Método de Explotación de Carbón Longwall

1. A SEMINAR ON….
LONGWALL TOP COAL CAVING
Presented by:
J. Anil
M.Tech-219MN1581
Department of Mining Engineering,
NIT Rourkela, Odisha

2. INTRODUCTION
 Long wall top coal caving (LTCC) is the method of extraction for
underground mining of thick seam, i.e. greater than4.5m.
 It uses a long wall setup and natural forces to aid in the winning of coal.
 With this method of coal extraction only a single long wall is developed at
foot of the seam accompanied by caving the reclamation of the top coal.
 The control of roof layer at the face by means of powered supports.
 At the face, the coal is mined with a shearer at a set height and
transported out of face length by AFC and ACC to rate of advance, the
upper coal section of seam is then induced to cave at the goaf side and is
removed by a second AFC called “REAR COAL CONVEYOR” which is
situated behind the face supports.

3. History of LTCC
Longwall Top Coal Caving was initially
developed in the former Soviet Union and
France in the 1950s and 1960s. The ‘Soutirage’
method which was developed in France in the
1960s is considered as the original form of
LTCC.
It was then applied in the former Yugoslavia,
Hungary, Romania, the former Czechoslovakia
and Turkey.
After the mid-1980s, LTCC was abandoned in
Europe because the levels of productivity from
LTCC faces were less than that from conventional
longwalls during that time.
Since the late 1980s, LTCC has been introduced,
developed and improved in China. The method is
widely applied to extract thick seams in China
with a significant innovation on equipment.

4. BENEFITS
OF LTCCC
This method provides greater resource recovery, as
it offers a variable means of extraction up to 75-80%
in the 5-9m thickness range.
Mine safety is improved as the cutting height is
lower relative to the high reach single pass longwall
method.
Reduced operating costs are possible as LTCC
method increases the longwall tonnage per meter
retract and also per meter of gate road
development.
Compared to other longwall mining methods (High
reach single pass longwall, Multislice longwall) LTCC
results in improved face control , smaller and less
expensive equipment and improved spontaneous
combustion control .

5. DRAWBACKS
OF LTCC
Roof and face alignment.
Roof support control.
Spontaneous combustion control.
Managing airborne dust.
Strata control.
Dust and significant face disruption
due to top coal drawing.

6. OPERATION OF LTCC
• This method employs both cutting of the lower portion of the coal seam
accompanied by caving and reclamation of top coal.
• Coal is first cut from the long wall face using a conventional shearer and AFC
arrangement working under a hydraulic face supports that incorporates a
rear coal conveyor and a cantilevers or flipper arrangement located on the
lower portion of rear canopy.
• Face cutting heights are generally in range of 2.8-3.0m.
• The roof support is advanced forward after the shearer and the rear conveyor
remains in place in preparation for caving sequence.
• This caving sequence allows the broken coal at the rear of supports to flow
from the goaf on to the rear conveyor, which conveys it to the gate end
transfer.

8. MECHANISM
OF LTCC
A secondary caving process may be repeated if further coal is
present before the rear conveyor and is finally advanced forward
under rear canopy of support ready for the next shearer cycle.
Once an area has been caved the rear cantilever is extended
blackout into the goaf stopping any further influx of goaf material.
The flow of coal on to the rear conveyor is controlled by the
retracting the rear cantilevers of selected supports exposing the
rear conveyor to the goaf coal which caves on to the face space.
Top coal fracturing occurs through shear failure and tensile
cracking.

9. CHALLENGES
TO
INTRODUCING
LTCC
Geological and
Geotechnical matters.
Mining Environment.
Equipment design
and performance.

10. GEOLOGICAL AND GEO
TECHNICAL MATTERS
 scientific & engineering studies and detail investigations are required to
determine a particular site’s potential for LTCC.
 The fracturing process begins ahead of face line when seam acted on by
abutment stress.
 The process of fracturing and crack evolution in top coal is critical to the
success of LTCC and is depend on abutment pressure and coal mass
strength.
 Top coal fracturing occurs through shear failure and tensile cracking.
 Poor fracturing will cause large blocks to form and this results in poor
caving through rear AFC.
 Excessive fracturing will in turn causes roof control problems ahead of
roof supports.

