The Fifth International Symposium on Mine Safety Science and Engineering (ISMSSE2021)

38 / 2021-08-13 00:25:57

Hard Rock Breakage with Soundless Chemical Demolition Agents

Hard Rock,,Soundless Chemical Demolition Agents,Explosive-Free Method

Drilling & blasting with explosives is a widely used technique for rock fragmentation in the mining industry. It is the predominant method for mine development and ore production. However, the use of explosives is associated with rigorous safety and environmental constraints as blasting creates toxic fumes, ground vibrations and dust. This study focuses on Soundless Explosive-Free Chemical Demolition Agents (SCDA), a more environmentally friendly method for rock breakage and a potential replacement of explosives. SCDA are cementitious powdery substances with quicklime (CaO) as primary ingredient that expands during the moist curing process which results in high expansive pressure when the CaO hydration reaction occurs in a confined space. The use of SCDA as an explosive-free method is on the increase considering the need for non-violent and pollution-free methods for breaking rocks in densely populated areas. Presently, SCDA are used for rock fracturing in urban areas, rehabilitation projects, reinforced concrete cutting, and granite and marble quarrying and excavating. Due to the negative impact of blasting in underground mining operations, it is crucial to develop a safe and environmentally friendly method to fracture rock in underground mines which does not involve explosives. (Habib et el., 2019). However, the presence of high in-situ stress in the rock mass in underground mines could limit the initiation and propagation of rock fractures. While this is true, a few parameters can be varied and optimized and potentially overcome high in-situ stresses (Habib et al., 2019) (Dessouki et al., 2011).

This work is part of a multi-phase project which aims to develop a sound methodology for fragmenting rock in underground mines with SCDA. The most critical parameter for the development of this methodology is the pressure generated by the SCDA injected in the rock. Previous studies on SCDA generated pressure typically rely on steel pipes or hollow cylinder experiments. These experiments demonstrate the effect of temperature, borehole diameter, and host medium elasticity. However, it is not clear from the research if the steel pipe experiments can adequately replicate the behavior of SCDA in rock, given the rock’s different elasticity, heat exchange rate, and heat capacity, among other factors. In addition, a rock medium in the field will also be subjected to overburden, tectonic, and mining inducted stresses which may hinder SCDA pressure generation in the borehole (Musunuri et al.,2009). Finally, given that the borehole perimeter will yield in tension before the maximum theoretical pressure in steel is attained makes it difficult to estimate the maximum generated pressure in the rock.

The work presented here consists of two parts. First, a granite block experiment which investigates the effect of borehole size and uniaxial compression of the block on SCDA performance (Refer to Figure 1). Second, a numerical model is built to back analyze the pressure generated in the block, and then to examine the effect of the relative elasticity of the rock to the elasticity of the SCDA, and the role of far field stress on the resulting contact pressure between the SCDA and the rock. It is shown that contact pressure is significantly affected by the far-field stress, potentially hindering fracture formation.