When thought is being given to replacing cracked and settled slabs on ground, repair by slabjacking should be considered. Slabjacking has many advantages: It is almost always faster and usually less costly than replacement; a slabjacking program can be planned in a way that minimizes interference with other activities; slabjacking work can be readily done at night or other off-hour times; the grout can be pumped several hundred feet, and access for large equipment is not needed; the surface texture and appearance remain the same, unlike the surface of slabs repaired by other methods. The method involves drilling holes through the concrete surface and injecting cementitious grout to fill any underslab voids and raise the section to the desired grade. The procedure can be used to raise virtually any rigid pavement.
There are some limitations. Unless special procedures are used for drilling the injection holes, they will be visible. Any cracks or other deficiencies that existed before will remain. Properly executed slabjacking will not create new cracks, but hardly visible existing cracks may tend to open.
The exact layout and spacing of the injection holes will depend on the thickness, condition and configuration of the slab. They normally will be placed in a staggered pattern with a spacing of 5 to 8 feet. Peripheral holes are usually located 1.5 to 2 feet from the slab edge. Holes that come within a few feet of existing cracks or joints are often adjusted to fall immediately adjacent to them. Such holes are favored for the actual lifting as the presence of the existing relief tends to cause fewer new cracks from lifting forces. Lifting is always started at the point of greatest settlement. It is usually done about 1/4 inch at a time at any given location. It is always started at the lowest point. Injection is changed frequently from one point to another so that no location leads another by more than about 1/4 inch.