Xiao Liang, Ye Ming, Xu Yongxin
College of Civil Engineering and Architecture, Guangxi University, Nanning, Guangxi, 530004, China.
Guangxi Key Laboratory of Disaster Prevention and Engineering Safety, Guangxi University, Nanning, Guangxi, 530004, China.
Ground Water. 2018 Nov;56(6):959-968. doi: 10.1111/gwat.12642. Epub 2018 Mar 30.
Transient confined-unconfined flow conversion caused by pumping in a confined aquifer (i.e., piezometric head drops below the top confined layer) is complicated, partly due to different hydraulic properties between confined and unconfined regions. For understanding mechanism of the transient confined-unconfined conversion, this paper develops a new analytical solution for the transient confined-unconfined flow toward a fully penetrating well in a confined aquifer. The analytical solution is used to investigate the impacts on drawdown simulation by differences of hydraulic properties, including transmissivity, storativity, and diffusivity defined as a ratio of transmissivity and storativity, between the confined and unconfined regions. It is found that neglecting the transmissivity difference may give an overestimation of drawdown. Instead, neglecting the diffusivity difference may lead to an underestimation of drawdown. The shape of drawdown-time curve is sensitive to the change of storativity ratio, S/S , between the confined and unconfined regions. With a series of drawdown data from pumping tests, the analytical solution can also be used to inversely estimate following parameters related to the transient confined-unconfined conversion: radial distance of conversion interface, diffusivity, and specific yield of the unconfined region. It is concluded that using constant transmissivity and diffusivity in theory can result in biased estimates of radial distance of the conversion interface and specific yield of the unconfined region in practice. The analytical solution is useful to gain insight about various factors related to the transient confined-unconfined conversion and can be used for the design of mine drainage and groundwater management in the mining area.
承压含水层抽水引起的瞬态承压 - 无压水流转换（即测压水头降至顶部承压层以下）很复杂，部分原因是承压区和无压区的水力性质不同。为了理解瞬态承压 - 无压转换的机制，本文针对承压含水层中向完全穿透井的瞬态承压 - 无压水流开发了一种新的解析解。该解析解用于研究承压区和无压区之间水力性质差异（包括导水率、贮水率以及定义为导水率与贮水率之比的扩散率）对水位下降模拟的影响。研究发现，忽略导水率差异可能会高估水位下降。相反，忽略扩散率差异可能会导致低估水位下降。水位下降 - 时间曲线的形状对承压区和无压区之间的贮水率比S/S 的变化很敏感。利用抽水试验得到的一系列水位下降数据，该解析解还可用于反演估算与瞬态承压 - 无压转换相关的以下参数：转换界面的径向距离、扩散率以及无压区的给水度。得出的结论是，理论上使用恒定的导水率和扩散率在实际中可能会导致对转换界面的径向距离和无压区给水度的估计出现偏差。该解析解有助于深入了解与瞬态承压 - 无压转换相关的各种因素，可用于矿区的矿井排水设计和地下水管理。
