2 rock scour hopkins

8/14/2019 2 Rock Scour Hopkins

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Scour of Rock at Bridge Piers

and Abutments

Scour of Rock at Bridge Piers

and Abutments

Tony L. Beckham

Former Research Geologist

Geotechnology Section

University of KentuckyTransportation Center

College of Engineering

Tommy C. HopkinsFormer Research Engineer

Program Manager

Geohazards 2009


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http://www.ktc.uky.edu/Reports/KTC_99_57_

SPR_157_94.pdf


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I 95 bridge collapse over Schoharie Creek

Amsterdam, New York--April 5, 1987

Focused national attendance on

bridge scour

Ten Fatalities


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I 95 bridge collapse -- Causes

Pier 3-- bearing on erodible soil.

Layers of gravel, sand and silt, interbeddedwith folded and tilted till.

High velocity floodwaters penetratedbearing stratum.


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Lessons Learned

Periodic Bridge inspections

Erosion protection measures

Selecting critical storm

Locating design footings deep

enough to avoid loss of support

Understanding the geology and

mechanical properties of bearingstratum

Importance of:


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. expansion of I 75 from 4 lanes to 6 lanes

in Fayette Co., Ky...

.What else motivatedthis study?

required new bridge over the Ky river..


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Place pier foundation

deep into bedrock to

avoid scour failure?

Limestone

Depth?

Place pier foundation

on or near top of rock

Depth?


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..Ky ---1100 miles of navigable streams--2ndonly to Alaska..

..and thousands of miles of smallstreams, or tributaries.


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Scourability of Rock? Guidelines?Scourability of Rock? Guidelines?

http://www.fhwa.dot.gov/engineering/hydraulics/

policymemo/rscour.cfm

Hardest of rocks can scour

No single index property generally

can be used to assess the potentialfor rock scour

FHWA MEMORANDUM HNG-31

July 19, 1991 (Last revised 11/22/2005)


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FHWA MEMORANDUM HNG-31 July 19,

1991 (Last revised 11/22/2005)

Scourability Potential, SpMethod

RQD < 50% Soil-like Scourable

> 50% Rock-like Sp Decreasing

Uc < 250 psi Soil-Like - Scourable

> 250 psi Rock-like - Sp Decreasing

Soundness: 12 % Na

18% Mg

SDI< 90 % Soil-Like -- Sourable

LA Abrasion Loss % < 40 Scourable

Threshold Loss rate < Sourable


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Scourability of Rock?Scourability of Rock?

Subsurface Investigation ID rock type/discontinuties/recovery

Geological FormationRock Type

Rock Quality Designation (RQD)

ASTM D6032-08

Unconfined Compression Test

Slake Durability Index Soundness

Abrasion

Observation of Past History and Performance


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OBJECTIVESOBJECTIVES

If necessary, recommend revisions in

design practices

Define the scope of the problem in KY

Observe the erosional nature of geological

rock units in KY at selected bridge sites

General Assessment of the need to locate

bridge foundations deep into bedrock

General Assessment of the need to locate

bridge foundations deep into bedrock

Examine the potential relationship between

rock scour and Rock Quality Designation(RQD)


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Geology and Soils in Kentucky

Sedimentary KY Geology

Limestone, dolostone, sandstone,

siltstone, shale (hard and clayey-like), coal

Soils in Kentucky are residual (90% clays

and silty clays)

Depth to bedrock is generally shallow ---

0 to 30 feet (Exception: Along major

streams and in far Western KY)


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Illinoisan

Ice Sheet

No glaciersadvanced

into KY

Ohio River

Kentucky

Ice Sheets

Pre-IllinoisanIllinoisan

Wisconsin


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KY

Older GlaciationsOlder Glaciations

Illinoisan


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Rock

Scour

2Billion

Ye

ars

Permian

Pennsylvanian

Mississipian

Older

Precam.

Devonian

Younger

Precam.

Cambrian Grand

Canyon

Or

dovician-500mil.?

Silurian425mil.?


