Balancing Diagram Mine Planning Mining Engineering Surface Mine Planning

1. Name- Arun Kumar
Sub- Planning for Surface Mine Mechanisation
(MN-451)

2.  Balancing diagram can be defined as the
graphical representation of the scheme to be
adopted for determining the suitable seating
position of the dragline in order to get
maximum overburden accommodation in
decoaled area with least rehandling for
achieving high rate of coal exposure and
ensuring slope stability.

3.  The balancing diagram assists in determining the
coal exposed by a dragline, the percentage of
overburden, rehandling and the volume of
overburden to be accommodated in the decoaled
area.
 Besides these, balancing diagram shows the
dragline cuts and spoil geometry (in two
dimensions) cross-section, height of dragline
bench and cut width taken by the dragline. The
cuts sequence by dragline, key cut (box cut), first
cut (next to key cut), and first-dig can be
estimated through the cross-sections drawn in
diagram.

4.  It shows the dragline cut sections i.e. key cut, first cut
(next to key cut), first dig (next to first cut) and rehandled
section (as per mode of operation).
 It shows the dragline bench height, cut width taken by
draglines, thickness of coal seam and gradient and various
slope angles.
 Determination of rate of coal exposure (daily/monthly or
annually).
 Calculation of workload distribution on each dragline in
respect of their annual productivity (i.e. cross-section area
taken by each dragline should be in the same ratio as their
annual productivity).
 Calculating the percentage of rehandling.

5.  Deciding the scheme to be adopted for dragline
operation i.e., .,horizontal tandem or vertical
tandem.
 Deciding the seating position of draglines so that
workload should be balanced In respect of their
annual productivity.
 Calculating the volume of overburden to be
accommodated In the in the decoaled area.
 Gives the linear advancement of each dragline and
hence rate of advance of mining operation.

6.  Step 1- Calculate Annual Production of Each
Dragline
 Ph= B/C *K*S*F*M*3600 (m3)
 Where
 Ph= Hourly Production
 B=Bucket Capacity(m3)
 c=Average Cycle Time(s)
 S=Swell Factor
 F= Fill factor
 M= Machine travel and positioning Factor
 K= Availability-Cum-Utilisation Factor

7. STEP 2: Decide Work Load on Each Dragline
 Amount of overburden removal by leading
(Primary/Independent) dragline and lagging (Secondary
/Dependent) dragline should be proportionate in terms of
annual production capacity of these draglines. Hence, the cut
section by each dragline should be in the same proportion as
their annual capacity.
 In the tandem operation of draglines, the workload
distribution is one parameter that severely affects the
planning of tandem operation. The work load should be so
distributed that the entire operation may run smoothly
without any perceptible jerks and stoppages in the system

8.  STEP 3: Assume Different Design Angles for Drawing
Balancing Diagram
Depending upon the past experiences and records, assume
appropriate angles, For the purpose of drawing the balancing
diagram.
For example,
 Angle of dragline cut in highwall side - 70°
 Angle of coal extraction -80°
 Angle of dragline cut In blasted overburden - 60°
 Permitted cutting angle of dragline dump at the height up to
35m - 40° (Bench slope angle for loose overburden)
 Angle of repose for loose overburden - 38°

9.  STEP-4 Decide Width of Cut
 The width of cut should be as large as possible in order to
maximize the coal exposure and minimize the percentage of
rehandling. Large cut width reduce relative time losses of
standby and unproductive moves of excavators. on the other
hand, it should be optimized in order to obtain a greater
height of the stripping bench. •
 It is also restricted by operating parameters of dragline i.e.
digging radius and dumping radius and system of working as
vertical tandem or horizontal tandem to be adopted
 The suggested cut width is a contentious value and is a
matter of subjective judgement. First, the maximum cut width
is determined on the basis of required rate of coal exposure
and operating radius of the dragline. The minimum cut width
is dictated by the manoeuvrability of coal loading and hauling
equipment.

10.  The height above the coal seam at which the dragline is positioned
is defined as the bench height. Selection of the bench height is
based on numerous operational factors.
 The complex relationship of bench height, cut width, dragline
dumping reach and dumping height, as well as material
characteristics such as swell and angle of repose, influence greatly
the draglines capability to dispose the burden off the coal.
 The bench height must be selected primarily on the basis of fitting
the dragline’s specific characteristics to the required geometry. In
general the bench height should be as high as possible within the
limit of required dragline reach.
 Height of dragline bench, considering dragline operational
characteristics is given by the following norms:- Height of bench <
0.8 times the dumping height of dragline used.

