Cyclic Resistance and Large Deformation Characteristics of Sands Under Sloping Ground Conditions: Insights from Large-Strain Torsional Simple Shear Tests

Abstract

AbstractUnderstanding the mechanisms for the development of large deformation of sand within sloping ground due to liquefaction remains one of the most challenging topics in earthquake geotechnical engineering, due to its complexity and the large number of factors that may affect the liquefaction resistance (e.g., soil density, soil type and fabric, stress conditions, etc.). Very often the use of stress conditions different from simple shear and technical limitations of testing devices (i.e., inadequacy to reach large shear strain levels or prevent large extents of non-uniform deformation of the specimens at higher strain levels) has limited the possibility to entirely define the effects of sloping ground on the cyclic resistance of sands. The development of a state-of-the-art torsional shear testing device that is capable of reproducing the simple shear condition and achieving 100% double amplitude shear strain (γDA), however, has made it possible to obtain new insights on this challenging topic. This paper provides first an overview of this large-strain torsional testing apparatus and the ad hoc procedure employed to carry out high-quality experimental tests, including the correction for membrane resistance. Following, results of undrained cyclic torsional shear tests with initial static shear conducted on loose (Dr = 25–30%) and medium dense (Dr = 44–48%) Toyoura sand specimens are reported. Specifically, the post-liquefaction response is scrutinized in terms of observed failure modes, strain development characteristics and cyclic resistance up to 50% single amplitude shear strain. The occurrence of strain localization observed at strain levels higher than 20% is described in detail, and the role of key factors affecting its properties is discussed.KeywordsFlow deformationLiquefactionResidual deformationShear failureSloping groundTorsional simple shear