Hollow Core Bar Micropiles at Hollow Core Bar Micropiles at the New - - PowerPoint PPT Presentation

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Hollow Core Bar Micropiles at Hollow Core Bar Micropiles at the New - - PowerPoint PPT Presentation

Dec 11, 2023 212 likes •655 views

Hollow Core Bar Micropiles at Hollow Core Bar Micropiles at the New Jersey Turnpike the New Jersey Turnpike Dr. Jess Gmez, P.E. Dr. Jess Gmez, P.E. Outline Outline Project Overview Project Overview Micropile Characteristics

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SLIDE 1

Hollow Core Bar Micropiles at Hollow Core Bar Micropiles at the New Jersey Turnpike the New Jersey Turnpike

  • Dr. Jesús Gómez, P.E.
  • Dr. Jesús Gómez, P.E.
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SLIDE 2

Outline Outline

  • Project Overview

Project Overview

  • Micropile Characteristics

Micropile Characteristics

  • Verification Testing

Verification Testing

  • Proof Testing

Proof Testing

  • Interpretation of Load Tests

Interpretation of Load Tests

  • Interpreted Bond Values

Interpreted Bond Values

  • Conclusions

Conclusions

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SLIDE 3

Introduction Introduction

  • Project Owner: New Jersey Turnpike Authority

Project Owner: New Jersey Turnpike Authority

  • Structural Designer: Fay,

Structural Designer: Fay, Spofford Spofford & Thorndike & Thorndike (FST) (FST)

  • Geotechnical Engineer: Matrix

Geotechnical Engineer: Matrix

  • Inspection:

Inspection: Greenman Greenman-

  • Pedersen, Inc. (GPI)

Pedersen, Inc. (GPI)

  • Micropile Contractor: PKF Mark III

Micropile Contractor: PKF Mark III

  • Schnabel retained by PKF as Geostructural

Schnabel retained by PKF as Geostructural Consultants Consultants

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SLIDE 4

Location Location

Bridge 0.42L Bridge 7.85

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SLIDE 5

Location Location

Bridge 0.42L Bridge 7.85

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SLIDE 6

0.42 Bridge 0.42 Bridge

Bridge 0.42L Bridge 7.85

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SLIDE 7

Existing Conditions Existing Conditions

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SLIDE 8

Retrofit of Existing Foundation Retrofit of Existing Foundation

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SLIDE 9

Retrofit of Existing Foundation Retrofit of Existing Foundation

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SLIDE 10

Bridge 0.42L (180 Micropiles) Bridge 0.42L (180 Micropiles)

P3 P2 P1

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SLIDE 11

Bridge 7.85 (80 Micropiles) Bridge 7.85 (80 Micropiles)

P2 P1

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SLIDE 12

Geotechnical Conditions Geotechnical Conditions

  • Bridge 0.42L

Bridge 0.42L

  • Very Soft Organic Silt

Very Soft Organic Silt

  • Sand with Silt (Medium

Sand with Silt (Medium-

  • dense to Dense)

dense to Dense)

  • Sandy Clay (Stiff)

Sandy Clay (Stiff)

Bridge 7.85 Bridge 7.85

  • Very Soft Organic Silt

Very Soft Organic Silt

  • Silty Clay (Stiff)

Silty Clay (Stiff)

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SLIDE 13

Micropile Characteristics Micropile Characteristics

  • Design Load 80 kip

Design Load 80 kip

  • Self Drilling, Self Grouting Bar. IBO Titan Bar 52/26

Self Drilling, Self Grouting Bar. IBO Titan Bar 52/26 Fy Fy = 80 ksi = 80 ksi

  • 9 5/8 in O.D. casing, 0.5 in thickness,

9 5/8 in O.D. casing, 0.5 in thickness, Fy Fy = 50 ksi = 50 ksi

  • Top Connection 12” x 12” x 1.5” steel plate

Top Connection 12” x 12” x 1.5” steel plate Fy Fy = 50 = 50 ksi ksi

  • Grout Compressive Strength

Grout Compressive Strength f’c f’c = 4 ksi = 4 ksi

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SLIDE 14

Micropile Characteristics Micropile Characteristics

  • Bridge 0.42L

Bridge 0.42L Minimum Cased Length 35 ft Minimum Cased Length 35 ft Minimum Bond Length 30 ft Minimum Bond Length 30 ft Nominal Grout Body Diameter 6 in Nominal Grout Body Diameter 6 in

  • Bridge 7.85

Bridge 7.85 Minimum Cased Length 45 ft Minimum Cased Length 45 ft Minimum Bond Length 40 ft Minimum Bond Length 40 ft Nominal Grout Body Diameter 9 in Nominal Grout Body Diameter 9 in

  • Grout Mix

Grout Mix

  • Drilling grout, 10 gallons water per 1 bag of cement

Drilling grout, 10 gallons water per 1 bag of cement

  • Final grout, 5 gallons water per 1 bag of cement

Final grout, 5 gallons water per 1 bag of cement

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SLIDE 15
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SLIDE 16

Micropile Observation Micropile Observation

  • Drilling Logs

Drilling Logs

Drilling advance rate Drilling advance rate Grout pressure Grout pressure Total micropile depths Total micropile depths

  • Specific Gravity

Specific Gravity

1.45 to 1.60 for drilling grout 1.45 to 1.60 for drilling grout Minimum 1.8 for final grout Minimum 1.8 for final grout