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ROCK SCOUR HAZARD RATING

SYSTEM(Numerical rating system)

Identify locations where rock scour may bea hazard

provide a means of evaluating rock scour

establish a priority list for remediation

locate sites for detailed rock scour studies

S C di Sh t


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County: Geology Description:

Rt. #

Stream/River:

Bridge #

Date:

Photo #s

Proximity:

Low/None 3 Point assesment:

Far 9 notes:

Near 27

Adjacent 81

enetration, dp :

None 3 Point assesment:

Up to 2" 9 notes:

Up to 6" 27

> 6" 81

Depth, dc:

None 3 Point assesment:

Exposed Footer 9 notes:

Exposed to bottom of Footer 27

Footer Fully Exposed 81

ds: None 3 Point assesment:

Up to 2" 9 notes:

Up to 6" 27

> 6" 81

AADT: 400 3 Point assesment:

800 9 notes:

1,200 27

1,600 81

Total Score:Low: 0-125

ock Scour Category: Moderate: 126 - 300

High: 301 - 500

Comments:

Far

Low, or No Scour

Far From Footer

Near Footer

Adjacent to Footer

3 points

9 points

27 points

81 points

>3'

< 3'

100 points u nderfoter

Scour Coding Sheet

Exponential Scoring

3 9 27 81

Scour Proximity

dc (above footerbottom)

dp (penetrationunder footer)

ds (depth below

footer bottom)

AADT (average

annual dailytraffic)


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Scour

Scour

Coding

SheetLow, or No Scour

Far From Footer

Near Footer

Adjacent to Footer

3 points

9 points

27 points

81 points

>3'

< 3'

100 points underfoter

Rock Scour Proximity

Under Footer 100 points


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Apparently footerbottom is not exposed

Scour depth at the

bottom of footer


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Scour depth below

bottom of footer

Erosion penetration

under footer bottom


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http://www.fhwa.dot.gov/BRIDGE/mtguide.pdf

Preliminary visual ratings (A B and C) of 394


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Preliminary visual ratings (A,B, and C) of 394

bridges: 34 bridges high scour --- A or B

Detailed numerical rating high: 8 bridges


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First pass through by a consultant: 2 877 Bridges


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First pass through by a consultant: 2,877 Bridges

all Hwy districts

Another survey Hwy D-10 and D-12: 777 Bridges

Another 5400 bridges inspected: no ratings

received

Perspective Typical Bridges Viewed


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About 50 % of bridges surveyed initially

by UKTC were single span

Perspective-Typical Bridges Viewed

Over 8000 bridges & culverts in KY

92 % of KY roadways are 2-lane roads

Rock

SoilFillExposed footer

Exposed rock

streambed

Two Span


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Two-Span

Pier / Abutments on rock

Two-Span

Pier on Rock

Abutment on Pt-

bearing Piles

Three Span


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Three-Span

Piers on Rock

Abutments on

Pt-bearing Piles

Unstable Approach

Embankment withToe Erosion


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RQD Rock Quality Designation ExampleRQD Rock Quality Designation Example


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RQD Rock Quality Designation -- ExampleRQD Rock Quality Designation -- ExampleCore Run = 60 inches (152.4 cm)

Core Recovery (in) Modified Core Recovery (in)10 -------------------------- 10

1 < 4 in-------------------- 03 < 4 in-------------------- 0

5 ---------------------------- 5

6 ----------------------------- 6

4 ----------------------------- 4

2 < 4 in --------------------- 0

3 < 4 in --------------------- 04 ----------------------------- 4

7 ----------------------------- 7

4 ----------------------------- 449 in.

Core Recovered =49/60 = 82 %

40 in.RQD = 40/60 = 67 %


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RQD DescriptionRQD Description0 - 25 Very Poor

25 - 50 Poor

50 - 75 Fair

75 - 90 Good

90 100 Excellent

@ RQD = 67% --- Fair

Lawrence County


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Lawrence CountyKY 707 Long Branch Creek

Shale highly

weatheredwith 1" - 3"sltstone layers

RQD

5

0

0

Scour Rating = 401

10

0 Shale highly weatheredwith siltstone layers

5 Ft. Penetration Scour3 Ft. Scour Below Footer

Constructed 1930 - 1933?

Conemaugh Shale

and Siltstone

Bridge # 64-B00035

Depth (ft.) ..FewExamples.


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ds = 36

Age=70yrs

RQD = 0

dp=60

Bath County


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Bath CountyUS 60 Hurricane Creek

Limestone withnumerous clay shale

seams

0

65

RQD0

7.5

Depth

Scour Rating = 458

Bridge Replaced in 1996

1.5

Limestone, weathered with

clay shale seams

2 Ft. Penetration Scour Below Footer

Constructed 1925

Bridge # 6-B00023


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Age = 75 yrs

ds = 24

dp=24

RQD = 0

Washington County


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Washington CountyCR 1243 Road Run Branch

