Confining Pressure Effect of Dynamic Failure of Limestone under Cyclic Impact
(1. Facility of Land Resources Engineering, Kunming University of Science and Technology, Kunming 650093;
2. YCIC Sixth Engineering Co., Ltd., Kunming 650034)
Abstract：
In order to optimize the blasting parameters for underground tunnelling in surrounding rock and control
the disturbance of surrounding rock caused by blasting, it is sorely necessary to identify the dynamic mechanical properties, failure characteristics and energy consumption of surrounding rock. By using the Split Hopkinson Pressure Bar (SHPB), the experimental study has been conducted under three-dimensional dynamic and static combined cyclic impact, so as to analyze how certain axial pressure, various confining pressures and cyclic impact coupling effect will affect the peak stress, dynamic compressive strength, failure characteristics and energy absorption rate of limestone. According to the results, under the given axial pressure and with the same number of impacts, the peak stress and dynamic compressive strength of limestone will increase and then decrease as the confining pressure increases,and the failure degree will decrease and then increase as the confining pressure increases. This indicates that proper increase of confining pressure will enhance the impact resistance of limestone. However, such enhancement is not
unlimited, because excessively high confining pressure will induce internal damage and degradation of limestone and consequently impair its impact resistance. The energy absorption rate of limestone is in a polynomial relation with the number of impacts. The impact incident energy absorbed by limestone will decrease and then increase as the confining pressure increases. Properly applied confining pressure will decrease the energy absorption of limestone, but excessively high confining pressure will cause the energy absorption of limestone specimen to increase markedly. Therefore, before blasting and excavation in underground engineering, the stress state of surrounding rock can be determined through surrounding rock stress measurement and thus the rock breaking effectiveness of specific explosive quantity in a sound can be predicted. This will afford the theoretical support for adjusting and optimizing the blasting parameters and controlling the damage and disturbance of surrounding rock caused by blasting.
2023, Vol. 60 