Investigation of blast fragmentation models in sandstone quarries

Drill and blast method makes it possible to excavate very hard rock economically. The method is used for not only produce raw material but also excavating long tunnels through hard rock, where digging is not possible. Blasting is the critical step in the rock-fragmentation process. Maximum profitability depends largely on success of blasting operation. Drilling and blasting are the first operations performed in any hard-rock quarry operation. Therefore, the results of blasting operation will affect downstream processes, such as loading, hauling and crushing, than any other processing operation. Efficient blast designs combined with the proper choice of explosive can produce better fragmentation with associated lower operating costs compared to blast designs and explosives used under adverse conditions. The efficient use of explosives, and proper borehole diameter selection, are the keys of a successful blasting program.. ANFO, emulsion and heavy ANFO blends are the common explosives used in quarries. ANFO remains one of the most commonly used products in quarry blasting Selection of the explosive is based on the quarry condition and rock mass characteristics which vary widely by region. It is a mixture of ammonium nitrate (94,5%) and fuel oil (%5,5). Ammonium nitrate is fully water soluble and therefore it is only usable in completely dry holes, or in holes that can be pumped dry and then lined. Emulsion and heavy ANFO are much better water resistant; hence these explosives must be preferred in such conditions that exists water. Detonators are used to initiate the blast. These may be electronic, electric or non-electric. Nowadays, most of the mines use delay detonators. Delay detonators are available as inhole detonator or surface connector. It is very important to use delay detonators to prevent air blast and ground vibrations. There is an important aspect of blasting on fragmentation; which is the size distribution of blasted fragments. Rock fragmentation is often assessed qualitatively, by visual inspection, as good or poor. It can also be measured quantitatively by image analysis techniques. Image analysis provide much better results than previous techniques and not intrusive to production processes. The size of fragments is the "seen" part of blasting results. It is very important in crushing as it effects production and downtime. Oversize fragmentation will reduce primary crusher throughput. Fragment material will lead to more downtime for clearing crusher bridging and plugging. Poor fragmentation will increase the feeding amount of secondary and tertiary crushing stages, if used, because there will be less undersize that can be split off to bypass these stages. This will affect productivity and energy consumption. It is highly probable that the blasted size distribution introduced to the primary crusher will affect the feed size distributions throughout the crushing stages. Blast fragmentation models play an important role in modern mining operations. Today, blast fragmentation is optimized not only for material haulage but also for comminuting and mineral processing as well. Various models have been put forward over the years, attempting to predict the size distribution resulting from particular blast designs. The engineering models consider four main factors; explosive properties, rock properties, blast design parameters and actual bench geometry. Three of them are independent variables that are engineers can choose (the most efficient explosive type, drilling pattern and bench geometry). Controllable parameters are hole diameter, burden, spacing, hole depth, type of explosive, detonator system and etc. Geology, joints, rock mess characteristics and presence of water are the non-controllable variables. The fragmentation must be optimal to obtain the lowest costs for the whole production process. Predictions and analyses of rock fragmentation have a vital importance on economy of quarries. Efficiency of blasting depends on fragmentation, overbreak, muckpile profile and displacement, vibration, airblast, flyrock and damage to wall or slope stability. Besides all these factors, haulage method must be considered when designing the blasting pattern. In this thesis, fragmentation is the key factor to assess the efficiency of blasting. Kuznetsov equation is the very first formula that makes it possible to calculate average fragment size using blast design parameters. In 1983, Cunningham contributes the approach with merging Kuznetsov and Rosin-Rammler functions and gave a new name, Kuz-Ram equation. Rock factor is key to define of rock mass characteristics, which is improved by Lilly in 1986. A new model, KCO fragmentation model, was introduced in 2005. All these approaches let engineers to predict average fragment size using blast design parameters and rock mass properties. In this thesis, blasting data from seventeen blasts at three different quarries were analyzed. As a first step, image analysis software was used to determine particle size distribution of muckpiles. Additionally, KuzRam and KCO fragmentation model compared to the results of the image analysis technique. The efficiency of KuzRam and KCO models were investigated and the important points to be considered while using fragmentation models were explained. It is required to measure blast design parameters preciously to calculate average fragment size and draw size distribution curve correctly with KuzRam and KCO models. In field work, these parameters were measured with ruler. Also, scales should not be located very close or very away from each other to avoid errors about image analysis software. In all blasting operations, the borehole diameter is 89 mm. and each blasting pattern has different burden, spacing and stemming length. The average spacing between adjacent hole is 2.6 m., bench height is vary from 6.5 m . to 15 m. and burden is 1.8 m. and 2.6 m.. Kuznetsov equation predicts average fragment size properly, especially 1, 4, 7, 9, 11, 13 and 15. blasts. There is 2.03 cm. absolute differences between estimated and measured average fragment sizes. Uniformity index is calculated as 1.42 with KuzRam model and 1.50 with WipFrag image analysis software. Also, there is no wide difference between measured and calculated characteristic sizes. The relationship between X50 ─ Yb, X50 ─ S, X50 ─ B and X50 ─ Pf investigated and as a result it is found that there is a high correlation between X50 ─ B, X50 ─ Pf. Consequently, KuzRam and KCO models can be used to determine fragment size distribution in quarries, Cendere region, İstanbul. Especially in blasts 1, 9, 15 and 17, the result of fragmentation models are coherent with the results of WipFrag image analysis software. Burden, spacing and charge height are three of the most important parameters that can affect the efficiency of blast. In quarries some bench faces are irregular, this faulty geometry of benches can cause decrease or increase in burden length. For that reason, engineers should mark the location of holes cautiously considering bench faces and etc. Lighting is one of the most important factors for photographs captured for fragmentation analysis software. Lighting determines shadow formation. In an ideal image, particles are clearly delineated by soft shadows. If shadows are too strong (dark), analysis suffers. Shadows will fall to one side of the material, and in the absence of fill light may be dark enough to obscure material or may be mistaken for particles. If shadows are absent, analysis suffers. It is possible to calibrate the KuzRam and KCO fragmentation models by the data obtained by image analysis. Engineers can predict blast fragmentation using the fragmentation models and they may change blast design parameters before blasting operation. KCO and KuzRam models were applied in Cendere region quarries successfully. It is believed that these models can be applied in other quarries in İstanbul.