Preliminary White Paper on Cascadia Earthquakes and Tsunamis Tsunami Evacuation Buildings (TEBs):

Preliminary White Paper on Cascadia Earthquakes and Tsunamis Tsunami Evacuation Buildings (TEBs):
Preliminary White Paper
on
Tsunami Evacuation Buildings (TEBs):
A New Risk Management Approach to
Cascadia Earthquakes and Tsunamis
by Jay Raskin, Yumei Wang,
Marcella M. Boyer, Tim Fiez, Javier Moncada, Kent Yu, and Harry Yeh
March 20, 2009 Version
Shirahama Tsunami Evacuation Structure. Photo by Professor Nobuo Shuto
Executive Summary
Chapter 1. Introduction on Tsunami Risk Management
Chapter 2. Cannon Beach City Hall Design Considerations
Chapter 3. Wave Energy Dissipation
Chapter 4. Structural Design Considerations
Chapter 5. Geotechnical and Scour Considerations
Chapter 6. Tsunami Simulator for Cannon Beach
Chapter 7. Next Steps
Appendix. Ad Hoc Design Team
Executive Summary
This white paper is a working document that discusses the need for tsunami evacuation
buildings (TEB) as new risk management approach to the Cascadia earthquake and
tsunami. Taking its starting point from FEMA P646 Guidelines for Design of Structures
for Vertical Evacuation from Tsunamis, it looks at how this conceptual approach would
work for rebuilding the Cannon Beach City Hall as a TEB. Preliminary design, technical
and social issues are considered, including tsunami dissipator to deflect wave energy
away from the TEB and geotechnical and structural design to survive a magnitude 9
earthquake and near field tsunami. Many issues remain unresolved, including the need to
determine tsunami evacuation scenarios, foundation conditions, funding challenges, and
many more.
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Chapter 1. Introduction on Tsunami Risk Management
Yumei Wang, PE
Background
Low lying coastal communities along the Pacific Northwest are at-risk of near-field
(local) tsunami inundation generated by Cascadia Subduction Zone (CSZ) earthquakes.
These communities were developed long before scientists understood the existing
tsunami hazards. As such, about 100,000 residents are in the tsunami inundation hazard
zone each day in Oregon. Some of these 100,000 people are in the high hazard portion of
the inundation zone nearest to ocean and river channels with long travel distances to safe,
higher elevation land. In addition, many of these communities attract tourists who come
to visit the ocean beaches, which are high risk areas. Coastal communities have been
responding to the tsunami risk by developing emergency operation plans that include
establishing evacuation routes and areas, and educational outreach programs.
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Figure 1-1a and 1-1b: Portion of Cannon Beach tsunami evacuation map and index (DOGAMI, 2008)
In 2009, new generation tsunami inundation maps will be issued for Cannon Beach,
Oregon (CB). Using improved scientific data and methods (i.e. post 2004 Sumatra), the
tsunami hazard maps will show greater risk hazards from Cascadia generated tsunamis
than previous maps. The 2008 CB evacuation map shows much of the downtown, the
elementary school, fire station, police station and city hall at risk from distant and local
tsunamis (Figure 1-1a and 1b) In addition, vulnerability studies have shown that certain
populations such as visitors and elderly are also particularly at risk. It should also be
noted that the people will be disoriented from the earthquake and that evacuation times
before the tsunami arrive range from 10-30 minutes for Cascadia events. The increased
tsunami risk has meant that Cannon Beach and other coastal communities can no longer
rely solely on the strategy of evacuation to higher ground but must look at tsunami
evacuation buildings, structures and berms.
Tsunami Evacuation Buildings (TEBs)
Tsunami evacuation buildings (TEBs) can be an important element to insuring that
schools, essential facilities, and government buildings are able to meet their everyday
purposes, and continue to function after the earthquake and tsunami. While this approach
has not been done in the United States, it has been done in Japan (See Cover Page Photo).
People who cannot safely evacuate the tsunami inundation zone should be able to
evacuate to a TEB. An estimated dozen or more TEBs should be available in Oregon
alone. TEBs must be able to withstand prolonged strong shaking and may be reinforced
concrete structures with deep scour-resistant foundations and a minimum of two stories
(Figure 1-2). The lowest story should be open space on the ground floor to allow for
water and debris passage. Or, the lowest floor may be designed to be sacrificial, such as
with break away walls. The elevation of the bottom of the second story should be higher
than the anticipated tsunami inundation elevation. The roof may be designed for general
purposes, such as for parking or recreation space. It may also be designed for emergency
purposes, such as for evacuees, heliport, emergency storage of food or medical supplies,
emergency generator, emergency vehicles and so on. Energy dissipation or deflection
structures may be designed to protect the TEB by reducing tsunami force and scour
effects. In addition, TEB design should accommodate rapid ingress by foot traffic during
tsunamis and be readily identifiable to evacuees. Accommodation must also be made for
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wheelchair access. TEBs should allow for a minimum area per evacuee depending on its
purpose, such as 0.5 sq m. Because tsunamis are rare, TEBs should serve a daily purpose.
Figure 1-2. Schematic Design of Tsunami Evacuation Building (TEB)
Cannon Beach City TEB and Design Team
The existing Cannon Beach City Hall is expected to be critically damaged during a local
and distant tsunami. Replacing city hall with a TEB would allow the community to
accommodate evacuation needs and rely on its continued function. A new Cannon Beach
City Hall TEB would serve as a demonstration project for other coastal communities with
high tsunami risks.
In order to better understand elements needed to construct a City Hall TEB, an ad-hoc
design committee was formed. The design team members of the committee include
engineers, an architect, and scientists and are listed in the Appendix. This design team
has developed this preliminary white paper on the Cannon Beach City Hall TEB’s
conceptual design and has identified a number of issues that need to be addressed.
