甘肃天水泥岩剪切蠕变行为及其模型研究

Study on shear creep behavior and its model of mudstone in Tianshui,Gansu Province

合理描述红层软岩的蠕变规律对于甘肃天水地区各类建筑物的长期稳定性和安全运营非常重要。为研究天水地区泥岩的蠕变特性,采用三轴蠕变仪,开展不同加荷方式和不同含水率的泥岩蠕变试验,获取应变-时间关系,分析其蠕变过程和蠕变特征,建立适宜的蠕变模型。研究结果表明,随应力水平和时间的增加,泥岩蠕变量有缓慢增长趋势,但最终保持某一稳定值。泥岩的蠕变量随着应力差、围压以及含水率的增长呈增大趋势;不同围压和含水率情况下,随时间的增加,泥岩的蠕变量逐渐增长,其等时曲线亦逐渐向应变轴偏移;从试样等时曲线拐点推测,一定应力水平下蠕变量达到了长期强度。基于岩石蠕变参数的辨识,西原模型、逻辑回归模型和指数型经验模型均与试验数据良好吻合,能很好地反应低应力水平下的从弹性变形到衰减蠕变、稳定蠕变的全过程,其中逻辑回归模型和指数型模型能更好地反应泥岩的蠕变特征曲线和参量。所建立的非线性蠕变模型可用于描述该地区红色泥岩的蠕变力学特性,因而具有一定的工程应用价值。

It is very important to reasonably describe the creep law of soft rock for buildings’long-term stability in Tianshui area,Gansu Province.In order to study the creep behavior of Tianshui mudstone,triaxial creep tester was used with different loadings and water contents.The strain-time relationship was obtained.The creep process and creep characteristics were analyzed.And suitable creep model was established.The results showed that with the increase of stress level and time,the creep value increased slowly,but eventually kept a certain stable value.The creep of mudstone also increased with stress dispersion,confining pressure and moisture content.Under different confining pressure and water content,the creep increased with time,and the isochronous curve gradually shifted to the strain axis.It is inferred from the inflection point of isochronous curve of the specimens that under certain stress level the creep reached long-term strength.Based on creep parameters identification,the Xiyuan model,logical regression model and exponential empirical model were in good agreement with the experimental data.The three creep models could well reflect the whole creep process from elastic deformation to attenuation creep and even to stable creep at low stress level.The logical regression model and exponential model can better reflect the creep characteristic curves and parameters of mudstone.The established nonlinear creep model could be used to describe the creep mechanical properties of mudstone in Tianshui,therefore it has certain significance for engineering application.