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Modelling horizontal ground loops for a horizontal ground source heat pump (HGSHP) system is complex and computationally expensive. The computation precision is highly reliant on the prescription of an undisturbed ground temperature in the unsaturated ground as well as realistic and accurate atmospheric processes at the ground surface boundary. Conventionally, modelling of such a system would include direct application of the atmospheric processes at the soil-atmosphere boundary and solve it in a single-stage approach. However, low efficiency is found for large spatial domain and long-term transient problems as the boundary processes need to be solved and expressed in terms of primary model variables at each simulation time-step. This paper proposes an equivalent two-stage modelling approach, for the first time, based on an advanced coupled thermal-hydraulic (TH) model to improve computation efficiency while maintaining adequate accuracy. In this approach, firstly, the model is solved for an intact ground that is imposed by complex atmospheric processes, e.g., rainfall, solar radiation, humidity, evaporation, etc. at the soil-atmosphere boundary, and the spatial and temporal variations of the primary model variables are recorded. Afterwards, the recorded data are incorporated in the simulator, as model inputs, for the same ground including a HGSHP system. Predicted results from both 2D and 3D simulations show that the ground temperatures calculated by the proposed two-stage approach are in good agreement with that of the traditional single-stage approach. However, the two-stage approach is computationally robust. For the presented 2D and 3D simulations, it required only 32% and 37% of the time of the single-stage approach, respectively, while maintaining great accuracy. This demonstrates the utility of the proposed two-stage approach for modelling complex scenarios of realistic HGSHP systems installed in a large spatial domain and for long-term operation.

This paper presents a coupled thermo-mechanical model to investigate the ground response during underground coal gasification (UCG). The model incorporated the temporal and spatial development of temperature, the gradual growth of the cavity, and temperature-dependent material properties. Model verification was made against two benchmarks to acquire the confidence for the predictive purpose. The first exercise demonstrated the correctness of the model implemented in COMPASS. The second exercise showed that using the ash-filled cavity to represent null or empty zones is a good option in the numerical modeling and provided highly comparable results to other models. Based on the Hanna UCG trial, different cases were simulated to investigate the effects of the cavity size in the coal seam and the thermal expansion coefficient of the caprock and base rock on key features that take place during the process of UCG. A maximum temperature in the range of 1200–1500 ℃ was induced by the gasification of coal, and a cavity with a maximum length of 13.5 m was formed after 30 days of simulation. Meanwhile, small vertical displacement in the range of -5–12 mm took place near the cavity because of the thermal expansion of the geologic materials and the reduction of the overall weight with the creation of the cavity. In addition, it was found the thermal expansion coefficients can influence the thermo-mechanical response of geologic materials, but the effects were insignificant when its order of magnitude was smaller than 10-6 K-1.

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.

This work presents a hybrid discrete fracture-dual porosity model of compressible fluid flow, adsorption and geomechanics during CO2 sequestration in coal seams. An application of the model considers the influence of hydraulic fractures on CO2 transport and the stress field of the coal. The low initial permeability of coal is compounded by the injectivity loss associated with adsorption-induced coal swelling, which is recognised as the major challenge limiting CO2 sequestration in coal seams. In this model, the natural fracture network and coal matrix are described by a dual porosity model, and a discrete fracture model with lower-dimensional interface elements explicitly represents any hydraulic fractures. The two models are coupled using the principle of superposition for fluid continuity with a local enrichment approximation for displacement discontinuity occurring at the surface of hydraulic fractures. The Galerkin finite element method is used to solve the coupled governing equations, with the model being verified against analytical solutions and validated against experimental data. The simulation results show that the presence of a hydraulic fracture influences the distribution of gas pressure and improves the gas flow rate, as expected. The stress field of a coal seam is disturbed by CO2 injection, especially the vertical stress, and the presence of a hydraulic fracture leads to a reduction in stress with permeability recovery starting earlier.

Predicting the transport and fate of organic and inorganic contaminants in co-contaminated soils is challenging, since various complex, inter-related processes are involved. In the presence of soil microbes that metabolise organic compounds (e.g., phenol), the chemical and the physical properties of the soil may alter and consequently affect the transport of inorganic trace metals e.g., Cu, Cd, Ni, Pb. However, the impact of their spatial distributions on the co-transport processes are still poorly understood and rarely available in literature. Here, we distribute the microbial colonies spatially in uniform and various non-uniform configurations and observe that the transport of weakly-sorbed Cd and Ni is greatly influenced by the distance of the colonies from the contaminant source rather than the size of the colonies. Whereas, for strongly-sorbed Pb and Cu, both the distance and the size are important. The spread of phenol in the model domain was substantially restricted by distributing the colonies more towards the transverse direction than in the longitudinal direction of the groundwater flow. In the context of co-contaminated soil remediation, this study demonstrates that optimum and efficient spatial distribution patterns can be obtained to restrict the spread of both organic and inorganic contaminants, with subsequent reduced environmental impacts.

Coupled thermo‐hydro‐mechanical‐chemical modelling has attracted attention in past decades due to many contemporary geotechnical engineering applications (e.g., waste disposal, carbon capture and storage). However, molecular‐scale interactions within geomaterials (e.g., swelling and dissolution/precipitation) have a significant influence on the mechanical behaviour, yet are rarely incorporated into existing Thermal‐Hydro‐Mechanical‐Chemical (THMC) frameworks. This paper presents a new coupled hydro‐mechanical‐chemical constitutive model to bridge molecular‐scale interactions with macro‐physical deformation by combining the swelling and dissolution/precipitation through an extension of the new mixture‐coupling theory. Entropy analysis of the geomaterial system provides dissipation energy, and Helmholtz free energy gives the relationship between solids and fluids. Numerical simulation is used to compare with the selected recognized models, which demonstrates that the swelling and dissolution/precipitation processes may have a significant influence on the mechanical deformation of the geomaterials.

