Wei Changfu

A NMR-based testing and analysis of adsorbed water content

The variation of adsorbed water content is the core issue in study of temperature effect of clay. The water content and distribution in soil is detected by NMR technique, combined with the difference of suction, freezing point and variation with temperature of capillary and water, a fast, nondestructive method is developed which can be used to determine the adsorbed water content of the soil. The variation of adsorbed water content with temperature and dry density is determined by the method. The result indicates that at room temperature, the adsorbed water of samples decreases with the increasing dry density. This is mainly due to the reducing space of soil particles during the increase of dry density and the overlapping of electric double layer. For unfrozen soil, the adsorbed water content is affected by soil constitutes and temperature. The adsorbed water content of the sample with a clay fraction of 70% increases with increasing temperature. But for samples with clay fraction of 30% and 50%, adsorbed water content increases with increasing temperature above 0℃ and decreases with the increasing temperature below 0℃ and the trend is especially obvious for sample with a clay fraction of 50%. Overall, the adsorbed water of three samples changes few with the variation of temperature. In warm path during a freezing-thawing cycle, unfrozen water in frozen sample is adsorbed water below -3.2℃ and linear scaling factor k between adsorbed water content ( S w ) and temperature ( T m - T ) changes between -0.867~-0.744 which has a big difference from the theoretical value (-1/3). We think the difference is mainly caused by the roughness of pore size, roughness of soil particles, electric force and some other complex factors.