地工止水膜產生破洞時的輸水率模式探討

Abstract

想要瞭解地工止水膜產生破洞時的滲流行為,求出地工止水膜和土壤介面輸水率是一個重大的課題，然而要以傳統的得實驗和數學的計算評估輸水率的狀況似乎相當困難。 在此研究裡以有限元素程式（FEMWATER）配合試驗結果來評估輸水率, FEMWATER是3D的有限元素方法可以用於飽和、不飽和、不固定密度的流體的地下水的運輸模式。FEMWATER乃由賓洲大學的葉高次於1992賓州大學所撰寫，並和美國國防部和葉高次合作的前置處理系統GMS相容。 我們分別以兩種土壤做為實驗的土壤材料分別為頭前溪砂和高嶺土，作為黏土和沙土的代表。以鋼珠模擬現地土壤石子，以製造地工止水膜和現地土壤間的不平整的接觸面依照實驗室的試體的情形建立網格。網格建構時建立了一層虛擬的網格層以模擬地工止水膜和現地土壤間的空間。以試誤的方式改變該虛擬層的平面方向的水利傳導係數kxx和kyy讓FEMWATER所模擬出來的流量的結果能和我們試驗時的流量的結果能夠相符合，藉之求出其輸水率。 研究的結果顯示藉由FEMWATER模擬出的輸水率可以合理的評估滲流的流量。鋼珠的數目對滲流的影響極大。當鋼珠的數增多的時候滲流量也增大,此乃當鋼珠的數目越多的時候地工止水膜和現地土壤間的輸水率也就越大。

To better understand the leakage behavior through the defects of geomembranes , the transmissivity plays an important role. However estimating the transmissivity is a difficult ask by performing either issued traditional experiment or mathematical analysis . In this research, a computer program based on finite element method, FEMWATER , is used to compute the transmissivity. FEMWATER is a 3D finite element, saturated/unsaturated, density driven, flow and transport model. FEMWATER is originally written by G.T. Yeh at Penn State University (Yeh, et al, 1992). The version of FEMWATER that is supported by GMS a special version that has been modified by G.T. Yenh and the U.S. Army Engineer Waterways Experiment Station. Two types of materials were used to perform the experiments, Tochen sand and Kaolinite, to represent sand and clay, respectively. Steel balls were used to simulate the gravel in the subgrade soil to produce discontinuity between the geomembrane and the soils. Meshes for FEMWATRER were built according to the experimental specimens. A virtual layer is assumed to simulate the space between the geomembrane and the soils. The conductivity of kxx and kyy of the virtual layer was adjusted by "trial and error" to let the discharge computed by FEMWATER meet the discharge of lab test. The results show that the discharge of leakage through defects of the geomembrane can be reasonably estimated by using the transmssivity computed by FEMWATER. The number of steel balls played an important role in affecting the leakage discharge. When the the number of steel balls increased, the leakage discharge also increased owing to the rise of transmissivity.