Investigation S20 brittleness index of limestone and effective parameters on it at dry and saturated states

Brittleness is an important problem in rock boring. So far, various methods have been introduced for determining rock brittleness but no method has yet been standard to measure it. In this paper, an empirical study was done to provide a reliable method for predicting the S20 brittleness index. The S20 brittleness test was done for 35 limestone blocks pick out from different parts of Iran in dry and saturated state. In addition, physical (dry density, porosity, electrical resistivity, Schmidt rebound hardness number and water absorption), mechanical (uniaxial comprehensive strength and point load index) and dynamical properties (P and S wave velocity) was measured. Finally, the classification of the samples was done based on the studying of petrography and mineralogy and statistical studies were done for each class. According to the results, predicting S20 based on the provided classification has a high degree of certainty. In addition, by studying the brittleness of the samples in dry and saturated state, it was determined that the presence of Montmorillonite clay mineral causes a decrease of brittleness and the presence of intergranular micro cracks and high porosity leads to an increase brittleness in the saturation state relative to dry state.