COMMISSION INTERNATIONALE
DES GRANDS BARRAGES------VINGT-QUATRIÈME CONGRÈS
DES GRANDS BARRAGES

Vienne, Juillet 2018-------DESIGN OF A TSUNAMI COASTAL LEVEE USING TRAPEZOIDAL CSG DAMTECHNOLOGY AND QUALITY CONTROL DURING CSG PRODUCTION(COASTAL OF HAMAMATSU CITY) ()Nobuyuki ITOH, Tsuyoshi TAKADA & Satoshi TERADA
Coastal construction Service Group, Hamamatsu Public Works Office,
SHIZUOKA PREFECTURE
Nario YASUDA
Director of Engineering DepartmentⅠ, JAPAN DAM ENGINEERING CENTER
Tomoi NAKASHIMA & Maho TANAKA
MAEDA CORPORATION
JAPAN

1.

INTRODUCTION

Terrace deposits and mudstone quarried at Mt. Akura in Hamamatsu City
shown in Fig. 1 are used for CSG (Cemented Sand and Gravel）material, toachieve effective usage of material in the field, it is mixed with locally produced
beach sands from excavation work executed to construct the coastal levee. To
surely design and construct CSG structure on sandy ground, the results of plateloading tests, standard penetration tests, and Swedish sounding tests performed
before the construction have been summarized and analyzed to develop amethod of evaluating bearing capacity and the foundation elevation of CSG
structure, which can be performed simply at the site. At this coastal levee, a new
approach to the quality control of CSG was performed. Applying the new “Quality
Control System” at the levee was a first step in improving and rationalizing “CSG(*)

Conception d’une digue côtière de tsunami à l’aide d’une technologie de barrage
trapézoïdal de type CSG et contrôle de la qualité au cours de la production duCSG (Côte de la ville de Hamamatsu)

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material quality control” during placing of CSG. Rationalization in particular iscounted on to lighten harsh labor and decrease costs by reducing manual test.

Fig. 1
Locations of the coastal levee and Mt. Akura
Emplacements des digues côtières et du Mont Akura

2.

2.1.

STRUCURE OF COASTAL LEVEE

BASIC CONDITIONS AND CHARACTERISTICS OF THE COASTAL LEVEE

The following are the basic conditions required for the construction of theHamamatsu Coastal Levee.
First, the crest height of the coastal levee is basically T.P.+13.0 m (Tokyo
Bay mean sea level; Tokyo Peil, T.P.), which was determined from the height ofLevel-2 Tsunami as reference. The crest height is lower than that of Level-2
Tsunami. Here, Level-2 Tsunami is a tidal wave which occurs as the result of adisastrous earthquake of Magnitude (M) 9 with a return period of several thousand
years, and which can cause enormous damage when it occurs. However, thelevee body has been composed of CSG which is a tenacious structure to resist
breaching against the overflow of sea water. CSG is made from cement, water,
rocky materials, and has been developed as the new design and construction
methods at dam engineering. CSG has the characteristics of the rapid
construction and the usage of materials obtained from the vicinity of the field withless restriction [1].
Secondly, the coastal levee is located in a seaside forest reserve, which
prevents the intrusion of blowing sand from the shoreline. Therefore, even after
the levee is completed, it is necessary to restore the forest reserve to maintain its
original protection function.

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As the basic structure of the coastal levee, CSG with trapezoidal shape andwide levee base is located in the center, constructing embankments at each end
to satisfy the above two basic conditions (see Fig. 2). Finally, the coastal levee
has the following special characteristics.
Embankment
・Placing embankments on both sides of CSG
enables placing soil and revegetating the slope
surface, ensuring the function of the seaside
protection forest

Crest protection(Soil cover)

Locally generated
material

CSG levee body・Placing CSG in the center provides a tenacious structurethat prevents failure caused by overflow and seepage
failure.
・The CSG levee body is firmly seated on the foundation
ground with adequate strength.

