Long -Term Deformation Of Some Gypseous Soils
Engineering and Technology Journal,
2008, Volume 26, Issue 12, Pages 1461-1483
AbstractTime-dependent deformation and stress relaxation in soils are important in a variety of
geotechnical problems where long-term behavior is of concern.
Previous studies on soils showed that the magnitude of delayed compression
(creep) is controlled by compressibility and soil sensitivity in addition to
In this paper, the time-dependent behavior of gypseous soils is investigated. The
soils used in this study were brought from three locations at Al-Tar region west of Al-
Najaf city in Iraq. These soils had gypsum content of (66%, 44% and 14.8%). The
mineralogical and chemical properties of the soils were determined.
Two series of tests were performed. In the first, collapsibility characteristics were
investigated for a long period (60 days) by conducting single and double oedometer
tests. In the second series, the effect of relative density on collapse with time was
investigated. The samples were compacted to 40%, 50% and 60% relative density and
then tested. The results of collapse tests showed that the relationship between the
strain and logarithm of effective stress has two vertical lines. The first one represents
the collapse settlement taking place within 24 hours, while the second one represents
the long-term collapse. The collapse potential in both single and double oedometer
tests increases when the gypsum content increases from (14.8%) to (66%) and when
the initial void ratio increases.
The results of double oedometer tests showed that the relationship between the
collapse potential and logarithm of time, for samples loaded to 800 kPa for 60 days,
consist of three distinct segments. The first segment is represented by a curve concave
downward in which the compressibility gradually increases. The second segment is a
straight line with a higher increase in the strain. The third segment which refers to
creep collapse depends on the gypsum content. Gypseous soil with low gypsum
content (14.8%) exhibited significant decrease (5.21% at 24 hours to 7.16% at 60 days)
in collapse potential with time.
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