True Triaxial Test Study Of The Influence Of Support Failure On Rockburst Ejection

Rockburst is one of the most serious disasters frequently encountered during underground excavation in depth. Before excavation, the rock masses are under a true-triaxial stress condition. Then, the excavation of an opening change the initial in situ stress, leading to the stress concentration and lowing the strength and carry capacity of the surrounding rock. When the excavated-induced stress increases to the rock mass strength, rock mass failure occurs accompanying with the release of elastic strain energy in the formation of fragment ejection. This phenomenon is called rockburst. Additionally, it is well known that support is one of significantly methods for preventing rockburst. But, it should also be noted that rockburst is still encountered in supported tunnel, and the support failure may trigger intensive rockburst. Therefore, it is meaningful to gain a good understanding of the influence of the support failure on rockbust, and furthermore provide a basis for support design of the tunnel with rockburst proneness.The aim of this work is to investigate the influence of the support failure on the rockburst. Firstly, the unloading test on the granite was performed using the true-tiaxial rockburst system to simulate the rockburst triggered by the support failure, and the whole rockburst process was reordered by using a high speed camera system. Then, the influence of the failure support force, support failure timing and the support failure rate on the rockburst was studied in detail in term of the kinetic energy of the ejected fragments, final failure form, accumulative AE energy and size distribution of fragments.The experimental results indicate that:(1) With the increasing of the support force, the pre-peak accumulated elastic strain energy increases, at the same time support force inhibit the development of rock fracture, the damages of the rock specimen declines, the accumulated AE energy decreases. Supporting failure, the kinetic energy of the ejection fragment and the ratio of the kinetic energy and release strain energy increase. (2) During the loading process before the stress exceeding the true-triaxial compression strength, the later unloading the minimum stress, which indicates the later support failure time, then more is the pre-peak accumulated elastic strain energy, the kinetic energy of the ejection fragment and the ratio of the kinetic energy and release strain energy. (3) With the increment of the support failure rate, the kinetic energy of the ejection fragment of the rockburst behaves a linear increasing trend with the support failure rate, the failure mode is transmit from the static failure to dynamic rockburst, the pre-damages of the rock specimen decreases, the accumulated energy of acoustic emission decreases, the intensity of the rockburst increases.