損傷理論を導入した多孔質岩盤における熱・水・応力・化学連成解析

Abstract

高レベル放射性廃棄物地層処分システムの安全性を担保する上で, 熱・水・応力・化学連成作用による廃棄体周辺岩盤の水理学特性変化の把握は必須である. 特に, 廃棄体処分坑道掘削時に形成されるき裂で生じる地化学反応は岩盤の長期透水性変化を予測する上で考慮すべき事象である. そこで, 本研究では損傷理論を用いたき裂発生・進展と, き裂領域内での鉱物溶解・沈殿プロセスを導入した熱・水・応力・化学連成解析モデルを構築し, 放射性廃棄物地層処分施設近傍の岩盤の透水性変化の長期予測解析を実施した. その結果, 坑道掘削に伴うき裂発生・進展により増加した坑道周辺の透水性が, き裂内部で生じる地化学現象(圧力溶解)により時間の経過とともに低下する傾向が得られた.

It is essential to examine the evolution in hydraulic properties of rocks near high level radioactive geological disposal facility for evaluating the performance of the disposal system under thermal-hydraulic-mechanical-chemical coupled conditions. Especially, geochemical reactions such as pressure solution within fractures should be understood for predicting long-term permeability change of the rock masses. In this study, we have developed a novel THMC coupled model that can consider the pressure solution occurring at contacting asperities within factures predicted by damage theory. Using the developed model, long-term prediction of rock permeability was conducted for fictitious porous rocks that are assumed to be purely composed of quartz. The predictions show that a number of fractures are generated near the disposal cavity and permeability increases in damaged zone during the excavation, and after excavation the permeability of the damaged zone decreases to that of intact zone due to pressure solution at contacting asperities within fractures.