基坑降水时长江Ⅰ级阶地互层土中地下水运移规律

Study on Groundwater Movement in Interbedded Soil of Grade Ⅰ Terrace of Yangtze River during Dewatering of Foundation Pit

在长江Ⅰ级阶地某深基坑进行现场群井抽水试验,观测了抽水过程中各含水层水位变化,发现互层土中地下水水位在降水过程中呈稳定下降趋势,但相对其下砂层承压水,互层土水位下降存在明显的滞后。在此结论的基础上,将互层土层视为由粘土层和砂层交互层叠而成,并假定这两类组成单元的渗透系数分别一致,推导了降水过程中互层土地下水水头随降水时间变化的公式。公式显示:互层土水头下降时间与其中粘土层厚度占总厚度的比例、土体体积压缩系数、土体孔隙度、互层土厚度的平方成正比,与粘土层的渗透系数成反比。

Field group well pumping tests were carried out in a deep foundation pit on grade I terrace of the Yangtze River. The water level changes of each aquifer during pumping were observed. It was found that the groundwater level in the interbedded soil decreased steadily in the process of dewatering, but the water level of the interbedded soil decreased obviously lagged behind the confined water in the lower sand layer. On the basis of this conclusion, the interbedded soil layer is considered to be formed by the interaction of clay layer and sand layer. Assuming that the permeability coefficients of the two components are identical, the formula of the variation of groundwater head with precipitation time in the process of precipitation is deduced. The formula shows that the head drop time of interbedded soil is proportional to the proportion of the thickness of clay layer to the total thickness, the volume compression coefficient of soil, the porosity of soil and the square of the thickness of interbedded soil, and inversely proportional to the permeability coefficient of clay layer.