序列滲流對地工皂土毯工程性質之影響

Abstract

地工皂土毯(Geosynthetic Clay Liners, GCL)為一種新近發展出之地工合成材，其主要用途為阻水(Hydraulic Barrier)。利用其中之皂土(Bentonite)夾層的低水力傳導度特性，減少液體滲流通過之量。地工皂土毯在歐美地區目前漸被推廣使用於廢棄物掩埋場中，以取代原經常使用的夯實黏土阻水層(Compacted Clay Liner, CCL)。主要因為此材料有兩項最大優點，一是其為工廠一貫作業生產，品質管制良好，工程性質一致；二是施工時鋪設容易，施工品質管制極佳，完工後之阻水系統效果較夯實黏土阻水層為優。地工皂土毯的工程性質在近年來已有一些研究成果，但是多以水或單一液體為皂土之水化液體；對於以一種以上不同性質液體序列滲流後對其工程性質的影響尚付諸闕如。序列滲流可能發生在濱海掩埋場，地工皂土毯先經海水反滲，再經滲出水滲流；或用於油槽防滲系統中時，經酸雨淋洗，再受有機液體滲流；以及受石灰質覆土中淋洗出鈣離子溶液滲流，再受滲出水或有機液體滲流等狀況。本計畫針對地工皂土毯在現地應用時，可能受到不同性質液體先後滲流的工程性質做一深入研究。

Geosynthetic clay liners (GCLs) are a group of recently developed geosynthetic materials. The majority of GCLs has been used as hydraulic barriers. GCLs rely on the low hydraulic conductivity of their bentonite component to retard liquid flow. GCLs have been used in landfills in the United States and European countries. In many cases, they are used as substitutes of compacted clay liners (CCLs). GCL has two major advantages over compacted clay liner which are the consistency in quality and the ease of installation. There have been increasing amount of information of GCLs including their engineering properties, the field behavior, and performance. However, most of the laboratory studies are done with using a single liquid whether it is water, chemical solution, leachate, or pure organic liquid. There appears to be a vacuum of information on behavior of GCLs subject to sequential leaching by more than one type of liquid. Sequential leaching of GCL by liquids can take place in many conditions such as when GCL is used in landfills by the seaside where GCL may be hydrated or permeated by sea water then permeated by leachate. Another example is that GCL is leached by acid rain after the installation before it is permeated by leachate or chemicals. Furthermore, calcium ions leached from calcium rich cover soil may permeate through GCLs before leachate does. The latter two scenarios may also take place when GCL is used as the hydraulic barrier in secondary containment systems. The purpose of the proposed study is to understand the effect of sequential permeation on the important engineering properties of GCLs.