Japanese National Committee on Large Dams. Dams in Japan, No. 10
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DAlrf,s
lh
NO.
lO
|
984
Jcpcnese
Nqlionql
Commiltee
on
Lorge
Dqms
Preface
The
Japanese
National
Committee
on Large
Dams presents
the
10th
issue
o
in
Japan"
to
all participants
who
attend
52nd ICOLD
Executive
Meeting
in
19i84,
as
well
as
53rd
ICOLD
Executive
Meeting
and
15th
Congress
in
Lausanne
Originally
this
book
of
Japanese
dams
are
periodically
compiled
and print
tht
ee
year
interval
to
present
to those
who
attend
each
Congress
of
Internatior
mission
on
Large
Dams.
In
1960,
however,
when
27th
Executive
Meeting
of ICOLD
was
held
in
T
rulie
waS
amended
temporally
to advance
it one
year
ahead
of
normal
schedule
bute
the
book
on
the
occasion
of the
first Tokyo
Executive
Meeting
in
1960.
This
time,
52nd
Executive
Meeting
will be
held
in
Tokyo
in
1984,
and
53
tive
Meeting
and
15th
Congress
witl be
held in
Lausanne
in 1985.
The
10th
Dzrms
in
Japan
will
be
utilized
during
both occasons.
Contents
of
the issue
were
to cover
those
large
dams
newly
completed
duri
lst.
1981
to
the
end of
March
1983,
as
well as dams
under
construction
as
of
th
March
1983.
The dams
included
in
above
category
are
as follows:
Type
Completed
TE
T3
ER
L2
PG
28
CBO
VAO
MVO
Total
53
Under
Construction
30
67
53
0
0
0
150
Out
of
above
dams
the
ad
hoc
Committee
selected
three
completed
dams
a
four
under
construction,
that
is,
twenty
seven dams
in total.
In
addition
to
the
above
presentation
of new
dams,
we
selected
three
more
dams;
the
oldest
dam
in
Japan (allegedly
buitt
in
2nd
century)
and
other
two
in
8th
and
17th
century
respectively,
all
earth dams
for
irrigation
purpose.
We
have
also
selected
other
thirty
five major
dams
in
operation;
they
are
Jatrlanese
dams
with
some
special
features
in
planning,
design
and
construciion.
Thus
number
of dams
selected
for this
issue
is
as follows:
"Dams
okyo
in
1985.
every
I
Com-
yo,
this
distri-
Execu-
issue
of
g
April
end
of
twenty
istorical
s
built
typical
Type
TE
ER
PG
CB
VA
MV
Total
Completed
before
April 1981
Completed during
April 1981 and
March
1983
0
3
0
0
0
0
3
Under
construction
as of
the end
of
March
1983
0
13
11
0
0
0
24
Total
4
7
T2
3
11
1
38
4
23
23
3
11
1
65
Type
Total
Number
TE
'1,,323
ER
IzO
PG
637
cB
18
VA
48
MV4
Total
2,L50
On
the
other
hand,
number
,of
all
Japanese
large
dams,
as of
March
31,
L983
classi-
fied
by
type
and
height,
is as
follows:
U.C.
30
67
53
150
We
hope
that
this book
will
enable readers
to obtain
the
general
picture
of
Japanese
dams
past
and present.
November
1.983
Tokyo,
Japan
(30
m 30-59
m
6V99 m 10f-149m
)150m
I,2t4
109
1
-
255725112
2r7
300
108
10
2
5382
4522152
L21-
1,,466
475
165
3g
6
L
4r.
Masanori
NOSE
rman,
Japanese
National
Committee
on
Large
Dams
Page
LOCATION
MAP
OF
DAMS
PRESENT
TENDS
IN
CONSTRUCTION
AND
OPERATION
OF
DAMS
IN
JAPAN
1
Historical
Dams
1.
IRUKA_IKE
DAM
12
2.
MANNO_IKE
DAM
14
3.
