Sustainable Ground Improvement Technique for Geo-Disaster Mitigation - Sustainable Practices in Geoenvironmental Engineering - page 454

CaCO 3 + 2HCl → Ca 2+ + 2Cl − + H 2 O + CO 2 ↑ (12.10)

1/2Ca Mg(CO 3 ) 2 + 2HCl → 1/2Ca 2+ + 1/2Mg 2+ + 2Cl − + H 2 O + CO 2 ↑ (12.11)

If the amount of CO 2 is obtained, the mass of calcium carbonate (CaCO 3 ) can be estimated
from Equation 12.10. The amount of CO 2 is estimated using the relationship between CO 2
gaseous pressure produced and pure reagent of CaCO 3 used. The conversion from CaCO 3
to CaMg(CO 3 ) 2 can be made by calculation. The content of carbonate C is deined as

m
m

C

= 100

(12.12)

where m c is the mass of carbonate and m is the mass of dry soil.

12.6 Artificial Diagenesis for Geo-Disaster Mitigation
The vulnerability of soft soils to geo-disasters is in large measure because of low quality
(undesirable) soil properties such as high compressibility, low strength, low bearing capac-
ity, and high liquefaction potential. Utilizing artiicial diagenesis as a tool for improvement
of low quality soil properties has considerable merit since this technique can be applied
in situ and is robust, sustainable, economic, and “environmentally friendly.” As seen in
Figure 12.9 with respect to laboratory studies, the time required to obtain carbonation—
carbonates that would act as cementation bonds between soil particles—is relatively short.

12.6.1 Injection of Microbes and Reactive Solution

Interactions between microbes and soil particles are dependent on many factors (Scheibe
et al., 2007). Since microbes usually have negatively charged surfaces, they tend to dis-
perse when mixed in the cultivated solution. After mixing with the reactive solution, the
microbes may adsorb cations (Ca 2+ , Mg 2+ , etc.) and since the surfaces of soil particles are
predominantly negatively charged, partitioning of microbes with adsorbed cations to the
soil particles will result. Transport of bacteria in soils is dependent on the low velocity
of the injecting solution, which in turn is related to the permeability of the soil and the
hydraulic gradient. A high low velocity can hinder partitioning of microbes onto the sur-
faces of soil particles.
Designating the cultivated solution of ureolytic strains as B-solution and the reactive
chemical solution as R-solution, if the concentration of microbes is high, e.g., B/R > 1.0,
locculation with the cations in the R-solution will occur—resulting in the formation of
precipitates that cannot act as binders. Lower B/R ratios are more effective in producing
cementation of soil particles. Examples for injecting the B-R solution into dry and satu-
rated sands reported by Fukue et al. (2012, 2013) showed that the distribution of microbes
and the low pattern in the cemented sands were inluenced by the boundary condition
and permeability of the sands and were different for coarse and ine sands. Application
of a relatively high hydraulic gradient induces a jet low. Figure 12.10a shows a cemented