This is an equation for porosity, n, derived from the void ratio, e.
The void ratio, e, is defined as e = `V_V` / `V_S`, where `V_V` is the volume occupied by voids and `V_S` is the volume occupied by soil solids
The porosity, n then is defined: n = `V_V` / V, where V is the total volume including both solids and voids
n = e / (1+e)