1. No Cell Phones, Please.
Thank You.

2. Central Artery / Tunnel Project Contract C09C1
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
Division of Layne Christensen Company

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

4. Design Applications 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.

5. Design Applications 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.

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

7. Temporary Condition

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

9. Temporary Condition 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.

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. Permanent Foundation Support
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.

13. Permanent Foundation Support
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
= sq. in.
Rock/grout friction stress =
200 x 1000/4069.4
= 49.1 psi

14. Pile Load Test Frame

15. Pile Load Test Frame

16. Installation of Drilled Micropiles
for Permanent Bridge Foundation Support

17. Experienced. Equipped. Committed.
Boston • Richmond • Salt Lake City • Los Angeles • Seattle
Pittsburgh • Hawaii • Puerto Rico • Italy
• LAYNE