Download - 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
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
Under scientific supervision ofDra. Laura Caldeira
Dr. Emanuel Maranha das Neves
PhD thesis prepared at
PhD thesis defence | 29th October, 2014