GEOTECHNICAL MAPPING IN AN ACTIVE MINE TO FORECAST THE ROOF STRATA BEHAVIOUR IN IT’S VIRGIN EXTENSION BLOCK : GEOTECHNICAL MAPPING IN AN ACTIVE MINE TO FORECAST THE ROOF STRATA BEHAVIOUR IN IT’S VIRGIN EXTENSION BLOCK Dr. D.N. Sharma
Dy General Manager(G)
Dy General Manager(G)
The Singareni Collieries Co Ltd. ABOUT SCCL….. : ABOUT SCCL….. Only Coal Producing Company in South India
36 Under Ground and 14 opencast mines
Target for the Year 2009-10 – 50.40 m.t.
Actual Production – 50.42 m.t.
Target for the year 2010-11 – 51.30 m.t.
Total Geological Reserves -9436 m.t. Slide 3: SCCL had collaborative agreement with CSIRO, Australia to work jointly on optimizing mining layout and design and developing effective operational strategies for achieving production level of over 2.0 MT in the proposed new Longwall mines of SCCL, under complex geological conditions. Collaborative Agreement with CSIRO, Australia Slide 4: SCCL identified two Longwall Blocks viz.
Adriyala Longwall Block
KTK Longwall Block
Generation of Additional Data
Drilling of additional boreholes by Full coring/partial coring/non-coring
Geophysical logging of all boreholes
Micro logging of core samples
Storage of core samples of one complete borehole
Core photography & to prepare composite log, using the core profiler software Contd…. : Contd…. In-situ stress & Permeability tests
In-situ strength of coal In under ground pillars
Highwall mapping near the punch entries
Geotechnical testing of core samples of roof, floor strata as well coal seams ADRIYALA BLOCK DETAILS : Adriyala Shaft block is part of the Ramagundam coalbelt.
Total area is 4.60 sq.km.
Geological Reserves 180m.t.
Initially, 57 BH’s with 30,300m.
After interacting with CSIRO, Australia, 19 additional BH’s drilled with a total of 10,200m.
Total number of boreholes 76 with a total metreage of 40,528.
Density of Boreholes is 16 BH’s/sq.km . ADRIYALA BLOCK DETAILS Slide 7: The Talchir Formation is the oldest unit of the Lower
Gondwana sequence proved.
The coal bearing Barakar Formation overlies the Talchir
Formation with a gradational contact.
Seven regionally correllatable coal seams viz., IA,I,II,IIIB,IIIA,III
& IV are developed in this block in descending order.
The Barren Measures succeed the Barakar Formations,
conformably with the gradational contact around 10 to 15 m
above No. IA seam.
Coal measures trend in N 10°W –S 10°E with
east-north easterly dips.
The gradient varies from 1 in 6 to 1 in 7.5 GEOLOGY AND STRUCTURE Slide 11: COAL BEARING DISTRICTS OF ANDHRA PRADESH Slide 16: Adriyala Shaft block is a virgin block .
Depth varies from 300m to 600m and is located on the dipside of existing underground mine of GDK- 10A Incl.
The top coal seam that is I seam is under exploitation through GDK-10A mine where longwall mining is in practice.
This Coal seam is mined by Conventional and Longwall method of mining. STATUS OF MINING UNDERGROUND GEOTECHNICAL MAPPING : UNDERGROUND GEOTECHNICAL MAPPING A detailed underground geotechnical mapping has been carried out in I seam of GDK-10A Incl. (where already Longwall mining is in practice) to pick up the trends of Faults / Slips, Joints, Cleats, Sedimentary structures etc. with an intention to forecast similar structures in the dipside extension that is in Adriyala block. Slide 19: In the study area, the following structural features are picked up -
8 faults / slips.
Besides above, Sedimentary features are observed viz.
Cut & Fill structures
Pinch out of sandstone bands in the coal seam.
Apart from all these features, major fractures with an opening of 8 cms. are common in the coal pillars. SANDSTONE DYKES : SANDSTONE DYKES Clay veins, clay stone dykes or sandstone filings are wedge shaped masses that occur in crevice of a coal bed.
The common feature is that of the “Sandstone Dyke” or “Stone intrusions” or “Stone eye” (irregular masses of sandstone) that occur within the seam or penetrating into the seam.
These generally range up to 1m in width.The pattern and character of these structures suggest that they formed as tension fissures in coal which later filled with clayey/sandy material and then were compacted after burial. Sandstone dyke exposed in the coal : Sandstone dyke exposed in the coal CUT & FILL STRUCTURE : CUT & FILL STRUCTURE Among the most troublesome obstacles met within a coal mine are those partial or complete removals of a seam known as “Cut & Fill / Wash outs”, which is the result of erosion at some period during or soon after the formation of the seam or seams. Cut and Fill Structure exposed in the roof of underground workings. : Cut and Fill Structure exposed in the roof of underground workings. JOINTS : JOINTS The rose diagram drawn for 64 joints reveals two distinct direction of joints viz. J1 and J2 .
Joints poles were plotted on equal area projection lower hemisphere.
The most prominent joint set J1 is in the direction of N5E and next prominent joints set J2 trends in N75W.
There is a coincidence that J1 joints are parallel to pronounced set of Face Cleat.
Along the J1 joints , calcite fillings are observed. Further J1 joints dip at steeper angles.
Spacing of these joints varies from 1m to 3m.
J2 joints are closely spaced joints in the sense, the spacing varies from 10 cm to 30 cm and are tight joints. No joint opening is observed JOINTS EXPOSED IN THE ROOF : JOINTS EXPOSED IN THE ROOF ROSE DIAGRAMS : ROSE DIAGRAMS Contour diagram of Joints plotted on equal area projection lower hemisphere : Contour diagram of Joints plotted on equal area projection lower hemisphere CLEAT PATTERN : CLEAT PATTERN Cleat is a conjugate set of fractures occurs in coal mostly at right angles to each other.
