Extraction of marble blocks by controlled blasting techniques - a case study

摘要

Blasting needs of marble is entirely different than conventional methods of blasting. The principle objective of blasting is to develop cracks in the rock so as to dislodge it from the surrounding rock without causing damage to it or to the remaining rock. Drilling is generally carried out by jackhammer but now a days compressed air operated hydraulic machines are coming into use. Conventional drill and blast techniques have proven to be disadvantageous and have low recovery of blockable marble. In addition to this micro cracks are developed in the remaining rock. Hence introduction of controlled fracture growth technique has important role in development of marble extraction techniques. For this purpose a field study was carried out in white marble belt of Rajsamand district, and pink marble belt of Udaipur district, Rajasthan. In this paper existing practices are analysed and some new practices introduced to reduce the cost of extraction and also to improve recovery of blockable marble by controlling fracture growth in desired direction. Field study showed that in D-cord splitting method, spacing between holes ranges from 0.08m to 0.0.30 whereas result of experimental trial using notched hole technique showed that hole spacing can be extended from 0.33m to 0.72m. On comparison it is clear that cracks in desired direction up to almost five times greater distance can be achieved by using prenotched blast hole technique as compared to D-cord splitting technique. By use of prenotched blast hole technique the extraction cost can be reduced up to half or one third. This shows that prenotched blast hole technique is beneficial to the marble stone mining.