Concrete piers are made up of segments(concrete cylinders) that are pressed into the soil beneath the foundation each on the top of the previous, forming a continuous column or "Pier" of concrete cylinders. There is a 3/4" hole through the center of each cylinder allowing for a steel pin that keeps cylinder from moving horizontally as it is pressed to the point of refusal.  After each pier is driven to the point of refusal (a point at which the bottom cylinder is against bedrock, or has reached a point in the soil that has little or no moisture and cannot be pushed further), the lift is performed.  All piers, in the area to be lifted, are lifted simultaniously to allow for a uniform lift which causes less distress on the house.