Underground Geotech Design and Procedures

Tembagapura, 21 June 2006

Flow chart for Geotechnical Design

• Pillar design• Ground support• Excavation

design

Pillar Design

Extraction level

Data collection

Wilson Pillar analysis (use FOS > 2.2)

Numerical modeling

Sill pillar

Crown pillar

• Rock mass classification

• Dimension of pillar

• Required life and long term plan

• Purpose of the excavation

• Caving and Mining Stress

• Expected personnel exposure

• Maximum allowable deformation

Pillar stability

Monitoring and Evaluation

Pillar Reinforcement

• Heavy support in medium to good ground

(Bolts + Mesh (two layers) + Shotcrete (2 layers) + T/bars

• Special support in poor ground

Steel set + concrete

Pillar Performance

• Partial closure at DrawpointsThe sill pillar failure was due to load from compacted muck in surrounding draw points.

The ground was classified as poor ground and regular ground support (bolts + Mesh + t/bar) was recommended

• Partial closure of panel Crown pillar failure occurred due to load from compacted muck.

The support is concrete but without steel set

• Slight damage at drawpoint pillarThe sill pillar is still stable though several of the surrounding drawpoints were compacted.

Special support with concrete and steel set was installed.

Pillar stability monitoring

P11-DP 5E/W P11-DP 5E/W

Condition Feb,14,2006 Condition Mar,07,2006

Mucking DB5 P10/11 Vs Conv.

Shutdown

Field Inspection

Convergence Monitoring

Recommendation/Action plan

Ground Support Design

Extraction/Undecut/Truck Haulage Level

Data collection

Ground support tables

Wedge analyses

Support FOS > 2.0 for Undercut level

Support FOS > 2.0 for Extraction level

Support FOS > 1.2 for other areas

Development support

Permanent support

Monitoring and Evaluation

• Rock mass classification

• Dimension of pillar

• Required life and long term plan

• Purpose of the excavation

• Caving and Mining Stress

• Expected personnel exposure

• Maximum allowable deformation

Minimum Required Standard Support

Classes of Minimum Ground Support

Classes of Minimum Ground Support

Light Support (Class 1A)Only Bolts

Not used anymore

Medium Light Support (Class 2)

Regular Support (Class 3)

Heavy support (Class 4) Extra heavy support (Class 5) Special support (Class 6)

Types of Development Ground Support

Map of extraction level showing Minimum Ground Support

Requirement

Quality control inspection

Monthly Goal

- New excavation

Monthly ground support

recommendation

Weekly Heading Check inspection/

Quality Inspection

Weekly Ground Support

recommendation

Collecting data

Collecting data Actual

To engineering and operation for improving the

installation

Not enough grout Loose Plate Short hole Protruding bolts

Laubscher’s Chart - Hydraulic Radius

CNI PREDICTION ACTUAL

Actual Hydraulic radius

UG Geotech inputs to Mine Operations

• Assistance in development of draw order based on convergence monitoring results

• Recommendations for minimizing the impact of abutment stress loading through additional blasting and/or re-support

• Evaluation of wet muck status and potential• Assistance in the sequencing of cave blasting based on

convergence monitoring and damage mapping• Sequencing the closure of draw points• Recommendations for the acceleration of development or

sequence for Underground Development• Review of ground support requirements in all production areas