Embankment dam deformations caused by earthquakes J. R. Swaisgood, P.E., C.P.G. Swaisgood Consulting, Conifer, Colorado, U.S.A.
ABSTRACT: An extensive review of case histories of embankment dam behavior during earthquake was undertaken after several major embankment dams were severely shaken by the 1990 Philippines Philippines earthquake. The objectives of the study, which continues to date, were to determine if there is a “normal” trend of seismic deformation that can be predicted and if there are certain factors that consistently have an effect on the amount of damage and deformation incurred during earthquakes. Nearly 70 case histories have been reviewed, compared and statistically analyzed in this effort. The results of this empirical study have shown that the most important factors that appear to affect dam crest settlement during earthquake include the peak ground acceleration at the site and the earthquake magnitude. A chart has ha s been prepared to summarize summarize the relationship between the amount amount of measured settlement and the peak ground accelerations experienced in the incidents that were studied. In addition, an empirical equation was formulated and a graph developed as an aid in estimating the amount of deformation to be expected.
1 INTRODUCTION An evaluation of case histories of embankment dam behaviour has been in progress since 1990 with two objectives in mind: °
°
Providing a tool for immediate assessment of a structure that has undergone seismic loading and Creating a method for estimating how much an embankment dam will deform based on actual dam behaviour during past earthquakes.
The findings from these ongoing empirical studies were last presented four years ago. Since that time, the research has continued, increasing the data base by nearly 30 percent. This paper presents the results of the extended examination and analyses of the entire data base. B ASE 2 CASE HISTORY DATA BA Previous work 2.1 Previous
During the 1990 Philippines earthquake, a review of incidents of seismically-induced deformation of embankment dams was initiated to to aid in evaluating the the damages exhibited by several major dams during that that event (Swaisgood and Au-Yeung, Au-Yeung, 1991). These studies continue continued d on with the results last presented in 1998 (Swaisgood, (Swaisgood, 1998). At that time , the screening efforts had produced 54 incidents that had been described with sufficient quantified data for meaningful comparative studies and statistical analyses 2.2 Updated version Continuing research has yielded an additional 15 case histories, making a total data base of 69 incidents. Pertinent details of all 69 of these incidents are presented in Table 1. The new additions include nine located in California California – Case Nos. 10, 25, 25, 26, 26, 36 to 40 (Tepel, et. al. 1996) and 19
Paper Number 014
(ICOLD 2001); four in Chile – Nos. 28, 66,67, and 68 (Pinos 2000); one in the Philippines – No. 46 (ICOLD 2001); and one in Peru (So. Peru Copper Corp. 2001). The entire data base is plotted in Figure 1 where the crest settlement is shown in relation to the peak ground acceleration at the site. Table 1. Earthquake induced settlement of embankment embankment dams dams GENERAL ID
INFORMATION
CREST
DAM
DH
CL
AT
EARTHQUAKE
No
NAME OF DAM
LOCATION LOCATION
TYPE
m
m
m
1
UPPER MURAYAMA
Japan
E-HF
24
320
3
1
Sep
Japan
E
41
309
11
1
California
HF
12
610
?***
2
DATE
DATA
SET TLE MENT
PGA, g.
m
*
%
**
RELATIVE DEGREE OF
M
D,km
DAMAGE
23
8.2
18
0.32
e
0.20
0.74
Moderate
Sep
23
8.2
98
0.30
e
0.27
0.53
Serious Serious
30
Aug
30
5.3
1
0.40
e
0.08
0.63
Moderate
3
ONO CHATSWORTH NO.2
4
MALPASSO
Peru
ECRD
78
152
30
10
Oct
38
VI+
n/a
0.10
e
0.08
0.07
Minor Minor
5
COGOTI COGOTI
Chile
CFRD
85
159
0
6
Apr
43
7.9
89
0.20
e
0.38
0.44
Minor Minor
6
SOUTH HAIWEE
Califor nia
HF
25
457
38
21
Jul
52
7.7
151
0.05
e
0.02
0.04
Minor Minor
7
HEBGEN
Montana
E
25
213
10
17
Aug
59
7.6
0
0.71
e
1.69
4.82
Serious Serious
8
MIBORO
Japan
ECRD
130
444
0
19
Aug
61
7.0
20
0.15
e
0.03
0.02
Minor Minor
9
MINASE
Japan
CFRD
67
210
?