(Soil cover)

Locally generated
material

Foundation CSG (thickness: 60cm)

Fig. 2
Typical cross section of the coastal levee
Coupe tranceversale typique de la digue côtièrea) Forming a trapezoidal shape of CSG in the center lowers vertical reaction
force of the structure base and reduces fluctuation of the basal reaction force
by changeable load caused by earthquakes etc. Additionally, a highly rigid
structure can be constructed on sandy ground. Furthermore, the trapezoidal
shape basically helps it resist overturning.
b) CSG is, as a mixture of rocky material with cement and water, material withhigher strength than foundation grounds and embankments made of earthmaterials, so a levee body composed of these materials can resist the failure
by seepage or overflow.
c) As a result of the above factors, the levee structure with extremely large yieldstrength against Level-2 Earthquake and Level-2 Tsunami, which will comefrom Nankai megathrust earthquakes, can be constructed.
d) Once liquefaction or other deformation of the foundation ground is caused byan earthquake, CSG dam body will also naturally be deformed. But the levee
body is composed of CSG and embankment, so it will be not destroyed
partially or completely by the succeeding tsunami. Therefore its reconstruction
after the disaster will be performed relatively easy.
e) Embanking on both sides of CSG part will enable the soil-covering andrevegetating the surface of levee, enabling the maintenance of the originalfunction of the seaside forest reserve.
Based on the above conditions, the basic structure and shape of the coastal
levee are obtained as shown in Fig. 2.

2.2.

STRUCTURAL STABILITY ANALYSIS OF THE COASTAL LEVEE

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The stability analyses of the basic structure of the coastal levee shown in
Fig. 2 considered I) stability of CSG body, II) stability against sliding through thefoundation, and III) subsidence caused by foundation liquefaction. In cases where
the above conditions were not satisfied because of insufficient strength of theground, improvement measures for ground were investigated and the stability wasconfirmed. Specifically, the structure of the coastal levee was studied by thefollowing steps as shown in Fig. 3.

Fig.3
Structure analysis flow
Flux d’analyse de structure1) Stability of CSG body (Usual time, Level -1 Earthquake, see Fig. 4.)
2) Stability against circular slip throughout the foundation (Usual time, Level -1
Earthquake, see Fig. 5.)
3) Confirmation of the amount of subsidence caused by liquefaction (Level-2
Earthquake (type-1), see Fig. 6)4) Required CSG strength of CSG body (Usual time, Level -1 Earthquake, seeFig. 7)
In cases where the external stability analysis described in 1) to 3) cannot
ensure the stipulated safety due to insufficient strength of the foundation, ground
improvement measures were studied.
Analysis will be continued until the stabilities in 1) to 3) above are satisfied.
Additionally, stabilities 1) and 2) were confirmed under Level-2 Earthquake(type-1) and Level-2 Tsunami.

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Where, Level-1 Earthquake: Ground motion by earthquake that occurs rarely
Level-2 Earthquake: Ground motion by maximum credible earthquake(Type-1(L2-1 type); oceanic plate boundary, Type-2(L2-2 type); Inland
crustal）
Level-2 Tsunami: Maximum class tsunami that causes serious disaster

Fig.4
Load condition at stability analysis of CSG body (external safety)
État de la charge à l’analyse de la stabilité du corps CSG (sécurité extérieure)

Fig.5
Stability analysis of CSG body and foundation (external stability)
Analyse de la stabilité du corps CSG et de la fondation (stabilité externe)
Required CSG strength of CSG body was obtained as a study of internalstability. The calculation was performed by FEM for usual time and Level-1
Earthquake as shown in Fig. 7, obtaining required CSG strength of 1.92 N/mm2 forthe elastic modulus of dam body of 1,500 N/mm2. Two CSG mixtures of unit
cement were applied corresponding to the height of CSG body as shown in Table
1.

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#
①
②
③
④
⑤

Location at crest
Shoulder of banking (sea side)
Crest of CSG (sea side)
Crest of CSG (central)
Crest of CSG (inland side)
Shoulder of banking (inland side)

Settlement (cm)
10.59
9.04
9.04
9.04
10.59

Fig.6
Settlement due to the liquefaction of foundation (external stability)
Règlement en raison de la liquéfaction de la fondation (stabilité externe)

Fig. 7
Calculation of internal stress (Level-1 Earthquake)
Calcul des contraintes internes (Tremblement de terre de niveau 1)
Table 1
Mix proportion of CSG
Unit cement content at lower elevation
Unit cement content at higher elevation

3.

