Support system (Underground Coal Mining) by Prof. S Jayantu.pdf

COURSE MATERIAL FOR
UCMT-MN-2102-
16.4.2020
for further interaction during the period of lockdown
SINGAM JAYANTHU, Professor, NIT-Rourkela

1. TITLE: CASE STUDIES ON DESIGN OF SUPPORTS
IN UNDERGROUND MINES
2. OBJECTIVE OF THIS CASE STUDY
To design suitable support system for roof and sides in
depillaring panels of RK-6 Incline-SCCL.
COURSE MATERIAL FOR UCMT-MN-2102-on 16Apr 2020
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3. GEOMINING CONDITIONS
Earlier 1A, 1seams were not proposed to develop due to low grade quality of coal. After
selective mining No. 1A and No.1seam are developed. No. 2B seam and No. 3 seam are partially
developed and stopped due to low thickness.
In RK6A Section, 1Aseam, depillaring is under progress with SDL machines this is done by
conventional method of mining .
No.1seam partial development; this is done by conventional method of mining. Presently part
of seam is Non-workable.
Table 1 and Fig 1 shows Strata section in Borehole number 534.
Fig 2 and 3 illustrates location of workings in panels 1AS1, 1AS2, and 1AS3.
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Seam 1A 1 2B 2A 2 3 4 5
Thickness(m) 3.60
-5.8
2.8-3.2 0.6-
1.2
1.5-
2.6 4.2-4.7
0.9-
1.2
1.6-
1.8 1.6-2.0
Parting(m) 18 40 11 25 35 12 11
Gradient 1 in 4
Overall quality E
Gassiness I degree
Extractable Reserves as on 01-08-2012 6 .00MT.
Panel No. No. of pillars Size of the panel
1AS1 36 400 M x 105 M
1AS2 23 225 x 145 m
1AS3 40 277 m x 175 m
Table1: Details of the strata section.
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Fig 1: Strata section in Borehole number 534
Meter age Strata
5.00 Surface soil
49.00 Brown sand stone
60.94 Grey sand stone
5.59 No.1A Seam (Proposed Panel)
3.32 No.1 Seam(Standing on pillars)
0.41 No.2B Seam(Virgin)
1.48 No.2A Seam(Standing on pillars)
4.85 No.2 Seam(Standing on pillars)
0.46 No.3 Seam(Virgin)
Surface RL 874.71 m
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3.2 Condition of the Workings
1AS3 panel of No.1A Seam having thicknesses is about 4.6 to 5.5 m dipping at 1 in 7
gradient having been developed up to 3.0m along the sand stone roof.
The number of the pillars and the size of the panel is presented in Table 2.
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Panel No.
Width of the
galleries
Height of the Galleries
(in m)
Size of the pillars (m) Depth of cover (m)
Max Min Avg Max Min Avg Max Min Avg Max Min Avg
1AS1 5.3 3.5 4.4 3.6 2.4 3.00 37 x 35 35X 33 35X 35 194 143 168.50
1AS2 5.3 3.5 4.4 3.6 2.4 3.0 47 x 35 37 x 35 42 x 35 187 143 165
1AS3 5.1 3.5 4.3 5.4 2.5 3.00 34 x 44 32 X 25 35 X
32
138 108 123.5
Table 2: Details of the pillars
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Fig 2: Location of panels 1AS1 and 1AS2 IN RK 6 incline
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Fig 3: Working plan of 1AS3 panel of 1A Seam
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Manner of extraction followed in the depillaring panel (Fig 4).
Level split with 4.5 m width was used along with dip slices leaving 2 m rib.
a) Each pillar shall be split into two equal parts by driving a central level split gallery not exceeding 4.50m in width.
Each half pillar so formed shall be extracted by driving dip slice not exceeding 4.00m in width. While driving a
slice a rib of coal 2.00m to 2.50 m thickness shall be left against the goaf which shall be extracted judiciously
while retreating from the slice.
b) Number and width of the slice shall also be so adjusted that while driving the last (out by) slice, a block of coal not
less than 3m to 4.00 m thickness is left against the adjacent original gallery.
c) Driving of a slice shall not commence until extraction in the immediate in bye slice is completed and goaf edge
support erected.
d) Extraction of pillars shall commence from the dip / in bye slice and proceed systematically to rise / out by side
maintaining a diagonal line of faces and avoiding formation of V in the line of extraction.
e) A maximum area of exposure shall be limited to 130 sq.m.
f) Stooks, if any left inside the goaf shall whenever possible be knocked down before retreating from the area under
extraction in consistency with safety.
g) The advance splitting shall be limited to within two pillars from the pillar under extraction.
h) While withdrawing supports, care shall be taken to see that the withdrawal from the corresponding stook/slice in
the seam.
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Fig 4: Manner of extraction followed in depillaring at
1AS2/1AS3 panels, RK 6 incline
