焚化底渣與地工合成材界面摩擦性之探討

Abstract

國內廢棄物的處理方式主要為資源回收、焚化、掩埋。往年多以直接掩埋為大宗，但為考慮台灣地狹人稠的特殊環境，自民國82年大型焚化廠陸續完工運作，廢棄物逐漸轉以焚化處理為主。垃圾在經焚化處理後，會殘餘約總重量20-25 %的不可燃灰燼，目前對焚化灰燼最終處理方式仍以掩埋為主。而因台灣許多掩埋場位於山坡地，邊坡上之地工膜布未能鋪設覆土保護層及集排水層，所以灰渣多直接與地工合成材接觸。 國內外對於焚化灰渣的再利用雖然有部分學者專家的研究成果，但有關灰渣自身的工程性質卻較少有研究。再且，雖可從文獻中了解地工合成材與土壤或其他形式地工合成材間的界面摩擦特性，但卻甚少有對灰渣與地工合成材界面摩擦特性作探討。 本研究針對焚化底渣經由一系列物性試驗初步了解其工程性質，再進一步利用直接剪力試驗在潮溼與泡水不同的環境下探討國內各類地工合成材與底渣界面的摩擦特性。 底渣屬於透水性良好且壓縮性低之材料。其顆粒大小不一，外形多呈角狀，且粗糙的表面易附帶細小的顆粒。比重2.31較一般土壤為輕。由土壤統一分類進行分析，可知底渣為優良級配的材料，粒徑分佈主要介於4號篩與40號篩間，類屬砂質材料。底渣具高剪力強度，摩擦角高達52.5度。剪力強度會隨著含水量的增加而降低，而摩擦角卻無太大差異。 進行底渣與地工合成材之界面直接剪力試驗以分析含水量及地工合成材對其試驗結果所造成的影響。含水量的增減對於地工膜布與熱熔不織布較無太大的影響。針軋不織布浸水後則因布料較緊緻，變形量變小，剪應力隨水平位移提升趨平緩。地工織布浸水後布料孔隙緊縮，底渣顆粒不易嵌入布料中，造成互鎖作用減少，亦或織布布料易受水潤滑而使界面易滑動，以致於降低了剪切阻抗。 而隨著與不同材料的接觸，其界面剪切阻抗亦不相同。由摩擦角有效係數分析，粗糙地工膜布以79-82 %為最，熱熔不織布以61-71 %次之，平滑地工膜布則為51-58 %。而地工織布與針軋不織布則以26-52 %及30-33 %最差。雖粗糙地工膜布接觸效率良好，但現地設計中卻多仍使用平滑地工膜布為主，此與粗糙地工膜布在製作過程影響自身強度特性有關。

In Taiwan, Municipal solid wastes (MSW) were primarily disposed in landfills in the past. Due to the limitation of population density and availability of land, the incineration of MSW has become widely used since 1993. After incineration, 20-25 % by weight of incinerator ashes are produced. Even if some researchers have conducted investigations with the possibility of incinerator ashes as a potential material for construction applications, landfilling is still the primary method of disposal of these materials. On the other hand, geosynthetics have become essential components of the bottom lining system of MSW landfills because of their capabilities of drainage, barrier, reinforcement, separation and filtration, etc. As a result, the incinerator ashes/geosynthetics interface friction is an important parameter in the design of landfills. In this study, an experimental program was conducted to determine the engineering properties of incinerator bottom ashes and the interfacial shear strength between ashes and geosynthetics. Direct shear test was performed for the incinerator bottom ashes and five geosynthetics (woven and two types of nonwoven geotextiles, textured and smooth geomembranes) interfaces. Furthermore, the shear tests on the interface between bottom ashes and geosynthetics were conducted to investigate the difference of shear strength parameters under water-saturated and unsaturated conditions. The results show that the incinerator bottom ash of MSW has advantages such as high permeability and low compressibility. The shape of the bottom ash is generally irregular, angular and rough. In addition, the specific gravity of the bottom ash is 2.31. According to Unified Soil Classification System（USCS）, the bottom ash can be classified similar to well-graded sand（SW）.The internal friction angle of bottom ash was approximately 52.5□. The shear strength decreased as the water content increased. The interfacial shear strength decreased as the interface was conducted under water-saturated. This effect might be attributed to the loss of the suction and the decrease of effective stress at the ashes / geosynthetics interface, especially for woven geotextiles. The interfacial friction angle between the bottom ash and geosynthetics ranges from 26-82 % of the internal friction angle. Although the textured geomembranes have higher friction angle efficiency（E□）, the smooth geomembranes are still the main materials in the liner system design.