10/18/2018 10/18/2018 Gardiner Dam’s Historic Movement and Ongoing Stability Evaluation Jody Scammell, M.Sc., P. Eng. Director, Dam Safety and Major Structures 1 10/18/2018 2 10/18/2018 Outline • South Saskatchewan River Project Introduction • Lake Diefenbaker Reservoir • Gardiner Dam – Foundation Conditions – Major Components – Movements – Previous Stability Evaluations • Grant Devine Dam Stability Evaluation • Expected Results – Not expected results 3 10/18/2018 SSRP Introduction Gardiner Dam Qu’Appelle River Dam 4 10/18/2018 SSRP Introduction • 1894 first consideration for large irrigation • 1968 completed • Total cost $120 million (1968 value) • Replacement value $2.41 Billion • Owned and operated by Water Security Agency • Operation, maintenance and monitoring complete by 8 onsite staff 5 10/18/2018 Lake Diefenbaker Reservoir 6 10/18/2018 Reservoir Drainage Basin • Three Regions • Effective Distribution – Eastern Rockies 50% Area / 80% Flow – Foothills – Prairies 50% Area / 20% Flow • 60% Snowmelt • 38% Rainfall runoff • 2% Glacier melt 7 10/18/2018 Reservoir Operation • Runoff patterns – Low winter flow – Spring peak, April – Summer peak, May/June – Recession, Aug/Sept 8 10/18/2018 Reservoir • Lake Diefenbaker • 225 km long (near Eston, SK) • 760 km shoreline • Volume 9.25x109 m3 • Usable Storage 3.95x109 m3 • Up to 58 m deep 9 10/18/2018 2013 Release • Largest flow released • 1600 m3/s spillway • 2000 m3/s total 6000 558 Lake Diefenbaker April 1, 2013 to March 31, 2014 5000 556 4000 554 3000 552 Inflow Flow (m3/s) Flow Outflow Elevation (m) Elevation median 2000 550 1000 548 0 546 10 10/18/2018 Gardiner Dam 11 10/18/2018 12 10/18/2018 Gardiner Dam Main (River) Major Components Embankment Plateau Embankment Coteau Creek Embankment Tunnels Spillway 13 10/18/2018 Gardiner Dam Embankments • Three zoned compacted- earth filled embankments Coteau Creek Embankment • Total Length 5000 m • Crest Elevation 562.4 m • Max height 64 m • Upper Slopes 2H:1V • Lower Slopes 85H:1V Plateau Main (River) Embankment Embankment 14 10/18/2018 Gardiner Dam Foundation 15 10/18/2018 Gardiner Dam Foundation • Till • River Sand – Eroded except on – In valley bottom abutments • Bedrock – Bearpaw Formation – Snakebite Shale – Ardkenneth Sandstone 16 10/18/2018 Gardiner Dam Foundation • Snakebite Shale Description – Upper Cretaceous Origin – Marine Deposited – Dark Grey Shale, flat horizontal lying strata – Jointed, Slickensided, and Bentonite seams – Highly Plastic – Presheared 17 10/18/2018 Gardiner Dam Foundation 18 10/18/2018 Gardiner Dam Foundation 19 10/18/2018 Gardiner Dam Movement 20 10/18/2018 Gardiner Dam Horizontal Movement • Occurring since start of construction • Shear plane located in shale foundation near the contact with the underlying sandstone – Approximately 114 m below the crest of the dam El.448 m 21 10/18/2018 Gardiner Dam Horizontal Movement • Movement rates and magnitude vary by position from the dam crest • Maximum movement rate and magnitude is occurring at toe of main embankment 22 10/18/2018 Historic Instrumentation Horizontal Movement • The movement is occurring on a defined shear plane in the shale 23 10/18/2018 Gardiner Dam Horizontal Movement • Movement rate generally slowing • On an annual frequency the movement rates indicate a trend with the reservoir 24 10/18/2018 Historic Instrumentation Time Comparison • The piezometric level fluctuates with reservoir 25 10/18/2018 Previous Analysis • 1948 -1953 • 1979 – Limit Equilibrium – Finite element stress – Total Stress Analysis deformation analysis • 1954-1965 – Computational limited – Limit Equilibrium • 1980-2009 – Effective Stress Analysis – Simple mechanical model with a spring and – Redesigned as the back damper to predict analysis of local slopes movement related to historic movement 26 10/18/2018 Previous Analysis • 2009 -2013 • It appeared there is a • Analytical Model correlation between total stress loading on the shale • Simple sliding block and pore water dissipation. evaluation 27 10/18/2018 Previous Analysis What does this all mean Next Steps • We don’t understand the • Detailed Finite Difference movement mechanisms Model (FDM) • The stability of the structure • Understand long term is not fully understood deformations and impacts on structures 28 10/18/2018 Detailed FDM Analysis Moving Forward Grant Devine (Alameda) Dam 2011-2014 • Similar problem as Gardiner • Process will be very similar but was moving faster 29 10/18/2018 Detailed FDM Analysis Moving Forward Grant Devine (Alameda) Dam • Stop construction to • Unanticipated shear redesign displacements during • Added toe berms construction Glacial Till (Foral/Battleford) Formation) Bedrock – interbedded sandstones, siltstones and clay shales (Ravenscrag Formation) 30 10/18/2018 Detailed FDM Analysis Moving Forward Detailed Geological Framework • Need to understand the • Develop a representative materials in the foundation model 31 10/18/2018 Detailed FDM Analysis Moving Forward 32 10/18/2018 Detailed FDM Analysis Moving Forward Start with a 2D • 2D model is required to – Establish appropriate minimize complications constitutive model of soil • Calibrate model • Once model behavior is – Lab tested material understood then move on to properties 3D – Actual deformation measurements 33 10/18/2018 Detailed FEM Analysis Moving Forward Move forward with 3D • Start with properties from calibrated 2D model • Calibrate again – Actual deformation 3D FLAC Model measurements – Measured porewater pressure Oblique Section – Shear Strain Contours34 Cut Along Oblique Section 10/18/2018 Expected Results • Understanding of long term • Limitations movements – Not expecting be able to • Understanding of the estimate annual stability of the structure displacement • Estimate of total – A traditional Factor of deformation and rate Safety is not possible • Impact on the ancillary structures – Spillway – Relief Well Drainage Conduit 35 10/18/2018 Summary • The dam is performing well • With over 50 years of • Monitoring and satisfactory performance maintenance activities are there is valuable lessons to ongoing be learned from this project • The embankment is moving • This project is a valuable downstream with rates asset to the province and slowing will remain to be in the future 36 10/18/2018 37 .