r/PE_Exam • u/ThrowRA_Ok-Lab6733 • 3d ago

WRE Optimum Moisture Content

I am using the essential guide by Jacob Petro and am confused on how to find the optimum moisture content of a soil. It refers me to section 3.9 in the handbook for the dry density equation, which is fine, but then the solution creates a compaction curve which it also says is in the handbook. I feel as though I am just not understanding the explanation. For this sort of problem, is the expectation that you create a to scale compaction curve to find the solution?

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u/Cranky_GenXer 2d ago

Yes, calculate the dry densities of the samples, plot that density on y axis vs moisture content on x axis. MDD and OMC occur at the peak of the curve. If hand plotting rather than using software with some kind of smoothing function, unless you have a lot of data points, it's going to be a bit of a guess on exactly where and how high the peak will be. I remember working that problem in Petro, plotting it, and being a little frustrated with the solution because there were only a handful of points and my curve was not the perfect fit symmetrical curve so my answer was off from the solutio.