Japanese Dam Technologies
Contributing to the World 2023

Tsuruda Dam

Tokuyama Dam

JCOLDJAPAN COMMISSION ON LARGE DAMS

It’s our honor to introduce
the following expertise
Advanced Technologies for Upgrading Dams under Operation………………………… 1
Inspection for Dam Safety………………………… 13

Appendix………………………… 19

Advanced Technologies for
Upgrading Dams under Operation1

Japan’s New Technology of Upstream Cofferdam Method～Needs and Development background ～By a social environmental change, the needs of dam arechanged.
✓ More hydraulic power, More flood storage , etc
For these needs, it is necessary to install new conduits or
penstocks in the dam body .
Highest water level during a flood

Highest water level during a flood

Flood storagege
Current
discharge
facilities

Current
discharge
facilities

Irrigation water capacity
Dead water capacity
Sediment storage capacity

Install new
conduits
at low level

Flood storage
ge
Drop in waterlevel due tofloodcontrolLowest water level
releaseSediment storage capacity

Able to use dead capacity in lower level of the reservoir
to new purposes such as flood control .

New technologies of construction were demanded,safely in the full reservoir , in low cost, in a short term .
Upstreamcofferdam

Install new conduits
Drillin a holl downstream

Full reservoir

Dam body

Image of the construction method

2

3

②

①

③
Bottomcover

Upper frame structure

Bracket
metal

Gate
sheet

②

①

③

Gate
sheet

Bracketmetal

Pedestal concrete (Deck)②①

Rank of excellence: S > A > B

Higher availability for lower water depth with lesspressure of the buoyancy

Availability,
restriction

B

②

①

①

②

Apparatus against floating

Gate sheet

Gate leaf③

Bottom
cover

Gate
sheet

Unnecessary

Not least. However, reuse to other projects
is advantage.

Local impact around apparatus, easy
access for inspection

Better watertightness thanks to theassembling in air

Shortest
Parallel construction is possible.

Least submerged work, Shallower work

S

S

S

S

S

S

Rank

Locating the integrated gate
The assembling of gate leaves is conducted inadvance on the reservoir and tugged to the dam.

Bottomcover

Reservoir

Gate
leaf

Floating prevention
apparatus③

Floating prevention
apparatus

New construction method
Floating body system cofferdam

No restriction in a dam height, water depth and No restriction in a dam height and water depth.
clearance of the cofferdam.
Possibility of reuse for other projects.

B

A little

Preparation work
below the cofferdam

Treatment of sedimentation and thefoundation for the pedestal concrete

Much support members

Total weight ofcofferdam andsupported members

S
A

LimitedB

Much load on the dam crest part

Impact to the dam

A

Least weight in total

More leakage due to in-situ assemblingunder water

B

Longer
The work is conducted step by step.

Rank
A

A

B

Pedestal
concrete

Submerged work for much concrete
placing, Deeper work

More leakage due to in-situ assemblingunder water

B

Longer
The work is conducted step by step.

Duration

②

①

①

Gate
sheet

①

Gate
sheet

In-situ assembling of separated gate leaves
The work includes prior excavation for the deck.

Pedestal
concrete

Reservoir

Gate
leaf

Gate
leaf

Possible leakage

B

Less submerged work, Shallower work

Rank

In-situ assembling of separated gate leaves
Each leaf is supported by anchors.

Bottomcover

Reservoir

Gate
leaf

Supportframe

Support
frame
Gate
leaf

Pedestal system cofferdam

Conventional construction method

Support frame system cofferdam

Character of theinstallation

Installation method

Temporal structures forthe buoyancy of thecofferdam during
construction【Major loads】① Dead Load
② Buoyancy③ Support pressure

Schematic diagram

Method ofconstruction

Comparison of upstream cofferdam construction method4―New Upstream Cofferdam MethodʖBulkhead

Safety improvement

Cost reduction

Improved workability

Shortened
construction period【Completion of Installation】

The barge for transportation－onto the barge on the reservoir―

1.Loading of Bulkheads on the barge

Dewatering－securing a dry working space inside the upstream
cofferdam―

5.Dewatering from the upstream cofferdam

Overview of bulkhead

Buoyancy chamber

Skin plate

The barge
Lowerbulkhead

Bulkheadunderassembly

Direction

Dewateringˏ
positioning－dewatering from the upstream cofferdam forfloating and positioning of the upstream cofferdam―

Overview of towing

Overview ofassembly

Lower bulkhead-under the water-

Integrated
upstreamcofferdam

Bulkheadunder assembly

４.Towing & Installation－assembly of all bulkheads―

3.Assembly of bulkheads on the reservoir

All work from assembly of bulkheads to installation of upstream cofferdam can be done on the reservoir

Assemblyarea－reservoir transportation―

2.Transportation of bulkheads to assemblyarea by the barge

The workability of the upstream cofferdam method can be significantly improved by airtight structure in each bulkhead to provide buoyancy

Floating Type Upstream Cofferdam Method

Floating type upstream cofferdam method
Overview of New Technologies

The cofferdam construction requires long diving hours at avery deep water depth, large temporary equipment, and along construction timeframe.
For the floating type upstream cofferdam method, steel plates(skin plates) are attached to both the inside and outside of thebulkhead to make an airtight structure, and this becomes thebuoyancy chamber to make the bulkhead float.
It is important to maintain the balance between buoyancy
forces and dead weight by filling and draining the bulkheads
blocks in the proper order.
And this new method was used for the first time in the
Tsuruda Dam upgrading.

