Nutana Slope Failure
2012 to Present:
2012
2013
Causes of the Failure 1
GEOLOGY
Weak soil
2
GEOMETRY
Steep slope
3
GROUND WATER
High water table due to increased precipitation
Causes of the Failure:
11th St Cherry Lane
1
GEOLOGY
2
GEOMETRY
3
GROUND WATER
Sask Cres GROUND WATER LEVEL
SLIP PLANE
10 Year Average Rainfall - Saskatoon
Groundwater Levels - Saskatoon
Status of Slope
• Not stable
Movement Possible
• Continued movement toward Sask Cres
Remediation Options
• Conceptual only •
Target: 50% MORE stabilizing force
• 4 general options evaluated No Movement
Option 1 • Do Nothing • Continued movement • Risk increases as groundwater increases
• Slide area will expand in time
Option 2 • Address
3
GROUND WATER
• Install dewatering trenches (11th St & Cherry Lane)
Option 2
GROUND WATER LEVEL
SLIP PLANE GROUND WATER LEVEL
Option 2 • Address
3
GROUND WATER
• Install dewatering trenches (11th St & Cherry Lane)
• Doesn’t meet stability target (only 20%)
Option 3: • Address
3
GROUND WATER
• Flatten the slope • Meets 50% stability target
AND
2
GEOMETRY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Option 3:
SLIP PLANE GROUND WATER LEVEL
Possible Remediation OPTION 3 Affected area
Option 3: • Address
3
GROUND WATER
• Flatten the slope • Meets 50% stability target
AND
2
GEOMETRY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
• Significant disruption to private lots
Option 4: • Address
3
GROUND WATER
• “Shear zone replacement” • Meets 50% stability target
• Keeps houses in place
AND
1
GEOLOGY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Option 4:
Possible Remediation OPTION 4 Affected area
Option 4: Possible Remediation OPTION 4:
• Address
3
GROUND WATER
• “Shear zone modification” • Meets 50% stability target
• Keeps houses in place
AND
1
GEOLOGY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Remediation Summary: OPTION 1) Do Nothing
PROS
3) Re-Grade Slope
•
Does not meet target stability
$4.5M
Meets stability target • Reduced long term • risk
Significant disruption Removal of structures
$6.5 – 10M
Meets stability target Maintains structures
Difficult to construct Costly
$10 – 20M
•
Minimal disturbance Lowers “wet year” risk
(and lower water table)
•
4) Shear Zone Modification
•
(and lower water table)
HIGH risk of continued failure
No cost
•
•
ESTIMATED COST
•
•
2) Lower Water Table •
CONS
• •
$0
Independent Review: Clifton Associates
• Independent analysis of the data • Purpose: To confirm remediation options • Conclusions: •
Agree on methodology
Verified the problem is large and • Differing interpretation of data even less stable costly to resolve • Remediation options feasible but may be even more costly
Public Safety Continues to be primary focus of the
• Continue detailed monitoring
• Provide residents with everything we know • Evacuation Alert
2012
2013
Causes of the Failure 1
GEOLOGY
Weak soil
2
GEOMETRY
Steep slope
3
GROUND WATER
High water table due to increased precipitation
Causes of the Failure:
11th St Cherry Lane
1
GEOLOGY
2
GEOMETRY
3
GROUND WATER
Sask Cres GROUND WATER LEVEL
SLIP PLANE
10 Year Average Rainfall - Saskatoon
Groundwater Levels - Saskatoon
Status of Slope
• Not stable
Movement Possible
• Continued movement toward Sask Cres
Remediation Options
• Conceptual only •
Target: 50% MORE stabilizing force
• 4 general options evaluated No Movement
Option 1 • Do Nothing • Continued movement • Risk increases as groundwater increases
• Slide area will expand in time
Option 2 • Address
3
GROUND WATER
• Install dewatering trenches (11th St & Cherry Lane)
Option 2
GROUND WATER LEVEL
SLIP PLANE GROUND WATER LEVEL
Option 2 • Address
3
GROUND WATER
• Install dewatering trenches (11th St & Cherry Lane)
• Doesn’t meet stability target (only 20%)
Option 3: • Address
3
GROUND WATER
• Flatten the slope • Meets 50% stability target
AND
2
GEOMETRY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Option 3:
SLIP PLANE GROUND WATER LEVEL
Possible Remediation OPTION 3 Affected area
Option 3: • Address
3
GROUND WATER
• Flatten the slope • Meets 50% stability target
AND
2
GEOMETRY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
• Significant disruption to private lots
Option 4: • Address
3
GROUND WATER
• “Shear zone replacement” • Meets 50% stability target
• Keeps houses in place
AND
1
GEOLOGY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Option 4:
Possible Remediation OPTION 4 Affected area
Option 4: Possible Remediation OPTION 4:
• Address
3
GROUND WATER
• “Shear zone modification” • Meets 50% stability target
• Keeps houses in place
AND
1
GEOLOGY
FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE UP
Remediation Summary: OPTION 1) Do Nothing
PROS
3) Re-Grade Slope
•
Does not meet target stability
$4.5M
Meets stability target • Reduced long term • risk
Significant disruption Removal of structures
$6.5 – 10M
Meets stability target Maintains structures
Difficult to construct Costly
$10 – 20M
•
Minimal disturbance Lowers “wet year” risk
(and lower water table)
•
4) Shear Zone Modification
•
(and lower water table)
HIGH risk of continued failure
No cost
•
•
ESTIMATED COST
•
•
2) Lower Water Table •
CONS
• •
$0
Independent Review: Clifton Associates
• Independent analysis of the data • Purpose: To confirm remediation options • Conclusions: •
Agree on methodology
Verified the problem is large and • Differing interpretation of data even less stable costly to resolve • Remediation options feasible but may be even more costly
Public Safety Continues to be primary focus of the
• Continue detailed monitoring
• Provide residents with everything we know • Evacuation Alert
