While writing my recent meta question, I've cited Dr. Gavin Chiu (趙善軒)'s article to explain the character '進' and its simplified character '井'. However, a user points out that the linked article is not real academic material, and that such explanation is invalid.
How do the glyphs '⻌' and '隹' come up together to bring the meaning of '進'?
In Shuowen Jiezi (說文解字), there's simply a one-line explanation.
Source of images for ancient scripts: The Complete Collection of Ancient and Modern Characters (古今文字集成)