Efficiencies of the technologies
Construction Method

Transport bulkheads on the resevoir

Assemble the bulkheads on the resevoir

For actual construction, bulkhead blocks made at local factories will be assembled
on the reservoir to standardize them and they will be towed to the installation
position by a ship, and subsequently pulled by a winch and secured.
And then, water is drained from the cofferdam.

Efficiencies of this method :This is dependent on scale of the cofferdam and construction
depth, as large temporary facilities, such as pedestal concreteand support framework, are unnecessary and diving work can begreatly reduced, costs and processes can be reduced, and safety
can be improved, leading to an increase in construction
efficiency.
Moreover, when drilling holes in the same dam, it is necessary
with conventional methods to dissemble and then reassemble
the bulkheads, but with this method there is no need todisassemble the bulkheads; flood the cofferdam and detach thebulkheads from the dam-body and tow it as is to the next
construction site where it can be installed.

Summary of the project【Dam Specifications】
Type：Concrete gravity dam
Height：117.5m
Length：450.0m
Volume：1,119,000m3
purpose：flood control and power generation

The concept of the project is to increase flood capacity and discharge facilities.
The increase in flood storage will increase to a total capacity of between 75 million m3 and 98 million
m3 by transferring the power generation capacity during flood season of 2.5 million m3 and dead water
storage of 20.5 million m3, for a total of 23 million m3, to flood storage.The discharge facility was
expanded to enhance discharge capacity by adding three conduit gates on the right dam-body (EL115.6) at a location lower than the current discharge facility (EL 130.0) in accordance with the declineof the lowest water level.

5

Controlled blasting technique with an electronic detonator
In the conventional blasting technique with a DS (decisecond‐level) electric detonator, the gas created by the previous blast escapes through the construction
joints before the next blast occurs, which makes this technique not suitable for concrete demolition. Therefore, by adopting the MS (millisecond‐level) electric
detonator, the next blast is successfully detonated before the gas escapes.
However, there were concerns about a blast vibration at private residence area exceeding the limit value set by management standard. Our solution was todeploy an electronic detonator (product name eDev II) and set one‐hole one‐step blasting with a time difference of 15 milliseconds, which enabled demolition
blast to generate moderate vibration that was significantly lower than the standard limit value.

Upstream side

25m

Downstream side

45.5m

Procedure of Demolition by Blasting

Part to Be Demolished by Blasting

Drilling

Charging explosives

Blasting completion【Characteristic】∙ Time setting in arbitrary milliseconds for each detonator is possible on the spot.
∙ Time setting can be set in 1 ms increments within range from 0 to 20,000 ms.
∙ The precision of the set time is ± 0.1%.
∙ Includes safety devices to protect integrated circuits in the detonator from high voltage such as static electricity or induced current due to lightning strike.
∙ Includes a capacitor that stores the energy necessary for communication with the explosive device as well as for ignition.
∙ Each explosive device can detonate up to 500 electronic detonators.
This technique is effective in cases such as blast vibrations need to be suppressed, especially when other properties are in close proximity, or in whenconstruction time is too limited to deploy conventional blasting technique.
【Regarding Environment, Surroundings, etc.】(Plan) Vibration level: not to exceed management standard value of 75 dB(Actual) Vibration level: actual value of 61 dB (average)【Future Prospects】∙ Among controlled blasting methods for demolition, this technique is the most superior at present.
∙ In the introduced case, we set 15 ms as the time difference, however, we are still working on finding the optimal setting.

【Dam】 Arase【Type】 Concrete gravity dam【Dimensions】 Height 25 m Length 210.8 m Volume 47, 167 m3【Purpose】 Power generation

Work Description【Phase2】Gate, Right Bank Gatepost and Management Bridge's Removal【Phase5】
Left Bank Gatepost and Management Bridge Removal【Phase6】
Left Bank's Removal【Phase1】
Drawdown Equipment's Installation and Gate's Removal【Phase4】
Right Bank's Removal【Phase3】Gate and Right Bank Water-Route Section's Removal【Purpose】
To remove water intake facilities and drainage
lines, which are structures inside the river, due tothe shutdown of the hydroelectric power station.

