Open Portal Slope and Support Design Dilokong Chrome

Open Portal Slope and Support Design: Dilokong Chrome Mine ASA Metals (Pty) Ltd Pieter Groenewald Yolanda Bester 18 September 2009 1

Contents § § § § Introduction Location Data Collection Data Processing Input Parameters Numerical Modeling Results Recommendations 2

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 3

Location § The Dilokong Chrome Mine situated on the eastern limb of the Bushveld Igneous Complex (BIC) is planning to exploit the LG 6 A and LG 6 Chromitite seams. 4

Data Collection § Field Work – Core Logging – Joint Orientation – Sample Collection § Laboratory Work – Young’s Modulus – Poisson’s Ratio – UCS 5

Data Processing § § Rock Mass Rating (Bieniawski ‘ 89) Q Rating Statistical Analysis Kinematic Analysis (DIPS and ROCLAB from Rocscience Inc) – Plane Failure – Wedge Failure – Toppling Failure 6

Input Parameters § Laboratory Results § Geotechnical Domains – Soil – Highly Weathered Saprolites – Weathered Pyroxenites – Fresh Pyroxenites § Water Table – Taken at 0. 5 m 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 7

Input Parameters § Joint Orientations (DIPS) – Circular failure – Plane failure – Wedge failure – Toppling § Support 8

Numerical modelling § ROCLAB § DIPS § Flac – Slope 5. 0 9

Results § Factor of Safety (FOS) 10

Results § Factor of Safety (FOS) § ROCLAB 11

Results § Factor of Safety (FOS) § ROCLAB § Bench Face Angle (BFA) from Flac / Slope – Soil – Weathered Saprolite – Weathered Pyroxenite – Fresh Pyroxenite 12

Results – BFA Soil 13

Results – BFA Saprolite 14

Results – BFA Weathered Pyroxenite 15

Results – BFA Fresh Pyroxenite 16

Results – Fresh Rock CFA Method § The CFA analysis indicates the following: – A BFA of 74º for the Highwall based on plane failure – A BFA of 75º for the Sidewall based on plane failure – A BFA of 64º for the Sidewall based on wedge failure 17

Results § Factor of Safety (FOS) § ROCLAB § Bench Face Angle (BFA) from Flac / Slope – Soil – Weathered Saprolite – Weathered Pyroxenite – Fresh Pyroxenite § Support 18

Support 19

Recommendations 20

Suggested Configurations § Highwall § Sidewalls 21

Actual Configuration 22

Questions 23