3.1.

60 kg／m3
40 kg／m3

CSG MATERIAL AND CSG STRENGTHBLEND RATIO OF CSG MATERIAL

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As CSG material, terrace deposits and mudstone quarried at Mt. Akura havebeen used. Each of sediments and mudstone is efficiently mixed with 20% or 40%
of beach sands produced during excavation of the levee foundation [1], [2]. The
blend ratios of materials from Mt. Akura and beach sands were set based on
in-situ conditions and the properties of CSG etc.
1) The difference between the amount of materials obtained at the site (about 2
million m3) and the amount diverted for use as banking material (about 1.4
million m3), was approximately 600,000 m3 and used as CSG material. This
corresponds to about 30 % of the total quantity of CSG body (about 2 million
m3).
2) Mudstone is rock debris and likely to be coarser than the terrace deposits ingrain size, so basically, the blend ratio of in-situ beach sand is larger for
mudstone.
3) From the mixing properties of CSG in laboratory test, the upper limit of theblend ratio of in-situ beach sand to mudstone is judged to be about 40 %.
4) The quantity produced in the area between Lake Hamana and Magome River
forming sand dunes, is larger than that between Magome River and Tenryu
River. Transporting material across the Magome River is difficult for a heavy
environmental load on the region.
Considering the above conditions, basic blend ratios were set as:・ Terrace sediment : In-situ sand = 80 : 20
・ Mudstone : In-situ sand = 60 : 40
In a case where mudstone is used at the construction area between Tenryu
River and Magome River, the following blend ratio was adopted because of theshortage of in-situ sand.
・ Mudstone: In-situ sand = 80 : 20
Fig. 8 shows the grain size distribution of CSG after blending.

3.2.

CSG STRENGTH

Standard cylindrical specimens (15 cm in diameter and 30 cm in height) with
CSG mixed at a unit water content of 100 to 130 kg/m3 were prepared, then,compressive strength test of the specimens ware performed to obtain the
diamond-shape of CSG. The tests by standard specimen were carried out
according to, “Trapezoid CSG Dam Design, Execution, Quality Control
Technology Document” [3]. CSG strength in the coastal levee was evaluated by
calculating peak strength (compressive strength) similarly to that in concrete.

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(1) Terrace deposit 80% + In-situ sand 20%(2) Mudstone 60% + In-situ sand 40%(3) Mudstone 80% + In-situ sand 20%
Fig. 8
CSG materials (Grading after blend)Matériaux CSG (nivellement après mélange)

Table 2 shows the test results of CSG strength using standard specimens
for each cement content using each CSG material, and Fig. 9 shows the diamondshape of terrace deposit 80% + In-situ sand 20 %.

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Table 2
CSG strength by standard cylindrical specimen3

Raw materials used
Terrace deposit 80% + In-situ sand 20%
Mudstone 60%+ In-situ sand 40%
Mudstone 80%+ In-situ sand 20%

Unit cement content（kg/m ）
80
60
50
40
―
2.34
1.91 1.64
1.60
1.26
0.93 0.65
2.94
1.70
―
0.71

(1) Unit cement content of 40 kg/m3 (2) Unit cement content of 60kg/m3
Fig. 9Diamond shape by standard specimen (terrace deposit 80% + sand 20%)
Losange de spécimen standard (terrasse de dépôt 80 % sable 20 %)

4.

4.1.

FOUNDATION EXCAVATIONPRELIMINARY SURVEY

In order to directly confirm the bearing capacity of the ground, a plateloading test was carried out during a preliminary inspection and trial execution. A
boring survey and Swedish weight sounding test were performed at the same timeas the plate loading test, comparing the bearing capacity obtained from the plateloading test with the N-value. Fig. 10 shows the positional relationship of the tests
and the test procedure is shown below [4].
The allowable bearing capacity at N-value of 15, is 273 kN/m2 as the medianvalue in the correlation zone, so here, the allowable bearing capacity at N-value of
15 is set at 270 kN/m2 (Usual time) and 405 kN/m2 (earthquake time). The bearing
capacity of 405 kN/m2 at earthquake time is 1.5 times as much as that of 270
kN/m2 at usual time.
1) A standard penetration test (SPT) was executed on the initial ground surface(ground surface of the original topography) at the same time as the boring
survey, to measure the N-value at each depth.

