Dynamic Properties of Undisturbed Guiyang Red Clay in the Small-Strain Range

Abstract

Red clay is commonly used as filler for roadbed or subgrade, but it always leads to engineering problems of uneven settlement and strength decay under cyclic dynamic loading because of its engineering characteristics such as high water content, high plasticity, and poor compaction. It is essential to assess the dynamic characteristics of undamaged red clay in the small-strain range, but few relevant researches are reported. In this study, the small-strain dynamic property of undisturbed red clay from Guiyang, Southwest China, was investigated. Multistage dynamic triaxial shear tests were performed to analyze the development of the skeleton curve (σd–ɛd), the maximum dynamic modulus of elasticity, the maximum dynamic shear modulus, and the maximum dynamic damping ratio in the small-strain range of undisturbed red clay with different confining pressures, consolidation stress ratios, loading frequencies, and water content ratios. Moreover, under the small-strain conditions, the small-strain dynamic deformation mechanism of the specimens with isobaric consolidation and anisotropic consolidation was analyzed. In addition, some empirical prediction models for the dynamic constitutive relationship, dynamic elastic modulus, and dynamic damping ratio of undisturbed red clay under small-strain range test conditions were proposed. Results indicate that the skeleton curve of undisturbed red clay showed softening behavior when the dynamic axial strain ɛd > 1.0%, the center of the hysteresis curve, shifted positively along the coordinate axis with the increasing confining pressure and the loading number. The undisturbed specimens exhibited mainly two types of deformation under small-strain test conditions, including axial compression deformation when the consolidation ratio Kc was 1.0 and bulging deformation when the Kc was 1.5 and 2.0. The proposed models could be used to predict the skeleton curve, dynamic elastic modulus, and dynamic damping ratio of the undisturbed red clay in the small-strain range.