Value-Engineering of H-Pile Foundations in Karstic Geology-Paper

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A 50 MW biomass power plant in southwestern Georgia was planned on karst-prone limestone. Its original foundation design used about 700 H-piles, including battered piles for lateral loads, with working axial capacities of 110–140 kips. To reduce cost and construction risk, the project team conducted pre-production pile testing and redesigned the foundations.<br /><br />The investigation combined existing borings with cone penetration tests and a microgravity survey to assess variable limestone and possible karst features. Seven H-pile test piles were dynamically monitored using a Pile Driving Analyzer, with CAPWAP analyses and restrikes to evaluate capacity and soil setup. Two lateral load tests and one tension test were also performed.<br /><br />Testing supported a working axial compression resistance of 220 kips per pile—about 1.5 to 2 times the original values—and a working lateral resistance of 25 kips for vertical piles. The redesigned foundations eliminated battered piles and reduced the planned pile count from approximately 700 to 484, a reduction of more than 30%. The tension test, which did not reach geotechnical failure, supported recommended working tension capacities of 135–180 kips, depending on loading conditions.<br /><br />During construction, delayed review of field records meant that piles with unusually low resistance along portions of their lengths were accepted and cut off prematurely. Additional testing showed that some lacked adequate capacity, so many had to be spliced and driven deeper. PDA data and time-dependent soil-setup analysis indicated that their long-term capacities could meet or exceed the target.<br /><br />The case demonstrates how focused design-phase testing can improve foundation economy and reduce uncertainty in complex geology. It also highlights the importance of timely, consistent communication between field quality-assurance personnel and design engineers.

Keywords

biomass power plant

karst geology

limestone foundation

H-piles

pile testing

CAPWAP analysis

lateral load test

tension test

soil setup

foundation redesign