Abstract
Drillability is influenced by many factors, including machine parameters and rock properties. The main machine parameters for drilling include rotational speed, thrust force, torque and flush pressure. The specific rock characteristics that affect penetration rate comprise uniaxial compressive strength (UCS), tensile strength, Young's modulus, hardness and brittleness. In this study, drilling rate index (DRI) is attempted to predict based on UCS and Brazilian tensile strength (BTS) of rocks. Simple and multiple regression analyses have been carried out to determine the best measure of the relation between DRI and two geomechanical properties. The DRI value is strongly related to the uniaxial compressive strength and indirect tensile strength. However, when the uniaxial compressive strength and tensile strength of rock are jointly considered, the correlation coefficient increases. The relationship between the geomechanical properties (UCS, BTS) and the DRI were determined using multiple regression analysis. Strong relationships were obtained from these analyses for the rock strength (UCS) above and below 100 MPa with the correlation coefficients 0.81 and 0.88 respectively.The results of the regression analyses show that for more precise prediction of DRI, rocks should be classified according to their strength.
Highlights
Drillability, one of the most important considerations in rock excavation, can be defined as the ease of drilling a rock mass at a certain time to a certain length with a drilling bit
After classifying the data according to uniaxial compressive strength (UCS) values, simple linear regression analysis was performed for UCS values, which are higher than 100 MPa, versus drilling rate index (DRI) and obtained a functional relation (Equation 4)
Drillability of a rock is affected by many different factors, such as drilling machine parameters and geotechnical characteristics of rock mass
Summary
Drillability, one of the most important considerations in rock excavation, can be defined as the ease of drilling a rock mass at a certain time to a certain length with a drilling bit. Yenice et al (2009a-b) correlated drilling rate index (DRI) with mechanical rock properties of marble samples and determined a strong relationship between DRI and UCS, tensile strength and specific destruction energy.
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