Development of a Numerical Model for Elasto-Plastic and Coupled Hydro-Mechanical Behavior of Bentonite and Its Benchmark Simulation: DECOVALEX-2027 Sandwich Task

Jung-Wook Park; Chan-Hee Park

doi:10.7474/TUS.2025.35.5.602

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2025 Vol.35, Issue 5 Preview Page Next Page

Original Article

Development of a Numerical Model for Elasto-Plastic and Coupled Hydro-Mechanical Behavior of Bentonite and Its Benchmark Simulation: DECOVALEX-2027 Sandwich Task 벤토나이트의 탄소성 거동 및 수리-역학 연계거동 해석을 위한 수치모델 개발 및 벤치마크 모델링: DECOVALEX-2027 Sandwich Task

31 October 2025. pp. 602-629

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Abstract

The present study developed a numerical model to accurately simulate the coupled hydro–mechanical behavior of bentonite, a key material in the engineered barrier system (EBS) of high-level radioactive waste repositories. For this purpose, the constitutive equations of the Barcelona Basic Model (BBM), a representative elasto-plastic model for unsaturated soils, were implemented in FLAC3D as a user-defined model, and a coupled OGS–FLAC analysis framework was established by linking with OpenGeoSys. The developed module was first validated against the Modified Cam-Clay (MCC) model under saturated conditions, and subsequently verified through representative benchmark scenarios, including swelling–collapse behavior induced by suction decrease, path dependency under combined loading–suction variations, and the interaction of SI–LC yield surfaces. These comparisons confirmed the theoretical soundness and numerical reliability of the implementation. Furthermore, by incorporating suction and degree of saturation computed in OGS into the BBM stress analysis, a stepwise OGS–FLAC coupling approach was proposed to simulate hydro–mechanical interactions under unsaturated conditions. The framework was applied to the international DECOVALEX-2027 Sandwich Task Step 0a, in which swelling pressure tests on Calcigel bentonite at three initial dry densities were modeled. The simulations reproduced the observed evolution of swelling pressure, degree of saturation, axial strain, and water uptake with reasonable accuracy. The developed BBM-based OGS–FLAC module was demonstrated to reliably capture the path-dependent volumetric deformations and coupled hydro–mechanical mechanisms of bentonite. The proposed modeling approach and calibrated parameters are expected to provide a robust basis for future applications to larger-scale experiments, including MiniSandwich, HTV-7, and Mont Terri in situ tests, and for international comparative studies.

Keywords

Barcelona basic model

Bentonite

DECOVALEX-2027

Sandwich Task

OGS–FLAC

본 연구에서는 고준위 방사성폐기물 처분장의 공학적 방벽 핵심 재료인 벤토나이트의 수리–역학적 복합거동을 정밀하게 모사하기 위한 수치모델을 개발하였다. 이를 위해 불포화 점토의 대표적 탄소성 구성모델인 Barcelona Basic Model (BBM)을 FLAC3D 내 사용자 정의 모델로 구현하고, OpenGeoSys와 연동한 OGS–FLAC 해석기법을 구축하였다. 개발된 모듈은 포화 조건에서 Modified Cam-Clay (MCC) 모델과의 비교를 통해 기본 정합성을 확보하였으며, 흡입력 감소에 따른 팽창–붕괴 거동, 하중–흡입력 교차 경로에 따른 경로 의존성, SI–LC 항복면의 상호작용 등 대표적 벤치마크 시나리오를 재현하여 이론적 타당성과 수치적 신뢰성을 검증하였다. 또한, OGS에서 계산된 흡입력과 포화도를 BBM 응력 해석에 반영함으로써 불포화 조건에서의 수리–역학 연계 거동을 단계적으로 모사할 수 있는 OGS–FLAC 해석 기법을 제시하였다. 이를 적용하여 국제공동연구인 DECOVALEX-2027의 Sandwich Task Step 0a 모델링을 수행하였으며, Calcigel 벤토나이트 세 가지 건조밀도 조건에 대한 팽윤압, 포화도, 수직 변형률, 유입 수량의 시간 변화를 실험 결과와 비교하였다. 해석 결과는 실험실에서 관찰된 팽윤압 및 수리적 거동을 합리적으로 재현하였으며, 이를 통해 개발된 BBM 기반 OGS–FLAC 모듈이 벤토나이트의 경로 의존적 체적변형 및 수리–역학적 복합 거동 메커니즘을 안정적으로 설명할 수 있음을 확인하였다. 본 연구에서 구축된 기법과 보정된 물성치는 향후 MiniSandwich, HTV-7 및 Mont Terri 현장 규모 실험에 대한 확장 적용과 국제 비교·검증 연구의 기초 자료로 활용될 수 있을 것으로 기대된다.

키워드

바르셀로나 베이직 모델

벤토나이트

DECOVALEX-2027

Sandwich Task

OGS–FLAC

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Information

Publisher :Korean Society for Rock Mechanics and Rock Engineering
Publisher(Ko) :한국암반공학회
Journal Title :Tunnel and Underground Space
Journal Title(Ko) :터널과 지하공간
Volume : 35
No :5
Pages :602-629
Received Date : 2025-09-18
Revised Date : 2025-09-29
Accepted Date : 2025-10-13
DOI :https://doi.org/10.7474/TUS.2025.35.5.602

Tunnel and Underground SpaceISSN:1225-1275(Print) 2287-1748(Online)한국암반공학회

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