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Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that improves the geotechnical properties of soils. The current study presents a field-scale, surficial application of MICP to improve the erosion resistance of loose, sandy soils and provide surface stabilization for dust control and future re-vegetation. Three test plots were treated with a bacterial culture and different nutrient solutions, while a fourth test plot served as a control plot. Improvement was assessed to a depth of 30 cm using dynamic cone penetration (DCP) resistance, and calcite content measurements. The most improved test plot developed a competent, sandstone-like crust measuring 2.5 cm thick, which exhibited strong resistance to erosion and could support the weight of field personnel. DCP resistance and calcite content measurements indicated improvement to a depth of approximately 25 cm.
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Bio-mediated Soil Improvement Field Study to
Stabilize Mine Sands
Gomez, M.G. & DeJong J.T.
Department of Civil and Environmental Engineering University of California: Davis, California, USA
Martinez, B.C. & Hunt, C.E.
Geosyntec Consultants, Oakland, CA, USA
deVlaming, L.A.
Geosyntec Consultants, Waterloo, Ontario, Canada
Major, D.W.
Geosyntec Consultants, Guelph, Ontario, Canada
Dworatzek, S.M.
SiREM Laboratories, Guelph, Ontario, Canada
ABSTRACT
Microbially Induced Calcite Precipitation (MICP) is a bio-mediated cementation process that improves the geotechnical
properties of soils. The current study presents a field-scale, surficial application of MICP to improve the erosion
resistance of loose sand deposits and provide surface stabilization for dust control and future re-vegetation. Three test
plots were treated with a mixture of bacterial culture and nutrient solutions at varying concentrations, while a fourth test
plot served as a control plot. Improvement was assessed to a depth of 43 cm using dynamic cone penetration (DCP)
testing, and calcite content measurements. The most improved test plot developed a competent, 2.5 cm thick,
sandstone-like crust, which exhibited strong resistance to erosion and could support the weight of field personnel. DCP
testing and calcite content measurements indicated improvement up to a depth of approximately 28 cm.
RÉSUMÉ
La précipitation de carbonate de calcium causée par des bactéries (MICP) est un procédé de cimentation à médiation
microbienne permet d’améliorer les propriétés géotechniques des sols. L'étude actuelle présente une application
superficielle à grande échelle de MICP afin d’améliorer la résistance à l'érosion des sols sableux, et de fournir une
consolidation de la surface pour le contrôle de la poussière et une future éventuelle re-végétation. Trois parcelles d'essai
ont été traitées avec un mélange de culture bactérienne et de solutions nutritives à différentes concentrations, tandis
qu'une quatrième parcelle a servi de parcelle témoin. L’amélioration des propriétés des sols a été évaluée jusqu’à une
profondeur de 30 cm à l'aide d’essais au pénétromètre dynamique, et de mesures de teneur en carbonate de calcium.
Dans la parcelle d'essai la plus améliorée une croûte de grès de 2.5 cm d'épaisseur s’est développée. Cette couche
présentait une forte résistance à l'érosion et pouvait supporter le poids de personnel de terrain. Les essais de
penetration dynamique et la distribution de la teneur en carbonate de calcium indique une amélioration du sol jusqu’à
une profondeur d'environ 25 cm.
1 INTRODUCTION
MICP is a biologically induced cementation process that
improves a soil’s geotechnical properties through the
precipitation of calcium carbonate (calcite) at soil particle
contacts (Stocks-Fisher et al. 1999, Martinez and DeJong
2009). This biogeochemical reaction is enabled by the soil
bacterium, Sporoscarcina pasteurii (S. pasteurii), which
harbours a highly active urease enzyme associated with
urea hydrolysis (Ferris et al. 1996). The urease enzyme
catalyzes a hydrolysis reaction, which converts urea into
ammonia and carbon dioxide gas. These compounds are
produced in the surrounding aqueous environment where
chemical speciation occurs in accordance with the pH of
the ambient solution. In the presence of sufficient calcium,
the increased availability of carbonate ions resulting from
urea hydrolysis causes the aqueous solution to become
supersaturated with respect to calcite, resulting in calcite
precipitation. Calcite precipitation occurring at soil particle
contacts can improve the geotechnical properties of the
soil by increasing soil shear stiffness and shear strength
(De Jong et al. 2006, Whiffin et al. 2007, Harkes et al.
2008).
Through laboratory experimentation at the bench-scale,
MICP technology has been proven as an effective method
to naturally cement sands (DeJong et al. 2006, Whiffin et
al. 2007, Chu et al. 2009, Burbank et al 2011, Hamdan et
al. 2011, Tagliaferri et al. 2011, Weaver et al. 2011, Chu et
al. 2012, Mortensen et al. 2010, Martinez et al. 2013). The
bio-mediated precipitation reaction offers a less intrusive
and potentially more environmentally favourable alternative
to traditional soil improvement methods such as cement
mixing and jet grouting. Field scale applications have been
demonstrated in the Netherlands (van Paassen et al.
2011), and are currently being implemented at a U.S.
Department of Energy site in Colorado (Smith et al. 2012).
Increased application of MICP technology at the field scale
can provide important information about the viability of
MICP techniques for practical geotechnical application.
In this study, a field-scale, surficial application of MICP
was completed at a mine site in Canada to assess the
potential of MICP treatment applications to improve loose
sands with respect to erosion resistance, surficial stability,
dust abatement, and to promote future re-vegetation.
Following previous laboratory work (Martinez and DeJong
2009, DeJong et al. 2010, Martinez et al. 2013, Mortensen
et al. 2010, and others), treatment solutions were
formulated to achieve soil improvement at levels that
aligned with the practical goals of the project. The overall
treatment scheme targeted a depth of soil improvement of
approximately 30 cm (1 ft.). The field trials involved the
application of treatment solutions on four test plots that
each measured 2.4 x 4.9 m (8 x 16 ft.). Three plots
received both bacterial culture and nutrient amendments
(test plots; TP2, TP3 and TP4). The control plot (TP1)
received only water at volumes equal to the treated plots.
The study explored the effect of different concentrations of
urea and calcium chloride on the degree of cementation of
surficial soils. To allow comparison between plots, a project
site with relatively uniform soil conditions was selected.
This site consisted of loose, poorly graded sand that was
representative of typical soils existing across the mining
site. The sands originated from the excavation of
overburden soils from an adjacent mining pit. These sands
are easily eroded by high winds and precipitation. The
control plot was located upwind of other treated plots to
reduce the occurrence of accidental treatment from wind-
blown treatment solution during application at adjacent test
plots. Sand berms, approximately 25.4 cm (10 in.) in
height, were also constructed around the perimeter of each
test plot to prevent surrounding sands from being blown
onto the test plots by high winds. Figure 1 presents an
image of the project site and test plots.
Figure 1. Test plots were established on loose, poorly
graded sands.
