Impacts of surface roughness and loading conditions on cyclic direct shear behaviors of an artificial frozen silt-structure interface

摘要

The mechanical properties of the interface between frozen soils and structures are of importance in practice to the design and safety assessment of a frozen soil-structure system in permafrost regions and artificial frozen soils. In practice, frozen soil-structure interfaces are subjected to complex loading conditions and the surface roughness of a structure varies in a certain range. Their impacts on the cyclic direct shear behaviors of an artificial frozen soil-structure interface are interesting but unsolved issues. In this study, a series of direct shear tests were conducted to explore these impacts through characterizing the cyclic direct shear behaviors of an artificial frozen silt-structure interface. Particularly, these direct shear tests, which include monotonic shear tests, constant normal stress tests, and constant normal stiffness tests, were carried out under circumstances of different frozen temperatures and/or interface roughness. Shear stresses and normal stresses (or normal displacements) were measured under cyclic loading. These experiments revealed the following mechanical behaviors of the artificial frozen interface: (1) in monotonic shear tests, maximum shear stress is observed at the shear displacement of approximately 0.7 mm. (2) The order of the magnitude of final shear stress from high to low is from constant normal stress tests, monotonic shear tests, constant normal stiffness tests, constant normal stress tests under rising temperature condition, and constant normal stiffness tests under rising temperature condition. (3) Both roughness and frozen temperature at shear have vital impacts not only on the maximum shear stress but also on the final shear stress. The roughness has much stronger impacts on the maximum shear stress than on the final shear stress. A critical roughness is observed from the relationship between the maximum shear stress and roughness. (4) Roughness, loading condition and cyclic loading time are three key factors to normal displacements. Both maximum dilation and final normal displacement increase with roughness increasing. The maximum dilation firstly increases with roughness increasing and then decreases from a certain roughness of about 0.8 mm. However, the loading conditions have slightly different impacts on the final normal displacement from the maximum dilation.