Japanese National Committee on Large Dams. Dams in Japan, No. 10

(o

)

(b)

t

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:

tl

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.jl

li

il

.

ii

,il

1i

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Fig.

5

Section

of

Concrete

Gravity

Dam

(a)

Section

with

theoretical

triangle

(b)

Section

with

upstream

filet

(c)

Section

with

mat

concrete

(c'

2.2.3 Embankment

Dams

on

River Deposit

several

methods

are adopted

for thi

treatment

of river

depnsir

on the

foundations

of

embankment

dams.

Recent

ex-

.ment of perviousness

are

the

earth

blanket

over

whole

reser_

r deposits

at

Funagira

Dam.

At

Ouchi

Dam,

stabiliw

of the

udflow deposit

on

foundation

of

rockfill,replacing

it Ly

rock

,f

the upstream

slope

J of reducing

seepige

water

from

the

reservoir

in constructins

!vJ!,,vr.

!u.'eu!,,,s

ro

".e,mperv,ous

portron

ot,n"

"*o*',?,jill.'TE:I,i.ffi?:*:XrJ'[i.?T;:$#:i..L;:i

intruding

into

the

abutment,

this

method

ii

more effective

and economical

compared-with

otrre

riettroos

suctr as grouting,

on

condition

that

the

scale

of dam

and reservoir

is

small and

topograprucal

conditions

are

favorable.

This

method

was

applied

to Higashibaru

reservoir

of the

tvriiistry.or

egricuttur",

r-".oy

uia

Fishenes.

purpose

of

the

reservofu

is

irrigation.

Total

storage

capacity

is thms

and normal

watir

surface

area

is

i.6ha.

Homogeneous

earth

dam

was

21m

high

with

303m

oest.length,

and

earth blanket

was

constructed

on

a depression

in

the

terraced

hill on

top of

land

to

be irrigated.

Geoloev

of the

site

consists

of

layers

of loam and

terac€-gravel

with permeability

coefficient

ranging

from

l0-'

to

lo-,cn/s,

and

iripervious

layer

of.anay

,noa"tooetying

at

the

aepth

of 30m.

The

embankment

materials

availabie

around

ihe site

are ieriace

gravei

and

loam.

The

former

has

rclatively

high

:*:*1.fl9 S,",1:I*

has low permeability.

The

former was

used

for

the

materials

ofl embankment

and

blanket

on

zontal

portions.

The

thickness

of

the

horizontal

blanket

was

rs

foundation,

drains

were

arranged

in fishbone

shape

under

Cown of

the

reservoir.

opment

Co.,

Ltd.

for

the purposes

of power

generation

and

,f

the Tenryu

River.

ite, and

the- riverbed

is overlaid

with

a

gravel

layer

60m deep.

I

prepared

-by_excavating

root_shaped

ridge

protruding

on the

6m respecively.

As

for

the

left

wing

of

the

dam,-a

levee

teposit.

rockfillsrructure

with_

c€ntral

impeNious

core.

Clay

grouting

oefficient

of permeability

of

deposit

ranged

from

10_t

to 10:

I to the bedrock

consisting

of

black

shist.

The

coefficient

of

Ue

station

being

constructed

by Electric

power

Development

t

4.4hm3

respectively.

The

foundation

of

Ouchi

Dam

is co_

rximum thickness

being

30m.

The

mud_flow

deposit

consists

density

is approximately

1.9vmr

and

angle

of

slleadng

resist-

The

deposit

was

temoved

ftom

the

foundation

of

the core,

bua.ol.lh"

foundation

of

rockfil,

the

least

nccessary

amount

of

materials

were

removed

and

replaced

by

ro"k

m"teriais.

itabitity

anatysis

wa.

""rial

"",

"r-ing

sliding

circle

I

method

including

foundation.

The downstream

slope was stabilized

by weighting

till.

However,

on

the upstream

slofre,

I'€ighting

fill

was not

adequate against

the combination

of earthquake

and

rapid drawdown;

and panial

excavation

and re-

placing

were

adopted.

During

excavation works,

in-situ tests

(direct

shear,

penetration,

and density

measurement)

and

stability

analysis

were

carried

out in

parallel,

to determine the final

shape of excavation.

