Strain-dependent Permeability Research Articles

Formulation and numerical realization of anisotropic permeability coefficient for fluid-solid coupling in underground engineering

Underground engineering soil functions as a typical porous medium wherein groundwater flow and alterations in pore water pressure can influence the medium’s porosity, thereby affecting soil permeability. Moreover, changes in porosity (volumetric strain) result in anisotropy in the permeability coefficient, complicating the accurate depiction of the entire fluid-solid coupling process using a uniform permeability coefficient. Fluid–solid coupling is achieved by establishing a connection between soil and fluid parameters in response to changes in the permeability coefficient during soil deformation. Considering the limitations of the deformation mode described by volumetric strain, this paper proposes different influencing factors of anisotropic principal strains (εx, εy , and εz ) on the anisotropic permeability coefficient k i, based on the Kozeny–Carman semi-empirical equation for the permeability of porous media. Additionally, a numerical simulation method for the fluid-solid interaction effect in underground engineering is implemented by incorporating variations in the permeability coefficient with strain, using a fish-parameterized programming language within the FLAC 3D software. The coupling effect of the seepage field with the strain-dependent permeability coefficient on the mechanical field is validated using a specific calculation example. This methodology presents a novel approach for expressing fluid-solid coupling processes.

Analysis and development of a sensor concept for multistable actuators with passive magnetic shape memory alloy

Abstract Based on the current state of research, the aim of this paper is to develop a position sensor for actuators using passive magnetic shape memory alloys. The presented sensor concept converts the strain dependent permeability of the magnetic shape memory alloy into an inductance change by using a sensor coil arrangement. The change in inductance of the sensor coil is converted into a change in the resonant frequency of a parallel oscillating circuit. A microcontroller detects the resonant frequency of the circuit and converts it into a position sensor signal. To evaluate the functionality of the sensor, a test rig is developed that deforms the magnetic shape memory element under realistic application conditions. Experimental measurements in a climate chamber are used to evaluate the performance and characteristics of the sensor. The characteristic, temperature drift and hysteresis behavior are analyzed. It is proven that the presented sensor concept can be used to determine the position of passive magnetic shape memory alloy actuators.

Failure in articular cartilage: Finite element predictions of stress, strain, and pressure under micro-indentation induced fracture

Articular cartilage is found at the distal end of long bones and is responsible for assisting in joint articulation. While articular cartilage has remarkable resistance to failure, once initially damaged, degeneration is nearly irreversible. Thus, understanding damage initiation is important. There are a few proposed mechanisms for articular cartilage failure initiation: (A) a single collagen fibril stress-based regime; (B) a rate-dependent regime captured by brittle failure at slow displacement rates (SDR) and ductile failure at fast displacement rates (FDR); and (C) a rate-dependent regime where failure is governed by pressurization fragmentation at SDR and governed by strain at FDR. The objective of this study was to use finite element (FE) models to provide evidence to support or refute these proposed failure mechanisms. Models were developed of microfracture experiments that investigated osmolarity (hypo-osmolar, normal osmolarity, and hyper-osmolar) and displacement rate (FDR and SDR) effects. Cartilage was modeled with a neo-Hookean ground matrix, strain-dependent permeability, nonlinear fibril reinforcement with viscoelastic fibril terms, and Donnan equilibrium swelling. Total stress, solid matrix stress, Lagrange strain, and fluid pressure were determined under the indenter tip at the moment of microfracture. Results indicated significant rate dependence across multiple outputs, which does not support (A) a single failure regime. Larger solid and fluid pressures at FDR than SDR did not support (C) a rate-dependent regime split by pressurization at SDR and strain at FDR. Consistent solid shear stresses at SDR and consistent third principal solid stresses at FDR support (B) the ductile-brittle failure regime. These findings help to shed light on the underlying mechanisms of articular cartilage failure, which have implications for the development of osteoarthritis.

