In my most recent games, combat only was going-on about 60% of the time. So, yes, there would be totally combat-less sessions. Those were with me as a player, though.........
As DM, I'd often put together ridiculous riddle/trap combos designed to confound players. The nature of the challenge was such that, if they didn't solve the puzzle correctly, death would ensue. Thus, it wasn't out of the ordinary for no combat at all to take place in an 8-hour span, just a lot of puzzle/riddle/trap deciphering/avoiding/removing.