A POST-TENSIONED MICROPILE FOUNDATION SYSTEM WITH GROUTABLE VOID FORMS (GVF)-Paper

Paper

Pdf Summary

The paper presents a post-tensioned micropile foundation system using groutable void forms (GVFs) as a smaller, lower-impact alternative to large concrete spread foundations, particularly for wind turbines and other renewable-energy structures.<br /><br />GVFs temporarily separate each micropile from the foundation cap, allowing the pile to move during testing and post-tensioning. Once the required loads are applied, the void is filled with cement grout so the system can transfer both tension and compression. The post-tensioning is applied in stages and balanced groups to control settlement and avoid overloading the soil. The authors argue that prestressing reduces foundation movement under changing loads and helps prevent fatigue-related problems.<br /><br />Two construction approaches are described: installing micropiles before casting the foundation cap, or drilling them through sleeves in a completed cap. The first allows larger-diameter holes. The second can use hollow injection-bored bars, which inject grout during drilling to form a larger grout body and improve ground contact.<br /><br />A Tehachapi, California, wind-turbine project illustrates the system’s application. The paper reports reductions of more than 75% in foundation area, more than 40% in concrete use, and more than 70% in reinforcing steel, with estimated total foundation cost savings of 20–30%. It concludes that micropile/GVF foundations can improve structural performance while reducing material use and cost compared with conventional mass-concrete foundations.

Keywords

post-tensioned micropile

groutable void forms

wind turbine foundation

renewable energy structures

micropile foundation system

foundation prestressing

grout injection

settlement control

Tehachapi California

material cost savings