SAYAMA_IKE
DAM
........
16
In
Operation
4.
ABUGAWA
DAM
18
5.
ARIMINE
DAM
2L
6.
EIGENJI
DAM
24
7.
FUKADA
DAM.
27
8.
HATANAGI_NO.
l
DAM
29
9.
KAJIKAWA
DAM
33
10.
KAMISHIIBA
DAM.
35
11.
KAWAJI
DAM
38
T2.
KAWAMATA
DAM.
4T
13.
KUROBE
DAM..
........
43
T4.
KUSAKI
DAM
46
15.
MANAGAWA
DAM
........
49
16.
MIBORO
DAM
........
sl
17.
MIHO
DAM.
55
18.
MIYAMA
DAM
(&
NUMAppARA
DAM)
57
19.
MIZUKUBO
DAM
62
20.
NAGAWADO
DAM
21.
NARUGO
DAM
68
22.
oDO
DAM
........
70
23.
OGOCHI
DAM
72
24.
OKURA
DAM.
75
25.
OKUTADAMI
DAM
77
26.
OSAKO
DAM
..........
81
27.
SAKUMA
DAM
84
28.
SAMEURA
DAM
88
29.
SHIMAJIGAWA
DAM
97
30.
SHIMOKUBO
94
31.
TAKASE
DAM.
97
INDEX
Page
32.
TEDORIGAWA
DAM.
.......101
33.
TERAUCHI
DAM
......104
34.
TORIDAM.
.......107
35.
UCHINOKURA
DAM
........110
36.
YAGISAWA
DAM..
...113
37
.
YAHAGI
DAM
...
117
38.
YOKOYAMA
DAM
....120
Completed
39.
TAMAHARA
DAM
..N2
Under
Construction
40.
AHA
DAM
........r24
41.
ARAKAWA
DAM
......T26
42.
ASEISHIGAWA
DAM
......128
43.
DASHIDAIRA
DAM
........130
44.
DONDO
DAM
...133
45.
FUKUCHI
DAM.
........136
46.
FUTABA
DAM
........138
47.
HTTOKURA
DAM
......
140
48.
IKIMIGAWA
DAM
.....142
49.
IMAICHI
DAM
...1M
50.
JOZANKEI
DAM
.......746
51.
KAMrosu
DAM
.......148
52.
MIYAKODAGAWA
DAM.
........1s0
53.
NITCHU
DAM
..82
54.
OGAKI
DAM.
.....1s4
55.
OKAWA
DAM
....1s6
56.
OMACHI
DAM
..158
57 .
OUCHI
DAM
.....
160
58.
SAGAE
DAM
.....
162
59.
SHICHIGASHUKU
DAM
...764
60.
SHINTSURUKO
DAM
.......766
61.
'TAKAMI
DAM
..
168
62.
TAMAGAWA
DAM
...17O
63.
TENZAN
DAM
.........
r72
64.
TOKACHI
DAM.
........174
65.
YASAKA
DAM
......:
...176
LOCATION
MAP OF
DAMS
a('-
o
I
Completed
o:
Under
Construction
0
100
200km
L------.-------
3i\
r4(ei18
ar"-?SS
PRESENT
TENDS
IN
CONSTRUCTION
AND
OPERATION
OF
DAMS
IN
JAPAN
r. PRESENT
TRENDS
IN
CONSTRUCTION
OF DAMS
,
The purposes
of
constructing
dams
in
Japan
are for flood
mntrol,
irrigation,
municipal
water
supply, power
generatron
and
supply
of
water
for
maintenance
of normal
tunction
of
the river.
In
"March
198,,
;;;d;;
;ii07'du*,
"r"
ond"r-
) multi-purpose
dams.
Among
the
single-purpose
dams,
irriga_
)wer generation
has
decreased;
and
especially
owing
to the ie-
storage
power
plants
and
dams
is sluggish.
or tdple_purposes,
namely
combination
of
flood control
and
I maintenance
of norma.l
function
of
the river,
or
combination
n.
cted to continue
i[ the
future.
