The document discusses the use of microbiology in geotechnical engineering, particularly through the application of biocement, a sustainable alternative to cement for improving soil properties. Biocement can enhance the shear strength of soil, mitigate soil liquefaction during earthquakes, and control water seepage and erosion effectively while being more environmentally friendly and cost-efficient. The paper also highlights ongoing research and potential applications of microbial technology in construction and soil improvement.

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Application of microbiology in geotechnical
engineering
Article by:
Chu, Jian
Department of Civil, Construction and Environmental Engineeri
ng, Iowa State University, Ames, Iowa.
Ivanov, Volodymyr
School of Civil and Environmental Engineering, Nanyang Techn
ological University, Singapore.
He, Jia
School of Civil and Environmental Engineering, Nanyang Techn
ological University, Singapore.
Last updated: 2013
DOI:
https://doi-org.ezproxy2.library.drexel.edu/10.1036/1097-8542.
YB130098 (https://doi-org.ezproxy2.library.drexel.edu/10.1036/
1097-
8542.YB130098)
Content
Enhancing shear strength of sand or to make a strong ground
Mitigation of soil liquefaction during earthquakes by using biog
as
Seepage and erosion control or construction of a water pond in a
desert
Outlook

2. Links to Primary Literature
Have you ever wondered how a high-rise building can be constr
ucted on soft ground? The answer is that the soft soil can
be improved before the construction of the high-rise building. I
n fact, bacteria, can be used to improve the engineering
properties of soil. In this article, the application of this microbi
al approach to geotechnical engineering, a discipline that
deals with soils and foundations, is discussed.
There are a number of ways to strengthen soft or weak soil. One
of the common ones is to use cement or chemicals to
increase the load-bearing capacity or the so-called shear strengt
h of the soil. The same process can be used to reduce the
water conductivity of soil or the rate of water flow in soil. This
is necessary when there is a need to prevent water from
flowing in the ground, for example, to cut off the flow of conta
minated groundwater. In this case, cement or chemicals are
used as binders and mixed with soil to either increase the shear
strength or reduce the water conductivity of the soil.
However, the use of cement or chemicals for soil improvement i
s not sustainable in the long run, because cement and
chemical production require a considerable amount of natural re
source (for example, limestone) and energy. The
production process also generates carbon dioxide, dust, and pos
sibly other toxic substances and thus is not
environmentally friendly. The use of cement or chemicals for so
il improvement is also expensive and time-consuming.
There is an urgent need to develop new and sustainable construc
tion materials that can reduce the need to use cement or
chemicals for geotechnical applications.
Using the latest microbial biotechnology, a new type of constru
ction material, called biocement, has been developed as an
alternative to cement or chemicals. Biocement is made by natura
lly occurring microorganisms at ambient temperature and

3. thus requires much less energy to produce. It is sustainable, bec
ause microorganisms are abundant in nature and can be
reproduced easily at low cost. The microorganisms that are suita
ble for making biocement are nonpathogenic and
environmentally friendly. Furthermore, unlike the use of cement
, soils can be treated without disturbing the ground or the
environment, because microorganisms can penetrate and reprodu
ce themselves in soil. Harnessing this natural and
inexhaustible resource may result in an entirely new approach to
geotechnical or environmental engineering problems and
bring enormous economic benefit to the construction industries.
The application of microbial technology to construction will
http://www.accessscience.com.ezproxy2.library.drexel.edu/
https://doi-org.ezproxy2.library.drexel.edu/10.1036/1097-
8542.YB130098
also simplify some 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 that of cement or chemicals. 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 much reduced or controlled if
required.
The principle of microbial treatment is to use microbially induc
ed precipitation of calcium carbonate or other approaches to
produce bonding and cementation in soil so as to increase the st
rength and reduce the water conductivity of the soil. A
number of studies have been done in recent years. Presently, mu
ch of the work is at the experimental stage. However, the
scale of treatment has increased rapidly with time and has reach
ed 100 m in recent years.

