BBUGS Mackay November 2011
LONGWALL SUPPORT SELECTION
GEOTECHNICAL ASPECTS
BUT FIRST
Strata Products Cuttable Supports:
28 day Compression Test 400x200 Link Blocks
45
40
35
Load (Tonnes)
30
25
20
15
10
5
0
0
5
10
15
20
Deformation (mm)
25
30
35
LONGWALL EQUIPMENT A BRIEF HISTORY
•
•
•
•
•
Basic longwall developed in Shropshire U.K. and Germany in the 17th century.
All hand Loading, with timber supports, and strike gulleys for coal removal. The words ‘Gob’, and
‘Goaf’ are from the Gaelic for cave or hollow.
Radial longwall layouts from central shaft started in the 1900, with steel supports instead of timber.
Very labour intensive.
Shortly after WW2, the advances in hydraulics found their way into mining, with the first hydraulic
chocks introduced.
A number of issues with stability and

flushing into the chocks.
•
The Armoured face Conveyor, and face

plough introduced from Germany in the

early 1950’s.
•

‘Shearer loader’ developed by Andersons
of Scotland in 1954.
HISTORY CONTINUED






The ‘Chock shield’ was developed in the late 1960’s with a solid connection
between the top canopy, and the base of the shield, to provide stability, and prevent
flushing.
Major changes in the 1980’s were the development of the ‘Lemniscate linkage’,
and the change from four to two leg supports.
Support loads increased dramatically, from 250 tonne supports in the early 1970’s,
to the current 1475 tonne supports available today.
This development is restricted at present due to space to place the large legs, and
limitations on hydraulic pressures and Flow.
Recent major improvements have been in terms of electronic controls, and
automation of the longwall equipment.
Face widths have increased from 150m to 350m over the last 15 years
FUNCTION OF THE SUPPORTS

Provision of a safe working area for the Operators on the face. This necessitates a clear walking
area, as well as canopies that adequately cover the working area
Provide a platform from which to advance the pan line, and shearer.

Provide an airway for ventilation across the face.



Support the roof in front of the canopies, and minimise deterioration of the roof, and
face in this area.
Control the roof above the supports, and provide a point at the rear of
the supports
where the
goaf forms.
BENEATH THE CANOPY, AND AHEAD OF THE LEGS?

Shearer Drum, and Web depth.
This is generally between 0.8m and 1.2m. Limitations due to seam thickness,
and cleaning ability. A wider web will produce more coal per shear, but exposes
more unsupported roof.
Push. Related to
web width
Drum Web
Width
BENEATH THE CANOPY, AND AHEAD OF THE LEGS?

Shearer, and Armoured Face Conveyor (A.F.C.)
4000
x 128hrs
x 50%requirements,
= 256 000 larger
tpw xand
48
With
the tph
increased
production
more
powerful
shearers
increasingly
wider A.F.C.’s are
weeks
(LW Move)
= and
12,288
m tonnes
being
installed.
Either
we only cut for 31 hours per week, or we
Is the increase in ‘nameplate’ capacity warranted?
definitely don’t use nameplate capacity!!!!
Capacity may be driven by ‘Project team’, who require a specific tonnage to make
a project ‘work’ . These figures are then ‘discounted’, ultimately requiring a really
high capacity coal clearance system to make the figures stack up.
Citect assessment of belt and shearer data indicates that, 80% of nameplate
capacity is used for only 2% of production time.
Engineering logic suggests that an over rated layout is less likely to be
‘overloaded’, and therefore should be less problematic, and last longer.
Geotech
Engineer
Mechanical
Engineer
WHAT HAS TO FIT UNDER THE CANOPY?
Bretby and Cable Tray.
Though they do not take up a lot amount of space, increased shearer power
requires larger power cables, and water hoses.

Front Walkway, and Pontoons.
Determined by ergonomics, and / or floor strength.
Requires space for operators to travel, though big hydraulic hoses has
impacted on this.
Weak floor & punching of the front of the supports into the floor
normally dictates the length of the front pontoons.
Relay Bars, and Clevices.
Web width dictates the length of relay bar, but with larger panlines,
clevices and fittings have increased in size, requiring additional ‘room’ in
front of the supports.
Why do we have three pin holes in the relay bar, as operators Always use
the outer hole. Please O.E.M.’s make one with only the inner hole!!!
WHAT HAS TO FIT UNDER THE CANOPY?

