Phd Defense | Ricardo Correia dos Santos

Experimental Investigation on Limitation of the Progression of Internal Erosion in Zoned Dams

by

Ricardo N.Correia dos Santos

ricardos@lnec.pt

Under scientific supervision ofDra. Laura Caldeira

Dr. Emanuel Maranha das Neves

PhD thesis prepared at

PhD thesis defence | 29th October, 2014

Question | ObjectiveQuestion | Objective

Upstream zoneUpstream

zone> Flow-limiting action

> Crack-filling action

Research question: ‘What is the influence of the upstream zone limiting the progression of internal erosion through a crack in the core ‘ ?

Sandy gravel Sandy gravel

Core Filter

Objective: Experimentally investigate what are the upstream materials that may provide these two actions

> Flow-limiting action

> Crack-filling action

> Flow-limiting action

> Crack-filling action

Previous laboratory testing on erosion in soils by others

SampleØ ~ 10 cmh ~ 12 cm

Core

Pea gravelCore

Ø ~ 2.5 cmh ~ 3.8 cm

Sample Sample

Ø ~ 10 cmh ~ 12 cm

Pointgauge

Cylindrical cellØ ~ 0.5 m

Core

> Erosion along a concentrated leak

Hole Erosion Test (HET)Wan and Fell (2004)

> Erosion of an immersed soil

JET Erosion testHanson and Cook (2004)

> Identification of dispersive clays

Pinhole test Sherard, Dunningan and Decker (1976)

> Susceptibility to suffusion of a soil

SampleØ = 30 cmh = 25 cm

Upward Flow (UF) seepage testWan and Fell 2008

Downward Flow (DF) seepage testWan and Fell 2008

SampleØ = 30 cmh = 30 cm

Drainage layer

Previous laboratory testing on erosion in soils by others

Filter

Core

SampleØ=20.5 cmCore: h = 10 cmFilter: h = 20 cm

A

A'

Section A-A'

Filt

er

Pea gravel

Crack

Core

Perspex

Crack

Sample fromProctor test

Core

Previous laboratory testing on erosion in soils by othersPrevious laboratory testing on erosion in soils by others

> Filtering in a hole

Continuing Erosion Filter testFoster and Fell 2000

> Filtering in a crack

Crack Erosion Test Maranha das Neves (1989, 1991)

Crack filling by upstream uniform sand

Upstream

material

CoreCore

Upstream

material

Filter

> Flow Limitation Erosion Test > Crack Filling Erosion Test

New test cell developed at LNEC | Two laboratory tests

63 cm 40 cm

Ø 30 cm1 cm thk

17 2512

> Test Cell

FLET

CFET

New test cell developed at LNEC | Two laboratory tests

Specimen preparation & cell assembly | Tests setup

> FLET setup > CFET setup

> Specimen preparation in FLET > Specimen preparation in CFET

Specimen preparation & cell assembly | Tests setup

Experimental study in the FLET/CFET (Soils tested)

> Upstream material

A

5 broadly-graded soils

N1, N2 and N3 – Rb Grande DamP1 and P2 – Odelouca Dam

2 uniform granular soilsSand A0 and Gravel A

6 gap-graded granular soilsGA1, GA2, GA3 and GA4GN and GP (5% fines)

13 Upstream

soils

> Core and Filter

2 Filters

2 Cores

Experimental study in the FLET/CFET (Soils tested)

> Characterisation of soils used in the FLET/CFET

Standard laboratory

testing

• Standard compaction tests• Maximum/minimum density tests• Permeability tests

Theoretical analysis

• Susceptibility of soils to internal instability• Ability of the soils to support an open pipe

Internal erosion tests

• 9 Upward Flow (UF) tests on gap-graded soils• 25 Hole Erosion Tests (HET) on core soils

Experimental study in the FLET/CFET (Soils tested)

> Erosion behaviour of gap-graded soils in the simpler UF test

UF test on soil GN25% sand | 5% fines (NP)

uf test_sufusion_gn.grfHydraulic gradient, i

Ave

rage

vel

ocit

y, V

(m

/s)

Per

mea

bil

ity,

k (

m/s

)

