1.1.1.1. Treatment under existing structures

Compaction grouting is a soil injection with low workability cement paste that remains homogeneous without entering in the soil pores. The cement mass extends, soil is moved and finally compacted.

Compaction grouting is a technique where a special type of cement mixture is injected into the ground. This mixture is designed not to seep into the soil but to push it outward. As this cement mixture expands, it compresses the surrounding soil, making it denser and stronger. This method is especially useful in areas that are prone to liquefaction, where the soil can lose its strength during an earthquake.

Imagine blowing up a balloon. As air fills the balloon, it stretches and pushes out against the balloon's surface. Similarly, when the cement mixture is injected, it fills the surrounding space, causing the soil to become tighter and more compact, just like the balloon gets larger.

The liquefaction improvement using compaction grouting divides into the following categories: (a) Treatment under existing structures; (b) Treatment in urban areas with low levels of vibration and noise; (c) Treatment in narrow areas.

Compaction grouting can be applied in various scenarios. The three main categories are: 1) Under existing structures, where it's crucial to stabilize foundations without causing vibrations; 2) In urban settings where disturbances must be minimized; and 3) In narrow spaces where traditional methods cannot be used. Each category is designed to address specific challenges related to soil stability and noise control.

Think of it like fixing a wobbly table leg. If you're working in a quiet cafe (urban area), you wouldn't want to create loud noise that disturbs customers (treatment in urban areas). Similarly, if the table is right next to a wall (narrow areas), your fix must be careful enough not to hit anything around it.

The execution of compaction by injection technology using bottom-up method takes place as follows. In the first stage, injection pipes set up on the foundation soil of the existing or future foundations using drilling machines. The injection process begins.

The process of compaction grouting involves several stages. First, specialized pipes are positioned in the ground. Then, the cement mixture is pumped through these pipes. The injection is done in a way that allows the pipes to be raised incrementally, treating all layers of soil effectively. This ensures that every portion is compacted and stabilized, making the overall structure more secure.

Consider a gardener planting seeds in a garden bed. They push the seeds into the soil evenly and make sure to cover them up. Just like this, the grouting process deliberately ensures that every part of the soil gets the cement mixture to strengthen it thoroughly.

The primary purpose of compaction grouting is to increase the density of soft, loose or disturbed soil, typically for settlement control, structural re-leveling, increasing the soil’s bearing capacity, and mitigation of liquefaction potential.

The main goals of using compaction grouting are to make weak soils stronger, reduce settling of structures, and make sure the ground can support buildings adequately. By increasing the density of soil, this method helps prevent the dangerous liquefaction that can occur during earthquakes.

Imagine you're filling a backpack with clothes. If you just throw items inside, it can easily fall over. But if you press the items down tightly, the backpack can hold its shape and support more weight. Compaction grouting does the same for soil, compressing it so structures can remain stable and safe.

Orense (2008) had a review of two case histories on the application of compaction grouting as liquefaction remediation was presented. One case involved the implementation in an open unrestricted space such as airport runways, while the second one was under an existing manufacturing plant.

In one case study, compaction grouting was successfully used at an airport runway, which is expansive and has few physical barriers. In another case, the technique was applied under a manufacturing plant, highlighting its versatility. The studies showed that compaction grouting was effective in improving the ground's on-site resistance to liquefaction.

Think of these case studies like different workout routines for strengthening muscles. Running in an open park (airport runway) is different from doing strength training in a crowded gym (manufacturing plant), but both help improve fitness. Similarly, compaction grouting can adjust to different environments while still achieving the goal of soil improvement.

The method of construction, whether “bottom-up”, “top-down” or combination of the two, affected the level of effectiveness and the resulting ground heave. The method was most effective on sandy soil with fewer fines content.

The success of compaction grouting depends on how the process is executed. Methods like 'bottom-up' or 'top-down' change how the soil reacts, including how much it may expand or heave during injection. It works best in sandy soils with less cohesion as these materials easily compact upon grouting.

Think about trying to pack a suitcase. If you have soft clothes (sandy soil), you can fit a lot more in and they squish together easily. But if you’re packing stiff items (soil with fines), the suitcase can become unwieldy and expand in unexpected ways. Choosing the right method and material ensures that everything fits well.

In addition, compaction grouting also increased the strength and the lateral earth pressure of the ground.

Aside from preventing liquefaction, compaction grouting strengthens the soil, which becomes crucial during seismic activities. The method effectively enhances the lateral support the soil can provide, making it even more resilient against external pressures.

Imagine fortifying a fence against strong winds. Thickening the base of the fence (like compaction grouting) means that it can withstand greater pressure without falling down. Thus, a well-compacted soil acts like that reinforced fence during earthquakes.

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