WA ST Dept. of Ecology Dam Safety Office Draft Seismic Practice
Jerald LaVassar 1, Lead Engineer July 2012 1
[email protected]
Slide 2
Portfolio Mentality Required Pend Oreille Mines Tailings
Facility City of Marysville Stormwater Pond Asamera
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WAs Consequence Dependent Risk Based Design Approach
Identifying a suitable minimum design performance goal
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Worksheet to Quantify Risk Selection of Design/Performance
Goals for Critical Project Elements, Appendix A, Technical Note 2
Controlling factor typically
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Design Performance Goal Where there is the potential for loss
of life design is at a minimum of Step 3
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Associating ground motions with design performance goal at a
specific dam
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Annual Exceedance Probability 0.1 0.001 0.01 0.0001 0.00001
Total mean hazard Cascadia Megathrust hazard Deep Intraplate hazard
WUS Crustal hazard 1.0 second Spectral Acceleration (g) 0.20.4 USGS
PSHA Dam Safety Office USGS event of interest is not generally
representative of DSO event of interest. USGS is interested in
predicting IMs at a given exceedance probability The DSO is
interested in predicting the annual probability of a dam failing.
To do that we need the individual hazard curves for the various
contributing source zones. Total Mean Hazard vs. Individual Source
Zone Hazard Curves
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Annual Exceedance Probability 0.1 0.001 0.01 0.0001 0.00001
Total mean hazard Cascadia Megathrust Deep Intraplate WUS Crustal
1.0 second Spectral Acceleration (g) 0.20.4 USGS PSHA Dam Safety
Office Idealized Process to Generate Suites of Ground Motion Time
Histories S A - g Period sec -> Accel - g Time - sec Cascadia
Megathrust Scenario S A - g Period sec -> Accel - g Time - sec
WUS Crustal Scenario Function of Individual Source Mean M w, R,
& Epsilon and
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Dam Safety Office practice in conducting our independent
seismic analyses
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Minckler Dam Project Locale
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Minckler Dam 1) Model problem geometry (LIDAR data &
surveyed dam cross-section) 2) Chose a constitutive model
(effective stress model tracks seismic induced pore pressure
changes) 3) Select suite of EQ time histories representative of
principal source zones contributing to the seismic hazard at a
consistent exceedance level
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Line 3000 Line 2000 9 12 15 17 20 22.5 27 29 14.5 17.5 20 25 V
S m/sec 190 210 230 >300 Lower Pond Upper Pond V S m/sec 190 175
190 210 230 250 270 290 >300 Minckler Dam B Cross-section JML
12/21/2010 380 390 370 05090 ? ? Unweathered Till N 1,60 >
>50 Weathered Till N 1,60 > 50 Less dense fill N 1,60 ~ 13.5
12 More dense fill N 1,60 ~ 20 250 270 All distances in feet Note:
Line 3000 was run along the downstream face. Raleigh wave solutions
assume the ground surface is level so that the wave direction is in
a vertical plane and that the vertical plane coincides with a
principal stress plane. This is not the case for Line 3000 and
thus, the shear wave velocities (V S ) are more suspect. I have
assumed that the level of compaction would be less near the dam
slopes where there is less horizontal confining stress to assist in
the compaction process and operators would have been reluctant to
get too near the edge for fear of rolling the hauling
equipment.
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2 1.91 1 Lower Pond Upper Pond 11 ft 24 ft 58 ft 70 ft 82 ft 84
ft 20 ft Existing dam Drained buttress Filter/Drained Buttress JML
3/2011 Note: Assumed engineered fill has same properties as Fill
between 12 to 16 feet in Table 1 of Model Soil Properties. Wide
drain at interface of old dam section with buttress not shown.
Assume similar properties for both buttress fill and that of
drain.
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Input earthquake record: 2001 Nisqually at DNR building in g.
The record was scaled to PGA 0.58g and only the first 30 sec was
run in the dynamic analysis.
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Vertical displacement after buttress addition. zdis maximum was
reduced from 1.3 ft to 0.4 ft along central reach of the dam
crest.
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Minckler Dam High Downstream Hazard Setting Case where multiple
source zones contribute in roughly equal fractions to the hazard
and thus, the recurrence intervals for each of the larger single
source zone hazard curves would be significantly larger than the
return period for the Intensity Measure cited in the PSHA.
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EZ-Frisk cuts the Gordian Knot
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Mean Spectral Acceleration at 0.5 second period @ 1% chance of
exceedance in 50 years Cascade Interface Composite -- 0.57 g PNW
Deep Gridded -- 0.61 g Strawberry Pt. -- 0.40 g Devils Mtn. Fault
-------- g Total Mean Hazard 1% chance of exceedance in 50 years -
SA 0.5 sec 1.04 g
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1% chance of exceedance in 50 years - SA 0.5 sec 0.57 g
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Not USGS 2008 Deagg! Case where Young et al. 1997 attenuation
relationship given zero weight Total Mean Hazard 1% chance of
exceedance in 50 years - SA 0.5 sec 0.90 g Mean Hazard Pacific Deep
Gridded Source Zone GMPE Weights Zhao 50% 67% 50% A & B 50% 33%
25% Youngs 0 0 25% M w 6.99 6.97 6.78 R (km) 63.5 63.7 69.8 1.36
1.39 1.64 SA 0.5 sec (g) 0.40 0.39 0.56
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Purchase 3 month/25 site license for EZ-Frisk once BC Hydro
& Zhao GMPEs are updated and we can get our hands on them Setup
& run USGS analysis to demonstrate it yields USGS results Rerun
analysis for a single source zone to yield SA hazard curve Select
SA value at desired exceedance probability for that single source
and deaggregate to obtain largest R/M/ bin contributor Compile
uniform hazard spectra/conditional mean spectra from GMPEs Select
suite of time histories to cover the spectra and run model If dam
survives, move on to next source zone and repeat above If dam
fails, find minimum SA/time histories necessary to fail the dam.
Determine the exceedance probability for that scenario.
Strategy
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Anxiously awaiting Processed subduction zone time histories
appropriate for PNW use Attenuation relationships (GMPE) that
reflect the dramatic increase in record numbers and at greater
magnitudes in both the Maule & Tohoku Earthquakes A study of
how actual dams performed in the above mentioned earthquakes/verses
how our engineering methods would have predicted them to have
performed.