Global warming and sea level rise have become major
concerns of the modern world with the Intergovernmental Panel on Climate Change
(IPCC) reporting that sea levels may rise by
52-98 cm in the 21st century. At the upper end of predicted sea
level rise, 50% of the world’s population will be affected, with 33% of coastal
land lost. As the majority of
buildings and transport infrastructure are
concentrated in these coastal areas, it is very important to understand of the longevity of these structures
in the face of sea level rise.
Soil-cement
columns are a geotechnical solution used for ground improvement in coastal
areas. However, after long periods of exposure, the strength of these columns
may decrease to below their designed safe bearing capacity ultimately resulting
in failure. In this study, needle penetration resistance tests, uniaxial
compression tests, thermogravimetric analysis, chemical and image analyses were
applied to determine the extent of deterioration in scaled soil-cement columns
exposed to synthetic seawater. The effects of high sunfate concentrations
(100%, 200%, 500% and 1000% that of seawater) on the durability of soil-cement
samples were also studied. The
experimental results show that the effects of
seawater (sunfate) are significant on the outer surface strength
development. For
samples exposed to seawater, inhibition of the portlandite and formation of
gypsum and ettringite are the main reasons leading to the destruction of soil-cement
samples. Moreover, the deterioration is strong
at the surface and develops inward with time.
An analytical model has been developed
and calibrated using the experimental data to predict the deterioration
depths and total strength change of the soil-cement columns as a function of
time and sunfate concentration. Results show that for the 0.5 m diameter
column exposed to 200% SW, the strength will fall below the minimum design
strength after 75 years. For higher sunfate environments (500% and 1000% that
of seawater), the same column would never reach the minimum design strength
requirement. Consequently, this has significant implications to stabilising soils
in high sunfate environments such as those containing pyrite which makes up
approximate 95,000 km2 of the Australian
coastline. |