MICHGAN BRIDGE CONFERENCE

Christopher Naida, P.E., SMEChris D. Johnecheck, P.E., Michigan Department of Transportation

March 17, 2015

Increased LRFD Axial Resistance Factorsfor Piling Using Static Load Test and

PDA Testing

OVERVIEW

How Load Resistance Factor Design (LRFD) is addressed in driven pile design• Two aspects: construction and design (estimating pile lengths)

MDOT implementation of Dynamic Testing (PDA) and Static Load Tests

Case studies

LRFD Design for Pile Driving

General LRFD Equation• Σ η*γ*Q ≤ φ*Rn η = Load Modifier (redundancy, operational importance) γ = Load Factor Q = Service Load or Force φ = Resistance Factor Rn = Nominal Pile Bearing Resistance (Ultimate)

Factored Geotechnical Resistance (RR):• RR = φ*Rn = φstatic*Rs + φstatic*Rp = φdyn*Rn

φstatic= resistance factor for static analysis method used to estimate pile lengths (Table 10.5.5.2.3-1)

φdyn = resistance factor for dynamic method used to verify nominal pile bearing resistance (Table 10.5.5.2.3-1)

Rs & Rp = pile side and tip resistance used to estimate pile lengths Rn is used as the basis for determining Rndr during pile driving

RR = φdyn*Rndr (assumes no scour or downdrag on pile)• φdyn value is based on type of quality control used in construction

Quality Control During Construction• Dynamic Formula (modified gates formula) φdyn = 0.5

• Dynamic Pile Testing (PDA) φdyn = 0.65*

• Static Load Test φdyn = 0.75 – 0.8* (may decrease based on site variability)

* Requires dynamic testing with signal matching, and best estimatesare made from a restrike

LRFD Design for Pile Driving (continued)

Saximeter

PDA Gauges

M-85 Load Test

TYPICAL NOMINAL PILEDRIVING RESISTANCE (Rndr)

Steel H Piles

Pile (Rndr)HP 10X42 275 kipsHP 10X57 350 kipsHP 12X53 350 kipsHP 12X74 500 kipsHP 12X84 600 kipsHP 14X73 500 kipsHP 14X89 600 kips

TYPICAL NOMINAL PILEDRIVING RESISTANCE (Rndr) continued

Cast-in-Place Concrete PilesPile Size (Rndr)Metal Shell 12" O.D. w/0.312" Walls 250 kipsMetal Shell 14" O.D. w/0.312" Walls 350 kipsMetal Shell 16" O.D. w/0.375" Walls 500 kips

Timber Pile(Rndr)

Timber Pile 150 kips

Factored Nominal Pile Bearing Resistance Example

Assume geotechnical engineer uses Rndr = 350 kips• Dynamic Formula (modified gates formula) RR = φdyn*Rndr

RR = 0.5 (350 kips) = 175 kips• Dynamic Pile Testing (PDA) RR = 0.65 (350 kips) = 227 kips

• Static Load Test RR = 0.8 (350 kips) = 280 kips

Designer can use higher factored resistance when specifying a more reliable form of Quality Control

Perform Economic AnalysisGeneral rules for Resistance Factor (φdyn)

(detailed analysis shall be performed)

* This resistance factor applies to the Beginning of Redrive (BOR) case.

Project Driven Pile

Cost

Pile Certification Method

ResistanceFactor (φdyn)

<$300,000 FHWA-ModifiedGates Formula 0.50

>$300,000 Dynamic Testing/Signal Matching (PDA Testing) 0.65 *

>$500,000 Static Load Test 0.55 ‒ 0.90

0.80

Estimating Pile Lengths forContract Documents

AASHTO Bridge Design Manual states (C10.7.3.3):The estimated pile length necessary to provide the required nominal resistance is determined using static analysis, local pile driving experience, knowledge of the site subsurface conditions, and/or results from a static pile load test program.

In lieu of local pile driving experience, consider the following equation using static analysis:• φdyn*Rn = φstatic*Rnstat (C10.7.3.3-1)

Rnstat = predicted nominal resistance from the static analysis used to estimate pile lengths

AASHTO Static Resistance Factors-φstatic

φdyn*Rn = φstatic*Rnstat .......equation estimates lengths reasonable when using the dynamic formula (modified gates) and associated φdyn = 0.5

Example: Assume Rndr = 350 kips, a sand profile, and using the modified gates formula for quality control

Using dynamic formula: 0.5 * 350 kips = 0.45 * Rnstat

….estimate pile length based on Rnstat = 390 kips

Caution: When using extreme limits of static &dynamic analysis:

0.8 * 350 kips = 0.45 * Rnstat ….. Rnstat = 620 kip

Estimating Pile Length Example

Contract Documentation of Design Note the Rndr on the design plans.

Note the dynamic resistance factor utilized in the design analysis on the design plans.

If loss of resistance due to scour or downdrag are expected, quantify these losses on the design plans.

Include dynamic testing or static load test SP in contract documents if specified on the project.

Increased LRFD Axial Resistance Factors for Piling Using Static Load Test and PDA TestingCase Studies

Benton Harbor Project Overview

• New 6-story building supported on H-piles (HP10x42)

• Designed for lengths of 150 feet to penetrate extremely dense sands

• Driven lengths of 150 to 190 feet• Construction manager getting

claims from piling contractor due to longer piles

Photo Courtesy of Yahoo Maps

Benton Harbor – Soil Conditions

• Loose sands and organics (e.g., peat) over extremely dense sands

Photos Courtesy of SME

Benton Harbor Results

• Drove P719 from 140 to 153 feeto Axial pile capacity was below the requirement

• Re-strike on P716 previously driven (3 days from initial drive)o Increased blow counts (resistance) met designo Reduced blow counts with driving (i.e., 10, 7, 6, 4, 2 bpi)o Localized loss of support from fine silty sands

Photo Courtesy of SME

Benton Harbor Results

• Pile and soil observationso Cycled loading from pile driving

• Increased pore water pressures, reduced skin friction and soil plug formation at pile tip• Led to softening and accumulation of deformation (e.g., decreasing blow counts and

capacity)o Setup and Re-strike (3 days later)

• Time allowed sands to reduce pore water pressure• Increased effective stress and pile capacity

Benton Harbor – “Easy” Initial Driving

Photos Courtesy of SME

Benton Harbor – “Hard” Driving during Re-strike

Photos Courtesy of SME

Thompson Township Project Overview

• New bridge supported on pipe-piles o 12.75 inch dia. with a 0.375

inch thick wallo 0.75 inch steel plated bottom

• Piles were designed for lengths of 35 feet to penetrate into dense sands

Photo Courtesy of Yahoo Maps

Thompson Township – Soil Conditions

• Loose sands and organics over dense sands

• Decreasing strength to medium dense sands over limestone

• Artesian water flow with positive pressure flow of 15 gal/min out of borehole

• Water flow occurred between elevations 567 to 544 feet

Photo Courtesy of MDOT

Thompson Township – Pile Installation Criteria

• Required nominal capacity of 115 kips• Initial drive of pile to minimum tip

elevation of 588 feet in dense sandso Measure capacity and stop if meto If needed continue driving

• Continue driving pile to maximum tip elevation of 569 feet (above artesian water elevation of 567 feet)o Measure capacity and re-strike as

neededo If required reduce capacity and add more

pilesPhoto Courtesy of MDOT

Thompson Township – Results

• Abutment B piles achieved capacity in upper dense sands

• Abutment A piles achieved capacity in lower medium dense sands

Photo Courtesy of SME

Questions?