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Guidelines Slope Stability Major Hazard Standard

MHS-16 DocsOpen Ref: 57484, 28/05/1999

Uncontrolled copy – check web for latest revision

Revision Reviewed Description of Changes Date Approved

0 First Issue 28/05/1999 K Thomas

Major Hazard Standard Related Document Guidelines for Slope Stability

** Uncontrolled copy. Use latest revision **

SAF-MHS16-R01 Rev. 0 DOCS: 57484 Issued: 28/05/99 Page 1 of 31

1 Guidelines for Slope Stability Dossier2 1.1 Overview............................................2 1.2 Dossier Details...................................2

2 Guidelines for Data Collection ..........16 2.1 Exploration and Prefeasibility...........16 2.2 Feasibility and Design......................17 2.3 Seismic Studies ...............................19 2.4 Underground Mining and Known

Voids...............................................19 2.5 Additional Investigations ..................19

3 Guidelines for Slope Stability Analyses ............................................19 3.1 Introduction ......................................19 3.2 Risk Assessment .............................19 3.3 Identification of Possible Failure

Mechanisms ...................................19 3.4 Slope Data Collection and

Interpretation ..................................20 3.5 Stability Analysis Methods ...............20

4 Guidelines foSlope Monitoring..........21 4.1 Introduction ......................................21 4.2 Visual Inspections ............................21 4.3 Survey Monitoring Techniques.........21 4.4 Instrumental Monitoring Techniques 21 4.5 Pit Wall and Pit Floor

Pillar Monitoring..............................21 4.6 Monitoring Technique Reviews ........22

5 Guidelines for Investigating and Mining Through Voids...................... 22 5.1 Void Investigation.............................22 5.2 Void Investigation Techniques .........23 5.3 Guidelines for Visual Inspection

of Voids ..........................................23 5.4 Guidelines for Probe Drilling for Voids23 5.5 Guidelines for Surveying or

Geophysical Investigation of Voids.23 5.6 Guidelines for Mining through for

Voids ..............................................23 5.7 Guidelines for Pit Planning...............24

6 Guidelines for Data Collection.......... 24 6.1 Drill Hole Surveying, Logging

and Preservation of Drill Cores.......24 6.2 Photography of Drill Cores...............24 6.3 Standard Terminology for

Geotechnical Mapping and Logging Drill Cores .........................25

6.4 Standard Codes and Database........27 6.5 Geotechnical Database System.......31




1 Guidelines for Slope Stability Dossier

1.1 Overview A Slope Stability Dossier is a collection of data and documents on a slope or group of slopes organised and stored in a standard way. Its purpose is to make it easier to: • Rapidly access or check previous work on the

slope • Keep track of the status of each slope • Monitor progress of work on slope stability issues.

It is a requirement of the Slope Stability Standard that a Slope Stability Dossier be maintained for all slopes as part of the Slope Management System and that all data and documents relating to slope stabilities be indexed and stored in the slope stability dossier. The Slope Standard also requires that the Guidelines for Data Collection be followed which in turn specifies the indexation and storage of data, reports and documents in a slope dossier. On a typical mine/project site there may be several dossiers covering different groups of slopes, for example: • Dossier 1 Pit XXXX slopes • Dossier 2 Pit YYYY slopes • Dossier 3 Stockpiles • Dossier 4 Dumps • Dossier 5 Water and tailings storages • Dossier 6 Natural and modified slopes.

The grouping of slopes into different dossiers is recommended to allow ease of access, reporting and clear identification of responsibilities. Grouping also allows a dossier to be closed and archived. For ease of use, all slope dossiers have a standard structure with the following sections: 1. Slope status reports 2. Slope identification plan 3. Slope risk and hazard assessment 4. Cross reference index of the document collection 5. Incident reports 6. Minutes of slope status meetings 7. Slope management instructions 8. Action plans.

All file notes, drawings, photographs, SWPs and relevant reports will be contained in a document collection The physical document collection should be securely stored in a cupboard or filing cabinet with an index and a section for recording all material borrowed from the collection (Item, borrower, date taken, date returned).

1.2 Dossier Details

Section 1 ⎯ Slope Status Report This is a tabulated summary of the current status of slopes (see example below).

Section 2 ⎯ Slope Identification Plan(s) Pit or site plan(s) showing the location/identification of the slopes.

Section 3 ⎯ Slope Risk and Hazard Assessment There are a variety of risk assessment tools that can be used to assess the risks associated with slope failures. • The Slope Risk and Hazard Matrix developed for

the various types of slopes (examples in this guideline) is intended to provide a simple means to indicate slopes that are potentially hazardous to personnel if they fail

• Identify which slopes should be monitored • Facilitate setting of priorities for any outstanding

work pertaining to slope safety.

The first step in assessment of slope stability is to use the Slope Matrix. The matrix is revised as work on the slope proceeds or as conditions change. The matrices are divided into four sections: 1. An assessment of the potential for causing

serious injuries or fatalities is given by the rating. 2. An assessment of slope vulnerability to failure.

Category 1 slopes are the most vulnerable to failure and Category 5 the least. This categorisation serves two purposes

– as a baseline indicator of the likelihood of a slope failure, and

– to set the standards required for data collection and analysis in the slope stability assessment, and the minimum standards required for slope safety measures.

3. Slope Stability Data in which the quality of the data used for slope stability assessments are ranked according to a set of guidelines. The most vulnerable Category 1 slopes require the highest level of confidence in the data and would be ranked 1 and Category 5, the lowest level of confidence (Rank 5). This serves to highlight where the data may be deficient. ie All input data for a Category 3 slope stability assessment should have a rank of 3 or less.




4. A Slope Safety Assessment in which the factors affecting the safety of the slope of the slope are ranked. This serves to highlight where catch berms, cable bolts etc require attention. ie All safety features on a Category 3 slope stability assessment should have a rank of 3 or less.

There are four types of Slope Risk and Hazard Matrices:

• Rock slopes • Soil slopes, waste dumps, leach pads, stockpiles

and earth embankments (ordinary and water retaining structures)

• Tailings storage embankments • Natural slopes.

An example of a completed matrix, proformas for the four matrices and the guidelines are given below. There are a variety of additional risk assessment tools that can be used to compliment the Risk and Hazard Assessment.

Section 4 ⎯ Cross Reference Index of the Document Collection The purpose of this index is to ensure that all related technical information/data is clearly referenced and can be easily found when required. Sites will need to develop their specific index headings. Suggested headings include: • Slope Stability Analyses • Geological structures and structural analyses • Risk areas identified in reports requiring further

investigation • Materials test work • Hydrology, hydrogeology and groundwater • Seismic risk assessments • Slope design parameters and slope reinforcement

designs • Slope stability monitoring and leading indicators • Slope failures • Slope remedial works.

Section 5 ⎯ Slope Incident Reports This is a compilation of all incident reports.

Section 6 ⎯ Minutes of Slope Status Meetings These may be the full minutes or extracts from the minutes of slope status meetings.

Section 7 ⎯ Slope Management Instructions This is a compilation of slope management instructions.

Section 8 ⎯ Action Plans This is a compilation of action plans relating to slopes.




Example of a Slope Status Report Slope Stability Status Report 1 November 1998

Slope

Location

Date of Last Inspection

Slope Status

Action

Action Status

Responsible Person/s

Action by Date

Safety Issues

Rd1 Redeemer North wall

31/3/98

Failure imminent - crack width increasing rapidly - 1mm/day

Pit abandoned – close haul road adjacent to north side of pit

Action complete - earth bunds constructed across haul road at two sections

A N Other Erect warning signs at bunds - no further monitoring - no personnel allowed in vicinity of north side of pit. D Milton to observe daily and report to RM

Rd3 Redeemer east wall

25 Oct 1998 Pit slope under review with view to steepen batter slope

Review of stability analysis required

Review of analysis under way – complete by 3/11/98

T Li 3/11/98 None

Rd4 Redeemer west wall, southern section

25 Oct 1998 Crack observed on berm at RL 220 on 30/10/98 – crack about 35m long and 5 mm wide

Monitor slope movement

Develop and implement SWP for work in vicinity of slope

Action plan to be reviewed and approved by RM and SEQ manager

SWP under compilation

Temporary safety measures implemented

D Milton – Action Plan

P Arthur - SWP

1. 2/11/98 Barriers to be erected to prevent vehicular access onto berm




Example 1

SLOPE RISK AND HAZARD MATRIX ROCK SLOPES

Pit Nil Desperandum Slope Sector 1 South east Batters 350–500 m

Assessor I M Notjoking Revision No 5 Date 2 Feb 1998

POTENTIAL CONSEQUENCE OF FAILURE

Potential human exposure Multiple X None

Regard as an action priority ranking SLOPE VULNERABILITY CATEGORY Category 1 2 3 4 5