2.3

ACTUAL

STATE OF RESERVOIR

SEDIMENTATION AND

(1)

Actual

State of

Reservoir Sedimentation

(A)

Investigation

into

the Actual

State of Sedimentation

The

River

Bureau

of the Ministry

of Construction investigated

the actual

state of sediment

encroachment

at 425 dams

with

total

storage

capacity

exceeding

thmr in 1978 and

1979. The result

(Table

1) revealed

that

the

quantity

of sediment

in dams

over

the whole

country was,

in 1977, approximately

800hmr or

about 6Vo of

the total

storage capaciiy

13,200hm'.

By

regions,

4OVo

of the

above-mentioned

s€diment was stored in dams

in Chubu Distdct.

And by

owners, TOV| of the tot-

al

sediment

was

stored

in dams of

power

companies. The River

Bureau suggests these

owners

to take

measures

to

marn-

tain

the original

functions,

so as not to

cause damages to third

parties.

(B)

Estimation

df Sedimentation

in 1985

Assuming

that

the

Progress

in sedimentation

until 191ry continues at

tbe same rate

in the future,

the inclease ill

sedi.

ment

from

1977 to

1985 is estimated

to be approximately 400hm1.

The total amount

of

sediment

in 1985 wil be about

1,200hmr,

or

approximately

9% of the

total storage capacity.

(C)

Amount

of Sediment

Removable

by Excavation

The

amount

of s€diment

stored at

shauow

parts,

water depth

being less than 20m,

is

rcgarded as removable

by

excavation.

This

amount of

sediment is estimated

to be approximately 300hm3

in 1977

and 500hm3

in 19E5.

These are

38Vo

znd

48Vo

of total

amount of

sediment in 197

and 1985, respectivelv.

(D)

Amount

of

Concrete

Aggregate Available

ftom Reservoir

Sediment

Crnsidering

the quality

of sediment,

the amount

of aggregate available

ftom removable

reservoir

sediment

is estimated

to

be approximately

190hmr

in 1977

and 2?0hmr

in 1985.

Table

I Actual

State of

Sedimentation

Investigated

in 1977

District

Number

of dams

investigated

Total

storage

(h*t)

Volume

of sedimentation

(hm')

Ratio

of sedimentation

to storage

Annual

volume

of

sedimentation

(hm')

Annual

volume

of sedimentation

per

dam

(103m3)

Hokkaido

39

1.,349

52

3.9%

3.1

80

Tohoku

38

980 44

4.5Vo

2.5

67

Kanto

36

1,L73

35

3.jVo

2.0

55

Hokuriku

73

3,079

t70

5.5Vo

8.0

111

Chubu

55

1,794

322

18.UVo

16.9

307

Kinki

38

L,553

56

3.6Vo

4.3

115

Chugoku

47

1,033

L6

1..5Vo

0.9

19

Shikoku

37

96s

60

63%

4.2

TI4

Kyushu

62

l,2u

70

5.5Vo

3.5

57

Total

425

L3,lgg

825

6.3Vo

45.5

107

(2)

Problems

in Removing

Reservoir

Sediment

Il is difficult

to fully

rely on the use

of sediment for conerete

aggregate

as measures

to

prevent

the malfunction

of re-

sewajirs,

if taken

into

account

the relation

between sediment inflow

and demand for

aggregatl

as wcll

as the

problems

con-

c€ming

the quality

of sediment.

However,

it is an effective method

for dams which

need

the restoration

of function

through

removing

sediment.

Thcrefore,

it is a

ptacticsl

measure

to execute

removing

of sediment

with the co-operation

of

the

oi'ner

of dams,

beginning

vdth

the dams

for which the restoration

of effective

storage in

bighly

needed.

This

survey

revealed

that TOVo

oI total

amount of sediment was

stored in

dams fot

porlr

generation.

High

rate of

sedimentation

is

seen in

small scale

dams with

small-storage capacity.

In these dams,

ttre

Ueneni of removing

;diment is

small

comParod

with

the cost

of removing

it. In other word,

these kind

of dams are

in less

need of restoration

of storage

capacrty

compared

with

other

kind of

dams.

