Micromechanics in geotechnical engineering

Hi all,

What is the prerequisite knowledge required for research in micromechanics, I did my masters in geotechnical engineering and thinking to continue Ph.D in micromechnics ( granular media).

As I am from geotechnical (Soil) Background, can anybody please inform me the prerequisite knowledge required like what course should I take, what software skills are needed to learn e.t.c.

Thank You in Advance