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Standard penetration test

Initial ground surface

SWS test

Test groundsurface

Test groundsurface

Plate loading
test★:Test result evaluation

Fig.10SPT test, Plate loading test and SWS test
Test SPT, test de chargement de plaque et test SWS2) The original ground is excavated to perform the plate loading test. The plateloading test is carried out on each ground surface which is lowed every 1 m bystage in order to compare the result with the N-value measured by SPT.
3) The Swedish weight sounding test (SWS test) is done near the same location
as the boring and plate loading test. This test is also done in a same manneras the plate loading test.
Regarding the bearing capacity of the foundation ground, the relationship of
the allowable bearing capacity obtained by the plate loading test performed in-situ
with the N-value at the adjacent boring was arranged as shown in Fig. 11.

4.2.

SURVEY DURING CONSTRUCTION

During construction, the SWS-test was done at 25 m long intervals along theaxis of the levee, confirming that the required bearing capacity could be obtained.
The SWS-test was influenced by looseness near the ground surface, but it
clarified by a preliminary survey that test results with the earth covering of 1 to 2 m
or thicker conform to the values of SPT as shown in Fig. 12. Therefore, as shownin Fig. 10, the SWS-test was done when the excavation had reached 2 m above
the planned foundation ground, and the excavation was continued till the required
bearing capacity near the planned foundation ground elevation was confirmed.

4.3.

GROUND IMPROVEMENT WORK

According to SWS-test results during execution, in cases where theelevation with the required bearing capacity (N value of 15 or higher) is partiallylower than that of planned foundation ground, the ground improvement work was
performed to ensure the stipulated bearing capacity.

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Fig.11
Relationship of N-value and bearing capacity from plate loading test
Relation valeur N et capacité portante de la plaque de test

Fig.12
Relationship of SWS test results and N-values of standard penetration test
Relation des résultats des tests SWS et des valeurs N du test de pénétration
standard
The ground improvement method was basically replacing the foundation
with good quality sediment. The replacement was accompanied by the shallow
mixing method in cases where the soft layer is thicker than 3 m (see Fig. 13).
Additionally, in cases where the groundwater is shallow and it is difficult to achieve

報－53adequate compaction under the existence of water springs, even if the soft groundis thinner than 3 m, the shallow mixing method was applied. The layout of theground improvement equipment is shown in Fig. 14.

Ground water
level

Soil improvement(Displacement work)
Soil improvement(Shallow mixing treatment）

Shallow mixing treatment
under ground water level

Fig. 13
Soil stabilization method and depth of stabilization
Méthode de stabilisation de sol et profondeur de la stabilisation
Silo

Back hoePower blender

Tank lorrynku

Slurry plant

Grouting pump

Fig. 14Equipment of soil stabilization and its arrangement
Équipement de la stabilisation des sols et arrangement

5.

5.1.

QUALITY CONTROLQUALITY CONTROL TEST
Quality control of CSG is performed according to the reference [3].

5.1.1.

Quality control of the raw material
The raw materials of terrace deposits from Mt. Akura and in-situ beach sandproduced in the vicinity were used in the section of the trial execution work. The
terrace deposits were screened to remove larger grain size over 80 mm from the
excavated material, then transported to the work field. The quality control of the
raw material was performed to confirm its density, water absorption, grain shape

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of gravel by visual observation and the hardness of the gravel by hammer tapping.
Quality control of CSG material
Quality control of CSG material also confirmed density, water absorption,
the distribution of grain size, surface moisture content at the primary andsecondary stock piles. In the trial execution work, a blend of terrace deposits andthe in-situ sand was tested to use as CSG material.
5.1.2.

Quality control of CSG materials and of CSG
Quality control of CSG materials and of CSG during placing was performed
as described below.

5.1.3.

