The effect of certain chemical solutions on some material properties of clay bearing rocks

摘要

The addition of water to rock is known to change its material properties. These changes can be both beneficial as well as detrimental in terms of rock strength, stability of rock excavations and the process of mechanical rock excavation. This paper presents the results of a study to exam what effect certain chemical solutions have in ameliorating the changes in material properties brought about after clay bearing rock is exposed to water. Two rock samples were used in the study sourced from coal mines in eastern Australia. The clay mineral in each sample was determined to be nacrite. The chemical solutions used in this study included potassium chloride and copper sulphate. A range of material property tests was undertaken including strength, hardness, weatherability and machine cuttability to assess any difference between rock immersed in water and in the chemical solutions. The study confirmed earlier findings of a decrease in rock strength and cutting properties after immersion of clay bearing rock inwater. Immersion in the chemical solution howeverwas found to neutralise the deterioration in property values achieving similar levels to that attained with dry untreated rock samples. The results also suggest there is a time dependency factor in the reaction between rock and chemical solution as the results differed with the period of immersion. Analysis of the solution before and after immersion confirmed a chemical exchange occurred with a reduction in the concentration of the potassium and copper cations substituted by cations of other elements leached from the clay and/or other minerals in the rock.