Leon van Paassen / Waldo Molendijk Deltares
Summary
SmartSoils : A decade of
research on biological
ground improvement
®
Building on and in soft, unconsolidated
soils involves large risks, as the behaviour
of soils is difficult to predict. In 2003
Deltares launched the concept of SmartSoils:
changing soil properties on demand by stimulating naturally occurring biochemical
processes in the subsurface. Using microbial activity in the underground, methods
were developed to seal leakages in waterretaining structures and cement sand into
sandstone using waste as cement.
This paper summarizes these SmartSoils
developments and current investigations,
which will be presented during the
17th ICSMGE conference (Den Hamer
et al. 2009; Molendijk et al. 2009;
Van Paassen 2009a,b).
Figure 1 Biochemical processes along the
roots of trees have induced calcium carbonate
precipitation in the Pinnacle desert, Western
Australia. Smartsoils aims at accelerating
such natural (bio)chemical processes.
Introduction
Major leakage events during the construction
of several underground constructions in The
Netherlands in the late 1990s inspired researchers
at Geodelft (now part of Deltares) to search for
unconventional solutions: What if we could stimulate the soil to transform? What if the soil properties could be engineered on demand by stimulating natural processes? In situ? During and after
construction? Without disturbing the soils functionality? This dream became the concept of
SmartSoils, which Deltares launched in 2003.
Figure 2 White calcite crystals formed by
microbially induced hydrolysis of urea form
cohesive bonds between sand particles.
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GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt
Sealing leaks in water-retaining
structures
In bioremediation projects in the 1980s researchers
observed that when they injected nutrients to
stimulate bacteria in the underground to break
down contaminants, the biochemical conversions
often led to local clogging of pores, which reduced
the permeability and effected the transport of
nutrients towards the contaminated sites.
Embroidering on this experience, the idea arose
to inject these nutrients in the proximity of a
leaking construction. Converging groundwater
flows would transport the nutrients towards the
leak, where bacteria would induce clogging and
reduce the flow rate through the leaking structure.
In 1999 GeoDelft started in collaboration with
contractor Visser en Smit Bouw and Delft
University of Technology a research project on
this new method of biological sealing of waterretaining structures. Within 4 years the idea was
developed from lab scale experiments to a field
experiment. In this full scale experiment perforated sea containers were used representing small
sheet pile supported excavations. The flow rate
into a leaking construction (buried sea-container)
was reduced by a factor 5 within 6 weeks and
eventually by a factor 30. The permeability
reduction remained for at least three months.
In 2005 the technique was named BioSealing,
and applied to stop leakages in natural clay and
peat-layers that were damaged during construction
of the aqueduct for the High Speed Railway
Amsterdam-Paris (Van Beek et al. 2008) and
recently a pilot has been carried out to seal
leakages in levees along the Danube in Austria.
Microbes turning sand
into sandstone in 12 days
In the mean time, it was observed that the
embankment of existing railway lines suffered
under dynamic loading and required extensive
maintenance. Consequently, unpredictable interruption of services had to be accepted on these
lines, but engineers wondered: Are there any
alternatives? In 2001 a Dutch newspaper reported
about research in Australia where bacteria were
used to strengthen sand and renovate monuments. At first sight the possibility of microbial
soil improvement sounded rather remote for civil
engineers, however things got serious after a bag
of sand was returned from Australia as a column
of solidified sand, resembling calcareous sandstone. The bio-cemented sample, later named
BioGrout, was extensively tested and one of the
properties that caught the attention was the
minor reduction in permeability, while it had
gained an unconfined compressive strength (UCS)
of several MPa. This is a unique advantage compared to traditional (chemical) grout injections
where all pores are stuffed with cement, polymer
gel or resin. In contrast to existing techniques,
the preservation of permeability enables multiple
treatments, the use of low injection pressures and
obtaining a larger treated volume per injection
point. BioGrout enables in situ treatment of soils
underneath existing buildings and infrastructure
without disturbance of their exploitation.
The concept of SmartSoils® was born. In 2004
GeoDelft started together with contractor Volker
Wessels, Delft University of Technology, the
Australian partners and in later stage French
contractor Soletanche Bachy research on
BioGrout: ground improvement by microbial
induced carbonate precipitation. The original
BioGrout process is initiated by injecting a
suspension containing specific bacteria in the
ground followed by an injection of several
batches of a solution with urea and calcium
chloride. The injected bacteria convert urea to
ammonium and carbonate. The carbonate
precipitates with calcium to form calcite, thus
producing material with similar physical
properties to (calcareous) sandstones. The
remaining ammonium chloride is removed.
processes. When nitrate is completely reduced,
nitrogen gas is the only side product, emphasizing
the sustainability of this new ground improvement method. (Van Paassen et al. 2009a).
