UFC 3-270-04
15 March 2001
faulted, the hole at the low corner should be set back to avoid raising the adjacent slab. Where
the pavement has settled and the slabs are in contact with the subbase, a single hole located in
the middle of the panel may be sufficient.
6.4. Drilling Holes. Holes that are 1-1/4 to 2 inches (32 to 50 millimeters) in diameter are drilled
by pneumatic drills, core drills, or other devices which are capable of drilling grout injection holes
through the concrete pavement and the base material. The equipment must be in good condition
and operated in such a manner that the holes are vertical and round. The down feed pressure,
whether by hand or mechanical means, should not exceed 200 pounds per square inch
(1,379 kilopascals). Where the concrete pavement is tight against the base material, the use of
an airline or blow pipe may be necessary to form a cavity under the pavement slab for the grout
pressure to take effect. Where the pavement is placed and bonded to a cement treated or other
stabilized base material, grout holes should be drilled completely through the base material.
The grout should be injected below the base material rather than between the pavement and
base material.
6.5. Grout Mixtures. A variety of grout mixtures have been successfully used for slabjacking.
They generally consist of three to seven parts fine aggregates or a mixture of aggregate and
pozzolans or flyash to one part portland cement with enough water to produce the desired
consistency. Wetting agents or other additives may also be used to increase the flowability. The
use of a wetting agent lubricates the grout and permits runs of up to 6 feet (1.8 meters), and it
also tends to reduce "pyramiding" (a stiff grout may form a pyramid under the slab, leaving
unfilled cavities). A definite method of proportioning the grout mixture should be used to ensure
uniform consistency. The proper consistency to be used for any given condition is best
determined by experience. Generally, a mix of stiff consistency is used to raise the pavement
slabs and a more fluid mix is used for filling voids. The consistency should be checked by a flow
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