This study presents a coupled dual porosity thermal-hydraulic-mechanical (THM) model of non-isothermal gas flow during CO2 sequestration in coal seams. Thermal behaviour is part of the disturbed physical and chemical condition of a coal seam caused by CO2 injection, and must be understood for accurate prediction of CO2 flow and storage. A new porosity-permeability model is included for consideration of the fracture-matrix compartment interaction. The new model is verified against an analytical solution and validated against experimental measurements, before being used to analyse coupled THM effects during CO2 sequestration in coal. A simulation of CO2 injection at a fixed rate shows the development of a cooling region within the coal seam due to the Joule-Thomson effect, with the temperature in the vicinity of the well declining sharply before recovering slowly. The temperature disturbance further from the well is more gradual by comparison. Under the simulation conditions studied, CO2 injection increases coal matrix porosity and decreases the porosity and permeability of the natural fracture network, especially in the vicinity of the injection well, due to adsorption-induced coal swelling. Compared with the effects of gas pressure and temperature, the matrix-fracture compartment interaction plays an important role in changes of porosity and permeability. Considering the temperature disturbance caused by CO2 injection under the set of representative conditions studied, the coupled model can provide an insight into the associated effects on CO2 flow and storage during its sequestration in coal seams. The first author gratefully acknowledges the financial support provided by the Welsh European Funding Office (WEFO), through the FLEXIS project. The financial support from the China Scholarship Council for the PhD studentship of the second author is also gratefully acknowledged.

This paper presents the development of a discrete fracture model of fully coupled compressible fluid flow, adsorption and geomechanics to investigate the dynamic behaviour of fractures in coal. The model is applied in the study of geological carbon dioxide sequestration and differs from the dual porosity model developed in our previous work, with fractures now represented explicitly using lower‐dimensional interface elements. The model consists of the fracture‐matrix fluid transport model, the matrix deformation model and the stress‐strain model for fracture deformation. A sequential implicit numerical method based on Galerkin finite element is employed to numerically solve the coupled governing equations, and verification is completed using published solutions as benchmarks. To explore the dynamic behaviour of fractures for understanding the process of carbon sequestration in coal, the model is used to investigate the effects of gas injection pressure and composition, adsorption and matrix permeability on the dynamic behaviour of fractures. The numerical results indicate that injecting nonadsorbing gas causes a monotonic increase in fracture aperture; however, the evolution of fracture aperture due to gas adsorption is complex due to the swelling‐induced transition from local swelling to macro swelling. The change of fracture aperture is mainly controlled by the normal stress acting on the fracture surface. The fracture aperture initially increases for smaller matrix permeability and then declines after reaching a maximum value. When the local swelling becomes global, fracture aperture starts to rebound. However, when the matrix permeability is larger, the fracture aperture decreases before recovering to a higher value and remaining constant. Gas mixtures containing more carbon dioxide lead to larger closure of fracture aperture compared with those containing more nitrogen.

© 2018, Canadian Science Publishing. All rights reserved. This paper presents the development of a dual porosity numerical model of multiphase, multicomponent chemical-gas transport using a coupled thermal, hydraulic, chemical, and mechanical formulation. Appropriate relationships are used to describe the transport properties of nonideal, reactive gas mixtures at high pressure, enabling the study of geoenergy applications such as geological carbon sequestration. Theoretical descriptions of the key transport processes are based on a dual porosity approach considering the fracture network and porous matrix as distinct continua over the domain. Flow between the pore regions is handled using mass exchange terms and the model includes equilibrium and kinetically controlled chemical reactions. A numerical solution is obtained with a finite element and finite difference approach and verification of the model is pursued to build confidence in the accuracy of the implementation of the dual porosity governing equations. In the course of these tests, the time-splitting approach used to couple the transport, mass exchange, and chemical reaction modules is shown to have been successfully applied. It is claimed that the modelling platform developed provides an advanced tool for the study of high-pressure gas transport, storage, and displacement for geoenergy applications involving multiphase, multicomponent chemical-gas transport in dual porosity media, such as geological carbon sequestration. Welsh European Funding Office

Soil atmospheric interactions play an important role within the thermal energy balance and seasonal temperature variations of the ground. This paper presents a formulation for the surface boundary conditions related to interactions between soil and atmosphere. The boundary condition formulated considers heat flow at the soil–atmosphere interface through mechanisms of shortwave radiation, long-wave radiation, sensible radiation and latent heat radiation. The effects of surface moisture flux on energy balance at the interface are explicitly included in the formulation. The developed boundary condition has been implemented in a numerical model for coupled thermal, hydraulic and mechanical behaviour of unsaturated soils. The evaporation component of the model is tested, and the results are compared with data from an experimental study at the surface of an area of agricultural land reported in the literature. The results of modelling have been found to compare favourably with the reported data set. The formulation developed for the soil atmospheric boundary condition allows climatic variables, including solar radiation, ambient air temperature, relative humidity, wind speed, rainfall and evaporation, to be incorporated in the long-term analysis of energy balance. This also enables a further detailed inspection of the climate’s role in ground thermal behaviour of ground source heat systems.

Clays are widely used in geotechnical and geoenvironmental engineering applications and it is crucial to understand its behaviour for the dynamic field conditions. The presence of a temperature gradient across clayey soils that exhibit semi-permeable membrane (or osmotic) behaviour may promote a number of complex processes, including thermal expansion or consolidation, thermally induced osmosis, thermal diffusion, along with other flow and deformation processes. Chemical-osmosis and chemico-osmotic consolidation that are significant in isothermal conditions are also affected by temperature. Publications on chemical-osmosis, and to some extent thermo-osmosis behaviour of semi-permeable clays under coupled conditions are widely available. However, studies that include the influence of both thermo-osmosis and chemical-osmosis together are rare. In this paper, a fully coupled numerical model is presented to study the effects of both osmotic processes on thermo-hydro-mechanical-chemical behaviour of semi-permeable clays. Solute spread in a landfill clay liner is investigated under the combined influence of mechanical, thermal, and chemical loading. Model results show that the clay deformation is sensitive to thermo-osmosis; and the effects of thermo-osmotic consolidation, excess pore water dissipation, and the overall settlement increases with temperature. Variation of the source temperature from 40 °C to 80 °C yielded an increase of 11.3% of the peak soil settlement. Significant contribution of thermo-osmosis on solute transport is noticed in this study and ignoring the process substantially deviate from the realism. Up to 80% overprediction of cadmium spread is observed in the clay liner when the thermo-osmotic processes are neglected.

