initial results in the determination of geotechnical scour numbers … · 2012-08-03 · modified...

INITIAL RESULTS IN THE DETERMINATION OF GEOTECHNICAL SCOUR NUMBERS FOR

FOUNDATION ROCK AT FIFTEEN WEST VIRGINIA BRIDGE SITES

William L. Niemann, Ph.D., P.G., E.I.T.

Marshall University Geology Dept.

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM (NCHRP) PROJECT 24-29 / REPORT 717:

“SCOUR AT BRIDGE FOUNDATIONS ON ROCK” (http://www.trb.org/Main/Blurbs/167222.aspx)

KEATON, MISHRA & CLOPPER (2012)

Context of Report: 1) Current methodology for scour prediction is inexact--considers rock as either erodible or non-erodible.

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM (NCHRP) REPORT 717: “SCOUR AT

BRIDGE FOUNDATIONS ON ROCK” (2012)

Context (cont.): 2) If rock is deemed erodible, scour prediction is typically based on behavior of sand, resulting in

overestimates of scour and unnecessarily expensive bridge designs.

3) Criteria for bridge design should better reflect realistic response of erodible rock to hydraulic forces. 4) Methodology required for estimating scour along with corresponding design and construction guidelines.

WEST VIRGINIA DEPARTMENT OF HIGHWAYS (WVDOH) RESEARCH PROJECT 273:

“CRITERIA FOR PREDICTIONG ERODIBLE ROCK IN WEST VIRGINIA”

• MICHAEL PUMPHREY (PC),

WVDOH RESEARCH AND SPECIAL STUDIES

• JOE CARTE (PM) & DOUG KIRK (PM), WVDOH

• BILL NIEMANN (PI) & ISAAC WAIT (PI), MARSHALL UNIVERSITY

• WAEL ZATAR (PI)

RAHALL TRANSPORTATION INSTITUTE

• TERRY DOWNS, BRAIN GREENE, GANNETT FLEMING, INC..

• JEFF KEATON, AMEC, INC.



1) Apply methodology from NCHRP 24-29 to bridge sites in West Virginia where scour has occurred and can be quantified. 2) Select sites from all 10 WVDOH districts and across a range in rock types and stream flow conditions. 3) Develop models that can more accurately predict rock scour under conditions typically found in West Virginia.



Deliverables (2013): 1) Summary of research including investigation and data analysis. 2) Map of scour-able areas in state. 3) Best management practices (BMP) to account for rock scour in bridge design and evaluation.

MODES OF SCOUR

• Cavitation

• Solution

• Quarrying / plucking (“dislodgement”) *

• Erosion / flaking * *

* NCHRP 24-29: developed methodology for

estimating depth of scour.

** NCHRP 24-29: developed methodology for estimating depth and rate of scour.

SITE SELECTION CRITERIA

• Geographic distribution

• Exposed rock

• Variety of rock types / rock structure

• Measurable scour

• Initial assessment of scour mode

• Availability of hydraulic / hydrologic data

• Drill-rig accessible

USGS, Prof Pap. 1110A-1110-L

10 of 15 sites

11

4

1

0

2

4

6

8

10

12

Sandstone Mudrocks Carbonate

No.

of B

ridge

s

Axis Title

Dominant Rock Types

1 2

5

2 3

2

0123456

No.

of B

ridge

s Presumed Modes of Scour

DRILLING AND SAMPLING

Bridge Plan View

Deck

Left Abutment

Right Abutment Flow

Flow

Boring 1

Boring 2


Bridge Cross-sectional View

Deck

Abutment Fill / Soil

Rock

Borehole extended 10 feet below

abutment

Scoured interval

Water level (variable)


• 15 bridges

• 10 districts

• 15 counties

• 17 days

• 694 feet of drilling

• 30 rock cores

• 391 feet of rock coring

• 45 samples for Modified Slake Durability (MSD)

ROARING CREEK BRIDGE Pendleton Co., WV • Sandstone: massive, hard, jointed • Pocono Group (Mississippian age) • Mode of scour: dislodgement

ROARING CREEK BRIDGE Pendleton Co., WV

COON CREEK BRIDGE Summers Co., WV • Sandstone: weathered, vuggy, poorly cemented • Princeton Formation (Mississippian age) • Mode of scour: erosion / flaking

COON CREEK BRIDGE Summers Co., WV

Process for estimating depth and

time rate of scour for bridges

affected by erosion / flaking

of foundation rock*

*no gage or historical cross-section data

MODIFIED SLAKE DURABILITY (MSD) TESTING


• Conventional slake durability tests (ASTM D4644) consist of two cycles of 10-minutes each and mass

is determined in a dry state.

• Modified slake durability tests consist of multiple cycles (5-9) of 60-minutes each

and mass is determined in a saturated-surface dry (SSD) state per ASTM.