Therefore,

at

the dams

in which

the restoration

of reservoir

capacity is not important,

removal

of s€diment is

carried

out

ftom

the

necessity

of river

control,

maintaining of

the originai function

of river

and also

ftom

economical

Doint

as

sources

of

aggregate,

but not ftom

the vie$,point

of restoration of

storage capacity.

i

I

I{owever'

the

dams

and reservoirs

are limited, imponant

resources in

Japan;

the

effective

capacity

of reservoir

is to be

pr€serv€d

and

utilized

cffectively.

h

case that some new

needs arise for thi

effective

capacity

of thJ

rescrvoir,

it

is effec-

tlve to

restore

capacity

considering

the benefit of use for aggregate.

(3)

Future

trends

in

countermeaiures

against

reservoil

sedimentation

(A)

Promotion

of

Utilization

for

Concrete Aggregate

In 1977,

330,000m'of

sediment was

excavated for concrete aggregate

throughout

the

country.

On the orher

hand, the

demand

for

concrete

aggregate

is approximately

480hm'.

Excavation

of rivei

deposit

for

concrete

aggregate

is not ex-

pected

to

grow

so much

in the future.

The resewoir

sediment

is

expected to

be remaining

.".ou.""

ii. concrete

aggre-

gate.

Removal

of reservoir

sediment

is effective

either

for owners

of dams or for

the assuration

of aggregate

resource.

Therefore,

the

investigation

into the

measure for

promoting

thls ls

necessary.

(B)

Promotion

of Debris

Dams

Debris

dam

is an effective method

for the removal of sediment

by trapping the

sediment in

the

upstream

shalow

part

of reservoirs,

reducing

the cost

for excavation- The

River

Bureau

of Ministry of

C-onstruction

is

promoting

actively the

construction

of

d€bris dams

and haul

roads for removing sediment from

1979, as reservoir preservation

works

or as subsidi-

ary

system

for

reservoir preservation

works.

(C)

Consideration

for Removal of Sediment

at Planning Stage

of Dam

In

many

cases, it

is difficult to remove

sediment from existing

dams, because of unfavorable

conditions-

It is necessary

to consider in

tbc iuture, about the rcmoval

of sediment at the early

planning

stage

of dams

by making

provisions

such

as

dcbris dams and haul

roads.

(D)

Studies

on

Mcthods

of Removal of

Sediment

An effective

method

for the removal

of sediment is to flush it with

river discharge. However,

nany

problems

are un-

solved

on its practical

applications.

Since

the scdimcnt flushing facilitics

are

gencrally

constructed

in d-am

body or

in the

abutments,

installations

of them after

the completion

of

dams are

difncult. Therefor€, installation

of

sediment

flushing

facilities

should

atso be considered

at the planning

stage of

dams.

(4)

Practical

Examples

(A)

Sakuma

Dam

- -Sakuma

Dam is

i conqete

gravity

dam

155.5m high

with

a catchment

area 3,82?km, conshucted

on the

Tenryu River

by

the

Electric

Power

Development

Co., Ltd. for the

purpose

of

power

generation.

During 26 yeas

of

operaiion, the

quantity

of

sediment

amounted

to approximately

83hm',

ot 25Vo of

thc total storage capacity

330hmr.

Owing

to

the sediment

trapping

€ff€ct at medium-scale dams

on the upper reaches

of the

River, sediment

encroach-

ment

in this

r€servoir

is

mainly mmposed

of

particles

finer tha! 5mm.

Sediments are

classified

from downsream

to up

stream

into

clay,

silt,

sand and fine

gravels.

_The

scdiment

at

the upstream part

is expected to be excellent quality

aggregate

for concrete.

Since large-hauling

trucks

cannot

be used

because of

steep

gorges

around the site,

I basic

plan

of hydraulic

transportation

Uy

pipetines

was

worked

out.

.

According

to the

basic

plan,

the

pipeline

is

to be

16km long,

annual

quantity

of transportation

being 800,000mr. For

the

execution

of this

project,

some

technical

problems

are left to

bc solved. Development

and

researctr-arc

underway us-

ing experimental

model

plant.