Slope height and steepness Steep/high X Low

Vulnerability & probability of natural events Vulnerable / High X Not Vulnerable

Likelihood of failure Highly likely X Unlikely

SLOPE STABILITY DATA Rank 1 2 3 4 5

Slope stability analyses Rigorous X None

Confidence level in material strengths Known X Assumed

Confidence levels in ground water conditions Known X Assumed

Confidence level in geological structures Known X Assumed

Design consideration of natural events Rigorous X Not considered

SLOPE SAFETY ASSESSMENT Rank 1 2 3 4 5

Crest and wall condition Sound X Poor/deteriorating

Cable bolt and other support Good X Poor/deteriorating

Catch berm and catch fence conditions Wide and clear X Narrow or full

PROTECTION MEASURES Not required Required

Protection fences and warning signs Good condition X Incomplete/faulty

Slope stability inspection and monitoring Operating satisfactorily X Planned/suspended

Slope specific SWPs In force X Pending




Example 2 Slope Risk and Hazard Matrix — Natural Slopes

SLOPE RISK AND HAZARD MATRIX NATURAL SLOPES

Location Slope Height

Assessor Revision No Date

POTENTIAL CONSEQUENCE OF FAILURE Potential human exposure Multiple

Regard as an actioSLOPE VULNERABILITY RANKING Category 1 2 3

Slope height and steepness High/Very steep X Probability of natural events High / critical ↓ Slope geological profile Hazardous ↓ Land use adverse effects Critical ↓ Likelihood of failure Highly likely X

SLOPE STABILITY DATA Rank 1 2 3

Confidence levels in ground water Known X Confidence level in geological structures Known X

Natural events in stability assessment Known & considered

SLOPE SAFETY ASSESSMENT Rank 1 2 3 Cliffs, breakaways and slope condition Sound X

Retaining walls and drainage structures Good / not required X Slope toe areas Wide and clear X


Protection fences and warning signs X Good condition Slope stability inspection and monitoring X Operating satisfactorily

Slope specific SWPs X In force Note: Likelihood of failure. Use lowest category




Proforma Slope Risk and Hazard Matrix — Rock Slopes

SLOPE RISK AND HAZARD MATRIX ROCK SLOPES

Pit Slope Batters



Potential human exposure to failure Multiple None

Regard as an action priority ranking SLOPE VULNERABILITY RANKING Category 1 2 3 4 5

Slope height and steepness Steep/high Low

Vulnerability & probability of natural events Vulnerable / High Not Vulnerable

Likelihood of failure Highly likely Unlikely


Slope stability analyses Rigorous None

Confidence level in material strengths Known Assumed

Confidence levels in ground water conditions Known Assumed

Confidence level in geological structures Known Assumed

Design consideration of natural events Rigorous Not considered


Crest and wall condition Sound Poor/deteriorating

Cable bolt and other support Good Poor/deteriorating

Catch berm and catch fence conditions Wide and clear Narrow or full


Protection fences and warning signs Good condition Incomplete/faulty

Slope stability inspection and monitoring Operating satisfactorily Planned/suspended

Slope specific SWPs In force Pending




Ranking Guidelines and Explanatory Notes — Rock Slopes

Ranking / Category 1 2 3 4 5

POTENTIAL CONSEQUENCE

OF FAILURE

Multilpe fatalities in a major failure

Single fatality in a major

failure

Serious LTI Possible LTI or MTI

No injures or loss

SLOPE

VULNERABILITY

Ranking based on factors of safety, probability of sliding or assessed stability relative to other slopes on site, taking into consideration the possible consequences a major failure. The possible influences

of underground mining must be considered.

Slope height and

steepness

FoS <1.2 or PoS >50% or severe cracking

or failing

FoS = 1.2–1.5 or PoS 20-50%

or minor cracking

FoS = 1.5–2 or PoS 5-20%

Apparently stable

FoS = 2–3 or PoS 0-5%

Apparently stable

FoS > 3 or PoS 0-5%

Stable

Vulnerability

&probability of natural events

Critical and >= 1 in slope life

Vulnerable and >= 1 in slope life

Vulnerable and >= 1 in 100 yrs

Vulnerable or >=1 in 100 yrs

Not vulnerable or <1 in 100 yrs

SLOPE STABILITY DATA Ranking of detail and/or thoroughness of the slope stability assessment

Slope design methods Rigorous Design Specific Design Based on Precedence

Assumed

Confidence levels in the rock mass strength parameters Material strengths Lab tests & back

analyses Lab Tests Limited lab tests Index tests Assumed

Confidence in influence of ground water Ground water

conditions Known or Fully drained slope,no phreatic surface

Known phreatic surface & no

seepage

Unknown phreatic surface

& no seepage

No drainage- seepage visible

No drainage – free flowing water visible

Confidence in the geological structural data and interpretation used Geological structure

and interpretation Detailed mapping & interpretation

Face Mapping interpretation

Limited face mapping

Borehole data Assumed

Vulnerability of the slope to an earthquake or exceptionally heavy rainfall event Natural event hazards

and Slope design

considerations

Probability and magnitude

assessed and incorporated in

design


assumed and included in design


assumed and considered in

design

Considered inconsequential and ignored in

design

Not considered

SLOPE SAFETY

ASSESSMENT Potential for the slope face or crest to become hazardous

Crest and wall condition

Sound batters and crests

Mild blast damage cracking

Moderate blast damage/Friable or fractured rock

Heavy damage Weathering

Unravelling severely cracked

Condition of cable bolting, mesh, shear pins or catch fences Cable and other

support Sound/not required

Mild corrosion or deterioration

Moderate corrosion or deterioration

Heavy corrosion Severely corroded

Capacity of berm to hold scat and rock falls Catch berm and

catch fence condition

Wide/clear Fall Capacity 20 BCM/m

Fall Capacity 10 BCM/m

Fall Capacity 5 BCM/m

Narrow/full




Proforma Slope Risk and Hazard Matrix — Soil and Broken Rock Slopes, including Water Retaining Embankments

SLOPE RISK AND HAZARD MATRIX SOIL AND BROKEN ROCK SLOPES




Potential human exposure Multiple None


Slope height and steepness Steep/high Low

Vulnerability & probability of natural events Vulnerable / High Not Vulnerable



Slope stability analyses Rigorous None

Confidence level in material strengths Known Assumed

Confidence levels in ground water conditions Known Assumed

Confidence level in retaining structures Known Assumed

Design consideration of natural events Rigorous Not considered


Crest and slope condition Sound Poor/deteriorating

Retaining structures Good Poor/deteriorating

Slope toe areas Wide and clear Narrow or full



Slope stability inspection and monitoring Operating satisfactorily Planned/suspended





Ranking Guidelines and Explanatory Notes Soil and Broken Rock Slopes and Water Retaining Embankments


POTENTIAL CONSEQUENCE OF

FAILURE



failure


No injures or loss

SLOPE

VULNERABILITY

Ranking based on factors of safety, probability of sliding or assessed stability relative to other slopes on site, taking into consideration the possible consequences a major failure. The possible influences of

underground mining must be considered.

Cohesive materials

Granular Materials

FoS <1.2 severe cracking or failing>> angle of repose

FoS = 1.2–1.5 minor cracking

> angle of repose

FoS = 1.5–2

= angle of repose

FoS = 2–3

< angle of repose

FoS > 3

<< angle of repose

Vulnerability &

probability of natural events

Critical and >= 1 in slope life

Vulnerable and >= 1 in slope life

Vulnerable and >= 1 in 100 yrs

Vulnerable or >=1 in 100 yrs

Not vulnerable or <1 in 100 yrs

SLOPE STABILITY DATA Ranking of detail and/or thoroughness of the slope stability assessment

Slope design methods

Specific Design Based on Precedence

Assumed

Confidence levels in the rock mass strength parameters Confidence levels material strengths

Lab tests & back analyses

Lab Tests Limited lab tests Index tests Assumed

Influence of ground and retained water

Confidence levels – ground and retained

water conditions

Known – Fully drained slope - no phreatic surface


seepage

Unknown phreatic surface & no

seepage

No drainage- seepage visible


& no seepage

No drainage – free flowing water

visible seepage visible

Confidence in the stability of the retaining structure

Confidence levels – retaining structure

Rigorous stability analyses

Limited analyses & precedents

Precedents None

Vulnerability of the slope to an earthquake or exceptionally heavy rainfall event Natural hazards

Slope design considerations

Probability and magnitude assessed and used in design


assumed and used in design


assumed and considered


design

Not considered

SLOPE SAFETY ASSESSMENT Potential for the slope face or crest to become hazardous

Crest and slopel condition

Sound slopes and crests

Some erosion/ rilling

Occasional overhangs

Frequent over-hangs/cracks

Condition of constructed retaining structures (e.g. Headwalls)

Retaining structures

Sound/not required Mild corrosion or deterioration

Moderate corrosion or det.