16
Jun
64
7.5
145
0.08
e
0.06
0.09
Minor Minor
10
California
E
32
335
?
18
Dec
67
5.3
11
0.20
e
0.02
0.06
Minor Minor
11
UVAS U. SAN F ERNAND O
California
HF
25
390
18
9
Feb
71
6.6
2
0.55
e
0.91
2.11
Serious Serious
12
OROVILLE
California
ECRD
235
1707
0
1
Aug
75
5.9
7
0.10
r
0.01
0.004
None
13
LA VILLITA
Mexico
ECRD
60
427 427
75
15
Nov
75
7.2
20
0.04
r
0.02
0.02
None
14
EL INFIERNILLO
Me xico
ECRD
146
340
0
15
Nov
75
7.2
23
0.09
r
0.02
0.02
None
15
EL INFIERNILLO
Me xico
ECRD
146
340
0
11
Oct
75
5.9
79
0.08
r
0.04
0.03
None
16
TSENGWEN TSENGWEN
Taiwan
ECRD
131
n/a
?
14
Apr
76
5.3
8
0.16
e
0.04
0.03
n / a
17
EL INFIERNILLO
Me xico
ECRD
146
340
0
14
Mar
79
7.6
95
0.12
r
0.13
0.09
Minor Minor
18
LA VILLITA
Mexico
ECRD
60
427
75
14
Mar
79
7.6
108
0.02
r
0.05
0.03
Minor Minor
19
VERMILION
California
E
50
1290
50
27
May May
80
6.3
22
0.24
r
0.05
0.05
None
20
LA VILLITA
Mexico
ECRD
60
427 427
75
25
Oct
81
7.3
31
0.09
r
0.14
0.11
None
21
EL INFIERNILLO
Me xico
ECRD
146
340
0
25
Oct
81
7.3
55
0.05
e
0.06
0.04
None
22
NAMIOKA
Japan
ECRD
52
265
0
26
May May
83
7.7
145
0.08
r
0.06
0.11
None
23
Califor nia
E
43
299
0
24
Apr
84
6.2
0
0.63
e
0.08
0.18
Minor Minor
California
ECRD
72
427 427
0
24
Apr
84
6.2
2
0.41
r
0.02
0.02
Minor Minor
25
COYOTE LEROY ANDERANDERSON ELMER J. CHESBRO
California
E
29
220
0
24
Apr
84
6.2
22
0.18
e
0.02
0.05
Minor Minor
26
UVAS
Ca li fornia fornia
E
32
335
?
24
Apr
84
6.2
29
0.14
e
0.02
0.08
Minor Minor
27
MAKIO
Japan
ECRD
77
264
29
14
Sep
84
6.8
5
0.57
e
0.50
0.47
Minor Minor
28
AROMOS
Chile
ECRD
43
220
9
3
Mar
85
7.8
45
0.25
e
0.09
0.177
Minor Minor
29
EL INFIERNILLO
Mexico
ECRD
146
340
0
19
Sep
85
8.1
76
0.13
r
0.11
0.08
Minor Minor
30
LA VILLITA
Mexico
ECRD
60
427 427
75
19
Sep
85
8.1
43
0.13
r
0.33
0.24
Minor Minor
31
LA VILLITA
ECRD
60
427 427
75
21
Sep
85
7.5
61
0.04
r
0.12
0.09
None
32
MATAHINA
Mexico New Zealand
ECRD
86
400
?
2
Mar
87
6.3
9
0.33
r
0.12
0.14
Moderate
33
NAGARA
Japan
ECRD
52
n/a
?
17
Dec
87
6.9
29
0.27
r
0.02
0.04
n / a
34
AUSTRIAN
California
E
56
213
0
17
Oct
89
7.1
2
0.57
e
0.85
1.51
Serious Serious
35
LEXINGTON LEXINGTON
California
E
63
253
0
17
Oct
89
7.1
3
0.45
r
0.26
0.41
Minor Minor
36
UVAS
California
E
32
335
?