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Chapter 2. Cannon Beach City Hall/TEB Design Considerations
Jay Raskin, AIA
Cannon Beach is a small community located on the northern Oregon coast eighty miles
west of Portland. The city has a full time resident population of 1,690 that is augmented
by around 3,000 part time residents. Tourists visiting the city can range from several
thousand to tens of thousands on any given day. Economic activity is centered on
tourism. The city has high risk factors for tsunami’s because a majority of the population
and economic activity is located in the tsunami inundation zones as well as many visitors
who also tending to gather in the tsunami inundation zones. In addition, the cities
population has a fairly high percentage of retirees. See Figure 2-1.
Cannon Beach, a Tsunami Ready community, has been active in preparing for the
Cascadia subduction zone earthquake and tsunamis as well as distant tsunami’s. Starting
in the 1990’s the Cannon Beach Rural Fire District installed a series of
siren/loudspeakers to warn visitors of approaching distant tsunami’s and started tsunami
education efforts. The City of Cannon Beach joined in these efforts by establishing the
Emergency Preparedness Committee which developed an Emergency Operations Plan,
identified evacuation routes and areas, created on-going community outreach and
education programs, established shelter sites (along with seismic evaluations of the
shelters), as well as other recommendations to the City to strengthen emergency response.
The Fire Station was relocated to high ground in 1994 and contains the Emergency
Operations Center (EOC) for the community.
Fig. 2-1 Inundation Confidence Levels, Cannon Beach Inundation Mapping Study, DOGAMI (2008)
Cannon Beach then turned its attention to relief and long term disaster recovery. It was
aided in this effort by a workshop funded by the Cascadia Earthquake Emergency
Workgroup (CREW.org), in which Oregon Natural Hazards Workgroup, Oregon
Emergency Management and USGS that brought community leaders, the school district,
utility companies, health care providers, and the business community together. Out of
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this workshop, the City created the “Prepare for Emergency Recovery Committee”
(PERC), a staff committee focused on relief and immediate post disaster recovery efforts,
and the Long Term Disaster Recovery Committee, which is an advisory committee
looking developing pre-disaster mitigation strategies. One important result of this process
was the realization that continuity of governance is essential and that this was
problematic with the existing City Hall, which was vulnerable to both earthquakes and
tsunamis.
New City Hall/Tsunami Evacuation Building
The decision to look into rebuilding the existing City Hall as a Tsunami evacuation
building was due both to the lack of availability of an alternate site above the inundation
zone and to the fact that it was well situated to provide refuge to residents and visitors in
the Downtown and Midtown areas, both highly populated and vulnerable areas. It is also
very visible from a major beach access. .
The existing building is 9,000 square feet and, if replaced, is large enough to provide
refuge to at least 800-1,000 people on the second level and possible roof terrace.
Figure 2-2 Cannon Beach City Hall/TEB conceptual Design Ecola Architects, PC (2008)
Design Considerations
The conceptual design that was developed incorporated the primary elements of a TEB.
(See Figure 2-2) The building was raised on columns to allow water pass beneath the
structure. The second floor level was set to be above not only the most likely tsunami
event, but most of the rare tsunami events as well. A roof terrace was designed to
provide additional refuge area and as a safety factor for inundation depth. Exterior stairs
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were placed as a very visible design feature to make the building readily identifiable as a
tsunami refuge. The lower level is open to provide parking. The building also was
designed to serve other functions so that the lower level can shelter the Farmers Market
and the roof terrace is a public open space where Haystack Rock is visible. Accessibility
is being planned for with the use of elevators designed to be functional after the
earthquake. Emergency power and supplies will also be included. Strategies for wave
energy dissipator to reduce tsunami actions on the TEB can be provided for in the
parking lot in front of City Hall.
Zoning Ordinances
The conceptual design must meet of the City’s zoning ordinances. These ordinances
included providing off street parking, setting the building back from the residential zone
south by 20 feet, providing landscaping, and a building height limit of 28’. The
conceptual design showed that all zoning ordinances can be met except for the 28’ height
limit. This would require a variance from the City, but is considered an acceptable
request given the nature of the project. The City also has as Design Review requirement
so that the aesthetics of the building must be acceptable to the community.
ADA Accessibility
ADA accessibility is a requirement for public buildings. The most straightforward
solution is providing at least one elevator to the building, built to a high seismic
resistance standard and provided with emergency power to insure function after the
earthquake. The option of an accessible ramp was examined and, at this stage, it was
determined that not enough space was available for the length of ramp required,
especially if the ramp had to reach to the roof terrace as well. Large ample stairs were
provided on the exterior of the building that met ADA standards
Aesthetics
The building has to readily identifiable as a refuge for a tsunami. The conceptual design
solution was to make the stairs to the upper level and to the roof terrace a very distance
and visible part of the design. The stairs were placed on the south side of the building
and made very visible to people evacuating along Hemlock Street, the main street in
town. The City of Cannon Beach has design review for commercial and public buildings
so any design also has to meet the design review guidelines. An initial attempt to meet
these guidelines included have a gable roof over part of the roof and using cedar shingles,
which are a common siding material in town. One design element that needs further
study is creating an attractive ground story. This level will need to be used for parking in
order to meet the zoning ordinances for off street parking. However, a possible
secondary use of the covered area for the new Cannon Beach Farmer’s market may
provide additional design parameters to create a pleasing space under the building.
Other Considerations
Relocating City Hall had been considered as an alternative when its vulnerability was
first realized. This thinking changed when it became evident that there was not suitable
available land within the City limits, or in close proximity. The existing location of City
was good for its proximity to the citizens and providing them services. Relocating the
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City Hall would have required mitigating effects on the daily lives of the citizens and was
deemed as not feasible.
