同列车轴重)、不同围压(模拟不同埋深)的动三轴持续振动试验。结果表明,在循环荷载作用下,土体刚度变化与振动次数、围压关系密切。根据动应力幅值大小的不同,循环荷载作用下饱和粗粒土的动应变随振次的发展形态可分为3种类型:稳定型、破坏型和临界型。根据试验所得出的动应力-应变关系曲线特点,建立了含围压和循环振次的骨干曲线模型。与传统的骨干曲线模型相比,该模型能反映土体刚度随循环振次的变化,更能反映列车往复作用的实际情况;同时该模型能用于估算路基土体动强度,对铁路路基核心层的动力变形稳定性评价和基于动力变形控制的路基设计具有参考价值。
The subgrade bed is the core component of the railway subgrade. It is generally coarse-grained soil with a thickness of 2.5-3.0 m. It can bear the repeated action of driving load directly for a long time. The deformation characteristics under the action of repeated moving loads are the key to evaluate the subgrade’s performance One of the elements. In order to study the stress-strain behavior of coarse-grained soil under the cyclic loading of train, a series of stress-controlled unidirectional cyclic loading large-scale triaxial tests were carried out to simulate the actual conditions of train loading and subgrade grading, including different Dynamic stress amplitude (simulating different train axle weight), dynamic test of three-axis continuous vibration with different confining pressure (simulating different depth). The results show that under the cyclic loading, the variation of soil stiffness is closely related to the number of vibration and confining pressure. According to the different magnitude of dynamic stress, the dynamic strain of saturated coarse grained soil under cyclic loading can be divided into three types according to the development pattern of vibration frequency: stable type, failure type and critical type. According to the characteristics of the dynamic stress-strain curve obtained from the experiment, the backbone curve model with confining pressure and cyclic vibration is established. Compared with the traditional backbone curve model, this model can reflect the variation of soil stiffness with cyclic vibration and can better reflect the actual situation of train reciprocation. At the same time, the model can be used to estimate the dynamic strength of subgrade soils, Layer stability of dynamic deformation evaluation and dynamic deformation control of roadbed design with reference value.