Static and dynamic behavior of collapsible soils

Collapsible soils, whether engineered or natural, may exist in seismic zones; therefore, there is a need to assess the pre and post cyclic behavior of collapsible soils even after wetting occurs. Consequently, emphasis was placed in this research on investigating the static and dynamic behavior of collapsible soils under different stress levels and wetting conditions, namely as-prepared (no wetting), soaked, and backpressure saturated conditions. Furthermore, tests were conducted on samples simulating compacted and natural samples, specifically compacted and natural density.; The image processing technique was adopted as a method of volume change measurement. The image processing technique was initially evaluated by undergoing a series of calibrations through which its effectiveness was assessed, indicating that volumetric strain measurements can be obtained with an accuracy of ±0.25%.; The volumetric collapse potential of the tested samples was initially evaluated by performing 3-dimensional response-to-wetting tests in the triaxial apparatus for both compacted and natural density samples. No significant difference was observed for volumetric collapse potential obtained under soaked and backpressure saturated conditions.; A series of consolidated undrained triaxial tests was performed in order to evaluate the static behavior of collapsible soils. Data obtained from the tests indicated significant reduction in static shear strength for compacted and natural density samples with maximum reduction in strength under backpressure saturated condition (i.e., S = 100%). The static shear strength was correlated with the degree of saturation in order to establish a relationship that can be readily used by practicing engineers.; Using data acquired through cyclic triaxial tests, a comprehensive study was conducted to evaluate the cyclic strength under different wetting conditions. A severe reduction in dynamic shear strength due to wetting was observed.; Post-cyclic shear strength was evaluated. The measure of post-cyclic shear strength with respect to the static shear strength was indicated by the Normalized Post Cyclic Shear Strength. Data acquired from the tests indicated a slight reduction in shear strength for the case of backpressure saturated samples. However, Normalized Post Cyclic Shear Strength for as-prepared and soaked samples showed values greater than 1.0, implying that samples have undergone further compression during cyclic loading and, in turn, strengthening under cyclic loading.