mechanisms and kinematics of three translational slides along the north saskatchewan river valley,...
TRANSCRIPT
K. W. Soe Moe, BGC Engineering Inc.K. W. Soe Moe, BGC Engineering Inc.D.M. Cruden, C.D. Martin, University of D.M. Cruden, C.D. Martin, University of AlbertaAlbertaD. Lewycky, P. R. Lach, The City of D. Lewycky, P. R. Lach, The City of EdmontonEdmonton
Edmonton LandslidesEdmonton Landslides
Keillor Road 2003
Whitemud Road 1999
Forest Heights 1900s
In Alberta, many of the river valleys are post-glacial
The valley walls are often steep
Large landslides and slow slope movements affect many of the valley walls
Long term slope movements
Delayed failures
Road SignRoad Sign
Road SignRoad Sign
KEILLOR ROAD LANDSLIDE (FALL 2002)KEILLOR ROAD LANDSLIDE (FALL 2002)
Started as a minor toe Started as a minor toe failure in 1989failure in 1989
Movement progressed Movement progressed upslope in 1994upslope in 1994
In 1997, an 8 to 15 m In 1997, an 8 to 15 m deep cast-in-place deep cast-in-place tangent pile retaining tangent pile retaining wall was constructedwall was constructed
A crack was observed A crack was observed across the roadway in across the roadway in August 2001August 2001
A major failure A major failure occurred in the fall of occurred in the fall of 20022002
From 2002 to 2005From 2002 to 2005 11 m slope retrogression Toe moved 30 m into the
river
History Keillor Road LandslideHistory Keillor Road Landslide
Pre-failure Slope Profile (1990)Pre-failure Slope Profile (1990)
620
630
640
650
660
670
Ele
vatio
n(m
)
GLACIAL LAKE CLAY
CLAY TILL1990 Slope Profile
Pile position before slopefailure
Pile position after slopefailure
BEDROCK
(a) Pre-failure slope profile - 1990 680
6100102030405060708090100110
Distance (m)
1989 Toe Failure
1995 Keillor Road Failure
Post-Failure Slope Profile (2003) Post-Failure Slope Profile (2003)
8
620
630
640
650
660
670
Ele
vatio
n(m
)
GLACIAL LAKE CLAY
CLAY TILL
1990 Slope Profile
2003 Slope Profile
Pile position before slopefailure
Pile position after slopefailure
Graben
Pile 2002
Pile 2003
Pile 2003
(b) Post-failure slope profile - 2003 680
BEDROCK
6100102030405060708090100110
Distance (m
Post-Failure Slope Profile (2004)Post-Failure Slope Profile (2004)
9
620
630
640
650
660
670GLACIAL LAKE CLAY
CLAY TILL
0102030405060708090100110Distance (m)
1990 Slope Profile
2004 Slope Profile
Pile position before slopefailure
Pile position after slopefailure
Graben
Pile 2002
Pile 2004
Pile 2004
(c) Post-failure slope profile - 2004680
BEDROCK
610
Field observation of slope movementsField observation of slope movements
September 2001
July 2003Keillor Road settlement
Movements of lower trail pile wallMovements of lower trail pile wall
May 2003
June 2004
Field measurements of piezometric pressureField measurements of piezometric pressure
A perched water table A perched water table was located in till layerwas located in till layer
Standpipes were dry Standpipes were dry after installation in the after installation in the bedrockbedrock
Piezometric readings Piezometric readings from the bedrock were from the bedrock were well below the well below the hydrostatic pressurehydrostatic pressure
Piezometers installed Piezometers installed below the displaced below the displaced material showed a material showed a reduction in pore reduction in pore pressure with time due to pressure with time due to dilation of the bedrock dilation of the bedrock
615
620
625
630
635
640
645
650
655
660
0 100 200 300 400 500 600Piezometric Pressure
Ele
vatio
n (m
)
Piezometric Pressure (Toe)
Piezometric Pressure (Behindthe slope crest)
Hydrostatic (Till)
Hydrostatic (Toe)
Sandstone
Clay Shale
Clay Till
700
Pore pressure distribution in the slide area
Horizontal displacement of crack metersHorizontal displacement of crack meters
Location2003
(mm/month)2004
(mm/month)
Main scarp 125 250
Graben 250 500
Toe 350 850
8
12
18
0
10
20
30
40
50
60
70
08/J
un/0
3
07/A
ug/0
3
06/O
ct/0
3
05/D
ec/0
3
03/F
eb/0
4
03/A
pr/0
4
02/J
un/0
4
01/A
ug/0
4
30/S
ep/0
4
29/N
ov/0
40
50
100
150
200
250
300
350
Dai
ly R
ainf
all (
mm
)C
rack
Dis
pla
cem
ent
(cm
) 13- Damaged in July 2004
16-Damaged in June 2004
9- Damaged in August 2004
Average movement of the slide body
Horizontal displacement of crack meters
Whitemud Road Landslide, October 23, 1999Whitemud Road Landslide, October 23, 1999
Whitemud Road LandslideWhitemud Road Landslide
Oct 23, 1999, 270 Oct 23, 1999, 270 m section along m section along Whitemud RoadWhitemud Road
Damaged 7 Damaged 7 residential lotsresidential lots
Resulted vertical Resulted vertical drop of 18 mdrop of 18 m
Major movements Major movements took place in a took place in a single daysingle day
Lot-
5
Whi
tem
udR
oad
Lot-
6
Lot-
7
Lot-
8
Lot-
9Lo
t-10
Lot-
11
0 m 50 m
Scale
BH-1976
BH-1979
BH-1999
BH-2001
BH-2000
N
LandslideBoundary
01-101-2
01-3
01-4
99-8 01-501-6
01-7 01-1001-9
00-5
99-501-8
00-4
00-200-12
00-7
00-8
00-300-13
99-3
99-2
99-1
99-6
99-4
00-1000-6
00-100-11
00-9
99-7
01-12
01-11
A
ANor
thSa
skat
chew
anR
iver
B
B
Lot- 12
Lot- 13
Central Zone
Nothern Zone
Southern Zone
76-03
79-2
79-176-02
76-01
Whitemud Road LandslideWhitemud Road Landslide
Landslide historyLandslide history
In 1967, a failure In 1967, a failure occurred 300 m occurred 300 m downstream downstream
In 1976, a second In 1976, a second failure occurred just failure occurred just north of the1967 north of the1967 failurefailure
From 1997 to 1999, From 1997 to 1999, displaced trees at the displaced trees at the river level as well as river level as well as significant debris and significant debris and tree accumulation are tree accumulation are visible in airphotos. visible in airphotos.
