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2007 MITSUBISHI LECTURE2007 MITSUBISHI LECTURE

HIGHWALL, STOCKPILE AND DUMPS:SAFETY AND PRODUCTIVITY

Tim SullivanPells Sullivan Meynink

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MINING AND RISK ?MINING AND RISK ?

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SURFACE MININGSURFACE MINING

Traditionally two General Subdivisions:– Hard Rock and– Soft Rock.

But

“…….all geotechnical materials are part of one continuous spectrum”.

“…….one continuous science extending from soft soils to hard rocks. All geotechnical materials behave according to the same engineering principles…”

“…….differences a function of degree rather than fundamental nature” (Johnston 1991).

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OPEN CUT MINE SLOPE DESIGNOPEN CUT MINE SLOPE DESIGNApplication of scientific methods and engineering principles to the materials of the earth’s crust for the solution of engineering problems.

MINE SLOPE DESIGN:

• Soil mechanics,• Rock mechanics,• Hydrogeology and• Geology.

Geologically based science.

Fundamental corner stone of all mine slope design is geology.

Success with mine design depends on the ability to understand the geology.

In particular, the Patterns, Subtleties and Variations.

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ENGINEERING AND SCIENTIFIC ENGINEERING AND SCIENTIFIC DISCIPLINESDISCIPLINES

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GENERAL SLOPE DESIGN OBJECTIVESGENERAL SLOPE DESIGN OBJECTIVES

What are the general slope design rules?

“achieve an optimum design – a compromise between a slope which is steep enough to be economically acceptable and one which is flat enough to be safe” (Hoek and Bray, 1981).”

What is the practical reality to statements such as:

“steep enough to be economically acceptable”or

“flat enough to be safe”.

The other general definition of the optimum pit slope design is:

“The best design is the one which falls down the day that the last truck leaves the pit”.

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SIMPLE GEOLOGY SIMPLE GEOLOGY –– RISK?RISK?

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COMPLEX GEOLOGY – RISK?

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HOW EFFECTIVELY HOW EFFECTIVELY CAN WE CAN WE

UNDERSTAND THE UNDERSTAND THE GEOLOGY?GEOLOGY?

COMPARISON OF COMPARISON OF DRILLINGDRILLING

AND INTERPRETED AND INTERPRETED FAULTSFAULTS

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TECHNICAL COMPLEXITY AND RISK?TECHNICAL COMPLEXITY AND RISK?

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MINE GEOMETRY AND RISK?MINE GEOMETRY AND RISK?

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MINE GEOMETRY AND RISK?MINE GEOMETRY AND RISK?

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MINE GEOMETRY AND RISK?MINE GEOMETRY AND RISK?

EXCAVATING A SLOT NEXT TO AN UNSTABLE HIGHWALL

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2007 MITSUBISHI LECTURE2007 MITSUBISHI LECTURE

PART 2CASE STUDIES

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CASE EXAMPLESCASE EXAMPLES“…slopes seldom fail without giving adequate warning” (Hoek

and Bray 1974)

Five Scales Of Problem:• Very Large Post Failure Deformations• Large Blocky Failures and

Collapses – Highwalls and dump• Bench Failure• Rockfall• Small Individual Blocks

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FREEPORT OVERALL VIEWFREEPORT OVERALL VIEW

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PRE FAILURE PRE FAILURE -- SOUTH WALLSOUTH WALL

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OVERALL OVERALL VIEW OF VIEW OF

FLOW PATHFLOW PATH

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FLOW PATH LOWER SLOPEFLOW PATH LOWER SLOPE

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MID HEIGHT BENCH 80m WIDE ? ENOUGH??

DEATHS OCCURRED HERE

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FLOW PATH IN TOEFLOW PATH IN TOE

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FLOW PATH MID SLOPEFLOW PATH MID SLOPE

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CRESTCREST

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FINE GRAINED ALTERED ROCK

SECTION THROUGH SLIDESECTION THROUGH SLIDE

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DRILL, SHOVEL AND TRUCKSDRILL, SHOVEL AND TRUCKS

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DRILL,TRUCK AND SHOVELDRILL,TRUCK AND SHOVEL

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TRUCKTRUCK

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MONITORINGMONITORINGSYSTEMS?SYSTEMS?

