Here is a set of examples leading to a proper circular barplot, step by step. The first most basic circular barchart shows how to take advantage of the
d3.scaleRadial() function to display bars around a circle. Once this concept is understood, it is relatively straight forward to add labels or another sery of bars.
Learn how to add labels for each bar. This can be a bit tricky since it recalls a few trigonometry concepts your learned in highschool.