Heavy corrosion Severely corroded

Capacity hold spillage or rill material

Slope toe areas condition

Wide/clear wide but in occasional use

Narrow frequent use




Proforma Slope Matrix — Tailings Storage Slopes

SLOPE RISK AND HAZARD MATRIX TAILINGS STORAGE SLOPES






Slope height and steepness Steep/High Low

Vulnerability to earthquake events Vulnerable Not Vulnerable

Probability of overtopping rainfall events High Low



Overall slope stability analyses Rigorous None

Design consideration of natural event risk Rigorous Not considered

Starter and embankment raise designs Downstream/Rigorous Upstream/None

Construction quality control and documentation Tested & documented Nil

Strength of tailings material near embankments Slow rise & tested Fast or Assumed

Construction and foundation material strengths Known Assumed

Slope and surface water inspections/monitoring Regular recordings Irregular/none


Crest, slope and embankment condition Sound Poor/deteriorating

Surface water ponding and retained materials Small pond/dry Large pond/wet

Toxicity of tailings Inert Toxic

Seepage through slope None Flowing water




Management process Yes No Active Tailings Management Plan Quarterly Tailings Management Inspection and meeting Daily TSF Inspections Management Risk High Low




Ranking Guidelines and Explanatory Notes — Tailings Retaining Structures



FAILURE



failure


No injures or loss

SLOPE VULNERABILITY

Ranking of detail and/or thoroughness of the global slope stability assessment

Embankment height

and steepness

FoS <1.2 or PoS >50% or

severe cracking or failing

FoS = 1.2–1.5 or PoS 20-50%

or minor cracking

FoS = 1.5–2 or PoS 5-20%

Apparently stable

FoS = 2–3 or PoS 0-5%

Apparently stable

FoS > 3 Stable

Assessed level of possible damage by an operating base earthquake

or overtopping due to earthquake shaking Vulnerability to

earthquake events Severe

embankment damage or low freeboard with slurry or fluid

Major damage, low freeboard

with slurry, fluid or liquefaction

potential

Sustainable damage or moderate

freeboard with slurry, fluid or

liquefaction

Minor cracks in embankments or moderate

freeboard and, low liquefaction

potential

No wall damageand

adequate freeboard

Probability of a rainfall event causing overtopping and critical embankment erosion

Probability of rain events

≅ 1 per year ≅ 1 in slope life ≅ 1 in 10 yrs ≅ 1 in 100 yrs ≅ 1 in 500 yrs

SLOPE STABILITY DATA

Ranking of detail and/or thoroughness of the slope stability assessment

Overall slope stability analyses & methods

Rigorous stability analyses

Deterministic & probabilistic

analyses

Deterministic analyses & precedents

Limited or simple analyses or precedents

None

Slope design consideration of the earthquake or exceptionally heavy rainfall risks Natural event hazards

Slope design considerations

Probability and magnitude assessed and incorporated in

design


assumed and included in

design


assumed and considered in

design


design

Not considered

Starter wall and embankment raises

Type of embankment and slope stability assessment of each embankment raise

Downstream construction

with select earthfill:

Rigorous analysis Limited analyses

Simple analyses or precedents.

No stability analysis

No analysis or drainage

Centreline rise construction

Rigorous analysis - Rigorous analysis -

Rigorous analysis or precedents.

Simple analyses or precedents

No analysis or drainage

Upstream using tailings

Rigorous analyses

Rigorous analyses -

Simple analyses or precedents




Hazard Ranking Guidelines — Tailings Retaining Structures(Continued)


Embankment construction ⎯ Quality Control (QC) and documentation

Wall and embankment raise

construction

Constructed to design specs., QC

tests & full documentation

Satisfactory construction

shown by investigation & in situ testing

Constructed to design specs.

No QC tests or no documents

Subcritical defects in construction

Gross defects in construction

Confidence in the retained material strengths and the degree of consolidation of the tailings near the embankment

Confidence levels – strength of tailings

materials near embankments

Lab & in situ tests and rate of rise

<1.5m/year, fully drained beach

Lab tests and

rate of rise 2 to 2.5 m/year

Assumed strengths or

unconsolidated rate of rise >3m/year

Confidence levels in the construction and foundation material strength parameters

Confidence levels – Construction

materials

Lab tests & back analyses

Lab Tests Limited lab tests Index tests Assumed

Visual and instrument observations of slope and phreatic surface

Slope and surface water inspections /

monitoring

Regular inspections & monitoring

Irregular inspections or

monitoring

No formal inspection or monitoring

SLOPE SAFETY ASSESSMENT

Potential for the slope face or crest to become hazardous

Crest and slope and embankment

condition

Sound batters and crests

Mild surface erosion

and no piping erosion

Minor crest or wall erosion &

no piping erosion

Crest cracks or mod. surface or

controllable piping erosion

Severe cracking, surface or piping

erosion or overtopping

Management of surface water and beach development and drying

Surface water ponding and

retained materials

Well managed small pool and

dry beaches

Moderate pool, and attention beach drying

Large poorly controlled pool, constantly wet

beaches Potential for tailings to cause contamination

Toxicity of tailings Inert, non-toxic Hyper - saline Toxic/harmful Potential for raised phreatic surface to cause instability

Seepage through slope

Depressed phreatic surface

Seepage through slope

High phreatic surface or

seepage evident




Proforma Slope Risk and Hazard Matrix — Natural Slopes

SLOPE RISK AND HAZARD MATRIX NATURAL SLOPES






Slope height and steepness High/Very steep Low/Shallow

Probability of natural events High / critical Low

Slope geological profile Hazardous Sound

Land use adverse effects Critical Minimal



Confidence levels in ground water Known Assumed

Confidence level in geological structures Known Assumed

Natural events in stability assessment Known & considered Ignored


Cliffs, breakaways and slope condition Sound Poor/deteriorating

Retaining walls and drainage structures Good /not required Poor/deteriorating

Slope toe areas Wide and clear Narrow or full



Slope stability inspection and monitoring Operating satisfactorily

Planned/suspended


Note: Likelihood of failure. Use lowest category




Ranking Guidelines and Explanatory Notes — Natural Slopes



FAILURE



failure


No injures or loss

SLOPE VULNERABILITY

Ranking on the basis of performance or factors of safety where analysed

Slope height and steepness

FoS <1.2 severe High cliffs or steep slopes

Major previous failure or cracking

FoS = 1.2–1.5 Cliffs and steep

slopes Cracking

Minor landslips

FoS = 1.5–2 Moderately Steep

slopes Soil Creep Small

slip scars

FoS = 2–3 Gentle slopes

No failures

FoS > 3 Flat

No failures

Probability of an earthquake or rainfall event affecting slope stability

Probability of natural events

≅ 1 per year ≅ 1 in slope life ≅ 1 in 10 yrs ≅ 1 in 100 yrs ≅ 1 in 500 yrs

Ranking on detail and/or complexity of the geological profile of the slope

Slope geological profile

Recent unconsol –idated sands or

volcanic ash Liquefaction

potential

Complex gouge filled faults or deep soft clay

Colluvium Deep weathering

Moderate depths of weathering

Flat dips Outcrops or shallow soils

Influence of land useage

Land use – Effects on Material

strength

Industrial / heavy earth disturbance

Flood irrigation Rice paddies light

earthworks

Irrigated crops Forestation Natural vegetation Grazing

SLOPE STABILITY DATA

Influence of ground and retained water

Confidence levels – groundwater

conditions

Known – Fully drained slope -

no phreatic surface


seepage

Unknown phreatic surface & no

seepage


& seepage

No drainage –flowing water or seepage visible

Confidence in the geological structural data and interpretation used

Confidence levels – Geological structure

Detailed mapping & interpretation

Exposure Mapping

interpretation

Limited mapping Borehole data Assumed

Consideration of risk of earthquake or exceptional rainfall event in slope stability assessment Natural events- Slope stability

assessment

Both risks assessed & considered

Both risk factors assumed and considered

Either earthquake or rain risks assumed and considered

Both considered inconsequential and ignored in

assessment

Not considered




Ranking Guidelines and Explanatory Notes — Natural Slopes (Continued)


SLOPE SAFETY

ASSESSMENT Potential for the slope face or crest to become hazardous

Cliffs, breakaways and slope condition

Sound slopes and crests

Some erosion/ rilling

Disturbed Occasional breakaways

Very disturbed Slumps or cracks

Condition of constructed retaining structures

Retaining walls and drainage

structures

Sound/not required

Mild deterioration

Moderate deterioration

Cracked or crumbling

Severely cracked or collapses

Capacity hold spillage or rill material

Slope toe areas - condition

Wide/clear Wide but in occasional use

Narrow frequent use

2 Guidelines for Data Collection

2.1 Exploration and Prefeasibility Stage It is important not to lose the opportunity to collect information that later developments on the site may obscure. This information may have a bearing on the course of future investigations and ultimately slope stability and safety. Further earthworks may obscure fault or shear exposures, sinkholes, old mine workings, old landslides and groundwater seeps. Copies of all reports, maps, logs, photographs and records shall be preserved for future reference in a secure place. There are four areas where opportunities to collect data may be lost due to the development of the site:

2.1.1 Geological and Geotechnical Mapping All available exposures in the project area and vicinity are geologically and geotechnically mapped and interpreted if sufficient data is available: • Feature checklist:

– Rock or soil types – Nature and orientation of structures: faults and

shear zones, joints, veins, bedding and foliation. – Lineaments and drainage lines

• Exposure checklist: – Outcrops and stream beds – Costeans – Road and drilling pad cuttings – Exploration adits and other workings.

