observation method: a new tool for the bridge scour …€¦ · scour depths 2. tamu-oms eliminates...

Jean-Louis BRIAUD

Distinguished Professor

Texas A&M University

and President of FedIGS

OBSERVATION METHOD: A NEW TOOL FOR THE BRIDGE

SCOUR ENGINEER

2Jean-Louis BRIAUD

Acknowledgements

• Texas DOT (John Delphia)

• Massachusetts DOT (Rich Murphy)

• Dr. Chen, Dr. Oliveira

• Anand Govindasamy, Dekay Kim, Inwoo Jung

SCOUR DEPTHS

Normal Water Level

LC

z(abut)

z(abut) Applies z(cont) Applies

Probable Flood Level

z(pier) z(cont)

4

0

100

200

300

400

500

600

700

800

900

1000

Co

ns

tru

cti

on

Co

nc

rete

De

teri

ora

tio

n

Ea

rth

qu

ak

e

Na

tura

l

Ste

el

Fir

e

Mis

c.

Ov

erl

oa

d

Co

llis

ion

Hy

dra

uli

c

Cause

Nu

mb

er

of

Failu

res f

rom

1966 t

o 2

005 (

1502 T

ota

l)

0%

10%

20%

30%

40%

50%

60%

Perc

en

t

SCOUR = NO.1 KILLER OF BRIDGES

1 BRIDGE FAILS EVERY 10 DAYS

5Jean-Louis BRIAUD

6Courtesy of the University of Kentucky at Louisville

13

IT IS GETTING BETTER

0

20

40

60

80

100

120

140

160

1966 -

1970

1971 -

1975

1976 -

1980

1981 -

1985

1986 -

1990

1991 -

1995

1996 -

2000

2001 -

2005

Year

Nu

mb

er

of

Sco

ur

Failu

res

fro

m 1

966 t

o 2

005 (

878 T

ota

l)

0%

5%

10%

15%

Perc

en

t

RESEARCH PAYS OFF

PROBLEM

1. Comparison between measured and calculated scour depths by current method exhibits a lot of scatter

2. Comparison between measured and calculated scour depths by current method shows excessive conservatism on the average

HEC-18 RESULTS

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Pre

dic

ted

max

. ab

utm

en

t sco

ur

de

pth

(m

)

Measurement (m)

Q100

Historic data

MEASURED ABUTMENT SCOUR DEPTH (m)

PR

ED

ICT

ED

MA

X. A

BU

TM

EN

T

SC

OU

R D

EP

TH

(m

)

BENEDICT DATABASEABUTMENT SCOUR

HEC-18 RESULTS

0 2 4 6 8 100

2

4

6

8

10

Measured Landers-Mueller Pier Scour, zmax

(m)

Dete

rmin

istic

HE

C-1

8 S

and, z

ma

x (m

)

Zpredicted/Zmeasured = 3.26

LANDERS-MUELLER DATABASEPIER SCOUR

17Jean-Louis BRIAUD

OMS-TEXAS & MASSACHUSETTS

y = 1.0669xR² = 0.8612

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0.00 1.00 2.00 3.00 4.00

Zp

re

dic

ted

(O

MS

)(m

)

Zmeasured (m)

0188-02-023

0072-04-020

170-0177-05-119

0382-05-021

B13001-1EA

B28032-0JC

D06002-0U4

B28009-0JD

D10005-367

D12026-1XX

E01001-41Q

Linear (Regression)

J.-L. Briaud, Texas A&M University

Jean-Louis Briaud – Texas A&M University

EFA - EROSION FUNCTION APPARATUS

Jean-Louis BRIAUD – Texas A&M University

POCKET ERODOMETERPET test result = Depth of hole in mm after 20 squirts at 8 m/s

22

$0.49 at

WalMart

Jean-Louis BRIAUD – Texas A&M University

23

EROSION CLASSIFICATION

0.1

1

10

100

1000

10000

100000

0.1 1.0 10.0 100.0

Velocity (m/s)

