低温环境下红砂岩蠕变特性及其模型

Creep property and model of red sandstone under low temperature environment

  • 摘要: 为研究低温环境下岩体工程的长期稳定性,以饱水状态下的陕西红砂岩为研究对象,采用MTS810岩石力学试验机进行不同温度(20,-10,-20 ℃)条件下的分级加卸载单轴蠕变试验,研究了不同温度条件下红砂岩的蠕变特性及温度对岩石蠕变特性的影响。根据蠕变试验结果,将岩样总应变分为瞬时应变和蠕变应变,瞬时应变由瞬时弹性和瞬时塑性应变组成,蠕变应变由黏弹性和黏塑性应变组成。结果表明,瞬时应变随应力水平的增加而增大,瞬时弹性应变与应力呈近似线性关系;随着应力水平的增加,黏塑性应变随时间逐渐增加,总应变中黏塑性应变的比例也趋于增大。随着温度的降低,岩样瞬时应变及相同应力水平下的蠕变应变均减小,蠕变持续时间延长,岩石破坏强度提高。根据岩样的变形特性结合蠕变试验结果,引入分数阶微积分,建立考虑低温影响的非线性流变模型;采用通用全局优化算法结合最小二乘法中的Levenberg-Marquarat算法对不同温度环境中的蠕变试验结果进行参数识别,理论曲线与试验结果吻合度较高,尤其加速蠕变阶段效果较好,表明该模型能够很好地描述红砂岩在低温环境下的蠕变行为;对不同温度条件下的模型参数进行分析,结果表明,随着温度的降低弹性模量E3(T)呈抛物线式增长,而弹性模量E1(T),E2(T)及黏性系数η1(T)呈指数形增长,为冻结法施工和寒区岩体工程长期稳定性分析提供理论依据。

     

    Abstract: In order to study the long-term stability of rock mass engineering in low temperature environment,multi-level loading and unloading uniaxial creep tests were conducted on Shaanxi saturated red sandstones at different temperatures (20,-10,-20 ℃ ) using MTS810 rock mechanics testing machine. The creep property of red sandstone under different temperature conditions and the effect of temperature on rock creep properties were studied. According to the creep tests results,the total strain of the rock sample was divided into instantaneous strain and creep strain,the instantaneous strain consists of instantaneous elastic and instantaneous plastic strains,and the creep strain consists of viscoelastic and visco-plastic strains. The results show that the instantaneous strain increases with higher stress level,and the relationship between the instantaneous elastic strain and the stress can be described by approximate linear expression. The visco-plastic strain keeps increasing with time,and the proportion of visco-plastic strain in the total strain also tends to increase when the stress is higher. The instantaneous deformation and creep deformation of the rock sample decreases with the temperature drop. The creep duration is prolonged. The damage strength of rock is increased. Based on the deformation characteristics of rock and the creep test results,a fractional calculus was introduced to establish a nonlinear creep model considering the influence of low temperature. The Universal Global Optimization algorithm and Levenberg-marquarat algorithm were taken to identify the model parameters of creep test results in different temperature environments. The theoretical curve agrees well with the experimental results,especially in the accelerated creep stage. It indicates that the model can well describe the creep behavior of red sandstone in a low temperature environment. The model parameters under different temperature conditions were analyzed. As the temperature drop,the elastic modulus E3(T) increases parabolically,while the elastic modulus E1(T),E2(T) and viscosity coefficient η1(T) increase exponentially. The study provides a theoretical basis for the long-term stability analysis of freezing method construction and rock mass engineering in cold regions.

     

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