(B)

Akiba

Dam

_.

Akiba

Dam

is

a concrete

gavity

dam

E4m

high, constructed

by Electric

Power Development

Co.,

Ltd. on the

Tenryu

Rivcr'

for

the

purposc

of

powcr g€neratioo.

Thc dam was

completed in 1958. Total

storag€

capacity is

34hrd and

catch-

ment

area

at the

dam

site is 4,490kmr.

_ ..In

order

to

maintain.thc

original

ctimated rivclbcd,

continuous

annual

rcmoval of

sedimcnt

of

350,000m' is necessary.

Sedimcnts

are classified

into clay,

silt, sand and

gravel

froin downstfeam to upstream,

though

these ai€

mixed at their

boundaries.

APpropriate

methods

of removal are

adoptcd dcpending

on the

particle

sizes

of matedals,

as mentioned

hereafter.

Downstream

reaches:-

Sediments between the dam

and a

point

4.5km upstrcam of the

dam

consist

of fine clay and

silt.

Annually

100,000m!

of them

are dredgcd by

pump,

ana

pitcd

lust

up6k€am of thc

dam. to

be flushed

with the river

discharge

during

flood

runoff.

Middle

reach€s:-

Sediments

b€tween

points

4.5km

and 8.2km

upstream of the

dam are wcll graded.

Annualty

200,000mr

of them arc

cxcavated

for the use as

concrete

aggregates.

Upstream

reaches:-

Sediments

up to a

point

of 8.2km

upstream

of the dam are

coarse

grained

gravels.

Annually

50'000m3

of

thcm ;re

excavated using

shovcl-type excavators, them partly

used for concrete

aggiegate

aid

partty

wasted

to

spoil

areas.

2.4

MATERIAIS

AND

CONSTRUCTION

METI{OD FOR

EMBANKMENT

DAMS

(l)

ImperviousMaterials

Soil

materials

or

artifrcial

materials

are used for impervious

materials.

Soil matedals

are

selected from talus soils,

:::th:1"9

resi'lual

soils,

riv€r

deposits or volcanic

deposiG. Owing

to the

compli€tcd geological

and topographicat condi-

trons

in

Japan

in general,

large

amount

of homogeneous materials

ar€

not avaitable

iom i single

bonow

pit.

.e,na in

many

cascs

natural

water

content

of materials

are considerably

higher

than

thc optimum

one, btuse of

w;t

ctmate

in

Japan.

The

core

materials

for zone-tyPe dam differ

preferably

little in

mechanical

properties

from materials

adjacent to these.

8

Good

trafficability

is also needed

for handling with

heavy equipments.

Therefore

coarse

grained

materials

are

preferable

as

long

as the

imperviousness

is

satisfied.

Rang€ of

gradation

meeting these

requirements

is narrow,

and the homogeoeity

is required'

To

cope with

the unbalance

of supply and

demand, mixing

of materials

is

effective

and often

aaopt"a in

Japan.

Mixing

of materials was

first

applied at the/constuction

of Miboro

Dam completed

in 1960,

Tedori

River Dam

being

the recent

example.

At Tedori

River Dam, matedals from

four

borrow

pits

were piled

and

mixed on two

stock

yards,

producing

900,000m'

materials

of excellent quality.

Through

this

practice,

it was

possible

to make

use the most of

the

construction

time for core materials,

which

had so lar been restricted

to less

than 100

days/year

owing to

meteorological

conditions.

The effective

control

of embankment was

also

possible

through

assurred homogineity

of maierials.

_ -

As the

artifficial

matedals,

asphalt

concete and

po

land cement

concrete are

adopted.

Asphalt

concrete

is used main-

ly for

upstream

membranes,

and sometimes

for surface membrances

of

pool-type

reservoir(Numappara

reservoir)

or inter-

nal

core

(Mu

Dam).

conqete has

not been

used for upstream membranes

of dam in

Japan sinci

1960.

(2)

Pervious

Materials

. .

Modem

rockfill

dams

in Japan originated

from Miboro Dam, 131m

high. Coane

sound rock

matcrials were

dumped

in

4m lifts

and

sluiced. Constructions

of large scale rockfill dams

continued in 1960s.