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NCHANGANCHANGA

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UNBENCHED FOOTWALL – 220m HIGH

OVERALL VIEW OF FAILUREOVERALL VIEW OF FAILURE

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CRESTCREST

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SHOVEL DESTROYEDSHOVEL DESTROYED

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SECTION THROUGH FAILURESECTION THROUGH FAILURE

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27ºKINK BANDS

SUMMARY OF FAILURE INFORMATIONSUMMARY OF FAILURE INFORMATION

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NchangaPrevious failure20,000,000 tonnesJune 1985

NchangaPrevious failure20,000,000 tonnesJune 1985

HISTORY OF FAILURESANTAMINA PERUANTAMINA PERU

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OVERALL SETTINGOVERALL SETTING

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LAKE SEDIMENTS LEFT IN VALLEY

SHOVEL AND TRUCK SHOVED ACROSS PIT SHOVEL AND TRUCK SHOVED ACROSS PIT FLOORFLOOR

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BULLDOZER BURIEDBULLDOZER BURIED

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?

INTACT ROCK BUNDLAKE

SEDIMENTS

DRILLSDRILLS

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CLOSE UP OF DRILLCLOSE UP OF DRILL

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ABERFAN ABERFAN –– EXCAVATING THE TOEEXCAVATING THE TOE

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OVERALL VIEW OF ABERFANOVERALL VIEW OF ABERFAN

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PREVIOUS SLIDE

ABERFAN WASTE DUMPABERFAN WASTE DUMP

21ST October 1966.144 deaths, including 116 children.

Colliery waste had been dumped above the village for more than 20 years.

Two previous dump failures had occurred; 1944 and 1963. The 1963 failure was in the same location as the 1966 failure.

Because mine personnel were not injured and the downstream environment was not significantly damaged, the 1944 and 1963 slides were ignored.

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SUMMARY OF ISSUES AND FINDINGSSUMMARY OF ISSUES AND FINDINGS

GEOTECHNICAL FACTORS

Dump formed over springs, lead to softening of the toe.Dumped materials a mixture of rock, coal slurry and water.High moisture content of dump material lead to liquefaction.Failure took a few minutes.

CONCLUSIONS OF INQUIRY

“…the Aberfan Disaster is a terrifying tale of bungling ineptitude by many men charged with tasks for which they were totally unfitted, and of total lack of direction from above. Not villains but decent men, led astray by foolishness or by ignorance or by both in combination, are responsible for what happened at Aberfan.”

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THREDBO LANDSLIDE

1997

18 DEATHS

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LOCATION IN LOCATION IN THE VILLAGETHE VILLAGE

LANDSLIDE MASSLANDSLIDE MASSONLY 1300 mONLY 1300 m³³

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VIEW OF TOP OF SLIDEVIEW OF TOP OF SLIDE

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MUDFLOW THROUGH THE LODGESMUDFLOW THROUGH THE LODGES

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“LOST FORGOTTEN OR IGNORED”

Over 40 year history of similar but infrequent slides in the area.

Site originally classified as “unstable and unbuildable”

Loose dumped fill at 40° over an old landslide.

High pressure water pipeline – Asbestos cement with simple push couplings– Approved and constructed through the site.

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2007 MITSUBISHI LECTURE2007 MITSUBISHI LECTURE

Part 3 Large Blocky Failures

HighwallsAnd

Benches

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CARTENGA COAL MINE COLUMBIACARTENGA COAL MINE COLUMBIA

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DRAGLINE SPOIL DUMP

BRIDGE

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LOADERLOADER

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?

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TOE OF FAILURETOE OF FAILURE

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OVERALL VIEW OF HIGHWALL FAILUREOVERALL VIEW OF HIGHWALL FAILURE

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GEOLOGICAL SETTING GEOLOGICAL SETTING UNDERCUTTING A DIP SLOPEUNDERCUTTING A DIP SLOPE

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10º

UNDERCUT HIGHWALL

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Mt. KEITH OVERALL SETTING Mt. KEITH OVERALL SETTING -- CUTBACKCUTBACK

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HAUL ROAD ON OUTSIDE OF CUTBACK

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TRUCK IN WATERTRUCK IN WATER

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ROCK MASS FABRIC IN CUTBACKROCK MASS FABRIC IN CUTBACK

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DAYLIGHTING PLANES

SLOPE AT THE LIMIT WITH STRUCTURE PARALLEL OR DAYLIGHTING

CONTINUOUS ROCK STRUCTURE FABRIC

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CLOSE UP OF ROCK FABRICCLOSE UP OF ROCK FABRIC

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“SMOOTH” INFILLED JOINTS

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ROCK MASS FABRICROCK MASS FABRIC