  • Concrete Compressive Strength Test (Grout Cube

Concrete Compressive Strength Test (Grout Cube Samples) Samples)

  • Jack Transfusions

Jack Transfusions

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SLIDE 17
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SLIDE 18
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SLIDE 19
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SLIDE 20
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SLIDE 21
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SLIDE 22

Verification Testing Verification Testing

  • Two verification tests at each bridge

Two verification tests at each bridge

  • 2.5 DL

2.5 DL

  • One verification test failed at each bridge

One verification test failed at each bridge

  • From tests taken to failure:

From tests taken to failure:

  • Micropiles in medium dense sand (Bridge 0.42L) :

Micropiles in medium dense sand (Bridge 0.42L) : Load Transfer Ratio = 10 kip/ft (Bond Strength = 44 Load Transfer Ratio = 10 kip/ft (Bond Strength = 44 psi psi) )

  • Micropiles in stiff silty clay (Bridge 7.85):

Micropiles in stiff silty clay (Bridge 7.85): Load Transfer Ratio = 4.1 kip/ft (Bond Strength = 18 Load Transfer Ratio = 4.1 kip/ft (Bond Strength = 18 psi psi) )

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SLIDE 23

Proof Load Testing Proof Load Testing

  • 100% of micropiles satisfactorily proof load tested

100% of micropiles satisfactorily proof load tested

  • Maximum proof load test limited by existing bridge

Maximum proof load test limited by existing bridge structure structure

  • 1.25 to 1.5 DL

1.25 to 1.5 DL

  • 12

12-

  • hour load hold under DL

hour load hold under DL

  • Tested groups of 6 and 8 micropiles

Tested groups of 6 and 8 micropiles

  • Four to six sacrificial flat jacks per group

Four to six sacrificial flat jacks per group

  • Lock off at 0.5 DL

Lock off at 0.5 DL

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SLIDE 24
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SLIDE 25
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SLIDE 26
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SLIDE 27
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SLIDE 28
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SLIDE 29

Proof Load Testing Proof Load Testing

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SLIDE 30

Proof Test Summary Proof Test Summary-

  • Sand

Sand

0.0 0.1 0.2 0.3 10 20 30 40 50 60 70 80 90 100 110 120 Load (kip) Deflection (in)

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SLIDE 31

Proof Test Summary Proof Test Summary-

  • Clay

Clay

0.0 0.1 0.2 0.3 0.4 0.5 20 40 60 80 100 120 Load (kip) Deflection (in)

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SLIDE 32

Load Test Interpretation Load Test Interpretation

τ α ∆s

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SLIDE 33

Load Test Interpretation Load Test Interpretation

Axial Load

b b be be

P EA L ∆ Σ ⋅ = δ 2

be b

L P a =

Pb ∆Pb δbe

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SLIDE 34

Load Test Interpretation Load Test Interpretation

  • Applied elastic length concept to calculate ultimate bond in

Applied elastic length concept to calculate ultimate bond in failed tests failed tests

  • Compared to measured average bond values

Compared to measured average bond values

  • In medium dense sand:

In medium dense sand: 12.4 kip/ft vs. 10 kip/ft measured 12.4 kip/ft vs. 10 kip/ft measured

  • In stiff silty clay:

In stiff silty clay: 5.9 kip/ft vs. 4.1 kip/ft (measured) 5.9 kip/ft vs. 4.1 kip/ft (measured)

  • The elastic length concept yielded reasonably accurate

The elastic length concept yielded reasonably accurate values of bond values of bond

  • Applied this concept to 260 proof tests

Applied this concept to 260 proof tests

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SLIDE 35

Bond Values in Medium Dense Sand Bond Values in Medium Dense Sand

5 10 15 20 25 30 4 6 8 10 12 14 16 18 20 More Load Transfer Ratio (kip/ft) Number of Micropiles

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SLIDE 36

Bond Values in Stiff Silty Clay Bond Values in Stiff Silty Clay

2 4 6 8 10 12 14 2 4 6 8 10 12 14 16 18 20 Load Transfer Ratio (kip/ft) Number of Micropiles

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SLIDE 37

Bond Values in Stiff Silty Clay Bond Values in Stiff Silty Clay

10 – 28 psi 9 - 27 psi Stiff Silty Clay 10 – 28 psi 27 – 53 psi Medium Dense Sand Bond Strength Suggested By FHWA Type B micropile Mobilized Bond Strength in Proof Tests Soil Type

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SLIDE 38

Closure Closure

  • Ultimate bond strength of hollow core bar micropiles

Ultimate bond strength of hollow core bar micropiles in sand significantly larger than typical design values in sand significantly larger than typical design values

  • In stiff silty clay, ultimate bond strength values similar

In stiff silty clay, ultimate bond strength values similar to typical design values to typical design values

  • Bond values from this work may be used as guidance

Bond values from this work may be used as guidance for preliminary design for preliminary design

  • Two more bridges and an additional 144 micropiles to

Two more bridges and an additional 144 micropiles to be proof tested be proof tested

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SLIDE 39

THANK YOU THANK YOU

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SLIDE 40
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SLIDE 41
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SLIDE 42

Verification Tests in Sand Verification Tests in Sand

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SLIDE 43

Verification Tests in Clay Verification Tests in Clay