Effect of hydraulic and mechanical stresses on cyclic deformation processes of a structured and homogenized silty Luvic Chernozem

The deformation behavior of soils is strongly affected by coupled mechanical and hydraulic stresses especially under cyclic loading. Contrary to static loading tests cyclic loading caused plastic deformation increments with ongoing loading cycles even for stresses in the re-compression range associated with alterations in the hydraulic stress state. The aim of this study was to proof the interference of hydraulic properties on the mechanical deformation behavior (cyclic compressibility) depending on soil structure and cyclic loading time. Cyclic loading tests with changing boundary conditions in terms of initial matric potential, loading time and magnitude on structured and homogenized silty soil samples were performed. Furthermore, pore water pressures during cyclic loading and the air conductivity of soil cores before and after cyclic loading were measured. The results indicated differences in the stress–strain response accompanied by typical hydraulic stress regimes. These were classified into five categories representing a typical development of pore water pressures according to soil structure and loading time. Predominantly at short-time cycles a built-up of pore water pressures with increasing number of cycles occurred resulting in a high cyclic compressibility of the homogenized soil. The loss of soil strength could be linked to the beginning of partial liquefaction processes induced by heavy soil loading of 150 kPa and by a higher initial matric potential. In contrast, the less compressible structured soil showed a better internal redistribution of pore water and faster dissipation of stress-induced pore water pressures compared to the homogenized soil. Finally, the influence of soil structure plays an important role in understanding hydro-mechanical relationships, especially since the reversal of pore water pressures back to the hydraulic equilibrium state was restricted by the time between repeated loading events.

► Higher cyclic compressibility of a homogenized soil compared to a structured one. ► Effects of loading time on cyclic compressibility are strongly structure-related. ► Hydro-mechanical interactions are influenced by soil structure and loading time. ► Short-time loading cycles initiate partial liquefaction of a homogenized soil. ► Faster dissipation of pore water pressures was enhanced by soil structure.