Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanRESTORATION POST MARCH 11 2011
EARTHQUAKE
Lian Ching OH
Director, Ground Anchorages Limited (NZ)
Auckland, New Zealand, lianchingoh@yahoo.com.sg

ABSTRACT: The destruction caused by recent earthquakes has indicated that thereconstruction of residential dwelling in particular needs to include the provision ofprotection against liquefaction and tsunami induced damages while maintaining andimproving the protection against ground motion induced damages. This can be achieved
by designing a foundation system with the desire engineering properties of high integrity,
ductility, bending moment and buoyancy to counter earthquakes and it’s after effects.
Key Words: Great East Japan earthquake, earthquake engineering, protection against
seismic motions, liquefaction and tsunami, buoyant foundation

1. INTRODUCTION
The large scale destruction of residential dwellings due to liquefaction and the high fatality caused bytsunami posed formidable challenges to the restoration of the earthquakes affected areas. The need ofrestoration is inevitable. It is expected to be urgent and massive. The ability to improve the resilienceof future dwelling against the forces of earthquakes is crucial for the restoration. This breakthrough isextremely far fetching and has high desirable multiplying effect. It includes the ability to carrying out
the restoration on those sites affected without the need to relocate. This as such ensures the restoration
can be executed in a prompt and economical manner. These are the most crucial properties of apotential solution for the restoration.
It is indeed ambitious to design a foundation system such that it has the resilience against groundmotion, shall remain serviceable during liquefaction including lateral spreading and during tsunami it
maintains the very basic function of protecting life by being waterborne. With the progress inengineering particularly geotechnical engineering, the ability to design and create such foundation
system is achievable. It is as such high time that segmental construction technique, post tensioning andbuoyancy be introduced to create the needed resilience of residential dwelling against the forces ofearthquakes. This solution allows the basic function of a dwelling which is to provide shelter andsecurity to be reclaimed back after it was completely destroyed by the recent earthquake.

2. DESIGN CONCEPT
To manage the forces of earthquakes which are randomly propagated, an isotropic three dimensional

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foundation system is required. The depth of the foundation system shall be large. (A 1.2m depth could
be adopted. This is about four times larger than the depth used by conventional raft footing.) The
possible dimensions of each segment could be 3mx2mx1.2m deep, 4tons in weight, as shown.
Reinforced concrete layer

Polystyrene block as in fill

Z

Y

Ducts for steel tendonsX

View of reinforced concrete segment in three dimension

Possible dimensions of RC segment of foundation system

Ducts for steel tendons
Polystyrene block as in fill

Reinforced concrete layer
Reinforced concrete hunch

Z

Z
Y

2000

1200

3000

X

Fig 1-Cross section, X axis

Ducts for steel
tendons
Polystyrene blockas in fill
Reinforced concrete hunch

X Y Reinforced concrete layer

Fig 2-Long section, Y axis

The foundation system must be packed with the desirable properties of high integrity, ductility,
bending moment capacity and buoyancy. To design and create these properties segmental construction,
post tensioning and buoyancy shall be utilized in total combination. As implied, manageable
reinforced concrete (RC) segments are used as the basic building elements. The steel tendons are
utilized to bind these segments into a robust integral three dimensional foundation system.
Since RC has high compressive strength, and extremely poor in tensile strength, the steel tendons
provide the much needed tensile strength in the foundation system. By installing the steel tendons inboth axes of the top and bottom edges of the RC segments, an isotropic three dimensional foundation
system is formed.
This arrangement of the steel tendons is efficient in stress transfer. As such the stress in the steel
tendons can be kept low to form a compressed foundation system. While it maintains all the RC
segments in a compressed state in both axes to minimize the formation of cracks in the RC segments,
it maintains the flexibility for the segments to rotate to counter imposed loads.
Since the earthquakes loads are dynamic and as such temporary in nature, the stress in the steel
tendons shall return the RC segments back to its original compressed state.
With large depth and the steel tendons located in extreme edges, it creates the large effective leverarm required for the development of high bending moment capacity. Similarly the installation of thesteel tendons in both axes creates high torsion capacity.

18832.1 Management of ground motion
With depth, the foundation system has large surface area to distribute any axial force imposed on thesystem. Since stress is inversely proportional to area, this foundation system has the capability tominimize the buildup of axial stress.
Combining the high bending moment and torsion capacity in both axes, it provides the foundation
system the three dimensional resilience against ground motions in any direction. The ability of thefoundation system to mobilize as one complete integral unit further provides resilience against groundmotion induced forces.
Base isolators in the form of compressed spring shall be installed between the foundation and thestructure of the dwelling to isolates the dwelling from the force of ground motion. Similarly energy
isolators in the form of a combination of lead (metal) and rubber could be incorporated verticallybetween the segments of the foundation. This is particularly desirable in the longitudinal direction tofurther facilitate movement and rotation within the foundation system if the need arises.