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SYSTEMATIC SUPPORT RULES FOR EXTRACTION OF PILLARS
4.1 Design of Supports
Support system was designed for depillaring workings of 1AS1 based on Rock Mass Classification,
and numerical modeling. Support system was implemented in 1AS2, and 1AS3, and strata behavior
studies were conducted for evaluation of the efficacy of the support system.
Systematic Support rules were also formulated on the basis of RMR and applied to the depillaring
area in panel # 1AS2 and 1AS3 in No.1A Seam where pillars were extracted by Caving method
using Side Dump Loader sat Ravindrakhani No.6 Incline mine.
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Estimation of Rock Load and Design of Support System in development Working
The Rock load = B × D (1.7-0.037 × RMR + 0.0002 × RMR2)
RMR = 52
Gallery span (B, width) = 4.2 m
Height = 3m
Density (D) = 2.1t/m2
Rock load = 2.75 t/m2
Hence, rock load in galleries and splits = 2.75 t/m2
The rock load is to be supported with higher load to protect the area from the roof fall. Since the safety
factor is used in equation, therefore the roof support is designed for rock load of 2.75 t/m2. Full column
grouted bolt is used as the support system (Fig 5).
Roof bolt support = 10 t
Bolt spacing = 1.5 m
Distance between two rows of bolts = 1.5 m
No of bolts in a row= 3
Support resistance = 30 t/5.4m2 = 5.1 t/m2.
Factor of safety = 5.56 / 2.75 = 2.02 for gallery.
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Fig 5: Design of Support System for Galleries and Splits
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Design of Support at Junctions
The junctions are unstable and experience more load when compared with galleries due
to large surface area (Fig 6).
The total area of the junction is 4.5 m x 4.5 m. Therefore the junctions are supported by
are Supported by 33% extra bolts.
Rock Load= 4.2*4.2*2.75 = 60.75 t
Support Resistance = 13*10 = 130 t
Factor of safety = 130/60.75 = 2.13
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Fig 6: Design of Support System at Junctions
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Estimation of Rock Load and Design of Support System in Depillaring Working
Rock load (Proof) in slice and goaf edge was estimated using NGI-Q system from the
following empirical relation:
Proof = 2/3 (Jn1/2/ Jr) x (5Q) –1/3
Where, Jn = 9, Jr = 1.5, Q = 2 for slice
and Q = 1 for goaf edge (Table 3).
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Table 3: Q-System Calculation
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Load in the slice is calculated to be (Proof) = 6.19 t/m2
and rock load at goaf edge is calculated to be Proof= 7.79 t/m2.
The slice and goaf edges are supported by steel props and chocks.
Slice width = 4m Rock load in slice, Proof is 6.19 t/m2 Breaker line bolt support = 8 t Chock with corner
prop support = 30 t
The support system will be three chocks with corner prop and five breaker line bolt as shown in Fig 7.
The above configuration leads to: Support resistance =130 t/12sq.m = 10.5 t/ m2
Factor of safety = 10.8/6.19 = 1.75 for slices the rock Goaf edge side will also have 3 chocks with corner
prop and5 breaker line bolts with spacing of 0.8m (Fig 8).
The other calculations are as follows:
The support resistance = 130 / 12= 10.8 t/m2
Factor of safety = Roof support / Rock load for goaf edge = 10.8 /7.79 = 1.39
It is good because goaf edge is supported for temporary period.
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Fig 8: Design of Support System for Goaf Edges
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Design of Support System for Sides of Galleries
Presence of 0.3 m thick clay band, 1 m above the floor of the seam reduces the stability of the
sides (Fig 8.1).
Therefore, the sides of the galleries are supported by stitching the wire ropes with the rock bolt.
Three rock bolts are installed in a row with 1 m spacing and distance between the rows is 1.5m.
Wooden lagging are provided at 1.5 m interval to increase the contact area of the stitching rope
and to provide better support
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Fig 8.1: Design of Support System for Sides
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Thank you very much
for patient hearing and
going through the slides
sent as a rehearsal sample
of online class for our
students
I look forward for your
queries and online
interaction through
Microsoft team access as
being planned by our NITR
16-04-2020 23

Support system (Underground Coal Mining) by Prof. S Jayantu.pdf

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