what are the remedies when one get water and sand layer at the bottom of bored under reamed piles ? piles can not go further below because of sandy soil.
Enlarging the bottom end of a pile can find some difficulties like this. It is for this that constant section piles are everyday more recommendable.
I first would analyze the safey loss if any of relevance.
To this purpose I would try different evaluations of the capacity, pile strength evaluation varies wildly following different authors. If with the help of one competent geotech consulting, also in settlement (that I would try myself if relevant, in any case).
For most cases water flow should not be as big as to prevent to form at least a bulb end, what would require some injection pressure, and likely the pile be sheathed.
And you can add more piles if proven the solution.
It should since both friction/adhesion surface and more importantly tip bearing resistance both increase, and these are the 2 items contributing to strength by most evaluations.
Agree with ishvaaag - I had a library project some time ago that required drilled piers with belled ends. The soil report had recommended these and the design required some pretty big belled diameters (12 foot as a max.)
When the contractor started drilling, the soil was much sandier than anticipated and the bells caved in. The geotech and I came up with a straight shaft option and abandoned the belled piers. The straight shafts were much larger than the shaft diameters of the belled piers but that was really the only other option. You cannot open-bell a pier in soil that will not hold its shape. And I'm not aware of any safe way to shore up the bells - I wouldn't go down there with unstable soils.