1999slide
1967slide
1976slide
Nor
thS
ask
atc
he
wa
nR
ive
r
N
Landslide stagesLandslide stages
680
670
660
640
630
650
620
610020406080100120140
Distance (m)
Ele
vatio
n (m
)
NORTHSASKATCHEWAN
CLAY
SAND
TILL
UPPER CRETACEOUS BEDROCK
MUDSTONE, SANDSTONE, SHALES, BENTONITE SEAM
BENTONITE SEAM
GWL1997 MINOR MOVEMENTS
SLIDE DEPOSIT
MAIN SCARP
Development of main scarp
Landslide stagesLandslide stages
680
670
660
640
630
650
620
610020406080100120140
Distance (m)
Ele
vatio
n (m
)
NORTHSASKATCHEWAN
CLAY
SAND
TILL
UPPER CRETACEOUS BEDROCK
MUDSTONE, SANDSTONE, SHALES, BENTONITE SEAM
BENTONITE SEAM
SLIDE DEPOSIT
MAIN SCARP
GWL
COUNTER SCARP
PASSIVEBLOCK
ACTIVEBLOCK
Development of a counter scarp
Landslide stagesLandslide stages
680
670
660
640
630
650
620
610020406080100120140
Distance (m)
Ele
vatio
n (m
)
NORTHSASKATCHEWAN
CLAY
SAND
TILL
UPPER CRETACEOUS BEDROCK
MUDSTONE, SANDSTONE, SHALES, BENTONITE SEAM
BENTONITE SEAM
SLIDE DEPOSIT
MAIN SCARP
GWL
PASSIVEBLOCK
ACTIVEBLOCK
Major failure due to downward movement of the active block
Pre and Post Failure Cross-SectionPre and Post Failure Cross-Section
Graben - the displaced material was completely disturbed. Graben - the displaced material was completely disturbed. The drilling records revealed that the till layer is missing The drilling records revealed that the till layer is missing and the sand is directly in contact with the bedrockand the sand is directly in contact with the bedrock
Main body - the displaced material was less disturbed and Main body - the displaced material was less disturbed and intact soil and bedrock strata were noted from the drill intact soil and bedrock strata were noted from the drill holehole
00-6
610
620
630
020406080100120140160
00-1
99-601-11
SAND
TILL
BEDROCK
BEDROCK
FILL
SAND
TILLGWL
Before failure
Failure plane
Piezometric elevationPiezometer
After failure
Ele
vatio
n(m
)
Distance (m)
00-12SlideDeposit
NorthSaskatchewanRiver
Graben
640
650
660
670
680
690
FOREST HEIGHTS PARK LANDSLIDE (EARLY 1900S)FOREST HEIGHTS PARK LANDSLIDE (EARLY 1900S)
Slope instability Slope instability dated back to the dated back to the early 1900’s when early 1900’s when coal mining was coal mining was conducted in the conducted in the areaarea
Park, 1000m long, Park, 1000m long, 150 m valley, with 150 m valley, with slope angle slope angle ranged from 10 to ranged from 10 to 40°40°
Continued slope Continued slope movements after movements after toe berm toe berm construction in construction in 1980s1980s
Steep scarps, Steep scarps, grabens, cracks grabens, cracks occupy the valley occupy the valley wallwall
River valley view of Forest Height Park (2004)
POST-FAILURE LANDSLIDE MECHANISMPOST-FAILURE LANDSLIDE MECHANISM
Rate of movements controlled by the groundwater Rate of movements controlled by the groundwater level in the crackslevel in the cracks
Downward movement of the displaced material inside Downward movement of the displaced material inside the graben contributed to retrogression of the slope the graben contributed to retrogression of the slope crest (3 to 4 m from 1980 to 2002)crest (3 to 4 m from 1980 to 2002)
TH
-241
660
670
650
640
630
620
610
600
TH-3
GWL
GWL
Assumed failure plane
0 20 40 60 80 100 120 140 160
Ele
vatio
n(m
)
Distance (m)
Sand & tillClay
Fill
Sand & Till
Upper Cretaceous Bedrock
Graben
Former Graben
NorthSaskatchewanRiver
ConclusionsConclusions
Landslides in Edmonton’s river valleys - a Landslides in Edmonton’s river valleys - a translational movement along a bentonite layer translational movement along a bentonite layer
Pre-failure slope movements - minor failures at Pre-failure slope movements - minor failures at the toe and the mid-slope areathe toe and the mid-slope area
A distinct graben feature appears at the head A distinct graben feature appears at the head of the displaced materialof the displaced material
Stability analysis considerationStability analysis consideration After a major failure, displaced material rests After a major failure, displaced material rests
on the rupture surface and the factor of safety on the rupture surface and the factor of safety improve with the new slope configuration.improve with the new slope configuration.
Post-failure movementsPost-failure movements Increase in groundwater level Changes in slope configuration Loading at the slope crest