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REAR RELEASEPLANES

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SHEAR ALONG JOINT PLANESSHEAR ALONG JOINT PLANES

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SHEAR AND DILATION ON MAJOR PLANES

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PREVIOUS FAILURE OF SAME TYPE IN THE PREVIOUS FAILURE OF SAME TYPE IN THE SAME SLOPE AT HIGHER ELEVATION ALSO SAME SLOPE AT HIGHER ELEVATION ALSO

AFFECTING HAUL ROADAFFECTING HAUL ROAD

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HAUL ROAD RE-ROUTED

PREVIOUS

NEW

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TRITRI--STAR COAL MINE STAR COAL MINE MARYLAND USAMARYLAND USA

1717THTH April 2007 April 2007 –– 2 killed2 killed

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OVERALL OVERALL VIEW OF VIEW OF

HIGHWALL HIGHWALL COLLAPSECOLLAPSE

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BACKHOE BURIED

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KIDSTON KIDSTON –– OVERALL VIEWOVERALL VIEW

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CABLE BOLTED FOOTWALL STEEPENED BELOW HAUL ROAD Pe

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PREPRE--SPLIT DRILL RIG SPLIT DRILL RIG DRILLING SECOND LIFT OF TRIPLE BENCHDRILLING SECOND LIFT OF TRIPLE BENCH

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Failure plane and collapseDrill rig located here

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CHARACTER OF FAILURE PLANECHARACTER OF FAILURE PLANE

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HOLES HALF FULL OF GROUT AND CABLES HOLES HALF FULL OF GROUT AND CABLES NOT GROUTEDNOT GROUTED

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COAL MINECOAL MINE

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UNCONTROLLED PLACEMENT OF UNCONTROLLED PLACEMENT OF WET TERTIARY IN DUMPWET TERTIARY IN DUMP

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EQUIPMENT EQUIPMENT DAMAGEDAMAGE

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LOSS OF PRODUCTIONLOSS OF PRODUCTION

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LOSS OF DRAGLINE? LOSS OF DRAGLINE? AND PRODUCTION LOSSESAND PRODUCTION LOSSES

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LAWLERS GOLD MINELAWLERS GOLD MINE -- FAIRYLAND PITFAIRYLAND PIT

BATTER SCALE FAILURE -27th January 2003 – FATALITY

Catastrophic failure of a portion of the western wall of the Fairyland open pit occurred near an excavator that was digging and loading ore into haul trucks. An ore control technician directing the activities of the excavator was fatally injured when buried under the rockfall.

Immediate suspension of mining and mobilisation of the Mine Rescue Team. Notification of all relevant authorities. An investigation by the Western Australian Police commenced immediately and by the Department of Mineral and Petroleum Resources early the next day. Nature of the failure prevented immediate rescue attempts. Recovery of the body 41 hours after the event

Earlier inspection of the wall shortly before the event by a geotechnical consultant and other staff gave no indication that failure was imminent.

Cause; proximity to pit wall.

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LOCATION OF FAILURELOCATION OF FAILURE

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2007 MITSUBISHI LECTURE2007 MITSUBISHI LECTURE

Part 4Rockfall Issues

AndConclusions

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Diagrama de sucesos

Accidente Fatal29 de octubre de 2003

Operaciones Mina Rajo AbiertoDivisión Mantos Blancos

Zona de probable Zona de probable desprendimiento de la desprendimiento de la

roca.roca.

Berma que delimita distanciaBerma que delimita distanciapara interactuar con elpara interactuar con el

talud del sector.talud del sector.

Talud 37Talud 37°° de pendiente.de pendiente.

Cargador Frontal 8703,Cargador Frontal 8703,operado por Jorge Campos,operado por Jorge Campos,a quien se le iba a entregara quien se le iba a entregar

el material de limpieza.el material de limpieza.

Imagen frontal del sector del suceso.

PosiciPosicióón final den final deCamioneta siniestradaCamioneta siniestrada

Imagen tomada desde el banco 780 hacia el banco 756.

Barra de perforaciBarra de perforacióón, con n, con 6 metros de avance 6 metros de avance aproximadamente.aproximadamente.

