STRESS MAPPING FOR RE- ORIENTATION OF GALLERIES IN PVK-5 Incl. Dr.D.N.SHARMA Dy.General Manager(Geo) Exploration Division / RG1 • In PVK mine, King Seam workings reached 400m depth. • Thickness of the King Seam in the study area is about 6.50m with a gradient of 1 in 8. • King seam was developed in the Top Section upto 116 Level, with Sandstone as immediate roof. • Since there is a problem with sever seepage of water along sandstone roof , an attempt was made to leave about 3.50m seam portion in the roof. • In the changed working section, another problem of severe roof failures in Level galleries cropped out. 1. PROBLEMS IN KING SEAM
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STRESS MAPPING FOR RE- ORIENTATION OF GALLERIES IN
PVK-5 Incl.
Dr.D.N.SHARMADy.General Manager(Geo)
Exploration Division / RG1
• In PVK mine, King Seam workings reached 400m depth.
• Thickness of the King Seam in the study area is about 6.50m with a gradient of 1 in 8.
• King seam was developed in the Top Section upto 116 Level, withSandstone as immediate roof.
• Since there is a problem with sever seepage of water along sandstone roof , an attempt was made to leave about 3.50m seam portion in the roof.
• In the changed working section, another problem of severe roof failures in Level galleries cropped out.
1. PROBLEMS IN KING SEAM
2. STRESS MAPPING IN QUEEN SEAM
With a similar problem in overlying Queen Seam workings that is beyond 110 Level at a depth of 350m, Stress mapping was carried out, during June 2004. The inferences of those studies were-
The Major Principal Stress axis inferred from most prominent Joint set (J1) is perpendicular to Level galleries are contributing for instability of level galleries.
Minor Principal Stress axis inferred from least prominent Joint set (J3) is parallel to level galleries.
Conversely, Dip galleries are stable as they are almost (with about 5 degrees) parallel to the Major Principal Stress axis.
Further, these findings were closely matching with that of Stress Orientation established earlier in the Queen Seam of adjacent VK-7 Shaft through similar Stress Mapping technique.
CONTOUR DIAGRAM OF JOINTS PLOTTED ON EQUAL AREA PROJECTION,LOWER HEMISPHERE,
QUEEN SEAM (100 JOINT POLES)
DIRECTION OF STRAIN ELLIPSOID DEVELOPED IN QUEEN SEAM
3. STRESS MAPPING IN KING SEAM
1. Stress mapping is carried out in the present study area in King Seam.2. The workings crossed 400 m. depth line and approaching the F16 Fault
(throw 20m) in the dip side property. 3. The details of structural features mapped are as follows -
SL.NO STRUCTURAL FEATURE NO.OF READINGS. MEAN TREND
1 FACE CLEAT140
N550E
2 BUTT CLEAT N350W
3 MOST PROMINENT SLIPS40
N450 E
4 LEAST PROMINENT SLIPS N650E
5 MOST PROMINENT JOINTS27
N550E
6 LEAST PROMINENT JOINTS N650E
3. STRESS MAPPING IN KING SEAMContd…
4. The causative factors of unstable roof conditions are due to :
• The most prominent Slips S1 aligned to the greatest principal stress direction (N450E) is responsible for the roof instability confined to level galleries.
• Roof strata consists of thin layers and leading to failure in level galleries with an indication of "Gutter roof". Trend of the "Gutter roof" ,largely helped to confirm the orientation of principal stress in the study area.
• As workings are enveloped by Faults, sympathetic slips developedand contributed for unstable roof conditions.
• These findings are closely matching with that of Stress Orientation established in the overlying Queen Seam.
FACE AND BUTT CLEAT
SLIP IN THE PILLAR SHOWING DISPLACEMENT OF BANDS
J1 JOINT EXPOSED IN THE FLOOR
4. ROCK MASS RATING (RMR)RMR classified the roof of working section of King Seam (Bottom Section) as "FAIR“ with a rating of 41, where 40 is border of “Poor”and “Fair” rock.
“ROOF GUTTERING” IN THE CENTER OF LEVEL GALLERY BEFORE RE-ORIENTATION
5. NUMERICAL MODELLING BY CIMFRNumerical modelling was taken up by CIMFR and the following conclusions and recommendations are made:
1. The magnitude of major and minor in situ horizontal stresses in King seam in the study area are found to be 7.15 Mpa and 3.68 Mparespectively.
2. The direction of the major in situ horizontal stress is found to be along N 450 E , which is almost perpendicular to the level galleries.
3. Keeping the above directions and magnitude of in situ horizontal stresses in view, level gallery can be driven along N 850 E toE 50 S (with a stress point of view).
6. ORIENTATION OF GALLERIES REFERENCE TO PRINCIPAL STRESS
N
N 7
° E
N 1
0°
E
N 2
4° E
N 55° E
N 69° E
N 62° W
N 47° W
F5R
E-O
RIE
NTE
D-1
DG
F18
F10 & J1
& FC
F9
F16
RE-ORIENTED-1.LG
S1N 4
5° E
N 65° E
S2 & J2
N 35° WBC
N 73° E
ORIGINAL DG
N 24° W
OR
IGIN
AL LG
INDEX
N 45° W
1
N5
°WR
E-O
RIE
NT
ED-2
DG
N85°ERE-ORIENTED-2. LG
S1 MOST PROMINENT SLIP
J1 MOST PROMINENT JOINTS2- NEXT PROMINENT SLIP
J2 NEXT PROMINENT JOINT
FC- FACE CLEATBC-BUTT CLEAT
1- MAJOR PRINCIPAL STRESS 3- MINOR PRINCIPAL STRESS RE-ORIENTED-1 DIP GALLERY