深部非均匀岩体卸载拉裂的时间效应和主要影响因素

TIME EFFECT AND MAIN INFLUENCE FACTORS OF UNLOADING SPLITTING OF DEEP-SEATED ROCK WITH NONUNIFORMITIES

深部地下工程围岩的拉伸破坏是一个常见的但没有得到充分研究的科学现象。岩石内部包含的缺陷和缺陷处的应力集中被认为与岩石在压应力作用下的拉伸破坏密切相关。基于应力集中的非均匀岩石拉伸破坏模型的理论框架,系统的研究3个影响岩石拉伸破坏的主要因素:加卸载速率(偏应变率)、缺陷尺度和初始地应力,对岩石内部缺陷处拉应力的产生和发展过程的影响。研究表明:(1)偏应变速率对缺陷处附加拉应力具有显著的影响,偏应变率越高,缺陷处的附加拉应力越大;(2)不同层次的缺陷对应于不同大小的偏应变率,偏应变率越高,对应缺陷的尺寸就越小;(3)缺陷处的附加拉应力与初始应力成正比,缺陷较大时,岩体是否发生卸载破坏由初始应力、应力集中系数和抗拉强度间的关系决定。引用模拟试验和现场观测的结果和现象对理论分析结果进行讨论,试验现象和现场观测数据均与理论分析基本吻合。

The splitting of stressed rock in the neighborhood of underground openings is a common phenomenon that is not well explained theoretically up to the present.The stress concentration at nonuniformities is believed to be the crucial one among the factors influencing the tensile failure process under pressure conditions.Based on the model of rock with nonuniformities,three main factors of the splitting fracture of rock,including unloading duration（or deviator strain rate）,scale of nonuniformities and initial geostress,are detailed investigated in order to reveal the mechanism behind the phenomenon of splitting.The results of theoretical analysis show that：（1） The excess tension stress of nonuniformities is affected by deviator strain rate significantly;and it increases nonlinearly as the unloading duration shrinks.（2） There is a nonlinear corresponding relationship between the scale of nonuniformities and the magnitude of deviator strain rate;and higher deviator strain rate tends to excite smaller nonuniformities.（3） If there exist nonuniformities with big scale enough,the maximum excess tension stress is proportional to the initial geostress.Therefore,the possibility of unloading splitting is determined by the relation among the three parameters：initial geostress,stress concentration coefficient and tensile strength.Results of an unloading test,in which the axial stress of hydraulic stressed rock samples is unloaded with different control modes,and data of in-situ core disking observation,are cited to verify the analytical analysis results.The main phenomena and critical stress condition of core disking predicted by the theoretical model coincide well with the results of the cited experiments and insitu observation data.