A Bee review of the more than 9,000 Caltrans data files created during tests of foundation piles of freeway structures found a new kind of problem that has not been publicly acknowledged by Caltrans officials: missing data readings.
Caltrans technicians examine concrete foundation piles for flaws by lowering a radiation probe into tubes cast into each pile. The probe, called a gamma-gamma logger, normally collects concrete density readings every tenth of a foot.
But on some occasions, including those displayed in the images below, technicians operated the probe improperly or a malfunction occurred, causing data gaps – areas for which no reading of concrete density was recorded. This suggests a momentary malfunction of the test device, according to James J. LoCoco, a manager at the manufacturer of the device, Denver-based Mount Sopris Instrument Co. Such lapses, if infrequent, should not cause concern, he said.
A few such data gaps occurred in Pile 4 of the new Bay Bridge signature tower foundation. That pile was tested by Duane Wiles, a former Caltrans technician who was found to have falsified data on other structures and has been implicated in irregularities involving the Bay Bridge piles.
Never miss a local story.
In the Caltrans engineering evaluation of Pile 4, the blank data readings were deleted from the data graphs and were not mentioned.
Caltrans Director Malcolm Dougherty declined to comment, and agency spokesman Matt Rocco did not respond when asked why the blank data were removed from the report.
In nearly all cases, including San Francisco's elevated Central Freeway and the Benicia-Martinez Bridge, engineers likewise deleted blank readings from reports – in some cases eliminating dozens of data points. Caltrans records show that re-testing was not requested, leaving uncertainty about the state of the concrete in those piles – particularly in structures with many data gaps. It's not known if a malfunctioning probe also might have recorded inaccurate data along with gaps.
Rocco said the blank data have been flagged "for further review and analysis."