Abstract: 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.

Key words: field test, double-tube test for drilling, aquitard, hydraulic parameters, analytical solution