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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/267158596 PRESENTATION ONLY: Instrumentation and Monitoring during Construction of the Ingula Powerhouse Caverns Conference Paper

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/267158596

PRESENTATION ONLY: Instrumentation and Monitoring during Construction of the Ingula Powerhouse Caverns

Conference Paper · December 2010

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3 authors, including: Gerhardus J Keyter SRK Consulting (South Africa) Pty Ltd

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BRAAMHOEK CONSULTANTS JOINT VENTURE

THE INGULA PUMPED STORAGE SCHEME

INSTRUMENTATION AND MONITORING DURING CONSTRUCTION OF THE INGULA POWERHOUSE CAVERNS December 2010 BY G Keyter, M Kellaway & D Taylor

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BRAAMHOEK CONSULTANTS JOINT VENTURE

PRESENTATION OVERVIEW

  • POWERHOUSE COMPLEX
  • SIMPLIFIED GEOLOGY OF THE POWERHOUSE COMPLEX
  • ANALYSIS AND DESIGN
  • INSTRUMENTATION DESIGN
  • TRIGGER LEVELS
  • INSTRUMENTATION
  • CONVERGENCE
  • DESIGN VERIFICATION
  • COMPARISON BETWEEN ANTICIPATED AND ACTUAL CONVERGENCE
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BRAAMHOEK CONSULTANTS JOINT VENTURE

INGULA POWERHOUSE COMPLEX

Machine Hall Transformer Hall

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BRAAMHOEK CONSULTANTS JOINT VENTURE

SIMPLIFIED POWERHOUSE GEOLOGY

  • VOLKSRUST Fm (UPPER ECCA GROUP, KAROO SUPERGROUP) 250-260my
  • thinly laminated siltstones, mudstones and carbonaceous mudstones.
  • UCS 90MPa (41 – 123MPa),
  • durability reduces with depth from overlying dolerite sill.
  • KAROO DOLERITE SUITE
  • sub horizontal dolerite sills and sub vertical dykes along existing faults or

shear planes. Hydrothermal veining.

  • STRUCTURAL GEOLOGY
  • sub horizontal bedding shear planes with brecciated, soft rock infill
  • normal faulting.
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BRAAMHOEK CONSULTANTS JOINT VENTURE

SIMPLIFIED POWERHOUSE GEOLOGY

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BRAAMHOEK CONSULTANTS JOINT VENTURE

SIMPLIFIED POWERHOUSE GEOLOGY

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BRAAMHOEK CONSULTANTS JOINT VENTURE

SIMPLIFIED POWERHOUSE GEOLOGY

Locally thinning out

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BRAAMHOEK CONSULTANTS JOINT VENTURE

ANALAYSIS & DESIGN

Example : UDEC model of Transformer Hall Cavern

Focus on:

  • Optimizing crown geometry
  • Stability, particularly of machine hall

with 26m span

  • Effects of seismic loading
  • Long term creep effects
  • Methods of excavation & support
  • Excavation & support sequencing

Using:

  • Kinematics: DIPS & Unwedge
  • Continuum: Phase2 V6 & FLAC3D
  • Discontinuum: Phase2 V7, UDEC &

3DEC Note: UDEC, 3DEC & FLAC3D work done in close cooperation with Tony Leach at Itasca

External review:

  • Dr Evert Hoek

BEDDING SHEAR

Example : Phase2 model of Powerhouse Caverns

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BRAAMHOEK CONSULTANTS JOINT VENTURE

EXCAVATION OF TOP HEADING

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BRAAMHOEK CONSULTANTS JOINT VENTURE

EXCAVATION OF BENCH 1

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BRAAMHOEK CONSULTANTS JOINT VENTURE

EXCAVATION OF BENCH 2

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BRAAMHOEK CONSULTANTS JOINT VENTURE

INSTRUMENTATION DESIGN

  • Located where greatest displacement is expected
  • On site design optimisation to assess the loading on support elements.
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BRAAMHOEK CONSULTANTS JOINT VENTURE

INSTRUMENTATION DESIGN

MHTH Bench 1 Bench 2 Bench 1 THTH

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BRAAMHOEK CONSULTANTS JOINT VENTURE

CAVERN TRIGGER LEVELS

5 10 15 20 25 30

Convergence (mm) Time

ALARM LEVEL WARNING LEVEL BASELINE LEVEL Time of primary support installation Time of secondary support installation Convergence measurements Projected convergence