2 MATERIALS AND METHODS
2.1 Treatment Solutions
Treatments were applied once per day in a series of five
four-day cycles (Cycle Day #1, 2, 3 and 4) for a total of 20
days of treatment. TP2, TP3, and TP4 received a single
day of bacterial amendment application followed by three
days of nutrient amendment application in each cycle. The
application of bacteria on the first day of each cycle instead
of every day was intended to maximize the efficiency of the
cementation process. Table 1 presents the treatment type
that was applied to test plots for each Cycle Day. For
brevity, only the results of the most successful treatment
scheme, TP4, and the control, TP1, are presented herein.
Table 1. Summary of Field Tasks
Cycle Day No. Treatment Type
1
Field Monitoring
2
1 Bacterial DCP, DS
2 Nutrient -
3 Nutrient DCP
4 Nutrient -
1 “Bacterial” and “Nutrient” indicate cycle days for application of
bacterial and nutrient amendments respectively.
2 “DCP” indicates cycle days when DCP measurements occurred
on test plots. “DS” indicates cycle days when discrete samples
were collected at similar locations for calcite measurements.
Table 2 presents the composition of the bacterial
amendment solution. Bacterial amendment solutions
contained the same calcium chloride, urea, and Difco
nutrient broth concentrations as the nutrient amendment
solutions, but were additionally augmented with S. pasteurii
at a cell density of 105 cells/mL. Nutrient amendment
solutions therefore did not contain the addition of bacterial
cells. Treatment formulations included varying
concentrations of calcium chloride and urea at equal ratios
(2 parts urea to 1 part calcium chloride). TP1 received only
water. The treatment volume applied daily was 378.5 liters
(100 U.S. gallons) per test plot. This treatment volume was
established after assuming an initial sand void ratio of 0.4,
and calculating the fluid volume needed to occupy
approximately 25% of the initial void space, considering
treatment to a depth of 25.4 cm (1 ft).
Table 2. Bacterial Amendment Solution Concentrations
Test
Plot
Type
Nutrient
Broth
(mg/L)
Urea
(g/L)
Calcium
Chloride
(g/L)
S.
pasteurii
(cells/mL)1
1 Control 0 0 0 0
4 MICP 58.7 15 13.875 10^5
1 Nutrient amendment solutions differed by having no S. pasteurii
addition.
2.2 Treatment Solution Mixing
Bacterial and nutrient amendments were prepared on-site
by mechanical mixing of water, nutrient broth (dry), urea
(dry), calcium chloride (dry), and bacterial culture in large
mixing totes. While treatment volumes of 379 liters (100
U.S. gallons) were applied to each test plot, batches of 568
liters (150 U.S. gallons) were prepared to limit distribution
pump suction problems and promote consistent application
of solutions. Treatment solutions were mixed until no
constituent particulates remained visible in samples from
mixing totes and the pH of each solution remained stable.
Solutions were mixed continuously during the application
process to promote full dissolution and provide consistency
in treatment solutions.
2.3 Treatment Application
Treatment solutions were prepared in portable mixing totes
and applied to the plots using a hose and application wand
assembly. A treatment application system schematic is
presented in Figure 2. Two 5,678 liter (1500 U.S. gallon)
polyurethane water tanks were used to store water on site.
Two 1,135 liter (300 U.S. gallon) intermediate bulk
containers were used to prepare treatment solutions.
Continuous mixing was achieved with laboratory grade
electric mixers. The sprayer and hose assembly attached
to the mixing totes was assembled from PVC pipe fittings
and a fine spray nozzle calibrated for 20 liters/minute (5
U.S. gallons/minute). Two separate 3/4 HP recirculating
pumps were used to pump water or solutions as needed
from the large storage tanks to the application wand, the
large storage tanks to the mixing totes, or the mixing totes
to the application wand. To avoid bacterial contamination
of the water tanks, one pump and hose assembly was
dedicated to water, while a second was used for treatment
solutions.
Figure 2. An application system schematic displays tanks
and pumps used during treatment.
2.4 Field Monitoring
Field measurements and sample collection were performed
over time to monitor both chemical and geotechnical
changes across the test plots. Dynamic Cone
Penetrometer (DCP) measurements were performed to
evaluate changes in penetration resistance. Discrete
samples were collected to perform laboratory
measurements of the treated soil’s calcite content.
Supported planks were used when collecting samples and
measurements to eliminate foot traffic on plots. Sample
locations were randomly selected but constrained to
provide a broad spatial distribution across each test plot.
The layout consisted of a 2.1 x 4.6 m (6 x 14 ft) grid, which
provided a minimum 30 cm (12-in) offset between any
sample and the test plot perimeter. Each grid was further
subdivided into three 1.8 x 1.4 m (6 x 4.7 ft) sections. On
each sampling day, sample collection and/or field
measurements were performed in each of these three
sections. All measurement locations were identical for all
test plots.
Monitoring was completed on specific days of each
treatment cycle and repeated for all five cycles. Table 1
presents the monitoring methods completed on each test
plots for each Cycle Day. On Cycle Day #1 both discrete
sample collection and field DCP measurements were
performed. On Cycle Day #3 only DCP measurements
were performed. On Cycle Days #2 and #4 no DCP
measurements or discrete sampling were performed. On
the final day of treatment (day 20 of the overall treatment
program), five discrete samples were extracted and nine
additional DCP measurements (twelve total) were
performed for each plot. These final DCP measurements
and discrete samples were taken at five identical locations
and distributed evenly across the test plots. Forty-four days
after treatment completion (day 64), an additional nine
DCP measurements were taken at similar locations as the
day 20 DCP measurements. In total, over the course of the
field trials, DCP measurements were performed at 48
locations and discrete samples were extracted at 20
locations on each of the four test plots.
2.4.1 Dynamic Cone Penetration Resistance
A dual-mass dynamic cone penetrometer (DCP) was used
to monitor changes in penetration resistance in accordance
with ASTM D6951. During the first ten days of monitoring,
hammer blow measurements were completed using an 8-
kg donut hammer dropped the full 57.4 cm (22.6 in)
specified in the standard. The data collected while using
the 8-kilogram hammer at full stroke did not provide
sufficient resolution with depth, as the DCP rod penetrated
too far with each blow to distinguish between small
changes in cementation. For the remaining ten days of
monitoring, DCP measurements were completed using a
lower energy 4.6-kg donut hammer at a quarter stroke,
14.4 cm (5.7 in).
A study was conducted to ensure that all data could be
normalized by the energy input to verify that DCP
measurements from both approaches were comparable.
DCP measurements were performed using four different
energy methods at similar locations. The different energy
methods included using an 8-kilogram hammer at full
stroke (57.4 cm) drop height (45 J equivalent), a 4.6-
kilogram hammer at full stroke (57.4 cm) drop height (25.9
J equivalent), a 4.6-kilogram hammer at half stroke (28.7
cm) drop height (12.9 J equivalent), and a 4.6-kilogram
hammer at quarter stroke (14.4 cm) drop height (6.5 J
equivalent). When plotted without energy normalization,
the lower energy methods displayed higher blow counts as
expected because more blows were required to penetrate
the same depth. When measurements were normalized
relative to the 6.5 J equivalent energy input of the 4.6 kg
hammer at quarter stroke method, measurements agreed
with depth for all techniques. As such, all DCP data
collected using the 45 J equivalent method was plotted
after energy normalization to the reference condition of 6.5
J equivalent per hammer blow. All DCP measurements
after day 10 however, were tested using the reference
condition and therefore did not require correction for
energy.