4. The microbiological processes induce calcium carbonate crystal
s, other minerals, or slimes, as shown by M. Van der Ruyt
and W. van der Zon (2009), L. A. Van Paassen and colleagues (
2010), and J. Chu and colleagues (2012). Those minerals
or slimes act as cementing agents between soil grains to increas
e the shear strength of soil and/or to fill in the pores in soil
to reduce the water conductivity, as shown in Fig. 1. The two pr
ocesses to increase strength and reduce conductivity have
been called biocementation and bioclogging, respectively. The p
rocess to deliver the biocement in situ to achieve
biocementation or bioclogging is called biogrouting. In the treat
ment of sandy soil, because the viscosity of biocement grout
is low, it is possible to pump it into the ground without mixing.
This will enable the construction process to be simplified. The
studies so far show that the biocement method is effective in bot
h increasing the shear strength and reducing the water
conductivity of soil. Some potential applications of biocement a
re discussed in the following.
3
Fig. 1 Schematic of the biocementation and bioclogging process
es.
Enhancing shear strength of sand or to make a strong ground
By using the microbially induced calcium carbonate precipitatio
n method, the shear strength of soil can be increased. We
know from our childhood experience building sand castles on th
e beach that dry sand will not stand. However, when dry
sand is treated with biocement, it not only can stand as a colum
n, it can also sustain a lot of weight, as shown in Fig. 2.
When cement or chemicals are used to treat soil, the amount of i
mprovement in the shear strength of the soil depends on

5. the amount of cement or chemical used. Similarly, when biocem
ent is used, the shear strength of the soil is affected by the
amount of metal precipitation. One way to measure the shear str
ength of soil is simply to compress a soil column between
two rigid plates, the so-called uniaxial compression test. The sh
ear strength measured by this method is called the uniaxial
compressive strength (UCS). In a study by M. Van der Ruyt and
W. van der Zon (2009), the UCS of biocement-treated
sand was measured for specimens having different calcium-carb
onate contents. The results are shown in Fig. 3. It can be
seen that the UCS strength increases with increasing calcium-ca
rbonate content. The highest UCS obtained was 27 MPa.
For normal applications, the UCS strength required is less than
3 MPa. This will only require a calcium content of 100 to
200 kg/m
. To achieve the same UCS strength for sand using cement grout
ing, the amount of cement required would be
between 250 and 300 kg/m
. Because the production of biocement can be cheaper, the overa
ll cost for biocement grouting
can be potentially lower.
3
3
Fig. 2 Sand column treated using biocement.
Mitigation of soil liquefaction during earthquakes by using biog
as
Soil liquefaction refers to a phenomenon in which a soil is trans
formed into a substance that acts like a liquid in response to
an external action such as an earthquake. When liquefaction occ
urs, the ground completely loses its bearing capacity and

6. undergoes large deformation. Soil liquefaction normally occurs
in saturated sand deposits during earthquakes. The ground
shaking causes the water pressure in the soil—
the pore water pressure—
to build up. When the pore water pressure has
increased to a certain point, soil liquefaction occurs. Soil liquef
action has been one of the major causes of earthquake-
related disasters. Liquefaction was largely responsible for the e
xtensive damage to ports and residential properties in the
earthquakes in New Zealand and Japan in 2010 and 2011.
Common methods that can be adopted for mitigation of soil liqu
efaction include densification and ground modification using
cement or chemicals. A new approach that is being developed is
called the biogas method. In this method, tiny gas bubbles
are generated in situ in saturated sand where liquefaction may o
ccur. When saturated sand is made slightly unsaturated by
the inclusion of gas bubbles, the amount of pore-water-pressure
generation in the sand under a dynamic load is greatly
reduced. According to research, if only about 5% of the water b
y volume is replaced by gas, the liquefaction resistance of
loose sand can be increased by more than 2 times.
However, it is not easy to introduce gas into the ground. Pumpin
g can be used. However, the distribution of gas bubbles
introduced by pumping will not be even. Furthermore, the gas p
umped into ground tends to be present in the form of
aggregated gas pockets rather than individual bubbles. As a resu
lt, the gas tends to escape from the ground. One of the
most effective ways to introduce tiny gas bubbles in situ is to us
e microorganisms. This method has the following three
advantages over existing methods. (1) Biocement can flow easil
y in sand, much like water. Gases can be generated easily
by bacteria anywhere underground using only a small amount of
energy. Thus the biogas method will be much more cost-
effective than any other method. The scale of treatment for liqu

