Concrete Blocks - Association of State Dam Safety Officials

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Concrete Blocks - Association of State Dam Safety Officials

ACBs –vs- Riprap


Angle of Repose


Major Differences

• Angle of repose

–Rock ~ 40 o

– ACBs ~ 80+ o


ACBs vs Riprap

42

40

Class 85L

42

40

38

38

36

36

34

34

32

32

30

30

28

28

Shear Stress (psf)

26

24

22

20

18

Class 40

L Series

26

24

22

20

18

Velocity (ft/sec)

16

16

14

12

Class 30S

14

12

10

10

8

8

6

6

4

4

2

2

0 2 4 6 8 10 12 14 16 18 20 22 24

Rock Size (ft)


Angle of Repose

Comparison of angle of repose

V=14, d=5

Rock size (ft)

4

3.5

3

2.5

2

1.5

1

0.5

0

Riprap

ACB

0 5 10 15 20 25 30 35 40

Side slope in degrees


Major Differences

• Angle of repose

–Rock ~ 40 o

– ACBs ~ 80+ o

• Range of sizes tested

– Rock – 2 to 12 inch

– ACBs – prototype


Major Differences

• Angle of repose

–Rock ~ 40 o

– ACBs ~ 80+ o

• Range of sizes tested

– Rock – 2 to 12 inch

– ACBs – prototype

• Effect of particle shape

– Inter-particle friction


Inter-Particle Friction


ACBs

Critical Shear Stress (psf)

60.0

50.0

40.0

30.0

20.0

10.0

0.0

0 50 100 150 200 250

Average Unit Weight (lbs)


ACBs

Critical Shear Stress (psf)

60.0

50.0

40.0

30.0

20.0

10.0

0.0

0 20 40 60 80 100

Average System Weight (psf)


ACBs

55

50

85L

Critical Shear Stress (psf)

45

40

35

30

25

20

15

10

30S

40L

40T

45L 50L

45

50T

50S

45S

55L

55

60T

55S

70L

75

70T

85

5

0

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Average System Weight (psf)

Tapered S - Open S - Closed Regular - Closed L - Open L - Closed


ACBs

Critical Shear Stress (psf)

55

50

L- Series

45

40

35

30

S- Series

25

Tapered

20

15

10

5

0

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Average System Weight (psf)

Tapered S - Open S - Closed Regular - Closed L - Open L - Closed


Articulating Concrete

Blocks


ACB Testing Program

• CIRIA 1987

– “Design of Reinforced Grass Waterways

• FHWA 1988

– “Minimize Embankment Damage During Overtopping Flow”

• FHWA 1989

– “Hydraulic Stability of Articulated Concrete Block

Revetment Systems During Overtopping Flow”

• St. Anthony Falls Lab, University of Minnesota 1995-2000

– Over 10 systems tested

• Colorado State University 1992-2012

– Over 65 systems tested

• Colorado Sate University 2007-Present

– Comprehensive analysis


Colorado State University

Engineering Research Center


Assessing Hydraulic Stability

• ASTM D7277 (2008)

State-of-the-practice

for full-scale hydraulic

performance testing of

ACB systems

– Full-scale hydraulic

testing data

• Measured discharge

• Bed elevation along at

given stations

• Water surface elevation

at given stations


Hydraulic Conditions During Embankment Overtopping

Subcritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Constant Velocity &

Depth

Subcritical Flow

Turbulent Flow

Potential Subatmospheric Zone

Reservoir

Critical Depth

Theoretical Nappe

Profile

Hydraulic Jump

on Slope

Normal Depth

Hydraulic Jump

At Toe of Slope

Tailwater

Embankment


System Installation


Finished Embankment


Prototype Flume Tests


Post Test Embankment Inspection


Loss of Intimate Contact


Inspect for Subgrade Damage


Gully Formation?!


Hydraulic Conditions During Embankment Overtopping

Subcritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Constant Velocity &

Depth

Subcritical Flow

Turbulent Flow

Potential Subatmospheric Zone

Reservoir

Critical Depth

Theoretical Nappe

Profile

Hydraulic Jump

on Slope

Normal Depth

Hydraulic Jump

At Toe of Slope

Tailwater

Embankment


Quantifying Performance Thresholds

Embankment Plot

First Hour Data

• ASTM D7276 (2008)

State-of-the-practice

for hydraulic analysis

and system stability

analysis of articulating

concrete block systems

– Water surface profile

(WSP) idealized to

compute shear stress

for non gradually

varied flow conditions

Elevation (ft)

104.00

102.00

100.00

98.00

96.00

94.00

92.00

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00

Station (ft)

