IDOT Pile Design Guide

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IDOT Pile Design Guide

Training on Bridge Pile Design by Spreadsheet

April 2021

Michael Nop, PE 515-239-1233 [email protected] Iowa DOT, Bridges and Structures Bureau

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TABLE OF CONTENTS County Problem 1A J30 - Integral Abutment - HP10x42, Modified IDOT ENR Formula, Cohesive Soil 3 County Problem 1B J30 - Integral Abutment - HP10x42, WEAP, Cohesive Soil, Setup 16 County Problem 2 H30 - Integral Abutment - HP10x57, WEAP, Cohesive Soil, Downdrag, Bedrock 24 County Problem 3 H30 - Pile Bent - HP14x73, WEAP, Non-cohesive Soil, Scour 37 Appendices

A. Friction and End Bearing Soil Charts 50 B. Soil Categories 52 C. Recommended Pile Penetration 53 D. Geotechnical and Target Driving Resistance Factor Charts 54 E. Fundamental Relationships 56 F. Plan Notes for Piling 59 G. Hand Calculations for County Problem 1A, 1B, 2, and 3 64 H. Frequently Asked Questions 68 I. Common Mistakes to Avoid and Other Helpful Hints 76 J. Additional Resources 78

DISCLAIMER: Neither the State of Iowa, the Iowa Department of Transportation nor their employees make any representations or warranties, express or implied, with respect to the use of or reliance on the data provided herewith, regardless of its format or means of transmission. There are no guarantees or representations to the user as to the accuracy, currency, completeness, suitability or reliability of this data for any purpose. THE USER ACCEPTS THE DATA "AS IS" AND ASSUMES ALL RISKS ASSOCIATED WITH ITS USE. The Iowa Department of Transportation assumes no responsibility for actual, consequential, incidental, special or exemplary damages resulting from, caused by or associated with any user's reliance on or use of this data, even if appraised of the likelihood of such damages occurring.

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County Problem 1A J30 - Integral Abutment - HP10x42

Modified IDOT ENR Formula, Cohesive Soil J30-06 Continuous Concrete Slab (CCS) Bridge Standards (https://iowadot.gov/bridge/standards/english/j30-06.pdf)

• 30’ roadway width • 0° skew • 140’ long bridge • 3 Spans: 42.5’ – 55’ – 42.5’ • Integral abutment • Pile type: HP10x42 • 10’ prebore required • Pu = 92.3 kips per pile • Generalized Soil Category: Cohesive • Construction Control: Modified IDOT ENR Formula

https://iowadot.gov/bridge/standards/english/j30-06.pdf

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See blow-up on next page.

ALL PILING HP10x42.

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Standard Sheet J30-34-06

Note: The Structural Resistance Level 1 (SRL-1) limit from BDM Table 6.2.6.1-1

(https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf) for an HP10x42 is 179 kips of nominal resistance. The factored resistance is (0.60)*(179 kips) = 107.4 kips which should be and, in fact, is greater than Pu = 92.3 kips.

Standard Sheet J30-34-06

Note: The above statement is in conflict with the statement in the J-standards on sheet J30-

01A-6 which prohibits the use of these standards when rock is less than 15 feet from the bottom of the footing – see next page. Note that both statements conflict with the 2020 BDM update in BDM Article 6.1.6.1.1.1 which requires 34 feet from the bottom of the footing to the top of the rock for an integral abutment with HP10x42 piles and 10 feet of prebore if no further analysis is performed (https://iowadot.gov/bridge/policy/06-01-00SubsLRFD.pdf).

Pu = (646 k)/(7 piles) = 92.3 kips per pile

https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf

https://iowadot.gov/bridge/policy/06-01-00SubsLRFD.pdf

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Standard Sheet J30-01A-06, GENERAL NOTES

Note: The above statement is in conflict with the 2020 BDM update in BDM Article

6.1.6.1.1.1 which requires 34 feet from the bottom of the footing to the top of the rock for an integral abutment with HP10x42 piles and 10 feet of prebore if no further analysis is performed (https://iowadot.gov/bridge/policy/06-01-00SubsLRFD.pdf). BDM Table 6.1.6.1.1.1-1 contains the full range of values for various conditions.

A reference to CADD note E177 is made in the plan notes above, but this note is no longer available in the BDM and is not required in the plan set.


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Soil Profile at West Abutment

Ftg Bot Elev 933

Prebore Elev 923

10’ prebore

Final ground surface

Existing ground surface

11’

Surface Elev 937

30’

Soft Silty Clay

Silty Sand

Firm Glacial Clay

Very Firm Glacial Clay

2’

9’

10’

Layer Elev 917

Layer Elev 907

Layer Elev 926

Fill

N = 4

N = 6

N = 12

N = 20 35’

Boring Bot Elev 872

SPT N values are in units of blows per foot

4’

Page 8 BDM Table 6.2.7-2. LRFD driven pile nominal unit geotechnical resistances for friction bearing

SOIL DESCRIPTION BLOW COUNT ESTIMATED NOMINAL RESISTANCE VALUES FOR FRICTION PILE IN KIPS/FOOT N60-VALUE (5) WOOD

PILE STEEL “H” GRADE 50

PRESTRESSED CONCRETE

STEEL PIPE

MEAN RANGE 10 12 14 12 14 16 10 12 14 18 Alluvium or Loess Very soft silty clay 1 0 - 1 0.8 0.4 0.8 0.8 0.8 0.8 0.8 0.4 0.4 0.4 0.8

Soft silty clay 3 2 - 4 1.2 0.8 1.2 1.2 0.8 0.8 0.8 0.8 0.8 0.8 1.2 Stiff silty clay 6 4 - 8 1.6 1.2 1.6 2.0 1.2 1.6 2.0 1.2 1.2 1.6 2.0 Firm silty clay 11 7 - 15 2.4 2.0 2.4 2.8 2.4 2.8 3.2 1.6 2.0 2.4 2.8

Stiff silt 6 3 - 7 1.6 1.2 1.6 1.6 1.6 1.6 1.6 1.2 1.2 1.6 1.6 Stiff sandy silt 6 4 - 8 1.6 1.2 1.6 1.6 1.6 1.6 1.6 1.2 1.2 1.6 1.6 Stiff sandy clay 6 4 - 8 1.6 1.2 1.6 2.0 2.0 2.0 2.4 1.2 1.6 1.6 2.0

Silty sand 8 3 - 13 1.2 1.2 1.2 1.6 1.6 1.6 1.6 0.8 0.8 1.2 1.6 Clayey sand 13 6 - 20 2.0 1.6 2.0 2.8 2.4 2.4 2.8 1.6 2.0 2.4 2.8

Fine sand 15 8 - 22 2.4 2.0 2.4 2.8 2.4 2.8 3.2 1.6 2.0 2.4 2.8 Coarse sand 20 12 - 28 3.2 2.8 3.2 3.6 3.2 3.6 4.0 2.0 2.4 2.8 3.6 Gravely sand 21 11 - 31 3.2 2.8 3.2 3.6 3.6 3.6 4.0 2.0 2.4 2.8 3.6

Granular material > 40 --- (2) 4.0 4.8 5.6 (2) (2) (2) (2) (2) (2) (2) Glacial Clay

Firm silty glacial clay 11 7 - 15 2.8 2.4 2.8 3.2 2.8 3.2 3.6 2.0 2.4 2.4 3.2 Firm clay (gumbotil) 12 9 - 15 2.8 2.4 2.8 3.2 2.8 3.2 3.6 2.0 2.4 2.4 3.2 Firm glacial clay(1) 11 7 - 15 2.4

[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6

[ 4.4 ] Firm sandy glacial

clay(1) 13 9 - 15 2.4

[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6

[ 4.4 ] Firm - very firm glacial

clay(1) 14 11 - 17 2.8

[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 4.0

[ 4.8 ] 4.4

[ 5.2 ] 4.8

[ 5.6 ] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0

[ 5.2 ] Very firm glacial clay(1) 24 17 - 30 2.8

[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0

[ 5.2 ] Very firm sandy glacial

clay(1) 25 15 - 30 3.2

[ 4.0 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0

[ 5.2 ] Cohesive or glacial

material(1) > 35 --- (2) 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] (2)

(2)

(2)

2.0 (4) [ 3.2 ]

2.4 (4) [ 4.0 ]

2.8 (4) [ 4.4 ]

3.6 (4) [ 5.6 ]

Table notes: (1) For double entries the upper value is for an embedded pile within 30 feet of the natural ground elevation, and the lower value [ ] is for pile depths more

than 30 feet below the natural ground elevation. (2) Do not consider use of this pile type for this soil condition, wood with N > 25, prestressed concrete with N > 35, or steel pipe with N > 40. (3) Prestressed concrete piles have proven to be difficult to drive in these soils. Prestressed piles should not be driven in glacial clay with consistent N >

30 to 35. (4) Steel pipe piles should not be driven in soils with consistent N > 40. (5) Use uncorrected N-values until N60-values are available.

