15 March 2001
6.1. Purpose. The purpose of slabjacking is to raise a slab in place permanently, prevent impact
loading, correct faulty drainage, and prevent pumping at transverse joints by injection of a grout
under the slab. The grout fills voids under the slab, thereby restoring uniform support (Figure 6.1.).
When necessary, it can also be used to raise the slab. This work must be done by an
experienced contractor due to work complexity and specialized equipment required.
6.2. Need for Slabjacking. Slabjacking should be considered for any condition that causes
nonuniform slab support, such as embankment settlement, settlement of approach slabs,
settlement over culverts or utility cuts, voids under the pavements, differences in elevation of
adjacent pavements, joints in concrete pavements that are moving or expelling water or soil fines,
and pavement slabs that rock or teeter under traffic.
6.3. Location of Injection Holes. Location of injection holes must be determined in the field.
The jacking crew superintendent normally locates the holes and must take into consideration the
size or length of the pavement area to be raised, the elevation difference, subgrade and drainage
conditions, location of joints or cracks, and the manner in which the slabs will be tilted or raised.
As a general rule, holes should not be placed less than 12 inches (300 millimeters) or more than
18 inches (450 millimeters) from a transverse joint or slab edge. The holes should not be placed
more than 6 feet (1.8 meters) center to center, so that not more than approximately 25 to
30 square feet (2.33 to 2.79 square meters) of slab is raised by pumping any one hole. Additional
holes may be required if the slab is cracked. The proper location of holes varies according to the
defect to be corrected (Figure 6.2.). For slabjacking a joint where faulting has not yet occurred, a
minimum of two holes can be used. For slabjacking a joint where one corner of the slab has