Long-term deformation of Some gypseous soils

Abstract EN

Time-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 reconsolidation.

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 odometer 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 odometer tests increases when the gypsum content increases from (14.8%) to (66%) and when the initial void ratio increases.

The results of double odometer 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.