17
Oct
89
7.1
10
0.40
e
0.02
0.06
None
37
STEVENS CREEK
California
E
37
305
?
17
Oct
89
7.1
16
0.30
e
0.02
0.04
None
38
ALMADEN ALMADEN
California
E
32
140
?
17
Oct
89
7.1
9
0.44
e
0.03
0.10
Minor Minor
39
CALERO
California
E
30
256
?
17
Oct
89
7.1
13
0.38
e
0.01
0.03
None
40
RIN COND A
California
E
12
73
?
17
Oct
89
7.1
9
0.41
e
0.02
0.15
Minor Minor
41
California
E
43
204
0
17
Oct
89
7.1
10
0.42
e
0.20
0.45
Minor Minor
42
GUADALUPE ELMER J. CHESBRO
California
E
29
220
0
17
Oct
89
7.1
13
0.42
e
0.11
0.39
Moderate
43
VASONA
California
E
10
149
8
17
Oct
89
7.1
9
0.37
e
0.05
0.27
Minor Minor
24
2
GENERAL ID
INFORMATION
CREST
DAM
DH
CL
AT
E A R THQUAKE
No
NAME OF DAM
LOCATION LOCATION
TYPE
m
m
m
44
LEROY ANDERANDERSON
California
ECRD
72
427
0
17
Oct
45
SAN JUSTO
California
ECRD
40
340
14
17
46
AMBUKLAO
Philippines Philippines
ECRF
120
450
5
47
MASIWAY
Philippines Philippines
E
25
427
48
PANTABANGAN
Philippines Philippines
ECRD
114
49
AY A
Philippines Philippines
ECRD
50
DIA YO
Philippines Philippines
51
CANILI
52 53
SETTL EMENT m
%
**
D,km
89
7.1
21
0.26
r
0.04
0.06
Minor Minor
Oct
89
7.1
27
0.26
r
0.04
0.07
None
16
Jul
90
7.7
10
0.49
e
1.10
0.880
Serious Serious
3
16
Jul
90
7.7
3
0.68
e
1.06
3.79
Serious Serious
732
0
16
Jul
90
7.7
6
0.58
e
0.28
0.24
Moderate
102
427
0
16
Jul
90
7.7
6
0.58
e
0.20
0.20
Minor Minor
ECRD
60
201
0
16
Jul
90
7.7
18
0.38
e
0.07
0.11
Minor Minor
Philippines Philippines
ECRD
70
351
0
16
Jul
90
7.7
18
0.38
e
0.04
0.06
Minor Minor
MAGAT
Philippines Philippines
ECRD
100
1296
0
16
Jul
90
7.7
81
0.05
e
0.01
0.006
None
California
CFRD
81
200
0
28
Jun
91
5.8
7
0.37
e
0.04
0.051
Minor Minor
54
COGSWELL ROBERT MATTHEWS
California
E
46
192
0
25
Apr
92
6.9
64
0.07
e
0.00
0.007
None
55
WIDE CANYON
California
E
26
678
?
28
Jun
92
7.5
30
0.20
e
0.01
0.048
Minor Minor
56
YUCAI PA No. 1
California
E
13
128
9
28
Jun
92
6.6
28
0.15
e
0.01
0.028
Minor Minor
57
California
E
15
146
9
28
Jun
92
6.6
28
0.15
e
0.00
0.019
Minor Minor
Arizona
E
13
247
1
29
Apr
93
5.5
77
0.02
e
0.00
0.004
None
California
HF
25
390
18
17
Jan
94
6.7
10
0.42
e
0.44
1.021
Serious Serious
60
YUCAI PA No. 2 UPPER LAKE MARY U. SAN F ERNAND O L. SAN FERNANDO
California
E-HF
38
537
6
17
Jan
94
6.7
9
0.44
e
0.20
0.460
Serious Serious
61
LOS ANGELES
California
E
47
671
0
17
Jan
94
6.7
10
0.43
r
0.09
0.188
Moderate
62
California
E
36
427
0
17
Jan
94
6.7
10
0.43
e
0.03
0.089
Moderate
63
NORTH DIKE [LA] LOWER FRANKFRANKLIN
California
HF
31
152
?