2.1.2 Topographic Mapping All topographic features should be mapped, and relevant local history regarding the mapped features recorded. Aerial and site feature photographs should be retained of the undisturbed site. • Feature checklist:

– Topography and surface features – Sinkholes and caves – Mine workings – Landslides and slips – Surface water ponding, channels, springs and

groundwater seeps.

2.1.3 Drill Cores It is important that for any potential mining project, all drill holes are surveyed, and the cores properly logged, photographed and stored, so that information may have a bearing on the course of future investigations and ultimately slope stability is not lost. The Guidelines for Core Logging and Exposure Mapping (see below).shall be followed. The following basic geotechnical data shall be logged • Interval (from … to) • Core recovery • Rock type • Alteration • Weathering • Fracturing, crushing or shearing • All the properties required for rock mass

classification in all major classification systems, vis the NGI (Barton’s) Q system, CSIR (Bieniawski’s) RMR system, GSI (Hoek) and the MRMR (Laubscher’s) Mining Rock Mass Classification system.




All major structures should also be individually logged as geotechnical zones if wide enough, or as single features with the following items recorded: • Depth or depth interval (or distances) • Intersection angle (alpha angle) or orientation • Structure type (fault, shear zone etc.) • Brecciation, shearing, infill strength and width • Wall rock alteration and weathering • Evidence of water • Additional geotechnical items to be logged if

present: • Stress induced core discing, borehole ‘caving’ or

borehole breakouts • Variations in rock densities and porosity.

2.1.4 Hydrology and Hydrogeology Complete histories of rainfall and stream flows are important. • As soon as a presence is established on site, start

recording rainfall and water flows • Collect and record historical and anecdotal rainfall

and water flow data • Monitor groundwater levels and quality in drill

holes • Drawdown measurement with groundwater

pumping tests.

2.2 Feasibility and Design Stage In a feasibility study all aspects, which could affect slope stability, should be investigated or identified for future investigation and the slope stability dossier initiated. Specific site investigations are required to determine foundation conditions for treatment plants, dumps, dams and tailings storage facilities. Specialist civil engineering geotechnical consultants normally undertake these investigations. These investigations should also address slope stability issues especially in high relief terrain. In the design stage further data collection may be required to improve the quality of data and to fill gaps identified during the feasibility study. However, due to practical limitations there may still be areas that cannot be fully investigated (previous underground mining is a case in point). These should be identified for investigation during the early construct stage to address any deficiencies. Key areas include:

2.2.1 Topographical Mapping Detailed ground or aerial topographical survey maps are essential prerequisites for other data collection. These should show all surface features including: • Cuttings, embankments and drains • Sinkholes • Mine workings • Landslides and slips • Surface water ponding areas and groundwater

seeps and springs.

The scale of the maps should allow all surface features to be shown in sufficient detail for project planning and with contour intervals that allow for recognition of drainage courses and areas of potential flooding. Ideally, the maps should be prepared in the following formats: • Drafting film for working plans • Digital strings for importation into mine planning

software • Digital GIS model for data presentation and other

studies.

2.2.2 Geotechnical Model A geotechnical model is a simplified representation of the real rock and soil properties in the project area, in which the area is subdivided into several zones (or domains) with similar geotechnical characteristics. It is based on an analysis and interpretation of the results of geological and geotechnical mapping and logging programmes. All available exposures and drilling data should be looked at and considered in this interpretation. A well-distributed and representative range of exposures, costeans and diamond drill cores should be selected and geologically and geotechnically mapped or logged. The specific objectives of this mapping and logging are to: • Understand project area geological structure - the

distribution and relationships of the main rock and soil types, the nature and location of faults, folds and inflections, facies changes, effects of weathering, etc.

• Determine the location, orientation, and nature of major structures (e.g. faults, shear, and crush zones, material contacts and weak beds)

• Identify and define structural domains and characterise the materials within them.

The required standard for the geotechnical mapping and logging is the Basic Geotechnical Logging Standard (see detailed description below).




The proportion of the surface exposures and exploration and resource evaluation diamond drill holes that should be geotechnically logged is site dependent. In all cases, it should be sufficient to identify all major structures and to define domains and characterise the rocks within them. In some cases additional geotechnical holes may be required to investigate specific structures or fill in gaps in the distribution of source data.

2.2.3 Materials Testing Tests are required to form the basis for estimates of the physical properties of the soil or rock in each domain. Durability tests to check the potential for loss of strength due to exposure, desiccation etc. may be required. Elastic moduli may also be required for modelling of stress in rock slopes. The test work should comprise both field index tests and laboratory tests on a suite of representative samples of all major materials. The choice and numbers of tests are dependent on the project ground conditions. Tests are to comply with Australian or International Standards. Ideally, sufficient tests should be performed on each material to provide confidence in the estimates of the material strengths.

2.2.4 Detailed Structural (Defect) Surveys and Analyses In hard rock domains slope stability is likely to be structurally controlled with the main failure mechanisms being toppling, planar, wedge or step-path failures on faults or shears, bedding and joints or a combination of these. For the design of slopes in these materials the orientation, spacing, continuity and shear strengths are required for: • Major structures, faults, shear and crush zones • Bedding planes and weak strata • Foliation partings • Joints and veins.

The data collection programme should include: • Structural and geotechnical line or face mapping of

representative exposures and costeans. Estimates of joint continuities can only be obtained from exposure mapping

• Geotechnical and structural logs of orientated diamond drill cores which are representative of the rock types in each of the hard rock domains

• Special geotechnical drill holes where required to provide an unbiased sampling of the structures and to fill in any gaps in the coverage

• In poor ground where the core orientation is not possible, applicable downhole geo-physical and sonic logging techniques such as the sonic Televiewer should be considered.

The Structural Mapping and Orientated Core Logging Guidelines (see below) shall be used for the geotechnical mapping and logging. This also details the requirements for orientated core drilling. The proportion of the surface exposures, exploration and orientated cores that are mapped or logged, should be sufficient to identify and characterise the joint sets and major structures in each domain. The drill holes should be orientated to ensure that critical joint sets and bedding or foliation planes are adequately sampled. In some cases supplementary geotechnical holes may be required to investigate specific structures or fill in gaps in drilling coverage.

2.2.5 Stress Regime High stresses can affect pit slope stability. Evidence of high stresses may be seen in discing in drill cores or borehole breakouts (frequently called “caving”). If high stresses are indicated, stress measurements may be required.

2.2.6 Hydrogeology Investigations Groundwater pressures can have a significant effect on the stability of slopes. These have to be taken into account in slope stability analyses and slope design. The design may incorporate water controls, slope drainage and/or depressurisation measures where appropriate. The following aspects should be determined: • Sources of water • Current water table(s) • Potential phreatic surfaces • Design criteria for wall rock drainage or wall

depressurisation • The potential for slope destabilisation by surface

water ingress, erosion, flooding.

Checklist of items to be investigated: • Cavities, caves and channelled water • Underground mine workings • Paleochannels • Perched water tables • Location and nature of aquifers and aquitards • Water quality. Test work may include packer, pump and air lift tests to determine porosity, permeabilities, storativity of the main aquifers and water bearing structures.




2.2.7 Surface Hydrology Slope stabilities can be affected by erosion arising from storm and floodwaters and the replenishment of groundwater. Adequate drainage and floodwater control measures should be incorporated in the site planning. The catchment area should be monitored for changes, which may increase the flood risk or modify the groundwater levels. Checklist of items to be investigated and monitored:

• Stream catchment areas • Rainfall data • Snow and ice accumulations • Stream gradient profiles, bed characteristics and

debris accumulations • Lakes and depressions • Man made modifications — bridges, dams,

embankments, road formations and subsequent alterations

• Stormwater and water supply pipelines.