Page 9 BDM Table 6.2.7-1. LRFD driven pile nominal unit geotechnical resistances for end bearing

SOIL DESCRIPTION

BLOW COUNT ESTIMATED NOMINAL RESISTANCE VALUES FOR END BEARING PILE IN KIPS [KSI]

N60-VALUE (8) WOOD PILE (1),

(3)

STEEL “H” GRADE 50

PRESTRESSED CONCRETE (2)

STEEL PIPE (4)

MEAN RANGE 10 12 14 12 14 16 10 12 14 18 Granular material <15 --- (5) (5) (5) (5) (5) (5) (5) (5) (5) (5) (5)

Fine or medium sand

15 --- 32 (5) (5) (5) 60 84 108 32 48 64 108

Coarse sand 20 --- 44 (5) (5) (5) 84 116 148 44 64 88 144 Gravelly sand 21 --- 44 (5) (5) (5) 84 116 148 44 64 88 144 25 --- 56 (5) (5) (5) (7) (7) (7) (7) (7) (7) (7)

--- 25-50 (6) [ 2-4 ] [ 2-4 ] [ 2-4 ] (6), (7) (6), (7) (6), (7) (7) (7) (7) (7)

--- 50-100 (6) [ 4-8 ] [ 4-8 ] [ 4-8 ] (6) (6) (6) (7) (7) (7) (7)

--- 100-300 (6) [ 8-16 ] [ 8-16 ] [ 8-16 ] (6) (6) (6) (7) (7) (7) (7)

--- >300 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Bedrock

--- 100-200 (6) [ 12 ] [ 12 ] [ 12 ] (6) (6) (6) (7) (7) (7) (7)

--- >200 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Cohesive material

12 10-50 16 (5) (5) (5) 28 40 52 16 24 32 52 20 --- 24 [ 1 ] [ 1 ] [ 1 ] 44 64 84 28 36 52 84 25 --- 32 [ 2 ] [ 2 ] [ 2 ] 60 84 108 32 48 64 108 50 --- (6) [ 4 ] [ 4 ] [ 4 ] 116 (6) 164 (6) 212 (6) 56 96 128 212 100 --- (6) [ 7 ] [ 7 ] [ 7 ] (6) (6) (6) (6) (6) (6) (6)

Table notes: (1) Wood piles shall not be driven through soils with N > 25. (2) With prestressed concrete piles the preferred N for soil at the tip ranges from 25 to 35. Prestressed concrete piles have been proven to be difficult to drive

in very firm glacial clay and very firm sandy glacial clay. Prestressed concrete piles should not be driven in glacial clay with consistent N > 30 to 35. (3) End bearing resistance values for wood piles are based on a tip area of 72 in2. Values shall be adjusted for a different tip area. (4) Steel pipe piles should not be driven in soils with consistent N > 40. See the 1994 soils information chart [BDM 6.2.1.5] for end bearing when a conical

driving point is used. (5) Do not consider end bearing. (6) Use of end bearing is not recommended for timber piles when N > 25 or for prestressed concrete piles when N > 35 or for any condition identified with this

note. (7) End bearing resistance shall be 0.0389 x “N” value [ksi]. (8) Use uncorrected N-values until N60-values are available.

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As of January 1, 2015, note E177 is no longer required to be placed on the plan set. The note has been removed from the spreadsheet. However, a reference to note E177 is still contained in the J-standards on sheet J30-01A-06.

Page 16

County Problem 1B J30 - Integral Abutment - HP10x42

WEAP, Cohesive Soil, Setup J30-06 Continuous Concrete Slab (CCS) Bridge Standards (https://iowadot.gov/bridge/standards/english/j30-06.pdf)

• 30’ roadway width • 0° skew • 140’ long bridge • 3 Spans: 42.5’ – 55’ – 42.5’ • Integral abutment • Pile type: HP10x42 • 10’ prebore required • Pu = 92.3 kips per pile • Generalized Soil Category: Cohesive with Setup • Construction Control: WEAP

https://iowadot.gov/bridge/standards/english/j30-06.pdf

Page 17


Ftg Bot Elev 933

Prebore Elev 923

10’ prebore


Existing ground surface

11’

Surface Elev 937

30’

Soft Silty Clay

Silty Sand

Firm Glacial Clay


4’

9’

10’

Layer Elev 917

Layer Elev 907

Layer Elev 926

Fill

N = 4

N = 6

N = 12

N = 20 35’

Boring Bot Elev 872


2’

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County Problem 2 H30 - Integral Abutment - HP10x57

WEAP, Cohesive Soil, Downdrag, Bedrock H30-06 Pretensioned Prestressed Concrete Beam (PPCB) Bridge Standards (https://iowadot.gov/bridge/standards/english/h30-06.pdf)

• 30’ roadway width • 0° skew • 188’-10” long bridge • 3 Spans: 59.917’ – 69’ – 59.917’ (B59 and B67 beams) • Integral abutment • Pile type: HP10x57 • Use maximum of 15’ prebore (due to presence of downdrag) • Pu = 135 kips per pile • Generalized Soil Category: Cohesive (bedrock present) • Construction Control: WEAP

https://iowadot.gov/bridge/standards/english/h30-06.pdf

Page 25


Page 26

Standard Sheet H30-05-06

Note: The Structural Resistance Level 1 (SRL-1) limit from BDM Table 6.2.6.1-1 for an

HP10x57 is 243 kips of nominal resistance. The factored resistance is (0.60)*(243 kips) = 145.8 kips which should be and, in fact, is greater than Pu = 135 kips.

Pu = 135 kips per pile

Page 27

Standard Sheet H30-01A-06, GENERAL NOTES

Note: The above statement is in conflict with the 2020 BDM update in BDM Article

6.1.6.1.1.1 which requires 34 feet from the bottom of the footing to the top of the rock for an integral abutment with HP10x57 piles and 10 feet of prebore if no further analysis is performed (https://iowadot.gov/bridge/policy/06-01-00SubsLRFD.pdf). If prebore is increased to 15 feet then 37 feet from the bottom of the footing to the top of the rock is required. BDM Table 6.1.6.1.1.1-1 contains the full range of values for various conditions.

A reference to CADD note E177 is made in the plan notes above, but this note is no longer available in the BDM and is not required in the plan set.


Page 28

BDM Table 6.2.4.2-1. Prebored hole depths for abutments (https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf)

BDM Table 6.2.4.2-2. Recommended H-pile penetration into bedrock (https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf)

Rock classification Recommended penetration, feet

Broken limestone 8 - 12 where practical Shale or firm shale 8 – 12 Medium hard shale, hard shale, or siltstone with 50 ≤ N ≤ 200

4 – 8

Sandstone, siltstone, or shale with N ≥ 200

3

Solid limestone 1 – 3

BDM 6.2.4.6. Target Driving Resistance – Consider Setup? (https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf) In the case of H-piles and cohesive soils with WEAP construction control the designer shall consider the benefit of setup in the determination of the target driving resistance except in the following cases:

• Piles driven to bedrock, • Piles subjected to downdrag, • Piles in contact with cohesive soil with an overall average N of less than 5, and • Piles used in accelerated bridge construction.

Even though the piles are steel H-piles, WEAP will be used for construction control, and the soil will be classified as cohesive the benefits of setup will not be considered for these piles since they are being driven to bedrock and downdrag is present.




Page 29


Ftg Bot Elev 933

Prebore Elev 918

15’ prebore *


Existing ground surface 7’

54’

Soft Silty Clay

Firm Silty Clay


23’

15’

Layer Elev 888

Layer Elev 903

Surface Elev 926

Fill Assumed N = 20

N = 4

N = 12

N = 20 15’

Boring Bot Elev 872


15’

Neutral Plane

Downdrag Zone

Bearing Zone

1’

Hard Shale, N = 162

Layer Elev 873

* Prebore was increased from 10’ to the maximum allowed of 15’ to reduce downdrag.

2’





STEEL PIPE








[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 13 9 - 15 2.4

[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 14 11 - 17 2.8

[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 4.0

[ 4.8 ] 4.4

[ 5.2 ] 4.8

[ 5.6 ] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


clay(1) 25 15 - 30 3.2

[ 4.0 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


material(1) > 35 --- (2) 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] (2)

(2)

(2)

2.0 (4) [ 3.2 ]

2.4 (4) [ 4.0 ]

2.8 (4) [ 4.4 ]

3.6 (4) [ 5.6 ]





SOIL DESCRIPTION



(3)



STEEL PIPE (4)


Fine or medium sand

15 --- 32 (5) (5) (5) 60 84 108 32 48 64 108


--- 25-50 (6) [ 2-4 ] [ 2-4 ] [ 2-4 ] (6), (7) (6), (7) (6), (7) (7) (7) (7) (7)

--- 50-100 (6) [ 4-8 ] [ 4-8 ] [ 4-8 ] (6) (6) (6) (7) (7) (7) (7)

--- 100-300 (6) [ 8-16 ] [ 8-16 ] [ 8-16 ] (6) (6) (6) (7) (7) (7) (7)

--- >300 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Bedrock

--- 100-200 (6) [ 12 ] [ 12 ] [ 12 ] (6) (6) (6) (7) (7) (7) (7)

--- >200 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Cohesive material

12 10-50 16 (5) (5) (5) 28 40 52 16 24 32 52 20 --- 24 [ 1 ] [ 1 ] [ 1 ] 44 64 84 28 36 52 84 25 --- 32 [ 2 ] [ 2 ] [ 2 ] 60 84 108 32 48 64 108 50 --- (6) [ 4 ] [ 4 ] [ 4 ] 116 (6) 164 (6) 212 (6) 56 96 128 212 100 --- (6) [ 7 ] [ 7 ] [ 7 ] (6) (6) (6) (6) (6) (6) (6)





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Page 37

County Problem 3 H30 - Pile Bent - HP14x73

WEAP, Non-cohesive Soil, Scour H30-06 Pretensioned Prestressed Concrete Beam (PPCB) Bridge Standards (https://iowadot.gov/bridge/standards/english/h30-06.pdf)

• 30’ roadway width • 0° skew • 188’-10” long bridge • 3 Spans: 59.917’ – 69’ – 59.917’ (B59 and B67 beams) • Non-monolithic pile bent • Pile type: HP14x73 • 10’ scour • Pu = 168 kips per pile • Generalized Soil Category: Non-cohesive • Construction Control: WEAP

https://iowadot.gov/bridge/standards/english/h30-06.pdf

Page 38


Page 39

Standard Sheet H30-47-06

Note: The Structural Resistance Level 1 (SRL-1) limit from BDM Table 6.6.4.2.1.1 for an HP14x73 is 265 kips of nominal resistance. The factored resistance is (0.70)*(265 kips) = 185.5 kips which should be and, in fact, is greater than Pu = 168 kips.

Pu = 168 kips per pile

See P10L sheet on next page.