Modern ‘enabling technologies’ and over a century of research and development have pushed underground coal gasification (UCG) beyond the proof-of-concept phase. Lessons learned from previous trials have demonstrated that UCG can exploit the energy stored in coal efficiently and with limited environmental impact compared with conventional coal-based energy technologies. Many countries in the EU (and worldwide) struggle to meet their energy needs despite containing very large reserves of coal, which cannot be exploited conventionally because of its depth. Application of modern UCG techniques, state-of-the-art drilling and monitoring technologies offer the opportunity to extract the energy from deep coal resources economically and with limited environmental impacts; however, several hurdles, such as public opinion and carbon dioxide (CO2) emission limits, must be overcome before UCG can be commercialised in the EU. Continued support by member states will attract more private investments, enable more field trials and allow Europe’s world-class UCG experts to demonstrate that the technology is ready to provide cleaner energy from coal for the EU in the twenty-first century. This is a review paper that aims to summarise the lessons learned from UCG trials and EU-sponsored work and to discuss what still needs to be done to commercialise UCG.

This paper presents the validation of a recently developed dual porosity numerical model and provides insights into coal core flooding experiments with N2 and CO2. Experimental data for anthracite coal from the South Wales Coalfield, UK, allows the coal-gas constitutive behaviour to be defined, leading to the validation of the model using gas flooding data for a mm long and mm diameter core. N2 and CO2 injection scenarios are considered with the coal initially saturated with CH4. It is demonstrated that the model can simulate the physical and chemical phenomena involved in multicomponent gas flow and storage in coal. Further analysis shows that N2 breakthrough in the effluent gas is controlled by dual porosity flow without significant influence of adsorption-desorption, whereas for CO2 this influence is greater. Coal swelling caused by CO2 is identified as the predominant factor, with the preferential displacement of adsorbed CH4 being limited by the time scale of flow across the core relative to the CH4 desorption kinetics. These insights are useful for future experiments concerning the influence of core size. The importance of using sorption data from intact coal rather than powdered coal is highlighted by comparing the numerical predictions and experimental measurements.

The feasibility of recovering heat energy from mine water contained within an abandoned coal mine in South Wales is assessed for a proposed district heating scheme. The study area is the village of Caerau, in the Upper Llynfi Valley, Bridgend County Borough, South Wales, UK, comprising around 750 residential houses, a primary school and 17 commercial properties. This paper describes: an archival geological and mining desk study focussed on Caerau colliery, consideration of regional mine linkages, GIS techniques used to create a 3D initial conceptual geological mine model of Caerau workings, permitting and licencing requirements, community engagement activities undertaken and the findings of a single exploratory borehole. The borehole intersected a void space in flooded mine workings around the horizon of the Six Foot seam at a depth of 224 m below ground level, as predicted by the conceptual mine model. The rest water level within the borehole lies at 92m below ground level and the measured in situ temperature of the mine water at the base of the borehole was 20.3 °C. An unexpectedly high and sustained geothermal gradient of approximately 53 °C/km was calculated from repeated measured temperature profiles.

The performance and sustainability of ground source heat systems is dependent on the thermal behaviour of the neighbouring ground. This paper presents a field-scale monitoring scheme which has been designed and implemented to inspect the ground behaviour in response to a horizontal ground source heat system providing space heating to a domestic property. The system comprises of 112 thermistors buried in the ground along with sensors to record the influential climatic variables and system heating loads. Soil properties were also measured throughout the site as part of a wider site investigation. Dataset collected during the first 13 months of research is presented within the scope of this work. The resolution and duration of the collected dataset facilitated an extensive analysis including thorough investigations of ground thermal distributions resulting from heat extraction and recharge. Findings indicate that the horizontal ground source heat system implemented at the site has provided a sustainable source for space heating during 13 months period of inspection. The unsymmetrical distribution of ground temperatures observed highlighted the importance of climatic variables on ground-loop design and in doing so also highlighted potential avenues for future optimisation. Further to this, the compiled dataset can be considered as a significant contribution to the scientific aspects of ground thermal behaviour due to heat extraction/recharge and provides a comprehensive benchmark for the development and validation of predictive models.

An analytical model for contaminant transport in multilayered capped contaminated sediments including the degradation of organic contaminant is presented. The effect of benthic boundary layer was treated as a Robin‐type boundary condition. The results of the proposed analytical model agree well with experimental data. The biodegradation of contaminant in bioturbation layer shows a significant influence on the flux at the surface of system. The maximum flux for the case with t1/2,bio = 0.07 year can be 4.5 times less than that of the case without considering the effect of biodegradation. The thickness of bioturbation layer has a significant effect on the performance of the capped contaminated sediment. The maximum flux for the case with lbio = 15 cm can be 17 times larger than that of the case without bioturbation layer. This may be because the effective diffusion coefficient of sand cap can be 28 times lower than Dbio. The mass transfer coefficient should be considered for the design of the capping system as the contaminant concentration at the top of system for the case with kbl = 2.5 × 10−5 cm/s can be 13 times greater than that of the case with kbl = 10−4 cm/s. The proposed analytical model can be used for verification of complicated numerical methods, evaluation of experimental data, and design of the capping contaminated sediment systems with reactive cap layers.

The empirical Darcy's law of water transport in porous media, Fick's law of chemical diffusion, and Fourier's law of thermal transport have been widely used in geophysics/geochemistry for over 150 years. However, the strong couplings between water, temperature, and chemicals in a membrane porous medium have made these laws inapplicable and present a significant hurdle to the understanding of multiphase flow in such a material. Extensive experiments over the past century have observed chemical osmosis and thermal osmosis, but a model for understanding their underlying physicochemical basis has remained unavailable, because of the highly cross‐disciplinary and multiscale‐multiphase nature of the coupling. Based on the fundamental principles of nonequilibrium thermodynamics and mixture coupling theory, a rigorously theoretical and mathematical framework is proposed and a general model accounting for all of the coupled influences is developed. This leads to a simple and robust mathematical matrix for studying multiphase couplings in a membrane porous medium when all chemical components are electrically neutral.