Reports and aerial photographs and/or GIS models of the catchment and project areas shall be placed in the Slope Stability Dossier for the purposes of change monitoring.

2.3 Seismic Studies Seismic risks should be assessed in terms of the regional geology, especially seismically active faults, and by probabilistic analyses of the earthquake record. In low seismic risk areas, the published studies may be sufficient, but in seismically active areas, a seismic study for the project is required to provide the following design parameters. Open pits, modified and natural slopes: • Earthquake magnitudes and return periods • Peak particle accelerations • Soil and topographic amplification factors • Material properties.

Dams and tailings dams: • Magnitudes and return periods • Maximum credible earthquakes • Design base earthquakes • Spectral accelerations • Material properties.

Refer to WMC Guidelines for the Design of Tailings Storages

2.4 Underground Mining and Known Voids Where there are voids in the vicinity of the proposed pit, dumps, tailings facilities and other slopes there should be a thorough search for all existing information. Where there is incomplete or insufficient information available specific investigations will be required. (see Guidelines for Investigating and mining through voids)

Due recognition should be taken of the probability that: • The actual limits of mining may differ from the

plans due to subsequent mining or stope collapses • Stope filling is incomplete.

The data should be assessed and recorded in the study documentation and Slope Dossier for further detailed investigation.

2.5 Additional Investigations There may be a requirement for specific or special investigations. These should be identified in the study documentation to ensure they are conducted at the appropriate time.

3 Guidelines for Slope Stability Analyses

3.1 Introduction The steps in slope stability analysis generally include (but may not be limited to): • Risk assessment (Hazard and Risk Matrix or other

appropriate assessment) • Identification of possible failure mechanisms and

appropriate analysis methods • Data collection and interpretation • Material testing • Back analyses • Stability analysis methods • A re-assessment of the hazard and risks • Recommendations for action or design • Documentation • Where a deficiency in the data is identified, this

will need to be addressed, and the slope stability analysis repeated.

The related procedures outlined in WMC’s GL 68 must also be followed for the design of tailings dams.

3.2 Risk Assessment As a guide to appropriate slope stability analysis methods, the slope stability risk and hazard rating should be used and complimented with a relevant technical standard method(s).

3.3 Identification of Possible Failure Mechanisms

The best data available should be used to determine the possible failure mechanisms at the site in question. The following is a checklist of the possible mechanisms:




3.3.1 Soil and Granular Materials, also Highly Fractured Rocks • Circular failures • Non circular failures • Combined failure slip circle and a weak substratum

or fault • Two wedge e.g. for spoil piles • Liquefaction.

3.3.2 Rock Slopes • Rotational failures on substratum or fault • Planar failures • Step-path failures • Wedge failures • Toppling failures • Ravelling failures • Rock falls.

3.4 Slope Data Collection and Interpretation Further data collection and or testing programmes may be required to meet the specific requirements of the analyses. Common data requirements for both granular and rock slopes are: • Slope geometry and the location of tension cracks • Slope material profiles and properties • Knowledge of geological structures • Ground water profiles • Seismic information.

The data requirements for slopes in soils and granular materials differ from rock slopes.

3.4.1 Granular Materials Mohr-Coulomb strength parameters are usually required. In fine-grained soils, these can be determined by laboratory triaxial strength tests on undisturbed samples. These should be three–stage drained or undrained tests as appropriate to the slope drainage conditions. In highly fragmented rock, the Mohr–Coulomb strengths can be estimated by an empirical method(s).

3.4.2 Rock Slopes Joint orientation data, joint spacing and continuity data, joint shear strength test data, (or estimates of joint strength data from joint properties) are required.

3.5 Stability Analysis Methods The analysis methods and path followed is dependent on the risk of slope failure and the failure mechanism. The greater the risk the more rigorous the analysis process. This may include multiple and sensitivity analyses. Analysis methods may include but are not limited to:

• Precedence or slope experience • Empirical • Kinematic • Numerical (deterministic or probabilistic) • Dynamic • Time dependant.

For example the following may apply:

3.5.1 Low-Risk Slopes For these slopes it may be sufficient to use slope design charts such as described in Hoek, E. and Bray, J. (1981), Rock Slope Engineering, revised third edition, Institute of Mining and Metalurgy. Where there are no geological complications, Haines and Terbrugge’s RMR (1995) based slope angle charts can also be used. Haines A. (1993) ‘Rock Slope Classification for Optimum design of monitoring networks’ in Swedzicki, T. 1993 Geotechnical Instrumentation and Monitoring in Open Pit and Underground Mining, Bulkema ISBN 90 5410 3213).

3.5.2 Medium to High-Risk Slopes More rigorous processes including computer based methods should be used. In medium risk slopes these can be deterministic, but probabilistic methods should be included in higher risk slopes. There is an increasing number of computer packages for the analysis of slope stability. It is important to choose the most appropriate package(s) for the expected failure mechanism. Wherever possible, the analyses should be repeated on another package. The slope stability analysis packages should allow modelling the effects of the following: • Position and depth of a tension crack • Water in the tension crack • Blasting and seismic loading • Ground water pressures • Different materials and properties • Geological structures.

In seismic risk areas, the effects of earthquake forces should be investigated. In medium risk slopes, it is sufficient to treat seismic forces as pseudo static forces, but in high-risk soil slopes dynamic modelling of the slopes may be required. The effect of topographic amplification factors should be considered. (Davis L. L. and West L. R. Observed effects of Topography on ground motion, bull. Sesm. Society of America, 63, 1, pp. 283–289). In weaker rocks or high stress areas, two or three dimensional stress/strength analyses should also be performed. Destabilising effects of voids requires special and rigorous consideration.




4 Guidelines for Slope Monitoring

4.1 Introduction The objective of slope monitoring is the early detection of developing hazards and identification of sections of slopes that may be approaching instability so that appropriate precautions can be taken. The Slope Risk and Hazard Matrix (see above) can be used as a guide to identify those slopes that will need to be regularly inspected and/or monitored. Some instrumentation may also be required. The nature of the hazard will determine the frequency and type of monitoring.

4.2 Visual Inspections Regular inspections of slopes should be carried out to check: • For potentially hazardous loose rocks • For deterioration in the condition of slopes due to

weathering, erosion, undercutting, loosening or blast damage

• The condition of berms and capacity of the berms to catch and hold scat and minor batter failures

• For corrosion of reinforcement • Opening cracks and subsidence in crests, berms

and haul roads as an indicator of possible impending failures.

The appearance of cracks can be an early sign of a major failure developing and it is essential that the development of the cracks be monitored. This may be done by: • Recording the number of cracks and their widths at

regular time intervals. This is suitable for low hazard potential failures

• Establishing a number of line traverses and logging the cracks (location and width) along each traverse. Repeating the logging at intervals will indicate whether the slope is stabilising or deteriorating

• Crack dilation monitoring instruments (e.g. measurement between pins driven into the ground and/or simple surface extensometers or other crack monitoring devices such as glass plates, wedges )

• Displacement monitoring by survey or extensometers.

4.3 Survey Monitoring Techniques The most common method of pit wall monitoring is to use a total station (Electronic Distance Measurement (EDM)/theodolite) to measure the distances from a base station to an array of survey markers (corner cube reflectors or prisms) mounted on the slope. It is critical that the EDM technique has an accuracy and precision appropriate to the expected rate and magnitude of displacement.

The minimum requirements for the system are: • Survey base stations located on stable ground, or

the means to check the location of the base stations by instrumental or survey methods. The base stations are best located opposite the slope to be monitored as the EDM distance measurements are generally more accurate than the angular measurements

• Adequate numbers of prisms located on the potential failure slope. The prisms should be mounted so that they are not easily disturbed or destroyed by deteriorating surface conditions on the slope and sufficient should be installed to cater for the inevitable losses.

The survey results should be graphed or mathematically analysed on a time-displacement basis. Predictions of the time of failure are frequently possible by manual or mathematical extrapolation of the displacement rates. When progressive failure conditions become apparent, the monitoring frequency should be increased to improve the prediction accuracy.

Other survey techniques may include: • Precise levelling • Global Positioning System • Triangulation • Photogrammetry.

4.4 Instrumental Monitoring Techniques There are a large number of instruments available for monitoring such as extensometers, inclinometers, shear detectors, and microseismic monitoring system. These should be installed in accordance with the manufacturer's recommendations. The monitoring programs should include devices capable of monitoring the displacement of the slope so that time-displacement analyses can be done and predictions of the time of failure made. Where the consequences of a failure could be life-threatening, instruments capable of monitoring slopes continuously and being linked to audible and mine radio alarm systems should be used where possible. In earthquake prone areas seismometers linked to audible and mine radio alarms should also be used.

