Need help with geotechnical engineering calculations

Hi,

This is probably my 2nd week of using mathcad and I've stumbled into a few difficulties.

1) Originally, I wanted to try to distinguish between granular and cohesive soils. For Fines content of less than 50%, this should be classified as granular while greater or equal to 50% must be classified as cohesive soils. I wasn't able to do this so I ended up getting the overburden and effective stresses by interpolating the unit weights. Can someone help write a code that can get the final effective stress by distinguishing whether it is granular or cohesive material?

2) In the tab N60 Correction for Overburden Stress, the answers are wrong - I tried this using excel but I don't know why the results from the excel file are not similar to the mathcad file.

Hope someone can help!