System in acompressed state

Tendons stressedto bind segments
together in X axis

Baseisolators

System has equal bending
moment capacity Mx for
top and bottom edges

Anchor
head

Mx
Z
Y

Steel tendons
X

Mx

System has the flexibility to rotate Rx

System in a compressed stateRx
Fig 3- Compressed cross section in X axis

Tendonsstressed
to bindsegments
togetherin Y axis

Z

Y
X

System in acompressed
state

System has equal bending
moment capacity My for
top and bottom edges

Ry

Base
isolators

My

Ry

My

Ry

Ry

My compressed stateMy

Anchorhead

Steeltendons

System has the flexibility torotate Ry bothways

System in a

Fig 4- Compressed long section in Y axis

2.2 Management of liquefaction including lateral spreading
As the load bearing capacity of the sub-grade foundation diminishes during liquefaction, the highmoment capacity of the foundation system in both axes has the ability to bridge across unevensettlement beneath, thus ensuring the redistribution of the stresses.

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The use of sand as
backfill is desirable as it
has the capability tooccupy voids readily.
This allows the system
to response tosettlement besides theability of the system torotate.

Segments shall rotate
to accommodate lateral
spreading
Rx

Z
Y

X

Fig 5- Lateral spreading in X axis

For severe settlement thefoundation system rotates toaccommodate theredistribution of stresses.
Though the system has highdegree of tolerance, it canbe reinstated by the utilizing
the buoyancy of the system
if the need arises.

Lateralspreading

The integrity and the bending moment capacity of the foundation system further ensure that thedwelling remains intact when lateral spreading occurs in any direction.
To minimize self load, the outer reinforced concrete layer of the segment is kept just sufficient tocomply with the engineering code of practice which is possibly 60mm in thickness. As the raftsegment is constructed cuboids’ in shape, it provides stiffness to the segment even though the outerreinforced concrete layer is thin. The segment could be further stiffened by hunching the edges andintroducing ribs if required. Each segment shall be cast with a large block of polystyrene embedded toperpetually secure the buoyancy.
Further protection again liquefaction could be derived by incorporating a layer of granular fill(propose minimum 500mm) wrapped with geo-membrane beneath the foundation. The geo-membrane
while acts as a separation layer maintaining the granular fill intact during liquefaction, further
regulates settlement as well.
The void that is secured in the granular fill by the geo-membrane allows the dissipation of porewater pressure. By incorporating large pipe culverts adjacent to the granular fill the pore waterpressure could be dissipated into the atmosphere in a desire direction and location. This provision ofdissipating the pore water pressure by filtration minimized the movement of the fine soil particles.
This as such minimized settlement once liquefaction subsides.

Embankment
Sand asback fill

Z
Y

Steel tendons to be post tensioned
Polystyrene blocks embedded
Clearance for maintenanceAnchor head
Base isolators
to lock offsteel tendons

Sand bedding layer
Perforated sub soil drain
Granular sub grade layer
wrapped with filter membrane
Wet pond lining if requiredX

Fig 6- Cross section of granular fill in X axis

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2.3 Protection against tsunami

The buoyancy of the foundation system ultimately maintains the most important basic function ofprotecting life during tsunami as it can act as pontoon to allow the dwelling to be waterborne as one
complete integral unit.

Pyramidconfiguration forstability of structure

Expected draft
required forstructure to bewaterborneZYX

Fig 7- A pyramid configuration for stability

This provides the old and handicapped in particular a chance to survive tsunami. As the magnitude
and direction of tsunami are random, it is desirable to secure the stability of the whole structure forturbulent uplift and when waterborne. By configuring the foundation system and the structure of thedwelling in a pyramid configuration it perpetually secure the low centre of gravity, thus ensuringstability at all times.

3. CONSTRUCTION TECHNIQUESThe ease of constructing and achieving the thin outer reinforced concrete layers of the raft segments
within close tolerance requires attention. While it ensures the uniform distribution of load in thesystem, it allows the ease of assembling the raft segments together.
3.1 Preplaced Aggregate Grout for Concreting of raft segments

In order to achieve the close tolerance required, the concreting of the raft segments can be carried out
by the “Preplaced Aggregate Grout” method. This construction technique is similar to the grouting
operation used in the ground anchor construction, grouting by tremie or pumping grout at the base.
The possibility of carrying out the operation in a closed form system allows all the form panels to becompletely locked together. As the placing of the grout is carried out under pressure, it is in otherwords self compacting. Vibration is introduced mainly to overcome the surface tension of the grout.
This as such allows the production of the raft segments with the desired tolerance to be achieved
readily with minimum construction skill. Large scale reconstruction with the participation of the local
construction communities which is desirable is feasible. The consumption of cement fines however is
expected to be twice the amount required as compared to the conventional concrete mix.
3.2 Assembling of the raft buoyant segments

As the raft segments slide together when tensioning is carried out, it is desirable to execute theassembling operation on a layer of sand bedding as leveling is achieved readily. The self compacting
property of sand underwater further facilitates maintenance if the need arises. Utilizing the buoyancyof the raft segments for the assembling operation could be a convenient alternative.