6

LIBRA-S Method: Temporary piers oblique tie installation method【Purpose】 To streamline the submerged brace installation work for temporary platforms.
【Background of selection of the method】
The brace installation work had been carried out using divers. However, the small range of visibility of the dam interior significantly harmed the work
efficiency. The high turbidity of water after floods suspended the work for several days. Due to these, this work method to streamline theunderwater operations was developed.
【Construction conditions】 Construction depth: 0 ‐ 30m【Outline of work method】
In constructing the substructure (brace) of a temporary platform, unit substructure members are assembled above water and slid downward andinstalled, thereby considerably reducing the diving operation.
・ Most of the braces are assembled on stages installed above water, which reduces submerged operations, leading to an increase in theconstruction efficiency and safety.
・ Once the work is completed, only bolts are loosened under water then the substructure members are collected in succession and demolishedabove water. This also results in higher safety and efficiency.
(1) Preparation work
（１）準備工electric chain (2) Temporary brace assembly work above water（２）ブレース材気中仮組立工
blocks

電 動ﾁ ｪｰﾝ ﾌﾞ ﾛｯｸ

ブレースバンド
brace bands

Temporary brace

ブレース材仮組立（気中施工）

仮止めバンド

作業用足場
working stage（３）ブレース材スライド(3)
Sliding down of braces(4) Repeating of sliding（４）スライド繰返し

スライド後仮固定(1) Preparation work
Install a hanging working stage above water.
Mount electric chain blocks onto the upper structure girder.
Tie brace bands onto steel pipe piles to couple braces andsteel pipe piles.
(2) Temporary brace assembly work above water
Install horizontal and diagonal members.
Hook the chain on a hanging jig on the upper horizontal
members.
(3) Sliding down of braces
Run the electric chain blocks to slide the braces one level
downward.
(4) Repeating of sliding
Repeat the above steps from tying brace bands in (1) to therest.

・ブレース材仮組立
Repeating of sliding・スライド（繰返し施工）Run the electric chain
blocks to slide the braces

ブレース材スライド
one level downward.
（気中⇒水中）Assemble members.

Mount electric chain blocks.

Slide downward.

Summary of the project【Dam】Kanogawa dam【Type】Gravity concrete dam【Specifications of the dam】
Height：61m、Crest length：167.9m、Volume：161,000m3【Purpose】
Flood control、hydropower【Purpose of work】
A tunnel spillway will be constructed on the right bank of the dam inorder to increase the flood regulation capacity of the existing Kano
River Dam 1.4‐fold.
Tunnel spillway:
Standard finished inner diameter: 11.5m; maximum cross section of
excavation: 320m2
Source: Ministry of Land, Infrastructure, Transport and Tourism,
Shikoku Regional Development Bureau pamphlet

7Full Rotation and Full Casing Method【Purpose】To bore holes for installing steel pipe sheet piles in the bedrock under water.

Construction site view with rotary excavator RT‐300【Background of selection of the work method】
・Relatively economical for the excavation of 2m‐dia. and max. 30m‐deep holes in submerged bedrock.

Stand pipe
Ø2300

・Has an operational record.
・Applicable to a wide range of bedrocks.
Excavation scale:
Width 10m x length 45m x maximum depth 30m
Excavation volume: 4,900m3
Excavation shape:
Width 11m x length 11m x average depth 10m

Rotary excavator
RT‐300Submerged pump

Excavator rack

Slush tank

Crawler craneOperator’s cabin
Ramp for fresh concrete vehicle

Revolving hydraulic unit

Hammer grab

Casing tube

Revolving jackTremie pipe

WeightConstruction equipment overview【Characteristics】
・This method can apply to a wide rangeof soils and also allows for greater
construction depth and excavation
diameter than other methods.
(Excavation depth: about 50m;
excavation diameter: 3,000mm)
・The method supports most soil
conditions.
・Clayey soil deposits on the outer
periphery of the casing could increase afriction resistance, possibly hampering or
preventing the revolving of the casing.

Summary of the project【Dam】Kanogawa dam【Type】Gravity concrete dam【Specifications of the dam】
Height：61m、Crest length：167.9m、Volume：161,000m3【Purpose】
Flood control、hydropower【Purpose of work】
A tunnel spillway will be constructed on the right bank of the damin order to increase the flood regulation capacity of the existing
Kano River Dam 1.4‐fold.
Tunnel spillway:
Standard finished inner diameter: 11.5m; maximum cross sectionof excavation: 320m2

Source: Ministry of Land, Infrastructure, Transport and Tourism,
Shikoku Regional Development Bureau pamphlet

8Underwater wire saw method【Purpose】A part of underwater concrete structure was cut and removed by the wire saw,
which was then placed above water level.
【Selection process of method】
Because of the lack of visibility in the reservoir (only 0〜1m), the original method, that themain body was set underwater was changed to the alternative method that the main bodywas set on the barge above water level and extend wire into water , since it will be difficult
to cope with incase of cutting the wire, and it has less ability of cutting, etc.
(Adopted wire saw：K‐WAC‐04､32.2Kw）【Conditions】 Water depth：0～30m、Concrete strength：Approximately 30N/mm2【Features】
・Under water concrete structure was cut by wire saw and was placed above water level.
・It is possible to execute when that the reservoir has the lack of visibility and it isdifficult to work underwater.
・Maintenance work is easy because the wire saw itself is placed above water level.
・It is not necessary for the wire saw to replace every place to cut off.
・Great depth result in the increasing the risk of cutting wire because the length of thewire saw is long.
・Since the method use crane, restraint
time will be longer.