However,

it was not

always

possi-

ble to

obtail

coarse

sound materials

owing to

the

geological

conditions

in Japan.

-,.In

many

dams,

relatively

line-grained

rock materials

were

placed

in layers

of 1-2m and

compacted

by automobile

traffic.

In 1970s vibratory

rollers

were widely

used. at almost all dams

for compaction

of the

pervioui

materials.

This

is

attributed

to the

progress

made receqtly in

researches on the

stability of

rockfill dams

as well as

on the testing

procedures

of

strength

and deformation

characteristics of rock

materials, r€sulting

in the

clarifications

of the effect

of com-

paction,

such

as indease

in strength,

decrease in deformability

and strengthening

of aseismicity.

3. RECENT

PROGRESS IN DAM

ENGINEERING

IN

JAPAN

3.1

ROLLER

COMPACTED

DAM.(R.

C. D.) CONCRETE METHOD

R.

C. D.

Method

is defined

as the

placing

poor-mix

concrete with

extremely dry

consistency

compacted

by vibratory

rollers.

The

River

Bureau of

Ministry of

Construction completed

in 1980 the

placing

of

dam'concrete

of

Sirimajigawa

99,

Agtt high

and

317,000mr in volume,

by means

of R. C. D. Method.

In the

same

year,

execution

of the mat-part

(widened

base

part

of dam

body at the interface

with bedrock) by R.

C. D. Method was

adopted

at

Okawa dam,

78m

high

and

1,000,000mi

in volume

with

suc€ss,. Placing

of corcrete started

in September

1978

and

July 1979 respectiveiy.

At Shimajigawa

Dam

some 300,0mm3

of concrete was

placed

in 25 months,

;hile the

mat concrete

6f Ok"*" darn, ZSin

thick

and

some

300,000mx in volume,

was

placed

in nine months.

These

placing

times include

the test

placing

periods

nec€ssary

for

the

actual executions.

There

is a

considerable

difference

in

placing

time of

both

dams.

This

shows the

charactedstics

of R. C. D.

Method.

With

resPect

to the

mat

part

of Okawa Dam

with wide

placing

surface

approimately

15,000m,,

the

placing

rate of conqete

could

be

heightened

without

restrictions

through enlarging the installed

capacity

of concrete productio-n

equipment

and

hauling

equipment.

The rate depends

only

on the economy. But

in the casi

of Shimajigawa

Ijam

which is

sgm high, the

Placing

nte was

limited

with restrictions

due

to the relatively small

placing

area, ttre

intricate

structures

within da;

body

such

as

insPection galleries

and also

to utilization

of frxed cable cranes

for vertical

transportations

in addition

to trucks.

The

River

Bureau

has

been carrying

out vadous

investigations

and researches

on the rational

executioD

of conqete

dams

since

1974.

R.

C. D. Method

was thought

to be an cffective

method, and a

special

committee

on it was

organized

by experts.

Based

on the

proposals

of the

committee, Large-scale field

tests

and supplemeltary

laboratory

tests were car-

ried

out.

Both

dams,

mentioned above,

are the fruits of these

researches, proving

ihe effectiveness

in the

actual execu-

tion.

'These

two

dams

were the

first examples

constructed by means

of R.

C.

D.

Method,conftonting

some difficulties

and

problems

left

to be

solved. However,

even

with the

problems

left

to the future,both

dams

are

prim!

examples to be high-

ly evaluated.

3.2

RECENT

PROGRESS

IN

ANALYTICAL

RESEARCHES

(1)

Recent

Analysis

Method

on

Aseismicity

of Embankment Dams

Research

results

of Central Research

Institute

of Electric Power

Industry

based

on seismological

observations, model

tests

and

dynamic

numerical

analyses

have

revealed high aseismicity

of rockfill dams.

-

For_

example,

the

rupture tests

on models

using

granite

cobbles

revealed

the following:-

The

rupture

took

place

as sur-

face

slides

in

the vicinity

of crest against

wide range of

period

of seiimic waves

includin!

natural

ieriod.

The

horizontat

response

acceleration

at rupture

is almost

constant independent

of

the

periods,

ranging

from

700

t; 800

gal.

