Well, an interesting take by previous replies. I have never run across "continuous" split spoon samplers (from which the SPT N value is obtained) - in Ontario (Golder and Geocon) we always did the sampling at 2.5 ft intervals to 15 ft, then at 5 foot intervals thereafter. In New Jersey, our driller would do three 24 inch drives to 6 ft, then go to 7.5 ft for the next test.
That's besides the point. I would suggest to the client that the thin-walled steel tube sampler is a more appropriate method of obtaining samples as well as giving a value (either by miniature lab vanes in the tip) or unconfined or triaxial testing for the undrained shear strengths as the OP is in clayey materials. Sometimes those who specify should leave the judgement to the geotechnical "expert".
When I was working in India, they would take an SPT at the surface, then a shelby at a depth of 3 m, then SPT at 6 m, etc. - really not good for what we were needing. I wanted to get a handle on the upper 6 m and 2 tests were not enough. As we were using 100 mm thin walled tubes, I would push a tube at, say, 1 m (1 to 1.45), then do an split spoon sampler (SPT) through the hole formed by the thin walled tube fomr 1.45 to 1.90. Drill to 2 m and do the same again. This way I got 6 thin walled samples and 6 disturbed samples (with SPT) in the first 7 m of the site. The bottom line is that we adjusted to the site conditions and didn't follow "standard" or "specified" protocol just to please when the protocols were not suitable.
