Micropiles Supporting a Wraparound Addition, from the Basement-Video

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Video Summary

A six-story retail and office addition was planned around a 21-story Atlanta office tower with a two-level parking garage. The existing structure’s drilled piers could not support the added loads, so new steel columns were routed through the garage to pile caps supported by micropiles. The design included 147 compression piles and 139 compression-tension piles, generally rated at 160 kips, with rock bond zones.<br /><br />Installation took place in the garage’s lowest level under tight-access, low-headroom conditions. Crews used compact rigs, three-foot casing sections, and short threaded-bar sections, with equipment staged above and supply lines routed through a ventilation shaft. A pre-production tension test on a 54-foot pile with an eight-foot rock bond zone showed ¼-inch deflection at the 160-kip design load. Dust control and air quality required added ventilation and combined air-water flushing. Work began during the COVID-19 shutdowns and was completed in about three months, installing more than 14,000 feet of micropiles.

Keywords

micropiles

Atlanta office tower

low-headroom installation

compression piles

rock bond zone