Page 40

See blow-up on next

page.

Page 41

Standard Sheet P10L

Note: The Structural Resistance Level 1 (SRL-1) limit from BDM Table 6.6.4.2.1.1 for an HP14x73 is (0.70)*(265 kips) = 185.5 kips. Additionally BDM Table 6.6.4.2.1.1 recommends a minimum height of the pile above the ground. For the HP14x73 this minimum height is 13’.

Page 42

Soil Profile at Pier 1

Cap Bot Elev 933

15’

Stream bed

1.5’

100’

Soft Silty Clay, N = 4

Fine Sand

Coarse Sand

7’

13’

Layer Elev 896

Layer Elev 913

Surface Elev 920

N = 13

N = 20 76’

Boring Bot Elev 820


3’

Scour Zone

Bearing Zone

Pile encasement

4’ Layer Elev 909

Fine Sand, N = 2

9’

89’

Surface Elev 918 2’





STEEL PIPE








[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 13 9 - 15 2.4

[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 14 11 - 17 2.8

[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 4.0

[ 4.8 ] 4.4

[ 5.2 ] 4.8

[ 5.6 ] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


clay(1) 25 15 - 30 3.2

[ 4.0 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


material(1) > 35 --- (2) 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] (2)

(2)

(2)

2.0 (4) [ 3.2 ]

2.4 (4) [ 4.0 ]

2.8 (4) [ 4.4 ]

3.6 (4) [ 5.6 ]





SOIL DESCRIPTION



(3)



STEEL PIPE (4)


Fine or medium sand

15 --- 32 (5) (5) (5) 60 84 108 32 48 64 108


--- 25-50 (6) [ 2-4 ] [ 2-4 ] [ 2-4 ] (6), (7) (6), (7) (6), (7) (7) (7) (7) (7)

--- 50-100 (6) [ 4-8 ] [ 4-8 ] [ 4-8 ] (6) (6) (6) (7) (7) (7) (7)

--- 100-300 (6) [ 8-16 ] [ 8-16 ] [ 8-16 ] (6) (6) (6) (7) (7) (7) (7)

--- >300 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Bedrock

--- 100-200 (6) [ 12 ] [ 12 ] [ 12 ] (6) (6) (6) (7) (7) (7) (7)

--- >200 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Cohesive material

12 10-50 16 (5) (5) (5) 28 40 52 16 24 32 52 20 --- 24 [ 1 ] [ 1 ] [ 1 ] 44 64 84 28 36 52 84 25 --- 32 [ 2 ] [ 2 ] [ 2 ] 60 84 108 32 48 64 108 50 --- (6) [ 4 ] [ 4 ] [ 4 ] 116 (6) 164 (6) 212 (6) 56 96 128 212 100 --- (6) [ 7 ] [ 7 ] [ 7 ] (6) (6) (6) (6) (6) (6) (6)





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Page 46

Page 47

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Appendix A. Friction and End Bearing Soil Charts End Bearing Soil Chart LRFD driven pile nominal unit geotechnical resistances for end bearing (BDM Table 6.2.7-1)

SOIL DESCRIPTION



(3)



STEEL PIPE (4)


Fine or medium sand

15 --- 32 (5) (5) (5) 60 84 108 32 48 64 108


--- 25-50 (6) [ 2-4 ] [ 2-4 ] [ 2-4 ] (6), (7) (6), (7) (6), (7) (7) (7) (7) (7)

--- 50-100 (6) [ 4-8 ] [ 4-8 ] [ 4-8 ] (6) (6) (6) (7) (7) (7) (7)

--- 100-300 (6) [ 8-16 ] [ 8-16 ] [ 8-16 ] (6) (6) (6) (7) (7) (7) (7)

--- >300 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Bedrock

--- 100-200 (6) [ 12 ] [ 12 ] [ 12 ] (6) (6) (6) (7) (7) (7) (7)

--- >200 (6) [ 18 ] [ 18 ] [ 18 ] (6) (6) (6) (7) (7) (7) (7)

Cohesive material

12 10-50 16 (5) (5) (5) 28 40 52 16 24 32 52 20 --- 24 [ 1 ] [ 1 ] [ 1 ] 44 64 84 28 36 52 84 25 --- 32 [ 2 ] [ 2 ] [ 2 ] 60 84 108 32 48 64 108 50 --- (6) [ 4 ] [ 4 ] [ 4 ] 116 (6) 164 (6) 212 (6) 56 96 128 212 100 --- (6) [ 7 ] [ 7 ] [ 7 ] (6) (6) (6) (6) (6) (6) (6)





Page 51 Friction Soil Chart LRFD driven pile nominal unit geotechnical resistances for friction bearing (BDM Table 6.2.7-2)




STEEL PIPE








[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 13 9 - 15 2.4

[ 3.2 ] 2.8

[ 3.2 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 3.2

[ 4.0 ] 3.6

[ 4.4 ] 4.0

[ 4.8 ] 2.0

[ 2.4 ] 2.4

[ 2.8 ] 2.8

[ 3.2 ] 3.6


clay(1) 14 11 - 17 2.8

[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 4.0

[ 4.8 ] 4.4

[ 5.2 ] 4.8

[ 5.6 ] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


[ 3.6 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


clay(1) 25 15 - 30 3.2

[ 4.0 ] 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] 3.2 (3)

[4.8] 3.6 (3)

[5.6] 4.4 (3)

[6.4] 2.4

[ 3.2 ] 2.8

[ 3.6 ] 3.2

[ 4.0 ] 4.0


material(1) > 35 --- (2) 2.8

[ 4.0 ] 3.2

[ 4.8 ] 3.6

[ 5.6 ] (2)

(2)

(2)

2.0 (4) [ 3.2 ]

2.4 (4) [ 4.0 ]

2.8 (4) [ 4.4 ]

3.6 (4) [ 5.6 ]




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Appendix B. Soil Categories Geotechnical resistance factors for design (contract length) and for construction (target driving resistance) were statistically calibrated by Iowa State University researchers for three generalized soil categories based on a 70% rule. Therefore the designer will need to use these same categories when selecting geotechnical resistance factors for design:

• Cohesive: Along the pile length in contact with soil, 70% or more of the length is through soils classified as cohesive according to the table below.

• Mixed: Along the pile length in contact with soil, 31% to 69% of the length is through soils classified as cohesive according to the table below (or 31% to 69% of the length is through soils classified as non-cohesive according to the table below).

• Non-Cohesive: Along the pile length in contact with soil, 70% or more of the length is through soils classified as non-cohesive according to the table below.

Soil category based on soil classification (BDM Table 6.2.8)

Friction Pile Charts BDM Table 6.2.7-2

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Appendix C. Recommended Pile Penetration If an H-pile is designed with end bearing resistance in bedrock the pile contract length should include the penetration length as indicated in Table 6.2.4.2-2. Prestressed concrete and steel pipe piles should be driven to bedrock only with approval of the Soils Design Section. Timber piles shall not be driven to bear on bedrock.

Recommended H-pile penetration into bedrock (BDM Table 6.2.4.2-2) Rock classification Recommended

penetration, feet Broken limestone 8 - 12 where practical Shale or firm shale 8 – 12 Medium hard shale, hard shale, or siltstone with 50 ≤ N ≤ 200

4 – 8

Sandstone, siltstone, or shale with N ≥ 200

3

Solid limestone 1 – 3 The design penetration for any pile should be a minimum of 10 feet into hard cohesive or dense granular soil and a minimum of 20 feet into soft cohesive or loose granular soil. Piles driven through embankments should penetrate 10 feet into original ground unless refusal on bedrock or a competent layer occurs at a lesser elevation. (BDM 6.2.4.2)

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Appendix D. Geotechnical and Target Driving Resistance Factor Charts

Geotechnical Resistance Factors: For end bearing on rock at the strength limit state the designer shall use a resistance factor of 0.70. For friction and end bearing in soil at the strength limit state the designer shall use the resistance factors in the following tables. Geotechnical resistance factors (φ) for friction and end resistance at the strength limit state for a single pile in a redundant pile group (BDM Table 6.2.9-1)

Theoretical Analysis (1)

Construction Control (Field Verification) (2) Axial Compression Resistance Factor for Design (3)

Driving Criteria Basis

PDA/ CAPWAP

Planned Retap Test 3-Days After EOD

Static Pile

Load Test

Cohesive Mixed Non-Cohesive

Iowa DOT ENR

Formula

WEAP φ φEOD φSETUP φ φ

Iowa Blue Book

Yes 0.60 0.60 0.50 Yes (4) 0.65 0.65 0.55

Yes (4) Yes 0.70

(5) 0.70 0.60

Yes (4) Yes Yes 0.80 0.70 0.60 Yes (4) Yes 0.80 0.80 0.80

Table notes: (1) Use the geotechnical resistance charts (i.e. soil charts) to estimate the theoretical nominal pile

resistance for friction bearing. If soil or rock at the pile tip is capable of end bearing, estimate the theoretical end resistance. Resistance factors in this table apply for friction and end bearing in soil; the resistance factor for end bearing in rock is 0.70.

(2) Use the construction control that will be specified on the plans. Except in unusual cases the construction control for state projects will be WEAP.

(3) These resistance factors are for redundant pile groups, which the office defines as five piles minimum except four piles minimum for abutments.

(4) Use the Blue Book soil input procedure to complete WEAP analyses. (5) Setup effect has been included when WEAP is used to establish driving criteria and CAPWAP is

used as a construction control. Note that the geotechnical resistance factor chart for friction resistance under axial tension is not included here. See BDM Table 6.2.9-2.