This paper presents the development of a numerical model for reactive transport of multicomponent chemicals in unsaturated soils. The model has been developed based on a coupled thermal, hydraulic, chemical, and mechanical (THCM) formulation, and extended by the inclusion of geochemical processes under mixed equilibrium and kinetically controlled reactions in–between the solid, aqueous, and gas phases in soil. This has been achieved by coupling the transport model, COMPASS, with the geochemical model, PHREEQC. Key coupling between the geochemical modelling and the flow of chemicals has been established via the inclusion of porosity modification from mineral precipitation–dissolution reactions and the consequential effects on flow processes. Verification of the developed model is addressed via a series of benchmark simulations with a focus on testing the coupling between the transport model and geochemical model. Good results have been achieved for the verification of the theoretical and numerical implementation of the new developments in the model. A simulation is presented to demonstrate the effects of mineral reactions on porosity evolution and chemical diffusion in a low porosity soil. The model developed is an advanced tool for studying the hydrogeochemical processes in unsaturated soils under variable THCM conditions.

An analytical solution for one-dimensional diffusion of chemicals under coupled chemical and thermal potentials is presented. The theoretical formulation considered includes heat conduction and chemical diffusion due to both molecular and thermal diffusion potentials. Laplace transformation technique has been used to derive the analytical solution to the problem in a semi-infinite domain. The results obtained by the proposed analytical solution have a good agreement with those obtained from the laboratory tests of thermal diffusion of a salt solution in a compact clay. Comparisons with the numerical model were also carried out to investigate the effects of transient heat conduction and temperature-dependency of diffusion coefficient on the chemical transport due to a thermal gradient. An application of the model to study the effects of thermal diffusion on chemical transport in a compacted clay liner (CCL) is presented. The results show that the base concentration and flux of the chemical in the CCL increases with the increase of the temperature and Soret coefficient. The 40-year bottom fluxes for the case with thermal diffusion are 2–11 times greater than the case with only molecular diffusion for a 0.6 m compacted clay liner. Based on the results achieved, thermal diffusion demonstrates considerable effect in the landfill design. In the simulation scenario with ST = 5 × 10−2 1/K, the base concentration and the flux of the chemical at 100 years is 1.5 times and 8 times larger, respectively than those obtained from the simulation without considering thermal diffusion. Using the analytical model presented, a series of dimensionless design charts are presented that can be used to estimate the thickness of the CCL, under non-isothermal conditions. The proposed analytical solution provides a simple method for the verification of alternative numerical models, evaluation of groundwater/soil remediation methods and preliminary design of landfill clay liners.

This paper present an investigation of coupled thermal, hydraulic and chemical behaviour of compacted bentonite buffer under heating and hydration conditions of the geological disposal of high level nuclear waste. The study presented provides further insight into the evolution of hydro-geochemistry of the compacted bentonite and the clay microstructure effects through a numerical modelling development of the reactive transport of multicomponent chemicals. The application/validation case study is based on a series of laboratory tests on heating and hydration of compacted bentonite for a period of 0.5 to 7.6 years reported in the literature. The effects of microstructure evolution during hydration and dehydration on the transport phenomena are included via a new approach that links the geochemistry of clay hydration/dehydration with the transport properties. The analysis results related to the moisture flow and chloride transport demonstrate close correlation with the experimental results by the inclusion of the effects of microstructure evolution in the transport phenomena. The results of numerical analysis of reactive transport of chemicals highlight the importance of accessory minerals present in bentonite on the distribution of some anionic species. The behaviour of major cationic species is shown to be mainly governed by the transport processes. Further insights into the processes associated with the elevated temperature effects of clay buffer are presented and discussed that are captured from the modelling results of clay-water-chemical system under coupled thermal and hydraulic conditions.

The drying suction – water content soil-water characteristic curves (SWCCs) of three clays (MX80 bentonite, yellow bentonite, and Speswhite kaolin) were experimentally determined using axis-translation, vapour equilibrium, and osmotic techniques. The shrinkage paths of the clays were established from Clod tests. The suction – water content SWCCs in conjunction with the Clod test results enabled establishing the suction – degree of saturation SWCCs and further determination of the air-entry values (AEVs) of the clays. Chemical analyses of the polyethylene glycol (PEG) solutions in the osmotic tests revealed an imbalance of the osmotic suctions between the expelled and the retained salts on either side of semi-permeable membranes. A decrease in the water content due to an applied suction for clays with significant osmotic efficiencies was explained by two mechanisms. In mechanism 1, the water content decrease prior to the air entry is controlled by the interparticle repulsive pressure, and in mechanism 2, a decrease in the degree of saturation following the air entry is primarily due to the matric suction. The agreements between the AEVs of the clays determined based on the osmotic suctions corresponding to various applied suctions and that determined from the suction – degree of saturation SWCCs were found to be very good.

The effects of post-compaction residual lateral stress and salt concentration in the hydrating fluid on swelling pressures of compacted MX80 bentonite is brought out in this paper. In order to release the residual lateral stresses, following the static compaction process during preparation of specimens, compacted bentonite specimens were extruded from the specimen rings and then inserted back prior to testing them for swelling pressures in isochoric condition. The swelling pressure tests were carried out at several dry densities of the bentonite with distilled water and solutions of NaCl (0.1 and 1.0 M) as the hydrating fluids. With water, the test results showed that specimens that underwent extrusion and insertion processes exhibited about 10–15 % greater swelling pressures as compared to the specimens those that were compacted and tested. The influence of saline solutions was found to reduce the swelling pressure of the bentonite, but their impact was less significant at high compaction dry densities.

This paper presents the results obtained through continuous and simultaneous measurements of gas flow, temperature and coal deformation during high-pressure gas injection in high-rank coal samples, obtained from the South Wales coalfield (UK). The results demonstrate that CO2 flow rates experience an initial decline due to internal coal swelling, followed by the flow rate recovery and global coal swelling. As the flow of high-pressure CO2 induces measurable temperature drop within the sample related to the Joule-Thomson cooling, the changes induced by the variations in thermal state of the system are associated with abrupt shift in coal response to reactive gas flow. However, subsequent injections of He and N2 show that the changes induced by CO2 sorption on coal permeability to gases are irreversible. This work demonstrates the importance of considering the coupled reactive gas and heat transport, and consequent coal deformation mechanisms while assessing the storage potential of coal seams.

