Premature refusal

[mshani]

What is "premature refusal" for driven piles?

 

[BigH]

Refusing before the depth of tip penetration expected was reached.

 

[mshani]

Thanks BigH. What is the main cause for this behavior?

 

[BigH]

Maybe you hit a boulder; maybe rock or glacial till was encountered higher in the stratum than the geotechnical investigation indicated; maybe you are using too light a hammer; maybe your pile buckled and is damaged . . .

 

[emmgjld]

BigH left out the embarrassing one.
The bedrock is quite a bit higher than believed. Usually a result of not enough test borings. I have been embarrassed.

 

[BigH]

I thought I said this as point 2 (maybe rock or glacial till was encountered . . .). emmgjld reinforces the point though.
In many locales, it is truly amazing at how much bedrock will differ in elevation in relatively short distances. At the plant site here, there was more than a 25 m elevation difference in bedrock over 35 m length. Very unstable (uneven) bedrock surface that even more boreholes would/could lead to even more confusion.

 

[BigH]

Oops - and add that various pile types will refuse differently as well.