一种青藏高原冻结砂土蠕变本构模型

为描述青藏铁路沿线冻结砂土的蠕变特性,建立一个考虑应力和时间耦合的蠕变本构模型.首先进行一系列不同温度、干密度条件下的冻结砂土三轴蠕变试验;其次以Nishihara模型为基础,考虑应力和时间对模型元件的耦合影响,将黏弹性元件中定常的黏滞系数修正为时间和应力的函数,引入损伤变量改进黏塑性元件,构建新的冻结砂土蠕变本构模型;最后基于试验数据验证其科学性.结果表明:试验数据与拟合数据吻合良好,改进模型能较好地描述不同温度和应力水平下冻结砂土的衰减、稳态和加速蠕变特性;改进模型中黏弹性元件的黏滞系数、剪切模量和黏塑性元件的黏滞系数均随温度升高和应力水平增大而减小,损伤变量参数随着温度升高、应力水平增大而增大.成果可为冻结砂土蠕变沉降预测提供一种新的选择,为蠕变理论研究积累资料.

Creep constitutive model for frozen sand of Qinghai-Tibet Plateau

To describe the creep characteristics of frozen sand along the Qinghai-Tibet Railway, a creep constitutive model considering the coupling of stress and time was proposed. First, the tri-axial creep tests under different negative temperatures and dry density conditions were carried out. Then, based on the Nishihara model, considering the coupling influences of time and stress on the model elements, the coefficient of viscosity in viscoelastic part was modified under the effect of time and stress, and the viscoplastic element was improved. By introducing the damage variable, an improved Nishihara model for frozen sand was proposed. Finally, the new creep model was verified based on the test results. It was found that the creep curves predicted by this model agreed well with the corresponding experimental results from low stress to high stress, and the model could describe the unsteady, steady, and accelerating creep characteristics accurately under different temperatures and stress levels. Besides, the coefficient of viscosity and shear modulus in viscoelastic part and the coefficient of viscosity in viscous plastic part decreased with the increase of temperature and shear stress, while the damage variable increased. This study could provide a new choice for the creep prediction of frozen sand, and accumulate data for the study of creep theory.