Sunday, June 20, 2010

Efficient Haul Roads

A Design and Maintenance Guide

Haulroad Design and Maintenance


Major Factors in Haul Road Design



Many factors need to be considered in the design and maintenance of efficient haul roads. Unfortunately there is no single simple rule to follow, however this manual will highlight areas of focus and possible solutions.

“A haul road begins at the load face and ends at the tip head”

Road Geometry

The following criteria needs to be taken into consideration in haul road design:
Equipment size and performance capabilities
a. Safety
b. Topography
c. Mine Life
d. Rolling Resistance
e. Future Plans

Haul Road Design



a. Haul road geometry should provide for the smooth and cost-efficient operation of a haulage truck fleet at the designed operating speed and payload.
b. The road construction should be such that the above criteria is maintained throughout normal mining conditions

Road Width



a. One way - 3 truck widths.
b. Two-way straights - 3.5 truck widths.
c. Two way corners - 4 truck widths.



Grade

a. Maintain smooth grade.
b. Maintain consistent percentage.





Grade


Haul roads should be of constant grade with minimum transitions to ensure optimum performance. The selection of grade should be based on the capabilities of the machine and the expected rolling resistance

Rolling Resistance


For Off-Highway Trucks running radial-ply tyres, assume a minimum RR (rolling resistance) of:

a. Hard, well-maintained road . . . . . . . 1.5%
b. Well-maintained road with flex . . . . . . 3%
c. 25 mm/1” tyre penetration . . . . . . . . .4%
d. 50 mm/2” tyre penetration . . . . . . . . .5%
e. 100 mm/4” tyre penetration . . . . . . . .8%
f. 200 mm/8” tyre penetration . . . . . . .14%

In practice, a 5% increase in rolling resistance can result in up to a 10% decrease in production and a 35% increase in production costs.

Haul Road Alignment:

Geometric elements for operation at normal speeds
Equipment operator sees ahead a distance equal to or greater than the stopping distance.



a. Speed
b. Weight
c. Slope



Design criteria for vertical and horizontal alignment.

Sight distance
Distance from driver’s eye to hazard must equal or exceed required stopping distance.

Vertical. curve crests
Horizontal. curves

Grades
Flatter grades incur greater costs.
Traditional optimum 7%-9%
Reasonable to accept 10% max. sustained

What do you think grades should be?

Horizontal and Vertical Alignment



Design corners and crests that allow excellent visibility at normal travel speeds.
Use worst-case scenarios.

Corners


a. Use maximum practical radii.
b. Employ super elevation for higher speed operations.
c. Use super elevation >10% with caution.

Vertical Curves



To maximise safe working, corners and crests must be designed such that machine operators are capable of seeing and avoiding hazards when travelling at normal operating speeds.

Super elevation of Curves

Negotiating curves can generate high lateral tyre forces. These forces contribute to high tyre wear and ply separation. Super elevating the curve helps eliminate these forces. The amount of superelevation depends on the curve’s radius and the speed at which it is negotiated. The following table is a guide for providing the superelevation necessary to eliminate lateral forces.



Super elevated turns present a danger when slippery. For this reason, curves super elevated over 10% should be used with caution. Unless the proper speed is maintained, matching the elevation of the curve, a vehicle may slide off of the lower edge of the roadway. Super elevated curves should be maintained in good tractive conditions.





Super Elevation Run out



“Correctly designed transitions properly load truck frame, suspension and tyres, as well as prevent spillage.”

Constant Crossfall

To facilitate effective drainage of a haul road, it is necessary to elevate one side of the haul road from the opposite side.

Recommended Crossfall = 1% - 4%

The limiting criteria for maximum crossfall, is as the slope increases, so does the potential for uneven tyre / bearing wear.



One-Way Crossfall





Two-Way Crossfall



Cross-slope


a. Flats
Apply minimum slope to maintain drainage
Use constant crossfall when possible
b. Grades
Minimal cross-slope required

Bench Width



Truck must clear loader under full acceleration.
Minimum width = machine turning radius + width of safety berm.


