HIGHWALL MINING AT MOCP

S C C L

A CASE STUDY

History High Wall Mining in the form of Auger

mining started in 1983 in U.S.A. ADDCAR system of high Wall mining started in 1990. The proposal of High wall mining was studied by Project Planning Department of SCCL and identified the mines having potential for extraction of coal by high wall mining technology. Board has approved the FR of extracting coal by high wall mining technology on 18.6.2005.

HIGH WALL MINING IN SCCL

SCCL is pioneer in India to adopt this technology to extract hidden coal from high wall of oc mine and other inaccessible places which can not be extracted by any other methods of mining.

In view of the conservation of coal it was proposed to gainfully extract the coal locked in the high walls and barriers of OC mines by “High wall mining technology.

HIGH WALL MINING IN SCCL

SCCL entered in to agreement with M/s Advanced Mining Technologies to extract about 6 million tonnes of coal from four OC mines in a span of 6 years.

Availability of high wall face is the main requirement for continuous working of this technology and there is potential in SCCL to meet this requirement.

Introduction 1. High Wall Mining operations started in SCCL in

December-2010 at RG OC.II and presently working at Medapalli opencast project since January-2012.

2. Medapalli Opencast project is situated on the Southern Bank of river Godavari. High wall mining is proposed to extract the left-out coal from V,IV,III,IIIA,II and I seams in ascending order beneath the final pit slope of Block-A and Block-B.

The workable seam details are as followsSeam Vertical

DepthThickness Parting Web

pillarLength

Web pillarWidth

Extractable reserves

(MT)I SEAM 26 - 71 4.56 125 3.7

15.74II SEAM 25 - 90 2.54 145 3.7 0.159

44.38IIIA SEAM 27 - 141 1.61 155 1.6 0.228

24.78III SEAM 30 - 170 6.50 200 6.0 0.809

13.51IV SEAM 44 - 192 3.60 220 5.7 0.589

21.14V SEAM 83 - 220 2.50 230 3.2 0.265

CIMFR has studied the mine and submitted the High wall mining design.

As per CIMFR study report, permission was obtained from DGMS authorities for working of High wall mining operations in Block-A at North West side of workings of Medapalli Opencast Project.

OBJECTIVE To recover the blocked coal of high wall which

is not feasible for extraction by any conventional method currently available, without sacrificing human safety.

The Biggest Dragline in INDIA. Video given below:- https://www.youtube.com/watch?v=FLg6ZPtfzHs

Highwall Equipment Overview Successful high wall mining requires favorable geological and

geotechnical conditions.

The Mining equipment consists of Advanced control and navigation systems to aid in accurate mining operations.

HORTA Navigation System

Inclinometers

Gamma Coal Thickness Sensors

Continuous Miner steering system

OVER VIEW OF HIGHWALL MINING SITE

Technical Details

High wall mining equipment mainly consists of the following. High wall miner. Launch vehicle Add cars Stacker conveyor Supporting equipment like Pan loader, dozer etc.

For Video Click the link below:-

https://www.youtube.com/watch?v=uqlmBm81aIw

HIGHWALL FEATURES

HORTA

Inclinometers

Gamma sensors

Odometer

Steering mechanism

Length - 10.6 mWidth - 3.5 mHeight - 2.5-4.6mGr.press -1.95kg/cm2

Cutter motors - 2* 200 HP pump motor – 70 HPGathering motors- 2*60 HP traction motor - 2*35 HP(DC)Scrubber motor - 35 HP

Head CH4 sensor

Rear CH4 sensor

CONTINUOUS MINER (12CM 15D)

SAFETY FEATURESPrestart warningEmergency stopsPull cordsBelt cross overFencing guards

Length : 29 mWidth : 9 mHeight : 8.5 mWeight : 300 TMotors : 2 x 150 KW, 1.1 KV ( operates hydraulic pumps)Belly belt motor : 56 KW x1.1 KVGround pressure : 1.95 kg/sq.cm

LAUNCH VEHICLE

ADD CAR

Length : 12.5m

Width : 3.1 m

Motor : 30 KW

Weight : 12 T

STACKER CONVEYOR Motor : 56 KW, 480 V

Pull chord

Emergency stop

LOADER, DOZER, MOBILE SERVICE VAN

LOADING OF COAL – SHOVEL AND DUMPER

HIGHWALL MINING AT MOCP About 2.06 MT of coal is identified at this mine for

extraction by high wall mining technology. This is the mine with tough geotechnical conditions The

operations at MOCP started from 15thJanuary 2012. Total coal to be extracted is about 2.06 MT at this project

from five seams i.e. 2Seam(0.159),3ASeam(0.228),3Seam(0.809),4Seam(0.589) and 5Seam(0.265)

For Video click the link below:-

https://www.youtube.com/watch?v=uqlmBm81aIw

MINING METHOD

High Wall mining is a remotely controlled mining method which extracts coal from the base of an exposed high wall face via a series of parallel entries driven to significant depth up to 500 Mtrs deep, within the seam horizon linking surface and underground operations. The method allows recovery of coal from surface pits that have reached final high wall position.

