riprap revetment ahn polvi trabant
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7/21/2019 Riprap Revetment Ahn Polvi Trabant
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Riprap RevetmentRiprap Revetment
Jungkyu AhnLina Polvi
Stuart Trabant
OutlineOutline
• Introduction
• Where riprap is used
• Riprap design
• Example design
• Types of riprap failure
• Design considerations: How to preventriprap failure
• Examples of riprap failure & success
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
IntroductionIntroduction
Riprap Revetment:Strengthen riverbanks against erosion
Factors that affect riprap resistance to erosiveforces
Materials : natural stones
▪ construction quality
▪ channel alignment
▪ cross section
▪ bank slope
▪
velocity distribution▪ ground water
▪ stone size
▪ shape
▪ weight
▪ durability
▪
gradation▪ layer thickness
Where Riprap Revetment is Useful:Where Riprap Revetment is Useful:
• On the outside ofbends
• At hydraulicstructures
• At flow contractions
• In man-made channels
• In widening channels• At locations with high
turbulence
Outside Bend Riprap, Rapid Crk, SD (MEI)
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
1. Stone size
There are two methods to determine stone size.(1) Shear-stress method
where dm : effective rock size (usually, dm ≈d65 ≈ 1.25d50)
τ 0 : applied shear stress
τ *c : critical value of Shields number γ : specific weight of water
G : specific gravity of riprap
θ 1 : side slope angle
φ : angle of repose of riprap
Riprap DesignRiprap Design
⎥⎥⎦
⎤
⎢⎢⎣
⎡−−
=
φ
θ τ
τ
2
1
2
*
0
sin
sin1)1(G
d
c
m
φ
(2) Velocity method
where ds ≈d65 ≈ 1.25d50
Vc
: critical mean flow velocity
Riprap DesignRiprap Design
φ
⎥⎦
⎤⎢⎣
⎡
−
−−≅
φsin1
θsin11)gd2(GK V
2
2
scc
φ tan4
log ⎟⎟ ⎠
⎞⎜⎜⎝
⎛ =
s
cd
hK
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Standard Riprap Sizing MethodsStandard Riprap Sizing Methods(Velocity(Velocity--Based)Based)
• U.S. Corps of Engineers, EM 1110-2-1601
• American Society of Civil Engineers
• US Bureau of Reclamation Method
• U.S. Geological Survey Method
• Isbash Method
• California Bank and Shore ProtectionMethod
• Federal Highways HEC-11
Riprap DesignRiprap Design
2. Stone shape (should satisfy the following)
i) Stone shall be predominantly angular
ii) Not more than 30% of stones a/c >2.5
iii) Not more than 15% of stones a/c >3.0
iv) No stone a/c > 3.5
where a : maximum length of long axis
c : maximum length of short axis
3. Stone weight
where D% : equivalent-volume spherical stone diameter
W% : weight of individual stone having diameter of D%
Riprap DesignRiprap Design
φ φ φ
3/1%
%
6⎟⎟ ⎠
⎞⎜⎜⎝
⎛ =s
W D
πγ
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
4. Filter i)
ii)
iii)
5. Riprap layer thicknessi) Riprap layer thickness >d
100& >1.5×d
50ii) Increase thickness by 50% when placing under water
Riprap DesignRiprap Designφ φ
40)(
)(
50
50 <based
filter d
40)(
)(5
15
15 <<based
filter d
5)(
)(
85
15 <based
filter d
6. Revetment toe protection
Toe protection may be provided by two methods
(1) Extend to maximum scour depth
▪ place end of toe below the expected scour depth or
▪ ground it on nonerodible material
(2) Place launchable stone
▪ Windrow : riprap placed at top of bank
▪ Trench-fill : riprap placed at low water level
▪ Weighted riprap toes : riprap placed at intersection of channel bottom and side slope
▪ Windrow ▪ Trench-fill ▪ Weighted riprap toes
Riprap DesignRiprap Design
φ φ φ
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Example Design:Example Design:
Yuba River, California Yuba River, California
• Purpose: Protect
outside of bend at
fish ladder exit
• Stone sizing
method: Velocity