Channel Lock 3 ' Test

106

104

102

100

98

96

94

Bed El

EGL

WSE

Meas. Bed

Pr ed. WSEL

Pr ed. EGL

Hour 1

Hour 2

Hour 3

Hour 4

92

90

0 5 10 15 20 25 30 35 40 45

St at i on ( f t )


Post Test Data Analysis

Flow Depth Calibration

2.40

2.20

2.00

Elevation (ft)

1.80

1.60

1.40

1.20

1.00

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00

Station (ft)

Model Flow Depths

Measured Flow Depts


Post Test Data Analysis

Channel Lock 3 ' Test

106

104

102

100

98

96

Meas. Bed

Pr ed. WSEL

Pr ed. EGL

Hour 1

Hour 2

Hour 3

Hour 4

94

92

90

0 5 10 15 20 25 30 35 40 45

Stati on (f t)


Momentum Analysis


F x

∆(ρqV)

Unit discharge q

Sta.1

P 1

P 2

d 1 , V 1

d 2 , V 2

L

0

Wsin

Sta.2

Wcos

W

Angle

X - axis

0 = ½((d1+d2)sin + (1/L){ (½)d 1 2 - d 2 2 )cos - q 2 (1/d 2 – 1/d 1 ) }


Momentum Analysis


Test Results

20

18

Shear stress or velocity

16

14

12

10

8

6

4

Velocity, ft/s

Shear stress, lb/ft 2

Maximum

Velocity 19.3 ft/s

Maximum Shear

Stress 11.9 lb/ft 2

2

0

0 10 20 30 40 50 60

Station (ft)


DESIGN

METHODOLOGY

• Riprap and accepted erosion control methods

– Utilize both analytical and empirical relationships

– Both based on concept of critical values

• ACB Systems

– Quantify hydraulics

– Performance thresholds defined through testing

– Design techniques developed for application


Safety Factor Method

Based on considering the forces on a particle on a channel bed sloping at

an angle, , with the moment arms about the point of rotation, PR.


Discrete Particle

FM FM Wsin

M Wcos

M

L

Wcos

F L

M 4

F d

3

Wsin

M 2

W

M 1

PR

4 d 3 2 1


Safety Factor Method

F L

FLOW

l F'

4

L

F F' D

D

W S1

W S2

l 1

l 2

l 3

F R

Pivot Point

of Rotation

Overturning Forces

F D

& F L

= Drag & lift force

F' D

& F' L

= Additional drag & lift force

from block protruding above ACB matrix

Restraining Forces

F R

= Inter-block restraint

W S2

= Gravitiy force normal to slope

W S1

= Gravitiy force parallel to slope

Figure 1. Moment balance on an ACB at incipient failure


Safety Factor Method

Top of Bank

W s

a

W s

sin 1

W s

1

Bed of Channel

A. Channel cross section view

Figure 2. Three-dimensional view of a block on a channel side slope

with factor of safety variables defined


Safety Factor Method

A

Horisontal

Streamline

A'

0

d

F D WS sin 1

Block Projection

Once in

Motion

b


W S

sin 0

Toe of Slope

0

Vertical

B. View normal to plane of channel bank - original

Figure 2. Three-dimensional view of a block on a channel side slope

with factor of safety variables defined


SF and free body diagrams

currently utilized for:

•Block design

• Thickness extrapolations

• Slope adjustments

• Projection height analysis


Hydraulic Conditions During Embankment Overtopping

Subcritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Increasing Velocity &

Decreasing Depth

Supercritical Flow

Constant Velocity &

Depth

Subcritical Flow

Turbulent Flow

Potential Subatmospheric Zone

Reservoir

Critical Depth

Theoretical Nappe

Profile

Hydraulic Jump

on Slope

Normal Depth

Hydraulic Jump

At Toe of Slope

Tailwater

Embankment


Manufacturer’s Disclaimer:

“The success or failure of any

engineering design is the

responsibility of the engineer of

record and not that of the

manufacturer of the revetment

system, its agents or

representatives.”


ASTM Standards for ACBs

• Hydraulic Modeling of ACBs

• Design of ACB Systems

• Manufacture of ACBs

• Installation of ACB Systems


1/2 Inch

FLOW


FLOW

1/2 Inch


ACB mats should abut each other & fastened …


Zippering UltraFlex Mats


Inadequate Spillway Capacity

~40% PMF ….

Shavers Creek Dam, PA


Approved ACB Systems:

Armorflex 50-T (Open Cell)

Petraflex H-916 (Open Cell)


50’

Existing Embankment Section


Drain Reservoir


Topsoil & Seed

Install ACBs

Install Drain Material (OGS)

Resurface Top of Dam

Concrete Cutoff Wall

Flatten Downstream Slope

Strip Downstream Face of Dam

Install Filter/Drain

Material


Flow

Detail At Top of Dam


Detail At Toe of Dam


Finished Grading, ACBs

Shavers Creek Dam

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