1) Controlling CSG material: The grain size and surface moisture content of
CSG material were controlled. Measurement intervals were principally
performed once an hour.
2) Weight measuring control: The control of CSG material, water, cement wasdone by automatic measuring control devices on CSG mixer (self-propelledsoil improvement machine) during CSG production.
3) Control at the placing field: During placing, the number of roller compaction
by the vibrating roller was controlled to obtain the required compactionenergy. After roller compaction, the RI (Radio isotope) method and sandreplacement method are used to measure the in-situ density, confirming thatthe quality of CSG is not changed by the placing work.
4) Confirmation using specimens: The strength fluctuation trend of CSG was
surveyed based on 7-day compressive strength of the standard cylindrical
specimens prepared with CSG produced in the field, confirming that thequality does not change. Simultaneously, large-scale specimens (30 cm indiameter and 60 cm in height) were prepared to confirm the relationshipbetween its density and the in-situ density (sand replacement method).
Table 3 shows items and test frequency of the quality control. Quality controlof CSG partially consists of the quality control of CSG materials. The
rationalization and improvement of quality control of CSG materials using ICT(Information and communication technology) are described at the following
section.

5.2.

QUALITY CONTROL OF CSG MATERIALS

5.2.1.

Quality Control System
The Quality Control System is an automatic quality confirmation systeminstalled on the in-situ production plant in order to rationalize productivity of CSG
quality control. Quality control performed manually can be rationalized applying
ICT [5].
Fig.15 shows the flow of measurements by the Quality Control System. At

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the Hamamatsu Coastal Levee, there is the main line of a conveyor belt fortransporting mudstone or terrace deposits (CSG material II) to the mixer and abranch line that supplies in-situ beach sand produced in the vicinity (CSG
material-I) to the main line. Each line is equipped with a microwave moisture
meter to measure moisture content of each CSG material. A separate system thattakes the mudstone or terrace deposits (CSG material-II) from the main line at thecertain interval is installed, and the moisture content of CSG material-II was
measured by microwave moisture meters installed on the separate line.
Table 3
Items and frequency of quality control

Control of
raw material

Control ofCSG
material

Control ofCSG
material andCSG

Items controlled

Measurement method

Weathering, hardness
Grain shape
Saturated –surface dry
density and absorption
content
Grading
Saturated –surface dry
density and absorption
content

Visual, Hammer diagnosis
VisualDensity and water absorption test

Grading
Surface water content
Grading
Surface water content

Dry method, JIS A 1102
Dry method, JIS A 1125
(Manual) simple method(Manual) simple method (watercontent)
Measuring device of mixture
Tracking control of roller
compaction machine
RI method, Sand replacement
methodLarge-scale specimen density

Weight measuring control
Compaction energy
controlIn-situ density
Specimen strength anddensity

Dry method
Density and water absorption test
+5mm JIS A1110-5mm JIS A1109

Large-scale specimen (age of 27days, compressive strength test)
Standard specimen (age of 7days, compressive strength test,)

Measurement
frequency
Once / dayOnce / week

Once / dayOnce / hourOnce / hour
Real time
Real time
Once (3points) / day
One set / day(3 specimens)

The grain size distribution of CSG material-II is measured by imaging andimage processing in the dark-room. The Quality Control System can automaticallycalculate the surface moisture content of CSG material using of thesemeasurement results. The mixture of CSG is corrected based on the surface
moisture content of CSG material, and the amount of water supplied to CSG isadjusted as needed. The Quality Control System permits confirmation of thequality quickly at the rate of once per 15 minutes. The continuous correction of
CSG mixture can allows the improvement of the quality control of CSG if
necessary.
5.2.2.

Grain size distribution
Grain size distribution is measured applying image processing technology[5]. The equipment includes imaging apparatus (high performance digital camera),

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personal computer, lighting apparatus, a conveyor belt that disperses, andseparately transports CSG material measured, and equipment that drops CSG
material down to image each grain clearly. Basically, at certain intervals, CSG
materials are separated from the main line of a conveyor belt and imaged with adigital camera, then, the image is processed. Finally, the grain size distribution of
the materials was estimated by statistically processing the parameters shown in
Fig. 16.