0 0.5 1 1.5 2 2.5 3 3.5 41E-6 1E-52E-6 2E-5

5E-6 5E-51E-5 1E-42E-5 2E-4

5E-5 5E-41E-4 1E-32E-4 2E-3

5E-4 5E-31E-3 1E-2

i cr

i star

ti b

oil

Velocity, VPermeability, k

uf test_sufusion_time_gn.grfTime (min)

Hyd

rau

lic

grad

ien

t, i

Flow

rat

e, Q

(cm

3/s

)

0 40 80 120 160 2000 0

0.5 31 6

1.5 92 12

2.5 153 18

3.5 214 24

iboil

Hydraulic gradient, iFlow rate, Q

Experimental study in the FLET/CFET (Soils tested)

> Erosion behaviour of the core soils in the simpler HET

Water content, w (%)

Dry

un

it w

eigh

t, d

(k

N/m

3)

12 13 14 15 16 17 18 19 2020.516.5

17

17.5

18

18.5

19

19.5

20

4.11

Sr = 100% 4.6

4.24

4.49

4.61

4.394.7

4.48

3.76

3.393.78

4.25

......

Erosion rate Index, IModified (core#4)No erosion (core#4)Standard (core#4)'Reduced' (core#4)Standard (core#20)

Core#4

Core#20

Experimental study in the FLET/CFET (Soils tested)

Experimental study in the FLET

> Testing conditions

19 FLETs on broadly-graded upstream soils

• DH = 2 m → i = 4

• Di = 12 mm (few with 10 and 16 mm)

• Core#4 (IHET = 4.1)

• Upstream soil: wopt or wopt ± 2% | 95 or 98%

14 FLETs on granular

upstream soils

• DH = 2, 1.5 or 1 m | Di = 12 mm

• Core#4 (IHET = 4.1)

• Upstream soil: low w | Dr of 100%

33 FLETs 1 year | ~ 3 tons of soil

Experimental study in the FLET

> Observed behaviour types | Type F1– Flow limitation (self-healing)

Experimental study in the FLET

> Observed behaviour types | Type F2– Flow limitation (non-erodible)

Q = 650 l/h Q = 750 l/h Q = 800 l/h Q

Experimental study in the FLET

> Observed behaviour types | Type F3– Slow down of erosion process

Experimental study in the FLET

> Observed behaviour types | Type F4 – Strong progression of erosion

Experimental study in the FLET

> Observed behaviour types | Type F4 – Strong progression of erosion

Experimental study in the FLET (Conclusions)

> Critical parameters influencing the flow-limiting action

dw vs pf200_broadly.grf

w wopt (%)

Fin

es c

onte

nt,

FC

(%

)

0

10

20

30

40

P2dry P2opt98;D10

P1opt

P2wet98;D16

N3dryN3dry;98%

N3wet

N2optN2dry N2wet

N1wetN1dry N1opt

P2opt P2wet

C#4

P1dry

N3opt

12%

5%

20%

dw vs pc4_broadly.grf

w wopt (%)

Gra

vel c

onte

nt,

GC

(%

)

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 380

70

60

50

40

30

20

10

0

P2dry P2opt98;D10

P1opt

P2wet98;D16

N3dryN3dry;98%

N3wet

N2opt

N2dry

N2wet

N1wetN1dry N1opt

P2opt P2wet

C#4

P1dry

50%

N3opt

Dry side Wet sideNearoptimum

N soils | P soilsType 1.Type 3Type 4

Type 1Type 2.Type 4

Broadly graded

soils

• Fines content• Fines plasticity• Gravel content• Water content

Gap-graded

soils

• Unlikely to limit flow• Low Hydraulic head, DH• Internal stabilityG

rave

l con

tent

(%

)F

ines

con

ten

t (%

)

w –wopt (%)

Experimental study in the FLET

> Proposed rules for estimation of likelihood of flow limiting action

Upstream material Upstream material is cracked Upstream material is not cracked

Water content Internally unstable soil with iU

Internally stable soil with kU (m/s)

Zone type

Fines content Fines type

dry side near opt wet side > 1 < 1 > 10-2 ‡ < 10-5 ‡

I NA NA 0 0 0 II <5% Any ** ** ** VU U VU *** III 5 to 12% SPF L* N* N* U N U L HPF‡ N* U* N* IV >12% SPF L* N* N* N L *** VL HPF‡ U* N* L* V 5 to12% NP ** ** ** VU N VU *** VI >12 to 20%‡ NP L* N* N* U N U L VII >20 to 30% NP N U U N L *** VL VIII >30% NP U VU VU N L *** VL

