不同应力条件下硬岩强度与破裂特性试验研究

深部工程围岩内的岩石可能处于一维、二维和三维应力状态下，分别对应室内单轴压缩、双轴压缩和真三轴压缩试验中岩样的应力状态。通过开展单轴、双轴和真三轴压缩试验，系统研究了不同应力状态和水平下岩石非常规破坏的发生机制。不同高宽比和宽厚比岩样的单轴压缩试验结果表明：随着岩样厚度的增加，单轴抗压强度单调增加；随着岩样高度的增加，单轴抗压强度往往先增加后减小，且矮薄岩样更容易发生岩爆和板裂等非常规破坏。双轴或真三轴压缩试验中岩样的抗压强度均表现出明显的中间主应力效应。在相同最小主应力下，随着中间主应力的增加，岩样的双轴抗压强度和真三轴抗压强度均呈先增加后减小的变化趋势，双轴抗压强度增长率则呈先减小而后小幅增大的趋势。通过定义强度增量参数ν和中间主应力位置参数λ构建了指数岩石真三轴强度准则。低围压限制、非对称围压限制和短裂纹扩展路径是引起岩石非常规破坏的主要条件。

Experimental Study on Strength and Fracture Characteristics of Hard Rock Under Different Stress Conditions

The unconventional failure phenomenon of rocks，such as slabbing and rock burst，occur frequently in deep engineering，which bring huge financial loss and casualties.The occurring mechanism of the un-conventional failure is still unclear，and the stress state and levels of rocks is the main factors inducing unconventional failure.The surrounding rocks of deep engineering is under a one-dimensional，two-dimensional or three-dimensional stress conditions，corresponding to the stress state of the rock specimen in the uniaxial，biaxial or true triaxial compression tests，respectively.In this study，the uniaxial，biaxial or true triaxial compression tests were carried out to reveal the occurring terms of the unconventional failure of rocks.The isolated ore pillars left after room-pillar mining are usually under one-dimensional compressive stress.Through uniaxial compression tests of rock specimens with different height-width ratios and width-thickness ratios，it is found that the strength of rock specimen exhibits obvious characteristics of non-linear changes as the height and width of rock specimen increase.As the thickness increases，the uniaxial compressive strength increases.As the height increases，the uniaxial compressive strength tends to increase first and then decrease.This is mainly related to the slabbing failure of the dwarf and thin rock specimens.Combining the uniaxial compression test of cuboid rock specimens and the reduction of rock mass mechanical parameters，the safety evaluation of the isolated pillars can be conducted.Based on the fact that the surrounding rocks of underground engineering are often under a two-dimensional stress state，and the fact that rocks far away from the boundaries of underground engineering are often under a three-dimensional stress state，the biaxial compression and true triaxial compression tests of cubic rock specimens have been carried out.The rock strength in biaxial or true triaxial test shows obvious intermediate principal stress effect.Under the same minimum principal stress，the biaxial compressive strength and true-triaxial compressive strength of rocks increases first and then decreases with the increase of the intermediate principal stress，and the change rate of biaxial compressive strength decreases firstly and then shows a little increase.An exponential rock strength criterion was constructed by defining the strength increment parameter ν and the intermediate principal stress position parameter λ.It is considered that low confining pressure limitation，asymmetric confining pressure limitation and short crack propagation path are the main terms for unconventional failures of rocks under multi-dimensional stress conditions.