Soil improvement and construction methods in peat - Geotechnics of Organic Soils and Peat - page 157

in the sense that acids are; however, if steel in a chloride solution is exposed to air,
rusting will occur at the junction of the liquid and air. Bicarbonate is noncorrosive (US
Army Corps of Engineers, 1995, Kazemian et al ., 2010).
6.6.3 Silicate chloride amide system
The silicate chloride amide system is a widely use silicate grout system containing
sodium silicate as a gel forming material. The silicate aluminates-amide system has
been used for strength improvement and water cut-off. Its behaviour is similar to the
silicate chloride amide system but is better for shutting off seepage or the flow of
water. The cost is slightly higher, and this system can be used in acidic soils. Amide
will act as a reactant and the calcium chloride and sodium aluminates will be used
as the accelerator. These reagents bring an almost instant setting time and produce a
very low penetrability-type gel that is unsuitable for permeation treatments (Rawlings
et al. , 2000; Kazemian et al ., 2010).
The function of the accelerator is to control the gel time and impart strength
to the gel. The effect of the accelerator is important at temperatures below 37 ◦ C and
increases in importance as the temperature decreases. Excessive amounts of accelerator
may result in undesirable flocculation or formation of local hardening. This causes
variations in both the gel and setting times that would tend to plug injection equipment
or restrict penetration, resulting in a poorly grouted area. Therefore, a retarder should
be added in the mixture to delay the setting time and formation of gel (US Army Corps
of Engineers, 1995).
Other chemical grouts such as, acrylamide, N-methylolacrylamide, polyurethane,
epoxy resins, aminoplasts, phenoplasts and lignosulfonates have been used for stabi-
lization of sandy soils and clays (Nonveiller, 1989; Kazemian et al ., 2010; Magill and
Berry, 2006; Vinson, 1970; Rawlings et al. , 2000; Karol, 2003).
6.7 CHOOSINGTHE GROUT
In order to choose a grout type, several properties of grout should be considered, such
as rheology, setting time, toxicity, strength of grout and grouted soil, stability or per-
manence of the grout and grouted soil, and the penetrability and water tightness of the
grouted soil (Rawlings, 2000). Moreover, the spreading of grout plays an important
role in the development of grouting technology. In the actual field, the grouting method
requires extensive consideration of the grout hole equipment, distance between bore-
holes, length of injection passes, number of grouting phases, grouting pressure and
pumping rate (Shroff and Shah, 1999). Guidance on selecting a particular grout can
be found in Table 6.3.
6.8 LIGHTWEIGHT FILL
An alternative is to utilize a very light material such as polystyrene blocks to cope
with extreme soils. A typical density of polystyrene is about 20 kgm − 3 , which may
possibly increase to 100 kgm − 3 as the material absorbs water from the ground. This