1. a. A pit with a straight ramp of 800m, with a gradient of 10%, supplies a ROM pad 1500m away via a level haul road all of loose gravel. Mining of a dipping ore body, with a specific weight of 2.5 t/m3, is required to be carried out at a rate of 10,000 tonnes/8 hour shift to feed the mill. Since truck speed is restricted to 50kmph, assume the average speed of a truck during a round trip is 45kmph, including reversing to load. Waste material of specific weight = 1.85 t/m3 is also to be mined, and deposited on a waste dump 200m from the pit. The waste dump already has a height of 10m, and an area of 100m x 60m from pre-stripped overburden. Excluding the overburden, the strip ratio is 1:4.5.
Other factors that are working assumptions are:
Availability of excavator 83%,
Swell factor of 30%
Bucket fill factor of 88%
Excavator cycle time 45 seconds
Rolling Resistance Factor (RRF) = 15 kg/t
Coefficient of Friction, µ = 0.25
Grade Resistance Factor = 20 kg/t
(i) Calculate required output by a single excavator appropriate to this production and select an appropriate machine.
(ii) Calculate cycle times for trucks.
(iii) Calculate number and size of trucks.
(iv) Ensure trucks are capable of carrying out this mining safely.
List and justify your assumptions.
Working Bench.
Consider a mining sequence on a working bench.
a. Define the width of a working bench with a neat sketch.
b. Design a working bench when a single shovel of 6.8m3 capacity details of which are supplied in the notes with single spotting is used:
Given:
design bench height =15m
shovel will move along one line parallel to the bench face
bench face angle 65°
parallel cut will be used with turn and back
single spotting
haulage by 50 tonne capacity truck
truck width = 5.5m
truck tyre rolling radius = 1.2 m
a safety berm is required
A Caterpillar 631 E tractor scraper has the following characteristics:
Maximum heaped volume = 19.6 Bm3
Maximum payload = 34,000 kg
The material hauled is earth with a density of 1825 kg/Bm3
Rolling resistance is 40 kg/t and operating conditions are average with a job efficiency of 45 min/hour.
The haul route comprises of the following sections:
Section 1 (200m) level-loading zone
Section 2 (1000m) 5% down grade
Section 3 (150m) level dumping zone
Section 4 (1000m) 5% up grade
Section 5 (50m) level turnaround area.
Estimate the machines production under these conditions using the travel time curves given in the Caterpillar Performance handbook.
4.
Design a spiral haul road system for the following surface mine:
pit consists of 8 benches
bench height is taken as 15m=H
crest-to-crest distance is 25m
bench face angle is 50°
a haul road having a width of 30m and 7% (=G%) gradient will be added to the outside of the pit wall
Answer the following:
a. Define stripping ratio and give three examples of the units it may be expressed in.
b. Define maximum stripping ratio.
c. Draw a section through an open pit showing the following:
i. Pit slope
ii. Bench slope
iii. Bench crest
iv. Pit floor
v. Bench toe
vi. Bench width
Draw a plan and cross-section of a dragline casting overburden from a new strip to an old strip in a coal mining stripping situation for a single seam and for a two seam operation
45) The average speed of an 18m3 scraper is 40 km/hr and its return speed uphill is 22 km/hr over a 400 m haul distance and a 450m return distance. Using a fixed time of 4 minutes, calculate the cycle time (min).