Slide 1
Design Optimization of Longwall Chain PillarsProf. Kazem Oraee,
PhDUniversity of Stirling, UKBehdeen Oraee, MScUniversity College
London, UKAmir H. Bangian, MScAzad University, Iran
29th International Conference on Ground Control in
MiningMorgantown, WV11Introduction
Longwall is an underground mining method High rate of production
capacity
Mechanization ability
Soft rock flat-lying bedded ore bodies
A widespread mining method in European coal mines (beginnings of
19th century).
In early 1960s , developed in US coal mines by development of
self advancing supports mechanisms.
22
ShearerArmoured FaceConveyorShield SupportsStage LoaderThe
Longwall Mining System3During 1990s and beyond, production rate of
underground coal mines using longwall doubled around the world.
The main reasons of this improvement:high level of
mechanizationproviding higher safetyoptimum design of panels
efficient ventilation systems4
4An appropriate design of panels consists of:
An accurate layout of the entries
Proper ventilation condition
A satisfactory level of the safety in the entries and the coal
face
Adequate system for conveying the extracted coal along the
face
5
5Appropriate depth of seem in longwall method can be: From less
than 100m to more than 2000m
Obviously, to design a panel that provides stability and safety
at the entries is more complex at higher depths compared to shallow
depths.
6
Obviously, to design a panel that provides stability and safety
at the entries is more complex at higher depths compared to shallow
depths. 6 Therefore :The number and the width of chain pillars in
both sides of a deep panel should be increased to provide the
required safety.
The recovery rate of coal in a deep longwall mining project is
decreased by increasing the number and the width of the chain
pillars.
Total cost of the project under such circumstances is raised by
decreasing the recovery rate of coal extraction.
Therefore, cost of ventilation increases.77 Thus:Pillar design
has to be carried out based on a highly accurate procedure
including;
Assessment of load distribution on pillars
Stress analysis in order to provide high safety with minimum
possible pillar dimension
88Tabas Coal Mine Iran
One of the largest coal resources in Iran Has created the
required conditions for using the longwall mining method:
Large volume of coal reserve
Appropriate geometry of coal seams9
910
10C1 Coal SeamThe main coal seam in Tabas
Average thickness 1.8m
Inclined openings
Longwall
Panels Width: 200m to 220m
Panels Length: about 1000m
Retreating method1111
Sketch of Central Mine Development 1213
Sketch of Tabas Mine Longwall Panels1314
Sketch of Tabas Mine Longwall Panels14Geomechanical parameters
of Coal & Overburden Rocks of C1 Tabas Coal Seam
15
15Coal Pillar Design MethodsShould achieve two goals:
High level of safety High level of coal recovery16
16Before development of personal computers, mining designers
designed coal pillar by manual procedures.
Therefore the empirical designing methods were gradually created
to design coal pillars based on experimental results.
Nowadays coal pillar design is carried out by using advanced
personal computers with high speed calculations but the design
procedure has not been changed.
Currently empirical coal pillar design methods are acceptable
procedures worldwide1717Empirical formulae are the equations which
have been developed based on the extracted experimental data of a
given coal pillar.
The attained results from empirical formulae have a good
conformity with the original field data obtained from the
experimental tests.
Developments of personal computers and numerical methods have
allowed the mining designers to apply numerical methods to coal
pillar design.
In this approach some main criteria are compounded together and
then the obtained results are applied to coal pillar design.
1818Customary equations for assessment of coal pillars
strengthSome of the most applicable formulae:
Bunschinger (1876);
Bieniawski (1967);
Bieniawski (1968);
Holland (1973);
New Formula (2007);19
19Numerical ModelingNumerical coal pillar design methods have
recently been widespread in engineering modeling because of the
development of personal computers and the progress in advanced
numerical techniques.
These methods are unlike empirical methods that simulate and
analyze the stress during loading of coal pillars.
FLAC3D software was used to analyze coal pillar strength and
stability.
2020In order to determine the loading capacity of a pillar, a
typical pillar has been modeled on the basis of the average coal
characteristics of Tabas coal mine.
In the model the height of the coal pillar is 3.2m, the length
of the coal pillar is 40m and the width of the coal pillar varies
from 20m to 60m.
In this procedure, the loading rate on the coal pillar increases
with the increase in width of the coal pillar. 2121A sample of the
modeled coal pillars by FLAC3D & the Displacement Velocity
Model
2222Comparison of the different coal pillar strength assessment
methods23
23The trend of coal pillar strength with respect to increased
UCS of intact coal24
24The increasing trends of the obtained data by the new formula
& FLAC3D based on: - Changes of the width of the pillar -
Intact coal sample UCS25
25ConclusionChain pillar design has a significant effect on
safety, economics and performance of longwall coal mining.
The results show that both the new formula and FLAC3D are
applicable methods.
Although as the new formula has been developed based on the
specifications of the coal in Tabas, the obtained conformity
amongst the achieved results and the field data was predictable.
2626As the produced data of the new formula are lower than that of
the produced data of FLAC3D, a higher safety factor than the
results of FLAC3D will need to be applied.
Loading capacity of coal pillars increase with the increase of
compressive strength of the intact coal.
The ratio of the obtained results by the new formula has a
linear trend but the obtained results by FLAC3D for range of UCS of
the intact coal changes from linear to a decreasing trend after
7.5MPa.2727It was also proved that an increase in the UCS of the
intact coal and an increase in the width of the coal pillar
simultaneously creates a higher level of loading capacity for the
coal pillar.
The attained results were proved by both the new formula and
FLAC3D software and it is finally concluded that, using
simultaneously the new formula and FLAC3D software can provide
reliable results for coal pillar design in the Tabas coal mine.
2828
Thank You29