Drainage and Safety Berms



Drainage system - sized to accommodate maximum rainfall.
Berm size - at least one-half wheel height.

Drainage



Any haul road design is only as good as the drainage capabilities of the design.
The key to maintaining a haul road in the best structural condition, is to limit the exposure of the surface water and to remove any surface water quickly.

If the construction of complex drainage is not feasible or economic, the simplest way to reduce water damage to a haul road is to elevate the haul road above the lay of the land.

Safety Berms (Windrows)



Berms are an effective way of preventing vehicles from straying into dangerous areas. They can be placed at intersections to control traffic and on the edges of steep slide slopes.
A berm should be a minimum ½ wheel height of the largest wheeled machine on site.

Pavement Cross Sections

A well structured and drained haul road is critical to the efficient operation of haul trucks.
The road base geometry is dependent on the capacity of the truck and the materials available.
Not all mines have the same base material properties….. But as long as the CBR (Californian Bearing Ratio) value is know, the depth of the base can easily be determined for a particular load.
The attached table, demonstrates a typical pavement cross section for the range of Cat Mining Trucks.

Summary:

a. Haulage way width
b. Max., sustained grades
c. Rolling Resistances
d. Stopping distance
e. Sight distance
f. Vertical curves
g. Super elevation rate, run out
h. Sub base
i. Surface materials
j. Sharp curves
k. Combined horizontal, vertical alignment
l. Cross slope
m. Typical cross sections

Thursday, June 17, 2010

Electric Hazards

Safety and Accident Prevention

1. Static Electricity
a. Can build up on equipment or people
b. Use anti-static footwear
c. Use anti-static hoses

Static Charge
a. Type of clothing
* Synthetic is bad
b. Conductivity of footwear
* Rubber soles are bad
c. Dryness of skin
* Dry skin is bad
d. Humidity of air
* Low humidity (<60%) is bad Static and ANFO

Pneumatically conveyed ANFO can build up a static charge if the humidity of the compressed air is low

2. Stray Currents
a. Faulty or damaged cable insulation
b. Conductive ground
c. Wet conditions

Minimising Stray Currents
a. Use a low resistance Earth
b. Electrically bond all rails, cables, pipes, etc.
c. Check cable insulation
d. Insulate firing lines and detonating cables from any stray currents and earths
e. Short and insulate all detonator wires until contact has to be made

3. Lightning
a. Use a lightning monitoring system
b. Devise a standard lightning warning signal
c. Stop blasting operations and evacuate the area when a storm is approaching

4. Radio Frequency Energy
Detonator wires can act as aerials and generate a current from sufficient radio energy
a. No walkie talkies
b. No cell phones
c. No mobile radios
d. All of these must be switched off, if not barred, from the blast area

General Recommendations
a. Leave detonators in their original containers, coiled and shorted, until required
b. Earth yourself and any equipment before coming into contact with explosives
c. Strive for a blast area free of stray currents


Monday, June 14, 2010

Stockpile

…. an accumulation of ore (!!) set aside for later processing ….

1. Use to top up the processing stream if the mine is “mine limited”
2. Use to manage grade if mine is “mill limited”
3. Use to extend the life of mine (plant)

What Stockpile?



Do You Need a Stockpile(s)

Definitely yes if:
1. The mined orebody has high grade variability
2. You want to optimize grade cut-offs
To improve cash flow, ROR
3. You are selling / providing a variety of products

Benefits

1. Allow blending so:
a. The mill is supplied with uniform grade ore
b. No preparation/processing is required
2. Provide buffer capacity to smooth out production variations
3. Facilitate higher overall value recovery
a. Easier cut-off grade management
b. Maximize ore recovery

All Roses Have Prickles …

1. Rehandling is involved; it costs money
2. Space needs to be available to accommodate stockpiles
More stockpiles = more needed space
3. Stockpiled material may deteriorate
Recovery drops?
4. Additional expense related to logistics and stockpile management

Material Flow With Stockpiles



How Many Stockpiles?