11. CAVING
ASSESMENT
• This will depends on following parameters.
1. Coal strength.
2. Vertical stress.
3. Thickness of top coal.
4. Degree of fracturing.
5. Interburden/stone band thickness.
• Modelling of LTCC complicated as the strata must
be modelled and assessed through the various
loading stages that will result in increasing
fracturing of top coal, from being intact to the
fully fractured and expanded.
• This requirement necessitates using two different
approaches known as CONTINUUM & DISCRETE
ELEMENT MODELLING to represent two coal
conditions

12. MINING ENVIRONMENT
 Use of the LTCC method causes changes to mining environment
particularly in air flow pattern, gas emissions and airborne dust
generation .
 LTCC uses four leg shield supports with rear AFC which significantly
alters ventilation behaviour on around the face.
 Additional airborne dust will be present on LTCC faces due to
addition of caving cycle that produces a large quantities of dust.
 Gas make into and out of LTCC goaves may be significantly different
compared to the conventional longwall goafs in the same
conditions ,it is due to larger extraction volume and its effect on the
surrounding strata and coal seam

13. EQUIPMENT DESIGN AND
PERFORMANCE
 An equipment manufacturer and mine operator must consider the
design life of equipment for LTCC applications.
 A short design life will allow for new equipment design while long
design life will be more expensive to purchase.
 The path chosen will depends largely on the mine operators
confidence in assessment of caving conditions.
 As with the all longwall faces the general guidelines for an efficient
face are maintaining correct face alignment and horizon control.
 Automation of caving process will involve programming the time of
the retraction and extension of rear cantilever.

14. PARAMETERS INFLUENCING TOP
COAL CAVABILITY
Coal seam
characteristics.
Surrounding
rock strata.
Stress
conditions.

15. COAL SEAM
CHARACTERISTICS
 Coal seam characteristics include
1. Coal strength.
2. Cutting height.
3. Coal discontinuities.
• The coal strength which indicates resistance to
failure. The Uniaxial Compressive Strength (UCS) is
generally used to represent the rock strength.
• The cutting height and top coal thickness are
considered to affect the quantity and quality of
coal cavity.
• The ratio of top coal thickness to the cutting
height should be reasonably set to obtain
successful caving and this value generally varies
from 1 to 3.
• Discontinuities is commonly employed as
collective term for all fractures in a rock mass that
have zero to low tensile strength.

16. SURROUDING
ROCK STRATA
CHARACTERISTICS
 The immediate roof must be certain thickness and
caves immediately or with little delay after advance
of support.
 If an immediate roof is weak and thin it will
converge to top coal due to the load from upper
strata and its own weight, this causes an increase
of stress on top coal that will facilitates the coal
failure. Therefore top coal will easier to cave.
 If an immediate roof is strong and thick it resists
the force from the upper strata and its own weight
on top coal. As a result top coal will be more
difficult to cave.
 The main roof affects the stability of immediate
roof and influences the top coal behaviour.
 A weak floor rock may result in support instability
or floor heaving. These issue disturb caving
sequence.

17. STRESS
CONDITIONS
• The underground mining cause stress
redistribution and forms a new equilibrium stress
directly affect material failure and therefore
influence the top coal cavability.
• For LTCC mining the vertical stress component is
redistributed and results in different stress zones.
• The formation of high vertical abutment stress
zones induces the top coal to fail and to cave
under the impact of gravity.
• The horizontal stress component, however has an
ambiguous effect on caving.
• On the other hand, it can constrain the load
transference from upper to lower strata. This
reduces the level of coal failure and finally
decreases cavability.

19. OTHER
PARAMETERS
 Panel design.
 Seam dip.
 Ground water.
• A face orientation at an angle of 45 degree
to the face vertical joint might cause a
better top coal recovery in centre of panel
width compared with non oriented panel.

20. CAVABILITY
ASSEESSMENT
METHODS AND
CLASSIFICATIONS
Chinese Approach:
1. Fracture index
method.
2. Fuzzy cluster
evaluation method.
3. Statical analysis
method.

21. NUMERICAL
MODELING
APPROACH
The numerical modelling provides a predictive and effective tool to
access the top coal caving.
1.CONTINUUM METHODS
Finite difference method (FDM).
Finite element method (FEM).
Boundary element method (BEM).
2.DISCONTINUUM METHODS
Distinct element method (DEM).
3.HYBRID METHODS
A hybrid FLAC method was developed to acess the top coal caving.

22. THANK YOU..