This paper presents an analytical solution for modeling the one-dimensional diffusion of organic contaminants through a composite liner, comprising a geomembrane, a geosynthetic clay liner and a soil liner system. The Laplace transformation technique is used to obtain a dimensionless analytical solution to the diffusion of organic chemicals through the triple-layer composite liners. The solution presented is verified against two alternative numerical solutions. The analytical solution is then adopted to provide a series of graphical design charts which can assist with the assessment and design of composite liners. Design examples are included for a composite liner having a geomembrane, a geosynthetic clay liner and a soil liner system. The proposed analytical solution provides a practical and relatively simple tool to assist with the design of composite liners and the validation of numerical models.

The Stern theory as applicable to interacting parallel clay platelet systems was used to study the compressibility behaviour of bentonites. For a constant surface electrical potential, the distribution of the total electrical charge among the Stern-layer and the Gouy-layer was found to have significant influence on the electrical potential at the midplane between clay platelets. Consideration of the Stern-layer was found to reduce the repulsive pressure or the swelling pressure between clay platelets at large platelet spacing, whereas the repulsive pressure increased significantly when the interacting Gouy-layers were pushed aside. A far greater repulsive pressure was noted for Ca-bentonite than that occurred for Na-bentonite at a platelet distance close to 1.0 nm. Similarly, strong interaction between clay platelets was noted due to suppressed Gouy-layers when the bulk fluid concentration was increased. The repulsive pressure generated due to the overlapping of the Stern-layers was found to be sensitive to changes in the specific adsorption potential, the dielectric constant of the pore fluid in the Stern-layer, and the surface electrical potential. Comparisons of the calculated pressure–void ratio relationships from the Stern theory and the Gouy-Chapman diffuse double layer theory with the experimental consolidation test results of Na- and divalent-rich bentonites showed that, in general, the Stern theory improved the predictions of pressure–void ratio relationships, particularly for pressures greater than 100 kPa; however, strong agreements were lacking in all the cases studied.

In the context of underground storage of nuclear waste, this paper presents the characterization and laboratory tests on compacted MX80 bentonite. Various laboratory testing techniques were used for establishing the water retention behavior of the bentonite. Compacted bentonite specimens were hydrated with fluids of low and high salt concentrations both at ambient and an elevated temperature of 70°C. The swelling behavior of the bentonite was also studied by stepwise wetting compacted specimens at various suctions under isochoric condition. The influence of thermal and thermohydraulic gradients on the mechanical behavior of the bentonite was studied in a thermohydraulic column cell. The investigation showed that the development of swelling pressure in compacted bentonites upon a decrease in the applied suction is accompanied by a decrease in the magnitude suction stress, which gets manifested in the development of the interparticle repulsive pressure and a decrease in the effective stress. The influence of an elevated temperature and an increase in concentration of salt in the hydrating fluid was found to reduce the swelling pressure of the bentonite. Both thermal and thermohydraulic gradients were found to be manifested on the development of axial pressures. Applications of thermal and thermohydraulic gradients were found to cause redistributions of water content, dry density, degree of saturation, and suction within compacted bentonites.

This paper presents a preliminary evaluation of the carbon dioxide (CO2) storage capacity of the unmined coal resources in the South Wales Coalfield, UK. Although a significant amount of the remaining coal may be mineable through traditional techniques, the prospects for opening new mines appear poor. Also, many of the South Wales coal seams are lying unused since they are too deep to be mined economically using conventional methods. There is instead a growing worldwide interest in the potential for releasing the energy value of such coal reserves through alternative technologies – for example through carbon dioxide sequestration with enhanced coal bed methane recovery. In this study, geographical information systems and three-dimensional interpolation are used to obtain the total unmined coal resource below 500 m deep, where the candidate seams for carbon dioxide sequestration are found. The ‘proved’, ‘probable’ and ‘possible’ carbon dioxide storage capacities of the South Wales Coalfield are then obtained using an established methodology. Input parameters are based on statistical distributions, considering a combination of laboratory coal characterisation results and literature review. The results are a proved capacity of 70·1 Mt carbon dioxide, a probable capacity of 104·9 Mt carbon dioxide and a possible capacity of 152·0 Mt carbon dioxide.

This paper presents an investigation of the reactive transport of multicomponent chemicals in clays under coupled thermal, hydraulic, chemical and mechanical framework, considering the diffusion processes in detail. More specifically, combined effects due to the electrochemical and the thermal diffusion potentials are investigated. A theoretical framework for coupling thermal diffusion, i.e. the Soret effect, with electrochemical diffusion in a multi-ionic system is provided. An explicit form of a definition for the thermal diffusion coefficient in a multicomponent chemical transport model is developed. Chemical transport is linked to an advanced geochemical model, PHREEQC (version 2), in order to include chemical reactions. The effects of the combined diffusion potentials on the reactive transport of multicomponent chemicals are investigated by a series of numerical simulations of coupled thermal, hydraulic and chemical behaviour.

In the laboratory, semi-permeable membranes and polyethylene glycol (PEG) solutions are used for applying suction in soils using the osmotic technique. In this study, the pore structures of cellulose semi-permeable membranes with molecular weight cut-off values of 3500 and 14 000 were examined via an atomic force microscope (AFM). Fourier transform infrared (FTIR) spectroscopy was used to identify any degradation of PEG molecules with elapsed time. Freshly prepared PEG solutions and solutions aged for 15 days were considered for this purpose. Osmotic tests were carried out on initially saturated MX80 bentonite specimens at two suction levels (0·44 and 7·04 MPa). Comparison of the AFM images of the semi-permeable membranes before and after the osmotic tests clearly revealed that the pore size of the semi-permeable membranes increased significantly, particularly at the higher applied suction that enabled passing of PEG molecules into the clay specimens. FTIR spectrums of PEG 20 000 and PEG 6000 did not provide any evidence of degradation of the PEG molecules with elapsed time.

