embankment dam deformations caused by earthquakes
DESCRIPTION
Trabajo de Swaisgood en donde recopila el comportamiento de presas de relaves y plantea un método para determinar desplazamientos.TRANSCRIPT
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Paper Number 014
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 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 been prepared to summarize the relationship between the 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.
2 CASE HISTORY DATA BASE
2.1 Previous work
During the 1990 Philippines earthquake, a review of incidents of seismically-induced deformation of embankment dams was initiated to aid in evaluating the damages exhibited by several major dams during that event (Swaisgood and Au-Yeung, 1991). These studies continued on with the results last presented in 1998 (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 Case Nos. 10, 25, 26, 36 to 40 (Tepel, et. al. 1996) and 19
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(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 dams GENERAL INFORMATION CREST RELATIVE
ID DAM DH CL AT E A R T H Q U A K E D A T A SETTLEMENT DEGREE
OF
No NAME OF DAM LOCATION TYPE m m m DATE M D,km PGA, g. m * % ** DAMAGE
1 UPPER MURA-
YAMA Japan E-HF 24 320 3 1 Sep 23 8.2 18 0.32 e 0.20 0.74 Moderate
2 ONO Japan E 41 309 11 1 Sep 23 8.2 98 0.30 e 0.27 0.53 Serious
3 CHATSWORTH
NO.2 California HF 12 610 ?*** 30 Aug 30 5.3 1 0.40 e 0.08 0.63 Moderate
4 MALPASSO Peru ECRD 78 152 30 10 Oct 38 VI+ n/a 0.10 e 0.08 0.07 Minor
5 COGOTI Chile CFRD 85 159 0 6 Apr 43 7.9 89 0.20 e 0.38 0.44 Minor
6 SOUTH HAIWEE California HF 25 457 38 21 Jul 52 7.7 151 0.05 e 0.02 0.04 Minor
7 HEBGEN Montana E 25 213 10 17 Aug 59 7.6 0 0.71 e 1.69 4.82 Serious
8 MIBORO Japan ECRD 130 444 0 19 Aug 61 7.0 20 0.15 e 0.03 0.02 Minor
9 MINASE Japan CFRD 67 210 ? 16 Jun 64 7.5 145 0.08 e 0.06 0.09 Minor
10 UVAS California E 32 335 ? 18 Dec 67 5.3 11 0.20 e 0.02 0.06 Minor
11 U. SAN FER-
NANDO California HF 25 390 18 9 Feb 71 6.6 2 0.55 e 0.91 2.11 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 75 15 Nov 75 7.2 20 0.04 r 0.02 0.02 None
14 EL INFIERNILLO Mexico ECRD 146 340 0 15 Nov 75 7.2 23 0.09 r 0.02 0.02 None
15 EL INFIERNILLO Mexico ECRD 146 340 0 11 Oct 75 5.9 79 0.08 r 0.04 0.03 None
16 TSENGWEN Taiwan ECRD 131 n/a ? 14 Apr 76 5.3 8 0.16 e 0.04 0.03 n / a
17 EL INFIERNILLO Mexico ECRD 146 340 0 14 Mar 79 7.6 95 0.12 r 0.13 0.09 Minor
18 LA VILLITA Mexico ECRD 60 427 75 14 Mar 79 7.6 108 0.02 r 0.05 0.03 Minor
19 VERMILION California E 50 1290 50 27 May 80 6.3 22 0.24 r 0.05 0.05 None
20 LA VILLITA Mexico ECRD 60 427 75 25 Oct 81 7.3 31 0.09 r 0.14 0.11 None
21 EL INFIERNILLO Mexico 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 83 7.7 145 0.08 r 0.06 0.11 None
23 COYOTE California E 43 299 0 24 Apr 84 6.2 0 0.63 e 0.08 0.18 Minor
24 LEROY ANDER-
SON California ECRD 72 427 0 24 Apr 84 6.2 2 0.41 r 0.02 0.02 Minor
25 ELMER J. CHES-
BRO California E 29 220 0 24 Apr 84 6.2 22 0.18 e 0.02 0.05 Minor
26 UVAS California E 32 335 ? 24 Apr 84 6.2 29 0.14 e 0.02 0.08 Minor
27 MAKIO Japan ECRD 77 264 29 14 Sep 84 6.8 5 0.57 e 0.50 0.47 Minor
28 AROMOS Chile ECRD 43 220 9 3 Mar 85 7.8 45 0.25 e 0.09 0.177 Minor
29 EL INFIERNILLO Mexico ECRD 146 340 0 19 Sep 85 8.1 76 0.13 r 0.11 0.08 Minor
30 LA VILLITA Mexico ECRD 60 427 75 19 Sep 85 8.1 43 0.13 r 0.33 0.24 Minor
31 LA VILLITA Mexico ECRD 60 427 75 21 Sep 85 7.5 61 0.04 r 0.12 0.09 None
32 MATAHINA New Zea-land 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