Cutting parts by wire saw under water

Cutting of the concrete structure

Cutting of the concrete structure undrewater by wire saw【Procedure of the work】(ⅰ) Set the wire saw body (cutting machine) on the barge and cut the concrete in theunderwater block into blocks of 20 t or less.
(ⅱ) Cut the concrete block by lifting it with a crawler crane (120 t) placed on the temporary
gantry.
(ⅲ) Dispose of the removed concrete lumps in large trucks after handling them to apredetermined location.

Lifting cut concrete mass in water

Summary of the project【Dam】Kanogawa dam【Type】Gravity concrete dam【Specifications of the dam】
Height：61m、Crest length：167.9m、Volume：161,000m3【Purpose】
Flood control、hydropower【Purpose of the project】
A tunnel flood discharge is newly constructed on the right bank of thedam, with the aim of setting the flood control capacity of the existing
Kanogawa dam 1.4 times.
A tunnel flood discharge:
Standard inside diameter 11.5m, Maximum excavate section 320m2
In the Kano River dam remodeling project, new low water discharge
facility "and "selective water intake facility" are constructed for the
purpose of preventing cold water discharge and prolongation of turbid
water discharge and suppressing eutrophication of reservoir.

Image of the project"Reprinted from the pamphlet of Yamasakizaka Dam Construction Office, Shikoku Regional
Development Bureau, Ministry of Land, Infrastructure and Transport"

9Drilling the existing dam body using road header
In the existing dam, a total five holes were drilled: three forthe expansion of discharge pipes and two to move thepower generation intake pipes.
To drill five locations in the same dam‐body is the largest
scale in Japan, as a dam upgrading work.
The drilling depth per hole is approx. 60 m, which contains asection of 1 m of upstream non‐vibration penetration
section (hole size: vertical 6 m, horizontal 6 m).
To drill the general section, a 200 to 240 kW class roadheader was used.
The vibration value on the dam‐body was mesured toconfirm if there are any effects on the dam‐body.
This picture shows the drilling work performed by a roadheader.
As it was reported from similar construction that vibration
would be the strongest at the time of penetration, the non‐vibration penetration technique was adopted to avoid
impact from vibration during penetration.

Summary of the project【Dam Specifications】
Type：Concrete gravity dam
Height：117.5m
Length：450.0m
Volume：1,119,000m3
purpose：flood control and power generation

The concept of the project is to increase flood capacity and discharge facilities.
The increase in flood storage will increase to a total capacity of between 75 million m3 and 98
million m3 by transferring the power generation capacity during flood season of 2.5 million m3
and dead water storage of 20.5 million m3, for a total of 23 million m3, to flood storage.The
discharge facility was expanded to enhance discharge capacity by adding three conduit gateson the right dam‐body (EL 115.6) at a location lower than the current discharge facility (EL130.0) in accordance with the decline of the lowest water level.

10Underwater Work Method by Shaft-Style Equipment
Remote Controlled Multifunctional Underwater Equipment
Underwater Operation Using an Equipment with Apprratures①Erection of Shaft②Instllation of Equipment, LaunchRemote control

Machine guidance

SummaryThis equipment enables a series of underwater operations such as rock crushing,excavation, debris, disposal, precise sounding, photography, etc. in a safe andreliable condition through remote controlling. These are carried out by using
various apparatus on a machine attached to a shaft which is lowered from a barge.
The machine moves up and down along the shaft.
The equipment has been developed to conduct various underwater works
without divers. It is especially advantageous for works in deep, steep and limited
visibility areas such as dam reservoirs. Significant improvements of safety andoperational efficiency are observed through remote controlled visualization
technology and computerized technology.

③Rock crushing, Debris collecting

Specific Features
a. Enables deep underwater ( ‐50m) works without divers
b. Applicable for all types of reservoirs
c. Applicable for very steep areas via an equipped casing auger
d. Applicable for deep and dark reservoir bases via equipped ultrasonic camera
e. Enables precise execution via equipped sounders④Dredging

Various Apparatuses

Summary of the projectThis method was adopted for the construction of the inflow and vestibule area of the tunnel discharge facility
in the Amagase Dam Redevelopment Project.

Amagase Dam Specifications
Model: Arched concrete dam
Dam height: 73.0ｍ
Crest length: 254.0m
Dam volume: 122,000m3

天ヶ瀬再開発完成予想図

ﾄﾝﾈﾙ放流設備

Total reservoir capacity:
26,280,000m3
Effective reservoir capacity:
20,000,000m3
Purpose : Flood control,
Waterworks,
Power generation

11

Inspection for Dam Safety

13

14

Security
Management

What are requiredfor dam facilities

Functional
Enhancements

Flood

Power Shortage

CarbonNeutrality

Sedimentation

Earthquake

Aging
Facillities

Outlets
Improvement

Increase Power
Generation
Capacity

Dam inspection technologies
to improve management and evaluate soundness

Advanced
Dam i nsp ecti on system
Forecastingand dam inspection with ICT
Comprehensive Earthquake
MethodDigitalIntegrated Dam Sediment
Resistance Transformation
Control
Operations

Raising
Dam Body

Improvement technologies
to enhance dam functions

Technologies that enable to upgrade
dam functions under operation
by installing temporary facilities“Faster, more reasonable,
more environmentally friendly”

Enhancement of dam functions
by upgrading existing damsDrought

Climate Change

Depopulation
Stable Growth

Changes in social, economic, natural environmentDo you inspect dams at the right time?
Aftera flood

Age-related
deterioration

Regularly

After
an earthquake

Do you inspect dams in adequate ways?
Deformation

Visual Inspection

Normal plumb line

Appearance inspection

UpliftLeakage

Bourdon pressure gauge

Drain hole

Triangular weir

Are there clogs
like this?

