specialty workshop: sites training and introduction to windam asdso dam safety 2008 part 2 – sites...
TRANSCRIPT
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SPECIALTY WORKSHOP: SPECIALTY WORKSHOP: SITES TRAINING AND SITES TRAINING AND
INTRODUCTION TO WINDAM INTRODUCTION TO WINDAM
ASDSO Dam Safety 2008ASDSO Dam Safety 2008
PART 2 – SITES EARTH SPILLWAYPART 2 – SITES EARTH SPILLWAY EVALUATION EVALUATION
B.B. Earth Spillway Integrity AnalysisEarth Spillway Integrity Analysisiii. Phase 3 (Headcut Advance)iii. Phase 3 (Headcut Advance)
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3 PHASE Spillway Erosion Model
1. SURFACE EROSION (Cover Destruction)
3. HEADCUT ADVANCE
2. CONCENTRATED FLOW EROSION
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HEADCUT ADVANCE
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OBJECTIVES
• Phase 3
– Inputs and equations
– Relation of downcutting to headward advance
– Concept of multiple materials and weakest line of attack
– Concept of unraveling (implications of threshold-rate governing relations)
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OBJECTIVES
• Phase 3
– Inputs and equations
– Relation of downcutting to headward advance
– Concept of multiple materials and weakest line of attack
– Concept of unraveling (implications of threshold-rate governing relations)
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DOWNCUTTING andHEADCUT ADVANCE
dX/dt
d/dt
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Parameters Impacting Phase 3 ErosionParameters Impacting Phase 3 Erosion
Multiple materials may be exposed in a single headcut face.
Downcutting controlled by the material exposed at the base for the time step.
Headcut advance controlled by the materials exposed on the headcut face.
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SITESSITESAUXILIARY SPILLWAY EROSION
PHASE 3 INPUT PARAMETERSPHASE 3 INPUT PARAMETERS
DOWNCUTTINGDOWNCUTTING
• PARTICLE DIAMETERPARTICLE DIAMETER• DRY BULK DENSITYDRY BULK DENSITY• PERCENT CLAY orPERCENT CLAY or• kkdd DETACHMENT COEFFICIENT DETACHMENT COEFFICIENT
HEADCUT ADVANCEHEADCUT ADVANCE
• KKhh HEADCUT ERODIBILITY INDEX HEADCUT ERODIBILITY INDEX
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SITESSITESAUXILIARY SPILLWAY EROSION: PHASE 3
DOWNCUTTINGDOWNCUTTING
eeddcc0.011 (H/d0.011 (H/dcc))0.5820.582
dd//ddt = kt = kdd((ee--cc))
HEADCUT ADVANCEHEADCUT ADVANCE
ddX/X/ddt = C (A - At = C (A - Aoo))
A = (qH)A = (qH)1/31/3
(NEH Part 628 Dams Ch 51 Eq 51-9)(NEH Part 628 Dams Ch 51 Eq 51-9)
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SITESSITESAUXILIARY SPILLWAY EROSION: PHASE 3
DOWNCUTTINGDOWNCUTTING
eeddcc0.011 (H/d0.011 (H/dcc))0.5820.582
dd//ddt = kt = kdd((ee--cc))
HEADCUT ADVANCEHEADCUT ADVANCE
ddX/X/ddt = C (A - At = C (A - Aoo))
A = (qH)A = (qH)1/31/3
(NEH Part 628 Dams Ch 51 Eq 51-9)(NEH Part 628 Dams Ch 51 Eq 51-9)
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SURFACE DETACHMENTSURFACE DETACHMENT
.
rr = detachment rate = detachment rate
kkd d = coefficient of = coefficient of
detachmentdetachmentee = effective stress = effective stress
cc = critical tractive = critical tractive
stressstress
.
a = exponent (~ 1)a = exponent (~ 1)
rr = k = kdd ( (ee - - cc))aa
Effective Stress, e
c
00
Det
achm
ent R
ate,
r
kd
1
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• EFFECTIVE STRESS AT THE HEADCUT BASEEFFECTIVE STRESS AT THE HEADCUT BASE
e= dc 0.011(H/dc)0.582
H
dc
e
PHASE 3PHASE 3Headcut DeepeningHeadcut Deepening
H
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CRITICAL STRESS for
Detachment
Critical stress based on loose particle condition for all materials.
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DETACHMENT RATE COEFFICIENTDETACHMENT RATE COEFFICIENT
The detachment rate coefficient may be externally determined and entered directly in SITES or estimated by SITES from soil properties.