Very High

Erodibility

I

High

Erodibility

II

Medium

Erodibility

IIILow

Erodibility

IV

Very Low

Erodibility

V

Erosion

Rate

(mm/hr)

-Fine Sand

-Non-plastic Silt -Medium Sand

-Low Plasticity Silt -Fine Gravel

-Coarse Sand

-High Plasticity Silt

-Low Plasticity Clay

-All fissured

Clays-Cobbles

-Coarse Gravel

-High Plasticity Clay

-Riprap

- Increase in Compaction

(well graded soils)

- Increase in Density

- Increase in Water Salinity

(clay)

Non-Erosive

VI-Intact Rock

-Jointed Rock

(Spacing < 30 mm)

-Jointed Rock

(30-150 mm Spacing)

-Jointed Rock

(150-1500 mm Spacing)

-Jointed Rock

(Spacing > 1500 mm)

SPSM CL

CHML MHRock

0.0001 0.001 0.01 0.1 1 10 100 1000 100000.01

0.1

1

10

100

1000

CRITICAL

VELOCITY,

Vc (m/s.)

MEAN GRAIN SIZE, D50 (mm) JOINT SPACING FOR

JOINTED ROCK

Vc=0.1(D50)-0.2

Vc=0.35(D50)0.45

Vc=0.03(D50)-1

US ARMY CORPS OF

ENGINEERS EM 1601

INTACT

ROCK CLAY SILT SAND GRAVELRIP-RAP &

JOINTED ROCK

28Jean-Louis BRIAUD

OBSERVATION METHOD FOR SCOUR

• Developed at Texas A&M University for

TxDOT

• Because of experience with calculating

scour depths that seemed unreasonably

large compared to observations by

inspectors in the field

29Jean-Louis BRIAUD

OBSERVATION METHOD FOR BRIDGE SCOUR

• Step 1: Observe maximum scour depth = Zmo

• Step 2: Find out the maximum flood the bridge

has been subjected to : Collect gage data, RI

from TAMU-OMS, Qmo/Q100, Vmo/V100

• Step 3: Extrapolate field measurements to

predict future scour depth

Zfut / Zmo = F (Vfut / Vmo)

• Step 4: Compare future scour depth to

foundation depth (pier) Zfut < Zfound / 2

30Jean-Louis BRIAUD

Step 1: Observe maximum scour depth = Zmo

31Jean-Louis BRIAUD

Step 2: Find out the maximum flood the bridge

has been subjected to = Vmo

930 Flow Gages in Texas

32Jean-Louis BRIAUD



Maximum flood analysis

33Jean-Louis BRIAUD



Maximum

RI map

between

1970 and

2005

Automated

with TAMU-

FLOOD

software

34Jean-Louis BRIAUD



Maximum

RI map

between

1920 and

2005

Automated

with TAMU-

FLOOD

software

35Jean-Louis BRIAUD

GETTING QMO/QFUT FROM RIMO/RIFUT

36Jean-Louis BRIAUD

GETTING VMO/VFUT FROM QMO/QFUT

Wide channel = 0.4

Narrow channel = 0.25

Most likely value = 0.35

37Jean-Louis BRIAUD

GETTING THE VELOCITY RATIO

FROM THE RECURENCE INTERVAL RATIO

0.350.35 0.261 0.091

100 100 100 100

v Q RI RI

v Q RI RI

38Jean-Louis BRIAUD

EVALUATING TAMU-FLOOD PRECISION

1

2

3

45

FLOW GAGE

39Jean-Louis BRIAUD

PRECISION OF TAMU-FLOOD

40Jean-Louis BRIAUD

Step 3: Extrapolates field measurements to

predict future depth


•Known = Zmo and Vmo

•Choose Vfut

•Obtain Zfut from charts

41Jean-Louis BRIAUD


predict future depth Zfut

The Z-Future Charts were developed by performing a large number (~350,000) of HEC-18 Clay simulations using

−Varying pier, contraction & Abutment scour geometry−Varying soil conditions−Varying velocities−Varying age of the bridge


