Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

A Comparison between the Dynamic Behaviour of Flexible Dual Row Walls
Founded in Dry and Liquefiable Sands
S. S. C. MADABHUSHI
Research Student, Engineering Department, University of Cambridge, Cambridge, United Kingdom
Email: sm854@cam.ac.uk

S. K. HAIGH
Senior Lecturer, Engineering Department, University of Cambridge, Cambridge, United Kingdom

ABSTRACTThe 2011 Tōhoku earthquake and Tsunami event devastated large parts of the Japanese coastline, causing widespread
damage to infrastructure and claiming many human lives. The dual row wall concept is potentially a robust and efficientsea wall design. However, loss of soil strength and stiffness from earthquake induced liquefaction is a prospective designconcern. Evaluating the resilience of the dual row system to earthquake loading is a complicated soil-structure-interaction
problem even when the walls are founded in dry ground. Further, soil liquefaction fundamentally changes the seismic
wall and soil response. Centrifuge modelling provides an avenue to explore the dynamic behaviour. Dynamic testing of
small scale centrifuge models of the dual row wall systems, founded in dry and liquefiable sands is detailed. Recorded
wall and soil accelerations are considered and the impact of excess pore pressure generation on the shear stresstransmission highlighted. Observable changes in the dynamic shear stress-strain behaviour of the soil rationalise thesystem responses. A modified approach to inferring the wall displacements from the accelerations and discrete
displacement measurements is discussed. Consistency between the results is verified and the differing displacement
modes obtained are considered in the context of the overall soil behaviour.
Key words: Disaster Prevention, Tsunamis, Centrifuge Modelling,

1. Introduction

highlight the integration of the defence into the coastal

1.1. Motivation for Study
The 2011 Tōhoku Earthquake and Tsunami event

scenery and urban infrastructure.

highlighted the importance of Civil Engineering inprotecting coastal communities. In the face of increasingly
extreme natural hazards, both practical solutions fromindustry and rigorous academic understanding is vital toform a globally resilient society.
The Dual Row Wall concept, which offers enhanced
protection against earthquake induced Tsunamis, centres
on implanting two parallel rows of sheet piles into an
existing coastal levee. A soil infill is placed between thewalls and the pile heads connected by tie rods. A
schematic illustration is shown in Fig. 1. Further, thepractical implementation of this system, as constructed by
Giken Ltd. in Kochi Japan is also shown. The photos- 265 -

Fig. 1

Dual Row Retaining Wall Concept and photos of

implementation by Giken Ltd. in Kochi, Japan

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

1.2. Objectives of Investigation
The lateral capacity of the dual row system arises

SF666 are assigned to the dry and saturated tests

from a combination of the strength and stiffness of both

system used in both tests are furnished in Table 1. The

the structural elements and the soil infill. However, theresults presented in this paper represent walls with flexural

evaluation of the dynamic performance of the system isstiffness at the lower end of those which would be usedcrucial to adjudge the resilience of the dual row wallpractically.

system to a combined earthquake and Tsunami event.

understanding of the soil-structure interaction.

respectively. The full prototype dimensions of the wall

This

was

done

to

facilitate

better

The dynamics of the soil structure interaction of thedual row wall system, even in dry sand, poses a significant
academic challenge. There is also additional complexity
added by founding these systems in saturated strata,
particularly if earthquake induced liquefaction can occur.
In this work the results from two dynamic centrifuge
tests are reviewed. The same dual row wall system istested under two cases; firstly founded in a dry sand bed
and secondly in a liquefiable deposit. An overview of themechanisms developed, structural performance and key
design considerations are compared and contrasted
between tests. The unique academic challenges andconsiderations for practicing industry of this potential
coastal defence are summarised.
2. Methodology
2.1. Centrifuge Modelling at the Schofield Centre
Similarity between the soil behaviours of the fullsized dual row walls and the small scale models isachieved using a centrifuge to elevate the model stresses.
The 10 m Turner beam centrifuge (Schofield, 1980) wasused to apply an acceleration of 60 g at a point 1/3 theheight of the dual row wall system. A high power

Fig. 2Centrifuge cross sections of test DF666 (top) and

Earthquake Actuator was used to impart the lateral

SF666 (bottom)

shaking onto the model (Madabhushi et al. 1998 & 2012).
Table 1.

