Experimental investigation on influence of loading rate on rockburst in deep circular tunnel under true-triaxial stress condition

Abstract

To investigate the influence of loading rate on rockburst in a circular tunnel under three-dimensional stress conditions, the true-triaxial tests were conducted on 100 mm×100 mm×100 mm cubic sandstone specimens with d50 mm circular perforated holes, and the failure process of hole sidewall was monitored and recorded in real-time by the microcamera. The loading rates were 0.02, 0.10, and 0.50 MPa/s. The test results show that the rockburst process of hole sidewall experienced calm period, pellet ejection period, rock fragment exfoliation period and finally formed the V-shaped notch. The rockburst has a time lag and vertical stress is high when the rockburst occurs. The vertical stress at the initial failure of the hole sidewall increases with loading rate. During the same period after initial failure, the rockburst severity of hole sidewalls increased significantly with increasing loading rate. When the vertical stress is constant and maintains a high stress level, the rockburst of hole sidewall under low loading rate is more serious than that under high loading rate. With increasing loading rate, the quality of rock fragments produced by the rockburst decreases, and the fractal dimension of rock fragments increases.

摘要

为了研究加载率对真三轴应力条件下圆形隧道围岩岩爆的影响, 对含有d50 mm 圆形贯穿孔洞的100 mm×100 mm×100 mm 立方体砂岩试样开展了真三轴试验, 采用微型摄像机实时监测并记录洞壁的破坏过程。加载率分别为0.02, 0.10 和0.50 MPa/s。试验结果表明, 岩爆过程经历了平静期、颗粒弹射期、岩片剥落期, 最终形成V 形槽。岩爆具有一定的时滞性, 发生岩爆时垂直应力较高。洞壁初始破坏时的垂直应力随着加载率的增加而增加。在初始破坏之后的同一时间段内, 岩爆的剧烈和严重程度随着加载率的增加而增强。当垂直应力恒定并保持在较高的应力水平时, 低加载率下洞壁的岩爆破坏程度要比高加载率下的严重。随着加载率的增加, 岩爆产生的岩片的质量减小, 岩片的分形维数增大。