The
following
are
the
major
,ars
to come
:
_first,
development
in
technology
of foundation
foundations
which
are
not
always
favorable,
io
cope v/ith
the
secondly,
investigation
of the
impacts
of dam
construction
on
ettlement
of communities
in
the
vicinity
of dam
and
reservoir.
a
o
l!
o
&
uJ
50
CD
l
z
Fig.
I
Purposes
of
Dams
under
Construction
(I)
Irrigation
(H)
Power
generation
(C)
Ftood
control
(S)
Municipal
water
supply
(D)
Dual-purpose
dams
(T)
Triple-purpose-dams
(O)
Quadri-
and quintuple-purpose
dams
o
50
H
e r
lorlr
tso
2@
Fig.
2
Classification
of Dams
by Height
(PG)
Concrere gravity
dam
(ER)
Rockfill
dam
(TE)
Earth
dam
(PG/ER)
Combination
of
pG
and ER
(VA)
Arch
dam
TElER
PG/
TE
3;
2\
.r$/
2.
PRESENT
TOPICS ON DAMS
IN
JAPAN
2,1
SAFETY
OF
DAMS
IN OPERATION
2.1.1.
Safety
of dams
during
flood$
_
In constructing
or operating
dams, it is
necessary to
take some measures
to
secure the
safety
against
flood discharge.
Two
stages
of
floods
are to
be considered.
One is the quantity
of flood
discharge
which
is ttre
oUi"ect
of control
in flood
control
dams,
or
the
quantity
of flood
discharge which
is to be approp
ately decided
in water
utilization
dams and
up to
which.the-
rapid
run-off
caused
by the
existence
of dams is to be dissipated.
Another
is the quantity
of flood
discharge
prescribed
by the
River
Law for the
safety
of dam structures
against such
accidents as
overtopiing.
-Irlaturally,
the
lattir
value
is larger
than
the former.
-
To
meet
the
first stage
of flood, in
flood control
dams, flood control
capacity
is
calculated
from
flood hydrographs
based
on the
flood
control
program,
and
the water
level corresponding to
thia cap;ciry
is to
be decided.
Also for water
utilization
dams,
the
reservoir water
level
necessary to deal with
this stage
of flood is
to be
decided.
The water
level
cor-
responding
to this
stage of
flood is defined
as
.,surcharge
water level',.
-
For
the
second
stage
of flood,
safety measures
are to be taken to
prevent
dam
failures,
Quantity
of
flood discharge
for
dam
safety
is defined
as
the
"design flood discharge
of dam". The reservoir
water
level
at which
desisn flood
flows
down
the
spillway
is defined
as the.,design
flood water
level,'.
-
IIl case
of
flood
control dams,
the flood
discharge corresponding
to surcharge
water
level
is to
be the flood
discharge
based
on the
flood
control program
of the river/river-basin.
For other
dams,
botl the flood
discharge
selected for
flood
control
dams
and
8070 value of the
desfun
flood discharge
for concrete dams
are to
be considered,
ih" 1".g".
one being
adopted.
- -F9t
tr:
design
flood
discharge,
the largest possible
flood from the
engineedng viewpoint
is
to be
adopted,
considering
fatal
situation
in-case
of overtopping,
such as ihe failure
of embankm"nt
dam".
-
In
the l,aw
is
prescribed
the followin!
procedure
of study
conc€ming
the design
flood
discharge, separately
for concrete
dams and
embank-ment
dams.
For
concrete
dams,
the largest
of the following
three is to be adopted:
(A)
The
flood
discharge
expected
to occur at
dam site },ith retum
period
of
200
years
(B)
The
largest
flood ever
recorded
at dam site
(C)
_
The
flood
discharge
which
is reasouably
expected to occur
at dam
site,
judging
from
the
hydrological
or meteoro-
logical
observation
data
of a ce
ain drainage
area which has
similar charactCrisiics
to
the
given
driinage
area.
