I am looking for some typical values of undrained shear strength (su) for saturated normally consolidated clay on the upper soil layer (mudline and first 1-2 meters).

Some typical values I found refer to deeper layers (eg 10-25kPa for soft clay). 

There is also the relationship of Wood (1990) which is su/σ'z = 0.25 but I am not sure if it is applicable for small depths. 

I would be grateful if someone could help!