Berma que delimita el Berma que delimita el acecamientoacecamiento a la zona de a la zona de

riesgo identificado.riesgo identificado.

Imagen tomada desde el banco 756.

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45 45 mtmt..25 25 mtmt..

Distancias de la camioneta hasta el talud y berma delimitadora de distancia.

Imagen tomada en el banco 684, sector del incidente.

Fragmentos de la roca.Fragmentos de la roca.

Fragmentos de la roca.Fragmentos de la roca.

Imagen tomada en el banco 684, sector del incidente.

Zona del impacto directo Zona del impacto directo de la roca en la camioneta.de la roca en la camioneta.

Imagen tomada en el banco 684, sector del incidente.

22°° zona de impacto de la zona de impacto de la roca (cabina)roca (cabina)

Zona de posiciZona de posicióón final de la n final de la roca.roca.

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SMALL RAVELLING FAILURESMALL RAVELLING FAILUREEVEN SMALL ROCKS CAN BE A PROBLEMEVEN SMALL ROCKS CAN BE A PROBLEM

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RESULTANT VEHICLE DAMAGERESULTANT VEHICLE DAMAGE

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PLACEMENT OF PLACEMENT OF SUMPS AND PUMPS SUMPS AND PUMPS

CONTROL OF CONTROL OF PERSONNEL PERSONNEL

ACCESSACCESS

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PROCEDURES AND CONTROLS FOR LIGHT PROCEDURES AND CONTROLS FOR LIGHT VEHICLE ACCESSVEHICLE ACCESS

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LARGE EXCAVATING EQUIPMENTLARGE EXCAVATING EQUIPMENTUSUALLY A PRODUCTION ISSUEUSUALLY A PRODUCTION ISSUE

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LARGE EXCAVATING EQUIPMENTLARGE EXCAVATING EQUIPMENTUSUALLY A PRODUCTION ISSUEUSUALLY A PRODUCTION ISSUE

BUT IT DEPENDS ON CIRCUMSTANCESBUT IT DEPENDS ON CIRCUMSTANCES

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FIXED INFRASTRUCTUREFIXED INFRASTRUCTURE

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OPERATOR ESCAPED UNINJUREDOPERATOR ESCAPED UNINJURED

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ROCKFALLROCKFALL-- WHO IS AT RISK?WHO IS AT RISK?

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ANCILLARY EQUIPMENT ?ANCILLARY EQUIPMENT ?

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LOCATION OF SUMPS AND ANCILLARY LOCATION OF SUMPS AND ANCILLARY EQUIPMENT, ACCESS ON FOOT? EQUIPMENT, ACCESS ON FOOT?

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Sump & pump location? Character of highwall ?

OPERATORS AND LIGHT VEHICLES ?OPERATORS AND LIGHT VEHICLES ?

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SLOPE FORM EXACERBATES ROCK FALL SLOPE FORM EXACERBATES ROCK FALL PROBLEMS PROBLEMS –– NO EFFECTIVE BENCHESNO EFFECTIVE BENCHES

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STEEP BENCH SLOPESSTEEP BENCH SLOPESPOTENTIAL FOR SUDDEN FAILUREPOTENTIAL FOR SUDDEN FAILURE

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ROCK FALL FENCESROCK FALL FENCESFALSE SECURITY ?FALSE SECURITY ?

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ACCESS CONTROLS ACCESS CONTROLS

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IMPORTANCE OF PROCEDURES AND IMPORTANCE OF PROCEDURES AND CONTROLSCONTROLS

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LARGER SCALE WALL FAILURES CONTRIBUTING FACTORSFATALITIES AND SERIOUS INJURY INCIDENTS

•••Slope failure onto mine personnel

?•••Large pit wall failure 1

?••Highwall failure onto equipment

•••••Failure leads to mudflow

•••••Failure undercuts equipment 1

••Loss of equipment over pit edge

••••Large pit wall failure

••Failure onto pre-split drilling rig

Inadequate Control of

Access

Inadequate Control of

Excavation

Poor Understanding of Significance of Monitoring

Failure to Appreciate

Post Failure Deformation

Failure to Appreciate

Role of Water

Risky Geological / Geotechnical

Setting Or Design Too

Steep

Inadequate Implementation of

Design

Poor Pit Design

Element

FAILURE TO HEED

EXPLICIT WARNINGS

CONTROL OF INPIT ACCESS AND EXCAVATION

GEOTECHNICAL ISSUESPIT DESIGN ISSUES

INCIDENT

Note 1 Failure to appreciate significance of previous incident (history)

• Principal Factor or Concern• Minor Factor or Concern

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LARGER SCALE FAILURESLARGER SCALE FAILURES

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The contributing factors in order of decreasing frequency:– Geotechnical Issues – 14 cases.– Access, Procedures and Controls – 3 cases.– Warnings Ignored – 2 cases.– Open Cut Design Issues,

including implementation of design – 2 cases.