This state is

well

simulated

using dynamic

analysis

based

on FEM.

_

F

9T

the

dynamic

analysis

of embankment,

time history

of the safety factor

on

potential

sliding

surface was

obtained.

The

minimum

value

coincides with

the safety factor

of convintional sliding

circle

m"ihod *ith

the

sieismic intensity

equiva-

le-nt

to the

average

of

response accelerations

along the sliding surface

at the time

of minimum

safety

factor.

Ihi average

of

response

acceleration

depends on

the

period

of

ground

motion

and the natural period

of

the ernbankment.

In

case that

the.safety

factor

is lower

than 1,

the stability

is to be evaluated through integrating

permanant

deformation

throughout

the

period

with

safely

lactor

less than

1

(2)

.Rcccnt

Analvsis

on

Hr.drodvnarnic

prcssurc

cluring

Earthquakes

Acting

on

Concretc

Dants

In order

to

clarify

the influences

of

bctundarv

anniitinn.

at the

bonom

of reservoir

.n

hydr.dynamic

pressure

and

re-

sponse

of

dam.

arralysis

mettrod

on dam-reservoir

system was

developed

by

the

central

Rescarch

Institute

of Elecric

power

Industr-\"

Response

against

horizontal

ground

motion was

obtain;d.

considering

only

the

first vibration

mocle

and

the

1lll9.'T"t"

partial

absorption

conditions

tt the

bottom

of reservoir-

Shear

forces

ani

m.ment

at the

base

of

dan, were

oOtarned

Then'

in

ordcr

to

investi-qate

nrore

strictly

into

the interactions

among

bedrock.

dam

and

reservoir.

a series

of an|lyses

were

carried

out

based

on

a model

including

above

three.

For the

analysis

code,

infiltration

condition

to

the

eround

which

is widel'

used.

for

example

in

FLUSH.

wia

extended

to water-bedrocks

system.

Distriburi""

"i

-tyar"r,",*

pressure

for

honzontal

stationary

vibration

was

obtained,

with the

results

similar to

the

above.

3.3

FULL

AUTOMATIC

GROUTING

PLANT

Foundation

of ouchi

Dam

consists

of Neogene

Tertiarv

tuff.

At rhe

riverbed.

a fault

exists

dipping

on left

bank

side.

The

left

abutment'

the

hansinq

side

of the

fault,

is

wiathered

and

deteriorated

on

the whole,

influ'enceo

by the

fault.

The

foundation

needed

to

be

ireitea with

grouting

including

the

fracture

zone

and

the

deteriorated

areas.

t.he

total

length

of

srouting

holes

was

estimated

to exceed

100,000m.

For the

improvem"nt

- qu"lir;';;;;;;i-"rl

,"utns

in ,n"n-

rstalled.

Ldary plants

and

injection

points.

The central

plant

is

com_

I room.

Mixing

units

produce

automatically

undiluted

grout

vey

rhe

undiluted

milk to

secondary

plants

where

the

milk

is

pressure

are

recorded

in

the

control

room.

and

the

return val

discharge.

and

pressure

at each

injection

point.

Through

mem

grout^milk

is changed

automarically.

The records

of in]ections

At

ouchi

Dam.

4

mixing

untis

and

7 conveying

uniis made

the simultaneous

operation

of 21 grouting

pumps

possible.

Through

grasping

at the

control

room

all

infor-mation

of the construction

site,

it is possiute

to"analys'e'all

data

and issue

necessarl'

directions

quickly.

thus

contributing

to the

improvement

of

quality

contiol

"r'*"rr

".

to

,rc

,lring

of

manpower.

5

,"

.;':

"I

..:

l!r

::::

-*S:T,'***l-

'al

d,.

-':

E:::

Fig.

6

Control

Room

of

Grouting

plant

l0

l..l

trSL.

oF

flllN

MEMIIRANh5

Soil ntat.'ri:tls

ol

concrclc malcrials

are

uscd for intpervious

matcrials

of

enrbankment

or

reservoirs.

ln reccnt

vears.

nowe\tr.attcnlpts

hlt'e'

bccn made

to

replace

this kinds of

nraterials with

thin

membranes

of

vinyl

chloride

or synrheric

ruooer

At

Nishictrya

Drtttt

of Tokyo

E,lectric

Power

Co.. Ltd..

thin

menrbranes

of

terrace

clcp6sl1.

