September/October 2023 - 102

able to successfully stabilize and lift the
structure to the requirements needed
and the structure has experienced no
settlement since completion.
Stabilization grouting (red represents high pressure,
green represents low pressure, and the
size of the cylinder represents
volume of grout
injected)
Construction - Prior to the grouting
contractor mobilizing, the general contractor
exposed the footings along the
western edge of the building. For this,
the footings needed to be excavated both
inside and outside.
Once the footings were exposed,
ground penetrating radar was used to
verify internal rebar locations prior to
coring to ensure the footings maintained
their integrity. Core holes were drilled
through the interior and exterior footings
at various locations to allow installation
of the compaction grout casing.
The project required a low headroom
style drill rig with a remote
hydraulic power unit located outside to
control toxic fumes. The first target
depth was approximately 50 ft (15 m)
below grade. Grout injection occurred
in ascending 1 ft (0.3 m) stages to the
surface or until undesirable movement
was noted, in which case grouting
Completed
grouting program
including the lifting sequence
The project required a low headroom style drill rig with
a remote hydraulic power unit located outside to control
toxic fumes.
Once the primary stabilization
Estimation of lift required to return to presettlement
elevations
operations were moved to the next
stage. Each grout casing was advanced
at 1 ft (0.3 m) increments and 5 cu ft (0.1
m3) of low mobility grout was injected
to stabilize the soft soils. Real-time
modeling of the compaction grout
co l umns i s ve ry bene f i c i a l in
identifying key areas where additional
grout injection may be necessary.
program was completed, the grouting
contractor was able to proceed with the
lifting program. Each footing spanned
the interior and exterior, with the
largest section located on the interior of
the building and a small section on the
exterior. The exterior section was
grouted first to stabilize and control
footing rotation and then the interior
was grouted to lift the structure. This
process was repeated at each spread
footing to gradually achieve the desired
amount of lift. The foundation elevation
was monitored using an optical transit
to observe rulers established on each
individual column.
The column and footing with the
most settlement was addressed first to
match the adjacent footing elevations.
Then the footings were gradually
releveled, beginning at the center
column (where the greatest settlement
occurred) and continuing to the outer
columns where the least amount of
settlement occurred. The center
foundation was raised approximately
3.5 in (90 mm).
During the lifting process with
compaction grouting at the footings,
push piers were utilized on the outside
of the stairway structure to limit the
lateral forces on the retaining wall that
was near the stairs. The push piers
102 * DEEP FOUNDATIONS * SEPT/OCT 2023
September/October 2023

Table of Contents for the Digital Edition of September/October 2023
