Transcript Tailings Dam Safety And Implementation Of Safety Guidelines By A Tailings Dam Operator.

Tailings Dam Safety And
Implementation Of Safety
Guidelines By A Tailings Dam
Operator
Why are Dam Safety Programs Important?
Los Frailes Spain - 1998
Merriespruit South Africa 1994
Dam Safety Program Implementation
• Guidelines provide
templates and flow
sheets for dam safety
programs
• Operator must
translate these into
activities that can be
carried out at the
tailings management
site to create an
effective dam safety
program
Dam Safety Program Development
• A good Dam Safety Program requires collaboration of a
number of groups.
• Operators, designers and regulators must all provide
input to the dam safety program
• Risk based approach can simplify the dam safety
program:
– Consider consequences of potential failure modes
– Focus program on key failure modes
• Program must consider the “tailings management
system” – not just the dam
• Program must be set up understanding that the system
and risks will change over the mine life – recognize the
changing conditions and changing risk
Roles and Responsibilities
• Roles and responsibilities must be clearly
defined
• The designer and the regulator do not control
the operation of the facility and are not involved
in the day to day operation
• Therefore, everyone must understand that the
owner/operator is ultimately responsible for
the safe operation of the facility
• The Mine Manager must accept this
responsibility and mandate that the dam safety
program will be followed without exception.
Training
• Best to have designer involved in training
– Present key aspects of the design, critical issues.
Helps to focus site staff on the key issues
– Designer to have at least annual review of
performance – field inspection and review of
documentation
• All personnel that will be in vicinity of facility
should be trained to identify conditions that
could lead to failure
• All personnel should know how to report a
potential problem
Inspections
• Frequency of inspections and monitoring data collection
depends on the rate of system changes
• Routine inspections on a weekly or monthly basis
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Frequency may change depending on the season
Daily to weekly during wet season or during snow melt
Monthly during dry season
By site personnel
• Engineering inspections on a semi-annual to annual
basis
– By designer
• Special inspections after significant events
– By designer and site personnel following earthquakes and floods
• A dam safety review every 5 to 10 years
– By independent engineer (not the designer)
Inspections
• Check lists for inspections
– Don’t miss key information
– Simplifies inspections – inspector can focus on the observations
• Inspection forms
– Information is presented in a consistent format, changes in
system performance are more easily identified.
• Completing the checklist does not mean the inspection is
complete
• Evaluation of the information collected is the important
step – how is the performance of the facility changing
and are these changes consistent with the expected
performance
Typical Inspection Forms
FACILITY INSPECTION SUMMARY REPORT – FORM 1
PROJECT: _____________________
VISUAL INSPECTION CHECKLIST
PROJECT: ____________________________
The FIRST RULE of inspection is that CHANGED CONDITIONS ARE IMPORTANT.
Below is a general checklist of items that one should keep in mind when examining the dams and
spillways of the ___________________________. The list should be reviewed for each dam and
spillway.
DAM CRESTS
 Cracks running along the crest of a dam are evidence of slumping or slope instability.
 Cracks across the crest of dam are evidence of differential settlement.
 Settlement and particularly differential settlement is easy to see. Settlement is serious if the
freeboard is reduced. Freeboard is the vertical distance between dam crest elevation and the
water level.
 Trees should not be allowed to grow on a dam. Tree roots cause disturbance and tend to seek
water. When the tree dies, the roots rot, leaving a pipe through a structure which can cause
failure.
UPSTEAM SLOPE
 Rip-rap protects the surface of a dam from waves and flowing water. Deterioration of
erosion protection can lead to slope deterioration.
 Sloughing may be indicative of slope instability and/or inadequate erosion protection
 Depressions and sinkholes may be indicative of internal erosion (piping) of material
thorough the dam. If an upstream depression (sinkhole) is noted, you should check for signs
of piping (dirty discharge) along the downstream toe of the dam.
 Shoreline erosion adjacent to the upstream face of a dam should be noted, as this may
require remediation and/or erosion protection.
 Animal holes in a dam can create a “pipe” through the structure, and could cause an internal
wash-out failure.
Sheet 1 of 1
All parts of this inspection form should be completed. Adverse conditions should be described and location stated. Additional
information and relevant photographs should be attached.
Inspecting Officer:
Inspecting Agency:
Report No.:
Inspection Date:
(DD/MM/YR)
WEATHER:
o
Temperature:
C
Last 3 Days
Current
Description:
Other Comments:
dry
frost
rain
snow
FACILITIES INSPECTED: (A separate report sheet Form A or Form B to be prepared for each structure)
Structure
Dam/Dyke
Spillway/Flow Control
Area I
Area II
DOWNSTREAM SLOPE
 Soft zones and sand boils along the toe of a dam are evidence of a developing quick
condition, which can progress to piping and internal erosion and eventually lead to a
wash-out failure.
 Dirty, sediment laden seepage water is evidence of piping and internal erosion.
 Increased seepage rates and/or new areas of seepage are a sign that an adverse change has
taken place within a dam.
 Bulging on the lower part of a slope may be the result of slope instability, slumping, frost
deterioration and/or lateral spreading.
 It is essential to ensure that drains are free-flowing and not blocked with sediment or
precipitates, as this can adversely affect the stability of the dam.
 Animal holes in a dam can create a “pipe” through the structure, and could cause an internal
wash-out failure.
SPILLWAYS
 Spillways should be free of obstructions and in good working order. The condition of
spillways are particularly important because plugging can cause an unwanted increase in
water level and the possible overtopping of dam crests.
 Erosion protection can be damaged during extreme flow events and should be repaired at
the earliest opportunity to prevent further erosion.
