2010 California Amendment to the 2010 California Amendment to the AASHTO LAASHTO LRFD RFD Bridge Design Bridge Design

Specifications, Forth EditionSpecifications, Forth EditionLRFD for theLRFD for the Design of Retaining Walls Design of Retaining Walls

September 9, 2011September 9, 2011

Presented by:

Dr. Ted Liu

Senior Transportation Engineer

ReferencesReferences• AASHTO LRFD Bridge Design Specification

(4th Edition)

• CA Amendments to AASHTO LRFD Bridge Design Spec (Sep 2010)

• Caltrans Memo To Designers 1-35: Foundation Recommendation and ReportsFoundation Recommendation and Reports

• Caltrans Memo To Designers 3-1: Deep Foundations

• Caltrans Memo To Designers 4-1: Spread Footings

• Caltrans Memo To Designers 5-20: Foundation Report/Geotechnical Design Report Checklist for Earth Retaining Systems

ReferencesReferences

• TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis for Seismic Design of Slopes and Retaining Walls

• NCHRP Report 611 (Volumes 1 and 2): Seismic Analysis and Design of Retaining Walls, Slopes & Embankments, and Buried StructuresAnalysis and Design of Retaining Walls, Slopes & 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

Current Design in CaltransCurrent Design in Caltrans

• LRFD for bridge supports

• LRFD for Abutments, Earth retention systems and Buried structures effective October 4, 2010.

• For more information, please refer to website of “Office of Special Funded Projects, LRFD Information”http://www.dot.ca.gov/hq/esc/osfp/lrfd-information/lrfd-information.htm

RETAINING WALLS

MAY 2006 EDITION STANDARD PLANS 2010 EDITION STANDARD PLANS

Retaining Wall Type 1 - H = 4' through 30', Plan No. B3-1 Retaining Wall Type 1 - H = 4' through 30', Plan No. B3-1

Retaining Wall Type 1 - H = 32' through 36', Plan No. B3-2 Retaining Wall Type 1 - H = 32' through 36', Plan No. B3-2

Retaining Wall Type 1A, Plan No. B3-3 Retaining Wall Type 1A, Plan No. B3-3

Retaining Wall Type 2, Plan No. B3-4

Counterfort Retaining Wall Type 3, Plan No. B3-5

Counterfort Retaining Wall Type 4, Plan No. B3-6

Retaining Wall Type 5, Plan No. B3-7 Retaining Wall Type 5, Plan No. B3-4

Retaining Wall Details No. 1, Plan No. B3-8 Retaining Wall Details No. 1, Plan No. B3-5

Retaining Wall Details No. 2, Plan No. B3-9 Retaining Wall Details No. 2, Plan No. B3-6

Retaining Wall Type 6 - 6'-0" Maximum, Plan No. B3-11 Retaining Wall Type 6 Details No. 1 - 6'-0" Maximun, Plan No.

B3-7

Retaining Wall Type 6 Details No. 2 - 6'-0" Maximum, Plan No.

B3-8

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

2006 Standard Plan

2010 Standard Plan

Retaining Wall Type 1A

2006 Standard Plan

2010 Standard Plan

Retaining Wall Type 5

2006 Standard Plan

2010 Standard Plan

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

2006 Standard Plan

2010 Standard Plan

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

2006 Standard Plan

2010 Standard Plan

TRB Webinar on February 17, 2010

NCHRP 12-70 Project

Need for NCHRP 12-70 Project“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Difficulties with retaining wall seismic design

� M-O method “blows up” with high back slopes, high

PGA’s, not appropriate for passive

� Appropriate seismic coefficient� Appropriate seismic coefficient

� 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

LRFD BACKGROUND

• Load and resistance factor design

principles

• AASHTO seismic damage • AASHTO seismic damage

philosophy

• Design ground motions

Review LRFD Principles

What is LRFD?What is LRFD?

Load and Resistance Factor Design

Resistance

Factor

Nominal

Resistance

Load factor

Load

Resistance

Load Modifier

Capacity/Demand Ratio.“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

LRFD versus ASD

• The following condition must be

satisfied

Load Effects ≤Resistance

• Difference in LRFD and ASD methods is • Difference in LRFD and ASD methods is

based on how uncertainties in loads

and resistances are accounted for

• LRFD: Load and resistance factors will

be refined with time

Load Combinations and Load Factors“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Limit States for Earthquake Design“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Load Factors for Seismic Design“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Resistance Factors“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Limit states for LRFDLimit states for LRFD

• Service Limit State:

Load combinations (LCs) to ensure structure performance for service life

• Strength Limit State:

LCs to ensure structural integrity despite LCs to ensure structural integrity despite distress and damage

• Extreme Event Limit State:

LCs to ensure structural survival during extreme events (EQ, VC)

• Fatigue and Fracture Limit State:

Not an issue in foundation design

How LRFD applied to Foundation DesignHow LRFD applied to Foundation Design

• Service Limit State (Permanent & total load):pile settlement, pile top deflection (φ=1.0)

• Strength Limit State (Comp & Tension):• Strength Limit State (Comp & Tension):Determine pile length w/ load from SLS (φ=0.7)φ=0.5 for CIDH tip resistance

φ=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 (φ=1.0)

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

• At the early stage of design (PFR)

Preliminary Foundation Design Data Sheet

SupportFoundation Type(s)

Considered

Estimate of Maximum Factored

Compression Loads (kips)

Abut 1 Class 140 140 per pileAbut 1 Class 140 140 per pile

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

• At the foundation design stage (FR)

Support

No.