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Extending this concept further, the cast-in-place technique could be exploited where all the raftsegments are cast right at the location where the dwelling is to be finally constructed. These raftsegments shall subsequently be floated for the jointing operations. The assembled foundation systemshall be lowered into position by dewatering. This minimizes the handling of the raft segments. In
situation where machineries are limited and costly particularly in rural and remote areas, this could bean effective option.
3.3 Post tensioning of the raft segments

Besides the vertical location of the steel tendons, the horizontal spacing and thickness of the reinforced
concrete segment are the other equally important factors influencing the stressing required.
The spacing of the steel tendons further influences the design of the anchor head that is required
for the steel tendons to be locked off.
Since this is an external tendon system, the maintenance and replacement of the steel tendons is
feasible. This facility allows the life span of the foundation system to be prolonged. To provide
protection and minimize stress relaxation, the steel tendon is to be grouted after stressing. It is
desirable that the stressing operation be executed in unison to ensure even stress distribution.
The influence of the stressing can be conspicuously shown in the force diagrams.

TensionForce
in steeltendons

RC segment

Z

Compression

Compression

RC segment

TensionThe RC segments are in a total
compressed state once the system is post
tensioned. This is ideal as it minimises
the formation of tension cracks which is
detrimental to the segments.

The steel tendons are equally stressed tocreate an isotropic three dimensional
foudation system. The stress is kept low
just sufficient to maintain the RC
segment in a compressed state

Force
in RC
segments

YX

Fig8-Long section, forces in system in post tensioningForce
in steel ZYtendonsX

RC segment

RC segment

Ry
Ground motion

TensionMy

As for the RC segments
the top edge relaxes andthe bottom edge further
compressess

Compression

Compression

TensionAs the system rotates upward
the top steel tendons arefurther tensioned whereas thebottom tendons relaxes

Force
in RC
segments

Fig 9-Long section, forces with imposed ground motion load

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As for the RC segments
the top edge further
compresses and thebottom edge relaxes

RC segment

RC segment

Z
Force
Y
in steeltendons X

TensionRy

Compression

Compression

TensionAs the system rotates
downward the top steel
tendons relaxes whereas thebottom tendons are further
tensionedMy
Liquefaction

Force
in RC
segments

Fig 10-Long section, forces during liquefaction

3.4 Backfill the foundation system with sandThe use of sand to backfill and surround the RC segments are highly recommended. It allows easy
maintenance, assists uplift during tsunami and settles responsively to fill up voids during lateral
spreading. It could be further capitalized to monitor the presence or the level of water in thefoundation system.

4. ADVANTAGES OF THE FOUNDATION SYSTEM

The foundation system as designed and configured allows other benefits to be further derived andexploited. Some of these benefits are as follows:
4.1 Connection of foundation to structure of dwelling

It is expected that the weight ratio of the foundation system to the structure of the dwelling is about
4:1. This allows the connection of the structure to the foundation to be further explored with thepossibility of further increasing the integrity and ductility. This is particular desirable if a tsunami
shelter is required within the dwelling.
4.2 Soil investigation

The combination of the large depth of the raft foundation system and the broad granular sub grade has
virtually eliminated the need of a comprehensive soil investigation. This allows prompt restoration
besides the desirable economies.
4.3 Foundation system is based on established engineering principles

Since segmental construction, buoyancy and post tensioning are established engineering principles, theadoption of this concept for the restoration could be well received and accepted. Furthermore thefoundation system shall response to any magnitude of tsunami as it utilizes the very basic property ofwater that is buoyancy.
4.4 Constructability of the foundation system

The configuration of the segment can be capitalized such that its self weight is manageable, the1888dimension coincides with the spacing of the joist bearer and stable. This flexibility allows the use ofsmaller and lighter construction equipments.
4.5 Flexibility of the foundation system

The construction concept and the inherent properties of the foundation system provides flexibility
toward maintenance, alteration or expansion of the foundation, reinstatement and re-leveling of thedwelling. The method of reinstating a tilted dwelling is as shown below.