Multiphase flow gas transport in a deep geological repository

Gas transport in porous media is of interest in many industrial applications, such as the oil and gas industry, geological storage, and deep geological repositories for radioactive waste. In a deep geological repository, gas will be generated due to the corrosion of metallic components and the degradation of organic materials. This leads to a build-up of gas pressure, which may activate gas transport through the host rock as well as the excavation-damaged zone around backfilled galleries.
 In order to understand different transport mechanisms involved, numerical simulations were performed, and the results were compared with laboratory data. In the framework of the EURAD/GAS project, a gas pressure-dependent permeability model was implemented into the finite element code OpenGeoSys-6 (OGS-6) [1]. The permeability alteration in this model is a function of gas pressure. The laboratory experiments showed that the rate of permeability change are different at low and high gas pressures. Therefore, the permeability model employed a threshold pressure ( to categorize this behaviour.
 and are empirical parameters. Moreover, two other permeability models were employed to study the hydro-mechanical behaviour of the host rock and permeability changes. In the strain-dependent permeability model, the permeability change was related to the elasto-plastic behaviour of the host rock, and in the embedded fracture model, it was related to the opening and closure of fractures [3] [4]. Thus, volumetric elastic strain and equivalent plastic strain are employed to be the controlling variables.
 The initial permeability of the intact rock samples were determined by applying a constant pressure at the upstream and downstream of the samples (i.e. constant pressure gradient). The imperical parameters were determined by matching experimental and numerical results.
 Two types of gas injection tests carried out by the Institute for Rock Mechanics (IFG GmbH, See Figure 1) were used to investigate the gas transport through Opalinus Clay and to examine the permeability models [2]. The first experiment demonstrates an advective-diffusiion gas transport through the sample and an elastic deformation. The second experiment highlights the formation of a tensile fracture (plastic deformation and preferred flow path). In both experiments the advective transport is the dominant transport mechanism. The strain-dependent permeability model was successfully applied to reproduce the hydro-mechanical behaviour of the host rock in both elastic deformation test and tensile fracture test (see Figures 2 and 3). The hydro-mechanical response of a saturated single phase flow model was compared with the behaviour of a saturated two-phase flow model. Both single phase and two-phase flow models were able to describe the hydraulic as well as mechanical behaviour of the experiments performed. Therefore, one can conclude that in these experiments the water phase (wet-phase) was immobile.
 A gas injection test under triaxial conditions was performed by École Polytechnique Fédérale de Lausanne (EPFL) in saturated Opalinus Clay (Fig. 4). The numerical simulations reproduced the hydro-mechanical behaviour of the sample during the gas injection test. A two-phase flow model was applied to simulate the experiment. The relative permeabilities and capillary pressure functions followed Mualem approach and van Genuchten formulation, respectively. The outflow volume and mechanical response of the sample were measured. The experimental results were in good agreement with the numerical ones. The results of the modelling illustrated the penetration of gas into the sample and hence, the displacement of water (see Figures 5 and 6).

Interstitial flow, pressure and residual stress in the aging carotid artery model in FEBio.

Vascular smooth muscle cells (VSMCs) are subject to interstitial flow-induced shear stress, which is a critical parameter in cardiovascular disease progression. Transmural pressure loading and residual stresses alter the hydraulic conductivity of the arterial layers and modulate the interstitial fluid flux through the arterial wall. In this paper, a biphasic multilayer model of a common carotid artery (CCA) with anisotropic fiber-reinforced soft tissue and strain-dependent permeability is developed in FEBio software. After the verification of the numerical predictions, age-related arterial thickening and stiffening effects on arterial deformation and interstitial flow are computed under physiological geometry and physical parameters. We found that circumferential residual stress shifts outward in each layer and its gradient increases up to 6 times with aging. Internally pressurized CCA displays nonlinear deformation. In the aged artery, the circumferential stress becomes greater on the media layer (82-158kPa) and lower on the intima and adventitia (19-23kPa and 25-28kPa, respectively). The radial compression of the intima reduces the total hydraulic conductivity by 48% in the young and 16% in the aged arterial walls. Consequently, the average radial interstitial flux increases with pressure by 14% in the young and 91% in the aged arteries. Accordingly, the flow shear stress experienced by the VSMCs becomes more significant for aged arteries, which may accelerate cardiovascular disease progression compared to young arteries.

Is the mechanical function of meniscal tissue altered in osteoarthritic knees?

BackgroundDeteriorating meniscal function is thought to play a role in knee osteoarthritis. Meniscal proteoglycans maintain mechanical stiffness of the tissue through electrostatic effects. This study aimed to investigate whether the mechanical properties of macroscopically intact meniscus are preserved in osteoarthritis. MethodsDiscs of lateral meniscal tissue two millimetres thick and of five millimetres diameter from osteoarthritic knees and from healthy donors were placed within a confined compression chamber, mounted in a materials testing machine and bathed in isotonic 0.14M PBS, hypotonic deionised water or hypertonic 3M PBS. Following equilibrium, a 10% ramp compressive strain was applied followed by a 7200 second hold. Resultant stress relaxation curves were fitted to a nonlinear poroviscoelastic model with strain dependent permeability using finite element modelling to determine mechanical parameters. All samples were assayed for proteoglycan content. Comparison of results was undertaken using multivariate ANOVA. ResultsThirty samples from osteoarthritic knees and 18 samples from healthy donors were tested. No significant differences in mechanical parameters or proteoglycan content was observed between groups. In both groups Young’s modulus (E) was significantly greater, and zero-strain permeability significantly reduced, in samples tested in deionised water compared to samples tested in 0.14M or 3M PBS (all p < 0.05). ConclusionMechanical parameters of intact lateral meniscus in osteoarthritic knees are similar to those found in healthy knees. Proteoglycan concentration and their electrostatic contribution to mechanical stiffness of the meniscus is maintained in menisci derived from osteoarthritic knees. Whilst macroscopic tears in the meniscal ultrastructure may contribute to osteoarthritis, intact meniscal tissue maintains its function.

