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Distinct element approach for the analysis of coupled thermal-mechanical processes in the near field of the HLW repository

個別要素法を用いた高レベル放射性廃棄物処分場周辺岩盤における熱-力学連成挙動解析

小山 倫史*; 清水 浩之*; 千々松 正和*; 中間 茂雄; 藤田 朝雄

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Nakama, Shigeo; Fujita, Tomoo

本研究では、2次元粒状体個別要素法(2-D DEM)において、新たに熱の移動及び熱-力学連成項の定式化及び解析コードへの導入を行った。新たに開発した解析コードを用いてスウェーデンのエスポ地下研究所で結晶質岩を対象とした原位置試験(Pillar stability test)の数値シミュレーション(熱-力学連成解析)を実施した。シミュレーションの結果は原位置における計測結果及び別途実施した2次元及び3次元の有限要素法(2-D, 3-D FEM)による解析結果との比較を行い、新たに開発した個別要素法による解析コードの妥当性を検討した。試験中の主応力・温度などの変化は原位置試験における観測結果及び2-D, 3-D FEMによる解析結果と定性的に良好な一致がみられた。また、原位置試験では試験孔壁面での岩盤の破砕及びV字型に破壊・欠落する現象が観察されており、2-D DEMでは初期に存在するマイクロクラックの存在割合に関するパラメータ・スタディを実施することで、その再現を試みた。

In this paper, the coupled thermal-mechanical processes in the $"A$sp$"o$ pillar stability experiments (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using 2 dimensional Distinct Element Method (2-D DEM) with particles. The main objective for large scale in-situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing in one of the borehole and heating processes. For the simulations, the heat flow algorism was newly introduced into original DEM code to consider heating processes in the APSE. For the DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface. The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculated stress distribution, displacements and temperature distribution were compared with the ones obtained from in-situ measurements and 2-D, 3-D FEM simulations. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The parametric study for initial microcracks was performed to reproduce the spalling phenomena observed in the APSE.

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