Influence of freezing directionality on the permeability of silty clay

Abstract

During artificial ground freezing, freezing may undergo in directions either parallel or normal to the flow of water, which may result in different permeability for the water to flow. Therefore, it is of significant importance to observe the influence of freezing directionality on the permeability of soils. A set of laboratory permeation tests were performed in this study on specimens subjected to three freeze-thaw modes. Considerable change in hydraulic conductivity subsequent to freeze-thaw event was found even under condition where volume change was not allowed. Vertical freeze-thaw resulted in the lowest level of hydraulic conductivity as compared with the other two cases, irrespective of dry density and moisture content. The permeability of specimen subsequent to radial freezing was approximately 34 times in maximum greater than that subsequent to vertical freezing. The occurrence of vertical cracks was responsible for the dramatical increase in hydraulic conductivity of specimens after radial freeze-thaw. Vertical freeze-thaw, however, resulted in an apparent reduction in hydraulic conductivity because of the local consolidation of soil structure during the growth of horizontal ice lenses. Processes that larger pores became larger but smaller pores became smaller contributed to the increase in hydraulic conductivity of thawed specimens even though the total void ratio was unchanged.