Impact assessment of strain-dependent permeability on reservoir productivity in CSS

Geomechanical analysis is essential to assess the productivity forecast of cyclic steam simulation (CSS) operations in heavy oil reservoirs. The high-temperature and high-pressure fluid injection, as well as depletion in unconsolidated and poorly cemented porous media during CSS, may generate a relevant stress–strain response at levels that can lead to irreversible changes in reservoir permeability. Therefore, it is fundamental to consider permeability dependence on rock strain to properly analyze the impact of geomechanics, pressure, and temperature on reservoir performance. This paper implements a proposed directional strain-dependent permeability model to assess the productivity and compare it with a conventional volumetric permeability model through numerical simulation, considering the effects of wellbore creation on the stress–strain initial state. An explicit coupling between CMG-STARS and the geomechanics in-house simulator GSIM is carried out to perform the simulations using the proposed model. The results of oil production rates and permeability profiles show competitiveness between dilation and compaction periods that modify the structure of the porous media. There is a significant influence of stress state, strain, and injected energy on the permeability parameter. The approximations of this study might be used for feasibility assessment and optimization of CSS when integrating reservoir flow and geomechanical behavior analysis in productivity forecast.

Simulation of dilatancy-controlled gas migration processes in saturated bentonite using a coupled multiphase flow and elastoplastic H2M model

Dilatancy-controlled gas flow in preferential pathways plays a key role in the safety analysis of radioactive waste repositories. This is particularly the case for bentonite, an often-preferred barrier material. Gas flow in preferential pathways is characterized by localization and spontaneous behavior, which is challenging to simulate in numerical models due to strong hydro-mechanical coupling. To analyze a laboratory experiment in the framework of the DECOVALEX-2023 project, this study introduced a new approach of combining continuous modelling methods with spatial material properties derived from material heterogeneities and experimental observations. The proposed model utilized hydro-mechanical spatial distributions, namely Young's modulus and gas entry pressure, and elastoplasticity combined with a linear swelling model. A conceptual strain-dependent permeability approach simulated dilatancy-controlled gas flow based on hydro-mechanical coupling. To test the effectiveness of the presented approach, a gas injection test in a compacted, saturated bentonite sample was simulated using the open-source code OpenGeoSys 5.8 and compared with experimental observations. The presented methodology is capable of simulating localized gas flow in preferential pathways. The spatial distributions of Young's modulus and gas entry pressure affect the swelling pressure, relative permeability and, in combination with the strain-dependent permeability model, also the intrinsic permeability. • This study presents a fully coupled hydro-mechanical model that is capable to simulate gas flow in preferential pathways. • The presented approach combines a strain-dependent permeability model with spatial material distributions. • The model yields good results of the breakthrough parameters for a gas flow test through compacted and saturated bentonite.

Biomechanical response of soft tissues during passage of synovial fluid in compression

The present study provides a novelty approach for the computational biological model based on continuum mixture theory in combination with power-law model for incorporating an accurate governing model for the synovial fluids. We investigated the biomechanical response of a soft tissue while passage of non-Newtonian fluid during act of loading at the rigid bony interface. A special kind of multiphasic deformation has been reported in these types of problems that justify nonlinear coupling between the fluid and solid. In modeling these types of problems, general assumption of mixture constituents incompressibility is often provoked. The mixture components are considered intrinsically incompressible; however, in the derivation of governing equations, viscoelastic behavior of the solid along with interstitial fluid was developed. The nonlinear interaction between the fluid–solid is modeled using strain-dependent permeability and is experimentally determined. This manipulation of linear model with nonlinear permeability required attention for the computational point of view. A system of nonlinear coupled partial differential equations is derived for the local fluid pressure along with an equation for solid deformation. The governing system of equations is solved numerically for the case of permeability dependent flow, whereas an exact solution is given for constant permeability case. Various interesting features, such as, pressure changes within the tissue, swelling behavior of the solid matrix, and effects of power law index on the tissue deformation have been presented graphically. A good qualitative agreement has been noticed between the exact and numerical solutions for constant permeability case.

