ABSTRACT:

A new non-explosive method to excavate hard rock and concrete has been developed, tested and demonstrated in a mining environment. The method uses high-pressure foam to initiate, pressurize and propagate controlled fracturing in rock. The foam is injected to the boRom of a relatively shallow pre-drilled hole in the rock or concrete to be broken by means of a barrel incorporating a hole boRom sealing method. The high viscosity of the foam (as compared to a gas) combined with its stored energy characteristics (as compared to a liquid) result in consistent and controlled breakage. The pressures required to fracture and excavate rock are significantly less than required in methods based upon the use of small explosive or propellant charges. Airblast and flyrock are reduced to very benign levels, allowing the method to be applied in a continuous manner and to be used in urban and other sensitive environments.

INTRODUCTION

For over a century explosive blasting has been the primary means used for the excavation of hard rock. Conventional blasting is limited in that it requires special precautions due to the use of explosives and can cause excessive damage to the rock or concrete being broken. In recent years several small-scale methods employing small explosive or propellant charges or specialized mechanical and hydraulic loading means have been proposed as alternatives to conventional blasting. The smaller-scale specialized techniques, while finding many niche applications, have been limited in their ability to break harder rocks or in having undesirable operating characteristics. For example, the small-charge explosive and propellant techniques still generate significant airblast, flyrock and toxic fumes.

Efforts to develop alternatives to conventional explosive excavation have included water jets, firing high-velocity slugs of water into pre-drilled holes, rapidly pressurizing pre-drilled holes with water or propellant generated gases, mechanically loading pre-drilled holes with specialized spliRers, various mechanical impact devices, and a broad range of improvements on mechanical curers. Each of these methods may be evaluated in terms of specific energy (the energy required to excavate or demolish a unit volume of material), their working environment, their complexity, their compatibility with other excavation operations, and their suitability for automation. A review of the positive and negative aspects of these methods indicates the directions that efforts to develop improved methods might take.

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