LADOTD DRIVEN PILE DESIGN & VERIFICATION USING LRFD

Jesse G

Rauser, PE

LADOTD DRIVEN PILE

DESIGN & VERIFICATION

USING LRFD

Not all of our policies, guidelines, and SOP’s are in the same location

Answer commonly asked questions about LADOTD pile design & verif ication procedures

Address misconceptions about pile design & verif ication processes used by LADOTD

Identify relevant research projects associated with driven piles

Highlight changes to Section 804 in the upcoming 2016 Standard Specif ications

Provide links to useful information and codes

OBJECTIVES

Geotechnical Investigations

In-House vs. Consulted

Site investigation guidelines

Lab testing requirements

Soil boring logs

Driven Pile Design Methods

Scour

Design procedures

Resistance Factor Selection

Research Projects

Constructability

Specification changes

Field Verification

Test Piles

Monitor Piles

Indicator Piles

Pile Setup

PRESENTATION OUTLINE

FHWA Geotechnical Library:

http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm

Louisiana Transportation Research Center (LTRC) Downloads:

http://www.ltrc.lsu.edu/downloads.html

LADOTD Bridge Design Section

http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Bridg

e_Design/Pages/default.aspx

LADOTD Pavement & Geotechnical Section

http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Pave

ment_Geotechnical/Pages/default.aspx

USEFUL LINKS



http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Bridge_Design/Pages/default.aspx


http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Pavement_Geotechnical/Pages/default.aspx


GEOTECHNICAL

INVESTIGATIONS

PROJECT ASSIGNMENT HIERARCHY

Project Management (or other)

Pavement/ Geotechnical Section

LADOTD In-House Crew

LADOTD Materials Lab

Geotechnical Retainer Contract

Bridge Design Section

Bridge Retainer Contract

Geotechnical Subconsultant

Geotechnical Consultant

“What are the LADOTD

boring and laboratory

testing requirements?”

GEC No. 5 – Evaluation of

Soil & Rock Properties

(FHWA-IF-02-034)

Table 3 provides guidelines

for minimum investigation

Also in LRFD Bridge Design

Specification Table 10.4.2-1

SITE INVESTIGATION GUIDELINES

GEC No. 5 Cover Page

http://isddc.dot.gov/OLPFiles/FHWA/010549.pdf

Number of Borings

When foundation layout is

known:

At least one boring at every

substructure (bent or pier)

Two borings per substructure,

for widths greater than 100’

When foundation layout is

unknown:

At least one boring every 100’

of alignment

Depth of Investigation

Use the greater of:

At least 20’ below anticipated tip

2x maximum pile group dimension

In general, we use 120’ for bridge foundations

Subgrade borings should terminate at least 8’ below f inished roadway elevation



For embankment/fill,

consider depth of influence

(based on width), not only

height of f i l l

It may be appropriate to drill

to depths over 2B

Penetrate through weak

strata into denser material

to terminate boring, when

possible

No SPT’s in clay! Stress Distribution Beneath

Continuous Strip (from Coduto)

Deep Borings

75% of all cohesive samples

tested with Atterberg Limits

and UU Triaxial tests

This easily covers costs of

testing sand instead of clay

Per form some consolidation

tests in f i l l areas

Data submitted electronically

in gINT format and printed in

the LADOTD log format

Subgrade Borings

Test enough samples to classify using AASHTO system

This should include hydrometer tests to identify silt content

pH & resistivity in culver t areas

Data submitted in gINT format, log format varies among consultants

LAB TESTING REQUIREMENTS

10-2GT – Geotechnical Database Phase 2 standardized the gINT database format

Soil boring log format was also standardized

We can now plot consultants’ data directly into charts, fences, etc.

This cuts down on errors introduced by retyping data & saves time

Double check -200 results before classifying (SP versus SP -SM, etc.)

Make sure SPT termination is repor ted properly ( Standard Penetration Test)

Stratify the soil borings:

Only group 2 adjacent consistencies (i.e., very soft to soft, med. to stiff)

Do not group different USCS types to avoid drawing additional layers

SOIL BORING LOGS

DRIVEN PILE DESIGN

METHODS

Certain constraints are set before pile design begins

Type & size of pile

Unsupported length & slenderness ratio

Type of field verification available due to budget or accessibility

Scour Considerations

Scour of ten has a major impact upon the pile design

BDTM 21 Describes DOTD Policy for Predicting Scour Elevation

DESIGN CONSTRAINTS

Bridge Profile with Scour Information

For permanent structures:

Subtract Contraction & Local Scour from the lowest point in channel

Apply this calculated elevation to all piers/bents and end bents

Abutment scour is not usually calculated – this does not mean to ignore scour at abutments!

