Abstract:
Collapse of soil skeleton due to variation in its loading and boundary conditions impacts the strength
and stability of soil in its unsaturated state. The present study is focused on the influence of matric
suction on collapsible behaviour and stiffness degradation of compacted unsaturated cohesive soil.
Collapse characteristic of unsaturated soil is assessed under sudden inundation and varying vertical
stress application. A series of dynamic triaxial, double oedometer and filter paper tests were conducted
on unsaturated Ahmedabad cohesive soil under as-compacted conditions at varying dry density and
water content to determine cyclic degradation index (δ), collapse potential and matric suction (u a – u w ),
respectively. Significant influence of matric suction was observed on collapse potential and stiffness
degradation of unsaturated cohesive soil. Larger collapse potential at higher matric suction clarified the
meta-stable state of compacted unsaturated cohesive soil under dry conditions. Cyclic degradation index
(δ) with number of loading cycles was found to be decreasing with increase in matric suction
representing brittle nature of soil possessing higher matric suction signifying soil skeleton to be highly
volatile and unsafe under dynamic loading conditions.
