Evolution of anisotropy during sandstone rockburst process under double-faces unloading

Abstract

Rockburst is one of the major disasters in deep underground rock mechanics and engineering. The precursors of rockbursts play important roles in rockburst prediction. Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility. P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus. The P-wave velocities were calculated in both two directions to analyze their patterns. To find a characteristic precursor for rockburst, the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k, defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes. The results show that rockburst occurs on the two free surfaces asynchronously. The rockburst failure occurs in the following order: crack generation, rock peeling, particle ejection, and rock fracture. In the process of rockburst under double-face unloading, the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy. The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one, i.e., isotropy. The rocks with horizontal bedding planes will reach the isotropic state before rockburst, which could be considered as a characteristic precursor of this kind of rockburst.

摘要

岩爆是深部地下岩石工程中主要的灾害之一,岩爆前兆信息在岩爆预测中至关重要。利用自主 研发的岩爆设备和具有水平层理的红砂岩开展了双面卸载应变岩爆实验。利用声发射设备自动采集了 实验过程中P 波的传播时间,并且计算分析了P 波在水平层理方向和垂直层理方向的传播速度。为了 找到岩爆的特征前兆信息,将垂直于层理的波速与平行于层理的波速的比值定义为各向异性系数k, 定量分析了岩爆过程中岩石各向异性的演化规律。实验结果表明,两个卸载面的岩爆并非同时发生, 岩爆主要包括裂纹萌生,岩片剥落,颗粒弹射,岩板断裂等过程。双面卸载岩爆实验的各向异性演化 特征可以总结为由各向异性向各向同性转化,而后再次向各向异性转化,并且快速卸载会对岩石产生 损伤,各向异性系数会突增。具有水平层理的岩石在岩爆之前会达到各向同性状态,可以将此视为岩 爆的前兆信息。