4.5 Pit Wall and Pit Floor Pillar Monitoring Where the pit is close to voids, monitoring of the stability of the pillars is essential. The location size and condition of the voids should have been investigated by probe drilling and/or geophysical or photographic techniques. As each bench is mined, the remaining pillars should be re-investigated by the most suitable of these methods.




Generally, pit mining face advances preclude longer term monitoring instruments such as extensometers, inclinometers, and shear detectors. Microseismic monitoring systems have the potential to remotely monitor failing ground, however these also pick up other pit operating noises and if these can be filtered out, they could offer continuous monitoring and links to audible, visual and/or radio alarm systems.

4.6 Monitoring Technique Reviews Periodic reassessments should be done on the type(s) of monitoring, location and density of instruments and frequency of observations. Adjustments should be made where necessary.

5 Guidelines for Investigating and Mining Through Voids

Where there are natural voids or underground mining on a site, precautions need to be taken to ensure that: • Open pit mining can proceed safely and stopes or

remaining pillars do not collapse and destabilise the pit slopes above it

• The pit floor does not collapse into an underlying stope and endanger the safety of personnel operating in the pit

• Dumps and tailings storage facilities are not constructed over potentially unstable slopes

For the feasibility study, a first pass estimate of the location, size and nature of the previous workings may be sufficient. This should include a review of the underground mine plans and stoping data while recognising that the actual limits of mining may differ from the plans due to subsequent mining or stope collapses. Through out this guideline the titles of Pit Supervisor, Geotechnical Engineer and Surveyor are used in a generic sense. Each operation may have a different title or name for this duty eg may be called Production Engineer or Mine Manager. The intent is clear in that a person shall designated to have specific responsibility for each of the steps or activities and be accountable for compliance with the step or process. It is critical that relevant experience or qualifications are held by the person charged with the responsibility.

5.1 Void Investigation Two or more stages of investigation may be required.

5.1.1 Initial Stage, to determine: • Whether the voids will affect the stability of pit

walls and floors or the safety of personnel working in the pit

• What void investigation techniques are required and can be safely used

• Safe working practices for further investigation of the nature and location of the voids

5.1.2 Advanced Stage In practice it may be necessary to make some conservative assumptions on the minimum distance in order to develop the pit to a position where the stopes can be investigated more fully. Probe and or geophysical techniques to determine: • The location and size and nature of the voids or

workings to a precision required for safe mining through the voids

• The state of the voids: – the condition of the ground forming the back,

walls and pillars – the presence of stope backfill, its condition, the

degree of stope filling and presence of water in the stope

– stope back reinforcement (cable bolting) and its condition

• The minimum distance that must be left between the open pit and stopes to ensure the stability of the stopes and stope pillars, open pit walls and floor. This would normally involve stress and displacement modelling with measured or estimated in situ stresses and rock mass strengths.




5.2 Void Investigation Techniques The following techniques can be used to investigate the location and size of the stopes: • Visual inspection of voids that are safely accessible

from underground • Borehole probe drilling (see Probe Drilling SWP

below): – Purpose drilled probe holes with closed circuit

television if the cavities are not flooded – Grade control drilling – Blast holes for small openings

• Remote cavity surveying techniques: – Cavity Monitoring System (CMS ) This requires

access to the void from underground – Cavity Auto Laser Scanner (CALS) a 100 mm

diameter survey instrument that can be lowered down a borehole

• Geophysical methods • Microgravity • Seismic tomography (e.g. RockVision) • Ground Probing Radar (GPR) • Radio imaging (e.g. RIM II). • Resistivity.

5.3 Guidelines for Visual Inspection of Voids SWPs shall be developed to ensure the safety of personnel undertaking the inspections Precautions shall include: • Examinations of plans sections etc so that

inspection personnel do not enter possibly unstable undercut areas

• Inspection and barring down of development backs to avoid rockfalls

• Personnel entering the void periphery wearing safety harnesses with SALA fall arrest blocks and safety lines properly secured to a safe anchorage

5.4 Guidelines for Probe Drilling for Voids The stages and responsibility for the work shall include: • Examinations of plans sections etc to identify

possibly undercut areas and determining minimum safe approach distances and planning the investigation (Responsibility Geotechnical Engineer and /or Pit Supervisor)

• Marking out the exclusion zones by red and white flagging tape (Responsibility Surveyors)

• Marking out the drilling traverse lines (Responsibility Surveyors)

• Drilling probe holes at specified intervals and angles and depths specified by the Pit Supervisor (Responsibility Driller)

• Logging the probe holes (Date, driller, Location ie bench, traverse and distance from start peg, depth to break through depth to floor) (Responsibility Driller and/or Sampler)

• Reporting voids located to Pit Supervisor (Responsibility Driller and/or Sampler)

• Plotting of reported cavities and re-examination of plans sections etc to determine minimum safe approach distances and planning further investigation (Responsibility Geotechnical Engineer and/or Pit Supervisor)

• Maintenance of up to date plans sections etc to determine shoeing void outlines, minimum safe approach distances and maintaining up top date exclusion zone flagging (Responsibility Surveyors)

• SWPs shall be developed to ensure the safety of personnel undertaking the investigations. Precautions shall include:

• Standing instructions that no one shall enter an exclusion zone marked by red and white flagging tape except certain persons instructed to do so by the pit supervisor to undertake specific tasks (Responsibility Pit Supervisor)

• Safety training of persons required to work in an exclusion zone and provision of belts and safety lines etc for them (Responsibility Pit Supervisor)

• Maintenance of the exclusion zone markers (if any red and white flagging tape is cut or moved it shall be restored immediately) (Responsibility all pit workers).

5.5 Guidelines for Surveying or Geophysical Investigation of Voids

The stages and responsibility for the work shall include: • Planning the investigation with due regard for

known undercut areas and minimum safe approach distances (Responsibility Geotechnical Engineer and Pit Supervisor)

• Conducting the investigation and reporting of results (Responsibility Geotechnical Engineer and Surveyor)

• Plotting of reported cavities and re-examination of plans sections etc to determine minimum safe approach distances and planning further investigation (Responsibility Pit Supervisor).

5.6 Guidelines for Mining through for Voids The stages and responsibility for the work shall include: • Analysis of all void data to determine a safe mining

strategy and detailed planning (Responsibility Geotechnical Engineer and Pit Supervisor)

• Appointment of personnel with specific responsibilities in the plan for mining through voids. The may include the appointment of a Void Officer to coordinate work and maintain records on voids. (Responsibility Mine Manager)




• Preparation of SWPs for the safety of personnel mining through and monitoring the stability of pillars between stope and pit See Guidelines on pillar stability monitoring (Responsibility Pit Supervisor)

• Mining operations and monitoring the stability of voids, pillars and slopes (Responsibility Geotechnical Engineer and Pit Supervisor).

Precautions should include: • Exclusion zones shall be marked by red and white

flagging tape and no one shall enter an except certain persons instructed to do so by the pit supervisor to undertake specific tasks (Responsibility Pit Supervisor)

• Safety training of persons required to work in an exclusion zone and provision of belts and safety lines etc for them (Responsibility Pit Supervisor)

• Backfilling of voids – This will be a normal procedure except where the void is too small to fill effectively or there is an obstruction that cannot be removed safely that will prevent adequate filling of the void (Responsibility Geotechnical Engineer and Pit Supervisor). Standing instructions shall be developed for the placement of the back fill (back fill materials, direct tipping, bulldozing etc.) (Responsibility Pit Supervisor) Until the void is filled to the satisfaction of the Geotechnical Engineer and Pit Supervisor, the exclusion zone markers shall be maintained (if any red and white flagging tape is cut or moved it shall be restored immediately - Responsibility all pit workers)

• Drilling and Blasting Pillars above Voids–Safe and effective procedures shall be devised for drilling and firing pillars next to or above voids (Responsibility Geotechnical Engineer and Pit Supervisor). Standing instructions shall be developed for the drilling and charging (Responsibility Pit Supervisor) Until the void is effectively destroyed to the satisfaction of the Geotechnical Engineer and Pit Supervisor, the exclusion zone markers shall be maintained.

The current Western Australia Department of Minerals and Energy Guidelines for Open pit mining through underground workings shall be consulted.

5.7 Guidelines for Pit Planning Pit shall be designed sot that all ramps avoid possibly undercut areas and within a minimum safe approach distances based on the size and condition of the void and duty of the ramp. (Responsibility Geotechnical Engineer and Pit Supervisor).

6 Guidelines for Core Logging and Exposure Mapping

6.1 Drill Hole Surveying, Logging and Preservation of Drill Cores

All drill holes used in slope stability assessments should have • Collar positions surveyed • Down hole traces surveyed.

Before the core is cut for assaying, all diamond drill cores shall also be: • Geologically and geotechnically logged • Photographed (see Guidelines for Core

Photography) • Representative samples of relevant materials are

preserved for later testing.

