What is Jack

Definition of Jack in Construction

Jack in construction is used to normally describe a vertical lifting of a material, structural unit or a horizontal surface, such as a concrete slab. The jacking of a material or structural unit is the lifting of that unit into position, or to accommodate the insertion of another element under the item that is being jacked up. A negative use of the term is when ice, frost or frozen material expands and jacks up a slab or a structural member in a negative fashion. The jacking due to freezing is a negative situation, and is the reason that precautions are taken to ensure that all structural elements are buried deep enough below the frost line, to prevent jacking of the item. Another use of the term jack is to describe the hydraulic pressure that is exerted, if the incorrect soil is used to backfill or place a slab or structural element on. If pressure is exerted on a clay or highly silty soil, there is a tendency to jack the adjacent structure due to transference of the downward pressure on the silt, clay and the lateral transmission of this force. Jacking in this case can be a very serious site characteristic that will need to be corrected prior to the placement of any type of foundation on this type of soil.