Experimental Investigation on Limitation of the Progression of Internal Erosion in Zoned Dams by Ricardo N. Correia dos Santos [email protected]Under scientific supervision of Dra. Laura Caldeira Dr. Emanuel Maranha das Neves PhD thesis prepared at PhD thesis defence | 29 th October, 2014
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Experimental Investigation on Limitation of the Progression of Internal Erosion in Zoned Dams
> 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