Design

Metho

d

Pile Type

Finish

Grade

Elevatio

n (ft)

Cut-off

Elevatio

n

(ft)

Pile Cap Size (ft)

Permissible

Movement under

Service 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”

Extreme Event Limit State

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

Support No.Degradation Scour

(ft)

Base Flood Scour (ft)

Total Scour

(ft)

Contraction Local

Abut 1

Bent 2

Abut 3

• Foundation Recommendation for Bents

(MTD 3-1 Attachment 1)

• Bent Pile Group

1. Calculate “Required Nominal Resistance” for

compression per pile (φ=0.7).

2. Calculate tip elevation for “Required Nominal 2. Calculate tip elevation for “Required Nominal

Resistance” for single pile.

3. Calculate “Required Nominal Resistance” for total

load per Support (φ=0.7=0.7=0.7=0.7).

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”.elevation from single pile is “Design Tip Elevation”.

6. If the group nominal resistance is smaller than the

required nominal resistance per support, increase pile

spacing or length of piles.

• Pile Data Table for Design Example

390420

• 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).

• Group Pile in LRFD Spec

2. CIDH and Driven pile group capacity in cohesive soil

- For compression, lesser of 1) Σ Nominal axial Nominal axial Nominal axial Nominal axial

resistance of each pile 2) Nominal axial resistance of resistance of each pile 2) Nominal axial resistance of resistance of each pile 2) Nominal axial resistance of resistance of each pile 2) Nominal axial resistance of

equivalent pierequivalent pierequivalent pierequivalent pierequivalent pierequivalent pierequivalent pierequivalent pier

- For uplift, lesser of 1) Σ Nominal uplift resistance of Nominal uplift resistance of Nominal uplift resistance of Nominal uplift resistance of

each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group

considered as a blockconsidered as a blockconsidered as a blockconsidered as a block

• 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) Σ Nominal axial resistance of each pile for

Driven pileDriven pile

- For uplift, lesser of 1) Σ Nominal uplift resistance of Nominal uplift resistance of Nominal uplift resistance of Nominal uplift resistance of

each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group each pile 2) Nominal uplift resistance of pile group

considered as a block (resistance factor=1.0 even for considered as a block (resistance factor=1.0 even for considered as a block (resistance factor=1.0 even for considered as a block (resistance factor=1.0 even for

strength limit state)strength limit state)strength limit state)strength limit state)

AASHTO

Seismic Damage PhilosophySeismic Damage Philosophy

Seismic Design Philosophy

Prescriptive Approach

� Explicit (quantified): Sustain damage without

loss of life or collapse in a large, rare

earthquake

� 7% probability of occurrence in 75 yr � 7% probability of occurrence in 75 yr

(1000 yr Rp)

� Implicit (not quantified): Withstand smaller,

more frequent seismic events

� Without significant damage or

� With repairable damage

Seismic Design Philosophy

Alternative approaches (Owner’s discretion)

� More rigorous performance standard

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

� Multi-level (performance-based) design

standardstandard

� Upper level event for “No Collapse”

� Lower level event for “No Damage”

� Often applied to facilities of high importance

� Critical bridges

� Lifelines routes

Design Ground Motions

Design Ground Motions“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Design Ground Motions“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Site Classification System“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

PGA Site Factor, FPGA“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Long-Period Site Factor, FV“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Retaining wall design“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

�Earth pressure determination

�External, internal, and global stability

�Guidance on AASHTO walls

Retaining Walls Types of Walls

� Conventional Gravity and Semi-Gravity Walls

� Mechanically Stabilized Earth (MSE) Walls

�Metallic Strips

�Polymeric Reinforcement�Polymeric Reinforcement

� Non-gravity Cantilever / Anchored Walls

� Discrete Elements (drilled shafts) with lagging

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

piles)

� Soil Nailed Walls

Types of Walls

Types of Walls

Gravity Walls

AASHTO LRFD M-O Equations“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Active Earth Pressures with Cohesion“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Passive Earth Pressure“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Design Approach“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Design Approach“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Retaining Walls

Design Guidelines“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Seismic slope stability“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

�Factor of safety (C/D) approach

�Displacement-based approach�Displacement-based approach

�Liquefaction issues

�Mitigation

Seismic Coefficient“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Seismic Coefficient“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Seismic Coefficient“TRB Webinar February 17, 2010: Load and Resistance Factor Design

Analysis for Seismic Design of Slopes and Retaining Walls”

Slopes and Embankments

Design Guidelines“TRB Webinar February 17, 2010: Load and Resistance Factor Design Analysis

for Seismic Design of Slopes and Retaining Walls”

Questions Questions about about Caltrans Caltrans LRFDLRFD

• Geotechnical consultants working on Caltrans

Projects may contact Caltrans LRFD Technical

Committee through geotechnical reviewer.

• Any question about AASHTO LRFD Specification

should be directed to AASHTO.

Thank you