地下水與環境對緩衝材料之沖蝕沉積行為與質量損失研究

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Title:	地下水與環境對緩衝材料之沖蝕沉積行為與質量損失研究
Authors:	王柏中;Wang, Po-Chung
Contributors:	土木工程學系
Keywords:	深層地質處置場;緩衝材料;沖蝕;沉降;Deep geological disposal;buffer;MX-80;erosion;sedimentation
Date:	2022-08-22
Issue Date:	2022-10-04 10:47:40 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究以MX-80膨潤土作為緩衝材料進行一系列模擬地下水流經母岩裂隙之相關研究，透過過去團隊完成之沖蝕實驗裝置，以兩塊透明壓克力板模擬裂隙，進行沖蝕與沉降實驗，其研究之環境因子包括以不同流量、裂隙內寬、裂隙傾斜角度與水化學進行質量損失比較。沖蝕實驗以幫浦抽送水溶液使之接觸到膨潤土的懸浮液被抽出，再透過濁度計與相機來量測每日沖蝕量與紀錄擴張歷程。沉降實驗以角鋼製作來設計一可控傾角之平台，將模擬裂隙之壓克力板放置於平台上，透過相機攝影記錄每日膨潤土於裂隙中不同水化學溶液與不同傾斜角度之沉降行為。研究結果發現，低流量環境下的沖蝕實驗，其質量損失仍會受水化學影響。在鹼性水化學環境下，膨潤土受到陽離子強度影響擴散雙層的發展，產生的絮凝或分散結構將影響沖蝕所造成的質量損失。比較不同傾角與不同水化學的沉降實驗裡，陽離子強度4 mM與8 mM環境下，因實驗進行的前5天膨潤土試體剛接觸到水溶液，為非飽和至飽和的階段，試體外側較易剝落而產生沉降行為，當陽離子強度發展為絮凝結構時(約第6天)則無明顯之沉降行為發生，去離子水環境則易受到重力影響，在傾角30度環境下仍有發生沉降行為。傾角60度沖蝕實驗裡，重力與水流剪切應力交互作用會對膨潤土質量損失有其影響，在去離子水環境下，其質量損失在30天已達總試體質量的69%，為本研究中最嚴重之質量損失環境。由此判斷在影響膨潤土質量損失的因子裡，水化學的影響最為顯著，發展顆粒間分散或絮凝的結構將影響膨潤土是否易被帶離原試體，而流量與傾角造成的水流剪切應力與重力則會使膨潤土顆粒移送使試體造成質量損失的動作。 ;This research using MX-80 bentonite as buffer to conduct a series of related researches on simulating groundwater flowing through the fracture aperture. Through the erosion test device completed by the team in the past, two transparent acrylic plates were used erosion and sedimentation test in fracture aperture. The environmental factors studied include mass loss comparisons with different flow rates, fracture aperture, crack inclination angles and water chemistry. In the erosion test, the water solution was pumped by the pump to make it contact with the suspension of bentonite, and then the turbidimeter and camera were used to measure the daily erode mass loss and record the expansion process. The sedimentation test is made of steel to design a platform with a controllable inclination angle. The acrylic plate to simulate the fracture aperture is placed on the platform, and the daily sedimentation of bentonite in the crack with different water chemical solutions and different fracture aperture angles is recorded by camera photography. The results of the test show that the mass loss of the erosion test in the low flow rate is still affected by the water chemistry. In an alkaline hydrochemical environment, bentonite is affected by the strength of cations to develop the diffuse double layer, and the resulting flocculated or dispersed structure will affect the mass loss caused by erosion. In the sedimentation test comparing different inclination angles and different water chemistries, under the environment of cation strength of 4 mM and 8 mM, because the bentonite sample just came into contact with water in the first 5 days of the test, it was in the stage of unsaturated to saturation, and the outside of the sample was easier to deposition behavior occurs due to exfoliation. When the cation strength develops into a flocculation structure (about the 6th day), there is no obvious deposition behavior.The deionized water environment is easily affected by gravity, and sedimentation still occurs in the environment with an inclination angle of 30 degrees. In the erosion test with angle of 60 degrees, the interaction of gravity and water flow shear stress has an effect on the mass loss of bentonite. In the deionized water environment, its mass loss has reached 69% of the total sample mass in 30 days, which is the most serious mass loss environment in the test. Therefore, it can be judged that among the factors affecting the quality loss of bentonite, the influence of water chemistry is the most significant. Therefore, it can be judged that among the factors affecting the mass loss of bentonite, the influence of water chemistry is the most significant. The structure of flocculated or dispersed will affect whether the bentonite is easily taken away from the original sample. The shear stress and gravity by the flow rate and the inclination angle will cause the movement of the bentonite particles to cause the mass loss of the sample.
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