深部花岗岩试样岩爆过程实验研究

EXPERIMENTAL STUDY ON ROCKBURST PROCESSES OF GRANITE SPECIMEN AT GREAT DEPTH

利用自行设计的深部岩爆过程实验系统,对深部高应力条件下的花岗岩岩爆过程进行实验研究。岩爆实验过程可模拟实际工程的开挖条件:对加载至三向不同应力状态下的板状花岗岩试样,快速卸载一个方向的水平应力,保持其他两向应力不变或保持其中一向应力不变增加另外一向应力。实验过程中采集3个方向应力随时间的变化数据,获得花岗岩岩爆全过程应力曲线。根据实验结果,将花岗岩岩爆全过程分为平静期、小颗粒弹射、片状剥离伴随着颗粒混合弹射及全面崩垮4个阶段;将花岗岩岩爆的破坏形式分为颗粒弹射破坏、片状劈裂破坏和块状崩落破坏;分析发生岩爆后花岗岩试样的微观结构破坏特征;根据卸载后发生岩爆的最大主应力与岩石单轴抗压强度的比值对岩爆强度进行分类;根据卸载后至发生岩爆现象的时间,将岩爆分为滞后岩爆、标准岩爆和瞬时岩爆,并对花岗岩岩爆发生机制进行初步探讨。

Rockburst is a nonlinear dynamical phenomenon when large amounts of energies release along free surface during excavation within underground rock masses at great depth. An experimental system has been designed to reproduce such a natural rockburst phenomenon by means of two processes, one is true triaxial stress loading process to simulate in-situ stresses; and the other is surface unloading process with unloading one direction stress fast to produce a free surface. During the process of one direction unloading, the stresses in other two directions are kept original or the loads in one direction increase with the other steady. Ten of granite plate specimens are tested. The relation curves of stress and time in the entire process of granite rockbursts are acquired based on the results of collected data. The experimental results show that the process of granite rockburst includes four stages-calm period, small grains ejection, rock flakes and/or grains ejection and collapse entire fracture. Rockburst intensity is defined by the ratio of maximum principal stress σ1 to uniaxial compression strength σc. According to the time between the unloading and the beginning of the rockburst, three types of rockbursts are classified, instant rockburst, standard rockburst and delayed rockburst. The microcosmic characteristic of the granite after rockburst fracture is analyzed. Three fracture styles of rockburst are classified--local grains ejection failure, flake spalling failure and block collapse failure. The mechanism of rockburst is preliminarily discussed. It is of great importance to study rockburst mechanism and to prevent rockburst in deep coal mine engineering.