Strength Characteristics of the Fractured-Mudstone and the Softened-Mudstone from Landslides in the Shimajiri-Group Area, Okinawa. Comparison of the Urasoe and the Yamakawa landslides.

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Other Title
  • 沖縄,島尻層群地帯の地すべりにおける破砕泥岩と軟化泥岩の強度特性 浦添地すべりと山川地すべりの対比
  • オキナワ シマジリソウグン チタイ ノ ヂスベリ ニ オケル ハサイ デイガン ト ナンカ デイガン ノ キョウド トクセイ ウラソエ ヂスベリ ト ヤマカワ ヂスベリ ノ タイヒ
  • Comparison of the Urasoe and the Yamakawa landslides
  • 浦添地すべりと山川地すべりの対比

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Abstract

The fractured-mudstone slide and the softened-mudstone slide occurred in the Neogene Shimajiri-group area of Okinawa were compared with each other in their shear strength. The Urasoe landslide was referred to the fractured-mudstone slide and the Yamakawa landslide to the softened-mudstone slide. Mudstone samples taken from the slip surface of both the Urasoe and the Yamakawa landslides gave the low peak strength. The low peak strength was attributed to the presence of cracks for the Urasoe landslide, while it was ascribed to softening of the mudstone for the Yamakawa landslide. Residual strength of the mudstone samples was quite different between the Urasoe and the Yamakawa landslides, and the value of φr was found to be 11° for the former and 25.5° for the latter, when cr was assumed as zero.<br>Both the Urasoe and the Yamakawa landslide contained smectite, mica, chlorite, and kaolinite as layersilicate minerals in the clay fraction, but the quantity of smectite was noticeably higher for the Urasoe landslide than for the Yamakawa landslide. Such mineralogical difference was considered to be a cause of the difference in the residual strength between the two landslides. Namely, well reorientation of platy clay minerals occurred, leading to the drop of the φr, in the Urasoe landslide having the considerable smectite content. However, reorientation of clay minerals hardly occurred in the Yamakawa landslide even after the large displacement, leaving the φr as high as the φsf. The difference in the magnitude of the residual strength between the Urasoe and the Yamakawa landslides could be related to the difference in the sliding behavior between them.

Journal

  • Landslides

    Landslides 32 (4), 26-33, 1996

    The Japan Landslide Society

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