Working inside the dome created challenges because of the tight spaces! Many of the micropiles were installed under the remaining bleacher creating a challenge with the very low overhead. Because this renovation was inside the domed stadium, we were not able to get the equipment inside the stadium to install the caisson that was needed to carry the load of the columns for the new sky boxes.
Situation: The renovation project included construction of new sky boxes. A foundation system was needed to carry the column loads for the sky boxes.
Additional Challenges: Caissons were designed to carry the column loads but because of the limited space inside the dome the equipment required was not able to access the area.
It was determined that the best solution would be to install the hollow bar micro-piles. They could provide the required point loads but could be installed with much smaller equipment. Each Micro-Pile had to be imbedded 10 feet into the rocky sub straight. This method uses a hollow drill bar and drill bit with a jet opening allowing for pressurized grout penetration while drilling. The bars are continuously threaded and become the reinforcement tendon, combined with a Portland cement grout body. The rough profiled surface of the grout body transfers tension and or compression loads into the ground. When the pile was installed to the correct depth a plate was attached to the top of the pile. The rebar can now be tied to the plated and the pier caps poured.
It was determined that the best solution would be to install the hollow bar micropiles. They could provide the required point loads but could be installed with smaller equipment. Each micro-pile had to be imbedded 10 feet into the rocky sub straight.
Conclusion: Arizona Foundation Solutions crew installed 36 micropiles to the required depth and steel plates were attached to the top of each pile to provide an attachment for the rebar cage. This process proved to be a time saver keeping the project on schedule!
Structural Engineer: GRAEF-USA
Geotech Engineer: AMEC
General Contractor: Barton Malow