2012 to Present: 2013 2012 Causes of the Failure 3 GROUND WATER - PowerPoint PPT Presentation

2012 to Present: 2013 2012

Causes of the Failure 3 GROUND WATER 1 GEOLOGY 2 GEOMETRY Weak soil Steep slope High water table due to increased precipitation

1 GEOLOGY Causes of the Failure: 2 GEOMETRY 11 th St 3 GROUND WATER Cherry Lane Sask Cres GROUND WATER LEVEL SLIP PLANE

10 Year Average Rainfall - Saskatoon

Groundwater Levels - Saskatoon

Status of Slope Movement • Not stable 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 GROUND WATER 3 • Install dewatering trenches (11 th St & Cherry Lane)

Option 2 GROUND WATER LEVEL SLIP PLANE GROUND WATER LEVEL

Option 2 • Address GROUND WATER 3 • Install dewatering trenches (11 th St & Cherry Lane) • Doesn’t meet stability target (only 20%)

Option 3: • 3 GROUND WATER 2 GEOMETRY Address AND • Flatten the slope FORCES PULLING SLOPE DOWN FORCES HOLDING SLOPE • Meets 50% stability target UP

Option 3: SLIP PLANE GROUND WATER LEVEL

Possible Remediation OPTION 3 Affected area

Option 3: • 3 GROUND WATER 2 GEOMETRY Address AND • Flatten the slope FORCES PULLING SLOPE DOWN FORCES HOLDING • SLOPE Meets 50% stability target UP • Significant disruption to private lots

Option 4: • 3 GROUND WATER 1 GEOLOGY Address AND • “Shear zone replacement” FORCES PULLING SLOPE DOWN FORCES HOLDING • SLOPE Meets 50% stability target UP • Keeps houses in place

Option 4:

Possible Remediation OPTION 4 Affected area

Option 4: Possible Remediation OPTION 4 : • 3 GROUND WATER 1 GEOLOGY Address AND • “Shear zone modification” FORCES PULLING SLOPE DOWN FORCES HOLDING • SLOPE Meets 50% stability target UP • Keeps houses in place

Remediation Summary: ESTIMATED OPTION PROS CONS COST HIGH risk of • 1) Do Nothing $0 No cost • continued failure Minimal • disturbance Does not meet target • 2) Lower Water Table $4.5M Lowers “wet year” stability • risk Meets stability • 3) Re-Grade Slope target Significant disruption • $6.5 – 10M Reduced long term Removal of structures (and lower water table) • • risk Meets stability • 4) Shear Zone target Difficult to construct • $10 – 20M Modification Maintains Costly • • (and lower water table) structures

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