基于蠕变曲线对称的蠕变模型研究及参数敏感性分析

Study on symmetric creep model based on creep curves and parametric sensitivity analysis

为了获得滇中引水隧洞围岩的蠕变特性和研究隧洞围岩的长期稳定性,采用中国科学院武汉岩土所自主研发的全自动三轴开展绿泥页岩的单轴蠕变试验,获得了绿泥页岩的轴向蠕变曲线和等时应力-应变曲线,并基于等时应力-应变曲线的特征确定出绿泥页岩的长期强度值。基于经典蠕变曲线特征与大量试验蠕变曲线,发现描述衰减蠕变曲线的方程可以通过对称处理,故假设加速曲线与衰减蠕变曲线是关于稳定蠕变曲线的中点对称的,得到一种基于蠕变曲线对称的加速蠕变模型,并基于蠕变试验曲线的特征提出一套确定蠕变模型参数的方法。最后,将引入加速蠕变模型中的参数进行敏感性分析,使得引入模型中的参数具有明确的物理意义。结果表明:随着轴向应力的不断增大,岩石的瞬时应变值和蠕变变形值不断增大,而第一级荷载作用下岩石的瞬时应变占蠕变总变形比值最大。所建立的蠕变模型不仅可以很好地描述绿泥页岩的衰减蠕变和稳定蠕变变形规律,也较好地弥补了西原模型无法描述加速蠕变的缺陷,且该模型曲线与试验曲线的吻合度要远远高于西原模型与试验曲线的吻合度,并且不同应力作用下模型曲线与试验曲线的相关性系数均在0.90以上;同时,通过不同类型试验曲线与模型曲线的验证也说明了该模型是可用于不同类型岩石蠕变曲线的预测。最终,引入参数j值控制了加速蠕变的变形速率和进入加速蠕变的时间,参数k值控制了蠕变时间和加速阶段的蠕变速率。

In order to obtain the creep characteristics of the surrounding rock of the Dianzhong water diversion tunnel and to study the longterm stability of the surrounding rock of the tunnel,a fully automated triaxial developed by Wuhan Institute of Geotechnics,Chinese Academy of Sciences,is used to carry out the uniaxial creep test of green mud shale.The axial creep curve and isochronous stress-strain curve of green mud shale are obtained.And the long-term strength value of green mud shale is determined based on the characteristics of isochronous stress-strain curve.Based on the classical creep curve characteristics and a large number of experimental creep curves,it is found that the equations describing the attenuation creep curve can be treated by symmetry.Therefore,it is assumed that the acceleration curve and the decay creep curve are symmetric about the midpoint of the stable creep curve.An accelerated creep model based on the symmetry of the creep curve is obtained.And a set of methods to determine the parameters of the creep model is proposed based on the characteristics of the creep test curve.Finally,the parameters introduced into the accelerated creep model for sensitivity analysis.The parameters introduced into the model have a clear physical meaning.The results show that with the increasing axial stress,the instantaneous strain value and creep deformation value of the rock are also increasing,and the instantaneous strain of the rock under the first stage load ac-counts for the largest ratio of the total creep deformation.The established creep model can not only well describe the attenuation creep and stable creep deformation law of green mud shale,it also better make up for the defects of the Nishihara model that cannot describe the ac-celerated creep.The agreement between the model curve and the test curve is much higher than that between the model and the test curve,and the correlation coefficients between the model curve and the test curve under different stresses are all above 0.90.Meanwhile,the val-idation of different types of test curves and model curves also shows that the model can be applied to the prediction of creep curves of dif-ferent types of rocks.Finally,the value of parameter j is introduced to control the deformation rate and the time to enter accelerated creep.The value of parameter k controls the creep time and the creep rate in the accelerated stage.