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.