A model of chemo-osmotic consolidation of clays in multi-dimensional domains is presented, with volumetric strains induced by both changes in the chemistry and osmotically driven pore water flow considered. Three fully coupled governing equations considering force equilibrium, pore water transport and chemical transport are presented and solved using the transient finite element method. The proposed approach is verified via consideration of chemo-osmotic consolidation of a compacted clay landfill liner and then applied to investigation of a hypothetical case with a local leachate leak in the compacted clay liner. An assessment of the impact of the two-dimensional nature of the system is made. The consolidation process is found to be dominated by osmotic consolidation in the early stages and subsequently by chemical consolidation. It is found that the surface settlement and the leachate concentration in the compacted clay liner may be highly overestimated by a one-dimensional analysis. Moreover, the peak negative excess pore pressure predicted by the two-dimensional solution remains in a shallow region under the leak while in the one-dimensional solution it moves progressively downwards.

This paper presents a first attempt at the inclusion of some biological impacts and influences in the authors’ continued research on coupled transport phenomena through unsaturated porous media. The work presented here forms an extension to an existing coupled Thermo-Hydraulic-Chemical–Mechanical Model (THCM) to include the biological aspects, as a first attempt towards a new THCMB framework. The biological model incorporates biodegradation kinetics of organic substrates and resultant effects in the inorganic geochemistry. In order to achieve this, the biological aspects of the model are coupled to an equilibrium geochemical model following a two-step partial equilibrium approach. Additionally, of concern in contaminant/pollutant transport studies, including the biological aspects, is the effect on human health. This paper therefore also presents some aspects of a health impact analysis model adopted in this study.

The drive towards energy-efficient, low-carbon buildings is a clear priority for many countries. Furthermore, ground heat transfer is understood to play an important role in the overall thermal performance of buildings. This paper presents the results of an in-depth investigation of heat transfer from buildings to the ground. The research involved in situ measurements of heat transfer to the ground from full-scale buildings. The results have been utilised to help develop and validate suitable predictive tools to aid thermal design. Numerical simulations have been undertaken that reveal the transient form of energy losses from typical buildings to the ground over a seasonal time frame. Comparisons are made between numerical results and measured data over an annual cycle. Overall, good correlation of results has been achieved. The thermal properties of foundation soils are known to be dependent on water content. A preliminary assessment of the significance of this aspect of the problem is also considered. In particular, it has been shown that an increase in soil moisture content may cause an increase in heat flux of over 20% for a two-dimensional test case. In summary, innovative low-energy sustainable design is receiving increasing attention. The current work will contribute to this overall objective by ensuring that adequate attention is given to subsurface heat transfer.

The thermo-hydraulic-mechanical behaviour of a large in situ heating test, the Buffer/Container Experiment (BCE), carried out at Atomic Energy of Canada's underground research laboratory, is considered. The work can be seen as an extension of the authors' previous research, investigating the behaviour of a large-scale test, the so-called ‘isothermal test’, to now include heating effects. Suggestions related to the micro–macro behaviour of bentonitic buffer materials subjected to resaturation in confined non-isothermal conditions are explored. Simulation of pre-heating phases of the experiment demonstrates the ability of the model to describe the hydraulic regime in the host rock and isothermal infiltration into the buffer. Consideration of the heating phase confirms that the temperature field is well understood, with a good correlation between the numerical and experimental results. In the moisture field it is found that the interaction between the emplaced buffer and host rock is of considerable importance. It is found that inclusion of micro–macro interaction effects, by way of consideration of the impact of swelling and micro–macro interactions on the hydraulic conductivity of the material, yielded significantly improved correlations between observed and calculated results in the moisture field. The results of the numerical simulations suggest that the interaction between the emplaced buffer and host rock is strongly influenced by the micro–macro behaviour of the bentonitic buffer material. It is concluded that the consideration of the impact of micro–macro interactions on moisture flow in bentonitic buffers is of considerable importance, and may be of some significance in considering the total resaturation time as part of the performance assessment of a nuclear waste disposal repository.

Compacted clay liners in landfills and brine ponds are subject to chemical concentration gradients between the soil water in the clay and the reservoir solution. Soil water is the solution residing in soil pores that is chemically composed of water $(H_2O)$ molecules and dissolved salts molecules (ISSS, 1976). These differences in salt concentration generate an osmotic suction difference: osmotic suction refers to suction arising from the presence of dissolved salts in water (Lu & Likos, 2004). This suction difference is dissipated through the diffusion of salts and flow of H2O molecules (Barbour & Fredlund, 1989). Changes in the dissolved salts concentration of soil water from salt diffusion in response to osmotic suction difference will alter the swell magnitudes of expansive clays, which are strongly influenced by salt concentration (Bolt, 1956; Mesri & Olsen, 1971; Yong & Warkentin, 1975; Mitchell, 1993). Osmotic suction differences between soil water and reservoir solution may thus alter the wetting-induced volume change behaviour of compacted clays used as liners in landfills and brine impoundments.

This paper presents a study of the behaviour of soluble salts (major ions) in a highly compacted bentonite subjected to a thermo-hydraulic gradient. This is achieved via the application of a numerical model, COMPASS, which implements a fully coupled thermo/hydro/mechanical formulation for unsaturated soils, including certain aspects of reactive chemical transport. In this study, thermal transfer is considered to take place via conduction, convection and latent heat transfer; moisture transfer in both the liquid and vapour phases due to liquid and vapour gradients, and chemical transfer due to both advection and hydrodynamic dispersion are also considered. Chemical reactions considered include ion exchange reactions involving major cations (Na+, K+, Mg2+ and Ca2+) and precipitation–dissolution of trace minerals (calcite, dolomite, anhydrite and halite). As a first approximation an elastic constitutive deformation model is implemented in this study. For the simulation of the thermal and moisture field it is claimed that the models can represent the important mechanisms occurring in the soil. Considering the behaviour of major ions, the model is able to qualitatively simulate the experimental behaviour. Therefore, confidence in the coupling of the heat, moisture and chemical variables has been gained. Moreover, since the ions are also undergoing simultaneous geochemical reactions, with the main processes being ion exchange and precipitation/dissolution reactions, confidence in the coupling between the geochemical and the chemical transport model has also been gained. As regards the mechanical behaviour, where an elastic model was assumed as a first approximation, in the absence of experimental results, the model showed acceptable trends.

