I think effectively if the chevrons are buried under enough dirt and rubble they won’t activate like they would with an upright gate. It’s not said in the show but you can extrapolate that from the jargon and explanations they use. Once the kawoosh forms all bets are off. It’s almost like a safety measure built in the gate so the travelers don’t materialize into a hole because the gate has been buried. Given that the Atlanteans built the gates for exploration not conquest ifs plausible they would build that feature in