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2. Division of Layne Christensen Company Specialty Foundation Construction Jet Grouting Drilled Micropiles Vibratory Ground Improvement & Stone Columns Construction Drilling, Grouting & Anchors Central Artery / Tunnel Project Contract C09C1 US Interstate 90 & Interstate 93 Interchange Boston, Massachusetts Presented By: Pier Luigi Iovino, Division President

3. APPLICATIONS… u Temporary Condition u Underpinning support of an abutment u 22 drilled micropiles installed u Permanent Foundation Support u Support for new bridge foundation u 90 drilled micropiles installed Design Applications

4. INSTALLATION TECHNIQUES… u Drilled micropiles were steel reinforced and cement grouted with a minimum rock socket diameter of 8-inches. u 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 Applications

5. SIGNIFICANCE… u Central Artery/Tunnel (CA/T) project is funded through the US Federal Highway Administration (FHWA). u Drilled micropiles are newly accepted method in US. u Drilled micropiles used as permanent bridge foundation component for FHWA funded project. u de facto acceptance of drilled micropiles as viable solution.

6. Design Considerations THREE COMPONENTS… u Threaded casing test results u tension; compression and bending u Structural / Seismic u Geotechnical

7. Temporary Condition

8. STRUCTURAL CONSIDERATIONS… u Pile Capacity = 67 tons / 134 kips. u Pile Diameter = 8 inches u Allowable design compressive stress of grout = 4,000 x 0.33 psi.

9. Temporary Condition GEOTECHNICAL CONSIDERATIONS… u Bearing stratum in bedrock. u Allowable friction stress in bedrock = 45 psi. u Length of rock socket = u 134 x 1000/(8 x 3.14 x 45 x 12) u = 9.87 feet u Pile lengths to be 100 to 135 feet with 10 feet into bedrock.

10. Installation of Drilled Micropiles for Temporary Underpinning of Abutment Drilled piles were installed in low headroom as part of a value engineered proposal replacing contract design of driven piles.

11. Permanent Foundation Support

12. STRUCTURAL CONSIDERATIONS… u Pile Capacity = 100 tons / 80 kips. u Pile Lateral Capacity = 2 kips. u Pile Diameter = 9 inches. u Steel pipe to be 7 inches diameter, O.D. t=0.5” N-80 steel. u Allowable design compressive stress of grout = 4,000 x 0.33 psi.

13. Permanent Foundation Support GEOTECHNICAL CONSIDERATIONS… u Bearing stratum in bedrock. u Pile to be minimum 12 feet into bedrock. u Skin friction area = u 9 x 3.14 x 12 x 12 u = 4069.4 sq. in. u Rock/grout friction stress = u 200 x 1000/4069.4 u = 49.1 psi

14. Pile Load Test Frame

16. Installation of Drilled Micropiles for Permanent Bridge Foundation Support

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