University of Arizona Medical Center
Location: Phoenix, AZ
Situation: The University of Arizona Medical Center building was being renovated.
The finished floor of the main entrance was to be lowered four feet, requiring
underpinning of all the load bearing walls in the area to be lowered.
The wall loads were up to 18 kips per linear foot. Due to the historic
nature of the building, no work was allowed to be performed on the exterior
of the building. All of the wall footings were un-reinforced. Access and
space restrictions would present several challenges for equipment associated
with some underpinning systems.
Solution: Several options were considered. Placing checkered board concrete under
the footings would have taken too long. Soil stabilization by grouting
wouldn’t strengthen the soils enough for the required loading conditions.
Underpinning appeared to be the best solution. However, the unbraced length
of the piles, lateral stability of the walls and equipment small enough
to work in the confined space with sufficient power to support the structural
loads were all issues that had to be addressed.
Conclusion: Ram Jack driven steel piles were the perfect solution. They can be installed
with hand carried hydraulics making it ideal for power and strength even
in the tightest of working conditions. The piles were installed with external
guide sleeves to increase their buckling capacity and staggered on each
side of the interior walls for stability. On the exterior walls, the underpinning
piles could only be placed on one side of the wall. Helical tieback anchors
attached to a strong-back were designed to provide the lateral bracing
at these locations. The underpinning work was completed in 5 days. The
work was completed on time and under budget. The historic exterior of
the building was untouched from the underpinning work.