Over thirty members and guests attended the second technical evening of the year on 12 March at the Mendip House Hotel, Frome. The talk entitled 'Alternatives to Blasting' was a joint presentation by Alan Matchett, Business Manager of Rammer, Metso Minerals (UK) Ltd, and David Glenn, MD of Huntsmans Quarries, based in the Cotswolds.

Alan began by outlining the advantages of using hydraulic hammers compared to conventional drilling and blasting, whilst acknowledging its productivity limitations. He described the two main uses of hammers in primary and secondary breaking with tonight's talk concentrating on the former. The key factors were the carrier/hammer combination and the characteristics of the rock.

Alan explained how crack propagation depends on the type and strength of the material and the length of pre-existing cracks. Rock will not break if the applied stress, in this instance hammer blow energy is too low. Taking into account the stiffness of the material, its density and the contact surface, one can predict fairly accurately if hammers can be usefully employed. The key factor is for the stress created by the hammer to be more than 60% of the rock strength.

Alan explained the importance of ensuring the correct hammer and tool combination is selected to match both the application and the carrier. He also emphasised that optimum bench heights should be between 2 - 5m.

David Glenn took over at this point to describe a case study based on his experience of primary breaking using hammers at Naunton Quarry. One of the key factors was a 'quick -hitch' system allowing the carrier to swop from the hammer to a claw or a bucket. He produced costings to justify the decision of using such a method, and concluded his talk by outlining the advantages it brought to his operation.

A question and answer session concluded a highly informative talk by two very knowledgeable speakers.