Inspection of geotechnical rock mass conditions in underground - PowerPoint PPT Presentation

Technical Meeting Webinar Inspection of geotechnical rock mass conditions in underground workings with an ultra-slim borehole scanner Torsten Gorka, Jason Henriquez Torsten.Gorka@dmt-group.com DMT Consulting Engineers Pty Ltd, Toowong QLD, Australia Technical Meeting Webinar, 11. June 2020 australia@dmt-group.com 11.06.2020 1 BBUGS Technical Meeting Webinar

Technical Meeting Webinar About me Torsten Gorka  Senior Geologist for Exploration & Geotechnics in Mining  Graduated in 2003 from the Ruhr-University Bochum, Institute of Geology, Mineralogy & Geophysics, Bochum, Germany  >15 years working experience in u/g coal mining  Exploration of coal and ore deposits worldwide; geotechnical and rock mechanical investigations; R&D; estimation of mineral resources and reserves; stratigraphical and structural investigations and interpretations; core logging, sampling, data acquisition, visualisation and interpretation 11.06.2020 2 BBUGS Technical Meeting Webinar

Technical Meeting Webinar CONTENT: (1) Introduction (2) Study site conditions and objectives (3) Work performance and the results (4) Technical characteristics and function of the applied slim borehole scanner (5) Additional examples (6) Conclusion 11.06.2020 3 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Inspection of rock mass conditions in difficult mining environment – Study case 11.06.2020 4 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Introduction Coal mining technology and roof support:  Multiple seam mining  Longwall excavation  Face length up to 520 m (AVG 340 m)  Double-drum shearer or plough Image source: Dietmar Klingenburg / RAG  Very deep mining: up to 1,650 m with 1,050 m average depth  High stress conditions and weak strata Longwall: Shield support, plough double-drum shearer 11.06.2020 5 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Coal mining technology and roof support  Most German gateroads are double-used  Almost all in-seam roadways in Germany are supported by yielding support systems . Rockbolt support as main roadway support also exists, but is relatively seldom.  Since 1995 the so-called combination support system is the predominant method applied in German roadways.  It is a yielding arch support with backfill, which is combined with rockbolts. The floor remains unsupported. Gateroad direction Mining Gateroad Top: Roadway support with Longwall face yielding steel arches Goaf area Bottom: Installation of Combi A support Closed mine drift Source: Junker et al. 11.06.2020 6 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Coal mining technology and roof support  Combi support Type A: - Firstly rockbolts are installed to support the rock mass. - At a distance of 10 to 50 m behind the roadway heading the arch support is subsequently installed - Behind the arches lagging sheets and canvas are fixed, and the cavity between the rock and this cover is filled up with backfilling material. - The convergences of a roadway equipped with combined support type A has been found to be Physical, scaled model of Combi Type Physical model of only roofbolted roadway in about 50% less than that of a roadway supported (here: „B“) in 1530 m depth 1,000 m depth solely by yielding arches. 11.06.2020 7 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Roof Geomechanical modelling bending 12 MPa 18 MPa 10 MPa mudstone Support deformation/ seam sidewall buckling Support Floor heaving 11.06.2020 8 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Study site: characteristics Inspection of roof rocks of a roadway with the intrinsically safe SBS (Slim Borehole Scanner)  Depth appr. 1,100 m  Roadway is built in difficult geologic and mining conditions  Combi-A support 11.06.2020 9 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Study site: characteristics  Faults and old working boundaries influence the stress field and lead to increased pressure and convergence  Several overlying old excavation boundaries (green, brown, blue, red and magenta hatched lines) - parallel and intersecting, up to 20 m close  Several faults (orange lines) - Overthrusts, running approximately parallel - Normal and strike-slip faults intersecting the roadway 11.06.2020 10 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Plan view: Timeline Seam excavation Seam excavation Raise drifts Timeline Gateroad Gateroad driving preparation (from 2 sides) Excavation Excavation above of seam above Gateroad length [m] 11.06.2020 11 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Geotechnical borehole log – Exploration phase Mineralization Roof rocks thickness condition structure Opening Bedding Bedding RQLD Joints Joints Core Bed  Compact sandy shale and sandstone  Good to very good RQD  Regular bedding  Some steep joints 11.06.2020 12 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Study site: characteristics & objectives  Inspection of roof rocks of a roadway with the intrinsically safe SBS (Slim Borehole Scanner)  Thin boreholes (32 mm) were drilled with a length of up to 2.7 m vertically into the roof and inclined to the roof sides  Inspection of the roof strata; image information is used for the quality control and optimization of the roadway support. B6 B4 B5 B3 Cross-section 1 Cross-section 2 Cross-section 3 11.06.2020 13 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Ultra-slim borehole scanner (SBS)  360° digital optical scanning of the borehole wall in ultra-slim boreholes (1“-2”)  23 mm tool diameter, 1.12 m length  Intrinsically safe version for application in firedamp-endangered atmosphere like coal mines [I M1 EEx ia I]  Determination of discontinuity spacing, aperture and orientation  Assessment of rock mass conditions  Mobile instrument for monitoring rock mass disintegration and convergence 11.06.2020 14 BBUGS Technical Meeting Webinar

