Drillability prediction: geological influences in hard rock drill and blast tunnelling

Abstract

Usually the main subject in preliminary site investigations prior to tunnelling projects is the prediction of tunnel stability. During the past years in conventional drill and blast tunnelling, problems have occurred also connected to the accurate prediction of drillability in hard rock. The drillability is not only decisive for the wear of tools and equipment but is -along with the drilling velocity -a standard factor for the progress of excavation works. The estimation of drillability in predicted rock conditions might bear an extensive risk of costs. Therefore, an improved prediction of drilling velocity and bit wear would be desireable. The drillability of a rock mass is determined by various geological and mechanical parameters. In this report some major correlations of specific rock properties and especially geological factors with measured bit wear and drilling velocity are shown.Drilling velocity is dependent on a lot of geological parameters: Those principal parameters include jointing of rock mass, orientation of schistosity (rock anisotropy), degree of interlocking of microstructures, porosity and quality of cementation of clastic rock, degree of hydrothermal decomposition and weathering of a rock mass. Drilling bit wear increases with the equivalent quartz content. The equivalent quartz content builds the main property for the content of wearrelevant minerals. For various groups of rock types different connections with the equivalent quartz content could be detected. In sandstone bit wear is also dependent on porosity or the quality of the cementation. Finally, an investigation program is submitted, which helps to improve the estimation of rock drillability in planning future tunnel projects.

Measures in the underground work method to determine the mathematical relations that predicts rock behaviour

“…The area under tension-deformation curve is the specific destruction work. Thuro [12] verified, by comparing the penetration velocities of different materials with their corresponding specific destruction work, in which the specific work is a parameter that presents a good correlation with the perforation velocity.…”

Fracture Propagation in Anisotropic Rock During Drilling and Cutting

“…Extensive field and laboratory studies have been performed to examine drilling or cutting progress and its correlation with foliation orientation and other rock properties [1], [2], [3], [4], [5], [6]. This research indicates that the drilling velocity as well as the disc cutter penetration is best orthogonal to foliation or schistosity and poorest parallel to it.…”

Rock Tale Drilling Prototype : An Innovative Design for Investigation of Rock Properties

“…uniaxial compressive strength, tensile strength, Young's modulus of elasticity, density, Poisson's ratio, etc., is very important for design and stability analysis of different structures, like, pillars, openings and slopes [14,17]. These properties are also important for optimizing many mining operations, such as, blasting and mechanical excavation of rocks and minerals.…”