Sand tank test on seepage characteristics of a single partially penetrating de-watering well from the bottom of an overlying aquifer

In order to study the seepage characteristics of dewatering from an aquifer bottom, a sand tank system was designed with the cross section being a sector of 60°,and the dewatering test from an unconfined aquifer bottom using partially penetrating dewatering wells with different well lengths was conducted. The results show that the phreatic line falls off with dewatering process, and a saturated capillary zone with negative pressure forms above it. The upper capillary zone, supporting capillary zone, saturated capillary zone and free water saturation zone can be formed above the dewatering well in aquifer, and the saturated capillary zone can effectively prevent the upper air from entering the well. The well inner pressure P includes four kinds of circumstances, which are P=0,P>0,P<0 and P_up<0 with P_down>0,and the distribution of quasi-steady flow pressure distribution can be generalized into seven models based on well inner pressure, saturated capillary zone and free water saturation zone. The water pressure transfer of free water cannot be interrupted as the partly-filled well. The distribution of water pressure head is no longer decreasing from bottom to top in the fully filled well, but increases first and then decreases from bottom to top when a phreatic line is formed above the well. The seepage flow will increase with well inner pressure decrease if the saturated capillary zone and free water saturation zone present a wide distribution. When the free water saturation zone disappears and the saturated capillary zone presents a small range vertical distribution, the well inner pressure decrease plays less influence on seepage flow increase. The seepage flow increases with the well length increase, however, when the well length is greater than a critical length, the seepage flow no longer increases with well length increase. In the dewatering process, the seepage flow is composed of static and dynamic recharge, and the static recharge decreases with an exponential function, while the dynamic recharge increases with an exponential function.