The

danr

is

21

-5nr

in

height

and 189.7m

in

crest

length.

right

bank

sitlc.

in

particular.

is covered

with

terrace

deposit

l0-7m

thick which

some

l-50m

as

far

as

the

foot

of

the hill.

vinyl

chlctride

were

usecl

fclr

the

treatment

Both

bank

of

the

dam

site

are terrace.

its

is

thousht

to

be

the

old riverbecl.

extendinc

-

To cope

\\'ith

thc perviousness

of

the terrrce

dept,sit. membranes

of vinyl

chloride

resin.2mm

thick, were

rnserted.

Its total

lensth

was

9l

5m' depth

being

8.35-l.5m.

The deposits were

removed

up to

the

bedrocks,

on which

the base con-

crete

rvas

placed.

The vinyl

membranes

wete

connected

to the water

stops

previouslv

embedded

in concrete.

soils and

sands

were

backfilled

around the viovl

membranes,

so

that

these would

form

tie vertical

impervious

membranes.

ln

the

case

of Akada

reservoir

of the

Ministry of

Agriculture,

Forestry and

Fisheries,

the

fan consisting

of sand and

gravel

on its

hottom was

blanketed

all

over, with

thin membranes

of synthetic

rubber.

In order

to protect

the

membmnes

and

supplement

its watertightness,l.6m

thick banking was

executed

on it.

Another

attempt

to shield

dams with

thin

membranes is

a bag-type

structure

made

of

rubber

cloth

mounted

on the

base

concrete.

to

be dilated with water

or air.

forming a new

type of durn,

u. show

in

Fig. 7.

So

far, this

method was

ap_

plied

to

coastal

levees

and a

small intake

dam for power generation,

Mikatagawa

Dam

oi Kansai

Electric

power

Co..

Ltd.

Researchcs

are

underway

to apply

this

method to

dams

wiih

larger

scale.

Tie Electric

eo*.t

o"ueiopln"ot

co.. Ltd.

con-

struct€d

in

1982

an experimental

inflatable

weir

of rubber

coated

fabric, 5m

high

and 15m

long.

This weir

is

thought to

be

srrited

for the

intake

of

small hydro power

plant

in mountainous

areas

whe-re

flash

floodslarry

Jo*n

t"rg. amount

of

debris.

Fig.

7

Experimental

Inflatabte

Weir

11

1.

IRT]KA.IKE

DAM

Location

Nearest

City

.

River

Purpose

......:....

.......::...........:...

Catchment

area

Mean

annual

discharge

Years

of

construction

.

Type

Foundation

Height

Crest

length

Volume

Spillway

rype

..................

....

Uncontrolled

Type

and

number

of gate

.................,....

_

Maximum

discharge

capacity

.................

160m%

Reservoir

Gross

capacity

..........

17.9x

106m1

Effective

capacity

......

15.2X

10tnl

Area

..................

.... 1.7km,

Drawdown

range

.................................

19m

Owner

................

...........

Iruka

yousui

Land

Improvement

District

Engineering

by

Construction

by

.....................

-

About

350 years

ago,

Iruka-Ike-Dam

was

constructed

by a lord

who ruled

over this

district

by accepting

a

petition

of

farmers

to secure

irrigation

water

for

land reclamation.

Ii

was a

great

achievemeut

in

those

days

to

embank

a huge

volume

of

about

3

X

lomr

in

a verv

short

time of

one and

half

year

fr6m

1632

to

1634,

owing

to

the lxceilent

teaaersrrip

of

the

feudal

lord

and the

diligence

oi the

tarrners.

Afterwards,

the

farmers

maintained

the

dam in

good

condition

for a

lon€

time and

even

improved

the

structure

by re-

peatrng

repai6,

but in

the

historv

of lruka-Ike

Dam,

in 1868

the farmers

suffired

from

inundation

wiriln-rvas

caused

by the

failure

of the

dam

embankment

which

caused

damage

to

fZ: ulffug",

in-tir"

fow

lying

land.

