ABSTRACT
Large diameter drill holes (250 mm) and wider blast geometry are implemented to achieve the targeted production and productivity from the opencast mine. Cost-effective operation, sometimes, leading to longer depth of blastholes (11-14 m) and wider blast geometry (5 × 6 m) poses a threat to sustainable survivability of structures located around the mine. The unacceptable consequences of blasting viz., ground vibration and air overpressure, are presently universally accepted as the pertinent parameters to cause blast-induced damage to structures. For blasting operation and safety of dwellings around the mine, various countries have enforced legislation to limit magnitude of vibration for different types of structures. However, for massive concrete or steel structures or for buried structures vis-à-vis pipelines, such conservative limits would serve no useful purpose and the limits would vary with site conditions. The dynamic behavior of structure and crack propagation in these structures would depend upon the magnitudes of strain developed in both in-plane and out-of-plane directions. Dynamic Soil-Structure Interaction (SSI) and the physical mechanism of load transfer to structure and its subsequent release is very important. The nature of interaction would vary with characteristics of wave propagated in soil, interaction between soil and buried structure and the gap between soil and buried structure. Furthermore, mathematically it is well established that for any fluid filled cylinder, the hoop stress developed on the inner wall is always higher than that developed on the outer cylinder wall. So, the thrust exerted due to blasting may compensate the differential stress
again divided into sub-blocks, the details of which are given in Table 1. The lumpy steel grey hematite and blue grey hematite within deposit no. 5 are excavated by drill and blast method with bench height 12 m. The geo-technical properties of the area under study are given in Table 2. Dumpers, 85t capacity, were used for transportation of ore. Blasting is carried out by using 250 mm diameter drill holes and loaded with SME and initiated with NONEL system of initiation. Staggered pattern of drilling, 6 m spacing and 5 m burden was practiced within this deposit.