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Target Driving Resistance Factors: The designer shall use the following table for target driving resistance factors at the strength limit state. For end bearing on rock at the strength limit state the designer shall use a driving resistance factor of 0.70. Target driving resistance factors (φTAR) at the strength limit state for a single pile in a redundant pile group (BDM Table 6.2.9-3)

Theoretical Analysis (1)

Construction Control (Field Verification) (2) Driving Resistance Factor for Construction Driving Criteria

Basis PDA/

CAPWAP Planned Retap Test 3-Days After EOD

Static Pile

Load Test

Cohesive Mixed Non-Cohesive

Iowa DOT ENR

Formula

WEAP φ φEOD φSETUP φ φ

Iowa Blue Book

Yes 0.55

(6) 0.55 (6) 0.50 (6)

Yes (4) 0.65

(7) 0.20 (7) 0.65 (7) 0.55 (7)

Yes (4) Yes 0.70 0.65 0.55 Yes (4) Yes (5) 0.75 0.40 0.70 0.70 Yes (4) Yes (5) Yes 0.80 0.70 0.70 Yes (4) Yes 0.80 0.80 0.80

Table notes: (1) Use the geotechnical resistance charts (i.e. soil charts) to estimate the theoretical nominal pile

resistance for friction bearing. (2) Use the construction control specified on the plans. Except in unusual cases the construction

control for state projects will be WEAP. (3) These resistance factors are for redundant pile groups, which the office defines as five piles

minimum except four piles minimum for abutments. (4) Use the Blue Book soil input procedure to complete WEAP analyses. (5) Use signal matching to determine nominal driving resistance. (6) Based on historic timber pile test data, reduce the resistance factor to 0.35 for redundant groups

of timber pile if the Iowa DOT ENR formula (modified for LRFD) is used for construction control. (7) For redundant groups of timber pile, reduce the resistance factor to 0.40 without increase for

setup if WEAP is used for construction control.

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Appendix E. Fundamental Relationships Pile design is concerned primarily with three aspects:

• Structural resistance • Geotechnical resistance • Target driving resistance

The focus of this training manual is on geotechnical resistance and target driving resistance since the structural resistance of the piles is handled implicitly in the H- and J-standard plans. Geotechnical resistance is concerned with determining the pile contract length needed so that the combination of friction and end bearing can resist the pile load. Target driving resistance is concerned with establishing the amount of pile capacity the contractor needs to achieve in the field at the end of drive. Structural Resistance

When using the J- and H-standard plans the structural resistance of the piles is handled implicitly in the standards primarily by limiting the following:

• Total bridge length and end span length • Individual pile axial load • Unsupported pile height

Geotechnical Resistance

φRn ≥ ΣηγQ + (γDD)*(DD) where:

φ = geotechnical resistance factor for friction and end bearing based on site soil category and method of construction control.

Rn = nominal geotechnical resistance determined from unit values for friction and/or end bearing.

ΣηγQ = Pu = total factored axial compression load per pile for a strength limit state. The load typically consists of factored dead and live load. The Pu value on the H-standard plans is the axial load per pile. For the J-standard plans, Pu needs to be divided by the number of piles in order to get the load per pile.

γDD = downdrag load factor = 1.0 DD = downdrag load. The load is determined from the friction bearing values when

downdrag is present. If there is no downdrag this term is taken as zero. Note that for Tee piers in the H-standards the geotechnical capacity of a pile must be able to resist a certain amount of uplift. Normally this should be relatively easy to achieve, but situations involving shallow bedrock and/or excessive scour could be problematic. The spreadsheet does not currently cover uplift resistance.

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Target Driving Resistance

Rndr-T ≥ [ΣηγQ + (γDD)*(DD)]/φTAR + RSCOUR where:

φTAR = target driving resistance factor for friction and end bearing based on site soil category and method of construction control.

Rndr-T = nominal target driving resistance at a defined time. Typically it is the target driving resistance at end-of-drive (EOD), but can also be defined as the target driving resistance for retaps in cohesive soils at 1-day, 3-days, or 7-days.

ΣηγQ = Pu = total factored axial compression load per pile for a strength limit state. The load typically consists of factored dead and live load. The Pu value on the H-standard plans is the axial load per pile. For the J-standard plans, Pu needs to be divided by the number of piles in order to get the load per pile.

γDD = downdrag load factor = 1.0 DD = downdrag load. The load is determined from the friction bearing values when

downdrag is present. If there is no downdrag this term is taken as zero. RSCOUR = nominal friction resistance for the soil that is subject to scour determined from

unit values for friction. Target Driving Resistance for H-piles in Cohesive Soil with Setup using WEAP The relationship to determine target driving resistance at EOD for H-piles with consideration of setup in cohesive soil and WEAP construction control is as follows:

Rndr-EOD ≥ [ΣηγQ + (γDD)*(DD)]/φTAR + RSCOUR where:

φTAR = φEOD + φSETUP*(FSETUP-7 - 1) < 1.0 φEOD and φSETUP values are provided in the spreadsheet, but can also be found in BDM

Table 6.2.9-3. FSETUP-7 is taken from the 7-day curve shown below based on the average SPT N60-

value, Na.

If target driving resistance at EOD for H-piles is not reached and retaps are relied upon to verify capacity, then the following target driving resistances are required to be met depending on the number of days from EOD to retap.

Rndr-1 for retap at one day is the smaller of: [ΣηγQ + (γDD)*(DD)]/φEOD + RSCOUR

and (Rndr-EOD)*(FSETUP-1) where FSETUP-1 is taken from the 1-day curve below

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Rndr-3 for retap at three days is the smaller of: [ΣηγQ + (γDD)*(DD)]/φEOD + RSCOUR

and (Rndr-EOD)*(FSETUP-3) where FSETUP-3 is taken from the 3-day curve below

Rndr-7 for retap at seven days is the smaller of:

[ΣηγQ + (γDD)*(DD)]/φEOD + RSCOUR and

(Rndr-EOD)*(FSETUP-7) where FSETUP-7 is taken from the 7-day curve below

The average SPT N60-value (Na) to use in the chart is determined as follows:

𝑁𝑁𝑎𝑎 =∑ 𝑁𝑁𝑖𝑖𝑙𝑙𝑖𝑖𝑛𝑛𝑖𝑖=1∑ 𝑙𝑙𝑖𝑖𝑛𝑛𝑖𝑖=1

where:

N = N60-value for cohesive soil layer in contact with pile l = thickness of cohesive soil layer in contact with pile

The designer should use the setup chart with caution for a soft clay layer with an SPT N60-value less than 5 (the shaded region of the chart or with undrained shear strength (Su) less than 1.04 ksf.

Page 59

Appendix F. Plan Notes for Piling Notes E177, E718, E719, E818, E819 are listed below. Note E177 is provided for information only as this note is no longer required. E177: Driven piles, service to LRFD comparison (E177 IS NO LONGER REQUIRED)

THIS PROJECT USES THE LOAD AND RESISTANCE FACTOR DESIGN (LRFD) METHODOLOGY FOR DETERMINING PILE CONTRACT LENGTH AND NOMINAL AXIAL BEARING RESISTANCE. NOMINAL AXIAL BEARING RESISTANCES WILL BE LARGER THAN BEARING VALUES IN THE PAST, BUT CONSTRUCTION CONTROL BLOW COUNTS WILL BE APPROXIMATELY THE SAME. ___ THAT GIVES THE RELATIONSHIP BETWEEN REQUIRED NOMINAL AXIAL BEARING RESISTANCE AND BLOW COUNT. FOR THE CONTRACTOR’S BIDDING PURPOSES, PARTICULARLY FOR THE SIZING OF THE PILE DRIVING HAMMER, THE APPROXIMATE PREVIOUS DESIGN METHODOLOGY BEARING VALUES AT END OF DRIVE (EOD) ARE GIVEN BELOW. THESE VALUES SHALL NOT BE USED FOR CONSTRUCTION CONTROL AND ARE GIVEN ONLY FOR COMPARATIVE PURPOSES.

• THE PREVIOUS DESIGN BEARING FOR THE ___ ABUTMENT PILES WOULD HAVE BEEN

ABOUT ___ TONS. • THE PREVIOUS DESIGN BEARING FOR THE PIER ___ PILES WOULD HAVE BEEN ABOUT

___ TONS. • THE PREVIOUS DESIGN BEARING FOR THE PIER ___ PILES WOULD HAVE BEEN ABOUT

___ TONS. • THE PREVIOUS DESIGN BEARING FOR THE ___ ABUTMENT PILES WOULD HAVE BEEN

ABOUT ___ TONS.

This note shall be added to the general notes for all projects that use the new ISU-calibrated LRFD pile methodology.

(1) In the first paragraph fill in the blank for the office, agency, or consultant that will be preparing

the construction control documents or substitute for the sentence. • For typical state projects fill in the blank with the following: A WEAP ANALYSIS AND

BEARING GRAPH WILL BE PREPARED BY THE OFFICE OF CONSTRUCTION. • For projects with Iowa DOT ENR Formula control fill in the blank with the following: ___

WILL MANAGE CONSTRUCTION CONTROL WITH THE IOWA DOT ENR FORMULA and fill in the local agency or consultant.

• For projects that use PDA/CAPWAP substitute the following for the entire sentence: A WEAP ANALYSIS AND BEARING GRAPH WILL BE PREPARED BY THE OFFICE OF CONSTRUCTION THAT GIVES THE RELATIONSHIP BETWEEN REQUIRED NOMINAL AXIAL BEARING RESISTANCE AND BLOW COUNT. PDA AND CAPWAP ANALYSIS ALSO WILL BE MANAGED BY THE ___. Fill in the blank with either CONTRACTOR or OFFICE OF CONSTRUCTION.

• For other projects revise the sentence with the blank to describe the method of construction control.

(2) Revise the note appropriately for number of piers.

(3) Fill in the abutment and pier blanks. See the tables in the commentary for the pile section for

bearing values for typical pile types and conditions [BDM C6.2.4.6]. Because this note is giving previous allowable stress design values, add to the bearing value 50% of the target driving resistance for scour, if pile is designed for scour.

