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.
