June 2016 No.72

IDI

Japanese Infrastructure Newsletter

Infrastructure

Development

Institute—JAPANRAKUNA-IVA
A New
New Double-Layer
Double-Layer System
System Wave-Dissipating
Wave-Dissipating Block
Block✓ High stability✓ Excellent durability✓ Big porosity (56.5%)✓ Low life cycle costNghi Son Refinery and Petrochemical Complex (Vietnam)

CONTENTS
Evaluation of Soil Liquefaction Potential by Screw Driving Sounding Test in Residential Areas

2

RAKUNA-IV : A New Double-Layer System Wave-Dissipating Block

5

Infrastructure Development Institute – Japan (IDI)
Suido-cho Bldg, 3-1, Suido-cho, Shinjuku-ku, Tokyo, 162-0811, JAPAN

Tel: +81-3-5227-4107 Fax: +81-3-5227-4109 E-Mail: idi17@idi.or.jp Website: http://www.idi.or.jp/english/00index.htm

Infrastructure Development Institute - Japan

Evaluation of Soil Liquefaction Potential by Screw Driving Sounding Test in Residential Areas
1. Background of Technology Development
Earthquakes are frequent in Japan. In manywith a sample taken from the borehole drilledcases large earthquakes have occurred, we havethrough the SWS test. Then, when the layer ofsuffered liquefaction damage particularly in softthe soil is determined to be a soft sand layer andsandy grounds or reclaimed lands to a greater oralso deeper than underground water level, it islesser extent. Especially after the 2011 Great

regarded as a liquefaction prone layer. When the

East Japan Earthquake caused extremely severe

soil layer is determined to be clayey or shallower

liquefaction damage to houses in reclaimed land,

than underground water level, it is regarded as a

the demand for predicting a liquefaction risk in

non-liquefaction

residential areas has been increasing.

liquefaction risk of ground is estimated throughlayer.

In

somecases,a

In Japan, a liquefaction risk of ground forthe thickness ratio of each layer. As the damage

large buildings is evaluated by estimating factor

caused to houses by the 2011 earthquake wasof liquefaction (FL) using the N value1 of the SPT2

conspicuously large although these investigations

and the fine content of the soil (Fc) taken with thehave been done, much more accurate evaluation

SPT

importantmethods of ground are essential not only forstructures, it may be directly evaluated from theimportant structures but also for residential

resistance of liquefaction (RL) of a soil obtained by

districts. The SDS has the potential to predict a

the results of cyclic undrained triaxial testliquefaction risk by estimating the N value andperformed with the soil. These methods, however,the Fc in a simple way at a low cost.

require too much time and too high cost to

study we carried out, it was verified that the N

investigate residential areas. At present, thevalue and the Fc obtained by the SPT could be

following process is taken to identify the grounddone by the SDS as well. Moreover, RL assessedstrength for the construction of small-sized

by the SDS results was compared with the values

buildings. First, a soil layer is investigated on thefrom the cyclic undrained triaxial tests and thestrength with the Swedish Weight Sounding test

SPT.

sampler.

In

case

of

more

In the(SWS), and classified on soil type and fine content

2. Estimation of Liquefaction Resistance
As

an

index

for

the

assessmentofa“Specifications for Highway Bridge” published byliquefaction risk, the liquefaction resistanceJapan Road Association in March 2012, FL isfactor (FL) is adopted in this report. Based on

defined by RL which can be calculated from the Nvalue and the Fc. It means a risk of liquefaction

1

The N-value provides an indication of the relative densityof the subsurface soil, and used in empirical geotechnicalcorrelation to estimate the approximate shear strength
properties of the soils.

