0910 Ernesto Villaescusa

Nuevas tendencias de la Minería Subterránea profunda Planeación, operación y estabilización del macizo rocosoBy © Ernesto Villaescusa, PhD Chair in Rock Mechanics WA School of Mines, CRC Mining & Curtin University Australia Introduction Western Australian School of Mines Research The overall objective is to characterize rock masses and their response to mining activities, so that stable excavations can be designed, constructed and supported. S801 Geological regime S807 New technology S802 Rock mass characterization S803 Performance prediction Rock Mass Characterization Excavation stability S806 Backfill mining voids S808 Shotcrete support S804 Ground support evaluation Ground Support Technology S805 Ground support implementation Introduction Orebody Orebodydelineation delineation Orebody delineation Rockmass Rockmass characterization characterization Mining method selection Access & infrastructure Stope & pillar sizes Global sequences (Stress analysis) Global Economics NO Geology Geology Geology & & rock rock mechanics INPUT DATA Mine planning Mine Mineplanning planning Rock Mechanics G L O B A L D E S I G N Mine planning & Rock Mechanics Mine planning Acceptable design YES Infill Infill delineation delineation drilling drilling Drill & blast design Rock reinforcement Detailed economics Extraction monitoring D E T A I L E D D E S I G N CLOSURE OF DESIGN LOOP Geology Geology Mine Mine planning planning Rock mechanics Mine planning Operations, Operations, Mine Mine planning planning Geology Geology & & Rock Rock mechanics mechanics YES Document Document results results NO Acceptable Acceptable design design END Flowchart of mine planning process (Villaescusa, 1998). Introduction – Mining at depth Conditions often become difficult beyond a 1000m or so 1000m Golden Grove Mine, Western Australia (Thompson, 2011) Maximum recovery – minimal dilution Continuous extraction sequence required to avoid pillars Hangingwall Depth of Failure vs. Hydraulic Radius 9 8 7 6 5 4 3 2 1 0 0 2 4 6 HR 8 10 12 14 Depth of Failure (m) Depth of 0-1m 1-2m 3-4m 4-5m >5m Golden Grove Mine, Western Australia (Thompson, 2011) Mining method selection & infrastructure Change of the mining method or infrastructure location SLOS 1000m SLC/SLOS Geotechnical monitoring requirements A need to understand the overall failure process and instability 1000m 1000m Seismic sensor array Mine induced seismicity Kanowna Belle Mine, Western Australia (Morton, 2013) Large scale geological discontinuities The global stability may be controlled by large scale structures 1000m Mount Charlotte Mine, Western Australia (Corskie, 2013) Seismic response of large scale structures The structures may become seismically active 1000m 1000m Fitzroy fault Kanowna Belle Mine, Western Australia (Morton, 2013) Mining method multiple lift - sublevel open stoping Used for tabular or massive – steeply dipping orebodies Cut-off slot . . . .. . . . . . . . . . . . . . .. .. .. .......... . ... .... .. .. Cut-off .. . . . slot . ... ..... .... . . . ....... Drill drives .. .... ... ... . .. ...... Case study - sublevel open stoping at depth 1000m Callie Mine, NT Australia (Graf, 2013) Multiple lift - Sublevel open stoping Primary-secondary extraction sequence Callie Mine, NT Australia (Graf, 2013) Multiple lift - Sublevel open stoping Cemented rock fill of stoping voids In-situ stress measurements - a key requirement Acoustic Emission from oriented core samples – No access required – only deep core Callie Mine, NT Australia (Graf, 2013) In-situ stress measurements - a key requirement Orientation and magnitude with depth determination - For all the stoping block areas planned Callie Mine, NT Australia (Graf, 2013) Intact rock strength determination For all rock types Callie Mine, NT Australia (Graf, 2013) Intact rock strength determination For all rock types Callie Mine, NT Australia (Graf, 2013) Intact rock strength determination For all rock types Callie Mine, NT Australia (Graf, 2013) Joint set number and orientation – block shape From development exposure and diamond drilled core Callie Mine, NT Australia (Graf, 2013) Joint condition determination From development exposure and diamond drilled core Callie Mine, NT Australia (Graf, 2013) Joint set characteristics Callie Mine, NT Australia (Graf, 2013) RQD from exploration core Changes with depth Correlation with large scale structures Callie Mine, NT Australia (Graf, 2013) Rock mass classification Block A Block B Block C Block D Callie Mine, NT Australia (Graf, 2013) Excavation performance under increased stress 13/08/2013 Excavation performance under increased stress 13/08/2013 13/08/2013 Excavation performance under increased stress Ground support strategy for an increasing stress 20 Stress Reduction Factor (SRF) 10 5 2 1 0.5 0.2 0.1 1 2 5 High stress Heavy rockburst zone σ1 = In-situ main principal stress σc = Uniaxial Compressive Strength of intact rock Near Surface 2.5 – 5.0 Medium confining stress Low confining stress 10 20 50 100 200 σc σ max Ground support strategy for an increasing stress The walls of the excavations become unstable due to vertical stress. Time dependent slow deformation Sudden, violent failure Ground support strategy for an increasing stress Rock bolting - with or without welded wire mesh A generalized form of support effective for shallow to moderate depths. Ground support strategy for an increasing stress At greater depths bolts, shotcrete and mesh required for backs and walls. Ground support strategy for an increasing stress Fibrecrete energy dissipation is not enough under high stress conditions Ground support strategy for an increasing stress Fibrecrete energy dissipation is not enough under high stress conditions Ground support strategy for an increasing stress Bolts + mesh embedded shotcrete + cables Sudden failure Ground support strategy for an increasing stress Rock mass demand Demand category Low Medium High Very High Extremely High Reaction pressure (KPa) <100 100-150 150-200 200-400 >400 Surface displacement (mm) <50 50-100 100-200 200-300 >300 Energy (KJ/m2) <5 5-15 15-25 25-35 >35 © E. Villaescusa WA School of Mines (Modified from Thompson et al, 2012 ) Ground support strategy for an increasing stress Example of low demand – unsupported lower walls Ground support strategy for an increasing stress Example of low to medium demand – fibrecrete and walls Ground support strategy for an increasing stress Example of low to medium demand – fibrecrete Ground support strategy for an increasing stress Example of high to very high demand – mesh embedded chain link Ground support strategy for an increasing stress WASM ground support design chart Ground support strategy for an increasing stress Excavation shape at depth will require changes Conclusions • Rock mass characterization from exploration core. • Selection of mining method with geotechnical considerations. • Geotechnical monitoring for global stability. • Strength vs induced stress ratios become unfavourable. • Mode of failure anticipation required. • Ground support strategy for high energy dissipation. • Change of excavation shape may be required.