Gardiner Dams Historic Movement and Ongoing Stability Evaluation - - PowerPoint PPT Presentation

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Gardiner Dams Historic Movement and Ongoing Stability Evaluation - - PowerPoint PPT Presentation

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10/18/2018 10/18/2018 Gardiner Dams 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

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10/18/2018

Gardiner Dam’s Historic Movement and Ongoing Stability Evaluation

Jody Scammell, M.Sc., P. Eng. Director, Dam Safety and Major Structures

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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

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SSRP Introduction

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Gardiner Dam Qu’Appelle River Dam

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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

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Lake Diefenbaker Reservoir

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Reservoir Drainage Basin

  • Three Regions

– Eastern Rockies – Foothills – Prairies

  • 60% Snowmelt
  • 38% Rainfall runoff
  • 2% Glacier melt
  • Effective Distribution

50% Area / 80% Flow 50% Area / 20% Flow

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Reservoir Operation

  • Runoff patterns

– Low winter flow – Spring peak, April – Summer peak, May/June – Recession, Aug/Sept

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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

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2013 Release

  • Largest flow released
  • 1600 m3/s spillway
  • 2000 m3/s total

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546 548 550 552 554 556 558 1000 2000 3000 4000 5000 6000 Elevation (m) Flow (m3/s) Inflow Outflow Elevation median

Lake Diefenbaker

April 1, 2013 to March 31, 2014

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Gardiner Dam

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Plateau Embankment

Main (River) Embankment

Coteau Creek Embankment Spillway Tunnels

Gardiner Dam Major Components

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10/18/2018 Plateau Embankment

Main (River) Embankment

Coteau Creek Embankment

Gardiner Dam Embankments

  • Three zoned compacted-

earth filled embankments

  • Total Length 5000 m
  • Crest Elevation 562.4 m
  • Max height 64 m
  • Upper Slopes 2H:1V
  • Lower Slopes 85H:1V

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Gardiner Dam Foundation

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Gardiner Dam Foundation

  • Till

– Eroded except on abutments

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  • River Sand

– In valley bottom

  • Bedrock

– Bearpaw Formation – Snakebite Shale – Ardkenneth Sandstone

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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

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Gardiner Dam Foundation

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Gardiner Dam Foundation

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Gardiner Dam Movement

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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

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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

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Historic Instrumentation

Horizontal Movement

  • The movement is occurring
  • n a defined shear plane in

the shale

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Gardiner Dam Horizontal Movement

  • Movement rate generally

slowing

  • On an annual frequency

the movement rates indicate a trend with the reservoir

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Historic Instrumentation

Time Comparison

  • The piezometric level

fluctuates with reservoir

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Previous Analysis

  • 1948-1953

– Limit Equilibrium – Total Stress Analysis

  • 1954-1965

– Limit Equilibrium – Effective Stress Analysis – Redesigned as the back analysis of local slopes

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  • 1979

– Finite element stress deformation analysis – Computational limited

  • 1980-2009

– Simple mechanical model with a spring and damper to predict movement related to historic movement

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Previous Analysis

  • 2009-2013
  • Analytical Model
  • Simple sliding block

evaluation

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  • It appeared there is a

correlation between total stress loading on the shale and pore water dissipation.

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Previous Analysis

What does this all mean

  • We don’t understand the

movement mechanisms

  • The stability of the structure

is not fully understood

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Next Steps

  • Detailed Finite Difference

Model (FDM)

  • Understand long term

deformations and impacts

  • n structures
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Detailed FDM Analysis Moving Forward

Grant Devine (Alameda) Dam 2011-2014

  • Similar problem as Gardiner

but was moving faster

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  • Process will be very similar
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Detailed FDM Analysis Moving Forward

Grant Devine (Alameda) Dam

  • Unanticipated shear

displacements during construction

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  • Stop construction to

redesign

  • Added toe berms

Glacial Till (Foral/Battleford) Formation) Bedrock – interbedded sandstones, siltstones and clay shales (Ravenscrag Formation)

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Detailed FDM Analysis Moving Forward

Detailed Geological Framework

  • Need to understand the

materials in the foundation

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  • Develop a representative

model

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Detailed FDM Analysis Moving Forward

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Detailed FDM Analysis Moving Forward

Start with a 2D

  • 2D model is required to

minimize complications

  • Calibrate model

– Lab tested material properties – Actual deformation measurements

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– Establish appropriate constitutive model of soil

  • Once model behavior is

understood then move on to 3D

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Detailed FEM Analysis Moving Forward

Move forward with 3D

  • Start with properties from

calibrated 2D model

  • Calibrate again

– Actual deformation measurements – Measured porewater pressure

34 3D FLAC Model Cut Along Oblique Section Oblique Section – Shear Strain Contours

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Expected Results

  • Understanding of long term

movements

  • Understanding of the

stability of the structure

  • Estimate of total

deformation and rate

  • Impact on the ancillary

structures – Spillway – Relief Well Drainage Conduit

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  • Limitations

– Not expecting be able to estimate annual displacement – A traditional Factor of Safety is not possible

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Summary

  • The dam is performing well
  • Monitoring and

maintenance activities are

  • ngoing
  • The embankment is moving

downstream with rates slowing

  • With over 50 years of

satisfactory performance there is valuable lessons to be learned from this project

  • This project is a valuable

asset to the province and will remain to be in the future

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