One of a major problem in geotechnical field is soft soil because of its low strength. In
order to be able to build a structure above soft soil, soil improvement has to be done.
Deep mixing is one of soil improvement implementation. Deep mixing is done by
forming soil pile of cement treated clay with in-situ mixing. However, when soft soil
is located in marine area that is considered as an extreme environment, the seawater
may cause corrosion to the soil pile. Sulfate is one of the chemical content in seawater
that is corrosive. Thus, the objective of the paper is to know about how severe the
deterioration of soil pile with variation of cement content (c
c
), water content (w
c
), and
curing time (t) after the pile exposed to sulfate. Magnesium sulfate is used to represent
sulfate with the content of 10% which is uniform for all piles. The exposure is
represented by the immersing of soil pile onto soil-sulfate mixture for 7, 14, 28, and 56
days. The deterioration of the pile is investigated using penetration test. The output of
penetration test is in the form of cone penetration resistance (R) vs penetration depth
(d) graph. The result of the test shows that deterioration depth decreases as the increase
of cement content, and the decrease of water content. Furthermore, the on the
undeteriorated zone, the resistance (R
reff
) increases along with the increase of c
c
. In
addition, Ca
2+
and Mg
2+
ion investigation is also done in order to know the content of
ion from the surface of the pile up to 1.5 cm below. It shows that the deeper, the more
Ca
2+
exists. In contrary to that, Mg
2+
decreases as the depth increases. This indicates
deterioration at the surface area which exposed to seawater.