1. The more, the better
a. Grade control
b. Uniformity of mill feed
c. Product quality
2. Stockpile grades not to overlap!
3. The more, the worse
a. Space is needed; may be at premium!
b. Logistics and material handling costs

Minimum Stockpile Grade

For one element:

Rehandling Cost + Processing Cost
-------------------------------------
SR x PR x Price

SR – Stockpile recovery
PR – Processing recovery
Price – Unit price of product

Using A Stockpile After Lane, 1988

….calculate mine cut-off assigning no value to waste and feed the stockpile material to mill when, and as long as, the result is an increase in the cash flow ….

… it might be better to draw lower grade material from stockpile when the price is low in order to preserve the higher grade material for the expected improvement in price…..

Optimizing Grade With Stockpiles Whittle’s Opti-Cut

1. When the project is “mine limited”, uses stockpile material to top up processing stream to improve cash flow
2. Process stockpile material after ore is mined out to provide additional cash flow

More of Opti-Cut


Stockpile vs. Leach Pile

1. Leach pile
a. No rehandling cost
b. No stockpile management cost
c. Usually earlier return on money spent

2. Stockpile
a. Grade management
b. Better mill / mine capacity utilization
c. Possible savings on processing cost

Binomial

How Big A Fleet Do I Need ?



How Many Trucks / Shovels?

1. Sufficient number to secure the required production, or
2. Sufficient number to meet the blending requirements, or
3. Sufficient number to provide required production rate with desired probability, or
4. Sufficient number to meet company objectives (cost, reliability, other)

Example: Binomial Distribution

Assume the shovel availability is 80%. Then the
probability that the shovel is available is:

(P) is 0.80 or 80%

The probability the shovel is not available:

(Q) is 0.20 or 20%

i.e. P = 0.80, Q = 0.20, and P + Q = 1.00

If there is more than one shovel in the fleet, say n units, then the probabilities of shovels being available and not available are given by the Binomial Distribution

Polynomial ------> (P + Q)n

Binomial Distribution

(P + Q)n
Let’s assume: P = 0.8, Q = 0.2
For two units: n = 2
(P + Q)n becomes (0.8 + 0.2)2

Worked out:
(0.8 + 0.2)2 = 0.64 + 0.32 + 0.04

Meaning there is:
1st: 64% probability that all two units are available
2nd: 32% prob. that exactly one units are available
3rd: 4% prob. that no units is available
Another conclusion: for 96% of time at least one unit is available
(meaning: either one or two units are available)

For three units: n = 3
(P + Q)n becomes (0.8 + 0.2)3

Worked out:
(0.8)3 + [3 x (0.8)3 x 0.2] + [3 x 0.8 x (0.2)2 ] + (0.2)3
Or (in “round figures”):
0.512 + 0.384 + 0.096 + 0.008

Meaning that there is:
1. 51.2% prob. that all three units are available
2. 38.4% prob. That exactly two units are available
3. 9.6% prob. That exactly one unit is available
4. 0.8% prob. That no units are available

Use polynomial formulas (math handbook?) to define probability distribution for larger fleets!

Probability That Exact No. of Trucks is available for a Fleet of 10 units & Availability of 70%



Cumulative Probability of Available Trucks for a Fleet of 10 and the Availability of 70%





How Does Availability Help?



Fleet Management

1. Define objectives
a. Minimize number of units?
b. Maximize production?
c. Other?
2. Equipment match
a. Undertruck?
b. Overtruck?
3. Unit assignments: optimize

Support Equipment

1. Improves working conditions
2. Rolling resistance
3. Drainage, spillage
4. Bench & dump leveling
5. Allows the main equipment:
6. To be used for primary production
7. To fully utilize available time





A Motor Grader Articulation; Crab Movement



How Big a Blade?



FLEET DISPATCH

How to get the best out of your fleet?

