some considerations in the assessment of...
TRANSCRIPT
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SOME CONSIDERATIONS IN THE ASSESSMENT OF THE
PERFORMANCE OF TAILINGS DAMSDURING EARTHQUAKES
by
I. M. IdrissDepartment of Civil & Environmental Engineering
University of California, Davis, CA 95616-5294e-mail: [email protected]
Presented at the
International Workshop on SeismicStability of Tailings Dams
Case Western Reserve University Cleveland, Ohio
November 9-10, 2003
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FOR PAST 40± YEARS, THERE HAVE BEEN SOME 80CASES OF TAILINGS DAM FAILURES
MOST OF THESE FAILURES HAVE BEEN ASSOCIATEDWITH EXCESSIVE WATER DUE TO RAIN, BURSTPIPES � ETC
SOME 15 CASES ARE EARTHQUAKE-RELATED �LIQUEFACTION OF TAILINGS
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AMONG THE MORE PROMINENT CASES ARE THEFAILURE OF THE EL COBRE
TAILINGS DAMS IN THE 1965 CHILE EARTHQUAKE.
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1,900,000 m3CopperChileEl CobreOld Dam
28 march 1965
Tailings traveled 12 km down-stream, destroyed the town of El Cobre and killed more than 200 people
350,000 m3Liquefaction of Tailings during earthquake �leading to dam failure & flow slides
CopperChileEl CobreNew Dam
28 march 1965
ImpactReleaseType of IncidentOre Type
LocationDate
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1.1. GEOLOGIC & SEISMOLOGIC CONSIDERATIONSGEOLOGIC & SEISMOLOGIC CONSIDERATIONS
2.2. SITE CHARACTERIZATIONSITE CHARACTERIZATION
3.3. ANALYSESANALYSES
4.4. ASSESSMENT OF PERFORMANCEASSESSMENT OF PERFORMANCE
ELEMENTS OF A SEISMIC SAFETYELEMENTS OF A SEISMIC SAFETYEVALUATION FOR TAILING DAMSEVALUATION FOR TAILING DAMS
5.5. REMEDIATION (or DESIGN MODIFICATIONS),REMEDIATION (or DESIGN MODIFICATIONS),AS NEEDEDAS NEEDED
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!!EXISTING DAMSEXISTING DAMS""OLD DAMSOLD DAMS
""RECENTLY CONSTRUCTED DAMSRECENTLY CONSTRUCTED DAMS
!!NEW DAMSNEW DAMS
These elements must be considered withinThese elements must be considered withinThe context of :The context of :
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From Vick (1983)
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From Vick (1983)
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From Vick (1983)
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EFFECTS OF FINES CONTENT ONSUSCEPTIBILITY OF COHESIONLESS SOILS
TO LIQUEFACTION
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PROBABLY, THE BEST MEANS FOR CHARACTERIZINGTAILINGS IS THE USE OF CPT WITH JUDICIOUSLY
SPACED SAMPLED BORINGS
UNDISTURBED SAMPLING IN "COHESIONLESS"TAILINGS IS COMPARABLE TO SAMPLING IN
CLEAN SANDS � MAY EVEN BE MORE DIFFICULT
RECONSTITUTED SAMPLES ARE ADEQUATE FOR"NEW TAILINGS", BUT COULD PROVIDE MISLEADING
RESULTS BECAUSE THEY WOULD NOT REFLECTTHE EFFECTS OF AGING
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THEREFORE,IN MOST INSTANCES WE WILL HAVE TO RELY
ON FIELD-BASED PROCEDURES FORASSESSING THE CYCLIC RESISTANCE OF TAILINGS
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FromRobertson & Wride (1997)
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FromCarraro, Bandini & Salgado (2003)
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FromCarraro, Bandini & Salgado (2003)
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Normalized Corrected CPT Tip Resistance, qc1N
0 50 100 150 200 250
Cyc
lic S
tres
s R
atio
, CSR
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Earthquake Magnitude, M = 7½; σσσσ'vo = 1 atm
RecommendedRelationship
Suzuki et al (1997)
Liquefaction - Adjusted PointsLiquefaction - Revised Points
No Liquefaction - Revised Points
CPT-Based Published Case Histories of Clean Sands(Fines Content, FC ≤ 5%)
Magnitude = 7½ and σσσσ'vo = 1 tsf (≈≈≈≈ 1 atm)
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Normalized Corrected CPT Tip Resistance, qc1N
0 50 100 150 200 250
Cyc
lic S
tres
s R
atio
, CSR
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Earthquake Magnitude, M = 7½; σσσσ'vo = 1 atm
RecommendedRelationship
Suzuki et al (1997)
Liquefaction - Adjusted PointsLiquefaction - Revised Points