Tilteddwelling

1
Removesand fillOnce settlement occured theentire foundation system acts
to redistribute stress by
allowing the segments torotateRx

2
Flood thefoundation

Z
Y

Settlement or lateral spreadingX

Fig 11a- Remove sand fill and flood the foundation

3
Once sufficientwater is introduced
beyond the draft
depth the foundation
shall be buoyant

Once in suspension the whole
foundation system begins toself adjust to revert back to
the original equilibrium ofprestressed state

Rx

4
Sand shall be
used to reinstate
the level of thefoundation backZ
Y X

Fig 11b- Buoyancy is capitalized for reinstatement.

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5
Dwelling
lowered to
the leveled
foundation by
dewatering

Once the whole structure islowered to a leveled platform,
further rotates occurs. This is
expected as the system revert
back to uniformly distributestress to the sub grade.

6
The foundation
shall be backfilled with sandsubsequentlyZ
Y X

Fig 11c- The system is reinstated by dewatering.

5. DISADVANTAGES OF THE FOUNDATION SYSTEM

The properties of the foundation system have other undesirable effect as well. It is as such appropriatethat these disadvantages be highlighted:
5.1 Limitations of the foundation system

It is noted that a 700mm draft of water is sufficient to mobilize the whole system. As such thisfoundation system needs to be constructed above the required flood level. As the foundation is shallow,
the limit of the gradient of the site suitable for the foundation system needs to be specified to avoid
building on the slip circle.
5.2 Periodical inspection and maintenance of foundation system

There is a need to carry out periodical inspection and maintenance of the foundation system to ensurethat the system maintained its designed properties. This is due to the tendency of corrosion andrelaxation of the steel tendons.
5.3 Possible of pounding and collision during uplifting of dwellings

The utilization of buoyancy of the foundation system to manage tsunami for areas with high density ofresidential dwellings required guidelines on setback as pounding and collision during the uplifting ofdwellings could be as disastrous.

6. PREVIOUS RELATED PROJECTSThis presentation is partly based on past experiences in constructing manageable raft buoyant
segments by shotcrete technique. Crack inhibiting fibers were incorporated into the dry shotcrete mix.
These segments were bound into desirable configuration and used as pontoon for the constructionof dead-man anchor blocks to improve the lateral stability of driven piles which set prematurely. Thesepiles were installed for the restoration of a marina resort damaged during the 2004 Indian Ocean
tsunami.

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.

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The dead-man anchor blocks were subsequently grouted by tremie under water.

7. CONCLUSIONSThe combination of segmental construction, post tensioning and buoyancy could provide a possible
solution for the restoration of particularly residential dwelling in the earthquakes affected areas. With
the resilience against earthquakes introduced into the foundation system there is a high chance of
carrying out the restoration on the site affected without the needs to relocate.
The benefits of the ability to restore the areas affected are extremely desirable. It allows therestoration to be economically and promptly carried out as identifying and developing new sites would
be costly and time consuming. The segmental construction concept allows the use of smaller andlighter construction equipments. It utilizes the basic construction materials. These factors can result in
substantial economies. The possibility of the local construction communities participating in therestoration further adds benefit to the system.
From the socio-economic point of view, it allows the fabric of the society to be restored back tonormalcy for those who survived besides providing the opportunity for the communities to salvage thehistory, landmarks and cultures associated with these places. These are desirable for speedy recovery.
As the pressure for land use increases the encroachment of development and population growth
into those areas that are in the path of earthquakes and it’s after effect is inevitable. This foundation
system as such could provide a solution for the values of these lands to be realized.
Most of all, it is hope that this foundation system which provides the solution to protect andminimize future lost of life due to earthquakes could play a major role in the restoration andreconstruction of the Great East Japan back to its former glory.

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8. REFERENCES

Ben C. Gerwick, Jr. (Second Edition). “Construction of prestressed concrete structures.”
Japanese Geotechnical Society (July 2011). “Geo-Hazards during Earthquakes and Mitigation
Measures”
New Zealand Society for Earthquake Engineering (Second Edition 2007). “Architectural Design for
Earthquakes”.
New Zealand Department Building and Housing, Te Tari Kaupapa Whare (November 2011). “Revised
guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence”.
British Standards Institution BS 8081(1989). “British Standard Code of practice for Groundanchorages”.
RF Warner, BV Rangan and AS Hall, Sydney (1976). “Reinforced Concrete”.
Francis D.K. Ching and Cassandra Adams (Third Edition). “Building Construction Illustrated”.
The Royal Society of New Zealand TeAparangi, IPENZ Engineers New Zealand, Sesoc, New Zealand
Geotechnical Society Inc., New Zealand Society for Earthquake Engineering (2011). “TheCanterbury Earthquakes: Answers to critical questions about buildings”.

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