Symbol /colour

Qualitative descriptor

Example of likelihood interval

VL Very Likely 0.98–0.999

L Likely 0.70–0.98

N Neutral 0.30–0.70

U Unlikely 0.02–0.3

VU Very Unlikely 0.001–0.02

Experimental study in the CFET

> Testing conditions

4 CFETs on broadly-graded

upstream soil

• DH = 2 m | Di = 12 mm or 16 mm

• Core#4 (IHET = 4.1) and Filter G (Dr = 100%)

• Upstream soil N1: wopt or wopt ± 2% | 95%

37 CFETs on granular soils

• DH = 2m | Di = 12 or 16 mm

• Core#4 or Core#20 (IHET = 4.1)

• Filter S or Filter G (Dr about 60%)

• Upstream soil: low w | Target Dr of 100%

1 ½ year | ~ 4.5 tons of soil41 CFETs

Experimental study in the CFET

> Observed behaviour types | Type C1– rapid ‘crack-filling’

Experimental study in the CFET

> Observed behaviour types | Type C2a – Filtering after ‘some’ erosion

Experimental study in the CFET

> Observed behaviour types | Type C2b – Filtering after ‘excessive’ erosion

Experimental study in the CFET

> Observed behaviour types | Type C3 – Continuing erosion

Experimental study in CFET (Conclusions)

> Critical parameters influencing the crack-filling action

Broadly graded

soils

• Highly unlikely to

fill cracks

Gap-graded

soils

• pA0 versus D15F

• 5% fines may decrease capability

• Core soil with I > 4 has no influence

Experimental study in the CFET

> Proposed rules for estimation of likelihood of crack-filling action

Key features of upstream zone

Embankment zoning in the erosion path at downstream of the core

Rapid crack-filling action

Formation of a self-filtering layer

No crack filling nor filtering mechanism

Fines content

Effectiveness of upstream soil

Key feature of the filter Estimate erosion zone by Foster and Fell (2001)

D15F < 2.9 mm

Transition

D15F ≥ 5.1 mm

No erosion

Some erosion

Excessive Erosion

Continuing Erosion

<5% psand > 30% and no fines content

VL L U VL L N U

Transition L L – U* U L N U U

psand ≤ 20% and 5% of fines

U U VU N U U VU

≥12% NA VU VL L N VU

Symbol /colour

Qualitative descriptor

Example of likelihood interval

VL Very Likely 0.98–0.999

L Likely 0.70–0.98

N Neutral 0.30–0.70

U Unlikely 0.02–0.3

VU Very Unlikely 0.001–0.02

Final conclusions

Initial question‘What is the influence of

upstream zones? ’

• Answer: Some soils compacted in certain conditions, when located upstream of a crack in the core, may effectively provide the flow limiting action or the crack-filling action.

Proposed objective

Experimental study of both actions

• Development of a new test device and of 2 laboratory tests (FLET and CFET), and their test procedures.

• Identification of the potential behaviour types and of the influence of critical parameters for each action.

• Proposed rules to aid practical engineers in the design phase or to estimate probabilities for dams in operation.

Future research

FLETFlow limiting

action

• Extend testing to greater variety of upstream soils prepared to a wider range of test conditions.

• Evaluate if self-healing ability of very dry upstream materials also occurs in soils with highly plastic fines.

• Investigate the influence of the permeability of coarse grained (stable) soils.

CFETCrack-filling

action

• Extend testing using materials from existing dams.

• Evaluate the relation pA0 versus D15F for other soils.

Both• Evaluate influence of the erosion rate of the core (for I < 4).

• Evaluate influence of the flow orientation.

Tunbridge Dam, AustraliaZoned earth dam (28 m) Source: Jeffery Farrar (2005)

Progression of internal erosion in the embankment

Hanson e Hunt (2007)

Homogeneous dam (25 m) Source: USDA

Experimental Investigation on Limitation of the Progression of Internal Erosion in Zoned Dams

by

Ricardo N.Correia dos Santos

ricardos@lnec.pt

Under scientific supervision ofDra. Laura Caldeira

Dr. Emanuel Maranha das Neves

PhD thesis prepared at

PhD thesis defence | 29th October, 2014