Water and Salt Migration with Phase Change in Saline Soil during Freezing and Thawing Processes
Water and salt transfer coupled with phase change may cause serious damage to engineering structures in saline soil regions. In this study, the migration of water and salt in silty clay collected from the Qinghai‐Tibet Plateau is explored experimentally and numerically during freezing and thawing processes. The results revealed that there are significant differences in the variations of liquid water content and solution concentration for different initial salt contents, due to salt crystallization and dissolution. The temperature‐induced water migration is determined by the soil properties, which can be well explained by the thermodynamics of mass transfer. The amount of salt migrated upward during cooling is slightly larger than that transported downward in the warming period, implying that salt may be accumulated in the surface soil after a large number of circulations and finally result in soil salinization.
Shear strength and damage mechanism of saline intact loess after freeze-thaw cycling
Abstract Salt accumulation in the surface of soil mass and the structural damage during freeze-thaw cycling are a critical cause for the collapse of loess slopes in northwestern China. A simple method is proposed for preparing intact specimens containing soluble salt, called the leaching method, by which salt infiltrated can be uniformly distributed with the disturbance to the soil structure minimized. Verifications prove that the prepared specimens exhibit evenly distributed water and sodium sulfate. Triaxial shear test results show that the cohesion of specimens decreases after freeze-thaw, and the reduction mainly occurs after 1 to 2 cycles. Specimens with more water or sodium sulfate also manifest lower cohesion. Two characteristic indexes including crack ratio and fractal dimension that quantifies the apparent cracks of specimens indicate that more pronounced cracks appear at higher salt contents. This trend is intensified after more freeze-thaw cycles. The cohesion-based damage coefficients are calculated based on a specific damage path considering both freeze-thaw and salt erosion. The damage coefficient of freeze-thaw decreases at higher salt contents while salt erosion accounts for a major part to the total damage at contents higher than 1.0%. The ratio of freeze-thaw damage coefficient to that by salt erosion decays with freeze-thaw, especially in the initial five cycles, beyond which it stabilizes, like the attenuation of cohesion. The mesoscopic damage due to coupled effect of freeze-thaw and salt erosion is analyzed based on the computed tomography (CT). Results show that the mean CT value (ME) exhibit similar variations to the shear strength after freeze-thaw while the standard deviation (SD) value grows.
Axonal sensorimotor neuropathy in patients with β-thalassaemia
Objective: The purpose of this study was to investigate the prevalence of peripheral neuropathy in patients with β-thalassaemia. Methods: Thirty six patients with a mean age of 29.2±8.2 years and 17 healthy controls with a mean age of 27.6±9.1 were included in this study. Measurements included the neuropathy symptoms score (NSS), the neuropathy disability score (NDS) as well as nerve conduction studies of two motor (ulnar and peroneal) and two sensory (ulnar and sural) nerves of the right limbs. Results: A mainly sensory axonal polyneuropathy was present in 19 out of 36 patients (52.7%). Eight out of these 19 patients also had abnormal NDS values. The neuropathy correlated significantly with the age of the patients and the hematocrit. However, it did not correlate with the presence of antibodies against HCV, the ferritin levels, or with a history of transfusions, desferrioxamine treatment, or splenectomy. Conclusions: This study showed a high prevalence of a predominantly sensory neuropathy in patients with β-thalassaemia. The electrophysiological data suggest that the underlying pathology is an axonopathy. Chronic hypoxia of the nerves resulting from severe anaemia may contribute to the pathogenesis of this neuropathy.