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