15 March 2001
gauges which contact the pavement and are attached to a firm base located off the pavement.
The dial gauges can be read visually or recorded electrically. When deflection is measured in this
way, any slab showing deflection in excess of 0.015 inch (0.38 millimeter) should be undersealed.
Other methods for measuring deflection to locate voids include nondestructive equipment such as
the Falling Weight Deflectometer, which measures the deflection response of the pavement under
a dynamic load (Figure 7.1.).
7.3. Need for Subsealing. For jointed concrete, pavement subsealing should be accomplished
as soon as significant loss of support is detected at slab corners. Symptoms of loss of support
include increased deflections, transverse joint faulting, corner breaks, and the accumulation of
fines in or near joints or cracks on traffic lanes or shoulders.
Subsealing should also be considered at all existing repairs that show evidence of pumping or
settlement. To be effective, subsealing should be performed before the voids become so large
that they cause pavement failure.
7.4. Hole Patterns. Hole patterns for effective distribution of cement grout under the pavement
are not easily determined in advance. Some preliminary testing is often necessary in advance to
locate holes in a way that will ensure good grout distribution. Where a hole pattern is selected for
repetition, it should provide sufficient holes to permit grout to reach all voids beneath the
pavement. The most common hole pattern is a four hole pattern with two holes on each side of a
transverse joint. The holes are located in the wheel tracks, with the approach slab holes nearer
the joint than the leave slab holes. Typical distances from the joint are 12 to 18 inches (150 to
450 millimeters) for the approach slab and 18 to 24 inches (450 to 600 millimeters) for the leave
slab. Additional holes may be required for voids under the longitudinal joints or at the shoulder.
Usually, one hole that is 24 to 36 inches (600 to 900 millimeters) from the shoulder and 4 to 6 feet
(1.22 to 1.83 meters) from the transverse joint is adequate. Ideally, the hole should be placed as