Ground improvement is the term given to a variety of construction techniques permitting construction on soils by changing their characteristics. Slurry walls, soil mixing, grouting, installing bio-polymer drains and reactive barrier walls are all techniques which can be employed for providing a sound foundation for buildings, earthquake protection and overall site improvement.
Slurry Walls
Slurry walls are deep trenches filled with an engineered mixture of clay and water which reaches down to the ground water. The thick solution prevents flow of ground water into nearby rivers or other bodies of water. This is particularly useful in preventing water pollution when the ground water is expected to be contaminated by factory run-off.
At clean sites slurry walls are used for a variety of purposes, such as preventing ground water from entering dig sites or flooding mines and quarries. They can also stop dammed lakes from losing their water to the surrounding ground, where it might bypass the dam.
Soil Mixing
Soil mixing (or auger mixing) is the practice of placing pillars of soil and cement columns into the earth. The purpose of these columns is for subsidence remediation, or the act of strengthening the ground for buildings placed upon it. Originally developed in America during the fifties, this practice was later employed by the Japanese to combat earthquakes.
Grouting
Grouting, or jet, soil and rock grouting, is the process by which the ground is either parted or filled. Jet grouting refers to a technique wherein highly pressurized water is used to blast the ground apart, often prior to soil mixing.
Soil and rock grouting refers to the process by which voids in the ground are filled. Voids are essentially holes or caves, so a mine would be a void in the ground, as would any gap opened via jet grouting. Slurry walls and soil mixing are both classified as soil and rock grouting, as is the process of injecting concrete into empty mines or holes in a damaged dam.
Bio-Polymer Drains
Bio-polymer drains are trenches which can be used for irrigation or pipe laying. It begins with a slurry wall which is then emptied, leaving only a small trace of nontoxic residue. A degradable polymer is used in the place of slurry to soften the ground and support high walls during excavation while a hydraulic excavator digs the trench further. The polymer is then degraded back into water and pumped out of the trench.
This is an inexpensive way to create trenches as the labor, effort and time required to create a trench of any length or depth quickly becomes more expensive than a quantity of degradable polymer and one excavator.
Reactive Barrier Walls
Employed to remedy contaminated soil and ground water without complex and expensive pumping and treating processes, a permeable reactive barrier wall is buried in a narrow trench between the contaminated soil and nearby water sources. The wall includes granulated iron, activated carbon, chemicals, clay and human engineered bacteria developed to deal with the expected contaminant. Occasionally, slurry walls are used to funnel contaminated water towards a reactive barrier wall as slurry walls are less expensive.
There are many other minor techniques which may be used, but these five are the primary methods by which soil is strengthened and cleansed.