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2010 California Amendment to the2010 California Amendment to theAASHTO LAASHTO LRFDRFD Bridge DesignBridge DesignSpecifications, Forth EditionSpecifications, Forth Edition

LRFD for theLRFD for the Design of Retaining WallsDesign of Retaining Walls

.

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ReferencesReferences AASHTO LRFD Bridge Design Specification

(4th Edition)

CA Amendments to AASHTO LRFD BridgeDesign Spec (Sep 2010) Caltrans Memo To Designers 1-35:

Caltrans Memo To Designers 3-1: DeepFoundations

Caltrans Memo To Designers 4-1: SpreadFootings

Caltrans Memo To Designers 5-20:Foundation Report/Geotechnical Design

Report Checklist for Earth Retaining Systems

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ReferencesReferences

TRB Webinar February 17, 2010: Load andResistance Factor Design Analysis for Seismic

Design of Slopes and Retaining Walls NCHRP Report 611 (Volumes 1 and 2): Seismic

Anal sis and Desi n of Retainin Walls, Slo es

& Embankments, and Buried Structures NHI Course 130094 (New!): LRFD Seismic

Analysis and Design of Transportation

Structures, Features, and Foundations Caltrans Standard Plans, 2006 Edition Caltrans Standard Plans, 2010 Edition

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Current Design in CaltransCurrent Design in Caltrans LRFD for bridge supports

LRFD for Abutments, Earth retentionsystems and Buried structures effectiveOctober 4, 2010.

For more information, please refer towebsite of Office of Special FundedProjects, LRFD Information

http://www.dot.ca.gov/hq/esc/osfp/lrfd-information/lrfd-information.htm

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200 2010 1 4' 30', . 31 1 4' 30', . 31

1 32' 3', . 32 1 32' 3', . 32

1, . 33 1, . 33

2, . 34

3, . 3

4, . 3

, . 3 , . 34

. 1, . 3 . 1, . 3

. 2, . 3 . 2, . 3

'0" , . 311 . 1 '0" , .3

. 2 '0" , .

3

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Retaining Wall Type 1 - H = 4' through 30'

2006 Standard Plan

2010 Standard Plan

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Retaining Wall Type 1A

2006 Standard Plan

2010 Standard Plan

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Retaining Wall Type 5

2006 Standard Plan

2010 Standard Plan

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Retaining Wall Type 6A - 6'-0" Maximum

2006 Standard Plan

2010 Standard Plan

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Retaining Wall Type 6B - 6'-0" Maximum

2006 Standard Plan

2010 Standard Plan

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TRB Webinar on February 17, 2010

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120 ,

Difficulties with retaining wall seismic design

M-O method blows up with high back slopes, high

PGAs, not appropriate for passive

Soldier pile, tieback, soil nail, and MSE walls

Lack of guidance for slope stability

Pseudo-static versus deformation approach Appropriate seismic coefficient

Ground motion amplification

Liquefaction effects

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What is LRFD?What is LRFD?Load and Resistance Factor Design

ResistanceFactor

Nominal

Load factor

Load

es s ance

Load Modifier

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/ . ,

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,

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,

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,

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,

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Limit states for LRFDLimit states for LRFD Service Limit State:

Load combinations (LCs) to ensurestructure performance for service life

Strength Limit State:

distress and damage Extreme Event Limit State:

LCs to ensure structural survival duringextreme events (EQ, VC)

Fatigue and Fracture Limit State:Not an issue in foundation design

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How LRFD applied to Foundation DesignHow LRFD applied to Foundation Design Service Limit State (Permanent & total

load):pile settlement, pile top deflection (=1.0)

Determine pile length w/ load from SLS (=0.7)=0.5 for CIDH tip resistance

=1.0 for uplift group (only for block analysis) in cohesionless material

Extreme Event Limit State (Comp &Tension):Determine pile length w/ load from EELS (=1.0)

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Information from Structure DesignerInformation from Structure Designer Foundation type (CIDH, Concrete pile, Steel pile)

Scour Data

Finished Grade Elevation

Cut-off Elevation

Pile Cap size

Permissible Settlement under Service Load

Number of Pile per Support

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At the early stage of design (PFR)

Preliminary Foundation Design Data Sheet

SupportFoundation Type(s)

ConsideredEstimate of Maximum Factored

Compression Loads (kips)

Bent 2Class 200 Pile Group

60 inch CIDH Pile Shaft

280 per pile

1850 per column

Bent 330 inch CIDH Pile Group

60 inch CIDH Pile Shaft1950 per column

Abut 4 24 inch CIDH Pile Group 170 per pile

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At the foundation design stage (FR)

Support

No.

