Foundation testing ‘in vivo’
New test seeks seismic safety, economy in construction

By Jessica M. Scully

This device tests the seismic strength of foundation piers by dropping a heavy weight onto them for a duration of about 0.1 seconds.

10 April 2002 | A series of seismic tests on drilled piers could help existing campus structures ride out quakes more effectively while cutting costs for constructing earthquake-safe buildings in the future.

“Drilled cast-in-place piers are a long-established part of constructing earthquake-safe building foundations,” says Michael Ordonia, project manager with Capital Projects. “The twist here is that rather than relying on scientific guesses as to the capacity of the piers, these piers were actually tested in situ to measure their ultimate capacity.”

As part of a continuing effort to lower the cost and improve the effectiveness of seismic design on the Berkeley campus, the testing was conducted last fall in a parking lot, near the site of four future student residence halls that are part of the Underhill projects. The goal was to assess the performance of drilled cast-in-place piers — not in a lab, but at an actual campus construction site.

Test results came as a pleasant surprise, according to Professor Jack Moehle, director of the Berkeley campus-based Pacific Earth-quake Engineering Research Center, which collaborated with Capital Projects on the tests. “The piers were three times stronger than was previously thought,” he said.

Foundation piers transfer the force of an earthquake from a building to the soil, at significant depths. But determining the size and number of piers needed for a safe transfer depends on the unique properties of the soil on which a building is constructed.

Traditional design formulas for cast-in-place piers are conservative, which often results in using more and larger diameter piers than necessary.

Capital Projects estimates that the campus could see a net savings of up to $400,000 in reduced construction costs, thanks to information obtained from the tests.

Test results have already been incorporated into the residential hall building project adjacent to the test site. And because the soils under the campus are fairly uniform, the research could be used for upcoming construction projects as well.

“The project,” noted Ordonia, “offered a unique opportunity for architects, structural engineers, geo-technical engineers, earthquake engineers, and university administrators to work together using performance-based engineering techniques.”