..
The design
flood
discharge
of embankment
dams is to be equal to
the design
flood
discharg!
of
concrete dam
multi-
plied-by
1.2,
considering
the danger of
overtopping
of embankment dams
which
may lead
to dam-failure.
.
In calculating
discharge(C),
"regional specific
flood discharge
diagram"
as shown
in Fig.
3 is
used
in
general.
The
above'mentioned
flood
discharge
and water
level are
the basic
vtluei
for
rlesign
of dams,
such'as
the
stability
analysisdeci-
sion
of
the height
of non-overflow
section as well
as the decision
of hydraulic
functions
oi structures,
to make
sure the
safe-
ty of
dams
during
floods.
roo
50
20
6J
E
!to
|J
q)
al,
|.n\
5
5
g
2
lo.L
\
S \
I
\
N
\
N s\
I HOKKAIDO
2 TOHOKU
3 KANTO
4
HOKURIKU
5
CHUBU
1
6
KINK
I
7
SOUTHERN
Kil
|
8
SAN'IN
I
9
SETOUCHI
IO
SOUTHERN
SHIK
II
KYUSYU&OKINI
\
OKU
rWA
A
(km2)
Fig.
3
Regional
Specific
Flood
Discharge Diagram
(q)
t
Specific
flood
discharge
(A):
Drainage
area
I
o.5
o2
2.1.2
SAFETY
OF
DAMS
DURING
EARTHQUAKES
(1)
Seismological
Observations
The
Japanese
islands
are
situated
in a
seismic
zone.
In
Japan
morc
thao
80
dams
are
equipped
with
seismographs.
For
example,
in dams
constructed
by the
River
e-"tru
or rnriii.iry
of
construction
exceeding
3orn
in
t.rgt
t, at
least
two
seismographs,
one
on
the
crest and;nother
in some position
in
il'"
rounautioo
depending
on its
characteristics,
are
to be
installed
For
more
detailed
seismic
observations,
concentrated
observations
are
carried
out by
means
of several
electro-
magnetic
seismographs
observation
during
earthquake
ii ,nuo",
in
-o"
cases,
on
accelerations,
and
in
certain
cases
oD
velocities
or
displacements.
Also,
earth.
p;surcs,
pot"
*ut"t
fr"*uro,
dynamic
water
pre;;;;;;;;;;*"
displac€ments
during
ea(hquakes
are
observed
depending
on
tt
"
obj""t,
ot ,"'r""r"h"".
The
recent
information
about
the
behiviors
of dams
durin!
.".tiqu"r.",
has
revealed
some
common
characteristics
of
both
conqete
dams
and
embankment
dams.
The
crest
movenients
are
arnplified
considerably
against
the acreleration
in-
put
into
the
foundation,
while
the
movements
at mid-height
are not
so
intensely
amplified.
There
are
differences
in
seis-
mic
-motions
between
the
central part
of the
foundation
ihictr
is treavity
toaoed
wittr
a",n
u"of
"ra
l.tt
abutment
which
are
free^o_f
loadin8.
To
investigaie,-in
detail,
into
these
phenomena,
more
intensive
",ro"go.J,io,
oir"rvatrons
are being
carned
out
on
some
dams.
The
information-about
dam;
during
stong
earthquakes
.ttuir"J,ir-"gf'16ese
observations
serve
for
safer
and
more
effective
aseismic
basic
design
of dams.
-
(2)
Inspection
of Dams
after
Earthquakes
and
Necelsary
Restomtion
Works
The
owners
of
dams
are
reouest;d
to
calry
out the
io[o;o!
"rr."t-upr
immediately
after
the
earthquakes
in
case that
the
seismic
inlensity
at
the
dam
site.
exceeds
one
third
of the Eesign
seismic
intensity
or;h";;;;;"
IV
or more
according
!o
the
Japanese
Meteorological
Agenry
scale:
(A)
Dam
body
(a)
Occurrences
of leakage,
or
change
in
leakage,
quantity.
