基于现场双管试验确定弱透水层水力参数的方法

弱透水层水力参数对基础工程设计、建设和地下水资源评价、地下水污染预测具有重要意义。现提出一种现场确定含水层系统中弱透水层水力参数的钻孔双管试验方法。利用麻花钻钻孔，到达地下水位线以下揭露到目的层位后布设外管，以起到护壁防止土层塌孔的作用。在外管内通过锤击的方式将内管嵌入到目的层中，使其下部管中有一定厚度的土样作为现场固定试验土柱。待内外管中地下水位稳定后迅速加高内管水头，并通过马里奥特瓶装置保持定水头。建立钻孔双管试验土柱的数学模型，推导了土柱顶底面单位面积流量随时间变化的解析解，将其无量纲化后作出标准曲线。作为该方法应用的实例，在长江下游三角洲苏锡常冲积平原的常州天宁区德安医院附近的空旷场地进行了专门的钻孔试验。确定了该地区的细砂质粉土和粉质黏土的渗透系数和贮水率分别为：K=1.66×10?6 m/s，?s =8.21×10?3 m?1；K=6.06×10?7 m/s，?s =2.26×10?3 m?1。结果表明，该方法对于现场确定弱透水层的水力参数有较好的适用性。

A method for determining aquitard hydraulic parameters based on double-tube field test

The aquitard hydraulic parameters are important for basic engineering design, construction, groundwater resource evaluation and groundwater pollution prediction. A new method of borehole double-tube test is proposed to estimate the hydraulic parameters of aquitard in aquifer system, including vertical hydraulic conductivity K and specific storage μs. The drill pipe is drilled below the water level line by auger drill, and the outer pipe is laid after the target layer is exposed, so as to protect the wall and prevent the collapse of the soil layer. In the outer pipe, the inner pipe is embedded into the target layer by hammering, and the soil sample with a certain thickness in the inner pipe is used as the fixed soil column in the field test. Then the water is injected into the inner pipe rapidly when the groundwater level in the inner and outer pipe is stable, at the same time, and the fixed head is maintained through the Mariot bottle device. A mathematical model of soil column in borehole double-tube test is established, and the analytical solution of unit area flow rate of top and bottom of soil column with time is deduced. The dimensionless analytical solution is derived and the standard curve is obtained. As an example of the application for this method, a special borehole test was carried out in the open field near De'an Hospital, Tianning District, Changzhou, in the alluvial plain of Suzhou-Wuxi-Changzhou, the lower Yangtze River Delta. The hydraulic conductivity and the specific storage of fine sandy silt and silty clay in this area are determined as follows: K=1.66×10?6 m/s, ?s =8.21×10?3 m?1；K=6.06×10?7 m/s, ?s =2.26×10?3 m?1, respectively, which demonstrates that the method has good applicability for determining the hydraulic parameters of aquitard in the field.