不同卸载方向下高应力岩石真三轴卸荷力学特性研究

Experimental study of mechanical properties of highly-stressed rocks under true triaxial unloading conditions with different unloading directions

深部岩体开挖过程中,围岩应力场在开挖面附近形成交替分布的应力升高区(加载区)和应力降低区(卸载区),极易引发高应力岩体失稳破坏。尽管目前已有诸多关于岩石加卸载破坏方面的研究,但在复杂真三轴应力路径下岩石加卸载破坏机理的认识仍不充分。针对这一问题,文章以山东玲珑金矿花岗岩立方块试样为研究对象,首先进行了不同侧向应力下真三轴加载破坏试验,并进一步开展了不同卸荷方向下真三轴卸载破坏试验,深入研究了花岗岩试样在复杂真三轴加卸载路径下的强度及破坏特征。试验结果表明:随着中间主应力的增大,真三轴加载条件花岗岩的破坏模式由张拉-剪切复合型破坏转变到张拉破坏,真三轴加载破坏强度先增大后缓慢减小;在相同中间主应力和最小主应力条件下,花岗岩的真三轴卸载破坏强度均小于其加载破坏强度,Mogi强度公式可以很好地拟合卸载最小主应力条件下的真三轴卸载强度。该成果可为深部岩体工程稳定性控制和设计提供重要的理论依据和指导。

During the excavation process of deep rock masses,the surrounding rock stress field forms alternating zones of stress increase(loading zones)and stress decrease(unloading zones)near the excavation surface,which can easily trigger instability and failure in high-stress rock masses.Despite numerous studies that have been conducted on rock loading and unloading failures,the understanding of rock failure mechanisms under complex true triaxial stress paths remains insufficient.This study focuses on cubic granite specimens from the Linglong gold mine in Shandong.To comprehensively investigate the strength and failure characteristics of granite samples under complex true triaxial loading and unloading paths,true triaxial loading tests under different lateral stresses were conducted,followed by further true triaxial unloading tests in different unloading directions.The experimental results reveal that with the increase of intermediate principal stress,the failure mode of granite under true triaxial loading condition changes from shear-tensile failure to tensile failure,and the true triaxial loading failure strength increases first and then decreases slowly.Under the same intermediate and minimum principal stress conditions,the true triaxial unloading failure strength of granite is smaller than its loading failure strength,and the Mogi strength formula fits well with the true triaxial unloading strength under the minimum principal stress condition.This study provides an essential theoretical basis and guidance for controlling and designing the stability of deep rock masses in engineering applications.