A very long time ago when I was 13 years old, I had a much smarter friend who was 15. He told me that the ends of the radials should be connected to driven grounds. I spent many weeks trying to pound 5 foot sections of electrical conduit into the hard soil in my parent's back yard at the ends of my 15 meter radials. Well, after almost 6 decades, I've never heard of or seen any suggestion that this was a good idea. Now, through the magic of the internet, I can ask if anyone else has heard of this. I think it was a total waste of time, energy and conduit.