Rec€ntly,

a big project

for rehabilitation

oflbe old

dam-was

carried

out ly

Aichi-ken

with

the

support

of the

government'

Now,

the

embankment

is

much

bigger

thari the

old dam,

and

all

the facilities

such

as

the

intake

work

and

the

spillway

has

been

also

reconstructed

into

mod;;n

structures.

-\Trash

Boom 24.Om

K

a

wa

ch

i

E

m b a

n k

men

t

?z

^--:--^--

aD-..

Inuyama-shi,

Aichi-Ken

lnuyama-shi

Shingose

Irrigation

34km'

1.1

m3/s

1632-r634

Earth

River

Deposit

26m

l24m

1,250,000m3

VB

/tl

/J

I

,-'-

-'-

,------=)-'--

Scale

t:4gg|

--==,

_

'

.-,)le==S(R

N)

PLAN

&

F

@

-./'^'

-'/'

-'/

UPSTREAM

VIEW

OExcavation

Lire

@

GrEWt

(Padbus

Foundarion)

@Gravet

and Clay

(P€.vious

Zon6)

@

clay

(

lmp€Nious

26€)

@Granule

size

Conglorcrate

and Gravel

(Semi

Pervious Zone)

@

Sand

,

Clay

.

and

Slat€

(Poryious

Zore)

O

Clay

(hp€wious

8bnk6i)

@

Riprap

@Fitt€r

mattrial

@

Curtain

Grout

100

m

90n

E0n

70m

60n

i

t

PROFILE

ALONG

DAM

AXIS

T3

2.

MANNO.TKE

DAM

Location

Nearest

City

.

River

Purpose

Catchment

area

Mean

annual

discharge

Years

of

construction

.

Type

Foundation

Height

Crest

length

Volume

Spillway

Type

and

number

of

gate

..

Maximum

discharge

capacrty

Reservoir

Gross

capacity

....,r.

Effective

capacity

Area

Drawdown

range

Owner

Engineering

by

Construction

by

.a

Manno-cho,

Nakatado-gun,

Kagawa-ken

Takamatsu-shi

Kanakura

Irrigation

86km'z

(including

interbasin-diversion

area)

0.5m'/s

70r-7M

Earth

dam

Fluvial

deposit

32m

155m

220,00m3

Uncontrolled

110m3/s

15.4

X

106m3

15.4X

106m3

1.4km'?

19m

Manno-ike

land

improvement

district

Monno

Dom

,i'

t4

Stillrng

Bosin

PLAN

9TIP

,:--__

The

Sanuki

distuict,

the old nam€

of the area wherc the Mannd-ike

dam is located,

belongs to

the dry

part

in Japan

because

the

monsoon

blesses little rain which

is intercepted by mountains

up in the south

and thi

north. Therefore,

miny

dams

and

reservoirs

have

been built there

for irrigation ftom ancient

times.

The

Mannd-ike

dam is one

of the oldest dams

in Japan, and

proud

of the

biggest storage

capacity

among them.

The darn

was

constructed

about 1,280

year

ago, but 110

yean

later it was washed

away

by flood

and a famous Buddh-

ist monk

named

Kdbd-daishi

reconstructed

it into

a larger structue.

According

to tradition,

the Emperor

learned that farmers were

suffering from drought

after the

dam was destroyed by

flood and

sent

many

poEons

to reconshuct

it. However, all of thom

were unsuccessful

due to their

inability

to control th;

river

runoff.

Finally

Kobd-daishi was

sent and successfully

completed it in only for

three

months.

,

The dam

has

many record

of being damaged

as have all other old

dams. The

dam has been

supplying irrigation

water

to

this area

maintenanced

by

farmers. In

1959, a big rehabititation

project

was executed

for the purposJ

of enlarging

the

storage

capacity

by two

times, and at

prcsent

it has changed completely

into a modern

dam.

TYPICAL

CROSS SECTION

PROFILE

ALONG

DAM

AXIS

o-,

lg ? T f

p'

15

Japanese National Committee on Large Dams. Dams in Japan, No. 10

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