Chapters 1 and 2 References
Cannon Beach City Hall/TEB Conceptual Design Study, July, 2008, Ecola Architects, PC
Variations in City Exposure and Sensitivity To Tsunami Hazards in Oregon, Scientific
Investigations Report 2007-5283, Nathan Wood, USGS; 2007
Cannon Beach Case Study Report; ONHW, 2006
Open-File Report O-08-12, Prehistoric Cascadia Tsunami Inundation and Run-up at
Cannon Beach, Clatsop County, Oregon, Rob Witter, DOGAMI, 2008
Oregon Department of Geology and Mineral Industries, Tsunami Evacuation Map:
Cannon Beach and Arch Cape Areas, Oregon, 8-26-08,
http://www.oregongeology.org/sub/earthquakes/Coastal/tsubrochures/CannonEvac.pdf
Oregon Department of Geology and Mineral Industries, Draft Tsunami Hazard Map of
the Cannon Beach Area, Clatsop County, Oregon, by George Priest and Rob Witter,
revised 4-18-08,
http://www.oregongeology.org/sub/earthquakes/Coastal/DRAFTCannonBeachMap.pdf
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Chapter 3. Tsunami Dissipation Wall for Cannon Beach City Hall
Javier F. Moncada
Introduction
Seawalls, bulkheads and revetments are coastal structures that are used to protect
shoreline land from erosion due to rising sea levels and waves. The shoreline structures
are constructed of structural soil fill, geotextile fabric, large stones, steel, reinforced
concrete or some combination of these materials. The optimal structure type is
determined by the predicted water levels, wave climate, material availability and soil
classifications.
Shoreline placed seawalls may have significant short and long term environmental
impacts. Short term water quality can be decreased from construction activity. Long
term sand circulation and displacement can affect habitat for marine life. Seawalls may
limit beach access and may be intrusive on the shoreline views.
Reinforced concrete seawalls can withstand higher wave forces than soil revetments and
stone bulkheads. They are designed to absorb breaking wave energy or reflect waves
seaward or upward.
In order to design a tsunami dissipation wall that reduces the tsunami actions the TEB,
we adpat the foregoing design concept of seawalls. When tsunamis propagate inland,
wave fronts can take the shape of either a bore or surge. These destructive waves can
carry debris, such as logs, creating high impact loads and cause extensive damage to
wooden and unreinforced masonry structures. To dissipate some of this tsunami energy,
the Canon Beach City Hall vertical tsunami evacuation building will have two reinforced
concrete seawalls along the west and east sides of the buildings.
Objective
The primary objective of the tsunami dissipation walls is to reduce some of the tsunami
energy and debris forces by wave front upward deflection and debris damming. The
more wave and debris energy that can be absorbed or dissipated by the wall prior to
reaching the building, the less robust the building will need to be. The seawall is not
intended to completely prevent tsunami inundation of City Hall, but merely to dissipate
some of the tsunami energy.
Environment
More investigation is required to determine the exact location of the tsunami seawall
relative to the Canon Beach City Hall. An estimate of the tsunami seawall location is near
the building and approximately 700 ft from shore. No environmental impacts are
anticipated at this time and the wall is not expected to limit beach access.
Tsunami Seawall Design Considerations
City Hall will have two pile supported reinforced concrete walls. The ocean side west
wall is rendered in Figure 3-1 and the landward east wall is rendered in Figure 3-2. Both
of these figures are conceptual and are modified figures from the Shore Protection
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Manual. The west wall is a combination stepped and curved face and the east wall is a
curved faced only.
The curved face of the wall will reflect the wave energy upward, causing the tsunami to
reflect some of its destructive energy before reaching the building. The wall will absorb
impact and damming debris forces. The west wall will dissipate wave energy from the
run-up and the east wall will dissipate wave energy from the drawdown. The rip rap will
resist scour from the run-up and drawdown. Greater scouring has been observed to occur
during drawdown.
Figure 3-1: Combination stepped and curved face pile support seawall, modified from
Figure 6-2, SPM II, proposed City Hall west tsunami wall. NTS
The seawalls will be constructed of steel reinforced concrete. The west wall would be
best located in the parking lot where a natural grade difference already exists.
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Conclusion
To build and design an effective and efficient tsunami seawall for Canon Beach, more
information is needed about the expected tsunami wave and the soil types below the
walls. The design tsunami wave shape, velocity, height and frequency will govern the
forces needed to design the seawalls. Local soil classification is needed to determine pile
depths and width of wall.
Figure 3-2: Pile supported, reinforced concrete curved face seawall, modified from
Figure 6-1 SPM II, proposed east City Hall tsunami wall. NTS
Chapter 3 References
FEMA P646, Guidelines for Design of Structures for Vertical Evacuation from
Tsunamis, June 2008
Design Tsunami Forces on Onshore Structures, Yeh, H, Journal of Disaster Research,
September 2007.
ASCE 7-05 Minimum Design loads for Buildings and Other Structures
Physical and Numerical Modeling of Stacked Geotubes subjected to Dynamic Loading,
V.K. Tyagi, J.N. Mandal, pp 356-365, Civil Engineering in the Ocean VI, ASCE,
October, 2004
Design of Coastal Revetments, Seawalls, and Bulkheads, USACE June 1995
Shore Protection Manual Volume II (SPM), 1984, Coastal Engineering Research Center,
USACE
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Chapter 4. Cannon Beach City Hall/TEB Structural Design Considerations,
Kent Yu, PhD, PE
Cannon Beach is located on the seismically active Oregon coast. It is likely affected by
tsunamis and strong seismic shaking generated by a Cascadia Subduction earthquake. In
order to function as a refuge from tsunami, the proposed Cannon Beach City
Hall/Tsunami Evacuation Building (TEB) must remain usable following a major seismic
event. This, in turn, requires the building to retain most of its pre-earthquake lateralforce resistance, experience little nonstructural damage, and be capable of resisting
expected tsunami loading effects. The building should be designed using performancebased earthquake engineering principles to meet Immediate Occupancy performance
objectives for the maximum considered earthquake (MCE) seismic event. At the MCE
event, the building shall retain sufficient lateral strength to resist forces associated with
the 2,500 year tsunami.
