Accurate SPT counts with upward seepage gradients

[FOS]

Does anyone have any experience measuring consistency or density of sands (SPT "N" value) during drilling where upward seepage gradients and drilling is causing disturbance at the base of the drill hole. I guess the best you can do is use wash boring techniques and keep a head of water in the casing at all times. Any other suggestions?

 

[georam]

I guess that is true. A trye measure for SPT count is supposed to be below the casing and for undisturbed soil. Keeping the water in casing, while cleaning materials inside the casing will certainly help.

 

[dirtman]

In my experience, it is best to have drilling mud in the hole when performing SPT testing.

Danny McCook

 

[Ron]

If you are having upward seepage gradients, that implies a highly permeable material, for which drilling mud would be necessary. If you are not already using a 24-inch split spoon sampler, suggest you go to that rather than the 18-inch.