Mapping of Blast-induced Fractures in Rock

摘要

The measurement of blast-induced fractures remains a key objective in all rock fragmentation research. Quantification of these fractures is not only important in routine blasting operations (e. g. , wall control, fragment size control, prevention of rock damage, etc.), but it is also one of the most important parameters available in modeling of the blasting process for prediction of blast results. Consequently, the study of blast-induced fractures has been of considerable interest for several decades. Because of the difficulty encountered in measuring the characteristics of rock fractures, much of the past work has been focused on measurement in laboratory scale studies using plastic and rock-like materials. The paper presents a systematic study of quantification of blast-induced fractures in three distinctly different rock types: a diorite host rock, and two types of ore, a titanomagnetite, and a massive nickel-bearing sulfide. Fracture patterns and their density as a function of the explosive load in selected core samples were characterized. Over 100 cores, each 100 mm in diameter and 130 mm in height, were cored from representative blocks of rocks. A lathe was used to diamond-drill centralized holes of two diameters, 6 mm and 10mm. The explosive load, in the form of a detonating cord, was placed along the central hole in each core sample. The strength of the detonating cord was either 1.1g/m or 3.2g/ m. The cord was adequately centralized in the charge hole. Three decoupling conditions were used air, water, and clay. Detailed petrography, strength, and elastic properties were also determined for the test samples prior to the blast. The fractures were produced with 1.1g/m and 3.2g/m cords for air, water, and clay coupling. The paper describes a novel and convenient method of characterizing the resulting cracks and their spatial distribution. These fractures are further distinguished in terms of those representing the crushed zone and those propagating beyond. Detailed petrography of the test samples were also performed after the blast, as well as fragment counts. The data presented here provides detailed information on the nature of crack initiation and propagation for a variety of blast loadings under controlled laboratory conditions, and should therefore provide valuable guidelines to the researchers as well as to the practitioners in blasting.