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E718: Pier piles, LRFD contract length and resistance

THE CONTRACT LENGTH OF ___ FEET FOR THE PIER ___ PILES IS BASED ON A ___ SOIL CLASSIFICATION, A TOTAL FACTORED AXIAL LOAD PER PILE (PU) OF ___ KIPS, AND A GEOTECHNICAL RESISTANCE FACTOR (PHI) OF ___ FOR SOIL AND ___ FOR ROCK END BEARING. TO ACCOUNT FOR SOIL CONSOLIDATION UNDER THE NEW FILL, THE FACTORED AXIAL LOAD INCLUDES A FACTORED DOWNDRAG LOAD OF ___ KIPS. PIER PILES ALSO WERE DESIGNED FOR A FACTORED TENSION FORCE OF ___ KIPS. THE NOMINAL AXIAL BEARING RESISTANCE FOR CONSTRUCTION CONTROL WAS DETERMINED FROM A ___ SOIL CLASSIFICATION AND A GEOTECHNICAL RESISTANCE FACTOR (PHI) OF ___ FOR SOIL AND ___ FOR ROCK END BEARING. PILES ARE ASSUMED TO BE DRIVEN FROM A START ELEVATION AT THE ___. DESIGN SCOUR (200-YEAR) WAS ASSUMED TO AFFECT THE UPPER ___ FEET OF EMBEDDED PILE LENGTH AND CAUSE ___ KIPS OF DRIVING RESISTANCE.

1. Fill in the contract length (ft). 2. Fill in pier number (1, 2…) or delete the blank if the note covers all piers. 3. Fill in soil classification for design (cohesive, mixed, or non-cohesive). 4. Fill in the total factored axial load per pile (Pu, kips). 5. Fill in the resistance factor (phi) for design in soil. If piles are to be driven to rock, add the

resistance factor (phi) for rock; otherwise, delete the end of the sentence beginning with “for”. If piles are designed for rock bearing alone, delete ___ FOR SOIL AND.

6. If piles are subject to downdrag, fill in the factored downdrag load (Pu, kips). 7. If piles were designed for tension, fill in the factored tension force; otherwise delete the

sentence. 8. Fill in soil classification for construction control (cohesive, mixed, or non-cohesive). 9. Fill in the resistance factor for construction control (phi). 10. Fill in location for start of pile driving (BOTTOM OF FOOTING for piers, BOTTOM OF

PREBORE if prebore is present, BOTTOM OF PILE ENCASEMENT for steel H-pile bents, PROPOSED GROUND ELEVATION or STREAMBED ELEVATION as appropriate for pipe and prestressed pile bents).

11. If piles were designed for scour, fill in the affected embedded length (ft); otherwise, delete the sentence.

12. Revise this note for special conditions not covered above. 13. For steel H-pile bents include the sentence below at the end of the 2nd paragraph. In general,

the optional start elevation for pile driving is assumed to be proposed ground elevation rather than existing ground elevation. IF THE CONTRACTOR ELECTS TO DRIVE PILES FROM A START ELEVATION OF ___ THEN AN ADDITIONAL EMBEDDED PILE LENGTH OF ___ FEET CAUSES ___ KIPS OF ADDITIONAL DRIVING RESISTANCE.

Modify notes 10 and 13 as necessary to fit special conditions.

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E719: Pier piles, LRFD driving and construction control THE REQUIRED NOMINAL AXIAL BEARING RESISTANCE FOR PIER ___ PILES IS ___ TONS AT END OF DRIVE. IF RETAPS ARE NECESSARY TO ACHIEVE BEARING THE REQUIRED NOMINAL AXIAL BEARING RESISTANCE IS ___ TONS AT ONE-DAY RETAP, ___ TONS AT THREE-DAY RETAP, OR ___ TONS AT SEVEN-DAY RETAP. THE PILE CONTRACT LENGTH SHALL BE DRIVEN AS PER PLAN UNLESS PILES REACH REFUSAL. IN NO CASE SHALL A PILE BE EMBEDDED LESS THAN ___ FEET. CONSTRUCTION CONTROL REQUIRES A WEAP ANALYSIS WITH BEARING GRAPH.

1. Fill in pier number (1, 2…) or delete the blank if the note covers all piers. 2. Fill in end of drive bearing (tons). 3. For cohesive sites with consideration of setup, fill in applicable retap blanks. If only one-day

retap is different, delete three-day and seven day-retap parts of the sentence. For cohesionless or mixed sites, piles driven to rock, or other cases with no difference in EOD and retap value, delete the retap sentence and add OR RETAP to the end of the first sentence.

4. If retap is specifically required for construction control, substitute the following sentence. • PILES SHALL BE RETAPPED AT ___ DAYS WITH A REQUIRED NOMINAL AXIAL

BEARING RESISTANCE OF ___ TONS. 5. For timber piles replace the contract length sentence with the following:

• THE PILE CONTRACT LENGTH SHALL BE DRIVEN AS PER PLAN UNLESS PILES REACH A DRIVING LIMIT OF 160 TONS.

6. If piles are subject to tension, scour, or other conditions requiring a minimum embedment length, fill in the length; otherwise delete the sentence.

7. Replace the construction control sentence if a method other than WEAP without planned retap is to be used. Alternate sentences are as follows: • CONSTRUCTION CONTROL REQUIRES AN IOWA DOT ENR FORMULA. • CONSTRUCTION CONTROL REQUIRES PDA/CAPWAP AND A WEAP ANALYSIS

WITH BEARING GRAPH. • CONSTRUCTION CONTROL REQUIRES A WEAP ANALYSIS WITH BEARING GRAPH

AND A RETAP AT ___ DAYS AFTER EOD. 8. Revise this note for special conditions not covered above.

Page 62

E818: Abutment piles, LRFD contract length and resistance

THE CONTRACT LENGTH OF ___ FEET FOR THE ___ ABUTMENT PILES IS BASED ON A ___ SOIL CLASSIFICATION, A TOTAL FACTORED AXIAL LOAD PER PILE (PU) OF ___ KIPS, AND A GEOTECHNICAL RESISTANCE FACTOR (PHI) OF ___ FOR SOIL AND ___ FOR ROCK END BEARING. TO ACCOUNT FOR SOIL CONSOLIDATION UNDER THE NEW FILL, THE FACTORED AXIAL LOAD INCLUDES A FACTORED DOWNDRAG LOAD OF ___ KIPS. ABUTMENT PILES ALSO WERE DESIGNED FOR A FACTORED TENSION FORCE OF ___ KIPS. THE NOMINAL AXIAL BEARING RESISTANCE FOR CONSTRUCTION CONTROL WAS DETERMINED FROM A ___ SOIL CLASSIFICATION AND A GEOTECHNICAL RESISTANCE FACTOR (PHI) OF ___ FOR SOIL AND ___ FOR ROCK END BEARING. PILES ARE ASSUMED TO BE DRIVEN FROM A START ELEVATION AT THE BOTTOM OF ___. DESIGN SCOUR (100-YEAR) WAS ASSUMED TO AFFECT THE UPPER ___ FEET OF EMBEDDED PILE LENGTH AND CAUSE ___ KIPS OF DRIVING RESISTANCE.

1. Fill in the contract length (ft). 2. Fill in abutment location (north, east, south, or west) or delete the blank if the note covers both

abutments. 3. Fill in soil classification for design (cohesive, mixed, or non-cohesive). 4. Fill in the total factored axial load per pile (Pu, kips). 5. Fill in the resistance factor (phi) for design in soil. If piles are to be driven to rock, add the

resistance factor (phi) for rock; otherwise, delete the end of the sentence beginning with “FOR”. If piles are designed for rock bearing alone, delete ___ FOR SOIL AND.

6. If piles are subject to downdrag, fill in the factored downdrag load (Pu, kips). 7. If piles were designed for tension, fill in the factored tension force; otherwise delete the

sentence. 8. Fill in soil classification for construction control (cohesive, mixed, or non-cohesive). 9. Fill in the resistance factor for construction control (phi). 10. Fill in location for start of pile driving (FOOTING for abutments with no prebore, PREBORE if

prebore is present). 11. If piles were designed for scour, fill in the affected embedded length (ft); otherwise, delete the

sentence. 12. Revise this note for special conditions not covered above.

Page 63

E819: Abutment piles, LRFD driving and construction control THE REQUIRED NOMINAL AXIAL BEARING RESISTANCE FOR ___ ABUTMENT PILES IS ___ TONS AT END OF DRIVE. IF RETAPS ARE NECESSARY TO ACHIEVE BEARING, THE REQUIRED NOMINAL AXIAL BEARING RESISTANCE IS ___ TONS AT ONE-DAY RETAP, ___ TONS AT THREE-DAY RETAP, OR ___ TONS AT SEVEN-DAY RETAP. THE PILE CONTRACT LENGTH SHALL BE DRIVEN AS PER PLAN UNLESS PILES REACH REFUSAL. IN NO CASE SHALL A PILE BE EMBEDDED LESS THAN ___ FEET. CONSTRUCTION CONTROL REQUIRES A WEAP ANALYSIS WITH BEARING GRAPH.

1. Fill in abutment location (north, east, south, or west) or delete the blank if the note covers both

abutments. 2. Fill in end of drive bearing (tons). 3. For cohesive sites with consideration of setup, fill in applicable retap blanks. If only one-day

retap is different, delete three-day and seven day-retap parts of the sentence. For cohesionless or mixed sites, piles driven to rock, or other cases with no difference in EOD and retap value, delete the retap sentence and add OR RETAP to the end of the first sentence.

4. If retap is specifically required for construction control, substitute the following sentence: • PILES SHALL BE RETAPPED AT ___ DAYS WITH A REQUIRED NOMINAL AXIAL

BEARING RESISTANCE OF ___ TONS. 5. For timber piles, replace the contract length sentence with the following:

• THE PILE CONTRACT LENGTH SHALL BE DRIVEN AS PER PLAN UNLESS PILES REACH A DRIVING LIMIT OF 160 TONS.

