Aloha!
My 12×20' outdoor bedroom has a sinkhole below it. The land is lava rock and here, the lava rock was bulldozed, so it was all broken up and indeed, there are lava tubes around these parts. The one below the bedroom has opened up several times and has been filled as much as possible with rocks of varying sizes and cinder.
I am thinking about using that expandable foam now. Any thoughts out there on that?
Best Answer
Foam sounds like a bad idea to me for a sinkhole. I've seen them cover old wells with large quantities of foam followed by earth, but your situation is a never ending geological process caused by water flow. Have you read this about the Guatemala sink hole? The article suggests the right way would be to layer rocks. Very large at the bottom and smaller as you go up so that the water can flow through that area but doesn't take the soil with it causing another sink hole. I'd go that route if it was me.