An inset is where a horizontal tunnel intersects a mine shaft, acting as the main access point to the orebody below. It must remain stable and dry to allow equipment passage. Insets are typically arc-shaped while shafts are circular or rectangular. Their size depends on hoisting needs, ventilation requirements, and the level of mechanization. Inset design considers supporting structures, ventilation, shape based on strata stresses, and is lined with reinforced concrete for strength.

1. Introduction to Inset
Design

2. Introduction
 The point of contact between the levels & the shaft
itself is known as the inset.
 In other words, it is the place where a horizontal
tunnel intersects a shaft or the underground roads
from the shaft. It is also known as shaft station.
 These are large structures which acts as a main
access to the orebody often found at considerable
depth in weak but dry coal measure rocks.
 They must remain dry & safe with sufficient
stability to allow rapid passage of winding &
transport equipment.

4. Difference between Shaft and Inset
Shaft
Inset
1. Shape – circular / rectangular 1. Shape –
Arc shaped
2. Axis – Vertical
2. Axis – Horizontal
3. Requires plain concrete 3.
Requires reinforced

5. Factors affecting size of Inset
 Duty and purpose of inset
 Type of winding
 Quantity of air passing through pit bottom
roadway
 Extent of Mechanization

6. Design of inset based on purpose of shaft
 For hoisting shaft:
The size of inset for a hoisting shaft depends on the width
and number of skips and cages being hoisted on this level,
number of decks in the cages, and maximums length of
supplies to be delivered.
 For ventilation shaft
As when ventilation shafts, which are without hoisting gear,
the insets for these types of shafts are designed to
minimise airflow resistance.

7. Aspects of Inset Design
 The Extension Heading
It was designed to prevent transfer of high stress
to the inset lining during later extensions of the
heading.
 Supported Structure
It was designed to take the full load ,thus
protecting the inset area during subsequent
construction activity.

8. Ventilation Requirements for Insets
 Proper and precise method is used to
check an inset sectional area for ventilation
requirements.
 For this ventilation requirements , air
velocity at 4 m/sec and at 8 m/sec had
been fixed for production shafts and
ventilation exhaust shafts respectively.

9. Determination of height of an inset
We can get height of inset as
H= (L cos Ω- D’)tan Ω
Where L =Max. length of
transported material
Ω=angle from level
D= shaft diameter
D’=free space between
shaft seams
H= Inset height
Now ,when
Ω= 45 degree
D’=0.7 D
We get H = 0.7(L-D)

11. SHAPE OF INSET
Shape of inset is decided mainly on two consideration:
 Strata stresses
The insets may be rectangular, semi-elliptical or elliptical. Rectangular
shapes are common in the area where the vertical and horizontal
pressure of the strata are low. When the strata pressures are high,
elliptical shape is preferred.
 Aerodynamic considerations
With large airflow through shafts and insets, pressure losses due to
sudden contraction in fluid cross-sectional area known as the vena
contracta.The remaining area between the vena contract section and
walls of excavation is normally filled with eddies the friction of which
causes pressure losses.

12. EXCAVATION TECHNIQUE USED FOR
DEVELOPMENT OF INSET
 An inset should not be cut faster than 2000
cu.feet/day with slushier mucking. It may be
cut at an average rate of 3500 cu feet/day
with an L.H.D. mucking unit.
 The minimum inset depth at a development
level to be cut during shaft sinking is 50
feet.

13. LINING OF INSET
 The inset lining is made up of reinforced
concrete which can resist high pressure,
offers less frictional resistant to air currents,
can be erected rapidly, stronger than brick
work but difficult to repair as crack
develops due to its rigidity.
 Hydraullic pressure cells installed at the
concrete interface to measure radial stress.