No Liquefaction - Revised Points
Robertson & Wride (1997)
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Normalized Corrected CPT Tip Resistance, qc1N
0 50 100 150 200 250
Cyc
lic S
tres
s R
atio
, CSR
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Earthquake Magnitude, M = 7½; σσσσ'vo = 1 atm
RecommendedRelationship
Suzuki et al (1997)
Liquefaction - Adjusted PointsLiquefaction - Revised Points
No Liquefaction - Revised Points
Robertson & Wride (1997)
Carraro et al (2003)
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SPT-Based Published Case Histories of Cohesionless Soilswith Fines Content Greater than or Equal to 35%
Modified Standard Penetration - (N1)60 - Blows/ft0 10 20 30 40
Cyc
lic S
tres
s R
atio
(CSR
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
50
50
55
80
75
40
60
92
75
38
67
484035
43
37
50
Fines Content(FC)
LiquefactionNo
Liquefaction
Revised Values forCases Published in 2000
Revised Values forCases Published in 1984
Derived Curve(FC ≤≤≤≤ 5%)
Derived Curve(FC = 35%)
NCEER (1997)(FC ≥ ≥ ≥ ≥ 35%)
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CPT-Based Published Case Histories of Clean Sandsand for Cohesionless Soils with Fines Content, FC ≥ 35%
Normalized Corrected CPT Tip Resistance, qc1N
0 50 100 150 200 250
Cyc
lic S
tres
s R
atio
, CSR
0.0
0.1
0.2
0.3
0.4
0.5
Earthquake Magnitude, M = 7½; σσσσ'vo = 1 atm
RecommendedRelationship for
Clean Sands
92 75
75
35
35
40
Clean Sands
Liquefaction - Adjusted PointsLiquefaction - Revised Points
No Liquefaction - Revised Points
50
66Fines Content, FC
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WHAT ABOUT RESIDUAL STRENGTHFOR TAILINGS?
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Sr Independent of σσσσ'vo vs Sr / σσσσ'vo
Adjustments for Fines Content
Extrapolation to Larger Values of Blow Count
ISSUES TO BE CONCERNED WITH
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0 cs
0 4 8 12 16 20
Residual S
hear Strength, S
r - psf
0
20 0
40 0
6 0 0
8 0 0
10 0 0
120 0
1
2
4
3
5
1. Lower San Fernando — fines content 25%2. Fort Peck Dam — fines content unknown3. Calaveras Dam — fines content unknown4. M ochi-Kochi Tailings — fines content 8 0 % 5. Lake M erced — fines content 3%
Range of residual strengthscalculated by S eed (19 8 7)
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0
0 4 8 12 16 20
Residual S
hear Strength, S
r - psf
0
20 0
4 0 0
6 0 0
8 0 0
10 0 0
120 0
3
45
6
7
89
1
2
Legend for Case Histories
Earthquake-Induced -- S PT & other param eters w ere estim ated
Earthquake-Induced -- S PT & other param eters w ere m easured
Construction-Induced
1. Upper S an Fernando — fines content 25 %2. Low er S an Fernando — fines content 25 %3. La M arquesa - D /S — fines content 20 %4 . W hiskey S prings — fines content 4 0 %
5 . Juvenile H all — fines content 6 5 %6 . La M arquesa - U/S — fines content 30 %7. Lake M erced — fines content 3%8 . M ochi-Kochi Tailings — fines content 8 0 %9 . La Palm a — fines content 15 %
S trengths calculatedby S eed (19 8 7)
S trengths calculatedby O lson & S tark (20 0 2)
Relationship Recom m endedfor Estim ating ResidualStrength Using M edian
M easured SPT
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0 cs
0 5 10 15 20
Sr/
σ σσσ'vo
0 .0 0
0 .0 4
0 .0 8
0 .12
0 .16
0 .20
(N1)6 0 values from
O lson & S tark (20 0 2)
A ll of Values -- as published byO lson & S tark (20 0 2)
CC S F S F
FP FP
(N 1)6 0 values from
S eed & Harder (19 9 0 )
Q uestionableParam eters
r
vo
S
'σσσσ
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0 cs
0 5 10 15 20
Sr/
σ σσσ'vo
0 .0 0
0 .0 4
0 .0 8
0 .12
0 .16
0 .20
All of Values -- as published byO lson & S tark (20 0 2)
C S F
FP
r
vo
S
'σσσσ
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0 cs
0 5 10 15 20
Sr/
σ σσσ'vo
0 .0 0
0 .0 4
0 .0 8
0 .12
0 .16
0 .20
All of Values -- as published byO lson & S tark (20 0 2)
r
vo
S
'σσσσ
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Equivalent Clean S and S PT Corrected B low count, (N1)6 0 cs
0 5 10 15 20
Sr/
σ σσσ'vo
0 .0 0
0 .0 4
0 .0 8
0 .12
0 .16
0 .20
All of Values -- as published byO lson & S tark (20 0 2)
r
vo
S
'σσσσ