This work focuses on the numerical modeling of coupled thermal, hydraulic and mechanical processes in transverse isotropic rock, with specific consideration of parallel computing aspects. We apply the previously developed parallel finite element scheme to analyze a real application, an in-situ heating test carried out in an Opalinus Clay layer of the Mont Terri underground laboratory. The definition of the problem is under the framework of the DECOVALEX-2015 project, an international research collaboration for advancing the understanding and mathematical modeling of coupled thermo-hydro-mechanical (THM) and thermo-hydrochemical (THC) processes in geological systems. Three-dimensional studies of the aforementioned experiment considering transverse isotropic material properties of the Opalinus Clay layer in the test site result in very long computation times using a single computer processor. Results discussed in this work convince us that the present parallel finite method has a good scalability in the context of modeling three-dimensional coupledTHM problems.


Coupled thermal, hydraulic and mechanical processes in rock mass are the phenomena of concern in underground geotechnical engineering such as nuclearwaste disposal and CO2 storage. A better understanding of these coupled processes under long-time conditions is the most important aspect in the context of design and operation of corresponding underground facilities, and it can be realized by numerical modeling (Noorishad et al. 1984; Stephanson et al. 2003; Rutqvist et al. 2005; Wang and Kolditz 2007; Rutqvist et al. 2008; Kolditz et al. 2012). For most applications, especially those requiring three-dimensional simulations, the numerical modeling of coupled THM processes is too time-consuming in computation with regard to a convenience time exposure. Therefore, high performance computing is an essential requirement in such modeling (Wang et al. 2009). In this work, we present a parallel finite element approach for the modeling of coupled THM processes in an in-situ heating test carried out in an Opalinus Clay layer of the Mont Terri underground laboratory (Gens et al. 2007), which is one of the subjects of theDECOVALEX–2015 project. In the test, a heater behaving like a nuclear waste canister applies thermal load at the surface of the hosting drift in the rock, which causes pore pressure change and evolution of deformation in the rock mass (Mont Terri Project). The parallel finite element method is realized by using the domain decomposition method for both the global assembly and the iterative linear solver (Wang and Kolditz 2010). Based upon test data, a threedimensional model is defined. Since the Opalinus clay in the test site is bedded, we consider transverse isotropic material properties in thermal and mechanical processes. The speedup achieved in the presented simulations assures that the discussed numerical parallel scheme provides a promising high performance computing method for the simulation of coupled thermal, hydraulic and mechanical processes observed for in-situ applications.

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