Mining Methods & Machinery

Surface Mining: Layout & Stripping Ratio

The stripping ratio that decides how much waste must move per tonne of ore — and the break-even ratio that draws the pit limit.

PART 1

Topic Breakdown & Traps

The Engineering Principle

Surface mining is governed by the stripping ratio (SR) — the amount of overburden (waste) that must be removed to win one unit of ore. It can be expressed as volume of waste per tonne of ore or as a tonnage ratio. Mining stays profitable only while the actual SR is below the break-even stripping ratio (BESR), where the value recovered just pays for ore production plus stripping. BESR sets the economic pit limit.

The Core Formula Matrix

Stripping ratio:

S R = \frac{waste removed}{ore mined}

.

Break-even stripping ratio:

B E S R = \frac{selling price - production cost}{stripping cost}

Units must match (e.g.

\

/\text{t}

o v er

/ m^{3}

⇒

m^{3} / t

The ‘IIT Traps’

⚠
SR is waste ÷ ore, not ore ÷ waste — keep the order.
⚠
Mine while actual SR < BESR. Once the actual ratio exceeds break-even, that block is uneconomic.
⚠
BESR uses *net* value (price − production cost) on top, stripping cost on the bottom.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

A pit removes

3 Mt

of waste to win

1 Mt

of ore. The stripping ratio is:

Q2MEDIUM2 Marks · NAT

An operation strips

12 Mm^{3}

of overburden to expose

4 Mt

of coal. The overall stripping ratio is ______ m³/t. (Round off to two decimal places.)

m³/t

Q3HARD2 Marks · NAT

Coal sells for

\

50/\text{t}

, cos t s

20/ t

to produce, and stripping costs

\

5/\text{m}^3$. The break-even stripping ratio is ______ m³/t. (Round off to two decimal places.)

m³/t