Specific constituents of certain soils tend to swell or shrink with variations in moisture. The extent of this movement varies from soil to soil. Those soils highest in clay content are generally more susceptible while those lowest in clay content are the least affected. In some areas the movement in insignificant; in others, it is quite pronounced. When unstable soils are used as a base for a foundation, the tendency for movement is transmitted to the foundation. Since soil movement is rarely uniform, the foundation is subjected to a differential or upheaval. The problem shows up in both slab, and pier and beam type foundations. Foundation settlement can be corrected by either mechanical or hydraulic leveling. The type of structure plus the degree and nature of the settlement determine which method should be used. Concrete slabs require hydraulic leveling or matrixing. Pier and beam foundations usually require mechanical leveling although this is often supplemented with hydraulic or chemical stabilization and /or back filling. Mudjacking is done by pumping a cement grout through small, strategically-located holes in the concrete slab. Once in place, the grout solidifies into a dense concrete mass and provides a competent bearing for the concrete slab. If a soil-cement-lime grout is used, the lime content of the slurry will impart the benefits of lime stabilization to the base or sub-base. This combined treatment not only restores the slab to proper grade but also stabilizes the sub-soil to prevent re-occurrence of the problem. Mechanical leveling involves the use of strategically placed mechanical jacks to lift the settled beam to grade. The beam must be raised carefully to avoid further or unnecessary damage. Once raised, the beam is held to elevation by a specially designed spread footing and pier. The footing is set deep enough so that it will be independent of variations in soil moisture. It is also designed to adequately distribute the load without creating unnecessary bulk or mass. The pier is tied into the footing with steel and supports the foundation beam.