Permeability Anisotropy of Loess under Influence of Dry Density and Freeze-Thaw Cycles

Loess, a kind of special soil, is widespread in the seasonally frozen soil regions and featured with well-developed joints and pore structure. Notwithstanding, the permeability anisotropy nature of loess can badly impact the safety of construction in such regions. Despite many influencing factors, the effect of dry density and freeze-thaw cycles plays a major role in the permeability anisotropy nature. This study uses the Global Digital Systems (GDS) triaxial permeability apparatus to investigate the permeability anisotropy nature of the Q(3) horizontally and vertically cut loess specimens retrieved from an excavation pit in Xi'an, Shaanxi Province. The experimental results show that the loess possesses a distinct permeability anisotropy nature, and it is intensified when subjected to the effect of particle densification. The higher the initial moisture content, the greater the pore structure change, and the weaker the permeability anisotropy nature. The increasing cycle number promotes the growth of pore ice and subsequently the bridging pore structure, improving the pore connectivity. Despite the bridging impeding the groundwater seepage in the vertical direction, the freezing-thawing cycle of more than five times, in turn, mitigates this phenomenon, and the pore connectivity in the vertical direction outweighs the horizontal one in the end.