Pre- and post-cyclic behavior of mixed clayey soils

Abstract

Soil structures are often comprised or supported by soils that are mixtures of cohesive and granular geomaterials. These soils are termed as intermediate or mixed soils and are widely found in natural deposits and man-made soil structures. The objective of this paper is to study the behavior of mixed clayey soils under monotonic, cyclic, and post-cyclic monotonic loading, with the main focus on the last of these three. For this purpose, a number of strain-controlled monotonic, cyclic, and post-cyclic triaxial compression tests were carried out on “clay–sand” and “clay–gravel” mixtures in undrained conditions. The effects of sand (or gravel) contents, number of cycles, cyclic strain amplitude, consolidation pressure, and grain size on the mechanical behavior of the mixtures are evaluated. The major findings from the laboratory study are: (i) the addition of granular materials to the clayey soils increases excess pore-water pressure during strain-controlled monotonic undrained shearing and cyclic loading and (ii) during post-cyclic monotonic shearing, mixed clayey soils behave similarly to overconsolidated soils; the higher the granular material is, the higher the overconsolidation ratio would be. Based on the research results, an algorithm for estimating post-cyclic mechanical parameters of mixed clayey soils, without conducting cyclic and post-cyclic tests, is suggested.

Two-dimensional numerical modeling of fault rupture propagation through earth dams under steady state seepage

“…This observation could be attributed to the higher shear strength of ST40, requiring a larger push to fully propagate the ruptures, and thus, generating higher pore pressures due to the increased compression. Monotonic undrained triaxial testing on these two materials [32] and other experimental findings [40] resulted in the same conclusion.…”

“…The post peak behaviors of ST40 and T100 were studied thoroughly by Soroush and Soltani Jighe [32]; they showed that these cohesive materials do not exhibit strain softening behavior. However, dense granular soils, like the filter and shell materials, usually exhibit strain softening behavior.…”

“…In the above context, Soroush and Soltani Jighe [32] carried out a number of undrained monotonic, cyclic and post-cyclic compression triaxial tests on pure clay (T100) and different clay-sand and clay-gravel mixtures. For example ST40, which was the main cohesive material for this study (Section 3.2), was a mixture of 40 volumetric percent of clay and 60 volumetric percent of sand.…”

Postcyclic behavior of low-plasticity silt with limited excess pore pressures

“…Soroush and Soltani-Jigheh [17] carried out strain-controlled cyclic triaxial testing on mixed clayey soils (clay-sand and claygravel mixtures), and the postcyclic soils not reconsolidated after cyclic loading. They concluded that the ratio of postcyclic undrained shear strength to initial undrained shear strength (S u(PC) /S u(M) ) and the ratio of postcyclic secant deformation modulus to initial secant deformation modulus (E 50(PC) /E 50(M) ) generally decreased as axial strain induced by cyclic loading increased.…”

Post-Cyclic Undrained Behavior of Compacted Composite Clay Subjected to Various Cyclic Loading Paths

“…Vaid and Thomas (1995) found that the post-cyclic shear behavior become more closer to the initial performance of soil with less excess pore water pressure for limited liquefaction tests. Soroush and Soltani-Jigheh (2009) carried out lots of strain-controlled cyclic riaxial testing for mixed clayey soils (clay-sand and clay gravel mixtures). It was presented that S u(PC) /S u(M) (ratio of post-cyclic undrained shear strength to initial undrained shear strength) and E 50(PC) /E 50(M) (ratio of secant deformation modulus after post-cyclic test to initial secant deformation modulus) decreased generally as e c (cyclic strain) increased, and that the reduction in the deformation modulus was comparatively more pronounced.…”