B3 2.5 2.5 m Technical Meeting Webinar 2.4 2.3 2.2 2.1 2 1.9 1.8 Shale, compact, 1st section 1.7 regulary bedded, small fractures 1.6 1.5 B3 1.4 1.3 1.2 1.1 Cross-section 1 1 Shale, crushed, 0.9 caving formation 0.8 Steel lagging mat 0.7 Bigger and smaller pores in backfill material 0.6 0.5 parting plane in backfill material Backfill material, with textile lagging mat 0.4 compact 0.3 0.2 0.1 Textile lagging mat Borehole mouth 0 [m] 11.06.2020 15 BBUGS Technical Meeting Webinar

1.9 Technical Meeting Webinar 1.8 2.5 m 2.5 1.7 1st section 2.4 1.6 B3 2.3 1.5 Cross-section 1 2.2 1.4 2.1 1.3 2 1.2 1.9 1.1 11.06.2020 16 BBUGS Technical Meeting Webinar

1.1 Technical Meeting Webinar 1 0.9 Shale, crushed, caving formation 0.8 Steel lagging mat 1st section 0.7 B3 0.6 Bigger and smaller pores in backfill material 0.5 Cross-section 1 parting plane in backfill material with textile lagging mat Backfill material, compact 0.4 0.3 0.2 0.1 Textile lagging mat Borehole mouth 0 [m] 11.06.2020 17 BBUGS Technical Meeting Webinar

2.62 m B5 2.6 Technical Meeting Webinar 2.5 2.4 2.3 2.2 B4 2.1 1.98 m 2 1.9 1.9 1.8 Shale, compact, 1.8 2nd section regulary bedded, 1.7 1.7 Shale, compact, small fractures 1.6 regulary bedded, 1.6 B4 B5 small fractures, 1.5 1.5 in lower part small 1.4 1.4 cavities 1.3 1.3 1.2 1.2 1.1 1.1 Cross-section 2 1 1 Shale, crushed, 0.9 0.9 caving formation 0.8 0.8 Shale, crushed, 0.7 0.7 Caving formation caving formation and cavities, brittle 0.6 0.6 pieces of Shale 0.5 0.5 Caving formation Steel lagging mat 0.4 0.4 Steel lagging mat Backfill material, 0.3 0.3 crushed 0.2 Backfill material, 0.2 Backfill material, crushed 0.1 0.1 Textile lagging mat Textile lagging mat compact 0 [m] 0 [m] 11.06.2020 18 BBUGS Technical Meeting Webinar

2.52 m B6 2.5 Technical Meeting Webinar 2.4 2.3 2.2 2.1 2 Shale, compact, 1.9 regulary bedded, small fractures 1.8 3rd section 1.7 1.6 B6 1.5 1.4 1.3 Caving formation 1.2 Shale, compact 1.1 1 Cross-section 3 Shale, fractured, 0.9 crushed 0.8 0.7 Shale,crushed, layered, 0.6 caving formation 0.5 0.4 0.3 Steel lagging mat 0.2 Backfill material, 0.1 compact Textile lagging mat 0 [m] 11.06.2020 19 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Broken rock mass, breakouts opening Steeply Broken and inclined fragmented open rock mass fracture with breakouts of Steeply the borehole inclined wall fracture Concrete 11.06.2020 20 BBUGS Technical Meeting Webinar

Technical Meeting Webinar Structural interpretation Structural interpretation  Picking of structures, e.g. open/closed joints, bedding planes, fault planes etc.  Determination of the discontinuity orientation  Measuring the opening width or thickness of the mineralization 11.06.2020 21 BBUGS Technical Meeting Webinar