I had an argument about a bridge with another engineer once. His design had pilings down to within 10-20 feet of bedrock (90 to 100 feet below the surface). For the additional cost, I thought that it would make sense to take them down to bedrock. He said that drag from the surrounding ground on the short piles was strong enough without doing that. I lost the argument.
One of the piers sunk and tilted before the deck beams were placed. It was an expensive fix. Much more expensive than extending the piles another 10-20 feet.
Recall the John Hancock Building, Chicago!
A friend was involved on this project.
I heard all about!
While setting a beam the engineer noticed a change in elevation!!
They had to jack the existing pours OUT, and go deeper!!
Prior to this event , it was a different name on the building, he ran out of funds!!
Khan’s design called for 57 caissons—8-foot-thick concrete columns—to be plunged into the bedrock to support the building’s 46,000-ton steel frame. One of those caissons had to be extended up to 197 feet below the surface, then a world record. But soon after the caissons were put in place, Khan received bad news from his field man at the site: One of the caissons had shifted seven-eighths of an inch: The base of the $100,000,000 building was sinking. Khan immediately called a meeting at the building site, looked at the concrete pillars, and cleared his head.
https://mentalfloss.atavist.com/the-man-who-saved-the-skyscraper
That’s crazy! Wouldn’t putting the piles into bedrock reduced the number of friction piles - and the cost?
I worked on the demolition of an 8-year old 16 story condo. The tension wires in the concrete had not been coated with epoxy when they were trimmed off. So the wires were rusting. They spent a few million trying to fix the problem, and when that didn’t work they had to tear the whole thing down.
All because some worker didn’t put a dab of epoxy on the ends. Although I mentioned that to one of the managers of the demolition and he said something like “Yeah - except his boss should have been checking, the company inspector should have caught it, and the city inspector should have caught it too. So you had at least four people not doing their jobs.”
The funny part was the building was owned and built by the Carpenter’s Union and was to be a source of income for their pension plan!