Support Legs
Diameter of legs has increased over time. Now there is no room within the
support for further increases. Wider supports (2.0m) give this space, but
canopy dimensions also increase, so results in approx the same max stress
being applied into the roof. maximum of +- 1.5 MPa
 Rear Walkway, Rear of Support.
The length of the rear of the supports is generally fixed by the length of the
D.A. rams, the rear walkway (if provided), and the rear of the pontoons, to provide
stability, and reduce floor loading.
Tip to Face Distance.
Tip to face distance dependent on:
Supports be used in conventional or IFS mode?
Cutting height? Increased cutting height gives Tip to Face distance.
Seam geology like? Structure, rolls etc need increased Tip to Face distance.
As the roof ahead of the supports relies on the strata bridging, this needs careful
consideration. Again the issues of Pins in the Relay bars !!!
Design
Personnel
Geotech
Engineer
LOADING INTO THE ROOF
Support Loading Profile.
The canopy of a standard two legged support is effectively a
see-saw that pivots around the top of the legs. It is kept in
Immediate
roof. This is the area that impacts on operations
balance by the loads applied by the roof. Obviously the
if not controlled well.
moments about the pivot point (top of legs)must be equal. This
defines the loading above the canopy.
a support
(+1000tonne) ram
has are
sufficient
capacity
to
 Generally
The impacts
of the compensating
very low,
equivalent
‘Support’
45mpoint
of material.
The across
supports
to movingabout
the pivot
by 100mm
themaintain
top of the
integrity
canopy by confining this material, and allowing ‘bridging’ to
occur at the front of the canopies, and in the unsupported
area.

SETTING THE SUPPORTS
THE MATHS!
Before working out the loads required to support the roof, let’s look at what loads
there are:
Drawing shows forces applied.

Support Loading Profile MNM
160.0
140.0
Horizontal component due to the angle of
the legs.
as being
It This
canhas
be been
seenmeasured
that there
are up
to 20
tonnes
very
low
loads generated at
The balance being taken up in the rear
the
tip of the canopy, and very
linkages.
high
at the
theroof to
This loads
confining
forcerear.
allowsIf the
material
atsupporting
the rear is
soft, and
form a self
beam.
When the
supports
are not
breaks
away,
the load
is correctly
set,
reduced
at the rear, and at the
or pressures are low, the confinement
same
time the front of the
is removed, allowing the roof to
canopy.
unravel.
120.0
100.0
80.0
60.0
40.0
20.0
0.0
-1.50
2.50
THE ROOF
Immediate roof is is generally taken as the material up to about 5m above the
supports.
Mentioned earlier, the shields only “Support” about 30m to 45m of roof material, the
balance has to be supported by the roof strata.
The average stress applied by the supports is relatively low.
i.e: 1000 tonne support with a 5m canopy, and 400mm tip to face = 1.07 MPa
Now we all know what 1 MPa concrete looks like;
By increasing the canopy length by 0.5m, the
applied load drops to 0.89 MPa, showing how
important it is to keep the canopy short, and the
supports close to the face!!
Effectively we assist the upper roof to be self
supporting, which is by forming a cantilever over
the supports, and goaf, and higher up in the roof,
spanning over the face, and goaf.
HOW DO YOU CALCULATE THE SUPPORT SIZE?
Smart Spring Model
Ground Reaction Curves
Detached Block
Model
CANOPY RATIO

