Pile Toe Design

[ajk1]

For a concrete caisson type of temporary shoring wall, what is the general practice with respect to the design of the toe of the piles? The wall has a steel soldier pile every 3rd caisson. The toes of the caissons extend 4 m below the bottom of the excavation. The soil within this 4 m length of the toe is a sand with blow count varying from 15 near the top of the toe to > 100 blows per 300 mm for most of its length. The site will be dewatered. Some of the possibilities seem to me to be as follows:

Consider the pile :
a) fixed rotationally and translationally at half the toe emdbedment depth, or
b) fixed rotationally and translationally at bottom of the toe embedment depth, or
c) fixed translationally but free to rotate at half the toe emdbedment depth, or
d) fixed translationally but free to rotate at bottom of the toe emdbedment depth

I suppose this could be modelled by putting in horizontal springs representing the soil stifness but I was wondering if there is some accepted simple practice.

 

[ishvaaag]

As you see from attachment -from ARBED sheet pile guide- the situations at embedment of pile walls vary from the barely stable to the fixity at end; so you need account depth of embedment and relative stiffness of pile wall to soil to get your situation.

If the question is reformulated in the way of what is the convenient assignation for the condition at end -and so what criteria must guide the selection of the depth- I would say that irrespectively of some text daring more, the nature of these works use to be one in that the works are generally of low reliability and there is always exposure of the workers to severe risk, so except where particular conditions of the soil makes it extremely impracticable, or no human exposure is nearly expected, the designer should go for fixity at the end to ensure the highest performance of this kind of foundation work.

 

[ajk1]

Thanks. Of course a caisson wall is much stiffer than a sheet pile wall, but you have reminded me that I hav seen these type of diagrams before. I will look up some of the books in the office library. Thanks for the suggestion of considering that there is fixity at the biottom of the toe.