The long-term strength and time-to-failure of brittle rocks has become increasingly important with the increased interest in the storage of used nuclear fuel in deep geological repositories. This paper critically reviews and analyzes the currently available time-to-failure data for various brittle rock types. The current best approach on estimating time-to-failure of rock samples at the lab scale under a constant stress is using semi-log data based on the driving stress ratio and the logarithm of time. In most studies, the applied driving stress ratio is calculated based on the average strength of the rock, however, sample strength can vary up to 15%. Therefore, it is proposed that the crack-initiation stress threshold for each sample be used to calculate sample specific ultimate strengths based on relationships determined in literature. It is proposed that if a sample fails during a long-term strength test within the first 1–10 s, the applied stress for that test can be assumed equivalent to the ultimate strength. Additionally, a modified exponential function with a horizontal asymptote at the crack-initiation threshold is explored as an alternative to the typical log-linear approach. The exponential approach is non-linear in semi-log space and does not require an arbitrary cut-off for time-to-failure at the static fatigue limit of the rock as is the case of the semi-log approach. Ultimately, it is shown that although the exponential function does usually provide a better overall fit to data at relatively short times (<1,000,000 s), there is little evidence to justify the asymptotic behaviour in the longer term. Common practice has been to present the driving stress ratio as a function of time-to-failure, however, in theory these axes should be reversed as the variable of interest to the reader is the time-to-failure based on in-situ stresses. The consequence of plot orientation and subsequent error calculation are explored. The goal of this paper is to provide users and researchers with a reliable methodology to predict time-to-failure of brittle rocks both at the lab and excavation scale as well as a basis for incorporating explicit time-to-failure calculations into a continuum numerical model.

随着人们对在深层地质处置库中储存废核燃料的兴趣日益浓厚，脆性岩石的长期强度和失效时间变得越来越重要. 本文批判性地回顾和分析了当前可用的各种脆性岩石类型的失效时间数据。当前在恒定应力下估计实验室规模岩石样品失效时间的最佳方法是使用基于驱动应力比和时间对数的半对数数据。在大多数研究中，应用的驱动应力比是根据岩石的平均强度计算的，但是，样品强度的变化可能高达 15%。因此，建议根据文献中确定的关系，使用每个样品的裂纹起始应力阈值来计算样品特定的极限强度。建议如果样品在前 1-10 秒内在长期强度测试中失败，则可以假设该测试所施加的应力等于极限强度。此外，在裂纹起始阈值处被探索作为典型对数线性方法的替代方法。指数方法在半对数空间中是非线性的，并且不需要像半对数方法那样在岩石的静态疲劳极限处对失效时间进行任意截止。最终，结果表明，虽然指数函数通常确实在相对较短的时间（<1,000,000 秒）内提供了更好的数据整体拟合，但几乎没有证据证明从长期来看渐近行为是合理的。通常的做法是将驱动应力比表示为失效时间的函数，但是，理论上这些轴应该颠倒，因为读者感兴趣的变量是基于原位应力的失效时间. 探索了绘图方向和随后的误差计算的结果。