Minimum tip elevation for scour:

20’ below scour elevation for piles less than 24” in diameter

25’ below scour elevation for piles 24” in diameter or greater

From “old” Bridge Design Manual, not in new Bridge Design Manual

For detour bridges, apply local scour from the design ground surface at each bent location

SCOUR CONSIDERATIONS

#1 Question: “What is the status of DRIVEN?”

FHWA does not want to be in the software development business

Other software exists, including DrivenPiles (successor to DRIVEN)

You could run DRIVEN in a Virtual Machine running an older Win OS

Create your own spreadsheet/software

LADOTD has no current plans to vet/endorse any specif ic sof tware package

A future research proposal may address this later – no timeline

Ultimately, we will accept methods providing results consistent with the DRIVEN methods

Cohesionless soil – Nordlund Method

Cohesive soil – Tomlinson/α Method

AXIAL PILE DESIGN

“Does guidance exist for designing driven piles?”

DOTD generally tr ies to adopt methods described in the NHI course manuals

An older (1998) version of the manual is available on the FHWA website

Newer versions (2006) are available to those who take the associated NHI course

AXIAL PILE DESIGN

FHWA HI 97-013 Cover Page


We have had success designing piles with CPT on recent projects

LTRC developed the PILE-CPT software to design piles

A new research proposal aims to evaluate newer CPT methods & update software

To develop experience, we recommend evaluating CPT & borings side by side for any projects with both

AXIAL PILE DESIGN BY CPT

Louisiana Pile Design by CPT Software

http://www.ltrc.lsu.edu/zip/pile_cpt_windows_7.zip

RESISTANCE FACTORS

Selection of φ must consider tradeoff between pile length & cost of f ield verification

Table 10.5.5.2.3-1 is a star ting point for φ

Region-specific research is also used to refine our selection of φ values

Site-specific φ calibration may be warranted on large projects

RESISTANCE FACTOR SELECTION

LRFD Bridge Design Specifications 2012


Resistance Factor Determination Method Resistance

Factor (φ)

Static Load Testing of at least 1 pile per site condition, plus Dynamic

Testing on at least 2% of production piles (minimum 2/site) 0.80

Static Load Testing of at least 1 pile per site condition, no Dynamic

Testing 0.75

Dynamic Testing conducted on 100% of production piles 0.75

Driving criteria established by Dynamic Testing, plus Dynamic Testing

of at least 2% of production piles (minimum 2/site) 0.65

Wave Equation Analysis, no Dynamic Monitoring or Load Testing 0.50

FHWA-modified Gates dynamic formula at end-of-drive only 0.40

Static Methods (α-method/Nordlund method) 0.35/0.45


From Table 10.5.5.2.3-1 (LRFD Bridge Design Spec - 6th Edition w/2013 Revisions)

Note: Dynamic Testing includes restrike testing and signal matching analyses

07-2GT – Calibration of Resistance Factors Needed in the LRFD Design of Driven Piles

Completed May 2009

14-1GT – Calibration of Region-Specific Gates Equation for LRFD

Draft report reviewed, implementation is imminent

11-2GT – Field Instrumentation and Testing to Study Set -up Phenomenon of Piles Driven into Louisiana Clayey Soils

Draft report reviewed, implementation plan in progress

03-1GT, 10-2GT, 15-1GT – Geotechnical Database Projects

Phases 1 & 2 complete, Phase 3 underway

RESISTANCE FACTOR CALIBRATION

Resistance Factor Determination Method LRFD LADOTD

Static: ≥ 1 pile/site

Dynamic: ≥ 2% production piles (≥ 2/site) 0.80

0.70-

0.75

Static: ≥ 1 pile/site

Dynamic: None 0.75 -

Static: None

Dynamic: 100% production piles 0.75 0.75

Dynamic: Used to establish driving criteria

Dynamic: ≥ 2% production piles (≥ 2/site) 0.65 0.65

Wave Equation Analysis only, no Dynamic/Static 0.50 -

FHWA-modified Gates dynamic formula at end-of-drive only 0.40 0.40 *

Static Methods (α-method/Nordlund method) 0.35/0.45 0.50


AASHTO LRFD Bridge Design Manual vs. Typical LADOTD Practice

* Implementation of new research should increase to 0.55

CONSTRUCTABILITY

Remember, conservative

strength parameters in

design become the opposite

when considering drivability

Designs must be

constructible and capacity

must be verif iable

We need to f ind a better way

for consultants to maintain

oversight during

construction phase testing

For 200-ton Strength Load

Static Test:

200t / 0.75 = 267 tons

Indicator Pile:

200t / 0.65 = 308 tons

Gates Method:

200t / 0.40 = 500 tons

Can the same hammer be

used to verify 267 tons and

500 tons?

