Enhancement of undrained shear strength and compressibility behaviour of marine clay by biomineralization under electrokinetic method
Marine clay soils imposed an instability problem under applied load due to the absence or limitation of its shear strength. This weakness of marine clay causes large settlements leading to failure of structures and loss of their efficiency and their working purposes. This problem typically occurs...
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Format: | Thesis |
Language: | English |
Published: |
2020
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Online Access: | http://psasir.upm.edu.my/id/eprint/89905/1/FK%202020%2064%20ir.pdf |
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Summary: | Marine clay soils imposed an instability problem under applied load due to the
absence or limitation of its shear strength. This weakness of marine clay causes large
settlements leading to failure of structures and loss of their efficiency and their
working purposes. This problem typically occurs in the areas near to seashores and
riverbanks. The presence of a large amount of water causes significantly large
deformations and settlements, which then caused damage to the nearest structures
and human safety. Accordingly, biomineralisation treatment under the electrokinetic
(EK) effect has been a recent approach to stabilise the soil. Biomineralisation
treatment shows a significant improvement in the undrained shear strength of weak
soils, as proven by previous researches on sandy soils. It was also applied to clayey
soils and showed a significant increase in undrained shear strength, but under EK
effect due to permeability limitations and pores limited size to the size of bacteria
cells. This method promises to stabilise soils efficiently without any side effects on
the environment. However, there is no research on marine clay treatment using
biomineralization under EK method. Also, there is no research investigated any
alternative metal source to CaCl2 such as MgCl2. In addition, previous studies were
focusing on increasing the undrained shear strength without considering the
homogeneity of the treatment and reduction of its variation. So that, factors like
distance and injection location should be considered to achieve better treatment of
marine clay soil. In this study, an improved method of biomineralisation treatment
under the electrokinetic effect was proposed and applied on marine clay to
investigate the efficiency of this method. Bacteria, Bacillus pasteurii was used and
was tested at three different cells concentration 2.00 × 107, 1.00 × 107 and 0.5 × 107
cells/ml. Two different metal sources were tested, which were CaCl2 and MgCl2 at
seven different molarities; 0.00, 0.75, 1.00, 1.50, 2.00, 3.00 and 4.00 M while
CO(NH2)2 was tested at four different molarities 1, 2, 3 and 4 M as the required
source of carbonate ions. The efficiency of Microbial Induced Carbonate Precipitation (MICP) was investigated by applying 192 different combinations of
bacteria, metal sources, and CO(NH2)2 for identifying optimum concentrations,
which were B1C1aU1 and B1M1aU1 for CaCl2 and MgCl2 respectively. Both
combinations were injected into soil specimens, where both shown a significant
increment in undrained shear strength after 7 days of treatment from 4.17 kN/m2 to
a range of 20 to 76 kN/m2. Both effects of distance between the two electrode cells
and location of CO(NH2)2 injection were also investigated by using a physical model
with dimensions of 1200 × 300 × 500 mm (L × W × H ). Three different distances
investigated were 450, 600 and 750 mm between cathode and anode cells. Results
show that undrained shear strength was inversely proportional to the distance. On
the other hand, four different CO(NH2)2 injection locations which were at zero, L/4,
2L/4 and 3L/4 from cathode cell were tested. Results showed that undrained shear
strength was inversely proportional to the CO(NH2)2 injection location from the
cathode cell, but the variation in undrained shear strength along the treatment path
between the two electrodes where it was decreasing as the CO(NH2)2 injection
location getting far from the cathode. Eventually, numerical equations were derived
to ease the prediction of concentrations of required materials for the targeted
efficiency of MICP and for optimum treatment of marine clay where the equation Su
= 53.862 - 1.534d - 17.305i - 0.045D - 0.023X could be used as a guideline and
estimation for undrained shear strength after treatment by biomineralization under
electrokinetic method for future research. |
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