Compaction grouting
Compaction grouting is a displacement method of improving the bearing
capacity of soil. Where low strength, low capacity or unstable soil does not
have the required bearing capacity for a specified load, a high density, very
low slump grout is injected into the soil. The grout is injected at designed
depths and locations in a grid pattern at high pressure. As a result, the viscous
grout forms into a bulb or column at the desired depth, displacing the soil,
densifying or compacting it, resulting in improved bearing capacity.
Compaction grouting is a proven method of foundation grouting with a long
history of successfully completed projects. With the correct soil conditions, it is
an advantageous technique for new construction and as a means of correcting
soil failure under an existing structure where unacceptable settlement is
occurring or has occurred.
Advantages
Precautionary measure under new construction
Remediation measure to stabilize and, if necessary, raise existing
structures
Using precision instrumentation, raising is done within specified
tolerance
Improves the bearing capacity of weak soils
Irregular fills or varying native soils become more uniform
The low slump grout has the tendency to improve the weakest soils
Completed without or with very little disturbance to landscape, floors,
roads, or nearby structures
Portable equipment is available for limited access. Hand carried
drivers and extractors can be used with low headroom limitations
of 6 feet (2M)
Grout can be pumped up to 200 feet also reducing disturbance and
damage near the soil or structure requiring remediation
Inexpensive & rapid compared to other soil stabilization techniques
A proven technique with a long history of successfully completed projects
How it works
Injection pipes are installed into soil at design locations to desired depths. The pipes
are driven, jetted, or drilled to the bottom of the zone needing correction. A low
volume, high-pressure pump is used to place the grout. Very low slump, paste consistency
grout is injected at low pumping rates. The grout forms into a bulb shape
exerting radial forces in all directions as it displaces and compacts the adjacent soil.
The low pumping rate is employed to prevent both soil fracturing and uplift by
allowing excess water to dissipate. Injection continues until a pre-determined refusal
pressure is reached or uplift occurs at the surface.
The injection pipes are then raised to a shallower depth and the process is repeated.
The ability of the soil to resist surface uplift or heaving usually limits the degree to
which compaction grouting can effectively compact the soil. Precise instrumentation is
used to detect upward movement in the soil or in a building. Settling buildings can be
stabilized and, if desired, precisely raised as needed to within exacting tolerances.
Soils applicable for compaction grouting are fine-grained with sufficient permeability
to allow excess water to flow and dissipate.
The effective radius of an injection hole varies with the soil type. For this reason, a
split-spacing method is generally used. Where large areas are being treated, the
primary hole pattern is either rectangular or diamond shaped. Holes are often on
5-10 foot centers (1.5-3 meters). Secondary check holes are placed in the center of
the primary pattern.
The soils
best suited
to compaction grouting are fine grained with sufficient permeability to allow excess water
to dissipate. The process has also been used successfully in a wide variety of soils and
fills. Irregular fills or varying native soils will become more uniform with compaction
grouting. An advantage of compaction grouting is the tendency to improve the weakest
soils. The effective radius of the grout hole varies with the type of soil being treated.
Where large areas are being treated, the primary hole pattern is a diamond or square
pattern with holes on 5 to 10 feet (1.5 to 3 meters) centers. Secondary or check holes are
placed to the center of the pattern.
Limited Access
Equipment and procedures
have been designed for limited access. Hand carried casing drivers and extractors can be
used with head room limitations as little as six feet (2 meters). Grout can be pumped
distances of up to 200 feet (60 meters) in extreme cases. The process can be completed
with only minor disturbance to the landscape, floors, roads, or nearby structures.
The portable equipment can be quickly mobilized if needed. A project
was recently completed under an emergency contract when a state highway required closing because of settlement.