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SITESSITESAUXILIARY SPILLWAY EROSION: PHASE 3
DOWNCUTTINGDOWNCUTTING
eeddcc0.011 (H/d0.011 (H/dcc))0.5820.582
dd//ddt = kt = kdd((ee--cc))
HEADCUT ADVANCEHEADCUT ADVANCE
ddX/X/ddt = C (A - At = C (A - Aoo))
A = (qH)A = (qH)1/31/3
(NEH Part 628 Dams Ch 51 Eq 51-9)(NEH Part 628 Dams Ch 51 Eq 51-9)
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HEADCUT MIGRATION
dx/dt = C (A - Adx/dt = C (A - Aoo))dX/dt = rate of headcut
migration,
C = material dependent advance rate coefficient,
A = hydraulic attack, and
Ao = material-dependent threshold.
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HYDRAULIC ATTACK
q
H
A = (qH)1/3
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MATERIAL-DEPENDENTPARAMETERS
AAOO & C are a function of & C are a function of
KKhh = headcut erodibility = headcut erodibility
indexindex
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AAOO = =
189 K189 Khh1/21/2exp(-3.23/ln(101Kexp(-3.23/ln(101Khh))))[[ ]]1/31/3
00 KKhh< 0.01< 0.01
KKhh> 0.01> 0.01__
ANDAND
C =C =
- 0.79 ln(K- 0.79 ln(Khh) + 3.04 K) + 3.04 Khh< 18.2< 18.2
0.75 K0.75 Kh h > 18.2> 18.2__
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HEADCUT ERODIBILITYINDEX, Kh
KKhh= M= MSS x K x Kbb x K x Kdd x J x JSS
MMSS= material strength number= material strength number
of the earth material.of the earth material.KKbb= block or particle size.= block or particle size.
KKdd= discontinuity or inter-= discontinuity or inter-
particle bond shearparticle bond shear strength number.strength number.JJss= relative ground structure= relative ground structure
number.number.
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Kb
Kd
Condition of the Joints• Rough or smooth• Open or closed• Gap size• material in joints
Js
Block size
Orientationto the flow
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Kh = 0.01
DESCRIPTION: SM, very loose sand with little bonding
SITE: Buck and Doe Run 33, Missouri
COMMENT: Eroding material in spillway breach: deep deposit
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Kh = 0.17
DESCRIPTION: CL , stiff
SITE: Rush Creek 12R, Oklahoma
COMMENT: Eroding material in headcut face.
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Kh = 0.5
DESCRIPTION: Disintegrated shale
SITE: West Fork Point Remove 5, Arkansas
COMMENT: Eroding material in Gully Bank.
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Kh = 20
DESCRIPTION: Jointed Sandstone
SITE: West Fork Pint Remove 5, Arkansas
COMMENT: Material remaining below surface erosion some minor detachment by flow.
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Kh = 35000
DESCRIPTION: Massive rock (ryolite)
SITE: Painted Rock Dam, Arizona
COMMENT: Spillway outlet, negligible erosion.
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OBJECTIVES
• Phase 3
– Inputs and equations
– Relation of downcutting to headward advance
– Concept of multiple materials and weakest line of attack
– Concept of unraveling (implications of threshold-rate governing relations)
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SITES erosion material parameters include surface detachment coefficient kd and the headcut erodibility index Kh
kd
Kh = 20
DESCRIPTION: Jointed SandstoneSITE: West Fork Pint Remove 5, ArkansasCOMMENT: Material remaining below surface erosion some minor detachment by flow.
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dX/dt
d/dt
H
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OBJECTIVES
• Phase 3
– Inputs and equations
– Relation of downcutting to headward advance
– Concept of multiple materials and weakest line of attack
– Concept of unraveling (implications of threshold-rate governing relations)
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KKhh for MULTIPLE MATERIALS for MULTIPLE MATERIALS
hi
h2
h3 Kh3
Kh2
Kh1
htotal
Kh = exp { }hi ln( Kh )i
h1
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Auxiliary Spillway Profile ReachesAuxiliary Spillway Profile Reaches
1 2 3 4 5 6 7 8
INLET CREST EXIT
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Auxiliary Spillway Profile ReachesAuxiliary Spillway Profile Reaches
1 2 3 4 5 6 7 8
INLET CREST EXIT
Reaches from the crest to valley floor are considered in integrity analysis.
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SPILLWAY GEOLOGY
STATION
EL
EV
AT
ION
, ft
, ft
All materials in spillway to elevation of valley floor are described along a weakest path.
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ERODED PROFILEE
LE
VA
TIO
N
STATION, ft
, ft
The eroded profile plotted in output is a composite of all headcuts considered while evaluating breach potential.
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file: a:\claystr.bmp
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OBJECTIVES
• Phase 3
– Inputs and equations
– Relation of downcutting to headward advance
– Concept of multiple materials and weakest line of attack
– Concept of unraveling (implications of threshold-rate governing relations)