Surface Blasting (1 Question, 6 Marks): 4. In a quarry, rock has an average uniaxial compressive strength of 110 MPa and is excavated in 12 m high benches. Drilling is carried out with a rotary percussive top hammer rig and a diameter of 102 mm. The explosives used are composed of cartridged slurry of 89 mm in diameter as the bottom charge and bulk ANFO as the column charge with respective densities of 1.2 and 0.8 g/cm'. Note that the blastholes are vertical. a) Determine the drilling pattern, and the lengths of bottom and column charges. (2 marks) b) Determine the powder factor. (2 marks) c) Determine the number of blastholes required for a corner blast with a length of 29 m and a width of 11.5 m, and calculate the specific drilling for the blast. (2 marks) Note: In your calculations, assume that the weight of the column charge compresses the bottom charge, and therefore the average diameter of the bottom charge becomes 10% more than its nominal value. Design Parameter - 3.57 Uniaxial Compressive Strength (MPa) Low (180) 39D 37D 35D 33D 47D 51D 43D 38D 34D 35D 32D 30D 12D 12D 10D 11D 40D 46D 30D 35D Burden - B Spacing-S Stemming - T Subdrilling - J Bottom charge length - If 4.79 3 26 Surface Blasting (1 Question, 6 Marks): 4. In a quarry, rock has an average uniaxial compressive strength of 110 MPa and is excavated in 12 m high benches. Drilling is carried out with a rotary percussive top hammer rig and a diameter of 102 mm. The explosives used are composed of cartridged slurry of 89 mm in diameter as the bottom charge and bulk ANFO as the column charge with respective densities of 1.2 and 0.8 g/cm'. Note that the blastholes are vertical. a) Determine the drilling pattern, and the lengths of bottom and column charges. (2 marks) b) Determine the powder factor. (2 marks) c) Determine the number of blastholes required for a corner blast with a length of 29 m and a width of 11.5 m, and calculate the specific drilling for the blast. (2 marks) Note: In your calculations, assume that the weight of the column charge compresses the bottom charge, and therefore the average diameter of the bottom charge becomes 10% more than its nominal value. Design Parameter - 3.57 Uniaxial Compressive Strength (MPa) Low (180) 39D 37D 35D 33D 47D 51D 43D 38D 34D 35D 32D 30D 12D 12D 10D 11D 40D 46D 30D 35D Burden - B Spacing-S Stemming - T Subdrilling - J Bottom charge length - If 4.79 3 26