報告書番号

380011

タイトル（和文）

異方性を有する片岩における大規模空洞掘削時の岩盤挙動解析－本川発電所空洞の解析－

タイトル（英文）

ANALYSIS ON BEHAVIOUR OF ANISOTROPIC ROCK MASS AROUND A LARGE CAVERN FOR UNDERGROUND POWER STATION

概要 （図表や脚注は「報告書全文」に掲載しております）

本川揚水発電所は地下式であり，その地下空洞は高さ約４７ｍ，幅約２５ｍ，長さ約９８ｍである。周辺岩盤は片岩であり，片理面がほぼ水平に発達しており異方性を有する。空洞掘削時にこれら異方的な岩盤がどのような挙動を示すかを事前の掘削解析で明らかにし，施工時の安全性に資することにした。まず岩盤の異方的特徴を各種試験により明らかにした。つまり，三軸圧縮試験によりせん断強度は異方性により最大と最小の比率は２であること，変形性の比率は１．５であることを明らかにした。これらの結果を用いて掘削解析を実施し，空洞掘削時のゆるみ領域は約７ｍの深さであることを明らかにした。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）

THE SHIKOKU ELECTRIC POWER COMPANY HAS THE PLAN TO CONSTRUCT A LARGE CAVERN FOR THE HONKAWA POWER STATION. THE AUTHOR CARRIED OUT FORECASTING THE BEHAVIOUR OF ROCK MASSES AROUND THE CAVERN DURING EXCAVATION BY THE NUMERICAL ANALYSIS METHOD DEVELOPED BY THE AUTHOR. THE ROCK FOUNDATION WAS SCHIST AND SO THE ATTENSION SHOULD BE PAID FOR THE ANISOTROPIC FEATURE. TRI-AXIAL COMPRESSION TESTS OF THE SCHIST HAVE BEEN CARRIED OUT. FROM THE TEST RESULTS, THE FOLLOWINGS HAVE BEEN REVEALED. (1) THE VALUE OF DEFORMABILITY OF THE SCHIST DEPENDS ON THE ANGLE THETA BETWEEN SCHIST PLANE AND THE DIRECTION OF LOADING. THE LARGEST VALUE WAS OBSERVED WHEN LOAD WAS APPLIED IN PARALLEL WITH SCHISTPLANE (THETA=0 DEGREE). THE VALUE WAS 1.5 TIMES THAT OF MINIMUM VALUE. (2) FAILURE ENVELOPES VARY GREATLY ON ACCOUNT OF ANISOTROPY, I.E. THE STRENGTH DEPENDS ON THE ANGLE THETA. THE RATIO OF MAXIMUM VALUE OF SHEARING STRENGTH TO MINIMUM ONE WAS ABOUT 2.0. USING THE RESULTS OBTAINED ABOVE, THE AUTHOR CARRIED OUT NUMERICAL ANALYSIS OF ROCK MASS BEHAVIOUR AROUND THE CAVERN FOR HONKAWA UNDERGROUND POWER STATION. THE RESULTS ARE AS FOLLOWS. (1) BEING THE DIP OF SCHIST PLANE AT HONKAWA SITE VERY SMALL, ATTENSION SHOULD BE PAID WHEN THEARCH PART IS EXCAVATED SO AS TO AVOID LOCAL COLLAPSE OF CEILING ROCK. (2) THERE ARE MANY FAULTS AROUND THE CAVERN, WHICH DOES NOT AFFECT THE STABILITY OF THE CAVERN. THE ABOVEMENTIONED RESULTS ARE VERY USEFUL IN THE EXCAVATION WORKS AS FOR THE REINFORCEMENT OF THE RELAXED ZONES AND SAFETY MONITORING.

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