空心圆柱仪模拟列车荷载下土中应力路径能力分析

土体作为各向异性散粒体材料,其动力特性依赖于所处的应力路径。列车荷载下地基土在最大剪应力空间呈心形线旋转应力状态,但目前还未见室内试验中模拟心形线应力路径的相关研究。首先提出了土体动力响应解的简化拟合形式,并通过典型列车荷载作用下地基土所受应力特征分析验证了该简化形式的合理性。针对目前国际上已有的3类空心圆柱仪(HCA),推导出模拟列车荷载下地基土应力特征的加载方式:(1)双向振动HCA可通过确定轴力和扭矩的应力形式来实现心形线应力路径加载,此时球应力p的变化规律与轴力的加载波形一致,中主应力系数b在内、外压相等时呈余弦变化规律;(2)三向振动HCA在模拟列车荷载下的应力特征时,可以保持p不变或b恒为0.5;(3)四向振动HCA能够通过控制轴力、扭矩和内、外压的共同变化来较全面地模拟列车荷载下土单元体的应力特征,并可实现b为任意合理值且保持不变的前提下p、q之间保持恒定线性关系。并推导了3类HCA的加载参数在正应力均以压应力为主及中主应力方向维持在直径方向时的约束条件。

Ability analysis of HCA to imitate stress path of soil caused by train load

As anisotropic granular materials, soil’s dynamic characteristics depend on the stress path. Foundation soil is in heart-shaped line rotation stress path of the maximum shear stress space under train load. Yet it is not reported that the heart-shaped line stress path is imitated in laboratory test. The simplified form of the soil’s dynamic response is proposed, which is justified by analyzing the stress path of foundation soil caused by train load. For imitating the stress characteristics produced by train load, the loading methods of three types of hollow cylindrical apparatus (HCA) are derived: (1) The two-directional vibration HCA can achieve the heart-shaped line stress path by determining the forms of axial force and torque. The variation of spherical stress p is similar to the load waveform of axial force. When the internal pressure is equal to external pressure, the variation of coefficient of intermediate principal stress b will like cosine curve. (2) When the three-directional vibration HCA imitates stress characteristics produced by train load, p can remain unchanged or b can be kept at the constant of 0.5. (3) With the control of the axial force, torque as well as the internal and external pressures, the four-directional vibration HCA can imitate stress characteristics of the foundation soil under train load. By setting a constant b, the linear relationship between p and q can be realized. Besides the constraint conditions on loading parameters are derived, under which the normal stress in soil is compressive stress and the direction of intermediate principal stress is kept at the diametrical direction all along.