6. If piles are subject to tension, scour, or other condition requiring a minimum embedment length, fill in the length (ft); otherwise, delete the sentence.

7. Replace the construction control sentence if a method other than WEAP without planned retap is to be used. Alternate sentences are as follows: • CONSTRUCTION CONTROL REQUIRES AN IOWA DOT ENR FORMULA. • CONSTRUCTION CONTROL REQUIRES PDA/CAPWAP AND A WEAP ANALYSIS

WITH BEARING GRAPH. • CONSTRUCTION CONTROL REQUIRES A WEAP ANALYSIS WITH BEARING GRAPH

AND A RETAP AT ___ DAYS AFTER EOD. 8. Revise this note for special conditions not covered above.

Page 64

Appendix G. Hand Calculations for County Problem 1A, 1B, 2, and 3

County Problem 1A Estimate Pile Contract Length Factored pile load, Pu = 92.3 k Bottom of prebore elevation = 923 Generalized soil category = cohesive Geotechnical design resistance factor = 0.60

Layer Type Pile Length Factored Pile Resistance Prebore 10’ Silty Sand, Friction 923 – 917 = 6’ (1.2 klf)*(6’)*(0.60) = 4.32 k Firm Glacial Clay, Friction 917 – 907 = 10’ (2.8 klf)*(10’)*(0.60) = 16.8 k Very Firm Gl. Clay, End Brg (1 ksi)*(12.40 in2)*(0.60) = 7.44 k Cumulative pile length = 10’ + 6’ + 10’ = 26’ Cumulative factored pile resistance = 4.32 k + 16.8 k + 7.44 k = 28.56 k Remaining pile capacity needed = 92.3 k – 28.56 k = 63.74 k Remaining pile length needed in Very Firm Glacial Clay, Friction = (63.74 k) / [(4.0 klf)*(0.60)] = 26.56’

Total pile length required = 26’ + 26.56’ + 2’ cap embed + 1’ cutoff = 55.56’ % of cohesive soil in contact with the pile = 100*(10’ + 26.56’)/(10’ + 26.56’ + 6’) = 85.9% Pile Length rounded to nearest 5’ = 55’ User chose to use a pile contract length of 60’. Estimate Target Nominal Pile Driving Resistance (Construction Stage), Rndr-T Generalized soil category = cohesive Geotechnical construction control resistance factor, φTAR = 0.55 % of cohesive soil in contact with the pile = 100*(10’ + 31’)/(10’ + 31’ + 6’) = 87.2% Rndr-T = [ΣηγQ + (γDD)*(DD)]/φTAR + RSCOUR

ΣηγQ = Pu = 92.3 k Rndr-T = (92.3 k + 0 k)/(0.55) + 0 k = 167.82 k = 84 tons

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County Problem 1B Estimate Pile Contract Length Factored pile load, Pu = 92.3 k Bottom of prebore elevation = 923 Generalized soil category = cohesive Geotechnical design resistance factor = 0.65

Layer Type Pile Length Factored Pile Resistance Prebore 10’ Silty Sand, Friction 923 – 917 = 6’ (1.2 klf)*(6’)*(0.65) = 4.68 k Firm Glacial Clay, Friction 917 – 907 = 10’ (2.8 klf)*(10’)*(0.65) = 18.2 k Very Firm Gl. Clay, End Brg (1 ksi)*(12.40 in2)*(0.65) = 8.06 k Cumulative pile length = 10’ + 6’ + 10’ = 26’ Cumulative factored pile resistance = 4.68 k + 18.2 k + 8.06 k = 30.94 k Remaining pile capacity needed = 92.3 k – 30.94 k = 61.36 k Remaining pile length needed in Very Firm Glacial Clay, Friction = (61.36 k) / [(4.0 klf)*(0.65)] = 23.6’

Total pile length required = 26’ + 23.6’ + 2’ cap embed + 1’ cutoff = 52.6’ % of cohesive soil in contact with the pile = 100*(10’ + 23.6’)/(10’ + 23.6’ + 6’) = 84.8% Pile length rounded to nearest 5’ = 55’ User chose to use a pile contract length of 55’. Estimate Target Nominal Pile Driving Resistance (Construction Stage), Rndr-T Generalized soil category = cohesive, consider setup in cohesive soil Geotechnical construction control resistance factors, φEOD = 0.65 and φsetup = 0.20 % of cohesive soil in contact with the pile = 100*(10’ + 26’)/(10’ + 26’ + 6’) = 85.7% Avg. N or Na for cohesive soil along pile = [(10’)*(12 blows/ft) + (26’)*(20 blows/ft)]/(36’) = 17.78 blows/ft By graph, FSETUP for 7 day = 1.57 for average N of 17.78 blows/ft By equation, FSETUP = RT/REOD = {[(a)*(log10(t/tEOD))/(Na)b] + 1}*(L/LEOD)

= {[(0.215)*(log10(10,080 min)/(1 min))/(17.78)0.144] + 1}*(1) = 1.57 Target resistance factor, φTAR = 0.65 + (0.20)*(1.57 – 1.00) = 0.764 Target nominal pile driving resistance, Rndr-T = REOD = (92.3 k)/(0.764) = 120.85 k = 60 tons Minimum retap resistance required = (92.3 k)/(0.65) = 142 k = 71 tons

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County Problem 2 Estimate Pile Contract Length Factored pile load, Pu = 135 k Bottom of prebore elevation = 918 Generalized soil category = cohesive with bedrock penetration Geotechnical friction design resistance factor = 0.65 Geotechnical end bearing design resistance factor = 0.70

Layer Type Pile Length Factored Pile Resistance Prebore 15’ Soft Silty Clay, Downdrag 918 – 903 = 15’ (-0.8 klf)*(15’)*(1.00) = -12.0 k Firm Silty Clay, Friction 903 – 888 = 15’ (2.0 klf)*(15’)*(0.65) = 19.5 k Very Firm Gl. Clay, Friction 888 – 873 = 15’ (4.0 klf)*(15’)*(0.65) = 39.0 k Hard Shale, End Brg. (12 ksi)*(16.7 in2)*(0.70) = 140.28 k Cumulative pile length = 15’ + 15’ + 15’ + 15’ = 60’ Cumulative factored pile resistance = -12.0 k + 19.5 k + 39.0 k + 140.28 k = 186.78 k > Pu = 135 k

Total pile length required = 60’ + 2’ cap embed + 1’ cutoff = 63’ % of cohesive soil in contact with the pile = 100% Pile length rounded to nearest 5’ = 65’ Add 6’ to pile length for recommended penetration into hard shale = 63’ + 6’ = 69’ User chose to use a pile contract length of 70’. Estimate Target Nominal Pile Driving Resistance (Construction Stage), Rndr-T Generalized soil category = cohesive with bedrock penetration Since pile extends to bedrock and has downdrag, we will neglect setup in the cohesive soil. Geotechnical construction control friction resistance factor = 0.65 Geotechnical construction control end bearing resistance factor = 0.70 % of cohesive soil in contact with the pile = 100% Total load = Pu + γDD*DD = 135 k + (1.00)*(12 k) = 147.0 k Friction resistance during driving = (0.65)*(12.0 k + 30.0 k + 60.0 k) = 66.3 k End bearing resistance required during driving = 147.0 k – 66.3 k = 80.7 k Percent of load resisted by friction = (66.3 k)/(147.0 k) = 0.45 Percent of load resisted in end bearing = (80.7 k)/(147.0 k) = 0.55 Rndr-T = [ΣηγQ + (γDD)*(DD)]/φTAR + RSdd,EOD Rndr-T = [(147.0 k)/(0.45*0.65 + 0.55*0.70)] + 12.0 k = 229.0 k = 114.5 tons

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County Problem 3 Estimate Pile Contract Length Factored pile load, Pu = 168 k Bottom of pile encasement elevation = 915 Generalized soil category = non-cohesive Geotechnical design resistance factor = 0.55

Layer Type Pile Length Factored Pile Resistance Scour 915 – 909 = 6’ Fine Sand, Friction 909 – 896 = 13’ (2.80 klf)*(13’)*(0.55) = 20.02 k Cumulative pile length = 6’ + 13’ = 19’ Cumulative factored pile resistance = 20.02 k Remaining pile capacity needed = 168 k – 20.02 k = 147.98 k Remaining pile length needed in Coarse Sand, Friction = (147.98 k) / [(3.6 klf)*(0.55)] = 74.7’

Total pile length required = 19’ + 74.7’ + 19.5’ cap embed + 1’ cutoff = 114.2’ % of non-cohesive soil in contact with the pile = 100% Pile length rounded to nearest 5’ = 115’ User chose to use a pile contract length of 115’. Estimate Target Nominal Pile Driving Resistance (Construction Stage), Rndr-T Generalized soil category = non-cohesive Target geotechnical driving resistance factor, φTAR = 0.55 % of non-cohesive soil in contact with the pile = 100% Rndr-T = [ΣηγQ + (γDD)*(DD)]/φTAR + RSCOUR

ΣηγQ = Pu = 168 k Rscour = (1.20 klf)*(2’) + (2.80 klf)*(4’) = 13.6 k

Rndr-T = (168 k + 0 k)/(0.55) + 13.6 k = 319.05 k = 160 tons

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Appendix H. Frequently Asked Questions 1.) How come the buttons in the Excel Spreadsheet are not functioning? Answer 1

If the buttons (macros) on the Excel sheet do not function, the issue usually has to do with the Macro Settings in Excel. The Macro Settings window (Figure 1) below can be found under File/Microsoft Office Button Options Trust Center Trust Center Settings… If the first option is selected then you cannot run any macros in the spreadsheet. If the second option is selected you may get the security warning shown in Figure 2. If you click Enable Content, then the macros/buttons should function. If you select the last option in Figure 1 then all macros are automatically enabled including any that may run automatically when you open a spreadsheet.

