Establishing Ground Vibration Threshold Level for Open Pit Mining Environment - A Case Study

To assess the impact of blasting activities on building structures in open pit mining districts in Ghana a study was carried out in Prestea, a township very close to the perimeter of the Plant North pit of the Bogoso Gold Ltd (now Golden Star Resources Bogoso/Prestea Mines), in the Western Region of Ghana. It was observed during the study that the quality of most 'residential building structures within the Prestea township and its environs were generally sub-standard. Most of the houses were in a deplorable state of disrepair with their conditions already triggering failure. Again, it was noted that no records were available to ascertain the structural state of the buildings prior to the commencement of blasting activities at the pit, necessitating the need to carry out a baseline study of buildings in nearby Himan townships for comparative analysis. It was also observed that even though management had selected 12 mm/s as its threshold for its operations in the pits only 6% of the over 542 blasts monitored over a two and half year period had ground vibration values in excess of 1.5 mm/s, with a maximum recorded value of 8 mm/s. It is recommended that management should not adopt ground vibration levels in excess of 2 mm/s for their pit operations because of the poor infrastructure within the surrounding communities. Even though this level can increase drilling and blasting costs considerably, it is considered a better option than expensive lawsuits in the likely event of any further damages that may be caused to building structures in the township.