0910 Ernesto Villaescusa

Nuevas tendencias de la Minería Subterránea profunda Planeación, operación y estabilización del macizo rocoso

By

© Ernesto Villaescusa, PhD Chair in Rock Mechanics

WA School of Mines, CRC Mining & Curtin University Australia

Western Australian School of Mines Research

The overall objective is to characterize rock masses and

their response to mining activities, so that stable

excavations can be designed, constructed and supported.

Excavation

stability

S801

Geological

regime

S802

Rock mass

characterization

S803

Performance

prediction

S804

Ground support

evaluation

S805

Ground support

implementation

S806

Backfill

mining voids

S808

Shotcrete

support

S807

New

technology

Rock Mass

Characterization

Ground

Support

Technology

Introduction

Stope & pillar sizes

Access & infrastructure

Global sequences

(Stress analysis)

Mine planning

Acceptable design

NO

Rock Mechanics

Mine planning & Rock Mechanics

Global Economics Mine planning

Mining method selection

Orebody delineation

END Document results

Drill & blast design

Acceptable design

Detailed economics

Mine planning

Rock reinforcement

Mine planning

Extraction monitoring Operations, Mine planning

Geology & Rock mechanics

NO YES

YES

Rock mechanics

Infill delineation drilling Geology



Global sequences

(Stress analysis)

Mine planning

Acceptable design

NO

Rock Mechanics


Rockmass characterization Geology & rock

Orebody delineation Geology



Global sequences

(Stress analysis)

Mine planning

NO

Rock Mechanics


Rockmass characterization Geology & rock

mechanics

Orebody delineation

END Document

results

Drill & blast design

Detailed economics

Mine planning

Rock reinforcement

Mine planning

Extraction monitoring Operations, Mine planning

Geology & Rock mechanics

NO YES

YES

Rock mechanics

Infill delineation drilling Geology

G

L

O B

A

L

D

E

S

I

G

N

D E

T

A I

L

E

D

D

E S I

G

N

INPUT

DATA

CLOSURE OF

DESIGN LOOP

Acceptable design

Mine planning

Flowchart of mine planning process (Villaescusa, 1998).

Introduction

Introduction – Mining at depth

Golden Grove Mine, Western Australia (Thompson, 2011)

1000m

Conditions often become difficult beyond a 1000m or so

Maximum recovery – minimal dilution

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10 12 14D

ep

th o

f Fa

ilure

(m

)

HR

Hangingwall Depth of Failure vs. Hydraulic Radius

0-1m

1-2m

3-4m

4-5m

>5m

Depth of

Golden Grove Mine, Western Australia (Thompson, 2011)

Continuous extraction sequence required to avoid pillars

Mining method selection & infrastructure

SLC/SLOS

SLOS

1000m

Change of the mining method or infrastructure location

Geotechnical monitoring requirements

Mine induced seismicity Kanowna Belle Mine, Western Australia (Morton, 2013)

Seismic sensor array

1000m

1000m

A need to understand the overall failure process and instability

Large scale geological discontinuities

Mount Charlotte Mine, Western Australia (Corskie, 2013)

1000m

The global stability may be controlled by large scale structures

Seismic response of large scale structures

Fitzroy fault

Kanowna Belle Mine, Western Australia (Morton, 2013)

1000m

1000m

The structures may become seismically active

Mining method multiple lift - sublevel open stoping

. . . . .

.

. . . . . . . . . . . . . . . . . .

.

. . . . . .

. . . . . . . .

. . .

. . . . . . . .

. . . . . . . .

.

. . . . . . . . . . . . Drill

drives

Cut - off

s lot

. . . . . . . . . . .

. . .

. . . . . . . . . . . . . . . . .

. . . . .

. . . . . . . . . . . .

Cut - off

s lot

Used for tabular or massive – steeply dipping orebodies

Case study - sublevel open stoping at depth

1000m

Callie Mine, NT Australia (Graf, 2013)

Multiple lift - Sublevel open stoping


Primary-secondary extraction sequence

Multiple lift - Sublevel open stoping

Cemented rock fill of stoping voids


In-situ stress measurements - a key requirement

Acoustic Emission from oriented core samples – No access required – only deep core


In-situ stress measurements - a key requirement

Orientation and magnitude with depth determination - For all the stoping block areas planned


Intact rock strength determination

For all rock types



For all rock types



For all rock types


Joint set number and orientation – block shape

From development exposure and diamond drilled core


Joint condition determination

From development exposure and diamond drilled core

Joint set characteristics



RQD from exploration core

Changes with depth Correlation with large scale structures


Rock mass classification

Block A

Block B

Block C

Block D

Excavation performance under increased stress

13/08/2013


13/08/2013 13/08/2013


Ground support strategy for an increasing stress

10

5

2

1

20

0.5

0.2

0.1

1 2 5 10 20 50 100 200

2.5 – 5.0

Medium

confining

stress

Low

confining

stress

High

stress

Heavy

rockburst zone

σ 1 = In - situ main principal stress

σ c = Uniaxial Compressive Strength

of intact rock Near

Surface

σ c

σ

Str

es

s R

ed

ucti

on

Fac

tor

(SR

F) 10

5

2

1

20

0.5

0.2

0.1

1 2 5 10 20 50 100 200

2.5 – 5.0

Medium

confining

stress

Low

confining

stress

High

stress

Heavy

rockburst zone

σ 1 = In - situ main principal stress

σ c = Uniaxial Compressive Strength

of intact rock Near

Surface

σ c

σ max

σ c

σ

Str

es

s R

ed

ucti

on

Fac

tor

(SR

F)


Time dependent slow deformation Sudden, violent failure

The walls of the excavations become unstable due to vertical stress.

Rock bolting - with or without welded wire mesh A generalized form of support effective for shallow to moderate depths.



At greater depths bolts, shotcrete and mesh required for backs and walls.

Fibrecrete energy dissipation is not enough under high stress conditions



Fibrecrete energy dissipation is not enough under high stress conditions


Bolts + mesh embedded shotcrete + cables

Sudden failure

(Modified from Thompson et al, 2012 )

Demand Reaction Surface Energy

category pressure (KPa) displacement (mm) (KJ/m2)

Low <100 <50 <5

Medium 100-150 50-100 5-15

High 150-200 100-200 15-25

Very High 200-400 200-300 25-35

Extremely High >400 >300 >35

© E. Villaescusa WA School of Mines


Rock mass demand


Example of low demand – unsupported lower walls


Example of low to medium demand – fibrecrete and walls


Example of low to medium demand – fibrecrete


Example of high to very high demand – mesh embedded chain link


WASM ground support design chart


Excavation shape at depth will require changes

Conclusions

• Rock mass characterization from exploration core.

• Selection of mining method with geotechnical considerations.

• Geotechnical monitoring for global stability.

• Strength vs induced stress ratios become unfavourable.

• Mode of failure anticipation required.

• Ground support strategy for high energy dissipation.

• Change of excavation shape may be required.

Documents

0910 Ernesto Villaescusa