Fig. 15
Quality control system
Système de contrôle qualitéFig. 16
Parameter for image processing
Paramètre de traitement d’image
The influence of the unevenness of grain size distribution of CSG material tothe estimation by this system was investigated. The study was performed using
terrace deposits with their grain size adjusted to finest grain size, average gain
size and coarsest grain size. But the moisture content is fixed. Fig.17 shows thecomparison of the estimated and the known grain size distributions and it isconfirmed this system estimates the grain size very well
5.2.3.

Surface moisture
The total surface moisture content of CSG material is obtained by summing報－57

up the surface moisture content for each grain size category. The surface
moisture content is calculated by measuring moisture content of CSG material.
Moisture content is measured using the microwave moisture meters which are
non-contact measuring devices and having the characteristics that theirmicrowaves are absorbed by water. Fig. 18 shows the measurement principle ofthe microwave moisture meter and a schematic diagram of calculation of the
moisture content.

Fig. 17Comparison of grain size distributions
Comparaison des distributions de taille de grain

Fig. 18
Microwave moisture meters and their measuring principal
Appareils de mesure de l’ humidité à micro-ondes et leurs principales mesures
Microwaves are electromagnetic waves with wave length from 1 m to 1 cm,
and frequency ranging from 300 MHz to 30 GHz. During measurement, themicrowaves attenuate as they pass through the material containing the moisture.
Obtaining the received voltage (Mv) by the microwaves for a specimen with known
moisture content, permits measurement of the moisture content of the materials
used. Fig.19 shows the relationship between the moisture content of CSG
material by dry method and that by a microwave moisture meter.

5.3.

RESULTS OF TRIAL OPERATION WITH AN IN-SITU PRODUCTION PLANT報－58

An element test of the Quality Control System described above verified thatit can measure moisture content and grain size distribution of material. In thissection, the measurement of surface moisture content and grain size distributionof CSG material is described using the Quality Control System attached to thein-situ production plant. The data used for this study is covering an approximately
1 month actual construction in April 2017 and mudstone was used as CSG
material-II in this construction period. Figure 20 shows temporal change of thepercent passing of each grain size of CSG material. In the current manual simple
method, the same materials are sampled from the materials measured by thissystem. Figure 21 shows temporal change of total surface moisture content
obtained from the manual simple method and from the Quality Control System.
Figs. 20 and 21 show that the Quality Control System presumably can clarify very
well the change of surface moisture content and grain size distribution obtained
from the current manual simple method.

Fig .19
Calculation of water content by two different methods
Calcul de la teneur en eau par deux méthodes différentes
Current method

80（kg/m3）

Surface moisture content

100

Quality control system

60
40
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Temporal change of surface moisture content
Variation temporelle de teneur en humidité de surface

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Dmax40 Mass passthrough percentage(%)

100
Finest grain size distribution：93.1%

80
60

Coarsest grain size distribution：51.8%

40
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Dmax20 Mass passthrough percentage(%)

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Current method

Current method

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Finest grain size distribution：73.0%

Quality control system

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Coarsest grain size distribution：23.7%(2) Dmax; 20 mm

Dmax10 Mass passthrough percentage(%)

100

Current method

80

Quality control system

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Finest grain size distribution：51.1%

40
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Coarsest grain size distribution：12.1%
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Dmax5 Mass passthrough percentage(%)

100
Current method

80

Quality control system

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Finest grain size distribution：36.0%

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(4) Dmax; 5 mm
Fig.21
Temporal change of grain size distribution(Comparison of two measuring method using same material)
Variation temporelle de la distribution de taille de grain(Comparaison de deux méthodes utilisant le même matériel de mesure)

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6.

CONCLUSION

In order to mitigate giant tsunami damage predicted to occur on the
Hamamatsu City Coastline, a coastal levee higher than Level-1 Tsunami is being
constructed about 17.5 km from Lake Hamana to the mouth of the Tenryu River.
The planned coastal levee is required to have tenacity enabling it to withstandoverflow of Tsunami, but strength equal to that of a concrete structure is notneeded, so a CSG structure, which has been developed by dam engineering, isadopted for the internal portion of the levee. The Quality Control System as ICT
was investigated in order to rationalize the quality control of CSG materials andgood performance was obtained. This system has operated since last Septemberin this field. The construction work of the Hamamatsu Coastal is being executed
vigorously aiming for completion in 2020.