(b)
Crack
occurrences
on
surfaces
oi
concrete
d;
(c)
Crack
occurrenc€s
on dam
crest
(d)
Any
changes
in upstream
membrane
or
rip-raps
(e)
Others
(B)
Areas
around
dam
abutment
and
reservoir
(a)
Occurences
of
leakase
(b)
Crack
occurrences
(c)
Collapseoccurrences
(d)
Landslide
occufiences
ally
has a
control
office
adjacent
to
the dam.
The
chief
controller
rs
to carly
out
rt
the
results
to
the superior
organs.
In case
of
smaller-scale
dams
where
the con-
eck-ups
are
also
possible
within
a
resonable
time,
since
inrp;;;;
can
reach
dams
r.d-leceldy_at
the dams
in
Japan
is,Miyagiken_oki
earthquake
in
197g
(with
eqic€n_
ups
were
carried
out.
rhe
,".un,
_,noJ#?ffil'jil;1,;""1TH";[1]*,"ffj::';;f$ffi
*":::"f::fj{Xjl;
dams
suffered
some
damages.
At the
concrete
da.
" ";;;;;;;;l;nt
at the
abutment
might
have
moved
slightly
and
temporary
water
leakage
was
observed,
but
the leakage
ceascd
severai
houn
afterward
withouianj-reiaiiing
,yorts.
with
respect
to
five
embankment
dams.
slight
damages
orithe
upstream
membran"t
.t
J"-,
.,
"r""ir'#ir"l'.',
,,, the
direction
of
dam
axis
were
observed,
neither
of which
-were
so ..ti'oui
""
io-ttrr""t"n
the
dam
safety.
However,
tic
restoration
works
of
these
damages
on
embankment
dams
were
execrted.
The increases
in optitt pr"ss,i.e
o,
i"Jp'a-g"
*at",
rroo,,
tt"
drain
holes
in
the
foundation
are often
observed
urt"r
"u.trrfuut"a.-
'I
n"r"
"-r"
temporary
phenomena
in
general,
and
the
f:,!-*j 9:**-
gradually
from
several
days
to
one
month;hib
the
uplift
pressure
ftom
several
days
to several
months.
rhrs
rs
assumed
to
be due
to
the slight-decrease
in volume
of the
pore
within'bedro;q;;;;;#l'irotions,
resulting
in
the
rise
of
Pore
water
pressure.
water
in the pa.*
it
"q"",iJ
rut
to
drain
holes
and
the pore
water
pressure
de-
creases
over
a
long
period
of time.
Japan
is
one
of
the
countries
with
intcnsive
seismic
activities
in the
world,
and
in most
cases
there
are densely
popu-
lated
areas
at
the
downstream
of
the
dam.
Therefore
,aams
in
rapan
are
always
designed
with
special
attention
to
aseismicity
ln
fact
the
dams
constructed
based
on modern
a"rign-"iJ
*nrt-"tion
method
have
so
far
suffered
no
serious
damages
against
major
earthquakes
in
the
past.
The dams
ou"ils,n
in
height
are
i^pr."d;;
th" ,;;J;;on
to
be equip-
p.ed
with
spillways.
Especialiy
the
embaniment
dams
are
to ue
equippco
;th
ouhr;;;krl"ria-..-tu#ip1r*"y
to
ton"",.
the
water
level
in
case
of
emereency'
The
equipment
to
lower the
ivaier
level is
also
thought
to
be
ihe rneans
to avoio
the
l1':t-*-
failure,
corsidering
tit"t
il"
a"."g.r
i tng
""nt
qu"ie,
"r"-
r*"ry
,o
occur
in
the
vicinity
of dam
crest.
There
1:-"-^*- -ti!t"*:"
of
conducting
large-scale
repair
woiks
of
ibms
constructed
-w,ith
modern
design
and
consrructron
proce-
qur_e'.suttering
damag€s
during
earthquakes.