The remaining cores after assaying are preserved for further inspection.

6.2 Photography of Drill Cores High quality and good clear core photographs are invaluable in establishing geological and geotechnical models. The preferable requirements for good core photographs are: • One core tray per photo • Photograph core after core recovery has been

measured, depth blocks have been checked and before the core is split

• Photograph in full sun, but avoid midday sun, as it is difficult to eliminate the photographer’s shadows, also avoid early morning and late afternoon as the colours may be distorted. Photographs on overcast days can produce acceptable results if colours are not critical to rock type differentiation

• Use colour print film and print on 100 x 150 mm paper is preferable but digital photos may be taken (1.3 to 1.5 megapixel/frame camera with prints reproduced by a colour laser printer on photoquality paper) A colour chart should be included in the header board to ensure consistent colours during printing.

• Use a frame to hold the camera directly above the centre of the core tray and heading board for best results, hand held cameras even disposable cameras can produce acceptable results if used with care

• Check that depth blocks are the right way up and not in deep shadow

• If the core is orientated, arrange core so that orientation line can be seen

• Arrange core tray to avoid shadows across it




• Use a heading board to record hole number, tray number and the start and end depths in the core tray and other comments (precollar depths, core loss, EOH etc.)

• Preferably place the heading board at the top of the tray, with the start of the core in the tray at the top left.

• Set camera focal length or distance so that the tray almost fills the frame. Check the other camera settings

• A light spray of water will enhance colours and help in rock type identification, however, if the rock is dark or black, structures are easier to see in photos of dry core

• Avoid artificial lighting (flash or fluorescent), especially if cores are wet.

• Standard Terminology for Geotechnical Mapping and Logging Drill Cores

6.2.1 Introduction Geotechnical data forms the basis for modelling and is essential in the efficient running of mines. This guideline outlines the standard terminology for data. Several terms used in the descriptions below to describe natural breaks in the rock mass. Defects include schistosity, foliation, bedding, veins, joints and faults. Discontinuity and fracture exclude schistosity, foliation, but include bedding, veins, joints and faults. Joints is used in the normal geotechnical sense ie the common discontinuities which define the shape and size of rock blocks.

6.2.2 Data Fields The following are a list of all the data fields currently used for geotechnical data. The codes only relevant to in-situ measurements are outlined:

• Recovered Core Length: total length of core recovered from interval (Recovery is calculated from it)

• Core > 10 cm: total length of all core > 10 cm (RQD may be calculated from it)

• Weathering: degree of weathering • QSI: estimated rock strength (or Qualitative

Strength Index) • Fractures per interval: calculates Fracture per

metre (FPM) or Joint Spacing • Fracture Type: Type of discontinuity • Joint Sets: degree of jointing • Joint Roughness: the nature of the discontinuity

wall • Fracture Infill: the type of joint infill and its

alteration • Fracture Infill Mineral: the main mineral in the

joint • Fracture Thickness: the thickness of the fractures • Fracture Length (only for in-situ measurements) • Fracture Spacing (only for in-situ measurements) • Fracture Termination (only for in-situ

measurements) • Seepage: water flow and free moisture in

discontinuities or rock mass (Joint Water Pressure) (only for in-situ measurements)

• Stress Reduction Factor: weakness zones intersecting excavation (only for in-situ measurements)

• Angle to Core Axis: angle to core axis (Alpha angle)

• Rotation Angle: called also (Beta Angle)




Outputs Geotechnical data is further processed for indexes to quantify rock mass quality. The main currently used indexes

are RQD, Q, RMR and MRMR. RQD is the percentage of core length>10 for the interval. The other indexes require more complex manipulation as illustrated below:

Field Q modified RMR MRMR Structure

Recovery

Core > 10 cm * * *

Weathering *

Rock Strength (*) * *

Fracture/m (FPM) * * *

Type *

Number of Sets * *

Joint Roughness * * * *

Alteration/ Infill * * * *

Infill Mineral *

Infill Thickness * * *

Seepage (*) * * *

Stress Reduction Factor (*)

Angle to Core Axis *

Rotation Axis * (*) full Q index

6.2.3 Core Logging for Open pits and Underground Mines

In Underground Mines, all diamond holes should be geotechnically logging within 20 m (true thickness) on either side of the orebody. In Open pits all diamond drill holes that intersect the current or possible future pit walls should be geotechnically logged. Logging forms shall designed to capture the following data to allow the rock mass to be rated in any of the above classification systems. For the hole: • HOLE ID: Hole number • LOGGED BY: Name of the logger • DATE: Date of logging • DIAMETER: The diameter of drill core. (Can be

obtained from other drill hole information) • HOLE COMMENT: Comment for hole.

For logging intervals (specific to geotechnical logging-does not require to be the same as assay intervals) • FROM : The start of the downhole interval for

similar rockmass • TO: The end of the downhole interval for similar

rockmass • CORE10: The total length of core greater >10 cm

for RQD • NO / FRACTURES: The number of fractures for

interval for fracture frequency (FPM) • QSI: The ISRM category for estimated UCS • TYPE: The nature of the dominant fracture • NO OF SETS: The number of discontinuity sets • JOINT INFILL: The type of joint infill and its wall

rock alteration (gouge, breccia carbonate cement, weathering, chloritic alteration, talcification, argillic or propylitic alterations must be recorded. The nature of the dominant infill if infill > 1 mm and wall rock alteration if infill < 1 mm

• THICKNESS: The thickness of the fracture • ROUGH: The topography of the continuity • COMMENT: Comment for interval.




The above format is very similar to most current geotechnical core logging forms currently used within WMC. It has to be mentioned that the core recovery and dip and dip direction are not included. The recovery measuring the recovered core length can be either captured for the logged interval or for different intervals on a different form e.g. between the drillers core blocks. The dip and dip direction for oriented cores should also be included with the alpha and beta angles.

6.2.4 Exposure Mapping In-situ mapping will be performed by line mapping or window mapping. The information is treated like a drill hole information and store in the drill hole Geodata\Geobase database. The following data is recorded for window mapping and the mapper may use the electronic Breithaupt Tectronic compass to reduce the data entry time.

For the location (not recorded in electronic compass): • FACERUN ID: The ID of the mapping location

(e.g. Mine prefix + level + number) • MAPPED BY: The mapper’s name • DATE: The date of the mapping • GRID_NAME: The name of the grid • NORTHING: The northing of the start of line (or

centre of the window) • EASTING: The easting of the start of line (or

centre of the window) • RL: The RL of the start of line (or centre of

window) • AZIMUTH: The azimuth of the line or window • LENGTH: The length of the line or window • ROCK TYPE: The rocktype for the line or

window mapping (rocktype can be assigned to interval for line mapping)

• SQI: The estimated UCS for the area (as for window can be assigned to line mapping if required)

• SET NO: The number of discontinuity sets • PHOTO: The reference to a photograph of the

location if any • COMMENT: Comment on the location.

For each fracture the following data is captured by electronic compass: • TYPE: The nature of discontinuity • INFILL: The nature of the dominant infill if infill

> 1 mm and wall rock alteration if infill < 1 mm • THICK: The thickness of the fracture • ROUGH: The topography of the continuity • SPACING: The category for the spacing of the

discontinuity by category

• LENGTH: The category for the length of the discontinuity

• END: The nature of the discontinuity termination • SEEPAGE: The water condition for the fracture.

The data can be then summarised for the particular window and display in software such as Datamine or other geotechnical packages.

6.3 Standard Codes and Database Each site has a standard technical database, Techbase. The logging part of the database uses properties to capture any type of information. For example, TYPE is the property name for fracture type and joi (for Joint) is the code assign to this property. Properties for geotechnical logging have been defined in the current database and the standards set up throughout WMC. While operations may select to capture only some selected fields, the codes used in the capture system will be identical between operations and will optimise the use of common ideas and systems. A table called drill_geotech is set up in the Techbase database in a spreadsheet type table to facilitate the data extraction process.

6.3.1 Recovered Core Length The recovered core length is the length (in metres) of core recovered for an interval. The most accurate way to measure it is by measuring the length of core between blocks. The recovery may have to be input by itself because the interval between the blocks is unlikely to fit the geotechnical domain interval.

6.3.2 Core > 10 cm The core >10 cm is the total of all the core greater than 10 cm in length, ignoring end of run and core tray breaks, within the interval. Joints that run parallel to the core axis are to be ignored.




