Abstract:
Braun Intertec served as the geotechnical design engineer of record and special inspector on a fast-paced multi-phase facility expansion project in Duluth, Minnesota. Michels Construction served as the deep foundation contractor, installing piles on the project. Based on our geotechnical investigation, the site consisted of 10+ feet of fill, 80 to 100 feet of glacial lake deposit, and glacial till. Phase 1 of the project was set up as a design-bid-build to establish standards and expedite construction with approved plans. Phase 2 of the project was a design-build, allowing the contractor to evaluate cost-optimization options. During the design phase, Braun’s experience in the glacial lake deposits geology of Duluth, our design models, and the previous testing program report for the original construction of the facility showed that 9 5/8-in-diameter pipe piles would be a viable option to support the design load of 120 tons.
We recommended a preconstruction testing program to evaluate driving criteria, including an initial drive and 3- and 7-day restrike testing. The program allowed us to save our client money by reducing the length of the piles needed. However, the test results also indicated the potential for higher design loads. During discussions with the design-build team, we identified the potential for higher loads and developed a load test program that included initial drives and 28-day restrikes. Based on this testing, we established criteria for 150-ton design-load piles, resulting in savings by reducing the total number of piles needed to support the buildings in phase 2.
Michels Construction installed approximately 171,000 linear feet of 9.625†closed end pipe pile filled with 3,000 psi concrete. The pile was installed with D19-32 and D30-32 diesel pile hammers. The D19-32 was utilized to install the first two sections of pile, and the D30-32 installed the final section.