Block caving is an underground mining method that involves undercutting large blocks of ore to induce caving from the top down. It is suited for large, low-grade ore deposits with certain rock characteristics. The process involves exploring the ore body, determining cavability, installing drawpoints in a pattern below the block, and systematically undercutting the block to remove supporting pillars and cave the ore. Draw control is critical to optimize grade, recovery and dilution as the ore caves and is drawn out of the mine. Block caving can be highly productive and cost effective for the right ore bodies, but requires extensive development and carries some safety risks.

1. BLOCK CAVING

2. INTRODUCTION
• Underground mining method that
has the potential to rival surface
mining in output and cost.
• This method was invented in the
years following World War I to
cope with the exploitation of the
massive low-grade copper
porphyry deposits of the south-
western United States.

4. INTRODUCTION
• Block caving is the mining method
in which masses, panel, or blocks of
ore are undercut to induce caving,
permitting the broken ore to be
drawn off below.
• Caving mechanics provides the basis
for understanding and controlling
the operating factors in block
caving.
• Good caving action generally
requires that the ore body have
fractures in three orientations.

5. THE METHOD
• To investigate the cavability of the ore body, drill cores are
obtained throughout the ore body using exploration openings.
• These cores are then often subjected to rock quality designation
(RQD) analysis, which measures the percentage of intact (>4 in.
Or 102mm) core recovered from a drill hole. The RQD value will
help to identify the caving characteristics of the rock mass.
• Cavability is not just a matter of achieving acceptable
fragmentation and optimum operating costs. From a safety
standpoint, the ore or capping must not arch over long distances
for long period of time. The formation of stable arches not only
disrupts the caving operation but very likely will cause air blast
and concussion in the mine when they suddenly collapse.

6. THE METHOD
• Determining the cavability of
an ore body is the first task to
be undertaken.
• After cavability is determined
for the ore body, the second
application of caving
mechanics is in draw control
and drawpoint spacing.
• Excessive spacing or deficient
one produces zones of draw
that may yield unsatisfactory
grade control and create
weight problems on sill
pillars.

7. THE METHOD
• In plan view, drawpoints may be arranged in a hexagonal or
square pattern.
• To ensure that the zones of draw completely blanket the ore,
drawpoint spacing is reduced somewhat, permitting minor
overlap of the zones.
• Once caving begins, the only means of regulating it, as well as
the production of ore, is through draw control.
• Because of irregularities in the contact between ore and
waste and, more important, because of funnelling in the ore,
some dilution is inevitable if a high recovery is achieved.
Effective draw control optimizes the combination of grade
control, recovery, and dilution.

8. THE METHOD
• The most critical spacings to
be designed into the block
caving operation are the
drawpoint spacings and the
spacings between levels.
• The spacing between levels
dictates how high a column of
ore is to be extracted through
the drawpoints.

9. VARIATIONS
• In block caving one of the critical parameters that determine
success is the size and shape of the area that is caved.
• Three methods are used: Block, Panel, and Mass.
1. In block caving, regular rectangular or square areas are
undercut in a checkerboard pattern. Usually these blocks are
mined in an alternating or diagonal order to effect better
caving action and draw control.
2. In panel caving, ore in continuous strips is mined across the
ore body.
3. For the coarser ore materials, loader caving is the best
choice. It also has the advantage of being the most versatile
and least expensive in terms of development costs.
4. Of the three methods, the loader method is often the choice
for today’s block caving operations.

10. SEQUENCE OF OPERATIONS
1. Mine level development commences from the shaft station
in the usual way, providing for high speed, high capacity
haulage and ample ventilation airflow capacity.
2. Main haulage ways are often paralleled by laterals,
interconnected by crosscuts, to ensure good ventilation and
to provide adequate lanes or stub crosscuts for loading.
3. One or more additional sublevels are required for grizzly or
slushier operation, increasing the development costs for
these two methods.
4. To provide ore-drawing facilities, chutes, drawpoints, or
trenches are prepared in the ore body under the block to be
mined.

11. SEQUENCE OF OPERATIONS
5. Finger raises to serve as prepass are then driven to the grizzly
sublevels above.
6. The most critical development step is undercutting the ore
zone, which is carried out in a manner similar to that of a
room-and-pillar mining operation, with the pillars being
withdrawn in a systematic manner across the cave zone.
7. The mining company generally relies on the knowledge of rock
mechanics to ensure that the caving proceeds in a predictable
manner.

12. CYCLE OF OPERATIONS
1. Drilling (undercut): pneumatic- or hydraulic-powered
percussion jumbos; hole size 2 to 3 in. (51 to 76 mm).
2. Blasting (undercut): ANFO, slurries; bulk charging by
pneumatic loader or pump, firing electrically or by
detonating fuse.
3. Secondary blasting (on sublevel or in haulage drift) : impact
hammer, dynamite bomb, drill and blast, mud cap
4. Loading (through bells and ore passes) : gravity flow to
chutes; LHD, front-end loader, slushier at drawpoints
5. Haulage (on main level): LHD, rail, truck, belt conveyor

13. CONDITIONS FOR APPLICATIONS
• Ore strength: weak to moderate or fairly strong, prefer friable,
fractured, or jointed rock, not blocky; should cave freely
under its own weight when undercut; free running, not sticky
if wet, not readily oxidized.
• Rock strength: weak to moderate, similar to ore in
characteristics.
• Deposit shape: massive or thick tabular deposit, fairly regular.
• Deposit dip: fairly steep(>60 degree) or vertical; can be fairly
flat if sufficiently thick.
• Deposit size: very large areal extent; thickness>100ft(30 m)
• Ore grade: Low, ideal for disseminated ore masses; most
suitable of underground methods for low-grade deposits.

14. CONDITIONS FOR APPLICATIONS
• Ore uniformity: fairly uniform and
homogeneous; sorting not possible
• Depth: moderate;>2000ft (600m) and <4000
ft (1200m)

15. ADVANTAGES
• Relatively high productivity.
• Fairly low minimum cost, least of the underground mining
methods (relative cost about 10%).
• Highest production rate of the underground stoping methods;
large-scale method.
• High recovery (90 to 125%).
• Rock breakage in production occurs entirely by caving induced
by undercutting; no drilling and blasting cost in production.
• Suitable for gravity draw or fully mechanized materials
handling; repetitive, standardized operation.
• Ventilation is generally very satisfactory; good health and
safety factors.

16. DISADVANTAGES
• Caving and subsidence occur on a large scale.
• Draw control is critical to success of the method.
• Slow, extensive, costly development.
• Dilution may be high (10 to 25%).
• Maintenance of openings in production areas is substantial and
costly if pillars load excessively.
• Rigid, inflexible method.
• Hazardous work because of hang-ups in the grizzly and slushier
sublevels; some risk of air blast throughout the mine.
• Possible spontaneous combustion in ore or rock during caving if
drawing is slow or delayed (risk is high if sulphide content is >45%)

17. CONCLUSIONS
• If an opening made during stoping is large enough, it will
eventually cave, even in the firmest and strongest rock, but a
caving system of mining like block caving.
• At the bottom the block is completely undercut i.e. a
horizontal slot is blasted, which removes the support of the
over-lying ore.
• Due to complicated preparation and narrow sections
mechanized methods are often difficult to apply, except for
the preparation of the main level below the block.
• Underground mining method that has the potential to rival
surface mining in output and cost.
• At present block caving is not adopted at any of the mine in
India.

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