鹿沼土の圧縮特性と構造変化

Kanumatsuchi (Kanuma pumice stratum) consists of pyroclastics originated from Akagi volcano (Gunma prefecture). This stratum composes the Takaragi loam stratum which exists in the Northern Kanto loam stratum. Its distribution region is Tochigi and Ibaraki prefectures, and its distribution area is about 9, 900km².<BR>Kanumatsuchi is mainly composed of weathered pumice grain of which the diameter is about 2-20mm.Other components are Imogolite, small pumice and small volcanic gravel. Kanumatsuchi has high water content and large void ratio. Therefore, its strength is very low and its compressibility is high. Moreover, the membrane penetration on triaxial compression test is conspicuous and its penetration volume is considerably large.<BR>In this paper, we investigated the compressibility of Kanumatsuchi, and analyzed the compressive mechanism based on the results by considering the membrane penetration. Compression test was conducted by consolidation test and triaxial compression test.<BR>As the results of this study, the following facts were obtained:<BR>1) Compression volume of Kanumatsuchi is very little within the region of low pressure, but when pressure is over the preconsolidation stress (2×98kN/m²), the volume becomes very large due to the crush of weathered pumices.<BR>2) Compression volume and degree of weathered pumice's crush are not considerably affected by the difference of loading system, but the compression velocity is much affected. That is to say, in the case of consolidation test, compression volume just after the loading is very high, but in the case of triaxial compression test, compression volume begins to increase ten minutes after the loading.<BR>3) Compression ratio of Imogolite and large pore are larger than that of weathered pumice, but constituent ratio of weathered pumice to the total compression volume is larger than that of other components, because the volume of weathered pumice is about 80% of the total volume of Kanumatsuchi.