分级加载条件下紫色泥岩三轴蠕变特性研究

流变性质是岩石材料的重要力学特性,以紫色泥岩为例,在分级加载条件下研究了其三轴蠕变特性。采用自行研制的重力杠杆式岩石蠕变实验机,并配备三轴压力室,对紫色泥岩实施分级加载三轴蠕变实验。实验结果表明,紫色泥岩在相同轴压条件下,围压越大,瞬时弹性变形和蠕变变形越小;在相同围压条件下,轴压越大,二者变形越大。紫色泥岩的蠕变速率具有相同的变化趋势,且在相同轴压条件下,围压越大,稳定蠕变阶段的蠕变速率越不明显。另外,应力与瞬时应变线性拟合结果表明,瞬时轴向应变与轴向荷载近似成比例增长。通过分析紫色泥岩蠕变曲线变化趋势,认为采用H/M模型进行模拟较为合理。并且采用MATLAB软件非线性回归分析进行模型参数拟合,最后得到实验曲线与理论曲线的最大误差在2e-5左右。证明采用的H/M模型能较好地描述紫色泥岩的蠕变特性。

Study of Triaxial Creep Properties of Purple Mudstone under Stepwise Loading

Rheological properties is an important mechanical properties of rock material. Triaxial creep properties of specimen made of purple mudstone were studied under stepwise loading. The experiment was carried out on a home-made gravitation lever style rock creep test machine and a triaxial pressure cell. Results show that under the same axial pressure,the greater the confining pressure is,the smaller the instantaneous elastic deformation and creep deformation of purple mudstone are;under the same confining pressure,the greater the axial pressure is,the larger both deformations are;the creep rate of purple mudstone has the same trend,and under the same axial pressure,the greater the confining pressure is,the fuzzier the creep rate at the stable creep stage is. In addition,results of the linear regression for stress and instantaneous strain show that the instantaneous axial strain and axial load approximated to grow proportionally. Through analyzing the purple mudstone creep curve trend,it is suggested that H/M model is reasonable to creep simulation. In order to implement the model parameters fitting,the nonlinear regression analysis of MATLAB software was adopted. Final results show that the maximum deviation between experimental curve and theoretical one is about 2e-5. This proves that H/M model can reasonably describe the creep properties of purple mudstone.