Design Process
One of the first things they do is hire a geotechnical firm like Kleinfelder or Signet Labs to drill and take core samples from the property and analyze the test results to decide what type of foundation would be the best for the area and the proposed structure. Usually all of the engineering firms agree on the recommendations before proceeding on the design and construction. If they decide to use a deep pile foundation they order usually 15 to 20 test piles that are longer than they need and drive them near where they took the core samples. They drive them to the point of refusal. The geotech engineer has computer leads connected to the top of the piles and as they are driven and analyzes the sound waves going thru them and how they are reacting to the soil. The average pile driving hammer weighs around 9000# and they adjust the fuel flow so it has a stroke of 4 to 11' depending on how hard the want to drive it. When they get to a depth where it takes around 35 blows to go 1' is where they would consider refusal. Any more force will tend to damage a concrete pile. Then a recommendation is made as to the number and length of the piles required to support the building.
A few blocks north of this site the 330' office building built in 2001 at 150 California St required
145-14" square concrete piles 102' long. The JP Morgan Chase building a few blocks west at 560 Mission St is 420' high and required 596-14" square concrete piles varying from 25 to 36' long. Must be some hard ground up the hill there. The dewatering process can cause problems. When the ground was dewatered in Sacramento for the new federal courthouse the parking garages around it settled and the walls cracked. A large PG&E utility vault settled and sheared off the main electrical cable supplying downtown Sacramento. What a traffic jam!
There had to be multiple screw ups on the Millennium project. I would bet on everyone involved suing everyone else before it is over.
Biting the hand that feeds IT
