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Division of Layne Christensen Company

Specialty Foundation ConstructionSpecialty Foundation Construction

Jet GroutingJet GroutingDrilled MicropilesDrilled MicropilesVibratory Ground Improvement & Stone ColumnsVibratory Ground Improvement & Stone ColumnsConstruction Drilling, Grouting & AnchorsConstruction Drilling, Grouting & Anchors

Central Artery / Tunnel ProjectCentral Artery / Tunnel ProjectContract C09C1Contract C09C1

US Interstate 90 & Interstate 93 InterchangeUS Interstate 90 & Interstate 93 InterchangeBoston, MassachusettsBoston, Massachusetts

Presented By: Pier Luigi Iovino, Division PresidentPresented By: Pier Luigi Iovino, Division President

APPLICATIONS…APPLICATIONS…

Temporary ConditionTemporary Condition Underpinning support of an abutment 22 drilled micropiles installed

Permanent Foundation SupportPermanent Foundation Support Support for new bridge foundation 90 drilled micropiles installed

Design ApplicationsDesign Applications

INSTALLATION TECHNIQUES…INSTALLATION TECHNIQUES…

Drilled micropiles were steel reinforced and cement grouted with a minimum rock socket diameter of 8-inches.

Rotary drilling technique utilized, with a permanent 5.5-inch O.D. steel casing connected to a 7-7/8-inch O.D. drill bit.

Design ApplicationsDesign Applications

Design ApplicationsDesign Applications

SIGNIFICANCE…SIGNIFICANCE…

Central Artery/Tunnel (CA/T) project is funded through the US Federal Highway Administration (FHWA).

Drilled micropiles are newly accepted method in US.

Drilled micropiles used as permanent bridge foundation component for FHWA funded project.

de facto acceptance of drilled micropiles as viable solution.

Design ConsiderationsDesign Considerations

THREE COMPONENTS…THREE COMPONENTS…

Threaded casing test results tension; compression and bending

Structural / Seismic

Geotechnical

Temporary ConditionTemporary Condition

Temporary ConditionTemporary Condition

STRUCTURAL CONSIDERATIONS…STRUCTURAL CONSIDERATIONS…

Pile Capacity = 67 tons / 134 kips.

Pile Diameter = 8 inches

Allowable design compressive stress of grout = 4,000 x 0.33 psi.

Temporary ConditionTemporary Condition

GEOTECHNICAL CONSIDERATIONS…GEOTECHNICAL CONSIDERATIONS…

Bearing stratum in bedrock.

Allowable friction stress in bedrock = 45 psi. Length of rock socket =

134 x 1000/(8 x 3.14 x 45 x 12) = 9.87 feet

Pile lengths to be 100 to 135 feet with 10 feet into bedrock.

Installation of Drilled MicropilesInstallation of Drilled Micropilesfor Temporary Underpinning of Abutmentfor Temporary Underpinning of Abutment

Drilled piles were installed in low headroom as part of a value Drilled piles were installed in low headroom as part of a value engineered proposal replacing contract design of driven piles. engineered proposal replacing contract design of driven piles.

Permanent Foundation SupportPermanent Foundation Support

Permanent Foundation SupportPermanent Foundation Support

STRUCTURAL CONSIDERATIONS…STRUCTURAL CONSIDERATIONS…

Pile Capacity = 100 tons / 80 kips. Pile Lateral Capacity = 2 kips.

Pile Diameter = 9 inches. Steel pipe to be 7 inches diameter, O.D. t=0.5” N-80

steel. Allowable design compressive stress of grout =

4,000 x 0.33 psi.

Permanent Foundation SupportPermanent Foundation Support

GEOTECHNICAL CONSIDERATIONS…GEOTECHNICAL CONSIDERATIONS…

Bearing stratum in bedrock.

Pile to be minimum 12 feet into bedrock. Skin friction area =

9 x 3.14 x 12 x 12 = 4069.4 sq. in.

Rock/grout friction stress = 200 x 1000/4069.4 = 49.1 psi

Pile Load Test FramePile Load Test Frame

Pile Load Test FramePile Load Test Frame

Installation of Drilled MicropilesInstallation of Drilled Micropilesfor Permanent Bridge Foundation Supportfor Permanent Bridge Foundation Support

Experienced. Equipped. Committed.Experienced. Equipped. Committed.

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www.laynechristensen.com • 888-79-LAYNEwww.laynechristensen.com • 888-79-LAYNE