How have the accumulated measured values changed over time?
Change over timeδEvaluation

Measurements and Countermeasures

Under a constant load condition,
the measured values have been
decreasing.
tδ

Under a constant load condition,Safe
themeasuredvalueshave(Stable & Sound)remained constant.

Usual measurements

t
δ

t
δ

Under a constant load condition,
the measured values have been
increasing, but the rate of theincreases have been decreasing.

Under a constant load condition,
the measured values have been
increasing at a constant rate.

Hazardous

Carrying out careful measurements
Examination of countermeasurestδt

Under a constant load condition,
the measured values have been
increasing with an accelerating
increase.

Implementation of countermeasures
Dangerous

15

Emergency countermeasures : Drawdown
Permanent countermeasures
Partial abnormality: Repair works

Widespread abnormality: Improvement works, etc.

Examples of dam inspections by ICT
After
a flood

Age-related
deterioration

Regularly

After
an earthquake

Example of displacement inspection and measurement by GNSS at fill dams
Visual inspection(Once a day ～ Once a week)

Measurement

Anytime, anywhere
Can be checked with a mobile phone

Continuous, high-accuracy measurementby GNSS

Early detection

Deformation after sudden changes in water level
Deformation after an earthquaqe(Once every 3 months)

GNSS

Weather
forecast

Periodic measurements cannot capture the rapid displacement
immediately after an earthquake

Mobile phone

Management
officeDamsiteδ

Monitaring center

GNSS sensor

Rapid
displacement

Time lag

GeneralofficeＴ● ： Electro-optical distance measuring： GNSS

Example of drone inspection of concrete dams
Shooting images

Analysis image

3D imageInspection without drone
Example of crack map

Inspection
with field glasses

Crack (0.2 mm to 0.5 mm)
Crack (0.5mm to 1.0mm)
Crack (1.0mm to 2.0mm)
Crack (2.0 mm or more)
Crack with free lime
Alligator crack
Leakage
Free lime, Deposit
Rock pocket
Surface peeling
Rust, Exposed steel bar
Repaired site
Others

Inspection
by visual

Conventional
visual inspection

Digital data management for the entire dam
through the use of ICT

Visual inspection
by drone

AnywhereDrones can take photos even any areas where people is not accessible

Abbreviation

Early detection

GNSS : Global Navigation Satellite System
ICT : Information and Communication Technology

Abnormalities immediately after an earthquake
Even small cracks, leaks, etc.

16

17
Mechanical Validation[Dam Manager]

Daily reservoir operation[Dam Inspector]

Operational panel inspection[Dam Manager]

Report inspection[Dam Inspector]

Dam Safety Inspection in Japan

 Inspection can revive your business longer

 Inspection can develop your engineers’ capacity

 Inspection can keep your dams active

Why Dam Safety Inspection Matters(iv) Reservoir(iii) Electrical equipment(ii) Mechanical equipment(i) Dam body and its foundation(iv) River flow condition(iii) Reservoir management system(ii) Dam management system(i) Arrangement of personnel

Inspection Items

Propose better O&M strategy

Revise O&M strategy[Dam Manager]- Judge dam safety- Propose future O&M strategy

Support the Inspection[Dam Inspector]

Dam Safety Inspection

Prepare for field investigation

Check data and field

Check the preparation

Check the preparation* Data history of seepage,
deformation, uplift pressure, etc.

[Dam Manager]
Prepare data* for inspection[Dam Advisory Experts][Dam Advisory Experts] from JAPAN[Dam Inspector] Your organization/authority/company[Dam Manager] Your organization/authority/company

How Dam Advisory Experts Works

Dam equipment and reservoir

Operation and MaintenanceCategory

Inspection Items

Dam Advisory Experts from JAPAN

18

Appendix
We have Original Advanced Technologies

19Current Dam Technology in JapanNew Construction Technologies
SP-TOM (Special Pipe Transportation Method)
This method can transport large quantities of concrete,soil and stone stably and continuously, by rotating asteel-pipe which several hard rubber blades are installed
in a spiral pattern inside. The pipeline is installed on theslope.
Materials
supply system
SP-TOM
transport device

Drive device

SP mixer (Special Pipe mixer)
This mixer was developed to mix CSG materials.
This method is to mix materials passing throughthe interior by rotating a mixing tube equippedwith blades inside the mixer.
The mixing tube is installed to incline. The
self-weight of the CSG materials cause them toflow through the mixer. This mixer has two
mixing effects inside its mixing tube; forced
agitation by drive power and falling.