Figure 1

Figure 2

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Answer 2 Occasionally Microsoft releases software security updates that can affect the functioning of the macros. Earlier in 2015, IDOT incorporated a Microsoft security update that disabled macro functionality in our MS Office software. The fix for this particular issue involved deleting files with an “exd” extension as shown below.

C:\Users\[user.name]\AppData\Local\Temp\Excel8.0\MSForms.exd

C:\Users\[user.name]\AppData\Local\Temp\VBE\MSForms.exd

C:\Users\[user.name]\AppData\Local\Temp\Word8.0\MSForms.exd

2.) When I click a Button in the Excel Spreadsheet I get an error something like the one shown in Figure 3 below. When I click the Debug button, a window pops open (Figure 4) with some text high-lighted in yellow. What’s going on?

This spreadsheet uses a built-in programming language called Visual Basic for Applications (vba). Macros are run by vba code. The errors below are generated when the vba code runs into an issue. There are a few reasons an error can occur. The user may have input a value into the spreadsheet that doesn’t make sense. The user may have moved or deleted cells that are used by the vba code. There may be a flaw in the programming logic that needs to be corrected. Whatever the case you can email Michael Nop for assistance.

Figure 3

Figure 4

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3.) How do I view the vba code inside the spreadsheet? In order to view the code you need to open the Developer tab and click on the Visual Basic button. In general, the Developer tab is not available by default. In order to add it to the ribbon, you need to click on File/Microsoft Office Button Options Customize Ribbon and then check the box for Developer as shown in Figure 6.

Figure 5

Figure 6

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4.) The new LRFD Iowa DOT Modified ENR formulas seem to indicate that some piles may reach bearing sooner than they did in the past. Does this make sense or am I doing something wrong?

The text below, with some modification, describes the concern expressed by some counties and the response provided by the ISU research team. The ISU research team response is given first.

ISU research team response: We have gone back and checked a few things. In summary we are not concerned with the LRFD Iowa DOT Modified ENR formula requiring a shorter pile length. What this means is that pile designed according to this method will have lower safety factor than in the past, but it will still meet the target reliability as per AASHTO. I understand that when you run into this situation, one needs to be cautious. If a county is still concerned about this, they could also use WEAP in addition to the LRFD Iowa DOT Modified ENR formula for a few piles to make sure we all feel comfortable with the reduced pile length. I would be more cautious when you are dealing with piles other than steel H piles because the available data came mostly from this pile type. Varying the pile capacity using WEAP is also more important for other pile types for the same reason. More details and other answers: 1) The SASD/SLRFD ratio should not be expected to be equal to 1 because the resistance factors

for the Iowa ENR formula were determined using the statistical-based method (FOSM) not by fitting to ASD approach as with the interim method. This also indicated that we will end up with a reduced factor of safety (FS) if one still wants to think in terms of FS. Section 6.3.7 and Table 6.21 of the LRFD report volume III provide FS values for LRFD and related discussion noting that LRFD FS is typically less than the FS used in ASD.

2) Based on your calculations below, the construction control of steel piles based on the LRFD approach will achieve the target resistance sooner than that based on ASD approach. This is consistent with information presented in (1).

3) The resistance factors calibrated for Iowa ENR formula (0.5 for sand; 0.55 for clay or mixed) are relatively higher than that recommended by the AASHTO for the ordinary ENR formula (0.1) and Gates Formula (0.4). If you recall, this research outcome satisfied the needs of Iowa county engineers of a) continuously using Dynamic Formula in their practices, b) avoiding a smaller resistance factor recommended by AASHTO, and c) satisfying the LRFD requirements. This statement taken from report III-the last paragraph on page 181: “Overall, this degree of conservatism associated with the LRFD is relatively low compared to the conventional ASD approach and its factor of safety” is validated by your example. Therefore, this example just demonstrates the expected outcomes of the research.

Description: A county is concerned that the new LRFD Iowa DOT Modified ENR Formula yields less conservative results than the previous ASD Iowa DOT Modified ENR Formula. They want to be sure their assessment of the situation is accurate since they will be driving some piles this summer based on the LRFD system. Probably the best way to illustrate their concern is with a simple example based on Track 2, Example 1 from the modified pile design guide that was developed.

See LRFD Pile Design Examples link at https://iowadot.gov/bridge/policy/06-02-00PileDesignExamplesLRFD.pdf

The pile driving formula can be found in the IDOT Standard Specifications 2501.03.M.2. http://www.iowadot.gov/erl/current/GS/content/2501.htm

https://iowadot.gov/bridge/policy/06-02-00PileDesignExamplesLRFD.pdf

https://iowadot.gov/bridge/policy/06-02-00PileDesignExamplesLRFD.pdf

http://www.iowadot.gov/erl/current/GS/content/2501.htm

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LRFD Procedure This example assumes the following:

• Pu = 128 kips per pile is the Strength 1 factored load • φTAR = 0.55 for cohesive soil for IDOT LRFD ENR Formula (setup is neglected) • Rndr-T = 128 kips/0.55 = 233 kips = 117 tons • Diesel hammer with steel HP10x57 piles. LRFD Iowa DOT Modified ENR Formula P = [(12E)/(S+0.1)]*[W/(W+M)]

o Delmag D19-42 at fuel setting 2 or 3 o Ram weight, W = 2 tons o Hammer stroke, H = 7.5 feet o Pile + Cap +Anvil weight, M = 3.25 tons o Energy per blow, E = W*H = (2 tons)*(7.5’) = 15 foot*tons o Nominal bearing resistance, P = 117 tons o Average penetration in inches of the pile per blow, S

Solve for S: 117 tons = [(12)(15 foot*tons)/(S+0.1)]*[(2 tons)/(2 tons + 3.25 tons)] S = 0.486 inches per blow

ASD Procedure

• Average load factor to get from ASD to LRFD is generally assumed to be 1.45 • PASD = Pu/1.45 = (128 kips)/(1.45) = 88 kips = 44 tons • Diesel hammer with steel HP10x57 piles. IDOT ASD ENR Formula P = [(3E)/(S+0.1)]*[W/(W+M)]

o Delmag D19-42 at fuel setting 2 or 3 o Ram weight, W = 2 tons o Hammer stroke, H = 7.5 feet o Pile + Cap +Anvil weight, M = 3.25 tons o Energy per blow, E = W*H = (2 tons)*(7.5’) = 15 foot*tons o Bearing resistance, P = 44 tons o Average penetration in inches of the pile per blow, S

Solve for S: 44 tons = [(3)(15 foot*tons)/(S+0.1)]*[(2 tons)/(2 tons + 3.25 tons)] S = 0.290 inches per blow

Comments The county is concerned that the ASD procedure requires about half the distance per blow than the LRFD system which means the ASD system is more conservative. This can be illustrated by the following:

SASD/SLRFD = 0.290”/0.486” = 0.597 Should this be closer to 1.00 or is the LRFD calibration correct?

You can see where this comes from, in part, by doing the following:

(SLRFD + 0.1) = [4*(SASD + 0.1)] / [(1.45/0.55)] = 1.517*(SASD + 0.1) (SASD + 0.1) / (SLRFD + 0.1) = 0.659

The factor between the ASD and LRFD formula is 4. On the “load side” the factor is 1.45/0.55 = 2.636 for clay/mixed. [The resistance factor for piles in sand is lower (0.50) and for timber piles the resistance factor is even lower (0.35).] The denominator of the various ENR formulas consists

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of different adjustments of 0.1”, 0.2”, and 0.35” for different pile types and hammer types as shown in the IDOT Standard Specifications. The ISU LRFD calibration was only done for steel H piles, but essentially what we are saying for steel piles that use the LRFD Iowa DOT Modified ENR Formula is that piles will reach bearing sooner than they did under ASD. Is this statement correct and is this the expected outcome from the research? From Volume 3 of the ISU research reports in Section 6.3.7 this seems to be the case.

http://www.intrans.iastate.edu/reports/tr-584_lrfd_vol_iii_w_cvr.pdf Should the results from the research be applied to all the formulas in the IDOT Standard Specs as was done?

5.) Why does the generalized soil category sometimes differ between cell F98 when determining contract pile length and cell F159 when determining the target nominal pile driving resistance?

The basic reason that the generalized soil category can be different in the two cells is that the amount and type of soil in contact with the pile can change between the two situations. For example, when determining pile contract length it is conservative to ignore any resistance from scourable material. However, when considering target driving resistance the scourable material is conservatively assumed to be present since it increases the target driving resistance. So, in cases where a pile is hovering around the 70% mark for a generalized soil category of either cohesive or non-cohesive you could see a mixed soil for contract length and either a cohesive or non-cohesive soil for the target driving resistance or vice-versa. When this happens the designer can either accept the results or perhaps alter the results such that the generalized soil category with the lower resistance factors is used for both cases. Note also that in theory it is also possible to cycle between two generalized soil categories when determining contract pile length or target pile driving resistance. For example, let’s assume the designer is trying to determine contract pile length and that WEAP is being used for construction control.

• The designer initially assumes the soil category will be mixed and selects a resistance factor of 0.65 for the mixed soil to use in cells F54 and F55.

• The designer then clicks the button to estimate the contract pile length and the spreadsheet dutifully determines a pile length of 100’. However, the designer notices that the soil category in cell F98 is listed as non-cohesive rather than mixed.

• So, the designer goes back to cell F54 and F55 and changes the resistance factor to 0.55 for non-cohesive soil.

• After clicking the button again the designer notices that the pile length has increased to 110’, but the soil category is now mixed. Essentially the designer is stuck in a loop and cannot get the soil category to be consistent with the resistance factor chosen.

http://www.intrans.iastate.edu/reports/tr-584_lrfd_vol_iii_w_cvr.pdf

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In this case, the end of the pile is in cohesive soil so that as the pile lengthens from 100’ to 110’ the soil category changes from 70% non-cohesive to mixed. For a case like this it is probably a good idea to conservatively use a 110’ pile length and assume the soil category is non-cohesive. The designer will simply have to alter the notes put out by the spreadsheet.

