Transcript Slide 1

Open Portal Slope and Support Design:
Dilokong Chrome Mine
ASA Metals (Pty) Ltd
Pieter Groenewald
Yolanda Bester
18 September 2009
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Contents
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Introduction
Location
Data Collection
Data Processing
Input Parameters
Numerical Modeling
Results
Recommendations
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Introduction
 Geotechnical data acquisition
 The use of empirical and numerical methods to transform
data
 Input parameters for FLAC/SLOPE modelling
 Probabilistic assessments and kinematic failure analyses.
 The portal geometry and support derived
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Location
 The Dilokong Chrome Mine situated on the eastern limb of the Bushveld Igneous Complex (BIC)
is planning to exploit the LG6A and LG6 Chromitite seams.
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Data Collection
 Field Work
– Core Logging
– Joint Orientation
– Sample Collection
 Laboratory Work
– Young’s Modulus
– Poisson’s Ratio
– UCS
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Data Processing
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Rock Mass Rating
(Bieniawski ‘89)
Q Rating
Statistical Analysis
Kinematic Analysis
(DIPS and ROCLAB from Rocscience Inc)
– Plane Failure
– Wedge Failure
– Toppling Failure
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Input Parameters
 Laboratory Results
 Geotechnical Domains
– Soil
– Highly Weathered Saprolites
– Weathered Pyroxenites
– Fresh Pyroxenites
 Water Table
– Taken at 0.5m below surface
 Rock Mass Ratings
– Uniaxial compressive strength of rock material
– Rock quality designation (RQD)
– Spacing of discontinuities
– Condition of discontinuities
– Groundwater conditions
– Orientation of discontinuities
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Input Parameters
 Joint Orientations (DIPS)
– Circular failure
– Plane failure
– Wedge failure
– Toppling
 Support
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Numerical modelling
 ROCLAB
 DIPS
 Flac – Slope 5.0
Soil
Jointing
Weathered Rock
Slope Angles
FOS Unsupported
Transitional Zone
FOS Supported
Fresh Rock
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Results
 Factor of Safety (FOS)
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Results
 Factor of Safety (FOS)
 ROCLAB
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Results
 Factor of Safety (FOS)
 ROCLAB
 Bench Face Angle (BFA) from Flac / Slope
– Soil
– Weathered Saprolite
– Weathered Pyroxenite
– Fresh Pyroxenite
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Results – BFA Soil
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Results – BFA Saprolite
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Results – BFA Weathered Pyroxenite
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Results – BFA Fresh Pyroxenite
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Results – Fresh Rock CFA Method
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The CFA analysis indicates the following:
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A BFA of 74º for the Highwall based on plane failure
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A BFA of 75º for the Sidewall based on plane failure
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A BFA of 64º for the Sidewall based on wedge failure
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Results
 Factor of Safety (FOS)
 ROCLAB
 Bench Face Angle (BFA) from Flac / Slope
– Soil
– Weathered Saprolite
– Weathered Pyroxenite
– Fresh Pyroxenite
 Support
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Support
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Recommendations
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Suggested Configurations
 Highwall
 Sidewalls
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Actual Configuration
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Questions
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