Canopy Ratio.
Possibly one of the most important areas when considering the stability of the
immediate roof. This is the ratio of the front to back of the canopy as shown
Too high (above 2.7 to 1) and the rear readily punches into the roof, or it is not possible
to fully use posi (high pressure) set. In addition, there is very poor load transfer to the
tips of the supports
Too low, and the cantilever effect of the upper roof will tend to push down the rear of
the supports. Load at the tips will however be improved, and it will be possible to set the
supports to full pressure, but the supports may “squat down”.
The choice of canopy ratio is very dependant on the nature of the immediate
roof, the direction of jointing, and the strength of the upper roof.
Generally the weaker the immediate roof, the lower the canopy ratio (2.3:1), while a
stronger immediate roof will allow for a smaller rear section, and higher canopy ratio
(2.6:1)
SUPPORT STIFFNESS
There is much discussion regarding the Stiffness of supports
There are three distinct areas of stiffness:
Hydraulic Stiffness
Considered only once the supports have set, the hydraulic stiffness is
displacement of the supports due to the compression of the fluid in the legs.
This is small; 12mm to 15mm for large supports. (100 bar pressure change
decreases the volume of 1 litre of water by 5ml)
Mechanical Stiffness.
The deformation of the structure, pins, canopy, and expansion of the cylinders.
Increases with age, Depending on where measured, between 10 mm and
75mm between zero and set pressure.
Setting Stiffness.
Crucial in maintaining stability of the roof, is the time taken from cutting the face,
to setting the supports. Thereafter the greater the amount of work put into the
roof as the roof deforms the better.
The hydraulic capacity, clean roof and floor, bank push, and use of Posi set all
have a large impact on the ability to rapidly set the supports to the roof. Minimise
leaks!!!
SET TO YIELD RATIO
Yield, Good or Bad
Obviously good, as it protects the supports from damage. Obviously bad, as it
allow the roof strata to deform. Beyond a certain amount of deformation, failure
will occur.
Set to Yield Ratio.
The action of any support (Shields, roof bolts, cables etc) in achieving stability of
the rockmass, is in providing confinement, and letting the rockmass become self
supporting. There is a direct relationship between the amount of work done by
the support on the rockmass, and the stability of the rockmass. Set to yield ratio,
and support stiffness are therefore related.
The basic principles: Get the support into the roof quickly, and then make the
roof do the most work possible when deforming.
The Negatives.
A high set to yield ratio will ensure that the supports (leg seals, valves, hoses etc)
all operate through a full load cycle, every cycle, thereby increasing the
probability of fatigue failure.
DOES SIZE COUNT?
When requesting an OEM for prices, the first question is HOW BIG?
With high capacity supports, the biggest impacts to operations are probably the
price, the size of components, and the weight of the supports.
Geotechnical Perspectives.
In an area that has been mined, or has neighbours that have mined a similar
seam, the selection of the longwall equipment is easier.
A full analysis is still required, but information on roof behaviour, and mining
conditions can be added to the equation.
Geological mapping from underground operations.
Information from Citect, and other monitoring programs:
Info they provide:
How quickly do the supports set,
Leaking legs, how many, and do they impact on support
How often do the supports go into yield? (S curves)
Spacing of yield (weighting?) cycles
SIZE
Geotechnical Perspectives.
Greenfield site. The decisions regarding support design, and capacity are driven
by:
Upper, and lower roof strengths and thicknesses. (spanning ability)
Stress environment. (How will the stresses interact with the longwall)
Depth (what virgin vertical and horizontal stresses will we have)
Longwall width (Sub critical, supercritical, possible spanning)
Cutting height (stiffness of face, and supports)
Geological structure. (What will we find, and how will it goaf / span)
Required Production. (what size do the Engineers want the equipment to be)
Budget. (what can we justify to the beancounters.) Quality is remembered long
after the price is forgotten!!!
Dust and Ventilation (how often do we forget about these issues)
Etc
“S” CURVES
Yield Pressure
time
Set Pressure
time
Idealised Support 'S' Curves
120
Start Posi Set
Cumulative % of Time
100
Posi Set
Yield pressure
5%
Over rated
80
This portion not
available, due to
being in yield
60
Just Right
40
Under rated
20
0
0
100
200
300
400
500
Support Pressure (bar)
Ideal Rating
Over rated
Under rated
Very under rated
Pressure at Yield
600
ACTUAL “S” CURVES
Actual S curves
Very little curling
over in the later
panels. 'Under
Cumulative % (time at pressure)
120
Extrapolated
results
100
80
Narrow
Longwall
60
Shallower
Longwall
40
Effective rating
required
20
0
200
250
300
350
400
Pressure (bar)
450
500
550
600
Thanks