Seismic Performance Objective
There is limited guidance available to explicitly address required seismic performance of
a TEB structure. FEMA P646 (2008) recommends that such structure be designed to
meet Immediate Occupancy performance (as defined in ASCE/SEI 41-06 Seismic
Rehabilitation of Existing Buildings) for the Design Basis Earthquake (DBE) and Life
Safety performance for the Maximum Considered Earthquake (MCE). However, we feel
that this recommended performance requirement couldn’t guarantee the usability for a
tsunami if the building experience significant structural damage at the MCE level, with
inadequate lateral resistance for a tsunami. A building that experiences substantial
structural damage or out of plumb may be considered as Life Safe. However, it can not be
re-usable without substantial repair.
To make evacuees feel comfortable entering the TEB and remaining in the structure
during the aftershocks, the structure is expected to remain plumb with limited structural
damage (especially near stairs and ingresses) that does not require any repair work prior
to being occupied. Since a tsunami evacuation building is expected to remain functional
and perhaps, be used for emergency response and/or medical care for a period of time, it
is important to have higher-level performance of nonstructural components with limited
damage. For the TEB, we feel that it is more appropriate to design the building to meet
Immediate Occupancy performance level for the MCE event. As part of the design
process, it is essential to perform verification analyses to ensure the performance
objective is met using available performance-based earthquake engineering techniques
such as ASCE/SEI 41-06.
Structural System and Design Consideration
Seismic Design Consideration
There are several structural systems founded on deep piles that can achieve the required
seismic performance and allow tsunami debris to flow through at the lower levels and
keep the hydrodynamic loads to a minimum: steel frames with dampers, post-tensioned
reinforced concrete frames [Figure 4-1(a)], and post-tensioned concrete shear walls
[Figure 4-1(b)]. The post-tensioned reinforced concrete frames and post-tensioned
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concrete shear walls rely on the post-tensioning tendons to re-center the structure to its
pre-earthquake position. When properly designed, the building with these systems tends
to have limited residual displacement even for the MCE event. Since the steel structure
is more prone to corrode in the coastal environment, post-tensioned concrete frames or a
combination of concrete frames with concrete shear walls parallel to the direction of
anticipated tsunami flow are more suitable for the TEB, and also compatible with the
planned function at the ground level of either parking or farmer’s market.
(a) Post-tensioning hybrid concrete frame (Sritharan et al. 2000)
(b) Post-tensioning concrete shear wall (Restrepo and Rahman 2007, Scheottler et al
2009)
Figure 4-1 Lateral-force Resistance Systems
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Figure 4-2 shows a conceptual layout of lateral-force resistance system for the Cannon
Beam TEB. It is expected that the site would likely experience liquefaction during the
seismic shaking, which could result in differential settlement of ground soil. Also,
significant scouring due to tsunami is likely to occur at the site. To minimize the
undesirable effects of liquefaction induced differential settlement and scouring on
structural system, pile foundation is recommended as shown in Figure 4-3 to support the
columns of both seismic and gravity frames. Pile caps are interconnected with grade
beams and ground slab to ensure lateral forces can be distributed to all the piles.
Figure 4-2 TEB Seismic System Layout: Plan view
Figure 4-3 Typical Post-tensioning Concrete Frame Elevation
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Tsunami-Resistant Design Consideration
The concrete columns in the lower level are designed with circular cross-sections to
minimize hydrodynamic loads and impact loads associated with waterborne debris.
At the city hall site, the tsunami inundation depth is estimated to range from 6 feet at the
most likely tsunami to 15 feet to 30 feet in rare events. Both the second level and a roof
terrace are planned for refuge. Given the uncertainty involved in the tsunami modeling
and estimate, if the first story height is set unconservatively low, the water run-up could
potentially exceed the first story height, wash away the contents in the second story, and
pose buoyancy and hydrodynamic uplift force on the 2nd floor concrete slab, as well as
the excess moments on the column structures Thus, the design team must exercise care
to properly set the story height for the first story.
The concrete floor framing and slab at the 2nd and the roof levels will be designed to
accommodate refuge live load. The slab to beam connection at the ground and the 2nd
floor levels need to be strong enough to resist any potential buoyancy and hydrodynamic
uplift forces on the slab.
In case that “break away” wood stud walls are used in the building, we will detail the
connections with a fuse at the top and sides to minimize the hydrodynamic loads on the
building structure (Yeh 1997). Due to uncertainties involved in the estimate of impact
forces associated with waterborne debris, the TEB design will incorporate considerations
of the “tie force” strategy and the “miss column” strategy in the design to reduce the
potential for progressive collapse if one column is severely damaged (FEMA P646).
Other Considerations for Post-Earthquake Response
After a major seismic and tsunami event, the city hall is expected to function for relief
and post disaster recovery. It is important to ensure that the nonstructural systems
including ceiling, communication system, fire suppression system, M/E/P distribution
lines and tall furnishings are properly braced to reduce the falling hazards and reduce the
potential for loss of function. Seismic design shall follow the recommendations
contained ASCE 41-06.
Chapter 4 References
1. FEMA, Guidelines for Design of Structures for Vertical Evacuation from Tsunamis,
FEMA P646, June 2008
2. ASCE/SEI 41-06, Seismic Rehabilitation of Existing Buildings
3. Yeh, S.H. (1997). “Behavior of Breakaway Wall,” PhD Thesis, North Carolina State
University, Raleigh N.C.
