Thanks to Janel who provided this free pattern. My daughter loves spiral skirts and she wanted me to make one for her. But I didn't know how to draft a spiral skirt. One day I found this free pattern on Janel's blog. I immediately took a print out and sewed this one. You can get this pattern here: www.Janelwashere.com.
I stitched this skirt with eight gores, one gore contains two pieces. I cut the pieces 1 and 2 separately and then joined the pieces to make a gore. Now, the gores are to be attached as done in the above fig.
And then I sew the waistband and left an opening to insert the elastic.
The elastic has to be inserted with a safety pin and the end of the elastic is to be pushed through the opening, the fabric is to be scrunched on the elastic and the elastic can then be pulled into the casing. This has to be continued until the elastic comes out the other side. Now the ends are to be overlapped and sewed. What remains is closing the opening. That's what you see in the above fig.