DCP measurements were recorded relative to a
reference elevation. The top of the ground surface was
designated as the zero reference to capture improvement
of the upper crust. This zero reference deviates slightly
from ASTM D6951, which designates the line above the
conical section of the cone tip as the zero reference. Once
the zero reference measurement was recorded, the free-
fall measurement reading was taken. The free-fall
measurement was the distance that the DCP cone tip
penetrates from the self-weight of the instrument.
Subsequently, depth measurements after repeated
hammer blows were recorded to develop blow per
centimeter (blow count) profiles with depth. DCP
measurements were terminated at a depth of
approximately 43 cm (17 inches), past the target 30 cm (12
inch) treatment depth. All holes generated by DCP
measurements were filled with uncemented, untreated off-
plot sand to reduce formation of preferential drainage paths
during subsequent treatment applications.
2.4.2 Discrete Sampling and Calcite Measurements
Thin-walled steel sampling tubes 25 cm (10 inches) in
length with 3.2 cm (1.25 inches) inner diameter were used
to obtain discretized, discrete samples from all plots for
calcite measurements. The sampling technique used was
modified as the project progressed to increase resolution of
calcite measurements with depth. All samples were stored
in sealed plastic bags for later laboratory analysis.
Samples were oven-dried for water content measurements
before performing calcite measurements.
Two calcium carbonate content chambers were used
to monitor changes in calcite content, in accordance with
ASTM D4373. Calcite chamber measurements were
performed on collected samples to evaluate the change in
calcite content with time and depth. Soil from a discrete
depth interval was mixed thoroughly to obtain a
representative sample. Approximately 40 mL of 1 M HCl
was then placed in the base of each calcite chamber, and
a dry representative soil sample of known mass was
placed in a plastic cup on top of the acid. Once properly
sealed, the chamber was tilted and agitated so that the HCl
and calcite in the soil sample could react. The reaction of
calcite and HCl results in the generation of carbon dioxide
gas and a corresponding increase in chamber pressure.
Previously calibrated laboratory relationships between
chamber pressure and calcite mass were used to calculate
calcite mass from observed chamber pressure. The total
dry mass of the soil sample was then used to determine
calcite content.
3 RESULTS AND DISCUSSION
3.1 Baseline Site Characterization
To allow comparison between test plots, it was necessary
to assess the degree of spatial variability across the project
site. Figure 3 displays DCP measurements with depth that
were taken on day zero at three locations on TP1 and TP4.
After reviewing these results, and considering visual
observations of the material with depth, it was established
that soils within the depth monitored were relatively
uniform. These initial DCP measurements are referred to
as “45 J” measurements because they were measured
using the higher energy 45 J equivalent method, which
resulted in larger penetration per blow than the 6.5 J
equivalent method. On the tenth day of the overall
treatment, additional DCP measurements were taken
across the project site at untreated locations using the
lower energy 6.5 J equivalent method and are referred to
as “6.5 J” measurements. These measurements were
completed to provide a higher resolution data set of
penetration resistance measurements that would likely be
comparable to the initial untreated day zero condition.
Measurements were taken at locations outside of, but
adjacent to, test plots so that these measurements could
be compared to the original day zero 45 J data set but with
higher resolution. Figure 3 also displays these 6.5 J
measurements plotted with the original 45 J measurements
taken on day zero to evaluate consistency between the
two. In general, 6.5 J measurements agreed with 45 J
measurements. In some cases, larger penetration
resistance values were shown for 6.5 J measurements.
These increases are likely the result of higher resolution of
data with depth from the lower energy method. Some
larger penetration resistance values may be due to the
presence of small gravel particles at depth, which were not
significant enough to influence the higher energy
measurements.
From this result, 6.5 J measurements were
concluded to be representative of the day zero untreated
condition and could therefore be considered as a higher
resolution day zero data set. As baseline measurements
exhibited consistent behaviour relative to depth across test
plots (i.e. similar degree of scatter over discrete depth
intervals), the overall spatial variability in results across the
site was considered to be relatively small. As such,
measurements taken on TP1 and TP4 were assumed to be
suitable for direct comparison of the MICP treatment to the
control.
Figure 3. The 45 J day zero measurements plotted with
depth show similarity between plots (left). These 45 J
measurements agreed well with higher resolution 6.5 J
measurements taken at untreated locations (right).
3.2 Penetration Resistance
DCP measurements obtained before treatment (45 J - day
0 and 6.5 J - day 0) and after treatment (day 20) were
compared for test plots to assess improvement resulting
from MICP cementation. From these penetration resistance
results, it was concluded that all treated test plots were
improved; however, TP4 exhibited the highest degree of
improvement. DCP measurements (day 0, 20, and 64) are
shown in Figures 4 and 5 for TP1 and TP4 respectively. It
is noted that measurements did not appear in the upper 5
to 7 cm of the soil profile for pre-treatment conditions
because the self-weight of the DCP was sufficient to free-
fall (0 blows) through this surficial soil. As cemented crusts
developed on test plots during treatment, measurements
then became obtainable in shallower depths (less than 7
cm). Dashed lines shown in Figures 4 and 5 are
interpretations of the lower and upper bound penetration
resistance values for day 0 on both TP1 and TP4. These
lines were included for all days to provide a comparison
between day 20 and day 64 values to the interpreted
untreated day 0 condition. When comparing the
measurements from day 0 and 20, the control test plot
(TP1) showed a slight reduction in penetration resistance.
Although it is possible that this reduction is an artefact of
spatial variability, it may also be a response to increased
soil moisture as a result of water application, or another
mechanism that has not been considered herein. When
comparing measurements from day 0 and 20 on TP4
significant improvement is observed. Several
measurements were obtainable in the upper 7 cm after 20
days indicative of the surficial crust developed. Improved
Figure 4. (above) TP1 DCP penetration resistance measurements are presented with depth for day 0 (left), day 20
(middle), and day 64 (right). Dashed lines shown for all days are interpretations of the upper and lower bound day 0
penetration resistance values.
Figure 5. (above) TP4 DCP penetration resistance measurements are presented with depth for day 0 (left), day 20
(middle), and day 64 (right). Dashed lines shown for all days are interpretations of the upper and lower bound day 0
penetration resistance values.
blow counts are also observed to approximately 28 cm
when compared with day zero measurements.
