What forces do all methods of anchoring tanks offset using the weight of the back-fill?

The correct answer is buoyancy forces. When underground storage tanks are installed below the surface, they are subject to hydrostatic pressure from the surrounding ground and groundwater. If the tanks are not adequately anchored, the buoyant forces acting on them can cause them to float or shift due to the upward pressure exerted by the displaced water.

When backfill material is added around the tank, its weight helps counteract the upward buoyant forces. This anchoring helps to ensure the stability of the tank and prevents it from rising out of the ground when the surrounding water level increases, such as during periods of heavy rain or flooding.

Gravity forces relate to the weight of the tank and its contents; however, the issue in question revolves around the forces acting on the tank due to its placement in a fluid medium. Pressure forces refer to the forces exerted by fluids at rest, but again, they do not specifically address the primary concern with anchoring tanks, which is to manage the effect of buoyancy. Tension forces typically involve forces acting on materials that stretch; these aren't the central focus regarding the anchoring of tanks in this context. Thus, buoyancy forces are the critical factor that all anchoring methods must offset effectively to ensure the safe and secure installation