Scour Rating = 327

0.0'-

5.0'Limestone,grey,

coarse grained, 2 - 4 incheslayers with clay shaleseams 2 -

4 inches

Constructed 1935

7

RQD

0

Depth

5.0

Lower Member

of Grant Lake Limestone

Bridge # 115-C00026

1 Ft. Vertical Scour,

3 Ft. Penetration

Scour at Pier

Washington Co. CR


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Age=65yrs

RQD = 7

ds=12

Washington Co. CR

1243

dp

=36

Harrison County


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Harrison County

CR 1006 Mouth of Cedar Creek

Scour Rating = 403

0.0'-

5.0'Limestone,grey,

coarse grained, 2 -

4 inches

layers with clay shaleseams 2 -

6 inches

Constructed 1981

17

RQD

0

Depth

5.0

Tanglewood Member

of Lexington Limestone

Bridge # 49-C00006


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ds=12

Age = 19 yrs

dp

=12

RQD = 17

Jessamine County


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Jessamine CountyElm Fork Road Hickman Creek

Limestone with

numerous clay shalepartings

17

25

RQD0

10

Depth

5

Scour Rating = 377

0.5 Feet Scour below Abutment Footer2 Ft. Penetration Scour

Built 1987?

Deck Only 1987?

Lexington Limestone

Bridge # 57-C00029NewDeck


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ds = 6

RQD = 17

dp =24

Ag

e>60

yrs?

Cumberland County


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Cumberland CountyKY 704 Pine Branch

Leipers Limestone

Limestone with clay

shale seams @ 0.2, 0.4,

0.7, 1.0, 1.1, 1.5 - 1.7,2.0,2.2, 2.6, 2.7, 3.9,and

4.4 ft.

Scour Rating = 3072 Ft. Penetration Scour

> 0.5 Ft. Scour below Footer

Constructed 1987?

Deck Only?

Bridge # 29-B00055

22

RQD

1.5

6.5

Depth

0

67

NewDeck


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ds = 8-10

Age = 77 yrs

dp =

24RQD = 22


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Owen Co


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Age=22yr

s

RQD = 44

Owen Co.

Ky 607

dp= ds = 0 ?

Adair County


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y

KY 704 Burns Creek

63

RQD

5

10

Depth

0

50

Bridge # 1-B00028

Scour Rating = 106Small (1 in.) Penetration Scour at

Corner of Pier Footer2 in. Scour Below Footer

Constructed 1952

Chattanooga Shale

Black Shale with

fractures @ 1.9, 3.1,

3.5, 5.0, 5.7, 6.2, 6.6,

7.0,7.3, 8.7, and 9.0 ft.

Mud seams @ 3.2,

5.1, and 9.2 ft.

Pyrite 1.9 - 3.1,

and 4.9 ft.


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dp = 1

Age=

48yrs

ds = 2

RQD = 63-50

Bullitt County


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yUS 31E Hough Run Creek

1.0 - 5.0 Limestonewith clay shale

seams@

2.0,2.2,3.2,3.3,4.0

67

RQD

0

Depth

Scour Rating = 365

Route being reconstructed in 1996, 1997

0-1.0 Limestone, weathered

with clay shale seams

1 Ft. Vertical Scour at Pier

Constructed 1924

5.0 4.7-4.8 Grey Clay shale4.8-5.0Grey Limestone

Bridge # 15-B00007

Age=76yrs

RQD = 67


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ds = 12

Age=76yrs

RQD = 67

Age = 62 yrs


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JacksonCo.

Age=62yrs

RockScour


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Ds= dc = 14

RQD = 68


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0

100

200

300400

500

0 20 40 60 80 1

ScourScore,Ss

RQD

Ss = 422 -

4.9(RQD) +0.0277(RQD)2

d = 20 46 (2 94) Ln(RQD)


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0

10

20

30

40

0 10 20 30 40 50 60 70 80 90 100

ds

= 20.46 (2.94) Ln(RQD)0.01

RQD

92

Depth

ofRoc

kScour

,d

s

RQD

FHWAKY*

KY* Modified RQD 4-in pieces not included if itcan be broken by hand


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dp= 53.855e-0.069RQD

R2= 0.61

010

20

3040

50

60

70

0 20 40 60 80 100

Rock Quality Designation (RQD) %

Penetra

tionSco

ur,dp(in

.)

CONCLUSIONSCONCLUSIONS


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Hundreds of bridge foundations are locatedon exposed rock in KY

Very Approximate relationships betweenRQD and rock scour depth and horizontal

penetration were obtained

Very Approximate relationships betweenRQD and rock scour depth and horizontal

penetration were obtained

FHWA guidelineRQDappears reasonable

CONCLUSIONS


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Generally, rock scour around bridge piers

and abutment footings is not a serious

problem in KY

Current practices concerning locating depths

of footers in bedrock appear sound following

current guidelines of the KTC and FHWA

Periodic inspections of all KY bridges andtheir foundations should continue

2 rock scour hopkins

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