Engineering and Construction

There are many grouting methods that can be used to strengthen the on-site soil (see Table 15.4). For example, in order to stabilize the ground, fluid grout can be injected into the ground to fill in joints, fractures, or underground voids (Graf, 1969; Mitchell, 1970). For the releveling of existing structures, one option is mudjacking, which has been defined as a process whereby a water and soil-cement or soil-lime cement grout is pumped beneath the slab, under pressure, to produce a lifting force that literally floats the slab to the desired position (Brown, 1992). Other site improvement grouting methods are as follows:

• Compaction grouting. A commonly used site improvement technique is compaction grouting, which consists of intruding a mass of very thick consistency grout into the soil, which both dis- places and compacts the loose soil (Brown and Warner, 1973; Warner, 1978, 1982). Compaction grouting has proved successful in increasing the density of poorly compacted fill, alluvium, and compressible or collapsible soil. The advantages of compaction grouting are less expense and dis- turbance to the structure than foundation underpinning, and it can be used to relevel the structure.

The disadvantages of compaction grouting are that it is difficult to analyze the results, it is usually ineffective near slopes or for near-surface soils because of the lack of confining pressure, and there is the danger of filling underground pipes with grout (Brown and Warner, 1973).

• Jet grouting (columnar). This process is used to create columns of grouted soil. The grouted columns are often brittle and may provide little or no resistance to lateral movements and may be broken by lateral ground movements (Seed, 1991).

• Deep mixing. Jetting or augers are used to physically mix the stabilizer and soil. There can be overlapping of treated columns in order to create a more resistant treated zone.