Patent:Incorporated Administrative Agency Japan Water
Agency; KAJIMA CORPORATION; OBAYASHICORPORATION; TOBISHIMA COPORATION;
Kumagai Gumi Co., Ltd.; The Zenitaka
Corporation;
Osakasaiseki
Engineering
Corporation

Contact Person:

Construction Management Dept.
Hitoshi Numoto

E-mail:numoto@kajima.com

Phone:+81-3-5544-1111

URL:

https://www.kajima.co.jp/english/welcome.html

20Current Dam Technology in Japan

Floating Type Upstream Cofferdam Method
Innovative Dam Redevelopment – A New Coffering System for Underwater Work–

Feature of technology

With the floating type upstream cofferdam
method, steel plates (skin plates) are attached
to both the inside and outside of the bulkhead,the upstream cofferdam barrier that is
integrated into the base is floated, and is
supported by installing an anti-buoyancy braceon the top barrier of the dam body. The
construction assembles barrier blocks made at
the site on the reservoir surface, tows them tothe installation position, pulls them by winch
and secures them. The floating type upstream
cofferdam method--assembling and installingwhile adjusting the ballast by filling anddraining water from a reservoir--is the first of its
kind in the world.
Single block used in the floating method Anti-buoyancy brace

Transporting on water

Skin plate
Dam-body drilling

Buoyancy chamber

Installation status

Water Filling or Draining works
Air

Ballast Water

Floating
TypeType
Temporary
Floating
Cofferdam
Figure of Structure

Technology developers:
Kajima Corporation; Hitachi Zosen Corporation
Joint developers:

Upstream

Figure of Structure

Cofferdam

Ministry of Land, Infrastructure, Transport and Tourism
Kyushu Regional Bureau; Japan Dam Engineering
CenterContact Person:

Construction Management Dept.
Hitoshi Numoto

E-mail:numoto@kajima.com

Phone:+81-3-5544-1111

URL:

https://www.kajima.co.jp/english/welcome.html

21

Current Dam Technology in Japan
CRT（The Continuous Rotary Tube）Mixer System
The Continuous Rotary Tube (CRT) Mixer System provides using the Cemented Sand andGravel (CSG) Method. By attaching agitating blades inside the steel drum and maintaining

specified rotation speeds and angles, the mixer is capable of producing mixtures of consistent andstable quality.

Contact Person:

Public Relations Department

E-mail:kouhoubu@nishimatsu.co.jp

Phone:+81-3-3502-7601

URL:

https://www.nishimatsu.co.jp/eng/

22

Current Dam Technology in Japan
Newly Developed High-performance CSG Mixer: Double Rotation Continuous Mixer
The newly developed double-rotation mixer combining the characteristics of a tilting mixer and a forced
circulating mixer produces high-quality CSG (Cemented Sand and Gravel) mixes at a rate exceeding
200 m3/hDrum

How Mixing Takes Place
PaddlesMaterial movement

Example of Concrete Plant Layout

Constant feeder

Cement silo
Receiving hopper

Double-rotation mixer

Backhoe

Cement silo
Double-rotation
mixer

Receiving hopper

23

BackhoeCurrent Dam Technology in Japan

Mixer Specifications
Rotating Drum Specifications
Drum inside diameter and height
Rotation speed and direction
Motive power
Drive system

φ1800×4200L
10 rpm (clockwise looking in the direction of movement)
37kw×220V
Chain drive
Roller (φ400 × 145L) × 4
Thrust roller (φ250 × 90L) × 2

Support system

Inner Paddle Specifications
Mixer outside diameter, pitch and number of paddle shafts
Rotation speed and direction
Motive power
Drive system

φ1100 × P1000 (two shafts)
38 rpm (counterclockwise looking in the direction of movement)
45kw×220V
Chain coupling drive, chain drive
Bearing
Plummer block (φ135)
30t-220-220
36 pcs.

Support system
Paddle inserts

Size
Quantity

Internal
paddles

Rotating
drum

MixingSectional View

Side View

SHIMZ CORPORATION
Contact Division:

Dam Engineering Dept.

E-mail:e.hasegawa@shimz.co.jp

Phone:+81-3-3561-3883

URL:

https://www.shimz.co.jp/en/24Current Dam Technology in Japan
New Water Filtration System (Advanced Membrane Filtration Process)In construction projects such as tunnel and dam construction and site preparation, proper treatment of
turbid water generated from construction work is important in order to protect the environment. There
has also been growing demand for higher water treatment performance than required by the current
standards of the local governments.
Conventional turbid-water treatment processes relied mainly on coagulation and sedimentation.
Shimizu's newly developed filtration system effectively removes suspended solids by use of amembrane filtration process to achieve higher water quality in an environmentally considerate mannerand provide solutions to current and emerging problems.
Features
・The filtration process reduces the SS concentration of turbid water to 5 mg/L.
・High turbidity (SS1000–3000 mg/L) water can be treated directly.
・The process is environmentally friendly because it does not use any organic polymer coagulant.
・The system footprint is compact because sand filtration is not used.
・The water treatment system is environmentally considerate because it requires only a small amountof electricity.
Turbid Water Treatment Test Data