 Concrete deterioration is easy to see and should be noted and monitored.
Area III
Other
Review Officer:
Review Agency:
Date Reviewed:
(DD/MM/YR)
ACTION REQUIRED:
none
Inspection Forms to Include
Photographs
July 2005
June 2006
PHOTOGRAPH North Dam 1: View to the east along the downstream toe of the North Dam near the west abutment.
Toe and face are in good condition. Small puddles of water in natural topographic depressions. Condition in 2006,
including the size and location of water downstream of the dam, is similar to that observed in 2005 as shown by
comparison of the photographs.
P7
P9
P10
P11
P15
P16
P17
P18
Pond
Time
24 Hour Precipitation
19/Dec/06
21/Aug/06
23/Apr/06
24/Dec/05
26/Aug/05
28/Apr/05
29/Dec/04
31/Aug/04
3/May/04
4/Jan/04
6/Sep/03
9/May/03
9/Jan/03
11/Sep/02
14/May/02
14/Jan/02
16/Sep/01
19/May/01
19/Jan/01
21/Sep/00
24/May/00
25/Jan/00
Head - Pond elev. (m)
4080
100
4060
90
4040
4000
60
3980
50
40
3960
30
3940
20
3920
10
3900
0
Precipitation (mm)
Graphical Presentation of
Monitoring Data Aids Interpretation
LOWER RIGHT ABUTMENT INSTRUMENTATION
80
4020
70
Key Learnings
• Training
– Everyone involved with the tailings and water
management facility should be trained to
identify and report conditions that could lead
to failure.
– Training workshops involving the designer, the
operators and the regulators are very
effective. The operators need to understand
what is important for dam safety, and why it is
important.
Key Learnings
• Inspections and Data Collection
– Continuity of personnel important
– Human eye can identify small or subtle
changes in a structure
– Filling out the inspection form is only the first
step. The inspection is not complete until the
interpretation of performance is complete.
– There is a learning curve to understanding the
performance of a dam
Key Learnings
• Review and analysis
– Continuity of personnel important
– There is a learning curve to understanding the
performance of a dam
– Important to have independent review and verification
of the dam safety periodically
• Responsibility
– The Mine or General Manager has the largest
influence on successful implementation of a dam
safety program. Dam safety must rank equally with
production.
General Comments
• Visit mines with similar types of tailings management
systems
– Discuss the dam safety program
– Discuss the good and bad parts of your program so that both can
learn
• Review case histories of dam failures
– Modern dam failures are well documented and the root cause of
the failure is often identified in the investigation reports.
• Obtain current copies of dam safety guidelines
– Guidelines are updated as the understanding of the mechanisms
of dam failures improves
• With modern communication systems, news of a tailings
facility failure is known worldwide immediately and will
affect the international mining community
Our goal: our tailings dams become an integral
part of the environment post-closure
Feedback on the UNECE
guidelines
• This document is a good starting point but to be
useful to industry (dam operators) guidelines need
to be specific
• There are a number of useful groups of documents
already in use – such as the CDA Dam Safety
Guidelines combined with the Mining Association of
Canada guidelines for designing a tailings facility
and for preparing operation, maintenance and
surveillance manuals.
• It could be helpful to collaborate with some other
agencies who have already developed regulations
and guidelines for the safe operation of TMF’s such
as ICOLD, CDA, or MAC.
An Operators perspective
• Operators require information on how to carry out the
activities, frequencies of activities, selection of design
criteria
• Some areas to be developed to make these guidelines
relevant to operators are
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how to assess risk
What factors of safety to use in construction
Details on preparation of operations manuals
Parameters such as return periods for inflow design floods
Seismic event parameters
Recommendations on planning tools to be used – such as water
management modelling tools
Deno Gold Mining Company,
Kapan, Armenia
– Kapan - Located in SW
Armenia
– Historical mining town
– Approx 250 years of mining
– 300km from Yerevan
– Two main deposits with
numerous smaller deposits
in the mines vicinity
DGMC - a little history
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2004
2004Dec 2005
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2005-
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2006
Sept 2006
•
April 2007
•
Sept 2007
•
End 2007
KOMPE mine bankrupted
Operated as DGMC
Starter loan by EBRD initiated
upgrade existing equipment and
environmental programmes
WAI work with site staff to write
EAP’s and proposed monitoring
programmes
Construction of Geghanush TMF
Dundee bought 80% company,
began corporate responsibility
programme
Begun environmental baseline
study
7 fulltime environmental staff and
25 local consultants, ~ 15
international consultants
Commissioning of Geghanush
Artsvanik Dam
• Small Tails Dam perched on very large Kadjeran TMF dam
structure
• Designed in 2003 by Armenian design institute
• Capacity 1.1 Million m3 Maximum dam height 20m
• Regular inspections from RA inspectors
• Regular inspections from International Tailings Dam Engineer
• Continuous monitoring by site staff
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Dam movement (triangulation surveys)
Water quality and level
Peizometer water level checked daily
Rainfall data collected and weather station in use
Drilling crest of wall and analysis undertaken of materials
Procedures in place to stop production in heavy rainfall or if
water level rises
Operate with lowest possible phreatic water level to maximise
capacity during rainfall events.
Geghanush Dam
• New dam over existing historic dam – capacity 11.0 million m3
• Construction included front and rear dam walls, completion of
diversion tunnel for river, gravity decant structures
• Plans and design were review by international tailings dam engineer
and modified to include recommendations including finger drains
• Recycling water to process plant should decrease discharge
significantly
• Same monitoring programme as Artsvanik to be implemented
• Discharge water system is gravity decanted however backup
submersible pumps will be available for extreme rainfall events
Thank You