锦屏一级水电站大理岩蠕变试验与流变模型选择

CREEP TEST AND RHEOLOGICAL MODEL SELECTION OF MARBLE OF JINPING I HYDROPOWER STATION

结合锦屏一级水电站地下厂房洞室群施工期和运行期围岩长期稳定性分析的实际需要,对厂区大理岩进行蠕变特性试验。对于用作比较的Hooke-Kelvin和Burgers两种常用流变模型及其模型参数确定问题进行简要阐述,推荐采用非线性最小二乘拟合的方法直接得到模型参数。对所采用的蠕变试验系统和蠕变试验方法,进行简要的说明和介绍。单轴和双轴蠕变试验结果表明,厂区大理岩试件在所处的应力状态下表现出一定的时效特征,经过一段时间的衰减蠕变后变形趋于稳定,符合Hooke-Kelvin流变模型所描述的蠕变特征,模型拟合曲线与试验数据能很好地吻合。因此,建议采用Hooke-Kelvin流变模型描述大理岩的流变性质。而Burgers模型不宜用来描述大理岩这样的硬质岩石的黏弹性性质,对于Burgers流变模型则应考察较长时间的试验数据。采用Hooke-Kelvin模型能够较好地解释锦屏一级水电站厂房洞室群开挖后变形最终趋于稳定的事实,试验所确定的流变模型及其参数可用于洞室群施工期和运行期的长期稳定性数值仿真模拟。

The creep tests on marble specimens from the underground powerhouse of Jinping I hydropower station of China are carried out to meet the demand of long-term stability analysis of the caverns during the construction and the operation periods.Two common rheological models,Hooke-Kelvin model and Burgers model,and their parameters determination are described with comparative discussion for the model selection.The least squares fitting to the testing results with the model curve is recommended to gain the model parameters.The creep testing system and the testing procedure are introduced briefly.It is manifested by the uniaxial creep tests and the biaxial creep tests that the considered marble shows time-dependent behavior to some extent under certain stress states.The deformation gradually approaches to corresponding constant after the early stage of creep attenuation,which accords with the creep characteristic of the Hooke-Kelvin model.The measured strains with respect to the loading time are close to the Hooke-Kelvin model curve.Therefore,the Hooke-Kelvin model is recommended to describe the rheological properties of marble.As for the Burgers model,the analysis shows that it is unsuitable for modeling the viscoelasticity of hard rock like marble.The creep behavior during relatively longer testing time,e.g.150 hours or so,needs to be examined if the Burgers model is adopted.The fact that the deformation of the underground powerhouse caverns of Jinping I hydropower station finally tends to become steady after excavation can be better explained by means of the Hooke-Kelvin rheological model.The Hooke-Kelvin rheological model and the model parameters obtained from creep tests may also be served as the fundamental data in the later long-term stability analysis of the surrounding rocks of the underground powerhouse caverns in the periods of construction and operation.