International Journal of Geomechanics

A multicomponent reactive transport model, coupled with an existing thermal, hydraulic, and mechanical model for porous media, is investigated. The model is based on conservation of mass/energy principles for the flow and stress-strain equilibrium for the mechanical behavior. The resultant model is coupled with a geochemical model to capture geochemical interactions. Numerically, the Galerkin FEM is employed for spatial discretization and an implicit Euler method for temporal discretization. The coupling of the transport and geochemical models is achieved through both noniterative and iterative approaches. A series of applications are considered to demonstrate the numerical performance and qualitative behavior, specifically in the context of multicomponent behavior. The model shows good convergence and computational efficiency.

An approach for the simulation of three-dimensional field-scale coupled thermo-hydro-mechanical problems is presented, including the implementation of parallel computation algorithms. The approach is designed to allow three-dimensional large-scale coupled simulations to be undertaken in reduced time. Owing to progress in computer technology, existing parallel implementations have been found to be ineffective, with the time taken for communication dominating any reduction in time gained by splitting computation across processors. After analysis of the behavior of the solver and the architecture of multicore, nodal, parallel computers, modification of the parallel algorithm using a novel hybrid message passing interface/open multiprocessing (MPI/OpenMP) method was implemented and found to yield significant improvements by reducing the amount of communication required. This finding reflects recent enhancements of current high-performance computing architectures. An increase in performance of 500% over existing parallel implementations on current processors was achieved for the solver. An example problem involving the Prototype Repository experiment undertaken by the Swedish Nuclear Fuel and Waste Management Co. [Svensk Kärnbränslehantering AB (SKB)] in Äspö, Sweden, has been presented to demonstrate situations in which parallel computation is invaluable because of the complex, highly coupled nature of the problem.

Modeling the behavior of unsaturated soils necessitates the measurement of soil suction and the establishment of its variation with the water content, which is commonly known as the soil-water characteristic curve (SWCC). Several methodologies have been developed for measuring either total suction $\psi$ (sum of matric suction ${\psi }_m$ and osmotic suction ${\psi }_o$) or ${\psi }_m$. While employing different methodologies for suction measurement, there is a possibility that various factors (viz., type of the soil, measurement methodology, range of the suction measurement, equilibration time, and presence of salts or contaminants in the soil) may influence the results and hence the SWCC. Therefore, it is essential to investigate the uniqueness of SWCC, determined by using some commonly adopted suction measurement methodologies. This study indicates that the SWCC established by adopting different methodologies may not be unique and is primarily influenced by the range of suction measurement. As such, it is essential to highlight the range of suction values involved for establishing the SWCC, to facilitate unambiguous modeling and to precisely understand the behavior of unsaturated soil.

Knowledge of the settling properties of polymer-amended slurries is pivotal for improving throughput and yield during metal extraction and for developing tailings streams with superior geotechnical properties. This paper focuses on the large strain settling behavior of laterite slurries. The investigated slurry exhibited two settling regimes—sedimentation occurred up to $e=e_m=8$ and consolidation started at $e=e_s=6.5$. Bipower law functions best described the entire process in the form of $e-{\sigma }^{\prime }$ and $k-e$ relationships. Polymer addition generally improved slurry compressibility and hydraulic conductivity. The settling behavior of polymer-amended slurries was governed by large interfloc voids during sedimentation and by small intrafloc pores during consolidation. The combined effect of polymer parameters was effectively captured by the term polymer characteristic coefficient. Fit parameters for the $e-{\sigma }^{\prime }$ and $k-e$ relationships were directly proportional to $Cp$. Both the settling rate and amount varied extensively during hindered sedimentation. Compressibility during consolidation converged at ${\sigma }^{\prime }=1,000\mathrm{kPa}$ and $e=2$, but this was not the case for hydraulic conductivity. Physicochemical interactions dominated sedimentation but were ineffective during consolidation. The liquid limit (${\sigma }^{\prime }=2\mathrm{kPa}$) was used to differentiate between the two settling regimes.

This paper presents an experimental and numerical investigation of coupled consolidation and contaminant transport in compressible porous media. Numerical simulations were performed using the CST2 computational model, in which a dual-Lagrangian framework is used to separately follow the motions of fluid and solid phases during consolidation. Diffusion and large strain consolidation-induced transport tests were conducted on composite specimens of kaolinite slurry consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Assessment of the importance of the consolidation process on solute transport is based on measured and simulated solute breakthrough curves and final contaminant concentration profiles. CST2 simulations closely match the experimental data for three different loading conditions. Diffusion and consolidation-induced advection made important contributions to solute transport and mass outflow in this study. Additional simulations indicate that consolidation-induced contaminant transport may also be affected by specimen boundary drainage and initial concentration conditions.

The temporary storage of hot water in openings excavated in rock may be worthwhile for multiple land-use applications, environmental safeguards, and energy conservation. When used for hot water storage, the rock mass around the openings will respond by coupled thermomechanical effects induced by the hot water. In this study, a submergence test of granite and sandstone at 20 and 95°C was used to examine the thermal behavior of the rock mass around the openings to obtain the mechanical properties of uniaxial compressive strength and elastic modulus. A uniaxial compression creep test of the rock at high temperatures was also performed and calculations with various constants for the creep were examined. With the results obtained in this work, the temperature and stress distribution around the openings when hot water is stored was analyzed by considering the creep properties. The thermal behavior and stability of the openings were also examined. The displacement of the openings was predicted to be approximately 2% of the diameter after 1,000 days.

Coupling of two-phase flow with mechanical deformation has important applications in many fields, including dense nonaqueous phase liquid (DNAPL)–water transportation through the subsurface. To understand and couple the different processes, numerical model studies are inevitable at all temporal and spatial scales. This study presents the characterization of DNAPL and water flow in a fracture under confining and fluid pressures. A comprehensive and simplified mathematical model and the conditions under which DNAPL will enter an initially water-saturated fracture under deformation are discussed. A numerical model to predict the quantity of each phase of their saturations is developed. The effect of varying confining stresses on the traverse time of DNAPL across a fractured aquitard is studied. The sensitivity analysis for physical and hydraulic properties, such as apertures, fracture inclination, and fluid and confining pressures, are performed and discussed. The temporal evolution of aperture is necessary to know the proper flow pattern of fluids within a fracture in a multiphase system. These studies are relevant for DNAPL trapped in fractures with very small aperture that can bring changes to flow pattern under deformation.

A study was conducted to elaborate a predictive model that deals with the hydraulic conductivity reduction of permeable reactive barriers (PRBs) used for the in situ treatment of contaminated groundwater. As PRBs are composed of reactive and permeable filters through which the contaminated groundwater flows, their longevity has to be studied from both hydraulic and chemical points of view. Therefore, one-dimensional (1D) column filtration experiments were performed at a pilot scale, and an integrated model based on the solution of the advection-reaction-dispersion (ARD) mass balance equation was developed to study the space and time evolution of the hydraulic conductivity. This model uses the well-known Kozeny-Carman relation, which considers that permeability depends on the porosity and specific surface of the porous media. The ARD equation is solved by using the PHREEQC software with numerous capacities on the chemical point of view. Thanks to specific assumptions on the geometry of the precipitations, by using the floating-spheres model and the introduction of the “balanced time principle,” the evolution of the profiles of conductivity are computed and compared with those deducted from differential pressure measurements in the laboratory. Results of numerical simulations conducted with the model show that the largest porosity reductions occur on a 10-cm-thick layer at the entrance of the PRB as a result of precipitation of calcite minerals (prefilter).