This paper describes the re-saturation behaviour of a large-scale in-situ experiment carried out at Atomic Energy of Canada's (AECL) underground research laboratory. The experiment, known as the isothermal test, examines water inflow, from the surrounding rock, into highly compacted, unsaturated buffer material. Comparisons of physical measurements and a finite element numerical simulation are presented of water uptake and distribution during the 7-year life of the test. The numerical simulations were performed using an approach developed to model the thermo/hydraulic/mechanical behaviour of the system. A comprehensive data set of the physical behaviour was available from AECL. The simulation of the experiment, using a ‘conventional’ hydraulic conductivity variation, revealed that neither the duration nor the pattern of moisture influx could be modelled accurately. Further study suggested that the expansion of the microstructure of the bentonite, as the material saturated, would tend to reduce the void spaces in the macrostructure, as the material, overall, was constrained from swelling. This in turn was likely to reduce the material's hydraulic conductivity. Incorporation of these ideas within the approach yielded significant results. Both the pattern and the rate of water uptake were now modelled with much greater accuracy. The approach adopted is different from the ‘conventional’ method, in the sense that the material's ‘effective’ hydraulic conductivity decreases as moisture content increases, as opposed to increasing, as is the ‘normal’ case. The repercussions may be significant in terms of total time for re-saturation of the buffer. The process is significantly delayed as a result of this phenomenon. Also, the pattern of moisture distribution during water influx is quite different. These general conclusions, in turn, may be significant when considering the overall performance of a disposal repository, as the total time for re-saturation would be increased. This in turn may be of interest in performance assessment considerations.

An investigation of the three-dimensional coupled thermohydromechanical behaviour of a prototype repository in fractured granitic rock is presented. The pre-placement behaviour of the repository is first considered, making use of a full three-dimensional simulation of the problem. An effective continuum approach, augmented with discrete features with a high hydraulic conductivity, is employed. The method adopted is found to be able to simulate accurately the highly anisotropic flow regime observed at the pre-placement phase. The major features of the full repository experiment under applied heating conditions were then successfully simulated. The range of buffer hydration rates, the thermal response of the repository, and the associated mechanical response were successfully simulated. Approaches to capture both the transient microstructural behaviour of the compacted bentonite (MX-80 type) and a MX-80 pellet material are incorporated. The repository behaviour was shown to be strongly influenced by complex coupled processes, including interactions between the system components. The adoption of a three-dimensional modelling approach proved to be essential to realistically simulate the behaviour of a repository incorporating anisotropic flow behaviour. Finally, potential impacts of the processes considered on performance of the barrier system and in safety assessment are considered.

Strengthening of contaminated materials using inorganic cementitious agents is becoming more widely used in the UK. The method has particular advantages for bulk fill operations such as highway earthworks. Research has been done into the chemical characteristics of leachates and leached solid samples from a study into the long-term durability of a lime strengthened silt/pfa mixture amended with sewage sludge. This involved determinations of chemical composition and mineralogy, and geochemical modelling using Minteqa2 . None of the heavy metals tested is present in the leachate at a concentration likely to pose a significant environmental threat, although some were present to a higher degree than expected based on the inorganic chemistry. This is ascribed to complexation of the heavy metals with dissolved organic matter.

This paper discusses the development of a model for the coupled flow of heat, moisture and air in expansive clays. In particular, the results of recent research work on the inclusion of expansive behaviour exhibited by some clays are presented. Initially, a fully coupled thermal/hydro/mechanical (THM) simulation of a heating experiment is presented. The observed THM behaviour in unsaturated soil was predicted by the model, with the best correlation found in the thermal field. The influence of the osmotic potential on the soil via the effect of chemical solute concentration is explored in a non-linear elastic constitutive relationship. The ability of such a model to represent the large strains that can occur during free swelling of expansive soils has been demonstrated. Finally, the representation of the development of irreversible strains within an expansive soil has been investigated via a double structure elasto-plastic relationship. The ability of such an approach to simulate the accumulation of plastic strains during wetting–drying cycles has been shown.

This paper presents a fully coupled heat and mass transfer numerical model describing the migration of a contaminant gas through an engineered clay liner of a sanitary landfill site. The governing system of non-linear partial differential equations are derived from a mechanistic approach where the mass and energy conservation laws are defined for a particular phase into which Darcy’s law and Fick’s law are substituted. The model treats the migration of liquid water, heat, air and contaminant gas separately with independent system variables of capillary potential, temperature, pore air pressure and molar concentration of the contaminant gas. A numerical solution is presented, which is compared against the classical advection–diffusion equation, to highlight the effect of a temperature gradient on the contaminant gas concentration.

A numerical model of the stress–strain behaviour of unsaturated soil is presented. An extended critical state elastoplastic constitutive model based on net stress and suction is solved via the finite-element method. Numerical techniques are proposed which allow for the development of an elastoviscoplastic solution algorithm within the context of a transient finite-element analysis. The simultaneous solution of the coupled partial differential equations provides variations of net stress, suction, specific volume and degree of saturation in an unsaturated soil. Several examples are then analysed which illustrate typical features of the behaviour of unsaturated soil samples. Expected patterns of behaviour are reproduced and good correlation is obtained between numerical results and an alternative solution of the theoretical model. Comparisons of numerical predictions with results obtained from two suction-controlled experiments on compacted kaolin and sandy clay are then presented. Good correlation is again achieved, yielding confidence in the validity of the numerical algorithm. Finally, the solution of a boundary value problem is attempted, namely the prediction of seasonal ground movement. Comparison of numerical results with field observed data shows good correlation is achieved. The ability of the new approach to solve boundary problems of geotechnical significance is thus illustrated. Nous présentons une maquette numérique du comportement contrainte–déformation d'un sol non saturé. Une maquette constitutive élastoplastique d'état critique étendue basée sur une contrainte nette et une succion est résolue par la méthode d'éléments finis. Nous proposons des techniques numériques qui tiennent compte du développement d'un algorithme de solution élastoviscoplastique dans le contexte d'une analyse d'éléments finis transitoire. La solution simultanée des équations différentielles épardelles couplées donne des variations de la contrainte nette, de la succion, du volume éspécifique et du degré de saturation dans un sol non saturé. Nous analysons alors plusieurs éééexemples qui illustrent les caractéristiques type du comportement d'échantillons de sol non saturé. Nous reproduisons les modes attendus de comportement et nous obtenons une bonne corrélation entre les résultats numériques et la solution alternative du modèle théorique. Nous comparons les prédictions numériques avec les résultats de deux expériences à succion sur le kaolin compacté et Pargile sableuse. Encore une foie, une bonne corrélation est obtenue, confirmant la validité de Palgorithme numérique. Enfin, nous essayons la solution d'un probléme à valeur limite, nommément la prédiction des mouvements saisonniers du sol. La comparaison des résultats numériques avec des données observées sur le terrain montre qu'on obtient une bonne corrélation. Nous illustrons ainsi Pefficacité de la nouvelle méthode à résoudre les problèmes limites à signification géotechnique.

