- 學位論文
Horizontal Permeability of Clay Mixture at Large Shear Deformations
Horizontal Permeability of Clay Mixture at Large Shear Deformations
摘要
日本東北大地震造成福島第一核電廠受到極大的損害，並產生了許多帶有核輻射污染的廢棄物。為了解決此問題，日本政府決定興建離岸廢棄物處理場，有別於一般的處理廠，含輻射之廢棄物具有更高的危險性，需要經過試驗以制定更嚴格的建設條件。在廢棄物封存的部分，為了防止放射性物質在衰變至安全範圍內(半衰期)就滲透到環境之中，封存所使用的材料是非常重要的，經過簡易的計算，封存材料的透水係數必須小於 ，而前人研究顯示，黏土加上皂土的黏土複合材料可以滿足此建設計畫所需的目標。但是依然有一些問題值得我們去關注，如果發生自然災害(如海嘯、地震等等…)，封存材料有可能會因為受到極大的剪應變而使得透水係數產生變化。 本研究為了瞭解黏土複合材料在受到大剪應變的情況下透水係數的變化，發展了一套對土壤用的新試驗方法，名為中空扭剪透水試驗(Hollow Cylinder Torsional Permeability Test)，相對於三軸試驗，此試驗方法藉由施加扭剪的方式來模擬土壤承受地震力時的應力狀態，本研究也提出了一種新方法來測量土壤橫向的透水係數。本研究主要結論為：(1) 藉由加入皂土可以降低黏土的透水係數；(2) 一個測量土壤橫向透水係數的試驗被提出，橫向的透水係數約為縱向的1.5到2倍；(3) 經過剪應變的施加，試體的橫向透水係數並無增長的趨勢，顯示剪應變對此封存材料的透水係數變化影響並不明顯。
並列摘要
After Tohoku Earthquake, huge amount of disaster waste including radioactive substances were released to the environment due to the accident of Fukushima No.1 nuclear power plant. To deal with these radioactive substances, Japanese government hope to build an offshore waste disposal facility for storing the waste materials. Different from normal disposal facility, this disposed waste is radioactive, therefore, more regulations were formulated by some researchers. In the part of sealing material, the radioactive substances may penetrated to outside and polluted the environmental. Avoiding this condition and confirm that the substances would become safe (half-life) is very important. By easy calculation, the coefficient of permeability of sealing material is 5×〖10〗^(-10) m/s. And find that a clay mixture, clay with bentonite, can achieve the target value. However, if some nature disaster happen, such as tsunami of earthquake, huge shearing deformation would force on the material and the permeability may change. Therefore, knowing the changing play an important role on this research. In order to test the changing of coefficient of permeability, this research developed a new testing method called Hollow Cylinder Torsional Permeability Test (HCTPT). This test can give some torsion to generate shear strain and test the permeability. In this way, the more real condition can be simulated. HCTPT also begin a new method of testing horizontal coefficient of permeability. In mixing the bentonite into clay can decrease the coefficient of permeability. Also, a new testing method to measure the horizontal coefficient of permeability by hollow cylinder torsional shear test is developed. The measured horizontal coefficients of permeability kh were in the range of 1.5~2.0 times that of vertical coefficient of permeability, as the measured value of kh did not increase by being sheared horizontally. It was found that there is no considerable increase of permeability due to the change of shear deformation.