7. efaction is normally very large, so the potential economic
benefit is significant. (2) The gas bubbles generated by bacteria
can be distributed more evenly than by other means. This
is because the gas bubbles are generated in situ rather than pum
ped. (3) The gas bubbles generated by bacteria are tiny
and less prone to escaping from the ground.
Some model tests using a shake table to generate ground motion
were done by our research group. A comparison of
ground settlement for a fully saturated sand layer and a sand lay
er treated with biogas is shown in Fig. 4. The settlement is
expressed as a settlement ratio, with the settlement for fully sat
urated sand being 100%. It can be seen from Fig. 4 that
Fig. 3 Unconfined compression strength (UCS) versus calcium c
arbonate content for biocement-treated sand. (After M.
Van der Ruyt and W. van der Zon, 2009)
2
with only 5% gas replacement, the ground settlement generated
by ground shaking with an acceleration of 1.5 m/s can be
reduced by more than 90%. Thus, the biogas method is effective
in preventing the occurrence of soil liquefaction or
reducing the damage caused by liquefaction.
Seepage and erosion control or construction of a water pond in a
desert
Biocement can also be used to reduce the water conductivity of
sand through the bioclogging mechanism, as shown in Fig.
2. One method that has been developed by our research group is
to use urea-reducing bacteria to precipitate a layer of
calcium carbonate on top of sand, as shown in Fig. 5. This hard
layer of crust has a water conductivity of less than 10

8. m/s and thus can be used as an impervious layer for water stora
ge. This means we now have a method for building a
water pond in the desert. The same method can also be used for
erosion control of a beach or riverbank. As the layer of
treatment is rather thin, the amount of biogrout used is small. T
hus the method can be more economical than conventional
methods.
Outlook
2
Fig. 4 Comparison of ground settlement induced by ground shak
ing under an acceleration of 1.5 m/s for a saturated sand
layer and a sand layer with 5% gas replacement.
2
−7
Fig. 5 Formation of (a) a thin impervious layer on top of sand u
sing the biocement method and (b) a water pond model built
using this method in sand.
The new construction material, biocement, has a number of adva
ntages over cement or chemicals for geotechnical
applications. Several potential applications exist for ground stre
ngthening, mitigation of liquefaction, and seepage or
erosion control. The new microbial technology provides a more
cost-effective, sustainable, and environmentally friendly
solution to ground improvement. However, a lot of research stu
dies still need to be done before this new approach can be
developed into common practice.

9. See also: Bacteria (/content/bacteria/068100); Cement (/content/
cement/118400); Engineering geology
(/content/engineering­geology/234000); Foundations (/content/f
oundations/270400); Grout
(/content/grout/301600); Microbiology (/content/microbiology/4
22200); Sand (/content/sand/600600); Soil
(/content/soil/631500); Soil mechanics (/content/soil-mechanics
/631900)
Jian Chu
Volodymyr Ivanov
Jia He
Links to Primary Literature
J. Chu, V. Stabnikov, and V. Ivanov, Microbially induced calciu
m carbonate precipitation on surface or in the bulk of soil,
Geomicrobiol. J., 29(6):544–
549, 2012 DOI: https://doi-org.ezproxy2.library.drexel.edu/10.1
080/01490451.2011.592929
(https://doi-org.ezproxy2.library.drexel.edu/10.1080/01490451.
2011.592929)
V. Ivanov and J. Chu, Applications of microorganisms to geotec
hnical engineering for bioclogging and biocementation of
soil in situ, Rev. Environ. Sci. Biotechnol., 7(2):139–
153, 2008 DOI: https://doi-
org.ezproxy2.library.drexel.edu/10.1007/s11157-007-9126-3 (ht
tps://doi-org.ezproxy2.library.drexel.edu/10.1007/s11157-
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J. K. Mitchell and J. C. Santamarina, Biological considerations i
n geotechnical engineering, J. Geotech. Geoenviron. Eng.,
131(10):1222–
1233, 2005 DOI: https://doi-org.ezproxy2.library.drexel.edu/10.
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M. Van der Ruyt and W. van der Zon, Biological in situ reinforc
ement of sand in near-shore areas, Geotech. Eng.,
162(1):81–
83, 2009 DOI: https://doi-org.ezproxy2.library.drexel.edu/10.16
80/geng.2009.162.1.81 (https://doi-
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L. A. van Paassen et al., Quantifying biomediated ground impro
vement by ureolysis: Large-scale biogrout experiment, J.
Geotech. Geoenviron. Eng., 136(12):1721–
1728, 2010 DOI: https://doi-
org.ezproxy2.library.drexel.edu/10.1061/(ASCE)GT.1943-5606.
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