2 Standard Penetration test (SPT) is a common in situ testing

can be verified without a series of high-cost cyclic
undrained triaxial loading tests. When FL isunder 1.0, the soil is regarded to be vulnerable tomethod used to determine the geotechnical engineering
properties of subsurface soils.
June 2016 No.72

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Infrastructure Development Institute - Japanliquefaction. The procedure of calculation is asFL =follows:

R
L(1)

where FL is a liquefaction resistance factor, R is a dynamic

γｄ：an attenuation coefficient of a seismic shear stress ratio in depth

shear stress ratio and L is a seismic shear stress ratio.

direction

R = CW RL

ｋhgL：a design horizontal seismic scale on the surface of ground(2)

where Cw is a correction coefficient of a seismic ground motion

σv：total overburden pressure (kN/m2)

characteristic and RL is a cyclic triaxial strength ratio.

σ´v：effective overburden pressure (kN/m2)

L = g d × khgL ×

σv
σ 'v

γ d = 1.0 − 0.015 x

x ：depth from the ground surface (m)(3)

3. The SDS Testii) Estimation of rod frictioni) Test machine and test method
Photo 1 shows an automatic SDS test machine. It is

In order to estimate torque and a load applied to theso small and simple that even one person can control it.

tip of rod accurately, rod friction was corrected in the

A rod equipped with a screw point is the same as that offollowing procedure during the SDS. Fig. 1 shows thethe SWS. The SDS adopts a monotonic loading system

concept of estimating rod friction. Wa, Ta, Wf and Tf are

where a rod rotates and penetrates constantly while adefined as applied load, applied torque, vertical rod

load is stepwisely increased at each rotation. The loading

friction force and horizontal rod friction torque,

started from 0.25kN of load and then kept on increasing

respectively. Moreover, when a load (W) and torque (T)by 0.125kN up to 1kN. Measured items were torque (T),are defined as values directly applied to a screw point,

total penetration length

the relationships between these loads and torques are(L)defined with the following formulas.

andsettlement

velocity (V). These wereTa = T f + T(4)measured

Wa = W f + W(5)rotation

at

every

rod.

The

of

τh ，ｖ hθ

loading was set back to
the initial condition at
every 25cm of settlement
and this process was
Photo1.SDS machine

made repeatedly. In order
to measure rd friction,

torque was measured immediately after the rod waslifted up by a few cm and rotated.

τv ，Vvτmax , V

Figure 1. Concept of a rods friction

4. Classification of soil using the SDS test
It was attempted to determine some soil

In addition, the relationship between loads andproperties using the result of the SDS. Fig. 2 shows

torque obtained at 25cm penetration is shown in Fig.

the depth distribution of torque obtained at the sites.

3, where data was plotted at two sections of 25cm

June 2016 No.72

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Infrastructure Development Institute - Japan

penetration. According to Fig. 2 and Fig. 3, thewhen W increased in the clayey soil without arelationships were obviously different depending on

frictional angle under the undrained condition of

the types of soil where T increased according as W

loading. Thus, it was concluded that the SDS was

increased in the sandy soil with a high frictional angle.

capable of categorizing soils by using these responses.

On the other hand, it was seen that T didn’t increase
Torque（Nm）
0

20

40

60

80

Borehole

050Earth Fill
Organic clay

1

Sand

4
5
6

T (Nm)

Depth (m)

3

30

Sand

20

y = 3.3998x + 6.4994

10

7

Silt

8

y = 28.177x + 14.822

GL-3.0～-3.25ｍ
GL-7.0～-7.25ｍ

40

2

0

Silt
0

0.125 0.25 0.375

0.5

0.625 0.75 0.875

1

W (kN)

9

Figure 3. Relationships between T and W
compared with Types of soil

Organic clay
10

Figure 2. Torque and Types of soil

Corrected Torque (Nm)Borehole log

5. Test site
Fig. 4 shows the result of SDS tests conducted at

Earth Fillsome sites in Katsushika Ward, Tokyo. It shows thesites are more than 360km far away from theepicenter of The 2011 off the Pacific coast of Tohoku
Earthquake. The soil profile is composed of earth fill

Depth (m)depth distribution of torque obtained at the sites. Test

Sand

from surface to 1.8m depth and sandy fill layer from
1.8m to 3.6m depth. The layer deeper than that isnatural deposited sand from 3.6m to 8.9m overlying athick natural clay layer.