However,
there
are
examples
of damages
".
"".tf;-a"-,,p
,o
about
20m
in
netght'
ln
case
of
slisht
damase.
it
is.restored
to the
original tbrm,
wiite
in
case
lf
,"fi;;;;;;.,'J;-;;il;;:
widening
of
embankmJnt
or
addltional
foudation
grouting
a?e pertormea.
2.2
INFLUENCE
OF
GEOLOGY
AND
GEOTECHNIQUES
ON
THE
DESIGN
OF DAMS
2.2.1
Sofl
Rocks
and
Design
of Dams
(1)
Characteristics
of
Soft
-Rocks
in
Jaoan
Soft
rocks
are characterized
by
poor
cementation,
low strength
and high
deformability.
These
are grouped
as follows:
(A)
Sedimentary
rocks of Neogene
Tertiary
(a)
Sedimentary rocks
in non-Green
Tuff region
(b)
Sedimentary
rocks in Green
Tuff regi6n
(B)
l,ow welded
volcanic
rocks
of
Quatenary
(C)
Weathered
granite
These
groupings
are convenient
to elucidate
the
problems in
dam construction
on
soft rocks.
Neogene
deposits
are distributed
along
sea coast almost all over
Japan, especially
in Nortbeast
Japan.
The regions
occuPied
by Neogene
rocks can
be broadly
subdivided, as mentioned
before, into
two
groups:
non-GreJn
Tuff
and Green
Tuff
regions,
as shown
in Fig. 4. The latter
region
is somewhat
different
from
the formir.
The
Green
Tuff
region is distributed
along the Coast of the
Sea of Japan and
on the
east side
of Fossa
Magna. As
this
region
subsided
from
late Oligocene
to early Miocene and remained
under deep
sea in the
latter
half of Miocene and
upheaval
took
place
ftom the end of Pliocene
to the beginning of Pleistcene,
most of
the formations
are
the
product
of sub-
maine
eruptions.
Lava is relatively
hard, and
tuff and tuff breccia of early
Miocene
are competent
enough to support
loads
exerted
by
arch dams.
-As
the volcanic
activity
was somewhat
calm and local in the latter
half of Miocene,
the
deposits
in this
age are mostly
mudstone
and
sandstone with some
intercalations of volcanic and
pyloclastic
rocks.
The sedimentary
rocks of this
age are
generally
poorly
indurated
and,
hence, low in
strength. Lava
in
Green Tuff regions
is
deteriorated
due
to the submarine
volcanic
activities,
and
the sedimentary rock
often contain clay montmorillonite.
While
sedimentary
rocks of
Neogene Tertiary,
including those of non-Green
Tuff region, generalty
have a tendency
to
d:1el9rlte
and
disintegate
by drying
and wetting
cycles, many of sedimentary
rocks in
Green
Tuff
region show
a rernark-
ably
high
tendency
of slaking and
swelling. By contrast,
as
the volcanic
activity in
non-Green
Tuff
region was
calm in
N-eogene
epoch,
the Neogene deposits
in
this region mostly consist of
sandstone and
mudstone.
The
delee of
induation
of these
rocks
is
generally
lower than
that of the
pyroclastic
rocks in the lower
formations
of
Green Tuffiegion
although
it
increases
as depth
increases.
_ __In
Quaternary
the
Japanese islands
took
the shape as they have now,
but volcanism
has
continued
mainly
in Green
Tuff region.
Volcanic
activity
in
Quaternary
took
place
mainly on land.
Hence,
the volcanic
rocks
covel
the underlying
older
formations
unconformably
which
often
poses
difficult and intricate problems
in dam
construction.
(2)
Design
of Dams
on Soft Rocks
_ .
Problems
on
design of
dams will be
mentioned
hereafter according
to the
grouping
mentioned
above.
