Mining & Mineral Economics

Haul-road Design & Equipment Selection

Rolling and grade resistance, rimpull and the truck–shovel match factor that balances a loading-and-hauling fleet.

PART 1

Topic Breakdown & Traps

The Engineering Principle

Hauling cost dominates surface-mine economics, so haul-road design and fleet matching are central. A truck must overcome total resistance = rolling resistance (tyre/road deformation, as a % of weight) + grade resistance (≈1% of weight per 1% of uphill grade). The engine supplies rimpull (tractive force at the tyre); the truck can climb only while

rimpull \geq total resistance force

. Fleet productivity depends on matching loaders to trucks: the match factor compares the loader's truck-filling capacity with the trucks' demand — a factor near 1.0 balances the fleet,

< 1

means the loader waits,

> 1

means trucks queue.

The Core Formula Matrix

Grade resistance:

GR \approx 1% of GVW per 1% grade

(force

= 0.01 \times grade \times W

)

Total resistance force:

F = (R R % + GR %) \times \frac{W}{100}

(

W

= gross vehicle weight)

Rimpull needed:

Rimpull \geq F

to maintain speed; surplus accelerates the truck.

Match factor:

M F = \frac{N _{t r u c k s} \times loader cycle time}{N _{l o a d er s} \times truck cycle time}

(target

\approx 1.0

)

The ‘IIT Traps’

⚠
Grade resistance ≈ 1% of weight per 1% grade — use the *percent* grade, not the angle in degrees (valid for small grades).
⚠
Add rolling and grade resistance before comparing with rimpull; one alone understates the demand.
⚠
Match factor target is 1.0. Above 1, trucks queue at the loader; below 1, the loader idles.
⚠
Rimpull falls as speed rises (constant-power curve); check rimpull at the required gradeability speed.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

A truck–shovel fleet with a match factor greater than 1.0 will typically experience:

Q2MEDIUM2 Marks · NAT

A haul truck has a gross weight of

300 kN

. Rolling resistance is

2%

and it climbs a

6%

grade. The total resistance force it must overcome is ______ kN. (Round to the nearest whole number.)

Q3HARD2 Marks · NAT

A loader fills a truck in

2.5 min

. Each truck's full cycle time is

20 min

. With one loader and

7

trucks, the match factor is ______. (Round off to two decimal places.)