“Face cleat” is a continuous one and “Butt cleat” is discontinuous and abuts against Face cleat.
A distinct cleat pattern is developed in the coal bands of I-Seam.
About 76 readings of Face cleat and Butt cleat each are taken.
The trend of cleat pattern is mapped and constructed a Rose diagram.
Face cleat trends in N5E and Butt cleat trends in N80W. Face and Butt Cleats in the Coal Pillar : Face and Butt Cleats in the Coal Pillar FAULTS/SLIPS : FAULTS/SLIPS Only 8 slips having less than 1m. throw are mapped.
It is inferred from the rose diagram that the most prominent slip trend is N85W. Down throw of the slips are mostly trending in N25E.
In most of the cases, the slip angle is 60 degrees and in few cases, the angle of the slip is 70 degrees.
Slickensides are observed along the slip planes. Slickenside along the slip plane : Slickenside along the slip plane ROSE DIAGRAM OF FAULTS/SLIPS : ROSE DIAGRAM OF FAULTS/SLIPS STRESS STUDIES : STRESS STUDIES Stress mapping is a technique extensively used to avoid heavy expenditure on conducting tests for In-situ stress measurements.
Features such as roof “guttering” or roof “pots”,orientation of Joints, Cleats etc. are mapped in underground workings and the stress direction is inferred.
Using such techniques, Stress mapping studies were conducted in the SCCL mining blocks viz. 5 Shaft & VK-7 Shaft of Kothagudem, Goleti-1 Incl etc., Slide 34: In the present study area, it is observed from the Tailgate and Maingate of Longwall Panels, the guttering is confined to dipside of the gateroadways.
Conversely, Dip Galleries are stable.
Further, the most prominent Joints (J1) and Face cleat trend are matching with the orientation of Principal Stress direction established in adjacent GDK-8 Inc block.
Hence it was presumed that in the study area, the Principal stress direction could be between N5E to N15E.
Subsequently, In-situ Stress Measurements were carried out in the deeper borehole (BHNo:1205) of Proposed Longwall Panel-1 of Adriyala block. 18 In-situ Stress Measurements were carried out from 77.50m to 522.00m depth in various horizons. As per the report, the major Horizontal stress 1 direction is varying from N11E to N23E. Roof Guttering in the dip side of Tail gate observed in Longwall panel-8 : Roof Guttering in the dip side of Tail gate observed in Longwall panel-8 ROCK MASS RATING (RMR) : ROCK MASS RATING (RMR) DGMS recommended to draw the support plan, based on geomechanical classification of the roof strata, using the ROCK MASS RATING (RMR) approach.
In GDK-10A Incl. I Seam (Top Section) is mined keeping sandstone as the immediate roof. This seam having an average thickness of 6.5m. The seam contains mostly coal, carb.shale and shale bands. RMR studies were carried out in in the underground workings. Slide 38: Based on the investigations, it is recorded that-
Combined RMR = 75.63%
Classification: II A GOOD
Rock Load =1.32 t/m2 GEOTECHNICAL HAZARD MAP : GEOTECHNICAL HAZARD MAP Added to the underground Geotechnical mapping, making use of the additional Exploration data being generated in Adriyala Shaft Block, to forecast the strata behavior of 1st Longwall Panel , Geotechnical Hazard map is prepared .
This Hazard map will be useful in anticipating the roof strata behavior both in the preparation as well in the retreat of the Panel. Steps involved in preparation of Hazard Map : Steps involved in preparation of Hazard Map The main gate and tail gate sections are constructed on the vertical scale. For this, 100m strata above the working seam up to one sequence of formation down below the working seam are considered. Within this 100m strata, different lithological units are taken into consideration.
The Clay forming the immediate roof of I Seam is shown both in the plan and sections.
Geological disturbances within the panel anticipated are taken into consideration.
Orientation of Principal stress direction with reference to Longwall panel. Contd.. : Contd.. 5. On the sections with bore holes, the seismic data and UCS from seismic logs are shown as < 30 Mpa and > 30 Mpa.
6. Immediate roof of I Seam is taken into consideration while constructing the Section and contouring the variation of its thickness on a plan.
7. Depth cover is taken into consideration in the process of preparing Hazard map.
8. RMR data of GDK-10A, classifying the roof strata of I seam is considered. HAZARD MAP : HAZARD MAP SUMMARY : SUMMARY Based on the underground geotechnical mapping the following observations are made-
Sandstone dykes, Cut & Fill structures and sandstone bands, pinch out are noticed in the coal seams.
The most prominent joints J1 are in the direction of N5E and coincide with the pronounced set of normal slips. Next prominent joint set J2 trends in N75W and are closely spaced.
Face cleat trends in N5E and Butt cleat is in the direction of N80W.
Minor Slips/faults are observed and are trending in N85W. Contd.. : Contd.. Based on underground mapping carried out in the present study area, it was presumed that Major Principal Stress direction 1 could be between N5E to N15E. Subsequent In-situ stress measurement tests conducted in this block, indicates that Major Principal stress 1 is in N11E to N23E. Contd.. : Contd.. RMR of the roof strata of I seam (Top section) is 75 and the rock load is 1.32 t/m2.
Further to supplement the underground Geotechnical mapping data in anticipating roof strata behavior, Geotechnical Hazard map is prepared and it will be immensely useful in the operation of Longwall Panel. CONCLUSIONS : CONCLUSIONS With all these studies, SCCL hope to achieve the Targeted Production from deep seated coal deposits by using Long wall Technology. Slide 47: THANK YOU