Method (after Julien,
2002)
• Stone Sizing
Equation:
⎥⎦
⎤⎢⎣
⎡
−
−−≅
φsin1
θsin11)gd2(GK V
2
2
scc
Proposed Riprap
Fish Ladder
Exit
Q
Example Design (cont):Example Design (cont):
Yuba River, California Yuba River, California
• From hydraulicmodel, Vc~8 ft/s
• Use particle stabilitydiagram (stone sizevs velocity curves)
• For bank slope of2H:1V, ds ~ 0.6 feet
• Use D50 = 9” (fromds ~ 1.25 D50)
• Therefore, D10 ~3”and D90 ~16”
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Example Design (cont):Example Design (cont):
ApplicationApplication
• Design Flow Depth=22’
• Freeboard=2’
• Est. Scour depth=6.6’
• Thickness=2* D50=18”
• Length=500’
• Factor of Safety=2 (for
self-launching toe
riprap)
• Total Volume=H*T*L*FS*sin ~760yd3
= 205 tons
θ
θ
110
120
130
140
150
160
170
0 10 20 30 40 50 60 70 80 90 100
Station (ft)
E l e v a t i o n
( f t )
Left Bank at Proposed Riprap
Riprap as constructed
Riprap After Scour and Launch*
*Assuming riprap lost during launch
Riprap Height=24 ft
Scour Depth=6.6 ft
Slope =1V:2H
Design WSE
Schematic of riprap design for YubaRiver with launchable toe (MEI)
Types of Riprap FailureTypes of Riprap FailureParticle Erosion:•Causes: Stone size too small, stones removed by
impact, bank sideslope greater than angle of repose
for riprap material, riprap gradation too uniform
•Solution: Coarser riprap, reevaluate riprap gradation
& angularity
Slide: Downslope mass movement of stones•Causes: Bank sideslope too steep, excess
hydrostatic pore pressure, loss of material at toe of
riprap blanket
•Solution: Strengthen toe of riprap blanket, use larger
stones near channel bed
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Types of Riprap FailureTypes of Riprap Failure
(cont.)(cont.)Slump: Mass movement within riprap
blanket•Causes: Bank sideslope too steep, lack of toe slope
support
•Solution: Add coarser material at toes of
embankment, reduce sideslope angle at top of
embankment
Sideslope failure: rotation/gravitational
movement along surface•Causes (related to shear failure of underlying base
material): Excess pore pressure in base material,
sideslopes too steep
•Solution: Reduce embankment slope, drain base
material
Design Considerations:Design Considerations:
Preventing Riprap FailurePreventing Riprap Failure• Tieback
– Tie upstream and
downstream ends of
blanket into bank
• Launching Apron
– Horizontal riprap on
foot of revetment
• Overlap revetment
– Overlap revetment
on opposite banks
Overlapping riprap on Rapid Creek, SD
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
General Design ConsiderationsGeneral Design Considerations
Alt ernating Riprap Design,
Puerco River, NM (MEI)
Riprap with d rainage,
Minera Yanachocha, Peru (MEI)
• Overlap riprap whenalternating left and
right banks
• Use proper drainage
for saturated soils
General Design ConsiderationsGeneral Design Considerations
(cont.)(cont.)
• Extend revetment
up and downstream
of active erosion
• Ensure riprap is
well-graded and
angular
• Use tie-back toprevent flanking Tie-back on Merrill Creek, TX (MEI)
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HYDRAULIC AND SEDIMENT
TRANSPORT MODELING OF SAN
JOAQUIN RIVER, FRIANT DAM TO
MENDOTA DAM
Examples of Riprap FailureExamples of Riprap Failure
Failed riprap on
Tijeras Arroyo, NM
due to poorgradation
Failed riprap on
Tijeras Arroyo, NM
due to slide orslump and further
bank erosion
Failed riprap
flanking on
Whitnall Park
Creek, WI
Examples of Riprap SuccessExamples of Riprap Success
Revegetation of riprap
along Rapid Creek, SD
Riprap along alternating bends
on Whitnall Park Creek, WI
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