報告書番号

U89021

タイトル（和文）

ＡＥによる岩盤ゆるみ域計測手法の開発（２）－花崗岩質岩盤の微小破壊時のＡＥ計測－

タイトル（英文）

DEVELOPMENT OF AE METHOD FOR MONITORING ROCKFAILURE AROUND AN UNDERGROUND OPENING(2)-IN-SITU AE MONITORING ON THERMAL CRACKING IN GRANITIC ROCK MASS-

概要 （図表や脚注は「報告書全文」に掲載しております）

空洞周辺岩盤や斜面の安定性の監視には，ＡＥ（ＡｃｏｕｓｔｉｃＥｍｉｓｓｉｏｎ）測定が有効と思われる。そこで当所では，原位置で高精度のＡＥ測定を効率よく行える，岩盤破壊音探査波形記録装置を開発した。その適用性を検討するため，稲田花崗岩の採石場の跡地に直径１００ｍｍの鉛直ボーリング孔を掘削し，深度３．３～５．３ｍの間をヒータで８００℃まで加熱し，加熱に伴って発生するＡＥを周辺ボーリング孔で６０時間にわたって測定した。震源を決定できた６３６個のＡＥの震源分布とボーリングコアの観察結果から，ＡＥの発生は花崗岩に貫入したペグマタイト部分と既存の割れ目のある部分に集中する傾向のあることが明らかとなった。今回の実験で，当所で開発したＡＥ測定手法が原位置岩盤の微小な破壊の探査に有効であることが確認されたため，今後はこの手法を電力各社が建設を始めている地下発電所空洞のゆるみ域評価に適用していく予定である

概要 （英文）

AE(ACOUSTIC EMISSION) MONITORING IS A GOOD METHOD TO DETECT ROCK FRACTURE AROUND AN UNDERGROUND CHAMBER AND IN A SLOPE. THE AUTHORS MADE NEW EQUIPMENT TO MONITOR AE ACTIVITY IN-SITU ACCURATELY AND EFFICIENTLY. IN ORDER TO EXAMINE ITS APPLICABILITY,THEY CARRIED OUT A SMALLSCALE IN-SITU EXPERIMENT IN AN OLD QUARRY OF INADA GRANITE. AN ELECTRIC HEATER WAS INSERTED INTO THE 100MM DIA BORED HOLE,AND THE TEMPERATURE ON THE HEATER WAS INCREASED TO 800DEGREE. AE WAS MONITORED FOR 60 HOURS WITH THE 12 SENSORS BURIED IN 4 HOLES BORED 1M DISTANT FROM THE HEATER,AND 636 AE HYPOCENTERS WERE LOCATED. THE DISTRIBUTIONS OF AE HYPOCENTERS AND THE OBSERVATION OF BORING CORES ELUCIDATED THAT AE HYPOCENTERS CLUSTERED IN PEGMATITE INTRUDED INTO GRANITE AND PRE-EXISTING JOINTS. IT WAS ALSO MADE CLEAR THAT THE TEMPERATURE IN WHICH AE STARTED TO OCCUR WAS ABOUT 60DEGREE IN GRANITE,WHICH IS THE SAME TEMPERATURE THE OTHER RESEARCHERS REPORTED ON THEIR LABORATORY EXPERIMENTS,HOWEVER,WAS LOWER THAN 60DEGREE IN PEGMATITE. BECAUSE THIS EXPERIMENT DEMONSTRATED THAT MICROCRACK OCCURRENCE CAN BE DETECTED WITH THE NEW AE MONITORING EQUIPMENT,THE AUTHORS WILL MONITOR AE ACTIVITY USING IT IN ROCK AROUND UNDERGROUND CHAMBERS FOR ELECTRIC POWER STATIONS AND CONTRIBUTE TO THEIR SAFE CONSTRUCTION.

報告者

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