i-20 mississippi river bridge vicksburg 3d numerical modeling€¦ · i-20 mississippi river bridge...

I-20 Mississippi River Bridge – Vicksburg

3D Numerical Modeling

State Project No. 700-33-0112

Federal Aid Project No. BR-3308-(503)

April 5, 2019

April 5, 2019 Numerical Modeling for I-20 1

The Mississippi Crossing at Vicksburg


Detail of the I-20 and US 80


As Built I-20 – Embedment of Piers


As Built E-1 – Embedment of Pier


Detailed Geometry Definition:CAD Version - New Survey/Topo


E1

E2

Geometry and Definitions in the numerical model


Fill within scour hole at the

east channelIsland

West channel

Preferred movement surfaces

Ele

vation

(ft)

Soil Properties for Plaxis and Limit Equilibrium


γ

(pcf)

C

(psf)

ɸ Tensile

Strength

(psf)

Ex103

(psf)

ν Kx

ft/day

Ky

ft/day

Loess 115 600 30

30 800 0.2 0.075 0.075

Pre loess

Clay

120 200-500? 21

25 900 0.25 0.01 0.002

Limestone 125 2000 25

200 4000 0.25 0.004 0.0004

Marl 120 300 30

15 1500 0.3

0.15 0.40

FH Clay 120 300 22

15 1200 0.25 0.00033 0.000033

FH Sand 125 60 35

5 2600 0.3

0.00052 0.00052

Clay 120 70 25

5 1200 0.3

0.00033 0.000033

LF Hill 2 120 500-

1000?

30

50 40000 0.25 0.0011 0.0033

Fill 110 200 27

10 1100 0.25

2 2

Heavy

Alluvium

110 15 20

5 1300 0.350.4 0.4

Alluvium 1

(interface

bottom)

110 0 6

0 300 0.3 0.4 0.4

Measured displacements


Incremental Displacement at Piers E-1 and E-2

Period Observed At elevation -63 ft

NGVD Pier E-1

Observed At elevation -63 ft

NGVD Pier E-2

(in) (in)

2004-2005 0.25 0.55

2005-2006 0.45 0.2

2006-2007 0.2 0.25

2007-2012 March 0.25 0.4

2012 March-2012 Sept 0.25 0.5

Selected river cycles elevations for 3-D Analysis


40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Elev

atio

n (

ft)

Day2005-2006-2007-2012 River elevations

Piers and Sliding Surface in the Island.


“Structures” in the Model


Horizontal Displacements Under River Cycles Loads


• Drawdown to elevation 45 in last cycle.

Analysis 4-11 B

• Horizontal Displacements at Station 800 (scour hole)


Horizontal Displacements at Station 1000 (I20 alignment)


Plastic points at the end of the 4th Cycle(2012)• . Notice close to critical conditions at the island .


Horizontal Displacements at Piers Locations


0

10

20

30

40

50

60

70

80

90

100-0.10

0.10.20.30.40.50.60.70.80.9

11.11.21.31.41.51.61.71.81.9

22.12.2

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Riv

er

Elev

atio

n (

ft)

Ho

rizo

nta

l dis

pla

cem

en

ts (

in)

Time (days)

Actual displacements E-1 Actualdisplacements at E-2 Floating E-1 (E-1)

Floating E-1 (E-2) Modeled River Elevations

Existing conditions downstream of piers E-1 and E-2


Fill brought in to stabilize the US 80 bridge during the 1930’s created a narrower

“entrance channel” and a “control section” that eventually lead to scour

hole/stilling basin to dissipate the flow energy downstream of the bridge.

Pier E-1

Pier E-2

Sect

ion

12

Alternative solution to be improved by hydraulic modeling


Alternative fill solution : create a flat platform for a wider control section at

elevation +40 NGVD to take the hydraulic jump downstream of the bridge .

Reduce the fill at the lower platform (+10 ) to maintain a substantial stilling basin

for energy dissipation .

Elevation 40

platform

Elevation 10

platform

Pier E-1

Pier E-2

Proposed Scour Hole Fill


Platform at elevation 10

Model 6-1-17 Deformation at -63 ft after 8 cycles


0.5 ft

0.6 ft

Deformations at -63 ft. after 8 cycles

One row at 9’ Wing version 8-22 Dr. G’s Recommendation 9-18


0.25 ft

0.2 ft0.25 ft0.35 ft

Deformation at -63 ft after 8 cycles

Model 11-7-17 two rows of pilesModel 11-22-17 three W beams per CSM panel (16”*42”) @3.5’


0.3 ft

0.4 ft

0.3 ft

0.4 ft

0.4 ft

Deformation at Elevation -63 ft after 8 cycles


0.2 ft

• Model 11-30-17 CSM wall

0.2 ft

Comparison of Deformation results

• Deformations shown in slides 21 through 24 indicate that the most efficient solutions from the deformation point of view are those of models 9-18-17 and 11-7-17 CSM wall.

• Modified Model 9-18-17 in Model 10-6 17 is fairly efficient, followed by Model 11-7-17 (two rows of piles at 9’).

• The least efficient model is using one row of piles at 9’ (Model 8-22-17).

• Design loads for the most efficient models are compared next.


Shear and Moments comparison for most efficient models

Maximum Force on Piles after 8 cycles

Model Description Q12 (x) M3 (around x)

(Kips) (Kips-ft)

8-22-17 One row of piles at 9' 4049 23630

10-6-17 Dr G's +Wings 3799 22450

11-7-17 2 rows of piles at 9' 2242 10720


Comparison of Forces on Piles

• Two rows of piles as defined in model 11-7-17 provided the smallest design forces on piles.

• Forces on Model 10-6-17 are almost double those on the piles for model 11-7-17, and would require significantly larger piles and reinforcing.

• Considering the forces involved in the shaft design, Model 11-7-17 required us to analyze different options of pile arrangement to minimize forces for shaft design.


Analysis 11 7 17


0

10

20

30

40

50

60

70

80

90

100-0.10

0.10.20.30.40.50.60.70.80.9

11.11.21.31.41.51.61.71.81.9

22.12.22.32.42.52.62.72.82.9

3

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200

Riv

er

Ele

vati

on

(ft

)

Ho

rizo

nta

l dis

pla

cem

en

ts (

in)

Time (days)

Actual displacements E-1 Pier E-1 Fill to 10 No Shafts Piles at 18 2 rows Modeled River Elevations

Key Findings & Discussion

• Improvements on the river bottom improved flow conditions and reduced scour downstream of the pier E-2.

• Partially filling the scour hole south of the I-20 bridge improved the factor of safety of the bluff, but did not improve the stability of the Island and pier E1.

• Likely critical sliding surface for the island was defined calculating the factor of safety for four potential alternatives.

• The installation of two rows of 6-foot diameter shafts at 18-foot spacing practically prevents displacements of pier E-1.

• Design forces on stabilizing piles were determined using the numerical model.


i-20 mississippi river bridge vicksburg 3d numerical modeling€¦ · i-20 mississippi river bridge...

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