Fragment size distribution and its probability distribution in blasted rock mass in a natural stone quarry

Abstract

The key objectives in the drilling and blasting design is the determination of a powder factor, explosive weight and distribution in rock mass, as well as some other parameters required to ensure the wanted quality of rock fragmentation by blasting. These objectives have different complexities but their common feature is the probabilistic nature of fragmentation results. An integral distribution function can provide an insight into the probability of yield of certain fragment sizes. This article describes fragment size estimation of blasted rock mass at Mikashevichi granite quarry. Mikashevichi quarry has 10 producing benches mostly 12 m high and uses the blasting method of quarrying. The quarry rock mass is watered, has a hardness factor of 15–20 on Protodyakonov’s scale and belongs to jointing categories III and IV. The multiple-row and short-delay blasting uses nonelectric detonators Iskra manufactured in Russia. The explosive is nitronite E-70. The continuous explosive charges are installed in polypropylene hoses placed in jointed rock mass. The workability of different models of fragment size distribution in rock mass after blasting in evaluation of blasting results in a natural stone quarry is analyzed. The theoretical and applied research and estimation of fragment sizes after blasting in different geological conditions uses various theoretical models, including the most popular gamma-distribution (Pearson type III distribution), Weibull distribution and log-normal distribution. The comparison of the theoretical distributions and in-situ estimates of fragment sizes in blasted rock mass using Pearson’s chi-squared test shows that the best model of fragment size distribution in blasted rock mass for a natural stone quarry is the Weibull distribution.