Extensive Indicator Pile Program with Significant Production Pile Adjustments-PPT Presentation

PPT Presentation

Pdf Summary

The project involved construction of a new power-generation station in North Dakota, including two combined-cycle units and supporting buildings and infrastructure. Subsurface exploration found glacial deposits over weathered bedrock. Although initial pile designs included several types, the final design used HP 14×89 piles with ultimate loads of 200 or 300 tons.<br /><br />A comprehensive indicator-pile program tested 40 piles using high-strain dynamic testing at installation and after a three-day restrike. Six static tests assessed compression, tension, and lateral performance. Dynamic results generally showed 2–4 times greater pile resistance after setup. Eight test piles reached refusal at penetrations of 18–30 feet, while one did not achieve the required resistance at its design length. Static compression and lateral tests passed; one tension test failed at 200% of design load, despite acceptable movement at the design load.<br /><br />Production began after the test program informed pile-length optimization. To protect the schedule despite an 8–12-week procurement period, the team pre-ordered some production material. Crews installed 3,839 piles—147,000 linear feet—using four crane-and-hammer setups. Winter weather caused 13 lost workdays, but material-supply challenges caused no schedule delays, and there were no recordable injuries.<br /><br />Early refusal proved a significant production challenge, particularly where uplift piles needed greater embedment. A tieback drill rig probed 1,363 locations; where obstructions were found, crews drilled 30-inch shafts and backfilled them with crushed stone. Because predrilling uplift-pile locations to 25 feet reduced skin friction in the drilled zone, installation criteria for compression resistance also had to be modified. Production test results showed substantial scatter between driving resistance and measured capacity, prompting refined wave analysis to revise driving criteria for both initial installation and restrikes.

Keywords

power-generation station

North Dakota

combined-cycle units

pile foundation

glacial deposits

HP 14x89 piles

dynamic testing

static load tests

pile refusal

wave analysis