Basics

To efficiently control the fleet performance we need to:

1. Know our objectives
a. max. production? Minimize fleet size? Other?
2. Know the status of the equipment
a. what is it doing at any given moment
3. Know the location of the equipment
a. where is it in any given moment?
4. Have the ability to process this information to define equipment assignments

Note: all this in real time!!!

“Need to know”

1. Current operating status;
a. Truck operational: haul, dump, return, queue, etc.
b. Truck down: refuel, m-ce, stand-by, waiting parts, etc.
2. Current location
3. Information which can be derived:
a. detailed cycle time, operating & down times, production by product and quantity, availability and utilization, production by source or destination

Monitoring The Status

1. Electronic & electromechanical sensors
speed, payload, brake application, tray position, engine status, transmission selection, etc

2. Mobile data terminals
terminals located in shovels, trucks, other equipment

Position Monitoring

1. Local positioning systems
a. beacon transmitters / beacon receivers
b. simple, cost efficient, owned & configurable
c. zones max 75 m, set-up & maintenance req’d

2. Global positioning systems
a. infinite monitoring, no set-up or m-ce
b. dependence on US military, deep pit problems



Truck Dispatch Systems

From:
manual input, report generation only

Through automated data acquisition & simple dispatch calculations

To:
Fully automated data acquisition and assignment calculation



Truck Dispatch: the Concept


Is it that simple?



Simple dispatch



Tt - Tc = W
Tt + Hw = C

Tt - travel time to the loading point (LP)
Tc - time committed at LP
Hw - hauler wait at LP
W - wait time
C - dispatch control factor



Dispatch Logic

1. Sort out all possible hauls and select the most efficient truck assignments
2. Assign trucks and start operation
3. Collect data: production rates, cycle times, etc for all haulers, loaders, dumps, crushers, etc.
4. Compare the collected data with the original ones and re-run assignment calculation if discrepancies exist
5. Rerun the calculation if non-scheduled events occur
6. Reassign trucks based on results of reruns
7. Continue data collection, checking for discrepancies and recalculating assignments (when needed)

Assignment Recalculation Events

1. Equipment status change; eg. ready to down
2. Addition/closure of a road segment
3. Change in measured travel time by a pre-set value
4. Change of blending requirements
5. Change of crushing/dumping rates
6. Change in shovel/dump priorities
7. Change in required/available truck ratio
8. At user predetermined interval
9. Other

Algorithm Management:Biasing

1. By loading site or a specific pit; eg room needed for subsequent operation
2. By stripping ratio; eg tie in stripping to ore excavation rate
3. By hauler - haul match; eg specific haulers working specific hauls
4. By dump area; eg restrict the dumping rate at specific dumps
5. By loading rate; eg. meet the pit advance targets
6. Other

Dispatch Strategies

1. Fixed dispatching: a truck (T) assigned to a specific shovel
2. Earliest loading: T assigned to assure its earliest loading
3. Minimum truck wait: T assigned to a shovel where it will have the shortest wait time
4. Maximum shovel utilization: T assigned to the longest waiting shovel
5. Minimum route saturation: T assigned to the route with lowest truck saturation
6. Minimum saturation & T cycle time: T assigned as above with consideration to its estimated cycle time



Modular Mining’s “Dispatch”

Sample Dispatch Objectives

1. Maximize truck utilization (fleet undertrucked)
2. Maximize loading equipment utilization (overtrucked mine)
3. Minimize rehandle
4. Maximize compliance with blending requirements

Fleet Dispatch: Supplemental Outcomes

1. All equipment monitored 24 h/d: no distortion from unscheduled time, idle time, opportune maintenance, etc
2. Status changes & event codes: clearly defined and consistently used across all shifts and crews
3. Performance ratios & indicators accurately defined
4. The above linked to the job functions

After Carter, 1995 APCOM

Implementation Issues

1. Well planned briefings for all employees
on operation of the system, information collected, way of collecting it and its use
2. Structured training programs in the operation and use of the system for all employees
3. Analysis of the impact
on each job role when the system is implemented
4. Identification of the information that each employee needs to effectively perform the job: “which” employees make “what” decisions & what logic should they use

Source: P. Carter, 1995 APCOM

SIMULATION

1. Building a simulation model
2. Model inputs
3. Model validation
4. Use of simulation for optimization of mine performance

What Model Do We Need?

