Actually, you can sink a post in a sea bed by running a common garden hose in under it and letting the pressure of the water shift the sand away so it will drop down into the bed. Possibly something similar was done. 
Actually, you can sink a post in a sea bed by running a common garden hose in under it and letting the pressure of the water shift the sand away so it will drop down into the bed. Possibly something similar was done.
Yep, that actually works. I've sunk long iron water pipes straight down that way, for use as electrical grounds. Just use an iron pipe to water hose adapter. Varies with soils. Your mileage may vary.