Piping around driven piles?

[Melzar]

I'm working on a small residential job on a lake. There is marl to a depth of about 30 ft, sand 30-45 ft, very soft clay (w.o.h.) to 65 ft, then alternating sand and soft clay layers. I'm considering driving closed-end pipe piles to bear in the lower sand and clay layers but am concerned about possible artesian conditions and piping around the piles. Artesian conditions are known to be present in the area based on nearby water well records. The adjacent residence bears on helical piers that went to 50 ft without a problem.

We drilled HSA as deep as 60 ft, but for our deep boring we set casing and rotary drilled to 140 ft. We did not have any flow for our HSA borings, but the geotech boring next door had flow with an explored depth of only 35 ft.

Should I feel comfortable that the soft clay will seal itself? Anybody have any lessons learned? The usual sources don't seem to offer much in the way of guidance.

 

[L0k]

Hi Melzar, I am a bit confusing whether your pile is being driven or being drilled. If it was a driven pile you have to drive up to 'set'. However you mentioned a drilled HSA and set casing, so I though it was a drilled pile. I doubt the soft clay will seal the artesian pressure. Have you check the height of the artesian pressure? My experience was to drilled the pile under water and extended the casing to the artesian height.

 

[Melzar]

Thanks for the reply. We did test borings with HSA, but had to return to the site to drill a deeper boring since the upper 60 ft was marginal and that was the limit of our equipment. For the deeper boring, we grouted in casing then rotary drilled the test boring.

I'm planning to drive pipe piles for the foundation support.

I don't know how much artesian head is present, only that nearby water well records report flowing conditions. We did not have artesian conditions in any of our HSA borings (deepest was 60 ft).

 

[Ron]

Assuming your foundation loads are not that high, I would consider an augered concrete pile (stopping in the sand at about 40 feet). The marl will remold around the pile. Specify a higher than usual concrete head during pile placement so that you get good lateral pressure and reduce the piping potential.