4. Pampanin, S., Priestley, M.J.N., and Sritharan, S. (2000). “PRESS Phase 3: The FiveStory Precast Test Building, Vol. 3-4 Frame Direction Response”. Report No.
SSRP-2000/08, Department of Structural Engineering, University of California, San
Diego, La Jolla, California 92093-0085.
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5. Sritharan, S., Priestley, J.J.N., Seible, F. and Igarashi, A. (2000). “A Five Story
Precast Concrete Test Building for Seismic Conditions – an Overview”, Proceedings
of the Twelfth World Conference on Earthquake Engineering, Auckland, New
Zealand, Paper No. 1299.
6. Schoettler, M., Belleri, A.,Zhang, D., Restrepo, J., and Fleischman, R. (2009).
“Preliminary results of the shake-table testing for the development of a diaphragm
seismic design methodology”, Winter, PCI Journal, pp.100 –124.
7. Restrepo, J.I., and Rahman, A. (2007). “Seismic Performance of Self-Centering
Structural Walls Incorporating Energy Dissipators,” Journal of Structural
Engineering, Vol. 133, No.11: pp. 1560-1570.
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Chapter 5 Geotechnical and Scour Considerations
Marcella M. Boyer, P.E., G.E.
Introduction
This chapter summarizes the deep foundation, earthquake and tsunami considerations for
the proposed Tsunami Evacuation Building (TEB). Residual liquefaction, caused by
cyclic shear stress and momentary liquefaction (enhanced scour) are defined. Tsunami
scour issues are discussed.
Deep Foundation Considerations
Subsurface conditions on the site of the existing Cannon Beach City Hall are not
specifically known, but we have reviewed geotechnical engineering reports from nearby
sites. The reports from nearby sites show variable layers of subsurface soils. The
subsurface soils generally consist of fill underlain by layers of silt with varying amounts
of clay and organics, gravel and sand. The layering is generally not similar between
borings. Perched groundwater could be present at depths as shallow as 6 feet. Static
groundwater can be present at depths as shallow as 13 feet based on nearby well logs on
file with the state, although it has been encountered at depths as deep as 30 feet.
The highly variable subsurface conditions reported in the vicinity are typical of coastal
lagoon, fluvial and shoreline alluvial deposits. Therefore, it would not be appropriate to
extrapolate the subsurface conditions due to likely rapid lateral and vertical subsurface
changes. Current thought is that the fill under the TEB location may be thicker than
adjacent sites because of the possible presence of a preexisting drainage that has been
filled. The depth of the fill will be unknown until borings can be advanced at the
proposed building location. Regardless of the thickness of fill at the site, it is our opinion
that deep foundations will be necessary for the TEB that is proposed for Cannon Beach
because of the potential ground response to a Local Cascadia Subduction Zone (CSZ)
Earthquake. The foundations would need to extend into firm material below anticipated
seismic (residual) liquefaction and/or enhanced scour depths. The firm material could
consist of dense beach sand, consolidated dune sand, dense gravel or bedrock or the
Quaternary Marine Terrace Deposits that are mapped in the area.
Many of the concrete structures survived the tsunami inundation in the 2004 Sumatra
Tsunami. Therefore, we recommend deep concrete foundations be used for the TEB.
Deep foundations are necessary so that uniform support for the structure is provided
during and after a local earthquake and during an after both the distant and local tsunami
event. Integrated grade beams could be added to create a stiffer system that better resist
earthquake ground shaking.
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Earthquake Considerations
A Local CSZ Earthquake (up to Mw = 9) would create high lateral soil forces on the
foundations and residual liquefaction of the underlying saturated loose to medium dense
sand/silty soils. Residual liquefaction occurs when saturated deposits of loose to medium
dense, cohesionless, sands and silts, are subjected to strong earthquake shaking. If these
saturated deposits cannot drain rapidly during cyclic loading, there will be an increase in
pore water pressure. With continuing oscillation, the pore water pressure can increase to
the value of the overburden pressure. The shear strength of a cohesionless soil is directly
proportional to the effective stress, which is equal to the difference between the
overburden pressure and the pore water pressure. Therefore, when the pore water
pressure increases to the value of the overburden pressure, the shear strength of the soil
reduces to that of a liquid (zero), and the soil deposits turn to a liquefied state. Dynamic
total and differential settlement would occur as a result of liquefaction. Deep foundations
could be used to extend below the depth of the liquefied soil. Ground improvement
techniques such as excavation and compaction, in-situ ground densification, grouting,
deep soil mixing and/or drainage improvements could be used to reduce or eliminate
residual liquefaction and potentially reduce the number and depth of the concrete piles.
Other earthquake hazards include severe ground shaking, lateral spreading and rapid
coastal subsidence. Lateral spreading is the downward horizontal movement of soil
toward a slope that occurs over or within seismically liquefied soil. Coastal subsidence is
defined as a large scale downward movement of the earth’s surface with little or no
horizontal movement. This document does not address these other hazards.
Tsunami Considerations
The TEB could be affected by tsunamis from two sources, but the effect on the structure
and foundation would be similar. One tsunami source would be the one that occurs
because of the Local CSZ Earthquake. In this case, the potential tsunami inundation
could occur within a several minutes after the CSZ Earthquake. The second tsunami
source would be a distant earthquake that occurs far away from the Oregon Coast without
any local earthquake effects. Localized tsunami scour and enhanced tsunami scour
would occur for both tsunamis. Deep concrete foundations would extend below the
anticipated scour depth.
