What Is Compaction Grouting? Compaction Grouting Applications and Installation Process

What Is Compaction Grouting? | Applications and Uses of Compaction Grouting | Advantages  and Disadvantages of Compaction Grouting

What Is Compaction Grouting?

Compaction grouting is the process of pumping a grout mixture into porous spaces beneath the ground in order to seal them.

Compaction grouting can be used for many purposes, such as installation of highways and residential driveways, installation of municipal storm drainage systems, installation of sewage collection systems, and preventing contamination from leaking or seeping underground sources.

The compaction grouting process is very different from the traditional techniques of grouting.

The traditional process involves a drill and a specially formulated grout, while compaction grouting uses a vibrator to push a small amount of pre-mixed concrete through a pipe and into the ground.

The pre-mixed concrete is then pushed into the porous space and vibrated until it hardens.

A compaction grouting machine consists of a mulcher, a pump, and a vibrator. The drill is removed from the traditional grouting machine.

The drill is replaced with an auger or paddle wheel which pulls the grout mixture out of the tank and pushes it through the pipe.

The pump then pushes the grout through the pipe to the ground where it is pushed into a porous space with a vibrator. The vibration causes the grout to expand, and thus fill the space between the spaces.

The grout mixture used for compaction grouting is a high-strength concrete slurry that is pre-mixed with water. The mixture was originally designed to prevent concrete from shrinkage caused by freezing temperatures.

Today, compaction grouting mixtures have also been developed for use in constructing highways and driveways, as well as for use in stormwater drainage systems and sewage collection systems.

Compaction Grouting Installation Process

Step 1: Hole is drilled or casing is driven to the bottom of the proposed treatment zone.

Step 2:  Compaction grout is then pumped through the casing until one of several refusal criteria have been reached.

Step 3: Casing is lifted to the next stage and Steps 1 & 2 are repeated.

Applications and Uses of Compaction Grouting

Compaction grouting is injecting a low slump mortar grout into loose, granular soils in order to densify them and stabilize subterranean cavities or sinkholes.

Applications include;

1. Used in stabilizing rubble fills, poorly placed fills, loosened or collapsible soils, soluble rocks, and liquefiable soils.
2. Prevent collapse of structures built into soils containing expansive clay minerals that can be triggered by fluctuating water table levels resulting from storm events. Because the columns do not require structural connection to the foundations, they are frequently used for treatment beneath existing buildings.
3. Stabilize River banks, stabilize excavation faces in tunnels and basements, and fill voids in open trenches.
4.  Reinforced compaction grouting is also used to construct reinforced concrete structures in the ground or underwater, such as bridges, utility tunnels, and other deep excavations. The pre-mixed concrete grout mixture is pumped into the ground where it hardens to form a monolithic structure inside the pre-excavated tunnel or trench.
5. Used in constructing underground facilities such as sewage collection systems (see “Types of sewage collection systems”) and stormwater drainage systems.
6. Used to stabilize soft natural materials, such as organic soils, during construction of infrastructure projects in particular rock quarries (see also “Types of rock quarries”).
7. Stabilize sinkholes or minimize sinkhole hazards by increasing bearing capacity.

Advantages of Compaction Grouting

1. High productivity and less expensive than traditional mechanical grouting methods.
2. Can be used to reduce traffic on, and improve traffic flow in, heavily trafficked streets.
3.  Reduces slope instability by better controlling the soil surrounding a highway or utility corridor, thus reducing the potential for sudden collapse due to soil settlement and subsidence phenomena.
4.  Provides permanent local improvements that can be used with normal maintenance practices, thereby minimizing the investment costs required by other technologies such as segregation.
5. Compaction grouting is a quasi-static technique with regulated injection pressure and rates. As a result, there is no risk of raising pore water pressure or causing post-construction settling.
6. Precise treatment is achieved by injecting grout to a specified depth and volume. Properly designed and constructed treatment will not result in a void or voids that could potentially be filled by non-grouted material.
7. Fast installation speed (under 5 days of normal installation times).
8. High-strength, non-shrinkable grout mixture is used to ensure the integrity of retaining structures even in freeze-thaw conditions.
9. Can be used to stabilize erosion and settle sediment around road edges as part of temporary traffic control measures following construction or after heavy rains.
10. It is non‐destructive and adaptable to existing foundations
11. Compaction grouting also has a wide applications range

Disadvantages of Compaction Grouting

1.  The process may be more expensive than traditional methods when sufficient access to remove excess excavated material is costly and time-consuming (i.e., tunneling).
2.  Longer construction schedule when compared to traditional grouting techniques.
3.  The compaction grouting process cannot be applied in all soils because it requires that there be enough loose and granular soil to allow the resin to flow into the voids, as well as having adequate amounts of fines for the resin to adhere to.
4.  The compaction grouting process is not able to achieve structural consolidation in stiff clay soils, because it does not sufficiently reduce the volume of loose pore spaces within the clay matrix.

Compaction Grouting FAQs

1. What is compaction grouting and how is compaction grouting done?

Compaction grouting is a ground improvement technique that is used to enhance the density of the soil. This grouting procedure is typically employed to repair the settling of delicate structures.

Compaction grouting is accomplished by injecting stiff mortar-like grout under pressure into cased boreholes to form bulbs, pushing the surrounding soil to the side and increasing its density.

This grouting procedure is used to treat a wide range of loose soils with reasonably excellent drainage, and it may be conducted at depths ranging from 2m to many tens of meters.

The process is done from the ground up, with the grout bulbs being formed in 1m increments from the bottom up.

The degree of densification is determined by the kind of soil treated and the grid pattern chosen for the injection sites, with injection rates ranging from 4 to 6m3 per hour in general, and as low as 2m3 per hour in especially sensitive situations. Injection pressures typically vary from 1 to 4 MPa.

Compaction grouting can also be performed from an existing basement or in areas with restricted headroom, and drilling through hard material to reach the low strength strata underneath for treatment is conceivable.

2. What is the basic principle of compaction grouting?

Compaction grouting improves the density of loose and permeable soil, typically around existing structures.

A grout mixture is forced into the ground via perforated casings with a pump and under pressure.

The grout has a high strength that stiffens the soil at depth, and this prevents settlement of the structure above it, as well as refloating sunken features such as pipelines.

The use of a mortar or concrete laterally compacts the soil without vibrations.

3. Is compaction grouting expensive?

The cost of compaction grouting depends on the size of the worksite, the method chosen for injection pressure and flow rates, and the soil conditions.

In general, the process is much less expensive than traditional mechanical grouting methods.

In many cases it may be a less expensive alternative to continuous excavation—especially when compared to underground transportation of excavated material.

4. What is displacement grouting?

The injection of grout under pressure with the purposeful goal of spatially displacing the host medium is referred to as displacement grouting.

Injection techniques such as compaction grouting and hydraulic fracturing are examples of displacement grouting

Injection grouting is the original form of compaction grouting and has been employed in the construction industry to increase bearing capacity and stabilize sites.

Resin injection grouting provides immediate structural consolidation by filling voids in loose, permeable soils or adsorbing water within bedrock to improve drainage while providing shallow compacting for deeper soil improvement.

Compaction Grouting  Process