Download - GeoSS Event Seminar 12 July 2012_slides
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Soil Treatment using Bacteria
GeoSS Seminar on 12 July 2012
Speaker: Chu Jian Research team: V. Ivanov, V. Stanikov, J. He, M. Naeimi and B. Li, A. Whittle (MIT) and K.P. Lam (JTC)
1. What is biocement?
Biocement A construction material made of naturally occurring microorganisms at ambient temperature.
Biogrouting - Use of microbial activities or products to reduce the permeability and/or increase the shear strength of soil.
Why biocement - It is one of the most promising solutions to a sustainable ground improvement.
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2. How does it work?
Original soil
Biocementation
Bioclogging
Strengthened soil
Clogged soil
Sand grain
Slime bonding
Sand grain
Sand grain
Slime bonding
Sand grain
Scanning Electron Micrograph (SEM) showing the formation of Crystals of CaCO3
Bonding of sand grains by slime
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2.1 Mechanisms
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33. Advantages of Biocement -1
Biocement is made of naturally occurring microorganisms at ambient temperature and thus requires much less energy to produce.
It is sustainable as microorganisms are abundant in nature and can be reproduced easily at low cost.
The microorganisms that are suitable for making biocement are non-pathogenic and environmentally friendly.
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Advantages of Biogrouting -2
It will also simplify some of the existing construction processes. For example, the biocement can be in either solid or liquid form. In liquid form, the biogrout has much lower viscosity and can flow like water. Thus, the delivery of biocement into soil is much easier compared with cement or chemical grouts. It becomes possible to treat soil without disturbing the ground or environment.
Furthermore, when cement is used, one has to wait for 28 days for the full strength to be developed, whereas when biocement is used, the reaction time can be controlled or much reduced if required.
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44. History of biogrouting
The microbial influence on soil strength has been observed for a long time (e.g., Bang, 1999)
In 2004, Whiffin completed the first ever PhD on Microbial CaCO3 precipitation for the production of biocement.
Introduction paper by Mitchell and Santamarina in ASCE in 2005. More groups (including NTU) began to work in this area from 2006. 1st Int Workshop on Bio-Soil Interactions in 2007 ASCE GeoFrontiers sessions (New Orleans) in 2008 ISSMGE (Alexandria) in 2009 Ground Improvement Conference (Singapore) in 2009 ASCE GeoFrontiers Sessions (Dallas) in 2011 2nd Int Workshop on Bio-Soil Interactions (Cambridge) in 2011 Brussels Ground Improvement Symposium in 2012 Geotechnique Symp in Print 2013.
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5. Current Status
It is still confined mainly as lab studies. However, the scale of samples have increased rapidly.
Field trials has started.
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56. Three Major Applications
Biocemention to turn sand into sandstone or soft clay to fill materials.
Bioclogging to form an imperious crust or layer on sand and reduce the porosity and hydraulic conductivity of soil or fissured rock.
Biogas to reduce liquefaction potential of sand by making it slightly unsaturated using biogas.
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BIOGAS FOR MITIGATON OF LIQUEFACTION
Application 1
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6Liquefaction effects
Cyclic strength doubles when the pore pressure coefficient B decreases from 1 to around 0.2 (or Sr = 85%).
After Yang (2004)
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7Mitigation of Liquefaction using gas Recent field studies have shown that liquefaction
potential of sand can be greatly reduced by injecting a small amount of gas into soil.
Inclusion of gas also improves the mechanical properties of sand.
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Biogas method
There is no effective method so far that can introduce tiny gas bubbles uniformly in-situ and keep the bubbles in soil for a long time.
Biogas method can produce very tiny gas bubbles in-situ. The bacteria and nutrient regents can flow like water and thus the distribution (or production of gas) can be more uniform.
Denitrifying bacteria have been used to produce nitrogen gas from nitrate. 5 C2H5OH + 12 NO3- 6 N2 + 10 CO2 + 9 H2O + 12 OH-
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8Triaxial CU compression tests Undrained compression of loose sands
B and Degree of Saturation
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9Liquefaction model tests
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acc1
acc2
lvdt
pwp3
pwp2
pwp1
las4
las3
las212345678910
las1
las6 las5
Cement block
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las1
Pore water pressure (amax=1.5 m/s2, Dr43~52%)
Sr=100%
Sr=90%
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Wat
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pwp1
pwp2
pwp3
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Biogas to reduce settlement
Conclusions
Liquefaction susceptibility of fully saturated sands can be greatly reduced by lowering degree of saturation;
Desaturation of sands can be achieved by microbial denitrification process.
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BIOCEMENTATION Application 2
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Biocementation of sand
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UC strength (UCS) versus calcium carbonate content for biogrout treated sand (after Van der Ruyt and van der Zon, 2009)
For normal applications, the UCS < 3 MPa. This requires a calcium content of 100 to 200 kg/m3. To achieve the same UCS strength for sand using cement grouting, the amount of cement used would be between 250 to 300 kg/m3.
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Biocementation of sand
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Mass CaCl2/Mass Sand (%)
Unc
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Wet Samples Dry Samples
Using Microbially-induced Calcium carbonate (CaCO3) Precipitation (MICP) method
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Turning sand into sandstone
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Potential Applications
To enable sand bund to be built with a steeper slope and become less erodible
To be used in where permeation grouting could not be applied very fine sand or silty sand
To turn soft soil or slurry into fill materials for land reclamation at a lower cost
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BIOCLOGGING Application 3
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Build water pond by biocemented crust
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Rupture strength = 35.9 MPa
k = 1.6 E-7 m/s
Conclusions
Biocement can be used for soil improvement to enhance the shear strength of soil, mitigate liquefaction potential and control seepage and erosion.
The use of biocement is more economical and environmentally friendly. It is also earlier to be delivered.
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References Ivanov V. and Chu J. (2008). Applications of microorganisms to
geotechnical engineering for bioclogging and biocementation of soil in situ. Reviews in Environmental Science and Biotechnology, Vol. 7, 139-153.
Chu, J., Ivanov, V., Lee, M.F., Oh, X.M. and He, J. (2009). Soil and waste treatment using biocement Proc. International Symposium on Ground Improvement Technologies and Case Histories (ISGI09), 9-11 Dec, Singapore.
Stabnikov, V., Naeimi, M., Ivanov, V., and Chu, J. (2011). Formation of water-impermeable crust on sand surface using biocement. Cement and Concrete Research, Vol. 41, 1143-1149.
Chu, J., Stabnikov, V., and Ivanov, V. (2012). Microbially induced calcium carbonate precipitation on surface or in the bulk of soil. Geomicrobiology Journal.
He, J., Chu, J. and Ivanov, V. (2012). Mitigation of liquefaction of saturated sand using biogas. Geotechnique (under revision)
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Thank you! Best wishes to GeoSS and ALL!