CONSTRUCTABILITY

“Why do you overdesign your

piles?”

The Required Pile Resistance

is almost 5x greater than the

Factored Load!

Common with high scour &

sandy soils

Feasibility of design must

consider overburden effect

In some cases, drilled shafts

may be a better choice

OVERBURDEN EFFECT

Pile Data Table with Significant Overburden Effect

OVERBURDEN EFFECT

Sand

Clay

Clay (Scour Zone)

0’

-10’

-20’

-30’

20’

Design Case: • Pile 1 = 122 tons

• Pile 2 = 122 tons

No Predrill Case: • Pile 1 = 187 tons


Predrill Case: • Pile 1 = 150 tons


Pile

1: 2

4”

Sq

ua

re P

PC

Pile

Pile

2: 2

4”

Sq

ua

re P

PC

Pile

20’ of Overburden:

• 56 tons • 46% of nominal

resistance

Alternate hammer approval

method has been removed

from Specs

Contractor’s Pile Driving Plan

must include WEAP analysis

Many were already doing so

DOTD will continue to look at

a basic drivabil ity analysis

during design process

Contractor is responsible for

the specifics of his proposed

driving system

PILE DRIVING – SPEC CHANGES

GRLWEAP Software

Contractor is responsible for Pile Construction Log

Documents all pile installation activities including predrilling

Provides a record of driving resistance for every foot of drive

Practical refusal broadly defined as 20 blows/inch at maximum stroke, for 3 consecutive inches

Hammer must be in working order

Dynamic monitoring may be needed to verify hammer efficiency

We will not accept a refusal condition on a hammer that is malfunctioning

Dynamic Load Test item renamed to “Dynamic Monitoring Assistance”

Dynamic Monitoring Instrumentation moved from nonstandard item into the Specif ication

PILE DRIVING – SPEC CHANGES

FIELD VERIFICATION

Test Pile (φ=0.70-0.75)

Driven in advance of the permanent piles

Load tested

Dynamic testing is typically done as well

Indicator Pile (φ=0.65)

Same as test pile, dynamic testing only

Monitor Pile

Permanent pile with dynamic monitoring

PILE CATEGORIES

Preparing to Drive a Test Pile

How many test p i les are needed?

1 per “site condition”

1 per pile size (unless similar enough to back out unit resistances)

Consider additional piles if end bearing conditions differ

Consider additional piles if additional information is needed for design

What is the maximum pi le test load under LRFD?

“Old” way was to use 300% of the design load

Now, use 150% of the Required Nominal Resistance (with predrilling) in plans

Spec Change: Spec now references ASTM D -1143, Procedure A , with minor modif ications:

Load is applied in 20 equal increments, or as directed by engineer

Load is removed in 5 equal increments, based on max test load

Deflection is measured with 3 independent gauges accurate to +/ - 0.001”

TEST PILES

TEST PILES

Load Test Reaction System

Testing schedule should be

f lexible

Some static tests done as

early as 7 days

Restrike tests do not have to

be exactly at 24 hours

Load test plus dynamic

testing allows us to verify

design methodology,

calibrate PDA, establish

setup criteria, and verify

hammer performance

Indicator Piles

How many Indicator Piles

are needed?

Same criteria as Test Piles

Can be used to establish

setup criteria but not

calibrate PDA to a load test

Permanent Piles

Spec Change – Modified

Gates to be used only when

specified in the plans

Based on research, we hope

to change φ from 0.40 to

0.50 or 0.55

INDICATOR & PERMANENT PILES

We use test piles and indicator piles to

Confirm static calculations

Reduce uncertainty

Assess pile setup behavior

Establishing setup rates may allow for accelerated f ield verif ication

In some cases, we can provide acceptance before reaching the nominal resistance

20-hr restrikes on LA-1 project (65% to 75% of capacity)

PILE SETUP

Pile Setup Curve Compared to Static Test Results

MACARTHUR BLVD. PROJECT

Pile Setup Curves

No room to do static testing

Used restrikes on monitor piles to establish setup behavior

Late restrikes had to be eliminated due to vibrations

In some piers, early restrikes saved the contractor t ime and allowed pile acceptance prior to 24 hours

Setup curves were used to estimate pile capacity deficiency and determine pile extension lengths

FHWA Geotechnical Library:


Louisiana Transportation Research Center (LTRC) Downloads:


LADOTD Bridge Design Section

http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Bridg

e_Design/Pages/default.aspx

LADOTD Pavement & Geotechnical Section

http://wwwsp.dotd.la.gov/Inside_LaDOTD/Divisions/Engineering/Pave

ment_Geotechnical/Pages/default.aspx

QUESTIONS?





