以等应变速率曲线为基础的岩石长期强度确定方法

长期强度是岩石时效强度的一种,是影响和评价岩体工程长期稳定性的一个重要性质.为更准确地求解长期强度,以等应变速率曲线为基础,提出了等应变速率曲线拐点法及极限应变法两种确定岩石长期强度的新方法.对锦屏二级水电站的绿片岩开展了单轴和三轴应力状态的常规和分级加载蠕变试验以验证上述方法,并利用文中提出的方法对绿片岩长期强度求解,得到了不同围压状态下绿片岩的长期强度值.同时,在极限应变法的求解过程中,结合蠕变曲线,得到了蠕变变形稳定时间以及相应的极限应变值.试验成果表明:两种方法均可求得长期强度,数值接近且符合长期强度的经验值;单轴以及三轴应力状态下长期强度分别为瞬时强度的66.9%(单轴)、68.0%(围压10 MPa)、79.6%(围压10 MPa).文中提出的确定长期强度的方法具有一定的可行性,同时,围压是影响长期强度的主要因素之一,具体表现为随着围压的升高,长期强度与瞬时强度的比值升高.

Methods for determining long-term strength of rock based on iso-strain rate creep curves

Long-term strength is one of important properties to predict the long-term stability for rock engineering. New methods for determining the long-term strength that could be called limit strain method and inflection point method were proposed based on the isostrain-rate creep curve. To verify these methods, the traditional tests and muti-stage creep tests were carried out to analyze the creep behavior of greenschist in Jinping II hydropower station. On the basis of the tests and proposed methods, the long-term strength under different confining pressure were obtained. Combining with the creep curves, the value of limit strain and stability time of deformation were also obtained in the solving process of long-term strength. The research results show that: the long-term strength can be determined by these two methods and the results meet the empirical value. The ratio of long-term strength and instantaneous strength were 66.9% (uniaxial), 68.0% (confining pressure 10 MPa), 79.6% (confining pressure 40 MPa). Therefore, the two proposed methods are reasonable and the ratio of long-term strength and instantaneous strength increases with the increasing of the confining pressure, and the confining pressure is one of the important aspects that influence the long-term strength.