Nominated for the Top Project Award, GRL Engineers, Inc., has been recognized for the contributions made during the construction of the 7Seventy7 apartments in Milwaukee, WI. The project consists of a 33-story building in Milwaukee, Wisconsin, USA, with two levels of below-grade parking across the entire building footprint. Timely and cooperative teamwork among the owner/developer, geotechnical engineer, testing agency, structural engineer, construction manager, and pile-driving contractor resulted in an efficient, cost-effective, high-capacity driven-pile foundation on a constrained urban site with significantly variable subsurface conditions. In 2016, a pre-production test program was performed on 16-inch-diameter steel pipe piles, driven closed-ended and subsequently filled with concrete.
The test program included dynamic monitoring of 10 piles during installation, and of select piles during long-term restrike testing with a drop hammer. CAPWAP® analyses were performed on both end-of-initial-drive and beginning-of-restrike dynamic test records. The relaxation potential of piles terminating in dense fine-grained granular deposits was also evaluated by performing short-term restrike testing. The site exhibited significant soil set-up, even after relatively short wait times. Test program objectives included characterizing set-up profiles (cumulative shaft set-up as a function of embedment length). To evaluate tension resistance, the long-term shaft resistance magnitude and distribution were determined. An axial compression static load test, internally instrumented with vibrating-wire strain gages, was also performed.
Test program results were used to assist in assigning individual capacities to damaged piles, to piles which experienced practical refusal, and to the undamaged piles in the group. This was done in close coordination with the structural engineer who evaluated the actual required load for each group, and for each pile within the group, where damaged piles occurred. These combined efforts reduced the number of replacement piles which would have otherwise been required by 50 percent, saving both cost and time.
Sources: GRL's Newsletter: No91_Safe and Accurate Measurement with the Static Load Testing System, High-capacity driven-pile Foundation for a 33-story high-rise in Milwaukee, Wisconsin, USA, conference paper