-
Landslides
and
Deformation
of
Rock Slopes
influence
of
gravity
without
the
aid
of
the
other
agents
of
erosion
such
as
fiowing
water,wide,or
ice.
Landslide
debris are
transported
off a slope
within a matter of seconds or minutes
to
the
imperceptible slow creep of individual particles
down a gradual
types of movements may be triggered by
the vibrations from earthquakes or the
mechanical
pushing
or
heaving
of
particles
downslope,or
they
may
occur
spontaneously
if
the
gravitational
forces
exceed
the
forces
holding
the
marerial to the basic types of
landslide are definded, based on the
type of movement
involved:
falls,
siumps , and creep.
Falls are created by the free fall of
rocks or coherent masses of sediment
from
steep
coarse
debris
that
breaks
loose
from
the
cliff
tumbles
over the slope and accumulates to form
talus or scree deposits at the base of
the are slope failures in
which a large mass of rock and debris
slips downslope along a
zone of
weakness,usually
a
bedding plane or structural
surface(a
fault
or joint).The
debris
removed
from the
slope may
come
to
rest
anywhere
from
a
meter
to
a
kilometer
downslope.A
scar
is
left
on
the
slope
delineating the area in which the
debris
originated.
Slumps
are generated when
a block of sediment breaks loose from
its bed and slides downward and outward
as a coherent unit along a
curved faiure the failed block rotates
from
its
original position,it produces a scarp or concave
scar on the g
and slumping may occur suddenly in one
great landslide or in a series of small
displacements
that
take
place
over
months
or
are
created
by
the
downslope movement of water
saturated material being transported
may
remain
semi
coherent
or
may
become
jumbled
and
soggy
masses
may
move
rapidly
downslope
in
a
few
centimeters
(mudflows
and
debris
flows
on
alluvial fans) or at a rate of only a
few
centimeters
or
meters per
hour or day
for
a
short
period
(solifuction
and
gelifraction);creep
is
the
extremely
Landslide
is
the
downslope
movement
of
rock,sediment,and
soil
under
the
slow,almost
undetectable
downslope
movement
of
soil
particles
in
the
upper
meter of the soil caused by a variety
of mechanisms. Particles may simply
roll
down
the
hillside,burrowing
animals
may
push
sediment
down
the
slope,or
particles
may
slowly
move
or freezing
and
thawing.
The term colluvium
is
used to
describe
sediments
that
are
eroded,trans-
ported,
and
deposited on and at the base of slopes by ial
deposits range
from
accumulations
of
coarse
rock
fragments
to
clay-size
particles
but
are
commonly
a
poorly
sorted
mixture of
both
coarse
and
fine-grained
particles.
In
a
slop
in
which
the
rock
is
jointed
but
where
there
are
no
significant
discontinuities
dipping
out
of
the
slope
which
could
cause
sliding.
In
an
extreme
case,where
the
rock
mass
consists
of
near
vertical
joints
separating
columns
of
massive
rock,toppling
movement
and
failure
may
occur.
For example aWahleach project is
located 120 km east of Vancouver and
power
is
generated from 620m of head between Wahleach Lake
and a surface powerhouseb
located
to
the
Fraser
flows
through
a
3500m
long
three
meter
diameter concrete encased steel lined
shaft inclined at 48 to the horizontal, a
300m long
lower
tunnel
and
a 485m long
surface
penstock
to the powerhouse.
The
tunnels
were
excavated
mainly
in
granodiorite
which
varies
from
highly
fractured
and
moderately
weathered
in
the
upper
portions
of
the
slope
to
moderately
fractured
and
fresh
in
both
the
lower
portions
of
the
slope
and
below the highly fractured
mass. Two main joint sets occur in the rock
mass,one
set
striking parallel to the slope and other
perpendicular to dip very
steeply .Average joint spacings range
from 0.5 to 1.0m.A few joints occur
sub-
parallel to
the ground surface and these joints are most
welldeveloped in the
ground surface adjacent to the inclined
gh
investigations
failed
to
reveal any
significant shear zones or faults oriented in a
direction conducive
to
sliding.
The top
of the slope is buried beneath colluvial and fan
deposits from two
creeks
which
have
incised
the
Fraser
Valley
slope
to
from
the
prominence
in
which
the
inclined
shaft
was
prominence
is
crossed
by
several
linear
troughs which trend along the ground surface
contours and are evidence
of previous down-slope movement of the
trees growing in these
troughs indicate
a
history
of
movement
of
at least several
hundred
years.
The
water
conduit
operated
without
incident
between
the
initial
filling
in
1952
and
May
1981
when
leakage
was
first
noted
from
the
upper
access
adit
located near the
intersection of the inclined shaft and the upper
leakage stopped
when two drain pipes embedded in the concrete
backfill beneath
the steel lining were plugged at their
upsteam holes had been eroded
in
these
drainage
pipes
where
they
were
not
encased
in
concrtete
and
it
was
concluded that this corrosion was
responsible for the conclusion
appeared
to
be
valid
until
25
January,
1989
when
a
much
large
water
flow
occurred.
Investigations in the dewatered tunnel
revealed a 150 mm wide
circumferential
tension
crack
in
the
steel
lining
of
the
upper
55
m
from
its
intersection
with
the
inclined
addition,
eight
compressional
bukle
zones
were
found
in
the
upper
portion
of
the
inclined
shaft,Subsequent
investigations revealed that
approximately 20 million cubic metres of rock
are
involved
in
down-slope
creep
which,during
1989
1990,amounted
to
several
centimeters
per
year
and
which
appears
to
be
downslope
creep
appears to be related to a process of
block rotation rather than to any deep
seated
sliding
as
was
the
case
at
both
the
Downie
Slide
and
Dutchman’s
discrete
element
models
may
give
some
indication
of
the
overall
mechanics of this type of slope
deformation,there is no way in which a
factor
of
safety,equivalent
to
that
for
that
for
sliding
failure,can
be
uently,
in
deciding
upon
the
remedial
measures
to
be
implemented,other factors have to be
taken into .After thorough study by the
BC
Hydro and
their consultants,it was decided to construct a
replacement conduit
consisting of
an unlined
shafte and
tunnel
section
and
a
stell
lined
section
where
the
rock
cover
is
insufficient
to
contain
the internal
pressure
in
the
tunnel.