2.2. Model Details, Preparation and Instrumentation
The complete model system was prepared at 1 g with

Details of wall system at prototype scale

Variable

S28 Hostun sand deposited in and around the dual row

Value

Height (m)12Embedment Depth (m)

6

wall

systemusing

anautomatic

spot

pluviator(Madabhushi et al. 2006). Test SF666 was flushed with
CO2 and saturated with 60 cSt fluid under vacuum with aWall Thickness (m)controlled mass flux.

0.18

Bending Stiffness (MNm2 /m)

34

The installation of the wall systems at 1 g means the

Tie Length (m)6construction sequence is not well captured by thecentrifuge models and the initial static conditions not

Fig. 2 presents the cross sections of the tworeadily comparable to the field. However, under moderate

centrifuge tests discussed in this paper and indicates theto large earthquake loading as the soil must tend to therelative density, Id, of the soil. Test identifiers DF666 andsame limit states the dynamic results from the centrifuge- 266 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

models become more analogous to the field case.

motion. By founding the dual row wall system in

The instrumentation in the models shown in Fig. 2liquefiable ground the ability of the soil to transmit shear

includes miniaturized sensors to register the soil and wallstresses has clearly been altered. The altered dynamic

accelerations,

response of the soil may be attributed to the generation ofpressures

in

the

pore

space

and

displacements of the walls.

excess pore pressures and thus a change in the material

It is also important to comment on the different
model containers used. For the dry test a rigid container
with a Perspex front was used to facilitate in-flight
imaging of the model cross section. The use of Duxseal
inserts can effectively minimise stress reflections from theboundaries (Campbell et al. 1991), especially for thelimited lateral deformations generated in dry sand models.
However, for SF666 where liquefaction was expected it
was crucial to use a laminar box where the free laminae
can deform equivalently to the enclosed material.
The following sections consider the results from thetwo tests described. Unless otherwise stated, the results
will be given at the prototype scale and the sign
convention that leftward displacements are positive isadopted. Heights are measured relative to the groundsurface.
3. Results
3.1. Accelerations and Excess Pore Pressures
The accelerations transmitted through the soil are
drastically altered by the presence of a liquefiable soil
layer. Fig. 3 shows the recorded accelerations in the soil
infill between the walls of tests DF666 and SF666. For thedual row wall founded in dry soil, there is a clear
amplification of the accelerations as they propagate
vertically through the infill.
By contrast, the propagation of accelerations in

Fig. 4

SF666 exhibits large attenuations relative to the input

Dynamic Shear Stress Strain Loops from the infill of
DF666 (top) and SF666 (bottom)

behaviour. With due care to the filtering parameters
selected, the dynamic shear stresses and dynamic shear
strains can be calculated from the recorded soil
accelerations (Brennan et al. 2005). In the loops presented
in this work, the lower and upper bandpass limits were
0.4 % and 90 % of the Nyquist frequency.
Fig. 4 exemplifies the changes shown by Fig. 3.
Continued cyclic loading actually results in a stiffening
Fig. 3Comparison of Infill Soil Accelerations between
DF666 and SF666

effect on the dry infill; the dynamic shear strains reducing
dramatically by later cycles. This may be attributed to- 267 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 5

Excess Pore Pressures generated around the right wallin test SF666

shear induced volumetric strains and the locking in of soil
stresses

under

the

prolonged

earthquake

motion(Madabhushi and Haigh, 2018).

