ベントナイトの変形挙動に及ぼす温度の影響

Effect of temperature on bentonite deformation

高山 裕介  ; 佐藤 大介*; 杉田 裕 

Takayama, Yusuke; Sato, Daisuke*; Sugita, Yutaka

高レベル放射性廃棄物の地層処分施設閉鎖後初期には、緩衝材中の温度が高くなることが想定されるため、緩衝材に用いられるベントナイトの基本特性の温度依存性に関する試験が実施されてきた。しかし、温度が膨潤圧や透水係数に及ぼす影響と比較すると、変形挙動に及ぼす影響に関する知見は少ない。そこで本論文では、温度制御可能な圧密試験機を用い、室温から80Cまでの温度一定条件で載荷・除荷・再載荷を行う試験、載荷圧一定条件で室温から80Cまでの範囲で温度変化を与える試験の2種類の試験を実施した。高温状態でより大きな圧縮変形が生じることや、温度変化に伴う変形は過去の応力履歴の影響を受け、正規圧密状態の場合には非可逆的な変形が生じることが明らかとなった。

During the initial phases after closure of a high-level radioactive waste repository, the temperature of the buffer material will increase. Therefore, fundamental properties regarding the temperature dependence of bentonite, which is the main material of the buffer material, have been tested. The number of tests for the temperature dependence of displacement behavior is less than the number of tests for the temperature dependence of swelling pressure and permeability. In this paper, two tests were conducted using a consolidation test device that can control temperature conditions. One is a cyclic loading and unloading test under temperature conditions from room temperature to 80 C. The second is a temperature rise and fall test from room temperature to 80 C under stable loading condition. It was clarified that large deformations occur in the specimen under high temperature conditions, that the deformation associated with temperature changes is affected by the past stress path, and that irreversible deformation occurs under normal consolidation conditions.