Additional DCP measurements were taken 44 days
after treatments were completed (day 64). These
measurements were compared with pre-treatment (day 0)
and post-treatment (day 20) measurements to evaluate
whether cementation was maintained and assess the
possibility that cementation may have continued following
final treatment. It is noted that fewer measurement
locations were used on day 64 (9 locations) than on day 20
(12 locations). When comparing day 64 to day 20
measurements, TP1 did not show significant changes in
penetration resistance as expected. Results for TP4
indicate that the improvement shown on day 20 was largely
maintained on day 64 with small differences potentially
resulting from modest spatial variability. The results from
post-treatment monitoring are promising and indicate that
the cementation on TP4 did not degrade significantly within
44 days of final treatment.
Free-fall distances of the DCP instrument were
recorded over time to provide a quantifiable measure of
surficial crust development. Figure 6 presents these free-
fall distances plotted with time for TP1 and TP4,
respectively. The 8 kg hammer measurements have
slightly larger free-fall distances than the 4.6 kg hammer
measurements due to an increase in hammer mass as
expected. Interpretation lines show the general trend of 4.6
kg hammer free-fall distances for each plot. Initial day zero
measurements showed that TP1 and TP4 had similar free-
fall distances before treatment. TP1 (control) free-fall
distances remained reasonably constant throughout the
treatment. As a result of cementation, TP4 had a reduction
in free-fall distance of about 6 cm to a condition nearly no
penetration under the self-weight of the DCP instrument.
The post-treatment results indicate that the TP4
treatment formulation was effective, and therefore the
results for this test plot warranted further analysis. All DCP
measurements taken throughout the project for TP4 were
compared with depth and time. These measurements were
binned into five different time intervals for day 0, days 2 to
6, days 8 to 12, days 14 to 18, and day 20. The binned
measurements plotted in Figure 7 show a progression in
time for measurements taken across TP4. Data from each
time interval were then averaged in 5 cm segments to
show the average trend of penetration resistance with both
depth and time. The averaged binned DCP measurements
are also presented in Figure 7 and are consistent with
previous observations made for TP4 with respect to
penetration resistance. The averaged profiles indicate that
crust formation was relatively slow before day 6 of overall
treatment, however improvement was observed thereafter.
An intersection between day 0 and day 20 lines occurs at a
depth of approximately 28 centimeters, indicating that
treatment resulted in some modest level of improvement
nearing the target 30 cm depth.
Figure 6. Free-fall distances with time are presented for
TP1 (top) and TP4 (bottom).
Figure 7. DCP measurements for TP4 were binned into
time intervals and plotted with depth (left). Binned
measurements were then averaged every 5 cm to create
profiles (right).
3.3 Calcite Content
Calcite content measurements for all test plots were
performed on collected samples to monitor development of
calcite cementation throughout the treatment program. TP1
(control) showed no change in calcite content with depth or
time, as expected. TP4 samples had calcite contents up to
2.1% near the ground surface and reduced to 0.5% or less
below approximately 10 cm, with measurable calcite
precipitation over the entire sampling depth. These results
indicate that significant calcite precipitation occurred on
TP4, consistent with the observations from the DCP testing
program.
3.4 Cemented Crust Thicknesses
Development of a sandstone-like crust was observed on
the TP4 test plot. Crust thicknesses were measured at four
locations on each test plot. TP4 was shown to have both
the largest maximum 2.5 cm (1 in) and the largest
minimum 0.64 cm (0.25 in) crust thicknesses of all test
plots. This visual record of crust formation is consistent
with both DCP and calcite content measurements
described previously. Figure 8 presents an image of
cemented crust material being measured at one location
on test plots.
Figure 8. Cemented crust thicknesses were measured on
test plots.
3.5 Water Jetting Erosion Tests
At the end of the treatment program, qualitative water
jetting erosion tests were performed to assess erosion
resistance. These tests were not based on an accepted
standard, but were used to evaluate the erosion resistance
of each test plot. Using the spray wand assembly, water
was applied from a height of approximately 107 cm (3.5 ft)
above ground surface to test plots using a flow rate of
approximately 22.7 liters per minute (6 U.S. gallons per
minute). When water was applied, TP1 experienced
significant surficial erosion almost instantaneously. After
one minute of water application an impression remained
where sand had been displaced and loose sand filled the
developing void. When water was applied to TP4 for one
minute, the existing crustal layer showed no significant
signs of erosion. Although this test was nonconventional,
the results have practical implications and indicate the
potential of MICP to stabilize loose sands.
4 CONCLUSIONS
The results of this study indicate that MICP techniques
using the TP4 treatment formulation improved existing soils
to a depth of approximately 28 cm (11 in.) following 20
days of treatment. Both DCP and calcite content
measurements were shown to be effective at indicating soil
improvement, while the DCP method achieved higher
resolution data with depth and was more spatially
representative.
The high degree of improvement on TP4, as measured
by geotechnical and chemical monitoring methods made
this test plot the focus of our analysis. This test plot was
observed to have a stiff competent surface crust that
measured up to 2.5 cm (1 in.) in thickness, a significant
increase in DCP resistance to depths greater than 5 cm (2
in.), and a measurable calcite content of up to 2.1%.
Modest spatial variability across TP4 was observed
through scatter among DCP and calcite content
measurements at similar depths. Additionally, improvement
throughout the 28 cm (11 in.) depth on TP4 was observed
to have no significant signs of deterioration 44 days after
the final treatment. The cemented crusts observed on TP4
were also observed to successfully support weight of
testing personnel after final treatment, and perform well
under erosion resistance water jetting tests.
ACKNOWLEDGEMENTS
The authors would like to thank Cameco Corporation for
providing a field test site and financial support to perform
this MICP pilot study.
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... It is well understood that surface treatment plays a vital role in promoting the cover condition of the slope by achieving aggregate stability and infiltration control. Conventional materials like geotextiles, wire meshes, cable nets, membranes, sheets or nails, which were physically installed to promote slope enforcement, are often expensive and their installment requires a high energy cost (Salifu et al., 2016), whereas chemical grouting methods are reported as environmental-unfriendly and unsuitable for large-scale applications (Gomez et al., 2013). Thus, an alternative remedial action for slope soil stabilization, the implementation of a bio-cement zone of MICP along slope surface, has been considered in this paper. ...
... Most of them have been performed based on a bio-augmentation strategy by introducing non-native ureolytic bacteria to the soil. Among them, Sporosarcina pasteurii is the most researched bacterium: it enables a highly active urease enzyme associated with urea hydrolysis (Gomez et al., 2013). The solidification of sand using S. pasteurii allows for significant control of surficial sediment erosion (Bao et al., 2017;Salifu et al., 2016) and reduces hydraulic conductivity while increasing the confined compressive strength (Jiang and Soga, 2017;Whiffin et al., 2007). ...
... The solidification of sand using S. pasteurii allows for significant control of surficial sediment erosion (Bao et al., 2017;Salifu et al., 2016) and reduces hydraulic conductivity while increasing the confined compressive strength (Jiang and Soga, 2017;Whiffin et al., 2007). Also, S. pasteurii was shown to form an impermeable stiff crust with a thickness of 2.5 cm which increases resistance to erosion (Gomez et al., 2013). Cheng et al. (2014) reported that Bacillus sphaericus can enhance the strength of silica sand with relatively retained permeability when 10 mM urea concentrated artificial sea water was used as cementation solution. ...