6.) What is the significance of the warnings in cell J90?

The 4 possible warnings are: • Pile tip is 5’ or less from a contact layer. • Maximum possible factored pile resistance is insufficient to resist total factored

axial pile load. • Pile extends below bottom of soil boring. • Factored pile resistance is less than total factored axial load.

The first warning does not necessarily require any action. It simply alerts the designer that the pile may be too close to a layer boundary in order to rely on end bearing. For example, if a pile tips out in a soil with relatively high end bearing, but there is a much weaker layer below the pile tip and within 5’ of the pile tip then it is more likely that the pile could punch through the bearing layer into the weaker layer. Note that the warning is not issued when the pile tip is within 5’ of the bottom of the boring even though the same issue could be present. The second warning requires action. The likely cause of this warning is that the user entered incorrect or inconsistent friction and/or end bearing values in the soil table such that the spreadsheet cannot determine a contract pile length. See #1 and #2 from Appendix I for more information. The third warning does not necessarily require any action. The spreadsheet assumes the last soil layer entered extends infinitely downward. Obviously there is no soil information for any soil below the bottom of the boring. So, if the pile extends below the bottom of boring, then it is possible that the spreadsheet’s assumption is incorrect. The designer needs to decide whether deeper borings are required. The fourth warning could require action if the factored pile resistance is significantly less than the total factored axial load. This warning will typically appear when the user supplied contract length is rounded down to the nearest pile increment rather than up. Typically this is a conscious decision on the part of the designer and therefore the warning is ignored.

7.) What is setup and do I need to consider it when I have a cohesive soil?

Soil/pile set-up is a time-dependent increase in pile capacity after pile driving, which can contribute significantly to long-term pile capacity. The exact mechanism by which this

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occurs is not fully understood, but the majority of set-up is likely related to the dissipation of excess pore water pressures within cohesive soil that is displaced and disturbed as the pile is driven, and subsequent remolding and reconsolidation of that cohesive soil. In Iowa, consideration of setup is limited to steel H-piles with a cohesive soil category and WEAP as construction control. However, just because you meet these conditions does not mean that setup must be considered. In fact, it is conservative to ignore setup. In order to ignore setup the designer only needs to enter “N” in cell F113 and then enter a resistance factor of 0.65 for cohesive soil in cell F115. Note that the effect of setup is not taken advantage of in determining pile contract length. Currently setup is only taken advantage of in the target nominal pile driving resistance. Essentially accounting for setup yields a larger resistance factor which, in turn, produces a lower target pile driving resistance. This means pile driving operations could be ended earlier. The idea is that the pile will pick up the additional capacity needed due to the setup that occurs over time. Particular situations where the designer should ignore setup include:

• Accelerated bridge construction (ABC) projects where the time between driving pile and placing superstructure is less than 7 days.

• Piles subject to downdrag. • Projects where the pile is being driven to bedrock. • Additionally the designer needs to be cautious about using setup for soft clay

layers with an SPT N60-value less than 5 or with undrained shear strength (Su) less than 1.04 ksf.

8.) On the “PlanNotes” tab in the spreadsheet, it says that the “Factored Tension Force” and “Minimum Embedment” will not be filled in. Why doesn’t the spreadsheet fill these in and do I need to fill these in?

The spreadsheet does not fill these values in because it does not have the necessary information in order to fill them in. The designer needs to determine if these statements need to be included in the pile notes. If piles were designed for uplift, then the factored tension force should be filled in; otherwise the sentence can be deleted. Adequate friction resistance to resist uplift is most likely to be an issue where shallow bedrock exists since the pile length in contact with soil will be minimal. Scour can be a compounding factor. If piles are subject to tension, scour, or other condition requiring a minimum embedment length, then the length should be filled in; otherwise, the sentence can be deleted. One potential mode of pile failure due to inadequate pile embedment in the soil is due to fence-post action. In this case a pile is not embedded deeply enough into the soil in order to develop enough lateral soil resistance to resist the applied lateral pile loads.

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Appendix I. Common Mistakes to Avoid and Other Helpful Hints

1.) Enter Bottom of Boring Elevation in cell E18, but do not include it as an entry in the Soil

Table. Sometimes users enter the bottom of boring elevation in the Soil Entry Table without entering a friction resistance or nominal end bearing resistance value. If the user does this and the pile doesn’t develop enough resistance before the bottom of boring elevation then the pile will be unable to develop the resistance because the last entry is treated as an infinitely deep soil layer with no resistance. Ideally all soil borings would be deeper than the pile length required, however this is not always the case. A common approach in design is to assume the last layer of soil (and its resistance) extends downward indefinitely which generally assures the pile will develop enough capacity at some point. The designer must determine if this approach has merit for their particular project.

2.) This issue is related to #1. If the last entry in the Soil Entry Table only includes end bearing

resistance (i.e. no friction resistance), then it is possible that the pile may not be able to develop enough resistance to resist the pile load. In other words, if the end bearing resistance of the last layer combined with the friction resistance of any upper layers is not large enough to support the pile load then the spreadsheet will not be able to determine a pile length. This issue has come up a few times in the past. Typically it will occur for a shallow bedrock situation since any friction resistance from the soil is small and friction in bedrock is typically ignored. Usually the end bearing resistance in the rock entered by the designer is just below what is required to resist the pile load and so the spreadsheet can’t determine a pile length. Essentially the designer needs to determine if the end bearing in rock can be increased.

3.) In general, for pile driven to bedrock the designer needs to enter additional pile length for

minimum bedrock penetration in cell L59 before clicking the button to “Determine Factored

Do not enter bottom of boring elevation in the soil entry table.

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Pile Resistance”. When you click the button to “Estimate Pile Contract Length”, the spreadsheet determines the exact pile length needed to resist the load and no more. In cases where bedrock is present the pile typically terminates at the top of the bedrock layer because the end bearing resistance in bedrock is quite large and of course is assumed to be effective as soon as the pile enters that layer. In reality the quality of the bedrock is likely not uniform and seating of the pile in the bedrock is desirable. Additionally, the layer elevation of the bedrock is not likely to constant over the width or length of the bridge. The last tab in the spreadsheet, “BedrockDriving”, contains recommended H-pile penetration depths into bedrock as does Appendix C.

4.) Pile bents are typically the trickiest substructure type to handle in the spreadsheet. The Iowa

DOT, Construction and Materials Bureau has indicated that contractors will typically drive piles in one of two sequences.

a. Presumably the most common method is for the contractor to excavate the soil to the bottom of encasement before driving pile.

b. A second, less common method is for the contractor to drive pile first and then excavate the soil to the bottom of encasement.

Neither of the above procedures affects the determination of the pile contract length. However, the magnitude of the target driving resistance for the construction stage can be significantly affected if one or both of the following exists:

• The difference in soil elevation between a. and b. is significant • The soil that is eventually excavated is of relatively good quality.

More often than not the difference in elevation between a and b is not very significant and in general the soil is fairly weak (low blow count material) such that the target driving resistance would not differ much between sequence a and b For those cases where the difference is significant the designer needs to consider how to address the issue in the plan notes. Sequence (a) was covered in County Problem 3. Sequence (b) can also be dealt with in the spreadsheet. Appendix J contains a link to some videos that explain how this situation can be handled. The plan notes in Appendix F were modified on January 1, 2015 in order to address this issue. In reality the situation just mentioned would be very similar to driving pile in a stream that may or may not have soil scoured away. The target driving resistance would change depending on whether or not the scourable material is present or not. However, scourable material is usually a weak soil that does not have a large effect on driving resistance.

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Appendix J. Additional Resources The links below contain some general information on LRFD pile design that may be useful.

• The county bridge standards can be found here: https://iowadot.gov/bridge/Bridge-and-Culvert-Standards/County-Bridge-Standards

• The general form of the LRFD pile driving plan notes (E718, E719, E818, and E819) can be found here: http://www.iowadot.gov/bridge/policy/13-00-00CaddNoteLRFD.pdf. Some explanation/instruction is provided below each note. Scroll down the PDF document to find the notes. Note E177 is no longer required to be placed on the plans and has been deleted from the manual and pile design spreadsheets.

• Additional LRFD pile design examples may be found here: http://www.iowadot.gov/bridge/policy/06-02-00PileDesignExamplesLRFD.pdf

• The LRFD pile design spreadsheet applications may be found by scrolling down the web page to the “Iowa DOT Substructure Applications” at the following link: https://iowadot.gov/bridge/Automation-Tools/Final-Design-Software

• The following videos were developed for H-standard LRFD pile designs using a spreadsheet, but should also be helpful for other standard bridge types: https://iowadot.gov/bridge/Automation-Tools/-Video-Index

• The October 2012 LRFD pile design workshop material is available at: https://iowadot.gov/bridge/lrfdworkshop

• Finally, general LRFD pile design information can be found in the Iowa DOT Bridge Design Manual (BDM): https://iowadot.gov/bridge/Design-Policies/LRFDdesignmanual. BDM Section 6.2 addresses driven piles in particular: https://iowadot.gov/bridge/policy/06-02-00PileLRFD.pdf. The nominal geotechnical resistance charts for friction and end bearing can be found on pages 25 and 26.

https://iowadot.gov/bridge/Bridge-and-Culvert-Standards/County-Bridge-Standards

https://iowadot.gov/bridge/Bridge-and-Culvert-Standards/County-Bridge-Standards

http://www.iowadot.gov/bridge/policy/13-00-00CaddNoteLRFD.pdf

http://www.iowadot.gov/bridge/policy/06-02-00PileDesignExamplesLRFD.pdf

https://iowadot.gov/bridge/Automation-Tools/Final-Design-Software

https://iowadot.gov/bridge/Automation-Tools/-Video-Index

https://iowadot.gov/bridge/lrfdworkshop

https://iowadot.gov/bridge/Design-Policies/LRFDdesignmanual


Documents

IDOT Pile Design Guide