JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ROCK FRAGMENTATION ENGINEERING Previous Question Paper (January/February - 2023 - R18)

Drill bits used in rock fragmentation are primarily classified based on their mechanism of rock penetration and the type of rock formation. The main types include:

1. Drag Bits (or Blade Bits): These cut rock through a scraping or shearing action, typically used in soft, unconsolidated formations.
2. Roller Cone Bits (or Tricone Bits): These utilize crushing and chipping actions via rotating cones with teeth or tungsten carbide inserts, suitable for a wide range of rock hardnesses.
3. Percussion Bits (or DTH Bits): These operate through impact energy delivered by a hammer, commonly used in hard rock drilling.
4. Diamond Bits (PDC or Impregnated): These use industrial diamonds to grind or shear rock, ideal for very hard or abrasive formations.

The rock breaking process involves the application of mechanical, thermal, or chemical energy to overcome the inherent strength of the rock mass, leading to fracture and fragmentation. The process typically follows three fundamental stages: stress wave propagation, crack initiation and propagation, and final fragmentation.

1. Stress Wave Propagation: Upon impact or explosive detonation, high-intensity compressive stress waves radiate from the source, causing localized deformation.
2. Crack Initiation and Propagation: As the compressive wave reflects off free surfaces or interacts with existing discontinuities, it converts into tensile stress. Since rock is significantly weaker in tension than in compression, tensile cracks initiate and propagate through the rock matrix.
3. Fragmentation: The coalescence of these cracks leads to the detachment of rock fragments from the main body, resulting in the desired size distribution of the broken material.