ベントナイト混合土(BMSL)の主材であるベントナイトの特性を明らかにすることは，三要素複合ライナーを構成するベントナイト混合土(BMSL)を難透水性にするため必要不可欠である。しかしながら，ベントナイトの品質と性能を示す世界的な規格は，石油ボーリング用途に用いるＡＰＩ規格だけである。市販ベントナイトの品質に関しては，掘削泥水に向けた希薄な懸濁液のレオロジー特性が中心であり，土の工学的性質に関する情報が十分に提供されていないのが現状である。

　ベントナイトの品質の良否は原砿石の特性に大きく影響され，用途により規格は異なるにもかかわらず200，250，300 メッシュなどのメッシュ番号（篩）でベントナイト混合土(BMSL)の製品規定として仕様書に記載されている。同一メッシュでも産地により品質に差があるため，市販ベントナイトの品質と性能を明らかにすることが急務である。

　本章では，商業的に市販される日本国内産及び米国産のNa型ベントナイト及びCa型ベントナイト18点と，第３章で使用したGM/GCLから機械的に分離採取したベントナイト2点を用いて，膨潤力と液性限界特性を評価した。

ベントナイトの液性限界と膨潤力

 ベントナイトの膨潤能と水封止力

 液性限界と膨潤力試験の課題

 まとめ

 参考文献

各種ベントナイトのコンシステンシー特性およびその他の基礎的特性に関する研究
水野克己・近藤三二・嘉門雅史

A Study On a Peculiarity of the Consistency of Various Bentonite Clays, and Interrelationships between the Consistency and Other Primary Characteristcs of Bentonite
Katsumi MIZUNO, Mitsuji KONDO and Masashi KAMON

Abstract

A peculiarity of the consistency of bentonite clay was profiled on the basis of the consistency limits and the parameters derived from the limit data, and the interrelationships between the consistency and other primary characteristics of bentonite were investigated and described for eighteen market samples of Ca- and Na- based bentonite, and two samples of bentonite from high-density polyethylene geomembrane-supported geosynthetic clay liners. The resulting regression equation between the water content (w, %) at the consistency limit and the specific volume (f, %) was f = 2.55w + 100, where f is percent volume ratio per volume of the soil particles, and a factor of proportionality, 2.55, is the statistical specific gravity of the soil particles. Therefore, the regression equation consists well with the theoretical equation. Another regression equation between the plasticity index (Ip) and the liquid limit (wL, %) was lp = wL - 58. The authors believe the constant, 58, to be the statistical plastic limit, because the regression equation is of same type for the definition of the plasticity index, Ip = WL - wp, where wp is the plastic limit. The magnitude of the liquid limit and the plasticity index is basically dependent upon the content of the colloidal particle size fraction (that is finer than I pm). Thereby, the extent of the liquid limit increases with the colloid fraction content. The profile can be divided into classes determined by the polymorphism of the free silica impurity (quartz and a-cristobalite) contained in bentonite. This cristobalite contributes significantly to the amount of the colloid fraction, and it is soluble in a heated sodium hydroxide solution and a measured quantity of the cristobalite may be characterized as an intercept of the soluble silica at the zero alkali-processing time on the bentonite. Bentonite containing the cristobalite has a tendency to form a soil structure that has relatively low shrinkage ratio and relatively high specific volume, resulting in a direct effect on the shrinkage limit measurements. A direct interrelationship between the liquid limit and the cation exchange capacity (CEC) was not apparent, however, significantly higher results for liquid limits were found at sodium cation / CEC equivalent ratios greater than 50%. The regression equation, Sp=0.04wL + 2.6, was obtained from the relationship between the swelling power (Sp, cm3/2g) and the liquid limit. The equation or the regression line is useful as a nomograph for rapid solution on the liquid limit from the swelling power that the testing is readily. An interrelationship between the swelling power and the liquid limit was described by introducing two dimensionless parameters, specific swell volume-change (fsp/fo, %) and specific volume-change at the liquid limit (fL/fo, %) that are volume ratios per volume at the shrinkage limit. The resulting regression equation, fsp/fo = 2.28(fL/fo - 13), was obtained. The equation describes that quantity of water contained in the swelling power of bentonite is 2.28 times as large as that of the liquid limit, and also, the constant in the parenthesis, 13%, is an additional dead space between domains or aggregates of the clay particles in the swelling power test. This is may be applicable to only the interaction of water with high plastic clay such as bentonite.