If piles aren’t driven to bedrock, they are driven to a “level of resistance” or “refusal” (refusal to advance). The level of resistance is a function of the hydraulic hammer force and blows per inch of advancement. (Literally how many hammer blows on the pile per inch of additional advancement, 50-60 might be considered “refusal”.). Having said that, some reasonably conservative assumptions about the underlying soil need to be made to be defined the required “level of resistance”. Propped hammer sizing is critical, propped pile shoes (protective end treatment) and construction inspection is critical.
Contractors have been indicted for collusion with inspectors to “pass” piles. There was a huge case in NY some years back.
Whom did the owner hire to do construction inspection and did they have any experience in pile driving?
(Structural Engineer, I’ve worked in both design and construction.)
I worked across the street when they were driving the piles for The Prudential Center in Boston (the fifties). The entire area is landfill.
My God,the noise,but the buildings are still there and doing quite well.
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Propped => proper ...sorry.
If I recall correctly from a previous article about this, one issue in this case is that after the building was built there was excavation in an adjacent lot.