35 LEXINGTON California E 63 253 0 17 Oct 89 7.1 3 0.45 r 0.26 0.41 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 California E 32 140 ? 17 Oct 89 7.1 9 0.44 e 0.03 0.10 Minor
39 CALERO California E 30 256 ? 17 Oct 89 7.1 13 0.38 e 0.01 0.03 None
40 RINCONDA California E 12 73 ? 17 Oct 89 7.1 9 0.41 e 0.02 0.15 Minor
41 GUADALUPE California E 43 204 0 17 Oct 89 7.1 10 0.42 e 0.20 0.45 Minor
42 ELMER J. CHES-
BRO 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
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GENERAL INFORMATION CREST RELATIVE
ID DAM DH CL AT E A R T H Q U A K E D A T A SETTLEMENT DEGREE
OF
No NAME OF DAM LOCATION TYPE m m m DATE M D,km PGA, g. m * % ** DAMAGE
44 LEROY ANDER-
SON California ECRD 72 427 0 17 Oct 89 7.1 21 0.26 r 0.04 0.06 Minor
45 SAN JUSTO California ECRD 40 340 14 17 Oct 89 7.1 27 0.26 r 0.04 0.07 None
46 AMBUKLAO Philippines ECRF 120 450 5 16 Jul 90 7.7 10 0.49 e 1.10 0.880 Serious
47 MASIWAY Philippines E 25 427 3 16 Jul 90 7.7 3 0.68 e 1.06 3.79 Serious
48 PANTABANGAN Philippines ECRD 114 732 0 16 Jul 90 7.7 6 0.58 e 0.28 0.24 Moderate
49 AYA Philippines ECRD 102 427 0 16 Jul 90 7.7 6 0.58 e 0.20 0.20 Minor
50 DIAYO Philippines ECRD 60 201 0 16 Jul 90 7.7 18 0.38 e 0.07 0.11 Minor
51 CANILI Philippines ECRD 70 351 0 16 Jul 90 7.7 18 0.38 e 0.04 0.06 Minor
52 MAGAT Philippines ECRD 100 1296 0 16 Jul 90 7.7 81 0.05 e 0.01 0.006 None
53 COGSWELL California CFRD 81 200 0 28 Jun 91 5.8 7 0.37 e 0.04 0.051 Minor
54 ROBERT MAT-
THEWS 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
56 YUCAIPA No. 1 California E 13 128 9 28 Jun 92 6.6 28 0.15 e 0.01 0.028 Minor
57 YUCAIPA No. 2 California E 15 146 9 28 Jun 92 6.6 28 0.15 e 0.00 0.019 Minor
58 UPPER LAKE
MARY Arizona E 13 247 1 29 Apr 93 5.5 77 0.02 e 0.00 0.004 None
59 U. SAN FER-
NANDO California HF 25 390 18 17 Jan 94 6.7 10 0.42 e 0.44 1.021 Serious
60 L. SAN FER-
NANDO California E-HF 38 537 6 17 Jan 94 6.7 9 0.44 e 0.20 0.460 Serious
61 LOS ANGELES California E 47 671 0 17 Jan 94 6.7 10 0.43 r 0.09 0.188 Moderate
62 NORTH DIKE [LA] California E 36 427 0 17 Jan 94 6.7 10 0.43 e 0.03 0.089 Moderate
63 LOWER FRANK-
LIN California HF 31 152 ? 17 Jan 94 6.7 18 0.30 e 0.05 0.146 Moderate
64 SANTA FELICIA California E 65 389 0 17 Jan 94 6.7 33 0.18 e 0.02 0.030 Minor
65 COGSWELL California CFRD 81 200 0 17 Jan 94 6.7 53 0.10 e 0.02 0.026 Minor
66 PALOMA Chile ECRD 82 1000 14 14 Oct 97 7.6 45 0.23 e 0.14 0.141 Minor
67 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
L E G E N D
DH = dam height
M = earthquake magnitude, surface-wave scale: M S
D = distance from nearest ground rupture or epicenter, whichever is closest
PGA = peak horizontal ground acceleration; e = estimated, r = recorded
HF = Hydraulic Fill
E = Earthfill
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
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0.001
0.01
0.1
1
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
PEAK GROUND ACCELERATION, g
CRES
T SE
TTLE
MEN
T, in %
(DH
+ AT)
CFRDECRDHFEarthfill
DH
AT
% STTLMT = ---------------- x 100DH + AT
RE
LAT
IVE
DE
GR
EE
OF
DA
MA
GE
NO
NE
SE
RIO
US
MO
DE
RA
TE
MIN
OR
0.001
0.01
0.1
1
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
PEAK GROUND ACCELERATION, g
CRES
T SE
TTLE
MEN
T, in %
(DH
+ AT)
CFRDECRDHFEarthfill
DH
AT
DH
AT
% STTLMT = ---------------- x 100DH + AT
% STTLMT = ---------------- x 100DH + AT
RE
LAT
IVE
DE
GR
EE
OF
DA
MA
GE
NO
NE
SE
RIO
US
MO
DE
RA
TE
MIN
OR
Figure1. Settlement of embankment dams during 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 relative 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.