Convergence Trigger Levels in the Cavern Crowns

  • Primary Support Cavern crown and sidewalls
  • Relate to the projected increase in convergence between subsequent excavation

stages

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BRAAMHOEK CONSULTANTS JOINT VENTURE

MACHINE HALL TRIGGER LEVELS

  • Secondary support in MH Cavern;
  • Relate to the projected TOTAL convergence with time as cavern excavation

progresses;

  • Measured at different points;
  • Working loads as measured in cable bolts and cable anchors;
  • Serve as a GUIDELINE;
  • A FULL ASSESSMENT OF THE STABILITY would require an assessment of the

encountered ROCK MASS, quality of WORKMANSHIP and PERFORMANCE of support elements.

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BRAAMHOEK CONSULTANTS JOINT VENTURE

MACHINE HALL TRIGGER LEVELS

1160 1166 1172 1178 1184 1190 1196 1202 1208 1214 1220 15 30 45 60 75 90 105 120 135 150

Relax ahead of CH, zero point for monitoring Rockbolts installed @ face in CH Cable bolts installed in CH crown Relax ahead of side headings Cable bolts installed in side headings Cable anchors installed in CH crown Relax ahead of 1st bench Cable bolts installed in 1st bench Cable anchors installed in side headings Relax ahead of 2nd bench Cable bolts installed in 2nd bench Cable anchors installed in 1st bench Relax ahead of drainage gallery GRPs installed in drainage gallery Relax ahead of 3rd bench Cable bolts installed in 3rd bench Cable anchors installed in 2nd bench Relax ahead of 4th bench Cable bolts installed in 4th bench Cable anchors installed in 3rd bench Relax ahead of 5th bench Cable bolts installed in 5th bench Cable anchors installed in 4th bench Relax ahead of 6th bench Cable bolts installed in 6th bench Cable anchors installed in 5th bench Relax into turbine pits Cable bolts & floor dowels installed in turbine pits Cable anchors installed in 6th bench Cable anchors installed into turbine pits Primary support removed Long term creep

Excavated Cavern Invert Level (masl) MH Crown Convergence (mm)

WARNING LEVEL ALARM LEVEL Excavated Invert Level (masl)

Expected Convergence Envelope

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BRAAMHOEK CONSULTANTS JOINT VENTURE

INSTRUMENTATION

  • MULTIPLE POINT BOREHOLE EXTENSOMETERS
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BRAAMHOEK CONSULTANTS JOINT VENTURE

INSTRUMENTATION

  • INSTRUMENTED ROCK BOLTS, CABLE BOLTS AND CABLE ANCHORS
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BRAAMHOEK CONSULTANTS JOINT VENTURE

CONVERGENCE DATA

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BRAAMHOEK CONSULTANTS JOINT VENTURE

ON SITE DESIGN VERIFICATION

  • Scheduling the installation of instrumentation following review of encountered

ground.

  • Review of Convergence Data
  • Initial review of data, identify any problems etc.
  • Assessing Reliability of Data (ground movement or other)
  • Scheduling Readings (Frequency)
  • High level summary – provide OVERVIEW & IDENTIFY POTENTIAL

PROBLEM AREAS.

  • Review by Designer & external Design Reviewer (DR. EVERT HOEK).
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BRAAMHOEK CONSULTANTS JOINT VENTURE

DESIGN VERIFICATION

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BRAAMHOEK CONSULTANTS JOINT VENTURE

MH E4 ARRAY

MHTH Bench 1 Bench 2 Bench 1 THTH

Bedding Shears

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BRAAMHOEK CONSULTANTS JOINT VENTURE

PROVISIONAL COMPARISON OF CONVERGENCE DATA

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BRAAMHOEK CONSULTANTS JOINT VENTURE

PROVISIONAL COMPARISON OF CONVERGENCE DATA

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BRAAMHOEK CONSULTANTS JOINT VENTURE

PROVISIONAL COMPARISON OF CONVERGENCE DATA

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POSSIBLE REASONS FOR DIFFERENCES IN EXPECTED AND ACTUAL CONVERGENCE

  • Sequence of excavation incl. overall sequence for PH complex
  • Support sequence – bringing forward the installation of cable anchors
  • Profile changes and variations in shotcrete support thickness
  • Performance of the support
  • Reliability of geotechnical instrumentation readings.
  • Local variations in the geology
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BRAAMHOEK CONSULTANTS JOINT VENTURE

MACHINE HALL

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