SS concentration (mg/L)

2500

2000

1500

1000
SS of raw water (mg/L)
SS of treated water (mg/L)
500

0
0

5

10

15

20

25

Time (hr)

30

35

40

45

25

50

Raw water and treated water

Current Dam Technology in Japan
System Flow
Inorganic coagulant
PAC storage tank
Membrane filtration unit
Filter tank

Raw water tank

Hydraulic head200～300mm

PAC reaction
chamber

ReleaseTreated water tank

Dewatering facility

Slurry storage tank

Dewatered cake

How Membrane Filtration Works

Membrane Filtration Capacity
Let A (m2) represent the area of themembrane surface. Then, membrane filtration
capacity V (m3/day) can be calculated asfollows:
V = A × 2 m3/day

Clean waterCore material
Filter fabric
Dirty
water

Dirty
water

Filtering membrane
Deposited turbidity

SHIMZ CORPORATION
Contact Division:

Dam Engineering Dept.

E‐mail:e.hasegawa@shimz.co.jp

Phone:+81‐3‐3561‐3883

URL:

https://www.shimz.co.jp/en/26Current Dam Technology in Japan
Remote Controlled Multifunctional Underwater Equipment
Underwater Operation Using an Equipment with Apparatus (T-iROBO UW)Remote control, Machine guidance

SummaryThis equipment enables a series of underwater operations such as rock crushing, excavation, debris
disposal, precise sounding, photography, etc.in a safe and reliable condition through remote controlling.
These are carried out by various apparatuses on a machine attached to a shaft which is lowered from abarge. The machine moves up and down along the shaft.
The equipment has been developed to conduct various underwater works without divers. It is especiallyadvantageous for works in deep, steep and limited visibility areas such as dam reservoirs. Significant
improvements of safety and operational efficiency are observed through remote controlled visualization
technology and computerized technology.

Specific Features
a.
b.
c.
d.
e.
f.
g.

Enables deep underwater works without divers
Applicable for all types of reservoirs
Applicable for very steep areas via an equipped casing auger
Enables a series of works to be carried out by various apparatuses
Equipped with I.T, machine guidanceApplicable for deep and dark reservoir bases via equipped ultrasonic camera
Enables precise execution via equipped sounders
TAISEI CORPORATION
Contact Division:

27

Dam Engineering Section

E-mail:kuroki@ce.taisei.co.jp

Phone:+81-3-5381-5282

URL:

http://www.taisei.co.jp/english/

Current Dam Technology in Japan
Various Apparatuses
Applicable for a series of works via various
apparatuses attached to a machine

Rock crushing with a breaker

Sand pump suctioning

Cleaning by an ejector

Examples of applicable works
Precise sounding

Edge cutting

Crushing concrete
Shaft

Shaft
Dam body

Sounding

haft

Shaft

Grab dredging

Surface treatment
Shaft

Instrument

Grab bucket

ｔtFoundation

haft

Air lift

Other applications

a. Drilling by an air drifterb. Surface cleaning by a rotary brushc. Rock & concrete cutting by wire-saw
d. Steel beam & pipe and reinforced concrete cutting by nibbler

28

Hydrodynamic Pressure on the Gate
The hydrodynamic pressure acting on the Gate is larger thanwhich acting on the Dam body (Westergaard’s formula)①Entire System Analysis Model (Dam-Gate-Rock-Reservoir)
Reservoir （Fluid element）

Analytical model： Dam-Gate-Rock-Reservoir Model
Analysis approach：3-Dimensional Linear Dynamic Analysis
Number of nodes and elements：About 250,000475

Gate（Shell element）
Dam（Solid element）
470

SectionAHigh

Elevation（m）

Rock（Solid element）
SectionB465

460

Westergaard’s formula

455

450
0

SectionA SectionB

Low

Distribution of hydrodynamic pressure

0.05

0.1

0.15

Dynamic Water pressure（MPa）②Gate Analysis Model
High

Analytical model：Gate Model
Analysis approach： 3-Dimensional Linear Dynamic Analysis
Number of nodes and elements：About 20,000

Low

Distribution of stress and displacement

 The hydrodynamic pressure acting on the Gate is derived from the entire
system analysis model.
 High reliable value of the stress on the Gate is calculated by Detail Gate
Analysis Model.

29

The Non-linear Analysis of Pier
Plastic deformation is visualized

Displacement（mm）①Before aseismic reinforcing work

Damaged area

200
150
100
50
0
‐50
‐100
‐150
‐200

Non‐Linear
LinearConcrete crack

Rebar yield
0

1

2

3

4

5

6

7
8
9
Time（sec）

10

11

12

13

14

15

Displacement response at the top
8
6

Stress（N/mm2）

4
2
0
‐2
‐4
‐6
‐8
-5,000■：Reinforced concrete element■：Concrete element

0

5,000
10,000Strain（μ）

20,000Stress-Strain relation②After aseismic reinforcing work
15

Reinforcement effect（initiation strain decrease）

10

1.9m

Stress（N/mm2）

Reinforcement area

15,000

4.5m

5
0
‐5
Reinforcement ratio×1.0
Reinforcement ratio×2.0
Reinforcement ratio×3.0‐10●Existing rebar●Added rebar‐15-5,0000