Sandy Silt
Figure 4. The results in Katsushika Ward,Tokyo

6. Estimation of FL using the SDS test
FL was estimated from the proposed equations bypieces of concrete or cobble stones. In Katsushika, theassuming a medium-scale earthquake, called level 1

values of FLSDS were almost the same as thoseearthquake. The example of the SDS result in

obtained from the laboratory test, while these were

Katsushika in Fig. 5. The results of the N value in therelatively different from the values calculated fromlayer from surface to 3.6m depth were omitted fromthe N value.

the graphs, as it contained impurities such as broken
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Infrastructure Development Institute - Japan

Figure 5. Estimated N, Fc and FL values from the SDS test in Katsushika compared with SPT tests and laboratory
test results

From the results, it was cleared that improvement

calculated from the N value and those obtained fromof the estimation accuracy was necessary in thethe laboratory tests. As a result, it indicated that theharder ground where the N value was more than 10.

SDS could estimate a risk of liquefaction as

On the other hand, for the results of the FL around 1,

accurately as the SPT could.

the FLSDS values were the same as both those

7. Conclusions
1) The estimation of RL obtained by the regression

by the SDS as accurately as the SPT, by estimating

analysis using the laboratory test data was more

RL in two ways calculating from the N value andaccurate than the one calculated from the N value

the Fc and using the laboratory test results.

and the Fc, even though there was not many
enough number of data for the estimation.
2) There is a possibility that FL is able to be estimated3) It was shown that the SDS is one of the simplest
methods to investigate a risk of liquefaction
efficiently.

Contact:
Technology developer: Three Parties (One of them)
Joint developers: TOKYO CITY UNIVERSITY, NITTO SEIKO CO., LTD, JAPAN HOME SHIELD CORPORATION
Contact Person: YUSUKE MAEDA, Japan Home Shield Corporation
E-Mail: yusuke.maeda@j-shield.co.jp
TEL: +81-3-5624-1553
FAX: +81-3-5624-2929

June 2016 No.72

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Infrastructure Development Institute - JapanRAKUNA-IV : A new double-layer system wave-dissipating block
1.

INTRODUCTION
A succession of natural disasters such as large

wave, wave-dissipating blocks is one of the essential

typhoons, huge earthquakes, massive tsunami, etc.

prevention measures. Ports and harbors are requiredcauses enormous damage for a great number ofto be completely safe to perform their intended

people. In order to protect national land as well asfunctions Nikken Kogaku Co., Ltd. has developed thehuman life from damage caused by a tsunami or highideal product with technologies to ensure that safety.

2.

Characteristics of RAKUNA-IV
RAKUNA-IV is a new double-layer system of

the hollows provide a habitat for marine organisms.

concrete armor unit which has been researched andSteel molds mainly comprising three side plates

developed in 2007 by Nikken Kogaku. Four hollows

and one bottom plate were used to manufacture thethat RAKUNA-IV has on its surface as unique

RAKUNA-IV concrete units. The central hollow parts

characteristics

andare fabricated into each plate, thus additional special

improve wave dissipating effect. Legs of RAKUNA-IV

methods for assembly/dis-assembly of the steel molds

interlock with hollows ofare not necessary. Therefore, workability of block

adjacent

blocks,manufacturing

prevents

expandingdamage,andimproves

stability

againstwaves.

increaseroughnessdegree

which

is

same

as

a

conventional

TETRAPOD.

of

When porosity is bigger, anumber of required blocks

Fig.1. RAKUNA-IV block

decreases, this means the
big porosity of RAKUNA-IV such as 56.5% can reduce

Photo1. Mold Fabrication

the total cost. Spaces with various shapes created by

3.