17
Jan
94
6.7
18
0.30
e
0.05
0.146
Moderate
64
SANTA FELICIA
Califor nia
E
65
389
0
17
Jan
94
6.7
33
0.18
e
0.02
0.030
Minor Minor
65
COGSWELL
California
CFRD
81
200
0
17
Jan
94
6.7
53
0.10
e
0.02
0.026
Minor Minor
66
PALOMA
Chile
ECRD
82
1000
14
14
Oct
97
7.6
45
0.23
e
0.14
0.141
Minor Minor
67
COGOTI COGOTI
Chile
CFRD
83
160
0
14
Oct
97
7.6
45
0.23
e
0.25
0.302
Moderate
68
SANTA JUANA
Chile
CFRD
113
390
19
14
Oct
97
7.6
260
0.03
r
0.02
0.015
None
69
TORATA
Peru
CFRD
120
600
0
23
Jun
01
8.3
100
0.15
e
0.05
0.042
Minor Minor
59
PGA, g.
*
M
58
DATE
DATA
RELATIVE DEGREE OF
L E G E N D DH = dam height M = earthquake earthquake magnitude, sur fac e-wave scale: scal e: M S D = distance from nearest ground rupture or epicenter, whichever is closest PGA = peak horizontal ground acceleration; e = estimated, r = recorded HF = E=
Hydraulic Fill Earthfill Earthfi ll
ECRD =
Earth Core Rockfill Dam
CFRD =
Concrete Faced Rockfill Dam
NOTES: * - Settlement shown is the single maximum reported or is an average from upstream, downstream and centerline readings ** - Determined as a percentage of combined dam height and alluvium thickness *** - If alluvium thickness unknown (?), it is considered to be 0 for % settlement calculations
3
DAMAGE
% STTLMT = ------------------------------ x 100 DH + AT
DH
AT
10 S U O I R E S
1 E T A R E D O M
T A + H D %0.1 n i T N E M E L T T E0.01 S T S E R C
R O N I M
CFRD ECRD HF Earthfill
E N O N
E G A M A D F O E E R G E D E V I T A L E R
0.001 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
PEAKGROUND ACCELERATION,g
Figure1. Figure1. Settlement of embankment dams durin g earthquake
3 ANALYSIS OF DATA 3.1 General Similar to the previous studies, crest settlement was selected as the parameter to represent earthquake related deformation because it was the most often mentioned quantified measurement of damage presented in the case histories. It also appears to be directly related to the severity of deformation and cracking, i.e., as the percent of crest settlement increases, the extent of deformation and cracking that occurs also increases. The ranges of the relativ relativee levels levels of damage are summarized in Figure 1. The data base of case histories was analyzed using statistical regression techniques for the purpose of identifying those factors that have a major influence on the deformation and damage of embankment dams during earthquakes. These statistical studies were performed using the percent of crest settlement as the dependent variable and the other factors to be evaluated as the independent variables.
