The Research on Design, Construction and Operations Management of the Underground dam

地下坝是水资源开发利用的一种方式，在海岛、半岛和干旱地区尤为有效。在日本的南洋群岛、冲绳和鹿儿岛县，一些地下水坝正在进行建设。本文对地下坝设计、施工和运行管理中的四个重要问题进行了研究：(1)渗流条件变化对渗流衰减机理的阐明本文采用压力耦合方程的半隐式方法对粘性渗流进行了数值分析，阐明了渗流速度和压力在砾石周围的分布。计算结果表明，水力坡度与渗流速度之间的关系可用二次多项式(Forchheimer定律)来表示。用Forchheimer定律模拟了抽水井周围的地下水流动。(2)定量P…降雨异常对地下水位抬升的影响及对策建立了饱和-非饱和渗流数值有限元模型，并应用于实际地下大坝。利用电阻率法进行含水层咸水侵入研究为了弄清地下坝址的咸水侵入情况，在口池县春野滨海地区进行了垂向测深。得到了垂直方向的电阻率分布。在海岸附近发现了一层深厚的低电阻层，推测为咸水层。用传统的曲线拟合法和新提出的数值分析与标准Powell法相结合的方法估计了其深度的水平分布。地下坝防渗基础和地下水位的优化估算方法在地下大坝的设计和运行管理中，需要用不充分的数据来估算防渗基础和地下水位分布。在这里，发展了协克里格估计技术，以显示地下水位和在使用不充分的数据集时的防渗基础。协克立格法可以得到合理有效的结果，因为它能够充分提取可用的互相关数据，因此可以插补较少的采样数据。较少

The underground dam is one method for water resources development, and especially, it is effective in islands, peninsula and arid regions. In Nansei Islands, Okinawa and Kagoshima Prefectures in Japan, some underground dams are carrying out the construction. In this study, following four items that become important problems in design, construction and operations management of underground dam have been investigated.(1) The Elucidation of Decrease Mechanism of the Pumpage with the Flow Condition Change in the Porous MediaThe viscous flow is analyzed numerically by Semi-Implicit Method for Pressure-Linked Equation to clarify the seepage velocity and pressure distributions around gravels. It is clarified from the calculated results that the relationships between hydraulic gradient and seepage velocity are represented by quadratic polynomial equation (Forchheimer's law). The technique is shown to simulate the groundwater flow around pumping well by using Forchheimer's law.(2) Quantitative P … More rediction of the Rise of the Groundwater Level with the Abnormal Rainfall and Its CountermeasureNumerical FEM model of saturated-unsaturated seepage is developed and applied to an actual underground dam. Three dimension characteristics of groundwater flow overtopping the dam body is obtained and examined.(3) The Research on Saline Water Intrusion of aquifer by Using Electrical Resistivity MethodIn order to clarify the saline water intrusion into the underground dam site, vertical soundings were carried out in costal area of Haruno, Kouchi Pref. and vertical resistivity distributions were obtained. A deep layer of low resistivity was found near coast, and it was concluded to be the layer of saline water. Horizontal distributions of its depth were estimated by conventional curve matching method and newly proposed method with numerical analysis and staodard Powell's method. Its result and validity are shown and discussed.(4) Optimum Estimation Method of Impermeability Basis and Groundwater Level Using Not Sufficient Data SetIn the steps of designing and operations management of underground dam, it is necessary to estimate the impervious basis and groundwater level distributions using not sufficient data set. Here, cokriging estimation techniques are developed to show the groundwater levels and the impervious basis in using the insufficient data set. Cokriging yields reasonable and valid results because it can interpolate less sampling data due to its ability to adequately pick up the available cross-correlation data. Less