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

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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,

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Technical Meeting Webinar

11.06.2020 BBUGS Technical Meeting Webinar 1

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 australia@dmt-group.com

Technical Meeting Webinar, 11. June 2020

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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

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(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

CONTENT:

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Inspection of rock mass conditions in difficult mining environment – Study case

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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
  • Very deep mining: up to 1,650 m with 1,050 m

average depth

  • High stress conditions and weak strata

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Longwall: Shield support, plough double-drum shearer

Image source: Dietmar Klingenburg / RAG

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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.

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Top: Roadway support with yielding steel arches Bottom: Installation of Combi A support

Source: Junker et al.

Gateroad Gateroad

Longwall face Goaf area Closed mine drift

Mining direction

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Technical Meeting Webinar Physical model of only roofbolted roadway in 1,000 m depth

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 about 50% less than that of a roadway supported solely by yielding arches.

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Physical, scaled model of Combi Type (here: „B“) in 1530 m depth

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Geomechanical modelling

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Support

12 MPa 18 MPa 10 MPa seam mudstone

Roof bending Floor heaving Support deformation/ sidewall buckling

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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

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  • 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

Study site: characteristics

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Excavation

  • f seam

above Gateroad preparation (from 2 sides) Seam excavation

Timeline Plan view:

Excavation above Gateroad driving Seam excavation

Gateroad length [m]

Raise drifts

Timeline

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Geotechnical borehole log – Exploration phase

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Roof rocks

  • Compact sandy shale

and sandstone

  • Good to very good

RQD

  • Regular bedding
  • Some steep joints

Bedding Joints Joints Opening Mineralization Bedding structure Bed thickness Core condition RQLD

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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.

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Cross-section 1 Cross-section 2 Cross-section 3

B3 B4 B5 B6

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Ultra-slim borehole scanner (SBS)

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  • 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

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1st section

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B3

Cross-section 1

B3 Borehole mouth

[m] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5

Textile lagging mat

parting plane in backfill material with textile lagging mat Bigger and smaller pores in backfill material Shale, compact, regulary bedded, small fractures Shale, crushed, caving formation Backfill material, compact Steel lagging mat

2.5 m

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1st section

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Cross-section 1

B3

1.9 2 2.1 2.2 2.3 2.4 2.5

2.5 m

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

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1st section

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Cross-section 1

B3 Borehole mouth [m] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 Textile lagging mat

parting plane in backfill material with textile lagging mat Bigger and smaller pores in backfill material Shale, crushed, caving formation Backfill material, compact Steel lagging mat

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2nd section

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B5

Cross-section 2

B4 B5

[m] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6

Textile lagging mat

Shale, compact, regulary bedded, small fractures Shale, crushed, caving formation Backfill material, compact

Steel lagging mat

Backfill material, crushed Caving formation

2.62 m

B4

[m] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

Textile lagging mat

Shale, compact, regulary bedded, small fractures, in lower part small cavities Shale, crushed, caving formation Backfill material, crushed

Steel lagging mat

Caving formation and cavities, brittle pieces of Shale

1.98 m

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3rd section

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Cross-section 3

B6

B6

[m] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5

Shale,crushed, layered, caving formation Backfill material, compact Shale, fractured, crushed Shale, compact Caving formation Shale, compact, regulary bedded, small fractures

2.52 m Textile lagging mat Steel lagging mat

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Broken and fragmented rock mass with breakouts of the borehole wall Broken rock mass, breakouts Concrete Steeply inclined

  • pen

fracture

  • pening

Steeply inclined fracture

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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

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Results

  • The performed scans with the SBS show compact sandy shale in the roof of the roadway.
  • This confirms the original exploration results from dd also here in local detail
  • In the lower part of the rock mass at the contact with the concrete, caving and separation parallel to the

bedding is observed. The maximum zone of broken rock reaches until a depth of 0.95 resp.1.3 m

  • The higher rock strata are quite compact
  • The shale shows clear bedding and some small fractures
  • In section 2 (B4 ad B5) the concrete is also fractured
  • Concrete thickness 30-40 cm, but 80 cm in B3, which demonstrates higher overbreak during

construction

  • Slight quality problems with the backfill (contractor), and also effect from tectonic and stress conditions

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Technical characteristics and function of the applied Slim Borehole Scanner (SBS)

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Animation

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Ultra-slim borehole scanner (SBS)

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Rod connection Batteries Signal-/Infrared-Window Front Centraliser LEDs Power Switch Camera Mirror Bottom Centraliser

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Ultra-slim borehole scanner (SBS)

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CMOS sensor hyperbolical mirror LED ring

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What are the differences to conventional well logging?

  • For ultra-slim boreholes (e.g. drilled for rock bolting)
  • No logging cable, winch, data logger
  • Internal memory and battery
  • Can be used in upward and horizontal holes
  • Pushed into the hole by hand

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Ultra-slim borehole scanner (SBS)

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Ultra-slim borehole scanner (SBS)

Development of a new depth recorder instrument

  • Independent measurement of the depth
  • No influence by borehole wall or other external factors
  • Time-depth-recording; synchronization with borehole image

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Analysing software ABS-Vision

  • Database
  • Image Optimization
  • Image Analysis
  • 3D Visualization
  • Document and Data Export

On site communication via Pocket PC

  • Probe settings
  • Borehole and location

details

  • Checking image lightning
  • Image preview
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Example: Roof bolt drill hole in a RSA coal mine with room and pillar workings

Objectives:

  • Determination of thickness of coal left in the roof

and depths of rock strata limits

  • CMRR and assist the planning of the rock bolt

support

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Claystone with siltstone interlayers, sand content incresing towards top Sandstone

Bedding

  • rientation
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Components of the Coal Mine Roof Rating - the CMRR system

Canbulat, I. et. al. (2005): final report, Safety in Mines Research Advisory Committee

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Parameters used for CMRR

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Input parameters Example value

Directly determined with SBS scan Indirectly determined

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Example: Control of injection measures for rock mass stabilization

Initial scans before injection:

  • Disintegrated rock mass
  • Numerous open joints and fractures

Scans after injection:

  • nearly all openings have been filled
  • only close to the borehole collars were some small
  • pen fractures still observed

Conclusion: Possible to stabilize the overall rock mass with the selected reinforcement method

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injection stabilized rock fragments

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  • Objective documentation of in-situ rock mass conditions in mining
  • Determination of orientation and exact position of discontinuities

→ calculation of potential sliding wedges → optimal adjustment of the rock bolting scheme according to the structural fabric

  • Supervision of the roadway roof and monitoring of the loosening of the roof rocks

→ convergence control and investigation of damages → optimised application of injection techniques and repair

  • Inspection and monitoring of covering (e.g. shotcrete thickness) and grouting
  • Digital image storing and integration into a database

→ reinterpretation of the data at any time → objective geological documentation of the on-site situation for a supplementary management

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Summary and Conclusions

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Thank you for your attention!

Further information & contact: Torsten.Gorka@dmt-group.com +49 201 172-1027