4
From these regression analyses, it was found that the only factors that had major, major, statistically significant effects on the amount of crest settlement included peak ground acceleration and earthquake magnitude. 3.2 Peak horizontal ground acceleration The peak horizontal ground acceleration (PGA) experienced by an embankment dam has a major, direct influence on the amount of crest settlement. This relationship relationship is apparent in the the plot shown in Figure 1. In general, dams dams that experience experience greater PGAs undergo greater deformations deformations and damage dam ages. s. In this study, it was found that serious levels of damage were reported only in instances where the PGA exceeded 0.2g. This finding finding supports one of the findings of an earlier investigation in which it was concluded that “there is ample evidence that well-built dams can withstand moderate shaking with peak peak accelerations accelerations up to at le ast 0.2g with no harmful effects” (Seed, Makdisi, and DeAlba, 1978). 3.3 Magnitude The amount of crest settlement is also directly related to the magnitude (M) of the earthquake. As the magnitudes increase, settlements increase. This relationship held true even at sites where the PGAs were identical because of the longer duration of strong motion shaking associated with the greater magnitude event. 3.4 Other factors considered Several other independent variables were analyzed statistically and were found to have only minimal relational effects on the amount of crest settlement. These factors included dam type, distance from seismic source to dam site, dam height, ratio of crest length to dam height, embankment slope angles, and reservoir water level at the time of the earthquake. 4 RESULTS OF REGRESSION ANALYSES ANALYSES The regression analyses also provided a mathematical relationship relationship between the crest settlement and the two factors, PGA and M. This relationship can be expressed as: % Settlement = e
(6.07 PGA + 0.57 M -8.00)
(1)
where % Settlement = the amount of settlement of the crest of the dam (in meters) divided by the height of the dam plus the thickness of the alluvium (in meters) times 100 (see. Fig 1); PGA = peak horizontal ground acceleration of the foundation rock (in g) recorded or estimated at the dam site; and M = earthquake magnitude (in surface-wave scale: MS). This relationship is illustrated in Figure 2.
5
10 % STTLMT = e (6.07 PGA + 0.57 Ms + 8.0)
% STTLMT = e
(6.07 PGA + 0.57 Ms + 8.0)
) T A 1 + H D ( % n i , T N E M 0.1 E L T T E S T S E R C D 0.01 E T A M I T S E
9 8 7 6 5 Earthquake Earthquake Magnitude Magnitude - Ms
0.001 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
PEAK GROUND ACCELERATION (PGA), in g
Figure 2. Chart for estimating crest settlement
5 OTHER OBSERVATIONS 5.1 Calculated vs. actual crest settlements Using the regression equation, crest settlements were calculated for each of the 69 case histories included in the data base. Calculated settlement values are compared to the actual values in Figure 3. It is noteworthy that the statistical fit of actual to calculated values was found to be similar to that for acceleration attenuation data from recent well-instrumented earthquakes including the Loma Prieta earthquake (Governor’s Board of Inquiry 1990) the Landers earthquake (Boore et al. 1993), and the the Nor Nor thridge earthquake (Finn et al. 1995). These statistical similarities suggest that prediction of crest settlement settlementss cannot cannot be improved improved unless the prediction of site-specific site-specific ground accelerations can be improved. Also, this observation supports the prudent use of the mean-plusone-standard-deviation value of the PGA for estimating crest settlements of critical, high-hazard structures. 10
1 T A + H D ( % , t n e m e l t t e S l a u t c A
Actual settlement is MORE than calculated
0.1
Actual settlement is LESS than calculated
0.01
0.001 0.001
0.01
0 .1
1
Calculated Settlement, % (DH + AT)
Figure 3. Actual vs. calculated settlements
6
10
settlement calculations calculations 5.2 Suitability of Newmark metho d for settlement
Currently, it is common practice to use one of several analytical procedures based on the Newmark method of analysis (Newmark 1965) to calculate theoretical crest settlements of embankment dams subjected to earthquak earthquakee loadings. This method is founded on the basic assumption that a rigid block of soil slides downward along a definite shear surface whenever a critical “yield” horizontal acceleration is exceeded. There has been some concern expressed by others that the Newmark method method may not correctly model crest settlement caused by earthquake. Day (Day 2002) demonstrated that it is theoretically possible possible for dry granular granular slopes to settle settle and spread laterally laterally without without earthquake earthquake accelera acceleration tionss exceeding yield values to initiate slides. slides. He says that the Newmark method may prove to be unreliable in some instances. Matsumoto (Matsumoto 2002) described centrifuge shake table tests and supporting nonlinear analyses for modelled accelerations up to 0.7g that revealed only shallow ravelling with no deep shear surfaces in the core zones and no definite slip surfaces anywhere in rock fill dam models. Accordingly, he says that the hypothesis of deep slide surfaces in the Newmark Newmark approach approach “may “may be somewha somewhatt erroneous”. erroneous”. Evidence from this case history study also refutes the settlement mechanism assumed in the Newmark Newmark procedure. procedure. Personal Personal inspection inspection (Swaisgood (Swaisgood & Au-Yeung Au-Yeung 1991) and review of many many photos photos of earthquake earthquake damages damages to dams dams disclosed disclosed that crest settlement settlementss and deformati deformation on (for structures struc tures not subject subject to liquefaction) liquefaction) seem see m to be from slumping and spreading movements that occur within the dam body without distinct signs of shearing displacement. This appears to be true for earth fill embankments as well as for rock fill dams. Longitudinal cracks along the crests have the appearance of tension cracks cr acks with little or no vertical offset. An exampl examplee of these crest cracks is shown in Figure 4.
