A sinking foundation is a soil problem wearing a concrete disguise.

Sinking Foundation: diagnosed and explained.

A foundation sinks when the soil beneath it can no longer carry the load, and it almost never sinks evenly. One corner or one side drops first, and the house above bends to follow it. That bending is what you actually notice: stair step cracks climbing the exterior, doors and windows racking out of square, drywall cracks radiating from frame corners, floors that lean toward one part of the home, gaps opening between walls and ceilings. The foundation itself rarely announces anything; the house does the talking. What weakens the soil varies. Poorly compacted fill keeps compressing for decades after construction. Expansive clay shrinks during drought years, pulling support away from footings. Water from bad drainage or a leak erodes fine soil out from under bearing areas. On hillsides, cut and fill construction leaves half the house on native ground and half on fill that never stops settling. What all these share is direction: the movement continues until the load is carried by something stable. That is the logic of underpinning. Steel piers driven or screwed down to load bearing strata let the house stand on ground that does not move, regardless of what the surface soil does next.

For the repair side of this, the foundation repair solutions page lists every method Dalinghaus installs, including the ones that fix problems other than sinking foundation.