The principle of slabjacking is simple. As grout is pumped under pressure into the hole under the pavement, it creates an upward pressure on the bottom of the slab in the area around the hole. The upward pressure lessens as the distance away from the hole increases, due to the resistance the grout meets as it flows away from the hole. That is why it is possible to raise one corner of the slab without raising the entire piece. Concrete pavements require reasonably uniform support rather than a strong subbase. Any condition that disturbs the slab support must be corrected as soon as possible to insure the serviceability of the pavement. Slabjacking can correct most of these conditions, as follows: pumping- frequent heavy loads passing over the pavement cause the slabs to deflect at the joints; advanced pumping and faulting- a neglected pumping condition will eventually cause the unsupported forward slab to crack and settle, resulting in a fouled joint or crack; faulting form densification- heavy traffic over undoweled pavement joints can cause the subbase or subgrade to consolidate around the joint, usually in front of it under the slab; and embankment settlement- subsidence of embankments causes the pavement to settle over extended section. Other conditions requiring slabjacking are culverts- usually occurring on short sections of pavement, settlements over culverts can be caused in several ways: inadequate fill compaction during construction, embankment washout by water flowing outside of the culverts, fill material flowing into open joints in culverts, and broken pipes; and settlements of approach slabs- one of the most common uses for slabjacking. To correct a dip or sag in the pavement, jacking should begin at its low point and progress in an orderly procedure, working longitudinally and staggering the holes transversely until the slab has been raised to the desired elevation. At this point, all holes should be pumped to assure that there are no remaining voids under the slab. In any slabjacking operation, a slab should be raised slowly and with uniform pressure. Therefore, holes should be drilled close enough together to ensure complete filling of the void and allow the grout to flow under the slab as it is raised. The movement of the grout can be checked by observing it through adjacent holes.