Important conclusions are:

1. The overriding influence of geotechnical issues in these serious larger scale failures.

2. The concern that specific warnings apparently went unheeded in two of the cases.

ROCKFALL CONTRIBUTING FACTORS TO FATALITIES AND SERIOUS NEAR MISSES

••Rockfall onto drill

••Rockfall onto truck and excavator

•Rockfall hits light vehicle

•••Ravelling rockfall on light vehicle

••Rockfall through Windscreen

•Bench failure and rockfall

•••••Rockfall below Cutback

•Rockfall below Cutback

•Rockfall below Cutback

Inadequate Separation

between Unstable Area

and Access

Location of Sumps,

Pumps and Ancillary Services

Inadequate Awareness and Access

Controls

Poor Control of Cutback

Excavation

Berm Loss

Poor Blasting Practices

Inadequate Support of Poor Rock Mass Zone

Slope too Steep for

Geotechnical Conditions

Inadequate Catch Fence

Design

ACCESS PROCEDURES AND CONTROLSEXCAVATION PRACTICESDESIGN ISSUES

INCIDENT

SMALLER ROCK FALLSSMALLER ROCK FALLS

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The main issues from the rockfall examples are:

1. Not possible to stop rockfall in mining environment.

1. 2. Identification of rockfall areas is essential.

2. 3. Education and awareness throughout the workforce is essential.

3. 4. Protocols required for what to do in the event of rockfall.

4. 5. Control of access by personnel and smaller ancillary equipment into risk areas is essential.

5. 6. The placement of ancillary items of infrastructure such as sumps, pumps, etc. requires careful consideration.

6. 7. Adequate separation between areas actively generating potential instability, such as cutbacks, and areas of general access is mandatory.

SLOPE DESIGN ELEMENTSSLOPE DESIGN ELEMENTS

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DEEP OPEN CUT MINE SLOPE DESIGN ELEMENTS AND RISK AREAS

•1•Height

•1••Angle

OVERALL

•1•Height

•1••Angle

INTER-RAMP

•••••Berm Width

•••••Height

•••••Angle

BENCHGEOMETRY

EconomicsSafetyEnvironmental FactorsMining SystemsGeotechnical

Issues

RISK AREAMAIN CONTROLLING ORINFLUENCING FACTOR

COMPONENTSLOPE DESIGN ELEMENT

• Principal factor or main concern• Minor factor or concernNotes: 1 Assumes a sound Pit Slope Management Procedure is in place.

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SLOPE DESIGN ELEMENTSSLOPE DESIGN ELEMENTS

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SHALLOW OPEN CUT DRAGLINE MINESLOPE DESIGN ELEMENTS AND RISK AREAS

•••Angle(mid light berm)

•••Height

SPOIL DUMP

•••Angle 1LOW WALL

••••Height

••••Angle

HIGHWALL

EconomicsSafetyMining EquipmentalSystemsGeotechnical Issues

RISK AREACONTROLLING ORINFLUENCING FACTOR

COMPONENTSLOPE DESIGN ELEMENT

1 It is assumed the location and hence height are defined by the LOX line and hence this element is fixed

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LESSONS LARGE FAILURESLESSONS LARGE FAILURES

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Role of HISTORY.

Importance of overall GEOLOGICAL SETTING.

Experience with MOVING SLOPES.

Critical role of pore pressure responses.

Understanding POST FAILURE BEHAVIOUR ANDDEFORMATIONS.

Experience base used to predict future performance, is it adequate or appropriate?

MONITORING must be right.

If the environment is different will the performance be the same; climate, stress, blasting?

LESSONS FROM SMALLER LESSONS FROM SMALLER FAILURESFAILURES

Potential risks at all scales.

Not feasible to completely remove the risk.

Those most at risk are people on foot, ancillary equipment and light vehicles.

Importance of:

AWARENESS, PROCEDURES and CONTROLS.

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