11.  For tandem operation of draglines, rate of advance (linear) of both
the dragline is same so that the entire operation may continue
smoothly without hindrance in the system
 Corresponding cross-sectional area taken by dragline is function of
bench height, which is calculated on graph paper taking into
workload distribution principle where bench height is inversely
proportional to coal exposure. It means as cut width increases, rate
of coal exposure also increases and vice-versa, and as the bench
height increases, rate of coal exposure decreases.
 Therefore, optimum cut width and bench height should be decided
simultaneously on graph paper by iterative procedures till we arrive
at required rate of coal exposure. It should always be borne in mind
that cut width and bench height is restricted by dragline reach and
dumping height respectively. The optimization of cut width and
bench height can be accomplished by applying computer graphics
methods more easy and accurately

12. a) Horizontal Tandem

16.  Key cut width is such that it must conform to stable bench slope
angle in a pit. The minimum width of the key cut bottom is equal
to 1.5 times widths of dragline bucket.
 Since, the key cut, is in the form of inverted truncated cone
(wedge shaped) hence, with the increase in overburden thickness
the width of key cut top also increases. Highwall angle (bench
slope angle) should be flatter with the increase in the overburden
height which means that at a height of 50m, bench slope angle
may be around 50 0 .,This would terribly increase the width of
key cut top and would subsequently decrease the first cut width
(next to key cut). At this situation the load distribution on the
draglines operating in tandem would be severely disrupted.

17.  Seating position of dragline is decided by its reach, bench
height and cut width taken by draglines. The dragline is
positioned at the end of the cut along the axis of the key cut
and strips all overburden from this position.
 This method is applicable where the overburden depth is
relatively shallow compared with the dragline dimensions.
The dragline is positioned on the spoil (decoaled area) side of
the key cut and is applicable where the overburden is so deep
that all of it can not be stripped without rehandling. The spoil
can be dumped farther away from this position. The swing
angles are however, increased upto l20 degree.

18.  Depending upon technological system of face
operation (whether horizontal or vertical tandem
operation) and reach of dragline i.e., the distance
between the dumping point and the axis of travel
of the dragline for each cut, decide the seating
position of the draglines. It should be noted here
that a wider cut width is possible in horizontal
tandem operation of draglines and a larger height
is possible in vertical tandem operation.

19.  The cross-section area of cuts and spoil geometry
is determined by trapezoidal rule, which is based
on measurements and calculations. The abilities of
the computer should be used to eliminate the
tedious and time consuming tasks involved in
drawing balancing diagram, such as repetitive
calculations and measurement.

20. CE = (P A / A ) X W X T X D X R (Mte/year)
Where,
 CE = Coal Exposure (Mte/year)
 P A = annual production of the dragline (Mm 3 )
 A = Cross sectional area taken by the dragline (m 2 )
 W = cut width (m)
 T = Thickness of coals seam( m)
 D = Density of coal (te/m 3 )
 R = Recovery factor
 Here, PA/A = Rate of advance of dragline

21. where SSH is the scheduled shift hour; MH,
maintenances hours; IH, idle hours; and BH,
breakdown hours.

22.  After collection of field data for cycle time, availability and
utilisation, the weighted cycle time was computed by a formula,
proposed by the authors, based on the amount of overburden
removal at different swing angles, as observed during the field work.
This formula is-
where C1 is the average total cycle time upto 90° swing; C2 , the
average total cycle time for 90° to 120° swing; C3 , the average total
cycle time for 120° to 150° swing; and C4 , the average total cycle time
for 150° to 180° swing.

23.  Computation of annual output in Mm3 for each dragline was
done by using the standard equation (6), namely
 where B is the bucket capacity of dragline, m3 ; C , overall cycle
time of dragline, s; K , overall utilisation factor (AU); S , swell
factor for loose, easy digging sandstone (0.719); F , fill factor for
loose, easy digging sandstone (0.933); M , machine travelling
and positioning factor (0.8); Nh , number of hours in a shift (8 h);
Ns , number of shifts in a day (three shifts); and Nd , number of
days in a year (365 days).

24.  The computation of efficiency for each dragline was done by
using the equation (7) as given

25.  The rehandling percentage was computed by using
the equation (9)
 where KRH is the rehandling percentage; A1 ,
rehandle area, m2 ; and A2 , total excavation area
[Key cut + First cut + First dig area], m2