Figure Figure 4. Tension cracks on Cogoti Dam crest after 1997 earthquake (Case No. 67)
6 CONCLUSIONS Conclusions from this empirical study of embankment dam settlement and deformation during earthquake include: °
°
°
°
The vertical crest settlement experienced during an earthquake is an index of the amount of deformation and damage incurred by the embankment The amount of crest settlement is related primarily to two factors: peak ground acceleration at the dam site and magnitude of the causative earthquake. An approximate estimate of the amount of crest settlement that will occur due to an assumed earthquake can be made by using mathematical formulas that relate deformation to the peak ground acceleration and earthquake magnitude. Deformation of a dam’s crest caused by earthquake is principally settlement and spreading; apparently, there is no slide failure along a distinct shear plane.
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REFERENCES: Boore, D.M., Joyner, W.B., and Fumal, T.E. 1993. Estimation of response spectra and peak accelerations fr om western North American earthquake s: an interim report, United States Geological Survey, Menlo Park, California, Open File Report No. 93-509. Day, R.W. 2002. Geotechnical earthquake engineering handbook. New handbook. New York: McGraw-Hill. Finn, L.,Ventura, C.E., & Schuster, N.D. 1995. Groun d motion s during during the 1994 North Northridge ridge earthqu ake. Canadian Journal of Civil Engineering , Vol 22, 300-315. Governor’s Board of Enquiry on the 1989 Loma Prieta Earthquake: George W. Housner, Chairman. 1990. Competing Competing Against Time, a report to Governor George Deukmejian. ICOLD 2001. Design features of dams to resist seismic ground motion. Bulletin Bulletin 120. Matsumoto, N. 2002. Evaluation of permanent displacement in seismic analysis of fill dams. In Proc third US-Japan workshop on advanced research on earthquake engineering for dams, dams, San Diego, 22-23 June 2002. Newmark, N. 1965. Effects of earthquakes on dams and embankments. embank ments. Geotechnique, Geotechnique, Vol 15 (2) 139-160 London. Pinos S. F. 2000. Instrumentación Instrument ación de presas de tierra, aplicaciones aplica ciones para evaluar la respuesta respues ta sísmica de presas presas chilenas. chilenas. University of Chile (Universidad (Universidad de Chile). Unpublished thesis presented to obtain the degree of Civil Engineer in Construction and Structures (Ingeniero Civil en Construcción y Estructuras). Seed, H.B., Makdisi, Makdisi, F.I., and DeAlba, P. 1978. The performanc e of earthfill dams during earthquakes. Jou rnal of the Geotechni cal Engineer ing Division, ASCE, Volume 104, No. GT7, pp. 967-994. Southern Peru Copper Corp 2001. Unpublished settlement monitoring data – Torata Dam. Swaisgood J. R. 1998. Seismically-induced deformation of embankment dams. In proceedings of sixth national conference on earthquake engineering. Seattle, Washington, U. S. A. May 31 – June 4 1998. Swaisgood, J.R. and A u-Yeung, Y. 1991. Behavior of of dams during the 1990 Philippines Philippines earthquake. earthquak e. Presented at the ASDSO 1991 annual conference, San Diego, 29 Sep- 2 Oct 1991. Tepel, R.E.; Nelson, J.L. & Hosokawa, A.M. 1996. Seismic response of eleven embankment dams, Santa Clara County, California, as measured by crest monument surveys. In Seismic design and performance of dams; Sixth annual USCOLD lecture, lecture, Los Angeles, 22 -26 July 1 996.
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