Advantage of double-layer system
Initial stability of RAKUNA-IV is about 1.6 times

adaptability with settlement of the soft foundation.

higher than conventional TETRAPOD with the aid

Interlocking of armor units become loose whenof four hollows in mid-section on block surface andsubjected to settlement. When a wave acts on the

hexagonal shape of legs to interlock. Though initialloose section, there is a possibility that original

stability is somewhat lower than that of the typicalstability performance of armor units is lowered.

single-layer

system, the spread of damage from

However, when the settlement occurs, the first layer

external forces on RAKUNA-IV is smaller. For thisin double-layer system follows flexibly to the ground.

reason, double-layer system with RAKUNA-IV has a

It is considered that the interlocking would be

low risk of collapsing for structure in a long term.

maintained because when the interlocking of blocks

Double-layerin 1st-layer becomes loose, blocks in 2nd-layer

June 2016 No.72

RAKUNA-IV

also

has

a

well

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Infrastructure Development Institute - Japansystem enter into the loose section. Even if the shapeConsequently, the life cycle cost which is the mostof breakwater is changed by settlement, it is clear toimportant in infrastructure projects can be reduced

maintain the original stability. Therefore, theby using RAKUNA-IV with high stability anddouble-layer system RAKUNA-IV is considered to

durability.

fulfill the requirement by the self-healing capacity.

Foundation moundPhoto2. Double-layer system

4.

Fig.2. Cross section of double-layer system

Major installation record
Nghi Son Refinery and Petrochemical (NSRP)

reductions will also lead to a lower construction costComplex is the second oil refinery to be constructed inand eventually contribute towards conservation and

Vietnam. RAKUNA-IV is being used for the

lowering of CO2 emission. The mold for producing the

rubble-mound breakwater protection in the NSRPRAKUNA-IV blocks for the NSRP project were locally

Project. The breakwater with the total length ofmade in Vietnam.

1.55km is completed in Dec.2015. Approximately 700

under the supervision of Nikken Kogaku and ensured

pcs of 12t block for roundhead and 23,000 pcs 8t block

same high quality as Japan.

The mold were manufactured

for the trunk section and the revetment were installedin the whole breakwater. In the comparison between
the use of RAKUNA-IV and of conventional
TETRAPOD, it is expected that the RAKUNA-IV will
yield a reduction of 12,000 ㎥ concrete volume, andsave up to 200 days of the installation periods. These

Photo3. Breakwater at NSRP Complex

June 2016 No.72

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Infrastructure Development Institute - Japan

Fig.3. Location of Nghi Son

5.

Photo4. Installation of RAKUNA-IV

Photo5. Site observation

Hydraulic experiments in Vietnam
The stability of the RAKUNA-IV for the NSRP

wave concentration were verified, high stability ofProject was verified in 2D and 3D hydraulic

RAKUNA-IV along with low overtopping in theexperiments conducted by Vietnam’s Thuy Loi

design crown elevation were proved, and the

University (formerly Water Resource University).

acceptability of the overall breakwater design was

Seaward and rear stability, wave overtopping andconfirmed by conducting these experiment.

Photo6. 7. 8. Hydraulic experiments in Thuy Loi University

6.

Conclusion
By working cooperatively with local institutes such

local countries. With its excellent and uniqueas university through experiments, the design whichcharacteristics and an advantage of double-layer

is adapted to local conditions is achieved. In addition,system, RAKUNA-IV will protect the safety of ports,

Japanese high quality and technology are kept

breakwaters, revetment and coast from the damage

because Nikken Kogaku send engineers who

caused by high waves, typhoon, tsunami, coastal

supervise the manufacturing through installation toerosion, etc. around the world.

Technology Developer: NIKKEN KOGAKU CO., LTD.
Contact Person: Yuka Kizaki, NIKKEN KOGAKU CO., LTD.
E-mail:kizakiy@nikken-kogaku.co.jp
TEL:+81-3-6361-0028
FAX:+81-3-5381-7377

June 2016 No.72

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Infrastructure Development Institute - Japan

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June 2016 No.72

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