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From these regression analyses, it was found that the only factors that had 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 is apparent in the plot shown in Figure 1. In general, dams that experience greater PGAs undergo greater deformations and damages. In this study, it was found that serious levels of damage were reported only in instances where the PGA exceeded 0.2g. This 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 accelerations up to at least 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
The regression analyses also provided a mathematical 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.
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0.001
0.01
0.1
1
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
PEAK GROUND ACCELERATION (PGA), in g
ESTI
MAT
ED C
RES
T SE
TTLE
MEN
T, in
%(D
H +
AT)
% STTLMT = e (6.07 PGA + 0.57 Ms + 8.0)
5
9
8
7
6
Earthquake Magnitude - Ms
0.001
0.01
0.1
1
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
PEAK GROUND ACCELERATION (PGA), in g
ESTI
MAT
ED C
RES
T SE
TTLE
MEN
T, in
%(D
H +
AT)
% STTLMT = e (6.07 PGA + 0.57 Ms + 8.0)
0.001
0.01
0.1
1
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
PEAK GROUND ACCELERATION (PGA), in g
ESTI
MAT
ED C
RES
T SE
TTLE
MEN
T, in
%(D
H +
AT)
% STTLMT = e (6.07 PGA + 0.57 Ms + 8.0)
5
9
8
7
6
Earthquake Magnitude - Ms
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 (Governors Board of Inquiry 1990) the Landers earthquake (Boore et al. 1993), and the Northridge earthquake (Finn et al. 1995). These statistical similarities suggest that prediction of crest settlements cannot be improved unless the prediction of site-specific ground accelerations can be improved. Also, this observation supports the prudent use of the mean-plus-one-standard-deviation value of the PGA for estimating crest settlements of critical, high-hazard structures.
0.001
0.01
0.1
1
10
0.001 0.01 0.1 1 10
Calculated Settlement, % (DH + AT)
Act
ual S
ettle
men
t, %
(DH
+ A
T)
Actual settlement isMORE than calculated
Actual settlement isLESS than calculated
0.001
0.01
0.1
1
10
0.001 0.01 0.1 1 10
Calculated Settlement, % (DH + AT)
Act
ual S
ettle
men
t, %
(DH
+ A
T)
Actual settlement isMORE than calculated
Actual settlement isLESS than calculated
Figure 3. Actual vs. calculated settlements
% STTLMT = e (6.07 PGA + 0.57 Ms + 8.0)
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5.2 Suitability of Newmark method for settlement calculations
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 earthquake 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 may not correctly model crest settlement caused by earthquake. Day (Day 2002) demonstrated that it is theoretically possible for dry granular slopes to settle and spread laterally without earthquake accelerations exceeding yield values to initiate 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 approach may be somewhat erroneous.
Evidence from this case history study also refutes the settlement mechanism assumed in the Newmark procedure. Personal inspection (Swaisgood & Au-Yeung 1991) and review of many photos of earthquake damages to dams disclosed that crest settlements and deformation (for structures not subject to liquefaction) seem 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 with little or no vertical offset. An example of these crest cracks is shown in Figure 4.
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 dams 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 from western North American earthquakes: 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 York: McGraw-Hill.
Finn, L.,Ventura, C.E., & Schuster, N.D. 1995. Ground motions during the 1994 Northridge earthquake. Canadian Journal of Civil Engineering, Vol 22, 300-315.
Governors Board of Enquiry on the 1989 Loma Prieta Earthquake: George W. Housner, Chairman. 1990. Competing Against Time, a report to Governor George Deukmejian.
ICOLD 2001. Design features of dams to resist seismic ground motion. 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, San Diego, 22-23 June 2002.
Newmark, N. 1965. Effects of earthquakes on dams and embankments. Geotechnique, Vol 15 (2) 139-160 London.
Pinos S. F. 2000. Instrumentacin de presas de t ierra, aplicaciones para evaluar la respuesta ssmica de presas chilenas. University of Chile (Universidad de Chile). Unpublished thesis presented to obtain the degree of Civil Engineer in Construction and Structures (Ingeniero Civil en Construccin y Estructuras).
Seed, H.B., Makdisi, F.I., and DeAlba, P. 1978. The performance of earthfill dams during earthquakes. Journal of the Geotechnical Engineering 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 Au-Yeung, Y. 1991. Behavior of dams during the 1990 Philippines earthquake. 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, Los Angeles, 22 -26 July 1996.