Formation of Bedding Fractures in the Cenozoic Formation around Osaka

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  • 大阪近傍の新生代層に見られる層状破砕の生成
  • オオサカ キンボウ ノ シンセイダイソウ ニ ミラレル ソウジョウ ハサイ ノ

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Framework of the present geological structure around Osaka was formed by the Quaternary tectonic movement, called“Rokko Movement”, becoming prominent since about 0.5×106 years ago. The movement is known to have affected even the Cenozoic sediments.<BR>Many large construction works have been done in the uplift district around Osaka on the national growth in recent couple of the decade. Many investigations have been done on new outcrops exposed by construction works. But there are few applied geological studies about various phenomena concerning with faults in sedimentary blankets. The author has offen observed imbricated sheared zone-which is ref ered to as“bedding fractures ”-locating in marine clay beds in parallel with bedding plane. The bedding fractures in hilly lands as well as in basin are recorded.<BR>The Osaka Group, which widely distributes in the Osaka Basin and surrounding hilly lands, is characterized by the alternations of marine clay and non-marine sand and gravel bed. The bedding fractures, therefore, were supposed to have been formed in marine clay bed owing to its brittle properties, near faults and flexure in the Osaka Group. The fractures are observed always with a fault or a flexure, but converses are not generally true. Many slope failures, which had filed with cutting hill side, almost happened along bedding fractures. This paper also presents the studies on the behaviours of the fractures associated with several construction works and on the mechanical properties of the fractured material.

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