Article
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Microbial Induced Calcite Precipitation (MICP) is one of the most popular biotechnological soil stabilization techniques since it results in significant improvements in the geotechnical properties of soil. The current study presents a laboratory-scale MICP investigation performed to demonstrate the feasibility of slope soil stabilization of the Hokkaido expressway through surficial treatment. The objectives of this preliminary study are to investigate the feasibility of (i) augmenting indigenous bacteria, and (ii) implementing commercially available inexpensive low-grade chemicals in microbial induced solidifications. Syringe solidification tests were carried out using indigenous ure-olytic bacteria under various temperature condition with the use of different injection sources. A high strength crust layer was achieved on the soil surface with 420 kPa unconfined compressive strength (UCS) as measured by needle penetration test after 10 days of treatment using pure chemicals (30 °C; 0.5 M cementation solution, every 24 h; bacterial culture solution, only at the beginning). However, by substituting pure chemicals with low-grade chemicals, a significant improvement in the UCS of soil (820 kPa at 30 °C) was obtained together with a 96% reduction in the treatment cost. The morphologies and crystalline structures of the precipitated carbonate were characterized by Scanning Electron Microscopical (SEM) observations. This alternative approach of introducing low-grade chemicals in MICP has the potential to provide significant economic benefits in field-scale applications.
... Biostimulation, the use of selective substrates and/or environmental factors to stimulate the growth of native microorganisms with desirable metabolic capabilities, has been researched extensively in the field of bioremediation (e.g., Atlas and Bartha 1973;Gibson and Sewell 1992) with success in several notable field-scale applications (e.g., Pritchard and Costa 1991;Pritchard et al. 1992;Truex et al. 2009). Despite the frequent use of biostimulation in the field of bioremediation, few researchers have considered the use of this treatment technique for enabling MICP (Burbank et al. 2013;Fujita et al. 2000;Gat et al. 2014Gat et al. , 2016Gomez et al. 2013Gomez et al. , 2017. Although some stimulated native species may complete ureolysis at rates slower than specialized laboratory cultivated bacterial strains (Gomez et al. 2017;Hammes et al. 2003), indigenous microorganisms may also be more resilient than augmented strains in natural subsurface environments (Acea et al. 1988;Armon and Arbel 1998), enabling the possibility of more sustained ureolytic activity throughout the treatment process. ...
... It uses localization methods using compatible indigenous bacteria in each region, which is both economical and compatible with the same area. Gomez et al. (2013) showed that native ureolytic bacteria can be stimulated in natural soils to precipitate calcite significantly. ...
Article
Full-text available
Many types of researches have been carried out on sandy soils to improve the fertility through bacteria. In this regard, after measuring the activity of urease enzymes in urea bacterial sediments, calcium carbonate was applied in Sirjan soil (southeast of Iran), and the native bacteria of this soil were isolated. The strains of these microorganisms, because of the Come and aridity in the region and the severity of the environmental conditions in the area, have a greater resistance to chemical and physical factors and are compatible with the environment of this region. In this study, we tried to use two types of soil bacteria: one is Sporosaercina pasturii, many researchers have been working on this bacterium and the effects of soil improvement, and another is the native bacterium found in Sirjan soil (Acinetobacter calcoaceticus strain Nima). Thirty samples were taken in the same conditions and experiments to evaluate the use of native bacteria of Sirjan in soil remedi-ation by direct shear testing, seismic electronic microscopy, and microscopic scanning (SEM) were performed on the samples. The treatment period for this study was 28 days. The results showed that the angle of internal friction increased for the treated A. calcoaceticus Nima (42%) and S. paturii (39%) compared to untreated samples. Also, adhesion between particles increased by 14.5 times for A. calcoaceticus Nima and 13.5 times for S. paturii. Finally, shear strength for soil treatment increased by4.6 times for A. calcoaceticus Nima and 3.9 times for S. pasturii. The use of indigenous strains in the natural environment due to the adaptation of strains to environmental conditions can increase the production of bio-cementation. It is, therefore, possible to use native bacteria for biologically improved soil as an appropriate alternative rather than traditional methods due to environmental problems. ARTICLE HISTORY
... However, Al-Thawadi (2011) reported that Microbial Induced Calcite Precipitation technique can offers low-cost treatment in the long duration treatment. Gomez et al. (2013) also proved the possibility of an on-field experiment on soil stabilization through MICP. ...
Conference Paper
Diverse biotic communities interact with beach sand which facilitate their survival and growth. The interactions are to achieve few specific functions and analogous to the system required in geotechnical engineering. The biological functions are governed by natural selection, adopting the same physical laws to the engineered environments addresses geotechnical challenges like erosion prevention by stabilizing sand particles. The synthesis of calcium carbonate interveined through soil particles using the Microbial Induced Calcite Precipitation process emerged as a promising technology in stabilizing the loosened sand. The present research focused to isolate the microbes from the coastal environment, which has been studied for their calcite precipitation potential. In the study, 13 isolates were identified from marine sediments, whereas six exhibited Urease positive activity. Among the six isolates, the strain NIOT 1 showed high calcification potential and was recognized as Sporsarcina pausterii NIOT-1. This strain was identified as one of the promising urease producing bacteria in the microbiological world. In the course of the laboratory study, utilizing the identified strain to stabilize the coastal beach sand, success was achieved with a maximum compressive strength of 740 Kpa. In the meantime the maximum ammonium concentration was observed as 323.54 mM with the pH of around 8.1. The gained compressive strength in this study with the beach sand was slightly higher than the international studies, and it is one of its novel types. The current research results have paved a new path to utilize the MICP techniques as a tremendous non-destructive alternate to stabilize the coasts by preventing the beach sand movement and protecting the coastal populace from the eroding shoreline
... In addition, Van Paassen et al. [10] conducted a large-scale consolidation test and found that loose sand after MICP treatment was successfully cemented into agglomerates and the rigidity improved. Gomez et al. [11] demonstrated through field-scale experiments that MICP can improve the erosion resistance of loose sand samples and inhibit dust to achieve surface stability. ...
Article
Full-text available
Microbial-induced calcium carbonate precipitation (MICP) has the potential to be an environmentally friendly technique alternative to traditional methods for sustainable coastal stabilization. This study used a non-pathogenic strain that exists in nature to experimentally investigate the application of the MICP technique on mitigating sandy beach erosion. First, the unconfined compressive strength (UCS) test was adopted to explore the consolidation performance of beach sand after the MICP treatment, and then model tests in a wave flume were conducted to investigate the MICP ability to mitigate beach erosion by plunger waves. This study also employed field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) to observe the crystal forms of MICP-treated sand after wave action. The results reveal that the natural beach sand could be consolidated by the MICP treatment, and the compressive strength increased with the increase in the cementation media concentration. In this study, the maximum compressive strength could be achieved was 517.3 kPa. The one-phase and two-phase MICP treatment strategies were compared of sandy beach erosion tests with various spray and injection methods on the beach surface. The research results indicate that the proper MICP treatment could mitigate beach erosion under various wave conditions; the use of MICP reduced beach erosion up to 33.9% of the maximum scour depth.
