Rock blasting — peak particle velocity against distance

Abstract

The potential damage which could be induced by blasting in rock is normally evaluated with reference to the peak particle velocity (PPV). It is well-known that closer distances lead to higher PPV values. In some cases, due to muck handling logistics, the ramps forming the access result in different elevations across the different parts of a very deep excavation. Deep excavation access ramps and the completed base excavation ready to receive the concrete casting can be in close proximity to each other. In order to meet the construction schedule, the base slab has to be concreted while blasting works are still on-going at the access ramps. Hence, an optimised blasting programme is required to assure that construction progress is not unreasonably compromised, while vibration is kept under control. This paper first discusses the effectiveness of trenches to reduce vibration based on the findings reported in the literature, showing that this solution could be difficult to implement in practice because a very deep trench is required especially for hard rocks. Therefore, in most rock blasting programs, a more practical solution is to establish the distance beyond which PPV measurements are acceptable. This paper presents the data obtained from field measurements obtained from the excavation of an underground station in limestone rock. The vibrations were monitored from three permanent tunnel rings which are adjoining the boundaries of the underground station box, for which blasting was still on-going. An attempt is made to approximate the PPV with distance, and at the same time considering other factors such as the explosive charge weights in each delay, height of the free face, drill depth, drill spacing and number of holes.