5,000
10,000Strain（μ）

15,00020,000Stress-Strain relation

Displacement response at the top

 Physical behavior of the pier concrete after cracking is derived and visualize Structural residual deformation on the pier after the earthquake is derived and visualize
Tokyo Electric Power Services Co., Ltd.
Contact Person:

Business Development Dept.
Ryoutarou MATSUMOTO

E-mail:r-matsumoto@tepsco.co.jp

Phone:+81 3 6372 5175

URL:

www.tepsco.co.jp

30

Current Dam Technology in Japan
Dredging method using amphibious bulldozer Model D155W
Since their first appearance as the construction equipment for marine excavation works in 1971,
the amphibious bulldozers have been engaged in over 1200 projects throughout Japan, taking fulladvantage of accumulated knowledge and experiences for over 50 years.
Technical characteristics

Amphibious bulldozers are radio remote-controlled construction machines that demonstrate theirpower in shallow water areas.
The dredger can dredge in areas where the water is too shallow to navigate or at depths of 0 to 7
meters where it is impossible to construct with land-based machinery.
This machine mainly performs dredging of underwater areas. Equipped with a bucket (3.36m3) infront of a large earth removal plate, it excavates underwater without letting the dredged soil
escape. Dredged material is transported underwater to shore. It is more accurate and economical
than other dredging methods.
Air intake
and exhaust tower

Ground pressure
95.1kN/m2(on land)
60.8kN/m2(under water)

Wireless Antenna

Tolerable static water level

Maximum water
depth of operation 7m

Hydraulic ripper

Maximum water
depth of operation 7m

Soil removing blade with an apron.
Bucket capacity:3.36m3

Radio remote-controlled amphibious bulldozer 43.5 t class

Outline drawing of amphibious bulldozer

Komatsu D155W

Specific features

・ The operator’s safety is ensured as the machine is remotely controlled using wireless control.
・ In the event of a sudden rise in water level, this machine can be quickly moved to a safe
location for evacuating.

・ Temporary construction work is minimal and cost-effective.
・ Capable of dredging in areas with high flow velocity up to about 2 m/sec, where work vessels
cannot be operated.

Dredging rangeof amphibious bulldozer

Main body of a large dam

Applicability of amphibious bulldozers in dam reservoir

H.W.L

The middle to upper reaches of the dam reservoir haverelatively high flow velocities and shallow water depths.

L.W.L

Mainly gravel
Mainly silt

mainly sandThe gravel and sand sediments formed in this area can beremoved by dredging with an amphibious bulldozer.

Downstream part

Midstream part

upstream part

Dredging range of amphibious bulldozer in a dam reservoir

Asunaro Aoki Construction Co.,Ltd.
Contact Division :Civil Engineering Technology Division

E-mail:tech-info@aaconst.co.jp

URL:

https://www.aaconst.co.jp/

Dredging situation at dam reservoir

31

Current Dam Technology in Japan
Title

High-lift dredging method that does not cause turbidity in water "High-lift non-turbidity

dredging method"〇Abstract
We have developed a dredging method that can remove
sediment from dammed lakes with a depth of 20 m or more
and a lifting height of 10 m or more without causing waterpollution. The method uses a combination of a powerful
vacuum generator and a high-concentration stirring pump toachieve continuous sediment removal at a high lift without
disturbing the lake bed. Due to the fact the new method does
not cause turbidity in water , the dam can continue to generate power during dredging operations
near the water intake. In addition, the new technique can be used throughout the year (including inflood season), which makes it far more flexible than existing methods.

mud separator
vacuum generator

sediment

treatment

conveying pipe

facility

work barge

relay pump unit
Lifting height
30ｍ

P

relay pump unit
vacuum suction tube

auger equipped suction machine

work barge

sedimentary sediment

auger equipped suction machine〇Features
1． It is possible to remove sediment with a lift of over 30m without polluting water quality, so the dam
can continue to generate power, even when dredging occurs near the water intake.
2． Collective management is possible from an ICT central control room with just one operator.
3． In addition to enabling compact maintenance operations without the need for large-scaleequipment, there is a degree of freedom in equipment organization that enables easy adaptation
to local site conditions.
〇Applications
・Where functional improvement and recovery of water intake facilities buried under sediment
・When the turbidity level of the reservoir
Fujita Corporationis unacceptable
・In environments where it is difficult to

Contact Person:

lower
the water level for maintenanceE-mail:yinami@fujita.co.jp

Phone:+81-3-3796-2278

・When it is necessary to continue using URL:
water for power generation, agricultural use,etc. whilst removing sediment.

32

Yuta INAMI

www.fujita.com

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Published by

JAPAN
COMMISSION
ON LARGE DAMS

Ningyo-cho Sun City Bldg. 2F,
1-2-7, Nihonbashi-Ningyo-cho,
Chuo-ku, Tokyo 103-0013, JAPANURL:http://www.jcold.or.jp