(A)
Sedimentary
Rocks
in Non-Green
Tuff Region
on Neogene Tertiary
The
topography
of these
areas is
generally
gentle,
steep
gorges
being rarely
found.
Thus,
majority
of dams
so far
constructed
in this
region are 40-50m
high,
at the highest. Because
of low
shearing resistance,
the maximum
height of
conqete
gravity
dam
is limited to approximately
30m. Designs are carried
out based
on
the results
of in-situ
direct shear
tests.
As these
rocks
are likety
to disintegrate
under the
cycles of wetting
and drying,
it is
necessary
to carry
our resrs,
keeping
the
rocks
wet and fresh.
Enough
care was
also taken
in foundation
heatment to
preserve
the wet
and
ftesh condition.
and th€ rocks
disinte-
grated
by
altemate
wetting
and drying
were
removed. Dams 40-50
mete$ high in
this
region
are in
general
of
embank-
ment type.
The permeability
of these
soft rocks is generally low
and the
improvement
by giouting
is no1
easily attained.
-
Sedimentary
rocks of
Neogene Tertiary
are not suited in
general
for
embankment
."teri"t
&
aggregates
for concrete
as
they
are mostly
unstable.
The
rock materials
for embankment
dams are
generally
obtained
from
oiherLurces.
Fig.
4
Green
Tuff Region
in
Japan
(shown
by hatched area)
'ertiary
e Tertiary
in
Green Tulf
region
are
the
products
when
sub_
of volcanic
rocks
and
pyroclastic
sedimentary
rocks.
These
they prevail
are
precipitous,
thus allowing
relatively
high
dams
However'
the
middle
formations
are less indurated,
and as is often the
case with
sedimentary
rocks
in
general
in
Green
Tuff
region,
layers
showing
mnsiderable
swelling
characte stics
containing
special
clay
minerals
are
in'tercalated.
The
sedimertary
rocks
of Neogene
Tertiary
show
low
peremeability
and high
groundwater
ievel.
It is desirable
to
select the
area
of high
ground
water
level
for the damsite,
to
use the
ponion
likely to
slake intact,
through
removing
the disintegrated
or
largely
deformed
portions.
-
In
Green
Tuff
region, there
are also
many
metallic ore mines,
in and
around
which
the foundation
rocks are
often
altered
due
to
mineralization
during
the
production
of ore deposit.
In locating
dams
in such
areas,
the method
of treat-
Teqt-
of-such
altered
zon€
usually
becomes
a difficult
and important
problem.
As
it is
very difficult
to
grasp
clearly the
distribution,
size and
depth
of altered zones
in
detail at design
stage,embankment
dam
type
is
usually
adopied.
With
respect
to
the conqete
aggregates
or rockfill materials,
even
the highly
indurated
sedimentiry
rocks
in older
formations-
of
Neogene
Tertiary
are not
reliable
in their durability,
hence
lava or
intrusive
rocks
are
mosfly
utilized.
However,
lava
is
often
altered into
incompetent
material.
Although intrusive
rock
is most
competent
and stable,
it is not
rare
that
its volume
is not
enough.
Alother
problem
in
N€ogene
Tertiary
in
Gre€n Tuff region is
an abundance
of landslides
around
damsites,
because of
sP€cial
clay
mineral
which cause
the disintegration
of sedimentary
rocks with
the variation
of the
environment.
Therefore,
investigation
on
the
distribution
of active
or
potential
landslides
are usually
carried
out to
take,
if necessary,
some
"qun-
tenneasures.
(C)
Quatemary Volcanic
Rocks
^
Most
of
Quaternary
volcanic
rocks in
Japan which
are nolv seen
on land
are tefiestrial
products.
Theretore,
of these
Quaternary
v-olcanic
rocks,
Poorly
welded
voicanic
rocks belong to
soft rocks,
represented
by
poorly
indurated
welded
tuff
and pumice
fall deposits.
welded
volcanic
rocks ranges
ftorn highly
wetded
one of
high
sirength'with
abundant
cooling
johts
to
Poorly
welded
one of low
stuength
with few
cooling
joinis.