Tsunami scour is different from scour from other types of wave action. The wave period
is long (a few to tens of minutes), the event duration can be 3 hours or longer, and the
inundation height could be as high as 10 meters (30 feet) or higher depending on the
location with an extreme pore water pressure gradient. The energy from a tsunami event
is classified as extreme.
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Tsunami Scour Issues and Depth Estimation
Tsunami scour depth is difficult to predict because of the many variables that govern the
scour mechanism. The key governing parameters are local geography, flow direction and
velocity, the number of piles, the shape, alignment and size of the piles and properties of
the soil around the pile. Other factors include the depth of the surge, the proximity to the
shoreline and wave breaking height. Current codes (ASCE 7-05) give consideration to
scour, but do not provide guidance for calculating the depth of scour.
The Coastal Construction Manual (FEMA 2000) recommends localized tsunami scour be
estimated as a percentage of still water depth (wave height) relative to soil type and
proximity to the shoreline. However, it is evident that floodwater velocity strongly
affects scour depths as summarized in the EERI/FEMA NEHRP 2006 document. See
Figures 5-1 and 5-2.
Rapid Retreat of
Tsunami Wave
Ground
Surface
Figure 5-1. Tsunami Scour. Tsunami runup height =
4.1 m, Inundation depth = 0.95m above the floor;
Scour depth = 1.2m. Photo provided by Harry Yeh.
Area of
Enhanced Scour
Figure 5-2. Enhanced Scour Sketch produced by Marcella
Boyer, P.E., G.E.
Momentary liquefaction (enhanced scour) occurs at the ground surface because the
saturated soil is easily transported as a liquid. Studies have shown that enhanced scour
can occur at the end of wave drawdown (wave retreat). During and after wave
drawdown, the pore water pressure gradients in the near surface soil increases and
momentary liquefaction can occur. Momentary liquefaction occurs with the rapid
reduction in total vertical stress (loss of wave height) in a soil saturated by water
inundation. The shear strength of the saturated soil reduces to zero and the soil behaves
like a liquid.
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Scour can be reduced by placing gravel, rip rap and/or concrete around the piles. Wave
deflection and energy dissipation could also be used to reduce scour.
Chapter 5 REFERENCES
2007 Oregon Structural Specialty Code, based on the 2006 International Building Code
deGroot, M.B., Bolton, M.D., Foray, P., Meijers, P., Palmer, A.C., Sandven, R., Sawicki,
A., Teh, T.C. “Physics of Liquefaction Phenomena around Marine Structures”, Journal of
Waterway, Port, Coastal, and Ocean Engineering @ ASCE, July/August 2006, pages 227
to 243
EERI/FEMA NEHRP 2006 Professional Fellowship Report, Tsunami Inundation Scour
of Roadways, Bridges and Foundations, Observations and Technical Guidance from the
Great Sumatra Andaman Tsunami
“Engineering Geologic Map of the Cannon Beach Quadrangle, Oregon”, State of Oregon
Department of Geology and Mineral Industries, 1972
FEMA 55: Coastal Construction Manual, “Principles and Practices of Planning, Siting,
Designing, Construction, and Maintaining Residential Buildings in Coastal Areas”, Third
Edition, May 2000
FEMA P646: Guidelines for Design of Structures for Vertical Evacuation from
Tsunamis, June 2008
Fuminori, Kato, Tonkin, S., Yeh, H., Sato, S., Torii, K., “The grain-size effects on scour
around a cylinder due to tsunami run-up,” ITS 2001 Proceedings , Session 7, Number 724, pages 905 to 917.
Minimum Design Loads for Buildings and Other Structures, ASCE 7-05
Seed, R.B., Cetin, K.O., Moss, R.E.S., Kammerer, A.M., Wu, J., Pestana, J.M., Riemer,
M.F., Sancio, R.B., Bray, J.D., Kayen, R.E., and Faris, A., “Recent Advances in Soil
Liquefaction Engineering: A Unified and Consistent Framework,” 26th Annual ASCE
Los Angeles Geotechnical Spring Seminar, Keynote Presentation, H.M.S. Queen Mary,
Long Beach, California, A[ril 30, 2003.
“Tillamook Head Quadrangle, Oregon-Clatsop Counties, 7.5 Minute Series” United
States Department of the Interior Geological Survey, 1949
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Tonkin, S., “Pore-Pressure Prediction of Fluidization and Scour,” Power point
presentation for the International Workshop on Fundamentals of Coastal Effects of
Tsunamis, Hilo, HI, December 26 to 28, 2006
Tonkin, S., Yeh, H., Fuminori, K., Sato, S., “Tsunami scour around a cylinder”, Journal
of Fluid Mechanics, Volume 496, pages 165to 192, 2003 Cambridge University Press
Witter, Robert C., “Prehistoric Cascadia tsunami inundation and runup at Cannon Beach,
Clatsop County, Oregon,” State of Oregon, Department of Geology and Mineral
Industries Publication O-08-12, 2008
Yeh, H., Robertson, I, Pruess, J., “Development of Design Guidelines for Structures that
Serve as Tsunami Vertical Evacuation Sites,” Washington Division of Geology and Earth
Resources, Open File Report 2005-4, November 2005
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Chapter 6. Tsunami Simulator for Cannon Beach
Harry Yeh, Oregon State University, and Tim Fiez, The Gartrell Group
An integrated simulator will be developed to evaluate the effectiveness of the planned
City Hall/TEB on the existing Cannon Beach City Hall site. In addition to evaluating the
effectiveness of TEB, the simulator will be used as a tool to improve both warning
systems and evacuation tactics for the City of Cannon Beach.
Tsunami Scenarios Simulations
A scenario simulator has been developed to support rational tsunami hazard and
vulnerability analyses. The simulator integrates three modules: 1) hydrodynamic
numerical simulation of tsunami propagation and runup, 2) warning transmission
simulation, and 3) evacuation simulation. Although the hydrodynamic simulation is
deterministic, the other two components are probabilistic.
