報告書番号

U91014

タイトル（和文）

東濃鉱山における花崗岩の断列系の特性調査と岩盤評価（２）－ボアホールテレビジョン装置による深部岩盤割れ目の分布特性－

タイトル（英文）

FRACTURE SYSTEM OF GRANITE AT THE TONO MINE(PART2) -EVALUATION OF CHARACTERISTICS OF FRACTURES DEEP UNDERGROUND BY BOREHOLE TELEVISION-

概要 （図表や脚注は「報告書全文」に掲載しております）

白亜紀の花崗岩に掘削したボーリング孔を用いて地表より震度５００ｍまでの割れ目分布特性をボアホールテレビジョンスキャナーによって調査し，以下のことを明らかとした。１）割れ目の卓越方向は位置によって異なり，この方向によって割れ目のグループ分けが可能である。２）緩傾斜の割れ目は主に花崗岩の生成時の割れ目と考えられ，傾斜の大きな割れ目は，後に構造運動によって生じた割れ目と考えられる。３）冷却時に生成したと考えられる割れ目は２００ｍ以深で急激に減少していた。４）間隙幅の０．５ｍｍ以下の割れ目は深度全体に分布し，開口割れ目全体の９０から９５％を占め，割れ目の密度，間隙率に大きな影響を与えていた。５）透水試験と割れ目の間隙との関係には正相関が認められる場合と，岩盤の変質や多数の連続性のない割れ目の分布するため相関が認められない場合があった。６）孔壁に付着した黒色沈殿物の分布から，地表付近

概要 （英文）

EVALUATION OF NATURAL BARRIERS IS VERY IMPORTANT FOR GEOLOGICAL DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE.CHARACTERIZATION OF ROCK FRACTURES IS ONE OF THE MOST IMPORTANT ISSUES IN THIS EVALUATION BECAUSE RADIONUCLIDES MAY MIGRATE BY FLOW OF GROUNDWATER ALONGFRACTURES. FRACTURE SYSTEMS IN CRETACEOUS GRANITES WERE INVESTIGATED IN TWO BOREHOLES FROM THE SURFACE TO A DEPTH OF 500 M BY A BOREHOLE TELEVISION SYSTEM (BTV) AND THE FOLLOWING RESULTS WERE OBTAINED. 1.TRACTUREORIENTATION VARIED WITH DEPTH AND FRACTURES WERE CLASSIFIED INTO FIVE GROUPS BASED ON ORIENTATION. 2.THE LOW-DIP FRACTURE GROUP WAS PROBABLY GENERATED PRIMARILY BY COOLING SHRINKAGE,AND STEEP-DIP FRACTURES WERE PROBALLY GENERATED BY TECTONIC MOVEMENTS AFTER COOLING. 3.THE FRACTURE DENSITY OF THE LOW-DIP FARCTURE GROUP DECREASED SIGNIFICANTLY AT DEPTHS BELOW 200 M. 4.FRACTURES WITH APERTURES SMALLER THAN 0.5-MM WIDE WERE COMMON IN THE OBSERVED INTERVAL AND CONYRISED 90% 95% OF ALL CUMULATIVE FRACTURE APERTURES. 5.PERMEABILITIES WERE CORRELATED POSITIVELY WITH FRACTURE APERTURES WITHIN THE TEST INTERVAL WITH SOME EXCEPTIONS WHERE THEY WERE LARGER THAN EXPECTED FROM FRACTURE APERTURES. THE LARGE PERMEABILITIES MAY BE DUE TO ALTERATION OF THE ROCK MATRIX,MICRO AND/OR DISCONTINUOUS FRACTURES,ETC. 6.BLACK MATERIAL,PRESUMABLY IRONHYDROXIDE,WAS PRECIPITATED ON MOST OF THE DRILL-HOLE WALLS BUT NOT ON THE WALLS JUST ABOVE MANY OF THE SHALLOW LOW-DIP FRACTURES. THIS INDICATES THAT THE CHEMISTRY OF THE GROUNDWATER IN SHALLOW LOW-DIP FRACTURES IS PROBABLY DIFFERENT FROM THAT OF THE WATER IN THE BOREHOLES.

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