報告書番号

N04028

タイトル（和文）

地下施設力学的相互作用解析のための軟岩クリープモデルの開発

タイトル（英文）

A proposal of constitutive creep model for soft rock to be applied to numerical analysis for mechanical interaction in the underground facilities

概要 （図表や脚注は「報告書全文」に掲載しております）

顕著な時間依存性挙動を持つ堆積軟岩地山中に放射性廃棄物地層処分の地下施設が建設される場合を想定し，電力施設の標準的な地盤掘削解析の力学モデルを基本として，堆積軟岩のクリープ挙動モデルの高度化を行った． 残留強度を長期的な破壊が発生する最小の応力レベルと仮定し，残留強度以上の応力レベルでは最終的にはクリープ破壊が生じ，残留強度以下では変形が収束するとして，それに対応した力学模型を設定するとともに、クリープ時の体積膨張・収縮特性を考慮しえるように改良した．その結果，軟岩のクリープ特性をより精度良く表現できるようになった． 本モデルを水・応力連成の有限要素法解析に取り込み，処分孔の掘削時挙動および長期挙動の解析を実施した．その結果，再冠水時の処分孔の長期挙動は岩盤のクリープだけでなく，再冠水による間隙水圧の変化の影響を受けることが示唆された．

概要 （英文）

In the case that the underground facilities of high-level nuclear waste disposal are constructed in soft rock mass, it is predicted that time-dependent behavior of rock has an important role both on the stability of surrounding rock mass after excavation and on the super long-term stability of barrier system. Existing creep model that has been applied to excavation problems in electric power industry is not sufficient in order to evaluate long-term behavior of the facility constructed in soft rock mass. Therefore, it is necessary to develop an appropriate creep model for soft rock. In this research, we try to develop a prototype of numerical tool for evaluating the stability during and after the excavation and super long-term stability after backfilling. Firstly, a simple rheological model for time-dependent behavior of soft rock is proposed. It is the key feature of this model that two different types of rheological model can be selected in order to describe both failure and non-failure processes. Rock continues to deform until failure in the case where stress applied to the rock exceeds its residual strength, although deformation of the rock finally ceases in the other cases. The applicability of this model is investigated by comparing the calculated results with those in laboratory test results. The proposed model can describe the time-dependent and dilatancy behavior of mudstone of Tertiary period observed in the drained triaxial creep test. Next, we apply the proposed model to the problem of time-dependent behavior of rock mass around a deposition hole. Numerical simulation for excavation problem and long-term mechanical interaction between buffer material and surrounding rock mass is carried out using a hydrological - mechanical coupled FEM code that includes the proposed model. Several mechanical models can be selected in order to apply to the mechanical behavior of materials consisting of underground facility. The main results obtained from this simulation are as follows; 1) Deformation of the hole ceases within a year because the stress state of few layers in surrounding rock mass is over the residual strength. 2) Deformation of the hole after backfilling is strongly dependent on behavior of pore water pressure.

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