報告書番号

380034

タイトル（和文）

節理の発達した花崗岩における大規模空洞掘削時の岩盤挙動の検討─異方性，ＰＳ工法，掘削順序の影響の解析的検討─

タイトル（英文）

STUDY ON THE BEHAVIOUR OF JOINTY GRANITIC ROCK MASS AROUND A LARGE CAVERN DURING EXCAVATION

概要 （図表や脚注は「報告書全文」に掲載しております）

奥矢作第２発電所は地下式であり，その空洞の規模は高さ５０ｍ，幅２３ｍ，長さ１０３ｍである。周辺岩盤は花こう岩で節理が発達しており異方性を有する。空洞掘削時にこれら異方性岩盤がどのような挙動を示すかを事前の空洞掘削解析で明らかにし，施工時の安全に資することにした。掘削解析結果によりつぎのことが明らかとなった。つまり，（１）２つの節理系が存在しているが，空洞建屋軸にほぼ平行している節理の影響が大きい。（２）ゆるみ領域は７～１７ｍとなる。（３）ＰＳ工の施工によりゆるみ領域は１～２ｍ程度減少する。上記の結果は空洞の補強設計の基本資料となるものであり，かつ掘削時の施工管理資料として有用である。

概要 （英文）

NUMERICAL EXCAVATION ANALYSIS HAS BEEN CARRIED OUT FOR MECHANICAL BEHAVIOUR OF JOINTY GRANITIC ROCK MASS AROUND A LARGE CAVERN. MECHANICAL PROPERTIES OF THE ROCK MASS WERE MEASURED BY INSITU TESTS SUCH AS JACK TEST, ROCK SHEARING TEST AND OVER-CORING STRESS RELIEF METHOD ETC. THESE DATA WERE USED IN THE ANALYSIS. THE FOLLOWING RESULTS WERE OBTAINED. (1) EFFECTS OF JOINT SYSTEMS: THERE WERE FOUR DOMINANT JOINT SYSTEMS IN THE GRANITIC ROCK MASS. THE STRIKE OF ONE OF THEM HAD THE DIRECTION IN NEARLY PARALLEL TO THE LONG AXIS OF THE CAVITY, WHICH CAUSED REMARKABLE DISPLACEMENTS OF SIDE WALLS AND RATHER LARGESIZE OF RELAXED ZONES. (2) EFFECTS OF EXCAVATION SEQUENCE: THE EXCAVATION SEQUENCE OF CAVERNS INCLUDING TUNNELS FOR DRAFT TUBES AND PENSTOCKSAFFECTED THE SIZE OF RELAXED ZONES AND DISPLACEMENTS OF ROCK MASS AROUND THE CAVERN. IT WAS RECOMMENDED THAT THE EXCAVATION OF MAIN CAVARN SHOULD FOLLOW THE EXCAVATION OF THE TUNNELS. (3) EFFECTS OF PRE-STRESSINGREINFORCEMENTS: OWING TO THE PRE-STRESSING REINFORCEMENTS FOR THE SIDEWALLS OF THE MAIN CAVERN, THE SIZE OF THE RELAXED ZONES DECREASED BY 1- 2 M AND DISPLACEMENTS BY 4 - 5 MM. THE ABOVE MENSIONED RESULTS ARE VERY USUFUL IN THE EXCAVATION WORKS AS FOR DESIGNING OF REINFORCEMENT OFRELAXED ZONES AND SAFETY MONITORING.

報告者

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