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Bridge Geotechnical Considerations and Designing for ScourPART IVChristopher Byrum, Ph.D., P.E. GeotechnicalSoil and Materials Engineers, Inc.

Brian Barkdoll, PhD, PE ScourMichigan Technological University

Box Culvert Scour Failure ShowingKey Embankment Widening Concepts

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“Suitable Material”

Typical Compacted Core Limits

Compacted CoreOf Embank.

Suitable Material

Compacted Core is level lifts under densitySuitable Material can be bad and is just bladed in with a dozer

ORIGINAL GROUND SURFACE

NEW EMBANKMENT

EXISTING FILL

EDGE OF ORIGINAL PCC PAVEMENT

1.51

1

1.5

WIDENING

SUITABLE MATERIAL

NEW UNDERCUTEXISTING UNDERCUT 1

1

NOTES: 1. STRIP EXISTING SIDE SLOPE SOIL TO THE LIMITS SHOWN.2. BENCH NEW COMPACTED ROADWAY CORE INTO THE EXISTING

COMPACTED FILL IN 27-INCH (MAX) BENCHES, 9-INCH LIFTS.3. EXTEND EXISTING UNDERCUTS TO REDUCE DIFFERENTIAL

SETTLEMENT AND USING CLASS III GRANULAR MATERIAL.4. 1.5H:1V CUT SLOPE MAY NEED TO BE FLATTENED BASED ON

GROUNDWATER AND MATERIAL TYPES ENCOUNTERED.5. NEW EMBANKMENT SHOULD BE CLASS III GRANULAR MATERIAL. 6. UPPER LIFT OF NEW EMBANKMENT SHOULD BE CLASS II SAND.

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Bridge Geotechnical for RiversFoundation Construction Under Water

-Drilling/Sampling in Open Water.-Construct-ability under Water.-Cofferdams.

BYRUM-2000

Scour During Flood Events-Presence of Piers Causes Holes to Form-Very Site Specific-Must Iterate with Hydraulics EngineersDuring Design

-Often Controls Geotech. Recommendations

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Pier 3 Cofferdam

Pier 3 Cofferdam

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Pier 3 Cofferdam

Pier 4 Footing Pour

Sheet-Pile Cofferdams

CLAY CLEAN SAND

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Sheet-Pile Cofferdams

Mud Mat TREMIE

Pump Water In

CLAY CLEAN SAND

Very Important!

Pumping Water In (Positive Head in Cofferdam) Forces

Liquid Concrete to FlowLiquid Concrete to Flow Outward Into Sheeting Joints

and The Subsoils

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TREMIE

Otherwise---Worm Holes, Flow In!

CLEAN SAND

Use Tremie Seals When….

1. For Silt and Clean Sands and Gravels, Head greater than about 2-3 feet.

2. Deep thick Clay Layers, Mud Mat for Head Less than 10-15 feet.

3. When the Geotechnical Engineer Says To.

Other Cofferdam Checks:

1. Seal Bond/Lift (5 psi on sheets, 10 psi on piling)2. Total Bouyancy Uplift- The Boat Effect3. Seal Bending Stress

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SCOURNormal Flow

Flood Events

Water Goes Up-Channel Goes DownWater Goes Down-Channel Fills InHigher Flow Velocity-Bigger Particles Suspended

Normal Water Surface

BYRUM-2000

Flood Events500 yr. Surface

100 yr. Surface

500 yr. Channel

100 yr. Channel

CONTRACTION SCOUR

Flood Events500 yr. Surface

100 yr. Surface

SCOUR WITH BRIDGE

BYRUM-2000

LOCAL SCOURThe pier is an obstruction to flow. The eddie currents around the pier (small tornado-like features) chew up the channel bottom locally around the pier

Abutment End Section Global Stability

BYRUM-2000Piles

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PIER DESIGN FOR SCOUR

M

Pv Pl (pin connection)

BYRUM-2000

Check:1. Stiff enough laterally?2. How deep below scour?3. How to get that deep?4. Abutment Stability

V

Soil

Piles

SHIP IMPACT ?

M

Pv Pl (pin connection)

BYRUM-2000

Check:1. Stiff enough laterally?2. How deep below scour?3. How to get that deep?4. Abutment Stability

V

Soil

Piles

DESIGN FOR SCOUR

M

Pv Pl (pin connection)

BYRUM-2000

Design Factors:1. Local Scour Depth2. Ship Impact3. Debris Impact4. Ice Impact/Flow5. Vertical/Lateral Loads6. Wind/Earthquake Loading7. Combinations of above

Check:1. Stiff enough laterally?2. How deep below scour?3. How to get that deep?4. Abutment Stability

V

Soil

Piles

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½ k Δ2 > F S (½ mv2)

Ship Impact

Use Energy Methods

Pier Strain Energy > (FS)Design Ship Energy

½ kpierΔ2 > F.S.(½ mv2)

Curvature + Axial Loadσtotal = σbending + σaxial

σtotal = My/I + P/A

R

BYRUM-2000

2

2

dyxdEIM =

Rdyxd 12

2

=

R = Radius of the CurvatureR

R

Study the Curvature ProblemSLABS- ALL CURVATURE-3D

BEAMS- CURVATURE AND SHEAR-2D

COLUMNS- CURVATURE AND AXIALEULER BUCKLING THEORY

Curvature Moment

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LOG JAM !

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Abutment End Sections

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Bridge ReplacementHard DirtBig River

M-59 over N. Br. Clinton River

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