... Through laboratory tests at bench scale, the MICP technology has been demonstrated as a candidate to improve stability of slopes and dams (Chu et al., 2012;Montoya et al., 2013), rehabilitate contaminated soils (Achal et al., 2012), heal cracks in concrete (Achal et al., 2009(Achal et al., , 2013, and control seepage (Gao et al., 2019b;Jiang et al., 2016Jiang et al., , 2017. Encouragingly, the MICP has recently shown promising potential for wind erosion control and fugitive dust suppression (Bang et al., 2009;Gomez et al., 2013;Maleki et al., 2016;Meyer et al., 2011;Stabnikov et al., 2013;Wang et al., 2018;Zomorodian et al., 2019). However, for one thing, there is still a lack of systemic research concerning the influencing factors of MICP to mitigate wind erosion in arid and semi-arid areas; for another, almost all of the previous studies have been confined to laboratory experimentation. ...
Article
This study examined the potential of microbially induced carbonate precipitation (MICP) in reducing wind erosion of desert soil. Field tests were conducted on artificial mounds and bare sandy land located in Ulan Buh Desert, Ningxia Hui Autonomous Region, China. Results showed that the MICP method could significantly enhance the bearing capacity and wind erosion resistance of the surficial soil through the formation of soil crusts. The optimal cementation solution (containing equimolar urea and calcium chloride) concentration and spraying volume, were 0.2 M and 4 L/m², respectively. Under this condition, the soil crusts, with a thickness of 12.5 mm and a calcium carbonate (CaCO3) content of 0.57%, remained intact on the surface of man-made mounds after being exposed to a 30 m/s wind for 2 min. For the sandy land, the soil bearing capacity could reach its maximum of 459.9 kPa (as measured with a 6 mm-diameter handheld penetrometer) within three days, and the depth of wind erosion was approximately zero after 30 days of exposure to the local weather conditions. Furthermore, the biocementation method showed its ecological compatibility at the optimal dosage. Scanning electron microscopy (SEM) tests with energy dispersive X-ray (EDX) confirmed the bridge effect of CaCO3 crystals. Longer-term durability of MICP treatment was evaluated, and the results showed that soil bearing capacity and wind erosion resistance of the sandy land was significantly improved over 180 days. These findings suggest that MICP is a promising candidate to protect desert soils from wind erosion.
... The Young's modulus of coarse biocemented sand varied between 75 and 125 MPa, whereas that of fine biocemented sand varied from 25 to 75 MPa when correlated with ranges of CaCO 3 varying from 2% to 6% for both materials. The trend toward lower UCS and stiffness for BEICP-treated fine sand compared with coarse sand at a similar level of CaCO 3 content was consistent with results previously reported by Gomez et al. (2013), Lin et al. (2016), Zhao et al. (2014, and Terzis and Laloui (2018) for MICP processing and by Hamdan et al. (2013) and Kavazanjian and Hamdan (2015) for EICP processing. In contrast, Cheng et al. (2013) mentioned that at a similar CaCO 3 content, fine MICP-treated sand achieved higher values of cohesion and friction angle than did MICP-treated coarse sand. ...
Article
Biological induced calcite precipitation is a potential method being investigated for improved soil stabilization. In terms of the associated urea hydrolysis concept, three main strategies have been developed over the last 2 decades: (1) using live urease-producing bacteria , (2) using plant-extracted urease, and (3) using bacterial-extracted urease. This paper focused on evaluating the comparative benefits of two of these methods (i.e., live bacterial cell or extracted bacterial urease methods for induced calcium precipitation) in terms of their biocementation performance. Cell-based induced carbonate precipitation (ICP) (i.e., MICP) testing was completed on standard Ottawa coarse-grained sand (#20/30), and bacterial-enzyme-based (i.e., BEICP) testing was conducted individually on both coarse-grained and fine-grained (#50/70) sands. Distinctly higher unconfined compressive strength (UCS) was achieved with the BEICP method when evaluated at similar levels of calcium precipitation. Residual permeability levels remained markedly higher after BEICP testing versus MICP. The UCS of BEICP coarse-grained treated sand was approximately 450-1,500 kPa, whereas that of fine-grained treated sand had a notably lower range (i.e., 250-900 kPa) when evaluated at similar levels of CaCO 3 production. These results indicate that calcium carbonate content is not the sole factor which impacts the strength of biocemented sand. Additional test-tube investigation of ICP-derived CaCO 3 precipitation was used to evaluate the chemical conversion efficiency for each method, i.e., live cells (i.e., Sporosarcina pasteurii) or bacterial-extracted urease. The calcite precipitation ratio declined at higher substrate chemical concentrations. However, this ratio increased with higher rates of enzymatic activity.
... Erosion protection 65 , targeting slopes and river banks 66 viii. Vegetation applications related to soil erosion 67 ix. Stabilization of tunnelling walls 68 x. ...
Article
Research and practice in the broader fields of civil and geotechnical engineering had long ignored the presence of living microorganisms in the subsurface and the way it impacts conventional practices. In the last 10 years, the term “microbial induced calcite precipitation”, or that of “biogrouting” have gained momentum in the scientific literature. They are often presented as the “next big thing” in geotechnical engineering applications that will solve many kinds of problems, ranging from soil erosion to landslide risk mitigation and liquefaction protection. Are the claimed benefits of the application of microorganisms in conventional geotechnical problems real? The present review work aims to shape a complete and comprehensive understanding of the progress reported in the field of bio-mediated soil improvement. Specific focus is put on pivotal points in this decade-long path which is marked by proof of fundamental concepts at multiple scales. Among the treated literature, reference is made to over forty studies produced after 2016. As soil bio-reinforcement makes its steps towards claiming a spot in mainstream geotechnical practice this review foresees to offer both a look back on how far research has gone and a look forward by evaluating opportunities and challenges which lie ahead.
... Again, due to the large permeability of the soil to be treated, microdosing was used to introduce the bacteria, and multiple cycles of percolation of cementation solution every 3-6 h were required to achieve the target treatment level (the exact number of percolations was not reported). Some other efforts have been made to apply MICP or a similar enzyme-induced carbonate precipitation (EICP) process for fugitive dust control (Bang et al. 2009;Meyer et al. 2011;Gomez et al. 2013Gomez et al. , 2015. Nevertheless, as noted by , the high permeability and hygroscopic behavior of fine sand and silty sand limit the available amount of cementation media and moisture in the surficial soils (i.e., water is a necessary component of the ureolytic reaction), significantly restricting the performance of conventional water-based MICP/EICP treatments for surficial stabilization. ...
