# Energy Generation and Attenuation of Blast-Induced Seismic Waves under In Situ Stress Conditions
## 4 A Case Study
### Seismic Energy Attenuation Analysis and Discussion
The theoretical, numerical, and case studies conducted in this paper indicate that during rock blasting under in situ stress, the blasting seismic energy generation and attenuation are closely related to the stress level and lateral coefficient. However, in the current rock blasting theory with respect to explosive energy distribution, seismic wave attenuation, vibration prediction, and safety standards, the role of in situ stress has not been properly addressed. This probably results in an inappropriate blasting design for deep mining and excavation, thereby affecting rock fragmentation and excavation profile formation. In severe cases, it may induce dynamic disasters such as rockbursts. As analyzed above, during rock blasting under in situ stress, more blasting seismic energy is generated, and the seismic energy attenuation becomes slower. Then the PPV caused by deep rock blasting is greater than that caused by shallow rock blasting at the same charge weight. This means that under the current blasting vibration standards that are developed in terms of PPV limits, the seismic waves generated in deep rock blasting are more likely to reach and exceed the limits. In order to prevent this from happening for statutory compliance, the charge weight is usually reduced by designers as it is directly related to the PPV. This is also the most commonly used optimization method in shallow rock blasting. However, simply reducing the charge weight may result in insufficient rock fragmentation, leading to large blocks and under-break for deep rock blasting. This is because, in this case, the explosive energy is reduced, and furthermore, in situ stress inhibits  
Figure 13: Regression analysis of seismic energy attenuation with distance along the monitoring points at different depths. the growth of the cracks caused by blasting. Conversely, it is inadvisable to blindly increase the charge weight to promote rock fragmentation. On the one hand, the vibration levels of blast-induced seismic waves are subjected to statutory compliance. More importantly, the superposition of the explosion-related energy and the rock strain energy due to high in situ stress is likely to exceed the rock energy storage limit. The excess energy causes rock spalling and is released in the form of violent rockbursts, threatening construction personnel and equipment safety, as well as cavern stability. Therefore, in order to ensure construction safety and quality in deep mining and excavation, it is urgent to develop the deep rock blasting theory, in which the influences of in situ stress on rock fragmentation and blasting seismic waves are considered. During the research in this study, several simplifications and assumptions are made, particularly in numerical modeling. For example, multiple-hole blasting is assumed to be a two-dimensional (2D) problem, and the rock mass is considered to be homogeneous without taking structural features into account. Notwithstanding its limitations, 2D modeling still reveals the role of in situ stress on the generation and attenuation of blasting seismic energy. In order to enrich the deep rock blasting theory, the vibration thresholds of rock damage for blasting under in situ stress need to be studied in the future.