利用土中水分蒸发特性和微观孔隙分布规律确定SWCC残余含水率

Determination of the residual water content of SWCC based on the soil moisture evaporation properties and micro pore characteristics

残余含水率在非饱和土渗流理论、强度理论等方面都是重要的参数,然而土-水特征曲线(SWCC)试验测量时一般难以达到残余阶段,常常通过经验法(包括模型拟合法)估算残余含水率,方法的适用性值得论证。以武汉黏性土为研究对象,制备不同初始孔隙比试样,利用压力板仪测量SWCC,通过模型拟合的方法计算残余含水率;进行自然状态下水分蒸发试验,根据失水速率定义了临残时间,依据临残时间确定残余含水率;利用核磁共振技术研究微观孔隙分布特性,解释控制残余含水率大小的微观规律。研究结果表明:模型拟合的方法可估算残余含水率,但准确性与模型选择及残余含水率初步范围的限定直接相关;水分蒸发试验是确定残余含水率有效可行的直接方法;武汉黏性土微观孔隙呈三峰分布,残余含水率与第1峰之前的微观孔隙水分紧密相关,依据弛豫时间小于0.267 38 ms的T2谱面积可较为准确地预测残余含水率,对于其他土体该方法需要进一步论证与完善。

Residual water content（RWC） is an important parameter for the study of seepage theory and strength theory of unsaturated soils. However, it is very difficult to determine experimentally from soil-water characteristic curve（SWCC） because the residual state can not be reached normally. In this case, the RWC is often estimated using the empirical methods including the model fitting, so the rationality of these methods is worthy to be studied. After Wuhan clay samples with different initial void ratios were prepared, SWCCs were measured by using the pressure plate apparatus and the RWCs were calculated by using the model fitting method. Water evaporation test was carried out in the natural state. Subsequently, the residual time was defined according to the rate of water loss and was used to determine the RWC. The micro pore characteristics were studied using the nuclear magnetic resonance（NMR） technique, which was used to explain the microscopic mechanism of the RWC. The results show that the model fitting method can be used to estimate the RWC, but its accuracy is directly related to the choice of model and the restriction of preliminary range in RWC. Water evaporation test is a direct and feasible method to determine the RWC. The micro pores of Wuhan clay are distributed in triple peak pattern, and RWC is closely related to the water content in those pores before the first peak. According to the T2 spectrum area with the relaxation time of less than 0.267 38 ms, the RWC can be predicted accurately, however, this method needs further demonstration and improvement for other type of soil.