• High Wall miner will be deployed in an earmarked area by providing 60m plotform. After extraction of the high wall coal from that area, the miner will be shifted to the next proposed area.

• The method consists of driving a series of parallel entries with 3.5m width into the High wall one after the other, separated by a rib(web pillar) of designed width.

• The coal cut by the high wall miner will be transported by a series of ADDCAR Conveyors to the launch vehicle located at the entry of the roadway. The elevating Stacker conveyor receives the coal from the belly belt on the launch vehicle, and transfers it to a stock pile which will be later lifted by a pay loader into dumpers/ trucks for transporting to surface.

• After completion of web cut it will be filled with Nitrogen (N2) and the mouth will be packed with overburden material with in 72hours.

Details of High wall Mining – Block-A, Medapalli OCP.SCCL.Seam 5 SEAM 4 SEAM 3 SEAM 3A SEAM

Thickness 2.5 Mtrs 3.6 Mtrs 6.5 Mtrs 1.6 Mtrs

Date of start 15.01.2012 29.05.2012 28.09.2012 Yet to start

Date of End 15.04.2012 21.09.2012 In progress -

No. of Web cuts Driven. 45 46 38 -

Length of Drivage mtrs 3768 5845 6730 -

Planned length of web cut drivage in mtrs

230 220 200 155

Max. Length of web cut drivage mtrs

115 207 200 -

Planned Production(Tonnes) 100191 153657 220000 40926

Achieved Production 63138.25 101347.79 216604.30 -

Percentage of Extraction against planned

63 66 98 -

Subsidence Management Subsidence is being monitored on the surface over block ‘A’. A

subsidence plan was designed and 76 subsidence pillars were constructed over the area and leveling of pillars is being done every month. Subsidence pillars are constructed along and across the highwall and subsidence reading record is being maintained. So far no traces of subsidence was observed. In addition to this slope stability monitoring is being done for knowing any movements in the slope of the highwall.

Drilling and Blasting in a bauxite OCP. Video is given below:-

https://www.youtube.com/watch?v=dNwSZq5T3bg

SECTION ALONG HIGH WALL

SECTION ALONG A-A’

Slope stability Monitoring

Slope of the highwall is being monitored by Slope stability Real time monitoring system “The Cyclops”, which has been developed by SOL DATA and IGN, the French National Geographical Institute.Instruments used: 1. T M 30 Leica total station.2. Tact computer for raw data collection3. Server computer with clops software for conversion of data.4. Siren 5. Reflector prisms.

Cyclops is a fully automated monitoring system comprising a motorized total station with video target acquisition under computer control. The system allies the latest developments in motorized total station technology with SOL DATA’s software to create an extremely powerful, versatile and user-friendly monitoring solution.

Special features of the Cyclops: Cyclops works night and day without lighting structures. Cyclops measurement time per target is around 12 seconds. Absolute movement of targets are given in X,Y,Z directions. Usual number of targets 50. Targets fixing: screwed into highwall Protection: Cyclops is installed with a special protective helmet. Information is visualized in real time. Can give Alert messages through alarms, cell phone alerts and e-mails.

Cyclops technical data Measurement range up to 500 meters Usual site accuracy: +/- 0.5 mm at 60 meters Longer range and higher accuracy are possible At Medapalli OCP 43 targets were fixed on the High wall and 6

reference targets were fixed around the instrument station. With total 49 targets total station will complete a cycle in 15 minutes. Measurements in X(in grades), Y(grades), Z(distance) directions are converted into movements by Cyclops. The process is continuous and the back up of the readings can be taken.

Limitations of High Wall Miner with ADDCAR system

Cutting Height with 12CM : 2.5m to 4.6 m Single Pass Up to 8 mtrs double pass with 14CM – 1.45 to 3.2 Span Width : 3.5 m Maximum Entry depth : Up to 610mtrs Maximum Seam Dip : +3 0 to –160. Bench Inclination : Up to +/- 5 0

SAFETY

It is a people free underground mining method relies upon the self supporting capacity of the strata above the series of parallel entries driven mechanically to a considerable depth without artificial roof support and ventilation in the seam horizon.

If you want to know something about a open cast coal mine then watch the video below:-

https://www.youtube.com/watch?v=JYeqqX7BaTw

Strata Control : Empirical web pillar design for seams in Block-A and Block-B

• Gallery stability also influenced with RMR , RQD values of immediate roof.

• Here the web pillars are designed with a factor of safety 2 keeping in view of long term stability of the pillars.

