Abstract
Leachate in landfill contains a great number of toxic and harmful substances and results in long-term contamination of the underground environment once it leaks. Therefore, constructing an impermeable layer at the bottom of sanitary landfills is the key to preventing the contamination induced by leachate leakage. Bentonite is an impervious liner material that is currently widely used in landfills. However, the performance of bentonite as an impervious material is likely to be greatly affected when leachate contains a high salt content. By modifying additives using bentonite, a salt-resistant bentonite can be acquired which satisfies the impermeability requirement imposed by a saline environment. Additionally, by carrying out various tests (including a free swell index test, compaction, hydraulic conductivity, heavy metal adsorption, and direct shear tests), the performance of developed bentonite and the mixture of weathered soil and modified bentonite were verified. The swelling capacity of salt-resistant bentonite in saline water was nearly equal to that in a fresh water environment. After salt-resistant bentonite was mixed with weathered soil in a proportion of 1 : 9, the hydraulic conductivity of the mixture in saline water was less than 1 × 10−7 cm × s−1, satisfying the basic requirement for use as a landfill liner material. Moreover, the relationship between the shear strength or the cracks in the liner soil and the initial moisture content of the mixed soil can be obtained by conducting direct shear and drying shrinkage tests on the mixture of weathered soil and modified bentonite. The results are expected to provide data support for the design of engineering construction works in a geo-environmental context.
Kurzfassung
Das Sickerwasser in Mülldeponien enthält eine große Anzahl von toxischen und gefährlichen Stoffen und führt zu einer Langzeitkonaminierung des Untergrundes, wenn es durchsickert. Daher ist die Konstruktion einer nichtdurchlässigen Schicht am Fuß von geordneten Mülldeponien ein Schlüssel, um die Kontamination durch Sickerwasser zu vermeiden. Bentonit ist ein abweisendes Auskleidungsmaterial, das momentan breitflächig für Abfalldeponien verwandt wird. Allerdings ist das Verhalten von Bentonit als abweisendes Material stark beeinflusst, wenn das Sickerwasser einen hohen Salzgehalt aufweist. Indem der Bentonit mittels Additiven modifiziert wird, kann ein salzresistenter Bentonit entwickelt werden, der die Erfordernisse bezüglich Undurchlässigkeit bei salinen Umgebungen erfüllt. Zusätzlich wurden für den vorliegenden Beitrag durch die Durchführung verschiedener Tests (einschließlich Tests des freien Schwellindexes, der Kompaktierung, der hydraulischen Leitfähigkeit, der Schwermetallabsorption und direkter Scherversuche) das Verhalten des entwickelten Bentonits und dem Gemisch aus Erdreich und modifiziertem Bentonit verifiziert. Die Schwellkapazität des salzresistenten Bentonits unter Salzwasserbedingungen war etwa gleich zu dem in einer Frischwasserumgebung. Nachdem der salzresistente Bentonit mit Erdreich im Verhältnis 1 : 9 gemischt wurde, war die hydraulische Leitfähigkeit des Gemisches unter Salzwasserbedingungen niedriger als 1 × 10−7 cm und erfüllte das Grunderfordernis für die Verwendung als Dichtmaterial für Abfalldeponien. Darüber hinaus konnte das Verhältnis zwischen der Scherfestigkeit oder Rissen in der Dichterde und dem anfänglichen Feuchtigkeitsgehalt der gemischten Erde durch direkte Scherversuche und Trockenschrumpfungsversuche mit dem Gemisch aus verwitterter Erde und dem modifizierten Bentonit ermittelt werden. Von den Ergebnissen ist zu erwarten, dass sie unterstützende Daten für die Auslegung von Ingenieurbauwerken im geo-umweltrelevanten Zusammenhang liefern.
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