Design

Metho

d

Pile Type

FinishGrade

Elevatio

n (ft)

Cut-offElevatio

n

(ft)

Pile Cap Size (ft)

Permissible

Movement underService Load (in)Number

of Piles

per

Support

B L DV DH

Abut 1 LRFD 1 0.25

Bent 2 LRFD 1 0.25

Abut 3 LRFD 1 0.25

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Support No.Total Vertical Load per Support (kip)

Lateral Load at Abutments (kip)

Total Load Permanent Load**

Abut 1

Bent 2

Abut 3

Support

No.

Strength Limit State (Controlling Group)Extreme Event Limit State

(Controlling Group)

Compression Tension Compression Tension

Per

Support

Max.

Per Pile

Per

Support

Max.

Per Pile

Per

Support

Max.

Per Pile

Per

Support

Max.

Per Pile

Abut 1

Bent 2

Abut 3

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Support No.Degradation Scour

(ft)

Base Flood Scour (ft)Total Scour

(ft)

Contraction Local

Abut 1

Bent 2

Abut 3

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Foundation Recommendation for Bents(MTD 3-1 Attachment 1)

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Bent Pile Group

1. Calculate Required Nominal Resistance for

compression per pile (=0.7).

2. Calculate tip elevation for Required Nominal

Resistance for single pile.

3. Calculate Required Nominal Resistance for totalload per Support (=0.7=0.7=0.7=0.7).

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4. Calculate group nominal resistance using the tip

elevation calculated for total load per pile (Group

efficiency factor).

5. If the group nominal resistance is greater than the

required nominal resistance per support, the tip

elevation from single pile is Design Tip Elevation.

6. If the group nominal resistance is smaller than the

required nominal resistance per support, increase pilespacing or length of piles.

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Pile Data Table for Design Example

390420

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Group Pile in LRFD Spec

1. Minimum pile spacing

- For driven pile, 36 inch or 2.0 pile diameters (CA

Amendment 10.7.1.2)

- For CIDH pile, 2.5 pile diameters (CA Amendments

10.8.1.2): sequence of CIDH pile installation required

in the contract documents (less than 3.0 pile dia).

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Group Pile in LRFD Spec

2. CIDH and Driven pile group capacity in cohesive soil

- For compression, lesser of 1) NominalaxialNominalaxialNominalaxialNominalaxial

resistanceofeachpile2)Nominalaxialresistanceofresistanceofeachpile2)Nominalaxialresistanceofresistanceofeachpile2)Nominalaxialresistanceofresistanceofeachpile2)Nominalaxialresistanceof

- For uplift, lesser of 1) NominalupliftresistanceofNominalupliftresistanceofNominalupliftresistanceofNominalupliftresistanceof

eachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroup

consideredasablockconsideredasablockconsideredasablockconsideredasablock

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Group Pile in LRFD Spec

3. CIDH pile and Driven pile group in cohesionless soil

- For compression, 1) group efficiency factor for CIDH

pile, 2) Nominal axial resistance of each pile for

- For uplift, lesser of 1) NominalupliftresistanceofNominalupliftresistanceofNominalupliftresistanceofNominalupliftresistanceof

eachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroupeachpile2)Nominalupliftresistanceofpilegroup

consideredasablock(resistancefactor=1.0evenforconsideredasablock(resistancefactor=1.0evenforconsideredasablock(resistancefactor=1.0evenforconsideredasablock(resistancefactor=1.0evenfor

strengthlimitstate)strengthlimitstate)strengthlimitstate)strengthlimitstate)

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Prescriptive Approach

Explicit (quantified): Sustain damage without

loss of life or collapse in a large, rare

earthquake

pro a ty o occurrence n yr(1000 yr Rp)

Implicit (not quantified): Withstand smaller,more frequent seismic events

Without significant damage or

With repairable damage

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Alternative approaches (Owners discretion)

More rigorous performance standard

e.g., 3% probability of occurrence in 75 yr

Multi-level (performance-based) design

stan ar

Upper level event for No Collapse

Lower level event for No Damage

Often applied to facilities of high importance Critical bridges

Lifelines routes

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,

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,

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,

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, ,

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, ,

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,

Earth pressure determination

External, internal, and global stability

Guidance on AASHTO walls

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Conventional Gravity and Semi-Gravity Walls

Mechanically Stabilized Earth (MSE) Walls

Metallic Strips

Po ymer c Re n orcement

Non-gravity Cantilever / Anchored Walls

Discrete Elements (drilled shafts) with lagging

Continuous Wall Elements (e.g., sheetpiles or tangent

piles)

Soil Nailed Walls

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,

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,

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,

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,

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,

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,

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,

Factor of safety (C/D) approach

sp acemen - ase approac

Liquefaction issues

Mitigation

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,

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,

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,

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,

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Thank you