Good point DRC1-It's true that when granular soils are partially saturated they can temporarily stand at angles greater than their internal friction angle-in fact it's the only reason we're able to build sandcastles. However, in this case though, the test was run undrained with pore pressure measurements so the sample should have been saturated during the test. There probably wouldn't have been any "apparent cohesion" as it is commonly called.
Also 22222222, I was looking at the stress levels you used in the tests. They are moderately high stresses, but certainly not the highest that have ever been used in a triaxial test. Depending on the sand type (grain type) and the gradation and possibly a few other factors, I still think it's possible to have some curvature to the shear stress-effective normal stress plot (the points on this plot are usually the peak stress ratios from your p-q diagrams.) The curve of the Mohr circle plot shouldn't be ignored when evaluating the strength and everything else, but just know that it is probably not caused by genuine cohesion, which is rare in most cases-even with most clayey soils.
There's another interesting thing to consider for your project too...if you need to perform a settlement analysis for your embankment, look into whether or not particle crushing will be a concern at these high stress levels and if it should be considered in addition to your normal settlement analysis which usually assumes the soil is a linear elastic material, without particle breakage. There is an good article by Lade, Yamamuro, and Bopp called "Significance of Particle Crushing in Granular Materials." It is in the Journal of Geotechnical Engineering, April 1996 edition. It may or may not be a concern, but wouldn't hurt to look at.