Steel Arches used in mining industry

1. Steel Arches and Cerchar Test
A Rock Mechanics Presentation by
Takudzwa Munyaka

2. STEEL ARCHES
• Background:
• This system developed from the earliest use of
timber supports underground, steel
• arches are now manufactured as rigid or yielding
supports. They are employed for
• long term, permanent rock mass support
especially in critical areas of roadways and
• intersections.

3. Basic structure
1.”W” strap 6. Collar Brace
2.Crown Joint 7.Steel Post
3.Steel Rib 8.Butt Joint
4.Blocking Pieces 9.Rib and Post support
5. Tie Rod 10.Foot Plate

4. Types of steel arches
A2 Y
• The Arch set forms the basic type
of Arch most commonly used in
the mining industry.
• The A2 Y is a yielding type used
where ground conditions are poor
and pressures uncertain
A3 Y
• The Arch set has a wide range of
applications in various sizes.
• Can be used with steel lagging
plates on the crown with timber on
the side walls.
• Ensures continuous access where
high pressures are experienced

5. Types of steel arches
A4 Y
• This Arch set with bowed legs is
suitable for large developments
or where sidewall pressures are
encountered.
• Used in mining and civil
engineering.
• Ideal for large civil tunnels as an
initial elastic support lining.

6. Types of Steel Arches
R1 Y
• Recommended for use where
extreme pressures from
different
directions are experienced.
• Ideal for high pressure
tunnels in
Civil engineering construction

7. Applications
• Suitable for any rock or soil types
• Highly fractured rock in tunnels,
roadways and underground chambers
• Ideal long service life permanent
support
• Damaged excavation opening-up
• Mining through dykes and faults
• Custom designed and shaped to suit
specific design requirements
• Reclaimable and reusable in some
applications

8. CERCHAR TEST
INTRODUCTION
The abrasivity of rock and even soil is a factor with
considerable influence on the wear of tools. Hereby
the wear is a question of material consumption and
is in addition to the excavation speed an important
indicator of rock excavation in tunnelling, underground
mining or quarrying. The wear depends on
the one hand on the machinery being used for
excavation;
that are the devices and all tools who havecontact to the
rock or loosened material

9. Apparatus and Arrangement Diagram
Setup of a modified Cerchar testing device according
to Cerchar (1986). 1 – weight, 2 – pin chuck, 3 – steel pin, 4 –
sample, 5 – vice , 6 – hand lever.

10. Sketch of the steel pin with rectangular shape before
the test (left) and after the test (right) with the wear flat d

11. Procedure
1. Set up apparatus as shown in fig.1
2. Set a static weight of 70N on the steel pin
3. The steel pin of a defined geometry scratches the test
sample
4. The diameter of the pin is measured as a result of the wear
on the pin
5. The Cerchar Abrasive-Index is then calculated from the
measured diameter of the the wear flat on the pin
CAI = 10.d/c
where CAI = Cerchar-Abrasivity-Index (-); d = diameterof
wear flat (mm); c = unit correction factor(c=1mm).