2565
Bio-mediated soil improvement utilized to strengthen coastal deposits
Amélioration du sol biologiquement négociée utilisée pour renforcer les dépôts côtiers
Montoya B.M., Feng K., Shanahan C.
North Carolina State University, Raleigh, NC, USA
aBstract - Vital coastal lifelines can be vulnerable during large storm events. large wave action and high sea levels erode the
sandy soil that supports coastal infrastructure, including highways, structures, pipelines, and other utilities. damage from these
events can result in severe property damage, loss of revenue, and large repair costs. natural bio-geochemical methods can be used
to reinforce the erodible sandy soil to help prevent damage to the infrastructure. Utilizing naturally-occurring biological metabolic
activity, calcium carbonate cementation can be induced
in situ
to bind the sand grains together, thereby improving the strength and
stiffness of the soil and in turn preventing erosion of the coastal deposits. microbial induced carbonate precipitation (micp) has
been shown to be an effective method to improve the soil behavior in saturated conditions subjected to undrained monotonic and
seismic loading in both laboratory and centrifuge tests. applying this proven natural treatment technique to unsaturated coastal soils
can improve the soil’s resiliency during large storm events. results indicate that the strength of the unsaturated soils increase from
intermittent surficial treatments. rigid-walled soil column tests were conducted to evaluate the effectiveness of treating sandy soils
by flooding the surface of the soil with the appropriate microbes and nutrients and allowing free drainage. clean fine sand, typical
of coastal dune deposits, was used in the soil column tests. the strength of the cemented sand was evaluated using unconfined
compression tests. a discussion of upscaling the results from the laboratory tests to application
in situ
to improve the resiliency of
coastal infrastructure is also presented herein.
1. introdUction
Vital coastal lifelines can be vulnerable during large storm
events. large wave action and high sea levels erode the sandy
soil that supports coastal infrastructure, including highways,
structures, pipelines, and other utilities. damage from these
events can result in severe property damage, loss of revenue,
and large repair costs. the outer banks of north carolina have
seen several hurricanes in recent years (irene in 2011, and
sandy in 2012) which have inflicted damage to vital coastal
lifelines as illustrated in figures 1 and 2.
natural bio-geochemical methods can be used to reinforce the
erodible sandy soil to help prevent damage to the
infrastructure. Utilizing naturally-occurring biological
metabolic activity, calcium carbonate cementation can be
induced
in situ
to bind the sand grains together, thereby
improving the strength and stiffness of the soil and in turn
preventing erosion of the coastal deposits. microbial induced
carbonate precipitation (micp) has been shown to be an
effective method to improve the soil behavior in saturated
conditions subjected to undrained monotonic and seismic
loading in both laboratory and centrifuge tests (montoya et al.,
2013, mortensen and deJong, 2011, deJong et al., 2006).
applying this proven natural treatment technique to
unsaturated coastal soils can improve the soil’s resiliency
during large storm events. results indicate that the strength of
the unsaturated soils significantly increase from intermittent
surficial treatments. rigid-walled soil column tests were
conducted to evaluate the effectiveness of treating sandy soils
by flooding the surface of the soil with the appropriate
microbes and nutrients and allowing free drainage. clean fine
sand, typical of coastal dune deposits, was used in the soil
column tests. changes in the strength of the sand from the
unsaturated cementation treatments was evaluated using
unconfined compression tests. a discussion of upscaling the
results from the laboratory tests to application
in situ
to
improve the resiliency of coastal infrastructure is also
presented herein.
figure 1. a section of highway 12 at the edge of rodanthe, n.c.
undermined by erosion due to the storm surge and wave action during
hurricane irene. (photo: news & observer, aug. 31, 2011)
