考虑扩容的围岩局部破坏过程中声发射及能量释放的数值模拟

Numerical simulation of the acoustic emissions and released energy in the tunnel surrounding rock subjected to a localized failure considering dilatancy

本文模拟了巷道开挖之后,围岩发生局部破坏过程中的声发射及能量释放的演变规律,其中考虑了围岩的峰后扩容特性。介绍了FLAC中扩容角的引入方法,对于剪切而言,仅第3塑性主应变的增量才与扩容角有关。阐述了统计声发射及能量释放的方法,前者仅统计事件的数目,而后者可以考虑事件的大小。研究发现,扩容角的增加会使巷道围岩中的剪破坏单元数及所释放的能量提高;会使V形坑变大、变钝、变深,这是由于第3主应力与剪切带之间的夹角增加的结果。解释了设置固定的抗拉强度,单元却发生拉伸软化及释放拉伸应变能的原因。从与能量释放有关的量的演变规律中一般能发现V形坑式破坏的前兆,而从声发射数上则不然,这反映了统计事件大小的优势。如果将扩容角置零,会低估围岩的破坏范围及释放的能量,但是对于巷道围岩的再次平衡却是有利的。

Evolution of the acoustic emissions and released energy during the process of the localized failure of the sur- rounding rock of a tunnel is simulated after the tunnel is excavated considering the post-peak dilatant nature of rock. The method to introducing the dilation angle into FLAC is discussed and the maximum principal plastic strain incre- ment for shear failure is related to the dilation angle. The method to calculating the acoustic emission counts and re- leased energy is presented. The former only considers the number of events, while the latter the magnitudes of events. It is found that higher dilation angle leads to larger number of failed elements in shear and corresponding released en- ergy in the tunnel surrounding rock. Higher dilation angle results in bigger, less sharp and deeper V-shaped notches because the angle between the maximum principal stress and the shear band becomes larger. The tensile strength is set to be a constant. However, the tensile strain-softening occurs and the tensile elastic strain energy is released. The reason for this phenomenon is explained. Generally, the precursors to failures of V-shaped notches can be found from the released energy, while does not from the acoustic emission counts. This reflects that the magnitudes of events should be considered necessarily. For zero dilation angle, the number of failed elements and corresponding released energy can be underestimated, while it is easier for the surrounding rock of the tunnel to reach the static equilibrium.