These rocks
are
risually p-orous
and
low in
speciftic
gravity.
These
rocks
have
not been consolidated
enough
by overburden
so
that the
permeability
of these
rocks
are
generally
ll4"l:l|i l*g:"e
sedimentary
rocks.
However;
seepage flow
through
cooling
lotnts
unioir*ntoimity
proouces
prob-
lems
rather
than
the seepage
through
rock
itself.
The maximum
depth
of a flow
unit of
Quaternary
volcanic
rocks seldom
exceeds
several
tens
of meters,
being
overlain
or underlain
by anotier
flow unit
or disconformity
jeposit,
wnicn
oten ue-
comes
problems
in dam
construction.
Cooling
joints
are open
in highly
welded
volcanic rocks
of the
euaternary.
Even
at deep parts
of
the abutments
there
ly welded,
often
showing
remarkable
permeability.
)ns of
euat€rnary,
damsites
are
selected
based
on the
Drinci_
ere
their
elevation
is lower
than
the
maximum
normal
water
meet this principle.
difficurt
to.improve
rheir permeablity
by
grouting,
," ,h", t, tJ
ff#;*ltltJ
ff":.til:
#:t li*jLff#:1
;:?"-",lj"il
i;
intadt
condition.
As mentioned
above'
the difricult
-problems
in
constructing
dams in
Quaternary
volcanic
rock
regions
anses
in
per-
|]]ib:T|;^tj11,:3
t:
tlrc
pj:b.lem:
in
highly welded
volcanic
rocks
and the
surface
ot uncontor-iiy
ruir,"i
tr-
trr"
piou-
rems
related
to the
low welded
volcanic
rocks
and
soft rocks.
(D)
Weathered
Granite
Weathered
granite
is one of
the typical
examples of
soft rocks that
resulted
from
weathering.
But
if the
granite
is of
coane-grained
type,
weathering
often
advances
to a deeper
portion,
producing
Foblems
in
select-ion
of
dam type
and mea-
lit:
jg.:"lug"
"ontrol.
Althou.gh
adopting
of embankmint
dam
may soGihe problems
on
strength
and deformation,
proDlem
relatrng
to
seepage
yrill
still
be left
unsolved.
.,^---9:T1tt',q:t
eability
is
higher
in intermediately
weathered portions
rather
than
in heavily
weathered
portions,
but
usually
permeability
of
intermediately
weathered
portions
can be
easily improved
by
grouting.
Grout
materials
of fine
grain
size such
as colloid
cement
and chemical
grouis
are often used
for hea.,nity
.,neattr"rei
graniie.
2.2.2
Concrete
Gravity
Dams
on Weak
Foundations
,
Recent
needs
for
constructing
dams
on foundations
with unfavorable
geological
conditions
tend
in some cases
to the
selection
of embankment
dams as a
solution.
In
certain cases, however,concrete-dams
are
more
"auuni"g"ou,
in discharg-
ing
floods
or in
river
diversion
works.
These
are the cases,
especiany,
where
the flood
aist
"rge,
"re
iuill.
There
ate
several practical
solutions
as
to the design
of concrete
giavity
dam on
weak
fouo?utionr,
"Jrrro*n
in rig.
s.
Enlarging
thc
base with
filet
on the
upstream
sidi is one solutio-n
of
constructing
.onar"i"
ltuuiiy
a"-s
on compara-
tively
weak
foundations,
for the
purpose
ofreducing
strcsses
in the foundations.
,^^,,11::n:t,."tu,ion
is
enlarging.the
base with
mat conqete.
This
method
is effective
not
only in
reducing
stresses
but in
reaolng
lo
more
unitbrm
distribution
of
stress€s
in the foundation.
Another
advantage
of
mat
concrete
isihe simple
con-
figuration
which
is
suited
for the
dcvelopment
of effective
construction
method.
t-