Cyclic direct shear behaviors of frozen soil-structure interface under constant normal stiffness condition

The frozen soil-structure interface is the key connecting component between structures and the soil in the permafrost regions. The soil-structure interface is usually subjected to seismic or wind loadings; consequently the cyclic shear properties of the interface are the key parameters of concern when considering the safety and durability of the structures in these permafrost regions. In this paper we present the results of measuring and analyzing the cyclic shear properties of an artificially frozen soil-structure interface; the experimental work being conducted on our self-developed, large-scale multi-functional direct shear apparatus (DDJ-1). These direct shear tests were conducted under conditions of constant normal stiffness, having a specific initial value for normal stresses (either 300, 500, or 700 kPa), and at a constant frozen temperature (i.e. -6, -10, or -14 degrees C) or a rising temperature (from -14 degrees C to -2 degrees C). Their cyclic shear stress and normal displacement were measured in 30 cycles for each of the constant frozen temperature settings, and in 13.25 cycles for the rising temperature. These test results show that: (1) The maximum shear stress is observed in the first cycle. This maximum shear stress is higher for lower frozen temperature and higher initial normal stress. Furthermore, the internal friction angle of the frozen soil-structure interface decreases with shear cycle and higher frozen temperature. (2) Under constant frozen temperature, the rates of increase of the normal displacement and normal stress slow down with cyclic loading time. However, these rates of increase are fast at the beginning, slow down, and then speed up again under the rising temperature. (3) The reversible normal displacement, expressed by the peak-to-trough distance of normal displacement, linearly increases with the initial normal stress when the frozen temperature is constant. (C) 2014 Elsevier B.V. All rights reserved.