不同应力途径下灰岩卸荷试验研究

Experimental Study on Limestone Unloading Under Different Stress Paths

考虑不同应力路径下的卸荷对岩石强度、变形模量等参数的影响,以铜坑矿区小扁豆状灰岩为研究对象,结合现场工程地质条件,开展了岩石卸荷力学试验,试验研究发现:卸荷岩石的破坏主要表现为脆性破坏,峰前卸围压的破坏程度大于峰后卸围压的破坏程度,峰后卸围压的破坏程度大于常规三轴的破坏程度,峰前卸围压破坏具有突发性,岩样由张性破坏过渡到张剪性破坏;在相同初始应力下,岩石卸载破坏所需应力比常规三轴压缩破坏对应的应力小,卸荷破坏时的变形比连续加载时大;衍生的卸荷裂隙随机发生,方向大体平行于X型共轭剪节理,对洞室开挖临空面定向破坏有判定性,由此现象引发片帮、冒顶等隐患需及时采取工程措施治理。

Considering the influences of unloading with differ- ent stress paths on the rock strength and deformation modu- lus, taking the lenticular limestone in Tongkeng mine as the research example, the unloading mechanical tests of rock were conducted by combining with the engineering geological conditions. The experimental study obtained the results as follows. Firstly, the unloading rock mainly presented the brittle failures. The failure degrees under different stress paths were from big to small with the sequence of pre-peak unloading confining pressure, post-peak unloading confining pressure and tri-axial pressure. The rock failure under pre- peak unloading confining pressure was explosive, and the rock sample was damaged from tensile failure to tensile shear failure. Secondly, under the same initial stress, the required stress for rock unloading failure was less than that for con- ventional tri-axial compression failure, and the rock deform- ation during unloading failure was greater than that during continuous loading. Thirdly, the induced unloading joints de- veloped randomly, and their direction was almost parallel to the X-conjugate shear joint, which could determine the direc- tional damage of free face during excavating cavern. And the engineering measures sould be timely taken to prevent the wall caving, the puking and other hazards caused by the joints.