Effect Of Stress And Suction Histories Dynamic Properties Of Statically Compacted Silty Sand

Abstract

This paper is devoted to the analysis of the experimental study whose intent is to find the effect of the stress/suction history on the dynamic properties of silty sand subjected to small- to mid-strains. The practical application of this study includes determining the effect on soil stiffness properties of increased soil suction (transpiration of water) followed by loading induced by shallow foundations and vice versa. Small-strain stiffness properties such as shear modulus, material damping, and shear wave velocity, are important subsoil parameters for proper analysis and design of unsaturated earth structures subject to static and dynamic loading. Traditional soil testing methods are unable to accurately assess this small strain behavior, thereby significantly underestimating the soil stiffness. Currently, a great deal of research effort is being made to assess the field and laboratory based measurements of soil suction, assessments of soil-water retention properties, and analyses of swell-collapse behavior; however, very few efforts have been focused on small strain response of unsaturated soils and their dynamic characterization at small- to mid-strains. The overall purpose of this research is to study the dynamic properties of unsaturated soils at very small shear strain amplitudes upon being subjected to various hydro-mechanical states via resonant column testing. This research work uses a suction-controlled, proximitor-based resonant column device featuring a PCP-15U pressure control panel that allows for the implementation of the axis-translation technique via the independent control of pore-air and pore-water pressures in the specimen. A total of two experimental series were conducted with varying loading paths. Each series of testing measured the small- to mid-strain stiffness properties of the soil at sixteen different suction and net mean stress state. The three series of suction-controlled resonant column tests were conducted on statically compacted samples of silty sand for a range of suction states between 50 kPa and 200 kPa, and at net confining pressures also ranging from 50kPa to 200kPa. Results show the critical role of matric suction in the small-strain response of the tested soil.