Hydrodynamic simulation models for tsunami generation, propagation, and runup have
been used often in practice (e.g., Titov & Synolakis, 1998; Lin, et al., 1999; Imamura,
1996). While the numerical algorithm itself is considered adequately accurate (e.g. Yeh,
et al. 1995), it remains difficult to determine practical tsunami-source conditions.
Fortunately, Oregon has just completed a thorough investigation to estimate the most
credible tsunami source for the Cascadia events; their study is an extension a previous
study (Priest, 1997) coupled with geological paleo-tsunami deposit data (Priest, 2008).
Furthermore, Zhang and Baptista (2008) have conducted detailed numerical simulations
specifically for the inundation in Cannon Beach. Hence, this best suitable numerical
output data will be utilitzed for the development of the scenario simulator.
The warning transmission module models both official (“broadcast”) and informal
(“contagion”) processes. The informal network (person-to-person oral communications)
is the primary method of warning transmission, since official warnings (processed by
government authorities and transmitted by loudspeakers, route alert vehicles, radio, and
TV) are relatively slow in responding to a locally generated tsunami and might be totally
destroyed by the earthquake causing the tsunami. In the model, informal communications
are controlled by four parameters: 1) the number of households, 2) the distances among
households, 3) the delay in initiating contact, and 4) preferential contacts . The
preferential contacts are based on a probabilistic biased network model (e.g. Rapoport,
1979; Fararo,1981; Skvoretz, 1985). In addition, there are control parameters
distinguishing “normal” days from those with stressed conditions during disasters. For
example, the number of contacts is larger during disasters, the communication distances
between contacts are shorter, and the preference parameter is weaker. A majority of
control parameters must be determined based on demographic data. Fortunately, thorough
collections of such data are available for Cannon Beach (Wood, 2007),. Additional
parameters control the loudspeaker warning system (loudspeaker locations, audible
distances, audience share, announcement frequency, and timing), route alert vehicles such
as police cars and fire engines (routes and speeds, dispatch timing, audible distance, and
audience share), and radio/television (audience share, announcement frequency, and
timing).
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Evacuation simulation is modeled in two steps: 1) individuals’ decision-making and
preparation processes for evacuation, and 2) the actual evacuation process. The first step
reflects:
• the number of repeated warnings received (and from which channels)
• evacuation actions taken by neighbors and friends
• location of the household
• prior knowledge and/or experience of tsunamis
• time to evacuate after the decision is made
. The current model only simulates the evacuation of individuals moving on foot toward
the closest shelters or high ground, but other evacuation methods (e.g., motor vehicles)
and potential setbacks (road blockage, bridge failure, etc.) can be incorporated in the
simulator in the future.
The integrated simulator uses a GIS framework to produce an animation of the tsunami
runup (typically occurring in multiple waves), warning transmission patterns, and
individuals’ protective responses. Figure 6-1 shows how the components interact. To
evaluate the overall outcome, the program determines 1) the number and spatial
distribution of households receiving a warning, 2) the temporal distribution of those
warnings, 3) the cumulative effects of informal communication (oral and telephone)
patterns, and 4) number of casualties. Tsunami fatalities in the simlulations are
determined with a newly developed casualty model (Yeh, 2009) that is based on whether
a person can remain standing within the tsunami flow, with the considerations of age and
gender differences. Figure 6-2 shows an example of the animated display for the scenario
simulator.
As stated earlier, the development of the tsunami scenario simulator will not only provide
quantitative evaluations for the effectiveness of the Cannon Beach tsunami shelter (i.e.
reduction in casualties), but will be useful in identifying the effects of hazard mitigation
measures (such as seawalls), emergency response resources (e.g., number and capacity of
evacuation routes, locations of tsunami shelters) and emergency response procedures
(e.g., amount of forewarning and routing of route alert vehicles).
Figure 6-1. Schematic representation of the integrated tsunami scenario simulator
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Figure 6-2.
An example of animated tsunami scenario simulation. Note that the
casualty numbers are shown in the upper right corner.
Chapter 6 References
Fararo, T.J. 1981. Biased networks and social structure theorems. Social Networks, 2, 118.
Imamura, F. 1996. Review of tsunami simulation with a finite difference method. In Long
Wave Runup Models (H. Yeh, P. Liu, and C. Synolakis eds.). 25-42.
Lin, P., Chang, K.-A., & Liu, P. L.-F. 1999. Runup and rundown of solitary waves on
sloping beaches, Journal of Waterway, Port, Coastal and Ocean Engineering,
ASCE, 125, 247-255.
Rapoport, A. 1979. A probabilistic approach to networks. Social Networks, 2, 1-18.
Shuto, N. 1986. A study of numerical techniques on the tsunami propagation and run-up,
Science of Tsunami Hazard, 4, 111-124
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Skvoretz, J. 1985. Random and biased networks: simulations and approximation. Social
Networks, 7. 225-261
Titov, V. V. & Synolakis, C. E. 1998. Numerical modeling of tidal wave runup. Journal
of Waterway, Port, Coastal and Ocean Engineering, ASCE, 124(4), 157-171.
Wood, N. 2007. Variations in City Exposure and Sensitivity to Tsunami Hazards in
Oregon, Scientific Investigation Report 2007-5283, U.S. Geological Survey, U.S.
Department of the Interior, 43pp.
Yeh, H. 2009. Gender and age factors in tsunami casualties, Natural Hazards Review
(under review)
Yeh, H, Liu, P. and C. Synolakis, 1996. Long Wave Runup Models. World Scientific,
Singapore.