R² = 0.9595

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 50 100 150 200 250 300 350 400 450 500

Wei

ght L

oss

(%)

Time (min)

Example test data

GEOTECHNICAL SCOUR NUMBERS • Stream Power: rate at which hydraulic energy is

expended

ω = Unit stream power [L*force/T/L2] = [force/T/L]

γ = specific weight of water [force/L3]

d = depth [L]

S = slope of the channel [L/L]

V = velocity of water flow [L/T]

GEOTECHNICAL SCOUR NUMBERS • Equivalent Stream Power from MSD:

ω = L * t [ W(X) + W(X+1) ] / [2 * A(1/8) ]

ω = equivalent stream power (force/L*T),

L = equivalent length (L),

t = incremental time of test interval (T),

[ W(X) + W(X+1) ] / 2 = average weight of sample during

test interval (force),

A(1/8) = fractional surface area of drum occupied by sample (L2).

GEOTECHNICAL SCOUR NUMBERS • Equivalent Depth of Scour (from MSD)

Hourly measurements result in a series of sample volume

losses, Vi , which are then normalized by a unit area to derive a depth of scour for each interval:

D(X) = Vi (X) / unit area

D(X) = depth of scour corresponding to test interval

x (= 60, 120, 180…) minutes (L),

Vi (X) = incremental volume lost during test interval x minutes (L3),

unit area = area in appropriate units (L2).

GEOTECHNICAL SCOUR NUMBERS

NCHRP 24-29

y = 2.42E-04x - 1.75E-03 R² = 7.95E-01

y = 1.38E-04x - 1.15E-03 R² = 5.43E-01

y = 1.00E-04x - 7.83E-04 R² = 8.87E-01

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

7.0E-04

6.0 6.5 7.0 7.5 8.0 8.5 9.0

Eq. S

cour

Dep

th (f

t)

Eq. Stream Power (ft-lb/s//ft2)

Roaring Creek

ROA-SEXP-01-01

ROA-01-11.2'-11.9'

ROA-02-11.2'-11.6'

Linear (ROA-SEXP-01-01)Linear (ROA-01-11.2'-11.9')Linear (ROA-02-11.2'-11.6')

presumed mode of scour:

dislodgement

Sandstone: massive, hard, jointed

y = 2.34E-04x - 1.69E-03 R² = 7.95E-01

y = 5.32E-04x - 4.66E-03 R² = 8.82E-01

y = 5.68E-04x - 4.84E-03 R² = 9.65E-01

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

7.0E-04

6.0 6.5 7.0 7.5 8.0 8.5 9.0

Eq. S

cour

Dep

th (f

t)

Eq.Stream Power (ft-lb/s//ft2)

Coon Creek

COO-SEXP-01-01

COO-01,9.7'-10.2'

COO-02,7.4'-8.0'

Linear (COO-SEXP-Linear)

Linear (COO-01,9.7'-10.2')

Linear (COO-02,7.4'-8.0')


erosion / flaking

Sandstone: weathered, poorly cemented, vuggy

NCHRP 24-29

y = 1.0E-03x

y = 1.0E-04x

y = 1E-05x

y = 3.0E-04x

y = 2.00E-04x

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

0 1 2 3 4 5 6 7 8 9 10

Eq. S

cour

Dep

th (f

t)

Eq. Stream Power ( ft-lbs / s / ft2 )

WVDOT -- GEOTECHNICAL SCOUR NUMBERS

Paden Fork SsCoon Creek SsRoaring Creek SsLaurel SsBridge Fork SsCucumber SsGrassy Run SsBeverly Siltst/Sh/ClaystLaurel X Sh (carb.)Caldwell Run Sh / CoalMish Ls

NCHRP 24-29

NCHRP 24-29

Non

-dur

able

rock

s –

sc

our b

y er

osio

n / f

laki

ng

THE NEXT PHASE: INTEGRATING LAB AND FIELD DATA

NCHRP 24-29

THE NEXT PHASE: INTEGRATING LAB AND FIELD DATA D

urab

le ro

cks

-- sc

our b

y

Qua

rryi

ng /

Pluc

king

Block thickness

y = 1.42E-04x - 1.07E-03 R² = 7.90E-01

y = 1.32E-04x - 1.02E-03 R² = 4.85E-01

y = 1.19E-04x - 6.72E-04 R² = 9.97E-01

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

7.0E-04

6.0 6.5 7.0 7.5 8.0 8.5 9.0

Eq. S

cour

Dep

th (f

t)

Stream Power (ft-lb/s//ft2)

Beverly

BEV-SEXP-001

BEV-01-18.7'-19.5'

BEV-02A-17.4'-18.0'

Linear (BEV-SEXP-001)

Linear (BEV-01-18.7'-19.5')


primary--dislodgement secondary--erosion/flaking

Claystone RQD?

0

1

2

3

4

5

6

7

8

9

10

0.0E+00 1.0E-04 2.0E-04 3.0E-04 4.0E-04 5.0E-04 6.0E-04

Thre

shol

d (E

quiv

alen

t Str

eam

Pow

er)

GSN

GSN vs. Threshold

Paden Fork Ss

Coon Creek Ss

Roaring Creek Ss

Laurel Ss

Bridge Fork Ss

Cucumber Ss

Grassy Run Ss

Mish Ls

Beverly Siltst/Sh/Clayst

Caldwell Run Sh / Coal

Laurel X Sh (carb.)

initial results in the determination of geotechnical scour numbers … · 2012-08-03 · modified...

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