This paper describes model-scale bench blasts on mortar blocks with distorted drill hole patterns, done in 2013-2014 at the Montanuniversitaet Leoben. The main aim of the project is to see if the fragmentation from and the crack development behind blasts with and without drillhole deviations differ significantly.
The dimensions of the test blocks were 660×280×210 mm (L×W×H). They were mounted inside a yoke that lets the blast waves escape. Three rows in each block were shot row by row with a nominal pattern of B×S = 70×95 mm. The same nominal delay, 73 μs between holes was used throughout. Apart from reference blocks, blocks with holes with stochastic collar position errors (variations in burden and in burden and spacing but constant row volume) and systematically shifted collar positions were shot (blasts with staggered pattern).
Apart from the sieving analysis, the remaining bench faces have been measured with a stereo-photogrammetric method and linear roughness profiles for each row have been constructed. Sawing slabs from block remains after the 3rd row and use of dye penetrant has allowed the construction of AutoCAD models of the internal blast damage.
Preliminary analysis indicates that none of the changes in bore hole collaring have had a significant effect on the sieving curve (median). The sieving results confirm earlier findings though that the fragmentation gets finer with the number of rows shot, implying that blast damage from earlier rows has an influence on the blasting results.
The manuscript will include an updated fragmentation analysis and ongoing work to correlate the roughness and internal damage data to the fragmentation results.