1. FPC type models: OEM/dealers, TALPAC of Runge, other
a. depend heavily on accuracy of inputs (15%?)
b. correction factors applied for existing mines
2. Simulation language based model
a. reflect probabilistic character of inputs
b. data acquisition and validation v. important
c. good for what-if scenarios
3. Dispatch based simulations

Data Collection / Model Validation

1. Data collection accounts for 70% expenditure and time
2. How to assure reliability of data?
a. sample field data: use summer students?
4. Model validation
a. a formal process
b. may require model adjustments/modifications

Sunday, June 13, 2010

Tires



Tire Selection: Considerations

1. Will it fit?
2. Will it carry the load?
3. Is the design suitable for the underfoot conditions?
4. Does the tire meet TKPH/TMPH requirements?

Functions: carry the load, cushion loading & haul impact, transmit driving & braking force, provide flotation, directional stability & cornering

Tire Types

1. Radial vs bias ply
strength, flexibility
2. Wide base vs regular width
flotation, contact area, comfort
3. Duals vs single
load capacity, rolling resistance
4. Regular vs deep tread
cooling, grip action, rock cut resistance





Radial or Bias?
Komatsu Handbook





Wide Base Tires



Extra Wide Base Tires



Tire Selection
Komatsu Handbook



Tire Life Factors

1. Proper selection (size) & rating
2. Operating within capabilities: TKPH
3. Haul road design & m-ce
* curves, grades, smoothness, firmness, cleaning of spillage
4. Tire maintenance:
* inflation, matching, repairs
5.Operator skill: speeds, stopping manner
6.Inspections: cuts, rim damage, etc

Tones-Miles-Per-Hour (or is it TKPH?)

1. TKPH is a performance rating of a tire defied as a product of:
2. Average Tire Load (tones)
3. Average Shift Speed (KPH)
4. Average tire load:
(Load empty + load full) / 2
5. Average tire speed:
(Round trip distance x No. of trips) / (No. of hours worked)

TMPH / TKPH







TMPH - Other Issues

1. Separate ratings for TMPH, TKPH
2. Ratings defined for 370C (1000F)
* corrections required if ambient temp. differs (always?)
3. Check all tires (load distribution varies)
4. Length of haul may impact the rating
* Correct TMPH for hauls over 5 km (Mich.)
* Correct TMPH for hauls less than 5 km (Brdg)
* Other……..
* Empty and loaded run are not always the same

Manage the cycles to fit TMPH !!!

Tire Wear

1. Fatigue wear
a. “ideal conditions”, tire life over 10,000 hrs
2. Thread wear - “worn-out”
a. the most desirable; consider compound
3. Cuts: face, side
* look at application; m-ce, operation & road cleaning all are important
4. Heat damage - “separation”
* are the tires overloaded? Too long cycles?
5. Running on underinflated tires?
6. Blowouts

How to Measure Wear?

1. Wear per distance run?
a. How do we measure how many were run?
b. Consider short cycle with lots of idling
* vs. log cycles, no idling
c. The best: relates wear to work done
d. Dispatch systems?

2. Wear per operating hour ?
a. Engine hour-meters? Easy to measure
b. How accurate?

Tire Thread





Tire Maintenance

1. Inflation pressure checks
a. hot: daily, cold: weekly
2. Periodic rotation program:
a. mach type, diameter, new tires on
* front wheels, rotate rears (see next slide)
3. New tires with new valves & o-rings
4. Never weld on rim with a tire on
5. Never use steel hammers on rim parts

Tire Rotation



1. New tires on front axle (LF, RF) till 20-50% worn
a. highest reliability: safety
b. steering
2. Rotate to inside rear (RIR, LIR)
3. Rotate to rear outside (LOR, ROR)
a. easy to change

Tire Size and Performance