REFERENCES[1] YOSHIZAWA, Y., ITOH, N. and HAKAMATA, M. Construction of a coastal
levee at Hamamatsu City Coastline (Part 1), Engineering for dams, No. 354,
pp.75-106, 2016, (in Japanese).
[2] ITOH, N., SUZUKI, T., TERADA, S., FUJISAWA, T., KINOUCHI, Y. and
YASUDA, Construction of a coastal levee at Hamamatsu City Coastline using
trapezoidal CSG dam technology”, 4th APG Symposium and 9th EADC on
Innovative technologies for dams and reservoirs toward the future generators,
2016.
[3] JAPAN DAM ENGINEERNG CENTER, Engineering manual for design,
construction and quality control of trapezoidal CSG dam, Japan Dam
Engineering Center, 2012.
[4] ITOH, N., TAKADA T. and TERADA, S., Construction of a coastal levee at
Hamamatsu City Coastline (Part 3), Engineering for dams, No. 370, pp.28-65,
2017, (in Japanese).
[5] ITOH, N., TAKADA S., TERADA, S., NAKASHIMA, T. and TANAKA, M.,
Rationalization and improvement of quality control of CSG material,
Engineering for dams, No. 373, pp.29-39, 2017, (in Japanese).

SUMMARY
In order to mitigate giant tsunami damage predicted to occur on the
Hamamatsu City Coastline, a coastal levee higher than Level-1 Tsunami is being
constructed about 17.5 km from Lake Hamana to the mouth of the Tenryu River.
Here, Level-1 Tsunami is a tidal wave which occurs as the result of an earthquakeof magnitude (M) 8 with the return period of roughly 100 year-150 year cycle along

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Suruga-trough and Nankai-trough. The planned coastal levee is located on a long
sandy beach, parallel to a seaside protection forest on the north side. Its location
imposed the design requirements for the conservation of valuable fauna and flora,and scenic appearance, and for the restoration of the seriously eroded shoreline.
The levee of CSG (Cemented Sand and Gravel) placed at the center andsurrounded with embankment are applied for raising the ground elevation of theseaside protection forest. The planned coastal levee is required to have tenacity
enabling it to withstand overflow of Tsunami, but strength equal to that of aconcrete structure is not needed, so a CSG structure, which has been developedby dam engineering, is adopted for the internal portion of the levee. Furthermore,
the usage of ICT is also attempted to rationalize and advance quality control of
CSG material.

RÉSUMÉ
Afin de limiter les dégâts du tsunami géant censé se produire sur la côte dela ville de Hamamatsu, une digue côtière plus élevée que les tsunamis de niveau
1 va être construite à environ 17.5 km du lac Hamana, à l’embouchure de larivière Tenryu. Ici, le tsunami de niveau 1 est un raz-de-marée qui survient à lasuite d’un séisme de magnitude (M) 8 avec une période de retour d’environ
100-150 ans le long de Suruga et de Nankai. La digue côtière prévue est située
sur une longue plage de sable avec une forêt de protection de bord de mer
parallèle à ce côté nord. Compte tenu de la conservation des plantes et animaux
précieux, du rivage sérieusement érodé et de l’aspect pittoresque du site,
fondamentalement, le niveau du sol de la forêt de protection de bord de mer estélevé, le CSG (ciment, sable et gravier) est placé au centre de la section de ladigue et les sections extérieures sont construites comme des digues de terre. La
digue côtière prévue est tenue d’avoir une ténacité lui permettant de résister auxdébordements dus aux tsunamis, mais une force égale à celle d’une structure en
béton n’est pas nécessaire; par conséquent, une structure CSG, qui a été
développée par l’ingénierie des barrages est adoptée pour la partie interne de ladigue. De plus, nous essayons d’utiliser la technologie de l’information pourégalement rationaliser et faire progresser le contrôle qualité du matériau CSG.

Key words; Quality control, Sounding, Strengthening, Wave

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