September/October 2023 - 100

By July 2019, Bin 4 had undergone
differential settlement on the order of
5 in (127 mm) from the south-west
quadrant to the north-east quadrant
and continued getting worse through
August 2019. Compaction grouting was
proposed as the least intrusive and most
economical method to stabilize and
relevel Bin 4 to acceptable operational
tolerances.
Design - To alleviate the settlement
and level the ring wall foundation, a
total of 67 compaction grout locations
were drilled through, and adjacent to,
the foundation. The grout holes were
drilled at differing angles to ensure
adequate soil densification and effective
releveling directly under the
spread footing.
Grout locations were laid out
utilizing a primary, secondary, tertiary
and quaternary sequencing. The
bottom-up method of grouting was
employed for each location.
To reduce the economic impact to
the owner, existing onsite soil was
screened and used for the primary
aggregate for the grout mix. Minimal
additional aggregate was imported.
Construction - Prior to the grouting
program, the grouting contractor performed
an initial elevation survey of the
silo foundation to establish a baseline for
releveling and continued surface movement
monitoring. A survey point was
placed approximately every 10 ft (3 m)
along the foundation perimeter.
Primary, secondary and tertiary
grout locations were installed at
5-degree, 10-degree and 15-degree
angles respectively. Flush joint steel
casing was drilled or driven through the
foundation to a competent bearing soil
layer, estimated at 18-30 ft (5.5-9 m)
below grade. The quaternary grout
locations were drilled or driven adjacent
to the foundation at a 25-degree
angle to a depth of 18-25 ft (5.5-7.6 m) to
assist with releveling. Actual depth of
each grout column was determined in
the field based on actual conditions
encountered.
100 * DEEP FOUNDATIONS * SEPT/OCT 2023
Grouting was performed in 1 ft
(0.3 m) increments as the casing was
extracted. At each grout stage, approximately
2-5 cu ft (0.05-0.14 m3) of
grout was injected until the bottom of
the footing elevation was contacted.
Multiple grout locations were injected
simultaneously to ensure the foundation
was lifted gradually and evenly.
This prevented further cracking or
other damage to the foundation and
overall silo structure. During grout
operations, advancement to the next
stage was determined when one of the
following occurred:
* A minimum pressure of 250-400 psi
(1.72-2.76 MPa), as measured at
the grout injection header, was
recorded.
* 2-5 cu ft (0.05-0.14 m3) of grout was
placed in any single stage.
* Undesirable lift or heave of the
structure.
During grout injection, movement of
the foundation was monitored using a
rotating laser level, water level or
optical transit. The primary and secondary
grout locations were used to
stabilize the structure while the tertiary
and quaternary locations were
used to relevel. Upon completion of the
releveling and stabilization program,
the interior concrete slab was checked
for any remaining voids between the
slab and subgrade soils. Any voids
encountered were filled with grout.
Quality Assurance and Quality
Control - Grout logs were used to record
location identification, maximum
pumping pressure at each stage, grout
volume injected at each stage, depth, infield
observations during grouting and
pump rate. The injection rate and grout
mix were modified in real time to
respond to in situ conditions. After each
sequence of grouting, a new elevation
survey at each 10 ft (3 m) perimeter
interval was completed by the grouting
contractor to verify the amount of elevation
recovery. Additionally, 3D modeling
of the grout columns was completed to
create a visual representation of the
work completed beneath the foundation.
Performance - After completion of
the compaction grouting program, the
difference in elevation throughout the
entire circumference of the ring wall
foundation was within 1.5 in (38 mm).
This was within the operational
tolerance of the silo. Shortly after
completion of the grouting program,
any necessary adjustments were made
to the silo filling equipment to return it
to full operational mode and the owner
was able to begin refilling the silo in
stages. The silo has remained fully
operational ever since.
3D modeling of the grout columns was completed to
create a visual representation of the work completed
beneath the foundation
3D modeling of compaction grout locations
beneath grain bin silo foundation
September/October 2023

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