After the principle of this method was proven,
optimal conditions for placement of the injected
bacteria and addition of calcium chloride and
urea were established for different sand types
(Harkes et al. 2009). Correlations between dry
density of the cemented sand or calcite content
and strength were established in the range from
light cementation (UCS 200 kPa at ca 30 g
CaCO3/kg) to high strength (UCS 30 MPa at
ca 600 g CaCO3/kg). Four years of research and
development resulted in a 100m3 scale experiment, in which 40 m3 of sandstone was produced
within 12 days reaching unconfined compressive
strength up to 12 MPa (Van Paassen et al. 2009b).
Currently, suitable pilot projects are being
prepared. Meanwhile, the potential for ground
improvement for other microbial induced
carbonate precipitation processes is being
investigated. Denitrification is one of these
Conclusion
Strengthening peat?
SmartSoils® research has resulted also in other
innovative concepts such as strengthened sludge
– a method to speed up hardening of dredged
sludge so it can be used as a building material –,
and biodegradable drilling mud to enable
construction of horizontal water extraction wells.
The latest idea involves biological strengthening
of peat. Exploratory experiments have shown
that when a solution of silicates and sugars is
mixed with peat, the silicate crystallizes on the
peat fibers due to biological acidification, reducing the compressibility and oxidation potential
of the peat significantly (Den Hamer et al. 2009).
Ten years of SmartSoils® research and consequential industrial scale up has uncovered numerous
opportunities for adaptation of the engineering
approach for complex constructions, building
environments and ground conditions (Molendijk
et al. 2009). Involvement of many different
stakeholders, from industry, government and
university proved essential for developments in
such a cross-disciplinary field. Still, tenacious
steps in coupled research and industrial scale up,
for at least another five to ten years, are still
required to expose and harvest the full potential
of bio-geo-engineering.
References
based solidification. 17th International
Conference on Soil Mechanics & Geotechnical
Engineering Alexandria, Egypt.
– Harkes, M.P., van Paassen, L.A., Booster, J.L.,
Whiffin, V.S. & van Loosdrecht, M.C.M. 2009.
Fixation and distribution of bacterial activity in
sand to induce carbonate precipitation for ground
reinforcement. Ecological Engineering published
online (10.1016/j.ecoleng.2009.01.004).
– Molendijk, W.O., Van der Zon, W.H. & Van
Meurs, G.A.M. 2009. SmartSoils, Adaptation of
soil properties on demand. 17th International
Conference on Soil Mechanics & Geotechnical
Engineering Alexandria, Egypt.
– Van Beek, V.M., Lambert, J.W.M., Blauw, M.,
De Louw, P.G.B. & Faassen, E. 2008. Application
of BioSealing for saltwater seepage reduction.
10th ConSoil conference, Milano, Italy.
– Van Paassen, L.A. 2009. Microbes turning
sand into sandstone, using waste as cement.
4th International Young Geotechnical
Engineering Conference Alexandria, Egypt.
– Van Paassen, L.A., Daza, C.M., Staal, M.,
Sorokin, D.Y., Van der Zon, W.H. & van
Loosdrecht, M.C.M. 2009a. Potential soil
reinforcement by biological denitrification.
Ecological Engineering published online.
– Van Paassen, L.A., Harkes, M.P., Van Zwieten,
G.A., Van der Zon, W.H., Van der Star, W.R.L.
& Van Loosdrecht, M.C.M. 2009b. Scale up of
BioGrout: a biological ground reinforcement
method. 17th International Conference on
Soil Mechanics & Geotechnical Engineering
Alexandria, Egypt. www.smartsoils.nl
– Den Hamer, D.A., Venmans, A., Van Paassen,
L.A., Van der Star, W.R.L., Van der Zon, W.H. &
Olie, J.J. 2009. Stabilization of peat by silica
Figure 5 Numerical simulation showing
the normalized distribution of reagents
in the 100 m3 BioGrout experiment after
10 hours of flushing corresponds with the
contours of the cemented sand body.
Figure 3 The exposed cemented sandbody
in the 100m3 BioGrout container test.
Figure 4 Application of BioSealing in a dike
along river Danube in Austria.
GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt
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