Permeameter testing the UBC perspective on progress · PDF filePermeameter testing – the UBC perspective on progress and ... the largest embankment dam in the world. ... Median Gradation

Permeameter testing – the UBC

perspective on progress and

needs

Imperial College London, 1 September 2017

Jonathan Fannin, Ph.D., P.Eng.

University of British Columbia

Overview

• Progress to-date

• Knowledge gaps and research needs

The Canadian context…

Canada is the world's biggest producer of hydroelectric power.

British Columbia generates almost 90 % of its energy from renewable

hydropower sources.

The Bennett Dam in British Columbia was, upon completion of construction

in 1967, the largest embankment dam in the world. Three dams (the Bennett,

Mica, and Revelstoke dams) generate over half of the province's electricity.

They represent an enormous investment by society-at-large and, like much

of our public infrastructure, these embankment dams are aging, yielding a

potential for water seeping from the reservoir to erode soil within the dam

and its foundation.

Internal erosion is a dam safety risk that was not understood at the time of

construction - it is now recognised to pose one of the greatest risks to dam

safety.

CGS annual conference (2000)

Internal erosion

Filter incompatibility

Internal instability

Empirical screening tools

Filter incompatibility: D15max/D15EE

Internal instability: (H/F)min:

Foster-Fell threshold index

Kenney-Lau threshold index

HOW: the process of internal erosion

Filter incompatibility: D15max/D15EE

Internal instability: (H/F)min:

(57 dams)

(23 dams)

Ronnqvist database

On progress and needs…

• Progress to-date

• Knowledge gaps and research needs

Knowledge gaps: research needs

• Empirical criteria provide a screening tool for evaluating the

susceptibility of a gradation to internal instability

• However they do not, indeed cannot, address the question

of where the onset of internal erosion occurs, nor the rate at

which it can be expected to progress.

• Laboratory testing, and companion theoretical development,

are needed to advance a mechanics-based understanding

of the response that offers potential to address these key

concerns for dam safety engineering.

SPATIAL

TEMPORAL

Internal instability

(∆ m)

(∆ k) (∆ V)

USBR-USACE

(2015)

Experimental Research

WAC Bennett Dam: core and transition materials

0

10

20

30

40

50

60

70

80

90

100

0.010.1110100

Grain size (mm)

Pe

rce

nt

Pa

ss

ing

#200#100#60#40#20#10#43/8"3/4"1 1/2"3"

GRAVELCoarse Medium Fine

SAND FINES

Silt

WAC Bennett Dam

Transition

Test T5

Median Gradation

Test T0

Rigid-wall permeameter I

Rigid-wall permeameter I

Test: T-0-25-D (iav = 11)

t = 1180 s t = 1240 s t = 1360 s

Rigid-wall permeameter I

“… for unstable materials, the critical hydraulic gradient

could be roughly 1/3 to 1/5 of the normal threshold of 1.0.”

cr ci i

Experimental Research

Rigid-wall permeameter II

0

4

8

12

16

210 240 270

Elapsed time (min)

Hydra

ulic

gra

die

nt,

ijk

i 13

i 34

i 45

i 56

i 67

i avi av

i 34

i 45i 13

Onset

0.0

0.1

0.2

0.3

0.4

0 2 4 6 8 10

Average hydraulic gradient, iav

Velo

city (

cm

/s);

Mass loss (

x100,%

)

0

1

2

3

4

5

Str

ain

(%

)

Velocity

Mass loss

Strain

6

1

3

5

4

2

7

iav = 6.6 and 7.3

i

ic

icr= ic

'2( 0.5 ' )vm wi

Cs

'

0vm

2

1

0

'

vm

Cu

Ci

γ'/γw

-0.5γ'/γw 0.5γ'/γw

Ai

As

Au αγ'/γw

Bi

Bu

Bs

'( 0.5 ' )1 0.5

vm wi

Path

Internal

instability

Heave

Stress reduction α-concept:

Fluidization

Internal instability

i

ic

icr= ic

'2( 0.5 ' )vm wi

Cs

'

0vm

2

1

0

'

vm

Cu

Ci

γ'/γw

-0.5γ'/γw 0.5γ'/γw

Ai

As

Au αγ'/γw

Bi

Bu

Bs

'( 0.5 ' )1 0.5

vm wi

Path

Internal

instability

Heave

Constantinople (1922) – London (1994) – Vancouver (2011)

Expanding the α-concept in stress-gradient space:

Stable gradations

Unstable gradations

Experimental Research

Flexible wall permeameter

Discharge velocity

Axial strain

Volumetric strain

vs.

Hydraulic gradient

Suffusion vs. Suffosion

(∆ m)

(∆ k) (∆ V)

- “normative” procedures for specimen reconstitution

and laboratory testing

- inter-laboratory comparison of test results

Summary remarks: experimental research

- a continuum

mechanics-based

theoretical modelling

framework

- a particulate

mechanics-based

conceptual

understanding

- model-informed

experimental investigations