This paper focuses attention on the development of a numerical model of the hydro/thermo/mechanical behaviour of unsaturated clay and its consequent verification and validation. The work presented describes on-going collaboration between the Cardiff School of Engineering and Atomic Energy of Canada. The model development, which was carried out at Cardiff, can be described as being based on a mechanistic approach to coupled heat, moisture and air flow. This is then linked to a deformation analysis of the material within a ‘consolidation’ type of model. The whole is solved via the finite element method to yield a computer software code named COMPASS (COde for Modelling PArtly Saturated Soil). Some aspects of verification and validation of the model have been addressed in-house. However, the purpose of current AECL work is to provide an independent, rigorous, structured programme of validation and the paper will also explore the further validation of COMPASS within this context. © 1998 by John Wiley & Sons, Ltd.

A parallel numerical finite difference model, employing the self-implicit method, for coupled heat and moisture transfer in unsaturated soil is presented. The model is programmed in Occam and executed on a parallel computing network of transputers. An assessment of the model was achieved via the simulation of a laboratory experiment. A very good correlation between experimental and numerical results was obtained. Comparison of results with those obtained from a parallel explicit method is also illustrated showing no significant difference. The computational time employing the new method was, however, found to be half of that obtained using the explicit method. The computational efficiency of the approach was also found to be very high.

An assessment of the validity of a theoretical formulation of coupled heat and moisture in non-deforming unsaturated soil is presented. This was achieved by comparison of results from the theoretical formulation with those obtained from controlled laboratory heating experiments. The work centred on one material, a highly compacted medium sand, for which the thermophysical parameters had been established independently of the heating experiments. A solution of the theoretical formulation was achieved by means of a numerical analysis, using the finite difference method. Very good correlations were achieved between experimental and numerical results. Confidence in the ability of the theoretical formulation to describe fully the physical processes involved is thus enhanced. Application of these conclusions to problems of heat and moisture transfer in non-deforming, cohesionless soils in general is now considered possible. The numerical results were achieved using parallel computing techniques. This methodology was shown to perform very efficiently, yielding a simulation of the full range of the transient behaviour for all the experiments considered. The potential of parallel computing systems for the solution of a computationally demanding problem of this type is thus revealed. Ľexposé évalue la validité d'une formulation théorique du couplage chaleur-humidité dans un sol non déformant non saturé. Cette évaluation repose sur la comparaison des résultats de la formulation théorique aux résultats d'essais contrôlés de chauffage en laboratoire. Les travaux se sont concentrés sur un matériau: un sable moyen fortement tassé, dont les paramètres thermo-physiques avaient été établis indépendamment des essais de chauffage. On a résolu la formulation théorique à ľaide analyse numérique en utilisant la méthode des différences finies. On a obtenu de triés bonnes corrélations entre les valeurs expérimentales et les valeurs calculées. On a maintenant une plus grande certitude que les formules théoriques peuvent décrire complétement les processus physiques qui entrent en jeu. On pense qu'il est maintenant possible d'appliquer ces conclusions en général aux problèmes du transfert de chaleur et d'humidité dans des sols non déformants sans cohésion. On a eu recours à des techniques de calcul parallèles pour obtenir les valeurs théoriques. Cette méthodologie s'est avérée triès efficace et a permis de simuler la gamme complète des comportements transitoires dans tons les essais envisagés. Cela montre qu'il est possible d'utiliser des systèmes de calcul parallèles pour résoudre un problème de ce type, qui est fort exigeant sur le plan du calcul.

Results of an experimental and theoretical investigation of heat and moisture movement in unsaturated MX-80 bentonite are presented. A thermo-hydraulic cell that allows measurement of transient temperatures and facilitates the determination of pseudo-transients of moisture content, dry density and chemical composition has been used to perform thermal gradient tests. Results of a number of tests are presented, and observation of the accumulation of chloride ions near the hot end clearly indicates that there is a cycle of vapour and liquid moisture movement, with vapour moving from hotter to cooler regions, condensing, and then moving as liquid towards the hotter regions. An empirical method is applied to calculate approximate vapour fluxes using measured variations in chloride ion concentration and moisture content with time. The vapour fluxes calculated empirically are found to be lower than those determined by some existing vapour flow theories. Subsequently, an existing vapour flow model is modified to represent the observed vapour fluxes more closely.

The development of a model of the thermo-mechanical-hydraulic behaviour of unsaturated soil is described. A step by step approach is adopted, taking as a starting point a potential-based model of coupled heat and moisture transfer. Extensions of this work to include the effect of air transfer and the deformation characteristics of the soil are presented. Constitutive relationships which accommodate non-linear elasticity, thermoelasticity and elasto-plasticity are considered. Numerical solutions of the various versions of the model are presented. Validation of the versions of the model, at their differing stages of development, is considered in turn and results presented in support of each case. The need for further, on-going research is also suggested, with a view towards resolving remaining problems of concern in safety assessment.

An in situ experiment being carried out to investigate the hydraulic behaviour of a bentonite—sand engineered barrier is described. Hydraulic interactions between the barrier, surrounding granite and a concrete sealing plug are being measured some 240 m below ground level at AECL9s Underground Research Laboratory (URL). Observations from the test to date indicate that the buffer mass is taking on moisture. Pore pressures in the near-field rock appear to be low but generally continue to change with time. In contrast, pore water pressures in the far-field rock essentially remain constant. Supporting numerical investigations are also described. An axisymmetric solution of Richards9 pressure head based flow equation is used. The model was calibrated against known experimental results and subsequently used to provide the anticipated response of the in-situ experiment. The importance of the unsaturated hydraulic properties of the granite are revealed, leading to the conclusion that further data on these properties, when subject to high suction values, are required.