Article
Full-text available
Microbially induced carbonate precipitation (MICP)–based biomediated soil improvement methods have been extensively studied recently due to their versatility, potential environmental sustainability, and potential low cost. However, an efficient MICP-based treatment method specifically designed for surficial soil stabilization against water-induced erosion is still urgently needed. This paper presents a preliminary experimental study on the application of a new polymer-modified MICP treatment for surficial soil stabilization to mitigate water-induced erosion. In the proposed method, the cementation solution for MICP is prepared in a water solution of polyvinyl alcohol (PVA) instead of water alone. Comparative tests are conducted to verify that the PVA-modified cementation solution provides a suitable environment for MICP, as well as to optimize the concentrations of cementation media used in the new method. The proposed method is then applied for bench-scale surficial stabilization of Ottawa sand. The performance of the surficial treatment is demonstrated by flume erosion tests, and the erodibility of the treated sand is evaluated more precisely using an erosion function apparatus (EFA). The experimental results show that the viscous polymer solution anchors the bacteria and cementation media in surficial regions and promotes the precipitation of calcium carbonate. Such a treatment results in a uniform soil crust in the surficial region and reduces the erodibility of sands. The critical shear stress of the treated sand is over 500 times higher than that of untreated sand as demonstrated by the EFA tests.
... For the control of surficial erosion and scour, an ideal soil improvement approach, considering its feasibility and efficiency, is a surficial treatment that increases the erosion resistance of the surficial soils to a desired level but leaves the underneath soils unchanged. Substantial efforts have been devoted to implementing such surficial treatment through biomediated carbonate precipitation processes (23)(24)(25)(26)(27). However, as noted by Hamdan et al. (28), there still remain two major difficulties which limit the performance of these approaches: (1) the high permeability of the water-based cementation solution in the fine sand and silt makes it hard to retain the reactants in the near-surface region; (2) the fast evaporation of moisture shortens the time-window for the MICP reactions, thus limits the amount of precipitated calcium carbonate in the surficial regions. ...
Conference Paper
Full-text available
Microbially-induced carbonate precipitation (MICP) is an emerging soil improvement technique that has enormous potential to become a sustainable and low-cost countermeasure for erosion and scour of granular soils. However, for field-scale surficial stabilization practice, it is still in urgent need of an efficient and applicable MICP-based treatment method. To address this demand, this paper presents a polymer-modified MICP treatment approach which is designed for surficial soil stabilization against water-induced erosion. In the proposed MICP treatment approach, a polymer modifier, i.e., polyvinyl alcohol (PVA), is added to the cementation solution to adjust its viscosity and moisturizing ability. Such modifications enable the control of the infiltration process of cementation solution in soils and prolong the time-window for MICP process, thereby significantly simplify the treatment process and enhance its efficiency. To demonstrate the advantages of the proposed polymer-modified MICP treatment approach, bench-scale experiments were conducted, in which samples of Ottawa graded sand were treated by one-shot superficially added MICP solution. The morphologies and crystalline structure of the precipitated carbonate in the treated sand sample were characterized using microscopic imaging techniques. The performance of the treated sand against water-induced erosion was evaluated by a series of water flume tests. The test results clearly demonstrate that the proposed approach an effective and applicable MICP treatment method, which can significantly enhance the erodibility of the treated granular soils and mitigate the water-induced erosion and scour.
Article
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Microbial precipitation of calcium carbonate takes place in nature by different mechanisms. One of them is microbially induced carbonate precipitation (MICP), which is performed due to bacterial hydrolysis of urea in soil in the presence of calcium ions. The MICP process can be adopted to reduce the permeability and/or increase the shear strength of soil. In this paper, a study on the use of Bacillus sp., which was isolated from tropical beach sand, to perform MICP either on the surface or in the bulk of sand is presented. If the level of calcium salt solution was below the sand surface, MICP took place in the bulk of sand. On the other hand, if the level of calcium salt solution was above the sand surface, MICP was performed on the sand surface and formed a thin layer of crust of calcium carbonate. After six sequential batch treatments with suspension of urease-producing bacteria and solutions of urea and calcium salt, the permeability of sand was reduced to 14 mm/day (or 1.6×10−7 m/s) in both cases of bulk and surface MICP. Quantities of precipitated calcium after six treatments were 0.15 and 0.60 g of Ca per cm2 of treated sand surface for the cases of bulk or surface MICP, respectively. The stiffness of the MICP treated sand also increased considerably. The modulus of rupture of the thin layer of crust was 35.9 MPa which is comparable with limestone.
Conference Paper
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Currently, several in situ ground improvement methods are being developed in which natural biochemical processes are stimulated, which change the geomechanical properties of soils, like reducing permeability to seal leaks in water retaining ground structures (biosealing) or increasing the strength and stiffness of unconsolidated sands and gravels (biogrouting). This paper gives an overview of the latest research and developments on bio-mediated ground improvement in The Netherlands, including the first pilot application of biogrouting to stabilize horizontal boreholes through gravel layers.
Conference Paper
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Microbially induced calcium carbonate precipitation (MICP) is attracting increasing attention as a sustainable means of soil improvement. Microbial denitrification has the potential to become the preferred method for MICP because denitrification does not produce toxic byproducts, does not require a water-soluble electron donor, can utilize nearly 100 of the electron donor, does not require exogenous organic nitrogen, is thermodynamically more favorable than other processes, readily occurs under anoxic conditions, and potentially has a greater carbonate yield per mole of substrate than other MICP processes. Bench scale bioreactor and column tests using Pseudomonas denitrificans have shown that calcite can be precipitated from calcium-rich pore water using denitrification. Recent experiments at Arizona State University and by others have sought to reduce potential environmental impacts and lower costs associated with denitrification by reducing the total dissolved solids in the reactors and columns and by addressing the loss of free calcium in the form of calcium phosphate precipitate from the pore fluid.
Article
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A novel permeability reduction process has been developed to control fluid flow in porous media. The procedure generally, involves use of bacteria to actively precipitate calcium carbonate as a mineral plugging and cementing agent. This process may be suitably employed to enhance the recovery of oil from oil reservoirs, cement unconsolidated sand underground, or to control the flow of contaminants in an aquifer. Introduction In heavy oil fields, water responds to pumping more readily than viscous oil, so wells on primary production commonly water out after low recoveries of the oil-in-place. This is a serious problem that can occur gradually over several years, or be a catastrophic event when water directly underlies the oil bearing zone. For both of these situations, control of excess water production may be accomplished by selectively plugging zones of water encroachment(1,2). A number of selective plugging systems for reservoir conformance correction have been developed. Chemically cross-linked polymers are available for use, but are expensive in pure form and perform unpredictably under reservoir conditions(3). Similarly, insoluble biopolymers and biomass generated by injected bacteria or by indigenous micro-organisms can be used to selectively plug off zones of high water permeability(1,4,5). The concept has been demonstrated in laboratory experiments; however, poor results have been obtained in field applications of microbial plugging systems(6). More recently, work has focussed on inorganically precipitated mineral plugs using polysulfides(7) or colloidal silica(8). This is expected to improve plug stability and extend use of the technology to more sophisticated production modes. The same advantages may be afforded by a novel bacteriogenic mineral plugging system developed to control fluid flow in porous media. Bacteriogenic mineral plugging involves using injected or indigenous micro-organisms to precipitate authigenic minerals in high permeability water channels. This can be accomplished byusing bacteria as passive nucleation sites while injecting an appropriate solution to oversaturate formation water with respect to a certain mineral phase,stimulating specific bacteria whose metabolic activity will bring about a mineral oversaturation, ora combination of the two processes. Precipitation of the mineral would be expected to selectively plug off the water bearing zones allowing oil production to continue (until further water breakthrough occurred). Of the various minerals that bacteria can precipitate, calcium carbonate is a particularly good candidate for bacteriogenic mineral plugging. Bacteria have been implicated as the causative agents for carbonate precipitation in a number of laboratory and field investigations(9-11). In addition, most heavy oil reservoir formation waters in Western Canada are near saturation with calcite(12). Consequently, stimulation of bacteria that generate alkaline conditions would promote an increase in carbonate concentrations and induce calcite precipitation(13). In this paper, experiments are described using bacteria to increase pH and precipitate calcium carbonate as a mineral plugging and cementing agent. Experimental Materials The bacterial strain used was Bacillus pasteurii NRS 673. Sand used for this work was number 16 silica. Whisling, Illinois. Analysis provided by the company indicated packed cores would have a 0.37 porosity with a permeability of 2.5 Darcies. Reservoir sand for enriched cultures of indigenous bacteria was also used.
