Abstract: Compared with cyclic triaxial and torsion shear apparatuses, the cyclic simple shear apparatus has obvious advantages, e.g., simulating in-situ conditions under earthquakes, and directly applying shear stress and measuring shear strain. However, applications of current cyclic simple shear apparatuses are still limited due to technical problems, such as non-uniform shear stress or strain, boundary condition un-determined, potential shear plane, and size effect of specimen. In this study, a new cyclic simple shear apparatus with hinged structures for a cubical specimen was developed to resolve these problems. The design concept and loading principle were proposed by considering the loading mechanics and stress-strain condition of current simple shear apparatuses. Several main components of the apparatus were presented in detail, including pressure cell, loading system, measurement system and automatic control system. The shear strain distribution of soil specimen subjected to loading from three different loading devices was analyzed by the three-dimensional finite differential program, which proved that the shear strain distribution of soil specimen subjected to loading from the new simple shear apparatus were more uniform than the other two. Finally, a series of cyclic simple shear tests on intact loess specimens were conducted with this developed apparatus under different vertical pressures, water contents and shear strain amplitudes. The results show that the apparatus is reliable and accurate in loading control. The dynamic load input can be reproduced with the acquired data. The formation process of seismic subsidence of loess and the corresponding influencing law are revealed by the relationships between vertical strain, shear stress, shear strain and the number of loading cycles.

Key words: cyclic simple shear apparatus, loess, cyclic simple shear test, seismic subsidence