Environmental Engineering Reference
In-Depth Information
12.6.3 Concepts in Design
There are at least two approaches that one could take in designing application of artiicial
diagenesis. One approach, which one would consider as the conventional approach, is to
use the desired soil or ground strength as the design target. The other approach seeks to
improve the soil without any target strength in mind, i.e., “let us see how much improve-
ment can be obtained from the treatment process.” It stands to reason that with this sec-
ond approach, there is an implicit requirement that the capability of the improved ground
must surpass anticipated design requirements.
12.7 Concluding Remarks
The discussion in this chapter dealt with an innovative concept of soil improvement that
utilizes
diagenesis
, which can be deined as the carbonation process for soils. Carbonation
is obtained with the hydrolysis of urea from strong ureolytic bacteria. Studies on sandy
soils cemented with carbonates induced by microbes have shown signiicant increases in
unconined compressive strengths attributable to the cementation effect from the presence
of carbonate in the soil.
Artiicial diagenesis can be promoted by injecting the mixed solution of microbes and reac-
tive agents into ine soils. The gain in strength can be governed by the numbers of injections,
and the carbonate content obtained can be predicted from the concentrations of agents and
the number of injection times. Success in obtaining diagenesis depends on whether or not the
microbes are well distributed into the target zone. A useful technique for application in soft
ine-grained soils is to install sand piles (sand columns) into the soft ine-grained soils, which
can then be injected with the B-R solution (Figure 12.15) to allow for iniltration of the B-R
solution from the sand piles into the pore spaces of the ine-grained soils.
Injection of
B−R mixture
Soft fine soil
Embankment
Cemented
sand pile
Sand pile
Carbonate bones
FIGURE 12.15
Application of artiicial diagenesis into soft ine soil using sand piles.
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