It is worth noting that the practical use of thisdefinition with the dual row system is complicated by anumber of factors. The initial vertical stress is calculated

For test SF666, Fig. 4 shows the reduction of theassuming a geostatic distribution caused by the soil’s self-

dynamic shear stresses transmitted but also shows thatweight. Broadly speaking, this correctly implies that thecomparable shear strains are developed. Though thelarge overburden pressure in the infill increases theliquefying soil softens considerably, the system is notresilience of the soil between the walls to liquefaction.

completely isolated from the ground motion and a cycling

However, there is likely a bulb of increased verticalin the dynamic response persists.

stresses below the dual wall system, as well as changes to

To gain further insight, the excess pore pressuresdeveloped inside and outside the right wall in tests SF666

the vertical stresses from the shear stresses applied by thewalls, which should be accounted for.

are plotted in Fig. 5. The generation of large positive

Nevertheless, when comparing the values of theexcess pore pressures leads to a corresponding drop inexcess pore pressures in Fig. 5 with the approximate

effective stresses and thus the ability of the soil to transmit

values needed for full liquefaction a number of trends may

the accelerations. However, there is considerable cycling

be discerned; during the shaking the relative suctionof the excess pore pressures during the shaking whichdeveloped between the walls could help limit the wallhelps rationalise the complex dynamic behaviour of thedisplacements. Externally though the soil tries to liquefy,

soil shown in Fig. 4.

the co-seismic drops in excess pore pressure reveals that

Fig. 5 additionally shows the excess pore pressure

the soil will cyclically regain some strength and stiffness

required for ‘full liquefaction’, based on the excess pore

which could also help reduce the overall wallpressure ratio (ru). The definition in Eq. (1) shows that full

displacements.

liquefaction, corresponding to ru = 1, means the excess

Finally, Fig. 7 offers a comparison of thepore pressure (uexcess) is equal to the initial vertical stressaccelerations measured along the height of a single wall

(σ’v0).

from both tests. The disparity between the soil behaviourof the two tests manifests in quite different structural𝑟𝑢 =𝑢𝑒𝑥𝑐𝑒𝑠𝑠𝜎′𝑣0(1)

accelerations experienced by the walls.
For DF666, both the wall and soil system experience- 268 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Left Wall

Right Wall

Fig. 6

Left Wall

Right Wall

Calculating Dynamic Displacements from Left andRight Wall Accelerations for DF666 (left) and SF666 (right)

amplified vibrations with height. Considering the wall andsoil accelerations together suggests that the system

3.2. Wall Displacement
It is clearly desirable to obtain the total wall

dynamically displaces in a ‘cantilever’ type mode whendisplacement to ascertain the performance of the dual wall

founded in dry sand. Further, the appearance of vibrations

systems. If model containers with Perspex windows canat double the driving frequency gives some clues as to thebe used digital imaging techniques are often the mostrole of the tie rod in enforcing symmetric deformations at

reliable and direct way to obtain the total static andthe heads of both walls.

dynamic deformations. However, when this method is notavailable, such as in test SF666, less direct methods mustbe pursued. The use of a combination of wall acceleration
measurements from MEMS and individual displacement
measurements from LVDTs is now detailed.
The wall accelerations can be double integrated withrespect to time to obtain the temporal displacement
variations. However, this process can introduce drifts in to
the integrated signal which are not physically justifiable
i.e. non-zero velocities at the end of the shaking event. To
remove these, a ‘high-pass’ filter can be applied to theFig. 7Comparison of Wall Accelerations between DF666 andsignals obtained from the integration. This will leave only
the dynamic component of the measured displacements,

SF666

with the removed components being a combination of
From the results of SF666 the partial isolation of thephysically real permanent displacements and unphysicalwall from the ground accelerations is highlighted. The soil

integration drifts.

was softened and moderate dynamic shear strains inferred.

In Fig.

6

thedynamic

component of the

However, the subtly of the co-seismic excess pore pressure

displacements inferred from the wall acceleration

variation could have large implications for the dynamic

measurements in DF666 and SF666 are illustrated. The

displacements that actually accrue, which are now

dynamic distributions shown are at opposite instants ofconsidered.

applied acceleration. Further, it is confirmed that the
dynamic displacement after the shaking ceases is zero.