Article
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In order to evaluate MCP as a soil strengthening process, a five meter sand column was treated with bacteria and reagents under conditions that were realistic for field applications. The injection and reaction parameters were monitored during the process and both bacteria and process reagents could be injected over the full column length at low pressures (hydraulic gradient < 1; a flow rate of approximately 7 m/day) without resulting in clogging of the material. After treatment, the column was subjected to mechanical testing, which indicated a significant improvement of strength and stiffness over several meters. Calcium carbonate was precipitated over the entire five meter treatment length. Improvement of the load bearing capacity of the soil without making the soil impermeable to fluids was shown with microbial carbonate precipitation, and this is a unique property compared to alternative soil treatment methods that are currently available for use in the subsurface.
Article
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Current methods to improve the engineering properties of sands are diverse with respect to methodology, treatment uniformity, cost, environmental impact, site accessibility requirements, etc. All of these methods have benefits and drawbacks, and there continues to be a need to explore new possibilities of soil improvement, particularly as suitable land for development becomes more scarce. This paper presents the results of a study in which,natural microbial biological processes were used to engineer a cemented,soil matrix within initially loose, collapsible sand. Microbially induced calcite precipitation MICP was achieved using the microorganism Bacillus pasteurii ,a n aerobic bacterium,pervasive,in natural soil deposits. The microbes,were,introduced,to the sand specimens,in a liquid growth,medium amended,with urea and a dissolved calcium,source. Subsequent cementation,treatments were,passed through the specimen,to increase the cementation,level of the sand particle matrix. The results of both MICP- and gypsum-cemented,specimens,were assessed nondestructively by measuring,the shear wave,velocity with bender elements. A series of isotropically consolidated undrained,compression,CIUC triaxial tests indicate that the MICP-treated specimens exhibit a noncollapse strain softening shear behavior, with a higher initial shear stiffness and ultimate shear capacity than untreated loose specimens. This behavior is similar to that of the gypsum-cemented specimens, which represent typical cemented,sand,behavior. SEM microscopy,verified formation,of a cemented,sand,matrix,with a concentration,of precipitated calcite forming,bonds,at particle-particle contacts. X-ray compositional,mapping,confirmed,that the observed,cement,bonds were,comprised,of calcite. DOI: 10.1061/ASCE1090-02412006132:111381 CE Database subject headings: Ground motion; Grouting; Biological operations; Sand; Liquefaction; Microbe; Shear.
Article
Bender elements are commonly used to monitor the shear wave velocity of soils in various tests, including triaxial, consolidation, and centrifuge tests. When used in aggressive soil environments, electromagnetic crosstalk can distort the received bender element signal, preventing accurate shear wave velocity measurements. Aggressive soil environments are defined herein as conductive soils with high relative permittivity. Under these conditions, the electrical source is transmitted from source to receiver bender, dominating any received shear wave signal propagating through the soil. Careful attention must be paid to reducing the transmission of the electromagnetic signal, particularly in aggressive soil environments. When the waterproof coating of a bender element degrades and the inner and outer electrodes become electrically connected in a saturated environment, the bender element will no longer operate. However, when the waterproofing material is degraded so that only a single electrode on the source element is exposed, electric current can enter the pore fluid and affect the received signal. Further, even if the waterproofing coating is intact, electromagnetic crosstalk from the induced electrical field generated by the transmitting bender element can still affect the received signal when the conductivity of the pore fluid is high. Bender elements can be constructed so as to greatly reduce the electromagnetic crosstalk, and simple tests can be performed to help ensure that the bender element system is not susceptible to crosstalk. The objective here is to present details and practical guidelines regarding the fabrication, operation, and health monitoring of bender elements that will help ensure clear shear wave velocity measurements in aggressive soil environments. The fabrication steps presented improve on previous recommendations. Bender element operation (including signal form, frequency, and amplitude) also affects signal quality and the accuracy of the measured travel time. Finally, recommendations for monitoring the health of the bender elements throughout the transducer life are outlined.
Conference Paper
Biocement is a new material that can be used to treat soil and waste in a way similar to ordinary cement. The mechanisms of this method is to use microbial process to strengthen soil or reduce the permeability of the soil. This new approach has the merit of both environmentally friendly and cost-effective. Different typess of microorganisms that are able to exert biocement ation or bioclogging effect have been identified. These include iron-reducing bacteria, urease-producing bacteria, nitrifying bacteria, and oligotrophic bacteria. For each type of microorganism, the biological process, cultivation procedure and cementation mechanism are briefly presented. The effectiveness of some of the treatment is also demonstrated.
Conference Paper
New opportunities for utilizing biological processes to modify the engineering properties of the subsurface have recently emerged at the interface of microbiology, geochemistry, and civil engineering. This paper presents an overview of bio-mediated soil improvement systems in the context bio-mediated calcite precipitation of sands. Micro-scale and macro-scale investigations of microbialinduced calcite precipitation (MICP) identify fundamental material properties and mechanical characteristics of bio-cementation. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) techniques reveal micro-scale calcite formation and degradation characteristics. Calcite minerals are found predominantly near the silica sand grain contacts, strengthening particle bonds. Fracturing of the cemented matrix is found to occur within the calcite phase. A 1-g scaled shallow foundation model is developed to evaluate how MICP treated sands may improve the performance of geosystems at the macro-scale. MICP treatment targets a passive treatment zone of loose sand directly beneath a footing. The spatial distribution of calcite within a sand matrix at the micro-scale translates to a reduction in settlement (or increase in load capacity) at the macro-scale. Comparison of load tests on the footing for MICP treated and untreated experiments reveals up to a five-fold reduction in foundation settlement.