6.3.3 Weathering Weathering field records the degree of weathering on the rocks. The data entry system uses the following codes:

Codes Summary Description

cw Completely weathered

All rock material is decomposed and/or disintegrated to soil. Original mass structure largely intact

hw Highly weathered

More than half of the rock material is decomposed and/or disintegrated to soil. Fresh or discoloured rock is present either as a continuous framework or as corestones

mw Moderately weathered

Less than half of the rock material is decomposed and/or disintegrated to soil. Fresh or discoloured rock is present either as a continuous framework or as corestones

sw Slightly weathered

Discolouration indicates weathering rock material and defect surfaces. All the rock material may be discoloured by weathering and maybe somewhat weaker than it is in fresh

fr Fresh No visible sign of rock material weathering, perhaps slight discolouration on major defect surfaces

6.3.4 QSI (Qualitative Strength Index) The qualitative strength index is an estimating rock strength by index tests as listed below.

Code Strength Description Approx UCS

(MPa)

ew Extremely Weak

Indented by thumbnail. 0.25-1.0

vw Very Weak Crumbles under firm blows with point of a geological hammer, can be peeled with pocket knife.

1.0-5.0

w Weak Can be peeled by a pocket knife with difficulty. Shallow indentations made with firm blows of a geological hammer.

5.0-25

ms Moderately Strong

Cannot be scraped or peeled with a pocket knife. Specimen can be fractured with a single firm blow of a geological hammer.

25-50

s Strong Specimen requires more than 1 blow of a geological hammer to fracture it.

50-100

vs Very Strong Specimen requires many blows of a geological hammer to fracture it.

100-250

es Extremely Strong

Specimen can only be chipped with a geological hammer.

>250




6.3.5 Fracture Number per Interval The fracture number per interval is the number of discontinuities for the interval. The fracture number per interval is processed to provide fractures per metre.

Fracture Type A fracture is defined as any plane or surface which is now or has been in the past been broken. Fracture type include joints, veins, faults, shears and bedding planes. Care must be taken in identifying major structures such as faults and shears as these are the key controlling features in slope stability. • Code

– joi: Joint – con: Lithological Contact – zon : Fault or Shear Zone – fol : Foliation Discontinuity – bed: Bedding Plane Discontinuity – vei : Vein Parallel Discontinuity – dis : Discrete Fault or Shear

Joint Sets The joint sets field define the number of joint sets present.. Joints are common discontinuities which define the shape and size of rock blocks. The codes are based on the Barton Tunnelling Quality Index Q. • Code

– mnf: Massive or few joints – 1js: One joint set – 1jr: One joint plus random – 2js: Two joint sets – 2jr: Two joint sets plus random – 3js: Three joint sets – 3jr : Three joint sets plus random – 4js: Four or more joint sets, random, heavily

joined – cre : Crushed rock, earth like

Joint Roughness Joint roughness refers to the nature of the discontinuity walls and to the small irregularities on the fracture surface. The codes are based on the Barton Tunnelling Quality Index Q. The RMR rating for joint condition is a combination of joint roughness, fracture infill and fracture infill thickness. • Code

– rad: Rough and discontinuous – smd : Smooth and discontinuous – rau: Rough and undulatory – ssd : Slickensided and discontinuous – smu : Smooth and undulatory – rap: Rough and planar

– ssu : Slickensided and undulatory or gouge filled and discontinuous

– smp: Smooth and planar – gpu: Gouge filled with nor rock wall contact and

planar and undulatory – ssp: Slickensided and planar

Fracture Infill The fracture infill records the type of joint fill and its alteration. The codes are based on the Barton Tunnelling Quality Index Q. • Code

– non: None or tightly healed or hard, non-softening, impermeable, unweathered filling e.g.quartz

– una: Unaltered joint with surface staining only – sli : Slightly altered or weathered joint walls,

hard mineral coating, may include small clay free sandy particles

– mod: Silty or sandy clay coating, small clay fraction

– sof : Soft infill including low friction clay, platy mica, talc, gypsum and graphite

– bad: Soft and highly weathered swelling clay filling e.g. Montmorillonite

Fracture Infill Mineral The fracture infill mineral field records the mineral in the fracture. The mineral codes are the standard WMC legend mineral codes. There are 586 mineral codes stored in the min.val file.

Fracture Thickness The fracture thickness records the thickness of the fracture measure at right angle to the fracture. • Code

– t<1: Thickness of infill < 1 mm – t<5: Thickness of infill 1 – 5 mm – t>5: Thickness of infill > 5 mm – nwc: Sheared with no wall contact or thick

zones of decomposed or highly weathered material.




Fracture Length The fracture length records the length of the fracture in metres. This is recorded in mapping by in-situ measurements. • Code

– l<.5: Length (m) < 0.5 – l<1: Length (m) 0.5 – 1 – l<2: Length (m) 1.0 – 2.0 – l<3: Length (m) 2.0 – 3.0 – l<5 : Length (m) 3.0 – 5.0 – l<7: Length (m) 5.0 – 7.0 – l<10: Length (m) 7.0 – 10.0 – l<20: Length (m) 10.0 – 20.0 – l<40: Length (m) 20.0 – 40.0 – l>40 : Length (m) > 40.0.

Joint Spacing The joint spacing records the spacing between the joints in metres. This is recorded in mapping by in-situ measurements. • Code

– sna: N/A - discrete feature – s>8: Spacing >8.0 m – s<8: Spacing 4.0 – 8.0 m – s<4: Spacing 2.0 – 4.0 m – s<2: Spacing 1.2 – 2.0 m – s<1.2: Spacing 0.6 – 1.2 m – s<.6: Spacing 0.4 – 0.6 m – s<.4: Spacing 0.2 – 0.4 m – s<.2: Spacing 0.06 – 0.2 m – s<.06: Spacing <0.06 m.

Fracture Termination Fracture termination is a measure of the continuity of the fracture. A fracture may be continuous across the core, terminate in the rock or terminate on another fracture. This measure is used in the in-situ mapping. • Code

– tir: Terminates in rock – low: Terminates in another set at <20 degrees – hig: Terminates in another set at >20 degrees – flo: Terminates by floor – roo: Terminates by roof – wal: Terminates by wall – log: Indeterminable (logistically) – cont: Indeterminable (continuity).

Seepage - Joint Water Pressure The water seepage (or joint water pressure) field is an estimate of the water flow through the rock. Seepage is an in-situ measurement and is not used in core logging. However it can be used in window mapping.

• Code – dry: Dry – dmi : Damp or minor flow – wet : Wet – drp : Dripping – mip: Medium inflow or pressure – lpc : Large inflow/high pressure in competent

rock – lhp : Large inflow/high pressure – ehd : Exceptionally high inflow decaying with

time – ehp: Exceptionally high inflow or pressure.

Stress Reduction Factor The stress reduction factor is an indication of the weakness zones which may be loosening of rock mass when a tunnel is excavated. This is an in-situ measurement but it has been included in the list because it can be used for face run in future line or window mapping. • Code

– sr3 : single weakness zones containing clay (depth of excavation > 50 m)

– sr5: single weakness zones containing clay (depth of excavation < 50 m)

– sr2.5: single shear zones in competent rock (clay free) depth of excavation > 50 m

– sr5.0 : single shear zones in competent rock (clay free) depth of excavation < 5 0m

– sr7.5 : multiple shear zones in competent rock loose surrounding rock

– sr10: multiple occurrences of weakness with clay

– sr12: loose open joints, heavily jointed or sugar cube.

Angle to Core Axis (Alpha angle) The angle to core axis is the angle between the core axis and the plane of the fracture. If the rotation angle (Beta angle) is measured, the true dip and dip direction can be calculated for the plane.

Rotation Angle (Beta angle) A plan in the core has an elliptical trace on the surface of the core. The rotation angle is the angle between the reference line and the up hole apex of the elliptical trace. If the angle to core axis (Alpha angle) is measured, the true dip and dip direction of the planar fracture can be calculated for the plane.




6.4 Geotechnical Database System

Data Flow The data flow of the geotechnical information is summarised below:

1. Log data either on a paper form or in the geological logging system (GLS)

2. If it is a paper form, enter the system on the geotechnical data entry system

3. Send the transaction files either from the GLS or from the geotechnical data entry system to the Geodata logging update directory.

4. The data is then automatically loaded to the Geodata database (e.g. Once a day)

5. Geodata geotechnical logging information is then down loaded automatically to the drill_geotech table in Geobase

6. Data can be then retrieved automatically or inter actively to a Datamine/Surpac format and include in the current Datamine extract used by all operations.

7. Geotechnical data can be retrieved on plans and sections with Geoview.

8. Data can be extracted to a text file to load to Excel spreadsheet or other software package.

9. Added value can be input back into the database. For example, it is quite common to assign lode codes to an interval (e.g. Hole XXXX from 100.6 to 112.00 lodecode = HV1). Similar practices could applied to geotechnical data and domain codes could be defined and stored in the database.

mhs16 slope stability guidelines for slope stabilitymirmgate.com.au/docs/mhs/16/57484.pdf · major...

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