42Jean-Louis BRIAUD

Category III Materials

Upstream Water Depth (H1): 5 m to 20 m

Contraction Ratio (Rc) : 0.5 to 0.9

Critical Velocity (Vc) : 0.5 m/s

Pier Diameter (D) : 0.1m to 1.0 m

thyd = 25 years

Vfut/Vmo

2.00

Zfu

t/Zm

o

2.8

1.0


predict future scour depth Zfut/Zmo = Vfut/Vmo

43Jean-Louis BRIAUD


predict future scour depth Zfut/Zmo = F(Vfut/Vmo)

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

2.1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Zfu

t/Zm

o

Vfut/Vmo

Zfuture Chart-CategoryIII-Abutment

Vmo=1.5*VcVc=0.781Vratio:0 to 1.5Vfut= Vmo*VratioMnning Co: 0.035Slope=0.001thyd=25yrs

Vmo=2.0*Vc

Vmo=2.5*Vc

44Jean-Louis BRIAUD

Step 4: Compare future scour depth to

foundation depth Zfut < Zfound / 2

45Jean-Louis BRIAUD

OMS-TEXAS & MASSACHUSETTS

y = 1.0669xR² = 0.8612

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0.00 1.00 2.00 3.00 4.00

Zp

re

dic

ted

(O

MS

)(m

)

Zmeasured (m)

0188-02-023

0072-04-020

170-0177-05-119

0382-05-021

B13001-1EA

B28032-0JC

D06002-0U4

B28009-0JD

D10005-367

D12026-1XX

E01001-41Q

Linear (Regression)

46Jean-Louis BRIAUD

Limitations

• Requires a good network of flow gages (and

rain gages). Interpolation could be refined

• Cannot be used directly for new bridges but

lessons learned (database) can be useful for

new bridges

• Estimate in filling (USGS research and a

TxDOT survey have found that it was rare

(10% of the time) and ranged from 2 to 4 ft)

• Not yet developed for layered soil (be careful

with thin hard layer over soft layer)

47Jean-Louis BRIAUD

Advantages

• Valuable tool to prioritize bridge repairs,

countermeasure decisions, asset

management

• Can serve as an input to FHWA risk

approach

• Part of the practical design concept

• No need for erosion testing

• Actual soil

• Actual flow history

• Actual geometry

• Based on observed measurements

48

COMPARISON

HEC 18 OMS

49

DIFFERENCES BETWEEN HEC 18

AND OBSERVATION METHOD

HEC 18

• Flume tests (scale pb?)

• Wrong worst soil (Fine

sand)

• Simplified geometry

• Simplified single

velocity

OMS

• Full scale

• Right soil

• Exact geometry

• Exact velocity

hydrograph

50Jean-Louis BRIAUD

CITY: SHEFFIELD HIGHWAY: MAPLE AVE RIVER: WATER HOUSATONIC RIVER

OMS RISK RATING = LOW

51Jean-Louis BRIAUD

CITY: DEERFIELD HIGHWAY: US 5 RIVER: WATER DEERFIELD RIVER

OMS RISK RATING = MEDIUM

52Jean-Louis BRIAUD

CITY: BUCKLAND HIGHWAY: STATE ROUTE 2 RIVER: DEERFIELD RIVER

OMS RISK RATING = MEDIUM

53Jean-Louis BRIAUD

CITY: BUCKLAND HIGHWAY: STATE ROUTE 2 RIVER: DEERFIELD RIVER

OMS RISK RATING = HIGH

54

1. TAMU-OMS significantly decreases the scatter between measured and calculated scour depths

2. TAMU-OMS eliminates the excessive conservatism

3. TAMU-OMS is a valuable new tool for the bridge scour engineer (e.g.: can be used to prioritize repairs, to evaluate risk, as a management tool, for practical design)

4. TAMU-OMS is available for all states in the country

observation method: a new tool for the bridge scour …€¦ · scour depths 2. tamu-oms eliminates...

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