6 Site Preparation Tutorial
.pdf
School
Curtin University**We aren't endorsed by this school
Course
DEPARTMENT OF CONSTRUCTION MANAGEMENT 314896
Subject
Mechanical Engineering
Date
Jan 14, 2025
Pages
3
Uploaded by ColonelUniverseChinchilla36
1)A quarry is planned to be working on a rock of Dolerite with an estimated productivityofabout 150,000 tonnes per month. What is the estimated requirement of explosives per month?Assume that the specific gravity of Dolerite is 2.6 and the powder factor for Dolerite is 0.7kg/m3.Solution: Powder factor or specific charge or blasting ratio: This is the ratio between the mass of explosives required to break a given quantity of rock and is normally expressed in kg/m3or kg/tonne. Volume of dolerite to be produced: 150000/2.6= 57692 m3Explosive required = 57692x0.7= 40384 kg 2a) A new shale deposit is to be worked by controlled blasting with 14m benches using 250mm diameter blast holes. The contractor has decided to use bulk ANFO with emulsion cartridges as primer. What burden should he adopt and how much explosive should he use per blasthole? Assume that the overall density of compacted ANFO and the primer is 0.65g/cm3. Assume also that the drilled blast holes are in a staggered pattern forming equilateral triangles.
2b) Suppose that in the mining operation as per part (a), the blast hole diameter is increased to 350mm and an emulsion explosive is to be used. Assume that the existing energy from the existing ANFO is 3.8kJ/g. The effective in-hole density, charge density and available energy of the explosive are 0.80g/cm3, 30kg/m and 3.4kJ/g. What burden should the contractor adopt and how much explosive should he use per blast hole? Solution: 3/110012=QSAZTQ = mass of 8 hole diameters = 8 x 0.25 x (charge density per unit of hole length) = 8 x 0.25 x (0.65 x π x 0.252/4) = 8 x 0.25 x 31.9= 63.8 kg Z= 1.5 (controlled blasting) A= 9 (shale is the hardest in the category) S =1 (ANFO is used) T= 8m U = 10D U= 2.5m = B/3 B= 7.5m S=1.15B S= 8.6m Blast hole length = H+U = 14 + 2.5 = 16.5m Charge length = 16.5-8 = 8.5m Amount of explosives in one blasthole: 8.5 x 31.9 = 271.1kg b) Scaling factor:16.225035065..08.380.04.322=××==aDbDaaEbbEKρρArea of influence: Ab=K2/3xAaAb= K2/3x Bax SaAb= 2.162/3x 7.5 x 8.6 = 107.72m2Ab=1.15Bb2Bb=9.7m S= 11.1m New stemming length: aTKbT×=3/1Tb= 10.3mNew subdrill: U = 10D = 3.5m New Blasthole length: 14 + 3.5 =17.5m
New charge length: 17.5 – 10.3 = 7.2m New mass per hole: 7.2 x 30 = 216kg 3)A reinforced precast concrete pile (450mm x 450mm) in cross section is driven by a drophammer. Given:• Maximum rated hammer energy = 25 kN.m• Hammer efficiency = 0.65• Weight of ram = 70kN• Pile length= 12m• Number of blows for last mm of penetration = 0.3Estimate the allowable pile capacity using a Factor of Safety of 5 using the EN formula.Solution: PWRWPWnRWCShREWuQ+++=2Weight of pile: WP = 0.45m x 0.45m x 12m x 4500kg/m3 = 109.4 kN Weight of ram. WR = 70kN n= 0.4 (recommended range in the lecture notes) WRh= max rated hammer energy= 25kNm S=1/0.3 =3.33 C=25.4 E= 0.7 (recommended range in the lecture notes) Qu= 0.297 N Qallowed=0.06 kN We know that this answer is not practical!