Zhang, Y., and Baptista, A.M. 2008. An efficient and robust tsunami model on
unstructured grids. Part I: inundation benchmarks, Pure and Applied Geophysics:
Topical issue on Tsunamis (in press).
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Chapter 7 Next Steps
This preliminary white paper includes conceptual design concepts for the future Cannon
Beach City Hall TEB. It provides the basis for a future feasibility study and case history
that could include subsurface exploration, tsunami evacuation modeling, further
development of the conceptual design to allow for preliminary structural design, further
development of tsunami wave dissipation design, cost scenarios, and more. The goal of
the future studies would be to test the feasibility of a TEB in real situations, which will
better allow coastal communities to understand the many technical, social, design, and
cost implications. This in turn, will allow coastal communities to develop appropriate and
comprehensive tsunami evacuation and mitigation strategies.
A future feasibility study could address a number of major issues involved with
constructing new tsunami evacuation buildings. The results from such a feasibility study
would be useful for any tsunami prone community. These issues, among others, involve:
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Multi-hazard issues, including design level earthquake and design level tsunami
Performance based goals and reliability, including ATC 58 and ATC 64
Scientific uncertainties
Engineering uncertainties
Wave energy dissipation structures, including on and off site structures and
impacts
Multi-use and function issues including livability, including pre- and post-tsunami
functionality
Structures with various footprints, heights, and area
Local zoning issues
Social issues, including evacuation routes and education associated with
evacuation buildings, and protection for vulnerable populations
Design and construction costs
Funding assistance
A feasibility study could include a bracketed range of earthquake design levels, tsunami
design levels, varying inundation heights, and various performance levels on different
soil and foundation types. For example, a building designed for MCE could be evaluated
with inundation heights of 5-10 ft, 10-15 ft, 15-20 ft, 20-25 ft, and 25-30 ft for life safety,
immediate occupancy, and fully operational conditions.
A number of communities in the Pacific Northwest are considering tsunami refuges. A
feasibility study would provide information that would be immediately useful for the
construction of a future TEB demonstration projects.
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Appendix
Ad-hoc Design Team for Cannon Beach Tsunami Refuge
A conceptual design for a new Cannon Beach City Hall that would serve as a community
tsunami evacuation building (TEB) was developed by this ad hoc design team. The
design team includes engineers and architects with expertise in risk management, tsunami
evacuation modeling, structural engineering, geotechnical engineering, wave energy
dissipation engineering, architecture, computer programming and local design
considerations (listed below). The conceptual design for a new tsunami evacuation
building is largely based on the FEMA 646 publication. It will be shared on September
28 and 29, 2009, at a field trip and workshop, which is being sponsored by the Cascadia
Region Earthquake Workgroup (CREW.org) and others.
Jay Raskin, AIA
Co-Leader, Architect and local contact
Ecola Architects, PC
P.O. Box 1160
368 Elk Creek Road, Suite 409
Cannon Beach, Oregon 97110
(503) 436-2162
Fax: (503) 436-0108
www.ecolaarchitects.com
Focus area: Assist Cannon Beach with long term recovery post Cascadia earthquakes and
tsunami. Provide design information so that meet both evacuation and primary functions.
Yumei Wang, PE
Co-Leader, Risk engineer
Oregon Dept of Geology and Mineral Industries (DOGAMI)
800 NE Oregon St., #28 Suite 965
Portland, OR 97232
(971) 673-1551
Fax: (971) 673 1562
www.OregonGeology.com
Focus area: The community is exposed to very high earthquake and tsunami risks from
the Cascadia subduction zone. Strategically located, multi-purpose, tsunami evacuation
buildings is a new aspect of coastal risk management. A City Hall TEB will help reduce
loss of life and allow for continued local response, recovery and rebuilding efforts.
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Marcy Boyer, P.E., G.E.
Geotechnical engineer, site conditions and foundation design concepts (for scour)
Principal Geotechnical Engineer
Chinook GeoServices, Inc.
1508 Broadway Street
Vancouver, Washington 98663
Phone (360) 695-8500
Fax (360) 695-8510
Focus area: Provide information on seismic hazards and foundation design
Tim Fiez, PhD
Geospatial Solutions and Software Architect, tsunami evacuation modeling
The Gartrell Group
107 SE Washington St. Suite 453
Portland, OR 97214
503-235-3579
[email protected]
www.gartrellgroup.com
Focus area: Provide tsunami simulation for Cannon Beach to inform evacuation options
Javier Moncada, EIT
Site engineering structures (wave deflection and energy dissipation)
BERGER/ABAM Engineers Inc.
700 NE Multnomah Street, Suite 900
Portland, OR 97232-4189
Voice 503-872-4100
Direct 503-872-4125
Fax 503-872-4101
Email [email protected]
http://www.abam.com
Focus area: Provide information on tsunami seawall options to reduce wave forces on
structure.
Harry Yeh, PhD
Wave dynamics, Tsunami Expert
Oregon State University
Coastal and Ocean Engineering,
School of Civil & Construction Engineering
Corvallis, OR 97331-3212
Voice: 541-737-8057
Fax: 541-737-3052
http://cce.oregonstate.edu/people/faculty/yeh.html
Focus area: Provide tsunami simulation for Cannon Beach to inform evacuation options
and provide technical oversight.
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Kent Yu, PhD, PE
Structural engineer, performance based building design
Degenkolb Engineers
707 SW Washington St., Suite 600
Portland, OR 97205
Tel: 503-419-4255
Fax: 503-242-1780
E-Mail: [email protected]
http://www.degenkolb.com
Focus area: The building is designed using performance-based earthquake engineering
principles to meet Immediate Occupancy performance objective for the MCE seismic
event. After the MCE event, the building shall retain sufficient lateral strength to resist
forces associated with the 2500-year tsunami.
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