- 269 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 8Illustration of obtaining an estimate of permanent
relative displacement from a LVDT signal

For test DF666 the results confirm that the dual row

this manner. The time variation of the filtered signal canwall founded in dry sand vibrates in a ‘cantilever’ type

be interpreted as an estimate of the wall displacement thatmode as suggested earlier. It is thus evident that the wall

would persist if the shaking was stopped at that instant.

founded in dry soil will develop flexural bending during

It is therefore proposed that a combination of thethe shaking. However, the results also imply that the wall

recorded accelerations and LVDT readings can produce

toes dynamically displace. The lack of full fixity from themore accurate estimates of the total wall displacements.

soil would reduce the dynamic bending moments induced.

Overall, the permanent components from the LVDT and

By contrast to the dry results, the distributions from SF666

dynamic component from the MEMS can be combined toreveals very small dynamic displacements are generated

give an estimate of the ‘total relative displacement’ of theduring the shaking which also implies the dynamic

walls.

bending moments generated will be small.

Fig. 9 shows the results of the entire process for both

From a structural design outlook, the failure of thetests DF666 and SF666 at two instants during the appliedwall system in bending might not be critical. This is

ground motion and the final configuration after theparticularly likely if the systems are founded in liquefiableshaking ceases. The cantilever vibration mode is thesoil, whereas the total co-seismic and post-seismic

dominant source of displacement in DF666. However,displacements may be of greater concern. The LVDTs

following the end of the motion the walls return to ameasure the total lateral displacement of the walls but atrelatively upright position, though with a small amount of

only a few discrete locations above the ground level.

permanent toe displacements and curvature locked in.

Further, the dynamic response of these instruments is

Further, accounting for the permanent wall displacements

inferior to the MEMS.

shows that the final toe displacements imply relative

The wall displacements obtained from the LVDTs
can be subjected to a ‘low-pass’ filter to give an indication

outward displacement, which is physically reasonable as
the infill settles downwards and outwards.

of the permanent displacement developed co-seismically.

By comparison, the displacement mode from SF666

It was required to zero the values with respect to those

implies moderate toe displacements and much lessbefore the earthquake so the displacements calculated

curvature is developed. The importance of accounting formust be described as the relative permanent displacements.

the total wall displacement in this test is exemplified.

Further, the small error which can arise when using

Though between the tests the wall systems have the same

horizontal LVDTs which are fixed relative to the moving

structural stiffness, relative to the liquefying and thus

laminae (Aversa et al. 2015) was ignored. Fig. 8 illustrates

softening soil in SF666 the system is able to behave more

the decomposition of an LVDT trace from test SF666 in

rigidly.

- 270 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Left Wall

Right Wall

Fig. 9

Left Wall

Right Wall

Calculating Relative Displacements from Left andRight Wall Accelerations for DF666 (left) and SF666 (right)

Nevertheless, the overall magnitude of displacements
for the saturated system are perhaps smaller than expected,

4. Concluding remarks
A combined effort from the academic community andparticularly when it is remembered that the system wasindustrial practice is required to engineer a safer,subjected to prolonged large magnitude shaking. A toe

economical and more environmentally friendly future. In

displacement of 0.2 m on a 12 m wall corresponds to lessparticular, there is a growing need to protect coastal

than a 1° rotation. The complexity of the soil behaviour,

populations from earthquake-induced tsunamis. The

particularly the cycling of excess pore pressures andconstruction of dual row walls represents a complex but

suction developed between the walls as a result of thepotentially lifesaving application of press-in engineering.

shear induced dilation, can limit the total horizontal

In this work, a comparison between the dynamic

deformations that are accrued.

performance of the dual row wall system founded in

However, there is also the potential for verticalsettlement of the dual row wall system when founded on

medium-dense dry sand versus a looser, liquefiable soil
deposit is considered.

liquefiable soils. To obtain an estimate of this, pore

The two dynamic centrifuge tests conducted revealpressure transducers were affixed to the dual row wallinteresting differences between the seismic responses ofsystem. The change of hydrostatic pore pressure before

the two relatively flexible systems. These could have large

and after the ground motion can then be used to back

implications for the practical design of the dual wall

calculate an estimate of the induced settlement of the wall

system in the field.

