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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

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.

8 After van Passen (2011)

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)

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

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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0 5 10 15 20

Wat

er h

ead

(cm

)

Time (s)

pwp1

pwp2

pwp3

0

10

20

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40

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0 5 10 15 20

Wat

er h

ead

(cm

)

Time (s)

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

0

200

400

600

800

1000

1200

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1600

0 2 4 6 8 10 12 14

Mass CaCl2/Mass Sand (%)

Unc

onfin

ed C

ompr

essi

ve S

tren

gth

(kPa

)

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!