• Safety factor = pillar strength / stress on the pillar.• Pillar strength(Mpa)=0.25*C*h(-0.36)+(H/250+1)*(w/h-1)• Stress on the pillar(MPa)=0.027*H

Where: C: uniaxial compressive strength of 25 mm coal cube sample(MPa)

h: height of extraction in m

H: Depth in m

w: Effective width of pillar in m

The CIMFR pillar strength equation has been developed over a couple of decades after analysis of a large number of pillar stability observations from a gamut of Indian mining scenarios.

On the basis of past experiences from Indian coalfields it has been observed that a pillar safety factor of more than 2.0 is long-term stable, i.e. for many decades.

A safety factor between 1.5 and 2.0 may be taken as medium-term stable, i.e stable for a few years. If the safety factor of the pillar is 1.0, it may be treated as short-term stable, with a standup time of a few months. Due to the presence of important surface features like Flood Protection Bund for Medapalli OCP, the web pillars are designed for safety factor of 2.0.

STRATEGY FOR EXTRACTION

All the seams are to be extracted from bottom to top, starting from Seam-V and proceeding upward to Seam-I, by filling the pit with overburden rock which will act as a platform for the launch vehicle. Since the web pillars are to be designed for long term stability, with SF> 2.0, from stability point of view, the order of extraction and protection of overlying seams are not issues

WEB- PILLAR DESIGN IN BLOCK ‘A’

Full Length Holes IntermediateLength Holes % Ext.

Seam Max Length

Web Width

Int. Length

Alt. Web

V 230 m 3.2 m 70 m 2.4m 52.20%

IV 220m 5.7M 70m 4.0m 28.05

III 200 m 6.0 M 60 m 4.8m 36.8%

IIIA 155M 1.6M - - 68.6%

HYPOTHETICAL CASE - HIGH WALL

SURFACE

BENCHES

FLOOR B/SEAM

T/SEAM

DUMP FILLING

WEB CUT – TOP/SEAM

HIGH WALL MINING

EXTRACTION OF THICK SEAMS

SURFACE

BENCHES

FLOOR B/SEAM

T/SEAM

Here w/h ratio effects the pillar strenth. Shall be kept in mind

MONITORING SLOPE STABILITY

SURFACE

BENCHES

FLOOR B/SEAM

T/SEAM

MONITORING STATIONS

Over view of High Wall Mining at MOCPSeam V IV IIISeam thickness in Mtrs(ht of extraction). 2.5 3.6 6.5Date of Start 15.1.12 29.5.12 28.9.12Date of End 15.4.12 21.9.12 03.07.13No.of working days 47 95No. of Web cuts driven 45 46 41Proposed Length of Drivage Mtrs 9027 9062 7978Actual Length of Drivage Mtrs 3768 5845 7182Average Length of web cut drivage Mtrs per

day 80.17 61.53 33.19

Max.Proposed length of Drivage in Mtrs 230 220 200Max. Length of web cut drivage Mtrs 115 207 200

Proposed Production in Tonnes 1,18,479 1,71,271 2,72,249

Achieved Production In Tonnes 63,138 1,01,347 2,38,065

Experiences Small faults/undulations caused sudden increase/decrease of

the gradient of the gallery, sometimes more than the limitation of the equipment due to which add cars got buckled by hitting to roof.

In this mine, the highwall was formed almost along the full dip of the mine, i.e, about 90 to 110 . Web cut direction is almost along strike direction. Bearing of the drivages is 357.900. Gradient of the drivage is 10 to 30 in up gradient.

As the drivage is in strike direction, a triangular piece of coal is left in the roof is falling down during the extraction. If the roof is shale this phenomenon is more frequent. To overcome the above problem it is proposed in lower Block-B for drivage of web cuts in full dip direction.

Stone intrusions in the seams caused disruption in the progress and sometimes machine was withdrawn prematurely with out completion of the holes.

As seam gradient is 1 in 6 shifting of launch vehicle and making of level platform is causing more time.

Due to thinness of seam and changes in seam gradient with the influence of faults , planned length of drivages could not be achieved in No. 4 and No. 5 seams.

No.3 seam with 6.5 M thickness having top shale of about 1.5m the drivage is done in 2 passes. While driving the web cuts the top portion of shaly coal layers, which is being left over in the roof has fallen frequently on miner and on the add car belts causing delays.To minimize damages due to fall of roof layers, the height of top pass in no.3 seam is reduced from 4.5 to 3m which is proved to be successful.

To avoid bog down of machinery while preparing platform over extracted galleries near merging benches wherever solid parting over developed gallery is less than 3 mtrs, it was disturbed with shovel and the mouth was adequately packed by pushing with overburden material to the extent possible.

CONCLUSION1. High wall Mining is proved to be suitable for extracting

locked up coal reserves from Highwall benches, where coal extraction is not permissible or economical by extending the opencast or to work by any other method.

2. Site investigations are required to be conducted to obtain comprehensive Geological information.

3. Keeping in view of conservation of coal, which otherwise would be lost under subsequent internal dumping within short span, the web pillar design may be modified for short term stability by suitably adjusting the factor of safety of pillar to increase the percentage of extraction.

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