system. For test SF666, the earthquake motion discussed

Accelerations obtained from the walls and the soil

resulted in an overall vertical settlement of 0.38 m. The

infill show that significant amplifications of the ground

impact of the model dimensions and particularly the

motion can occur. A combination of the dynamic

proximity to the base of the container could have a bearing

component of the integrated wall acceleration data withon the vertical settlement observed. Nevertheless, theboundary conditions provided by the static component ofliquefying system has some in-built resilience against

the discrete displacement measurements was used to infervertical settlement as the overburden pressure from thethe total displacement mode. For the dry wall a ‘cantilever’

infill reduces the extent of liquefaction, as witnessed bytype vibration was observed, though the system developed

the excess pore pressures studied early. Practically, thevery little permanent displacements. The insight offeredpotential impact of vertical settlement on the ultimate

by the dynamic shear stress-strain loops show continued

Tsunami load that could be withstood should be borne incycling results in a stiffening of the soil infill - which may

mind.

be attributed to a combination of the shear induced- 271 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

volumetric strains and ‘locked-in’ soil stresses – and canCentrifuge.

explain the resilience of such systems.

Modelling in Geotechnics 12 (2), pp 77-88.

International

JournalofPhysicalWhen founding the dual row wall system in a

Madabhushi, S. P. G., Houghton, N. E. & Haigh, S. K.

liquefiable soil there is a greater tendency for toe

2006. A new automatic sand pourer for model

displacement of the walls and the excess pore pressure

preparation

generation leads to observable drops in the stiffness of theProceedings of the Sixth International Conference on

soil. However, the accumulation of wall displacement is

Physical Modelling in Geotechnics, Hong Kong, pp.

restricted by the complicated shear induced cycling of

217–222. Taylor & Francis.

atUniversityofCambridge.

In

excess pore pressures. In this regard, the performance ofMadabhushi, S. S. C and Haigh, S. K. 2018. Measuring

the flexible dual row wall system founded completely in a

the behaviour of dual row retaining walls in dry sandsliquefiable ground is also shown to be quite resilient tousing centrifuge tests, 9th International Conference onlarge cyclic ground motions.

Physical Modelling in Geotechnics 2018, London.
Schofield,

5. Acknowledgements
The authors are grateful for the collaboration with
Giken Ltd, and in particular wish to thank President
Kitamura, Mr Ishihara and Ms. Ogawa for their insightfulcomments and discussions during this research.
References
Aversa, S., de Sanctis, L., Maiorano, R. M. S., Tricarico,M., Viggiani, G., Conti, R., & Madabhushi, S. P. G.
2015. Centrifuge modelling of retaining walls
embedded in saturated sand under seismic actions.
Experimental Research in Earthquake Engineering,pp. 543-562.
Brennan, A. J. N., Thusyanthan, I. & Madabhushi, S. P. G.
2005. Evaluation of Shear Modulus and Damping in
Dynamic Centrifuge Tests. Journal of Geotechnicaland Geoenvironmental Engineering 131 (12), pp.
1488–1497.
Campbell, D. J., Cheney J. A., & Kutter, B. L. 1991.
Boundary effects in dynamic centrifuge model tests.
In Centrifuge 1991: Proceedings of the International
Conference Centrifuge 1991, Boulder, Colorado, pp.
441–448. A.A. Balkema.
Madabhushi, S. P. G., Schofield, A. N. & Lesley, S. 1998.
A new Stored Angular Momentum (SAM) based
earthquake

actuator.

In

Proceedings

of

The

International Conference Centrifuge ’98, Tokyo,
Tokyo, Japan, pp. 111–116.
Madabhushi, S. P. G., Haigh, S. K., Houghton, N. E. &Gould, E. 2012. Development of a Servo-Hydraulic
Earthquake Actuator for the Cambridge Turner Beam

- 272 -

A.

N.

1980.

Cambridge

GeotechnicalCentrifuge Operations. Géotechnique. 30 (3), pp.
227–268