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 a

nd 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

ms =8.21×10

-3

m

-1

;K=6.06×10

-7

m/s

ms =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.