构皮滩软岩流变模型原位载荷蠕变试验研究

Rheological model of soft rock in Goupitan by in-situ plate-loading creep tests

针对构皮滩水电站破碎页岩进行2点原位刚性承压板载荷蠕变试验,采用1级循环加载方式,试验压力为工程应力水平,试验历时1686,2299 h。试验揭示了该软岩如下蠕变特性:在工程应力下,岩体经历起始阶段减速蠕变和682,910 h较长时间的等速蠕变后,蠕变速率趋于零,总体呈衰减蠕变,并不发生塑性流动;卸荷后,经历瞬时回弹、弹性后效,存在较大的残余变形,残余变形大于总变形的50%。提出一种加载呈弹性、卸载不回弹的单向弹簧元件[HI]描述残余变形,将其与广义Kelvin模型串联组成变异广义Kelvin模型,该模型结构简单,可综合描述软岩加载呈衰减蠕变、卸载存在较大残余变形的蠕变特性。视岩体体积变形为弹性、畸变遵循变异广义Kelvin模型,基于相应性原理推导了岩体表面蠕变方程,以岩体蠕变方程拟合试验蠕变曲线,得到了模型参数。

Two in-situ plate-loading creep tests on fracture shale in Goupitan Hydropower Station are conducted, in which the pressure is at the same engineering stress level and is loaded under one cycle pattern and the test durations are 1686 and 2299 h, respectively. Some creep characteristics of the soft rock are revealed as follows：（1） Under the engineering stress level, after decelerating creep at the initial stage and the subsequent constant-rate creep continuing for a period of 682 and 910 h, the creep rate tends to zero instead of occurrence of plastic flow, showing that the creep is the attenuation creep in total.（2） After unloading, there＇s instantly rebound deformation and anelasticity and residual deformation, which is over 50% of the total deformation. A kind of one-way spring element（[HI]）, which will behave as elastic object under pressure but not rebound after unloading, is used to describe the residual deformation. By connecting the [HI] element with the generalized Kelvin model, a changed generalized Kelvin model is established. It has simple components and can comprehensively describe the creep features of soft rock, that is, it is the attenuation creep while loading and there is the residual deformation after unloading. The constitutive equation of the model is derived, and the creep formula is also derived based on the corresponding principle. The model parameters are inversed by taking the creep formula to fit the trial curves.