Critical Evaluation of Blast- Induced Structural Damage Criteria for Buildings around Metal Quarries at Thudugala, Kaluthara

Abstract

Quarrying can generate a number of on-site and off-site environmental effects as a result of blasting, excavation, crushing, screening, stockpiling and transport activities. Blasting is necessary for recovery of ore and production of aggregates in most underground and open cut mines, as well as in quarries. However, blasting can cause noise and ground vibration, which can have an impact upon nearby structures and people living close by. Hence, proper control of blasting practices is necessary to ensure both the safety of employees and the protection of the community from adverse effects. In Thudugala, in Kaluthura district, people those who are living close to quarries are highly subjected to these effects due to quarry blasting. In these circumstances, it was decided to conduct a research into the ground vibration impact in the area. Due to complexity of structures ranging from wattle-and-daub structures which do not have proper foundations to those built with good foundations, the applicability of single criteria of 5 mm/sec PPV level of vibration which is currently being used in Sri Lanka is inadequate. It is also noted that the above vibration criteria has been adopted in Sri Lanka without a proper theoretical foundation. In this research program, the propagation of cracks due to the blasting was assessed at the initial stage of the project. At the final stage, the optimum PPV values will have to be found for different types of structures by constructing them. In this area soil overburden is less. Therefore most of the structures have been constructed on rock. When blasting takes place, rock tends to vibrate and the intensity perceived is very high. Therefore crack propagation is high in these particular structures. It is also noticed that the cracks have further developed between the period between pre-blast crack survey and post-blast crack survey. It is due to large number of un-monitored blasts that have been conducted during that period. Therefore to solve this problem, it is recommended to carry out continuous monitoring of blasts.