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SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

PART 2 – SITES EARTH SPILLWAY EVALUATION Earth Spillway Integrity Analysis iii. Phase 3 (Headcut Advance). SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008. SURFACE EROSION (Cover Destruction). 2. CONCENTRATED

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SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

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  1. PART 2 – SITES EARTH SPILLWAY • EVALUATION • Earth Spillway Integrity Analysis • iii. Phase 3 (Headcut Advance) SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

  2. SURFACE EROSION • (Cover Destruction) 2. CONCENTRATED FLOW EROSION 3 PHASE Spillway Erosion Model 3. HEADCUT ADVANCE

  3. HEADCUT ADVANCE

  4. 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)

  5. 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)

  6. DOWNCUTTING and HEADCUT ADVANCE dX/dt de/dt

  7. Parameters 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.

  8. SITES AUXILIARY SPILLWAY EROSION PHASE 3 INPUT PARAMETERS DOWNCUTTING • PARTICLE DIAMETER • DRY BULK DENSITY • PERCENT CLAY or • kd DETACHMENT COEFFICIENT HEADCUT ADVANCE • Kh HEADCUT ERODIBILITY INDEX

  9. SITES AUXILIARY SPILLWAY EROSION: PHASE 3 DOWNCUTTING de/dt = kd(te- tc) te = gdc0.011 (H/dc)0.582 HEADCUT ADVANCE dX/dt = C (A - Ao) A = (qH)1/3 (NEH Part 628 Dams Ch 51 Eq 51-9)

  10. SITES AUXILIARY SPILLWAY EROSION: PHASE 3 DOWNCUTTING de/dt = kd(te- tc) te = gdc0.011 (H/dc)0.582 HEADCUT ADVANCE dX/dt = C (A - Ao) A = (qH)1/3 (NEH Part 628 Dams Ch 51 Eq 51-9)

  11. kd 1 Detachment Rate, er tc 0 0 Effective Stress, te SURFACE DETACHMENT . r = kd (e - c)a . r = detachment rate kd = coefficient of detachment e = effective stress c = critical tractive stress a = exponent (~ 1)

  12. PHASE 3 Headcut Deepening • EFFECTIVE STRESS AT THE HEADCUT BASE • te= dc 0.011(H/dc)0.582 dc te  H H

  13. CRITICAL STRESS for Detachment Critical stress based on loose particle condition for all materials.

  14. DETACHMENT RATE COEFFICIENT The detachment rate coefficient may be externally determined and entered directly in SITES or estimated by SITES from soil properties.

  15. SITES AUXILIARY SPILLWAY EROSION: PHASE 3 DOWNCUTTING de/dt = kd(te- tc) te = gdc0.011 (H/dc)0.582 HEADCUT ADVANCE dX/dt = C (A - Ao) A = (qH)1/3 (NEH Part 628 Dams Ch 51 Eq 51-9)

  16. HEADCUT MIGRATION dx/dt = C (A - Ao) dX/dt = rate of headcut migration, C = material dependent advance rate coefficient, A = hydraulic attack, and Ao = material-dependent threshold.

  17. HYDRAULIC ATTACK A = (qH)1/3 q H

  18. MATERIAL-DEPENDENT PARAMETERS AO & C are a function of Kh = headcut erodibility index

  19. [ _ 189 Kh1/2exp(-3.23/ln(101Kh)) ]1/3 Kh> 0.01 AO = 0 Kh< 0.01 AND - 0.79 ln(Kh) + 3.04 Kh< 18.2 C = 0.75 Kh > 18.2 _

  20. HEADCUT ERODIBILITY INDEX, Kh Kh= MS x Kb x Kd x JS MS= material strength number of the earth material. Kb= block or particle size. Kd= discontinuity or inter- particle bond shear strength number. Js= relative ground structure number.

  21. Condition of the Joints • Rough or smooth • Open or closed • Gap size • material in joints Block size Kb Kd Orientation to the flow Js

  22. 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

  23. Kh = 0.17 DESCRIPTION: CL , stiff SITE: Rush Creek 12R, Oklahoma COMMENT: Eroding material in headcut face.

  24. Kh = 0.5 DESCRIPTION: Disintegrated shale SITE: West Fork Point Remove 5, Arkansas COMMENT: Eroding material in Gully Bank.

  25. Kh = 20 DESCRIPTION: Jointed Sandstone SITE: West Fork Pint Remove 5, Arkansas COMMENT: Material remaining below surface erosion some minor detachment by flow.

  26. Kh = 35000 DESCRIPTION: Massive rock (ryolite) SITE: Painted Rock Dam, Arizona COMMENT: Spillway outlet, negligible erosion.

  27. 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)

  28. kd SITES erosion material parameters include surface detachment coefficient kd and the headcut erodibility index Kh Kh = 20 DESCRIPTION: Jointed Sandstone SITE: West Fork Pint Remove 5, Arkansas COMMENT: Material remaining below surface erosion some minor detachment by flow.

  29. dX/dt H de/dt

  30. 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)

  31. Kh for MULTIPLE MATERIALS { } hi ln( Kh )i Kh = exp hi h1 Kh1 htotal h2 Kh2 h3 Kh3

  32. Auxiliary Spillway Profile Reaches 1 2 3 4 5 6 7 8 INLET CREST EXIT

  33. Auxiliary Spillway Profile Reaches Reaches from the crest to valley floor are considered in integrity analysis. 1 2 3 4 5 6 7 8 INLET CREST EXIT

  34. SPILLWAY GEOLOGY ELEVATION , ft All materials in spillway to elevation of valley floor are described along a weakest path. STATION , ft

  35. ERODED PROFILE , ft ELEVATION The eroded profile plotted in output is a composite of all headcuts considered while evaluating breach potential. STATION , ft

  36. file: a:\claystr.bmp

  37. 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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