Evaluation of the impact of strain-dependent permeability on reservoir productivity using iterative coupled reservoir geomechanical modeling

Permeability an important property plays a key role in reservoir performance, numerical reservoir simulation, drilling and production planning. In such reservoirs, stress and strain alters induced by extraction and injection of fluid may substantially change permeability in an irreversible manner. With regard to this phenomenon, several reservoirs may require to consider straindependent permeability, in order to have an accurate performance. In such reservoirs, especially carbonate reservoirs which are a significant proportion of the world’s hydrocarbon reserves, to present the mechanical behavior of rocks, the cap elastoplastic model is may be required. Therefore, the goal of this paper is to evaluate the strain-dependent permeability using coupled reservoir geomechanical modeling with considering the cap elastoplastic model. This coupling is implemented using a fixed stress iterative coupled scheme. In this coupling, the governing equation for fluid is presented by Darcy’s law in which the permeability is nonlinear. The geomechanical module is analyzed using Biot’s theory and cap elastoplastic model. To indicate the mechanical behavior of reservoir rock, the DiMaggio-Sandler elastoplastic model which is a cap envelope is selected. The numerical approximation is done by employing mixed finite element for reservoir module and a continuous Galerkin finite element for geomechanics. Several numerical simulations are performed to verify the models and analyze the effect of strain-dependent permeability on reservoir productivity.

ION-INDUCED DEFORMATION OF ARTICULAR CARTILAGE WITH STRAIN-DEPENDENT NONLINEAR PERMEABILITY AND MHD EFFECTS

ION-INDUCED DEFORMATION OF ARTICULAR CARTILAGE WITH STRAIN-DEPENDENT NONLINEAR PERMEABILITY AND MHD EFFECTS

The effect of highly inhomogeneous biphasic properties on mechanical behaviour of articular cartilage

Background and objectiveInvestigating the biomechanics of cartilage could help to understand the unique load-bearing property of the cartilage and optimize the scaffold design in tissue-engineering. It is important to model the cartilage as a highly inhomogeneous fibril-reinforced biphasic material to represent its complex composition and structure. The depth-dependent and strain-dependent properties of the cartilage would also play an important role in its mechanical behaviour. However, the differences in representing the cartilage as a highly inhomogeneous model or as simplified models still remain unclear. Hence, in this study, a highly inhomogeneous fibril-reinforced biphasic cartilage model considering both the depth-dependent and strain-dependent properties was constructed; the effect of highly inhomogeneous properties on the mechanical behaviour of articular cartilage was investigated. MethodsA finite element model of the cartilage was developed based on a flat-ended indentation test. Compressive forces were applied to four various inhomogeneous layered models through a porous indenter (Model 1: nine layers with strain-dependent permeability; Model 2: three layers with strain-dependent permeability; Model 3: single layer with strain-dependent permeability; Model 4: nine layers with constant permeability). ResultsModels 1 and 2 provided similar results with less than 3% difference in the peak effective stress, contact pressure, fluid pressure as well as fluid support ratio. However, Model 1 to Model 3 differed in stress and strain distribution patterns along depth over prolonged loads, which may provide an important insight into the highly inhomogeneous depth-dependent properties of cartilage. In addition, Model 1 with strain-dependent permeability demonstrated an enhanced capability on fluid pressurisation as compared with Model 4 which had constant permeability. ConclusionsA highly inhomogeneous fibril-reinforced biphasic model considering both depth-dependent and strain-dependent properties was developed in this study, in order to illustrate the effect of highly inhomogeneous properties on the mechanical behaviour of the articular cartilage. The number of layers in the models with depth-dependent properties should be selected according to the research questions and clinical demands. The model with strain-dependent permeability offers an enhanced capability on fluid pressurisation. In future studies, the proposed model could be adopted in cell-models to provide more in-depth information or in tissue-engineering to optimize the depth-dependent scaffold structure.

Evaluation of shear slip stress transfer mechanism for induced microseismicity at In Salah CO2 storage site

Stress transfer caused by injection-induced fault reactivation plays a significant role in triggering induced seismicity. This work aims to investigate to which extent the shear slip stress transfer mechanism might have contributed to a 4-month period of heightened microseismicity around one of the horizontal injection wells (KB-502) at the In Salah CO2 storage site. Building upon previous reservoir modelling and history matching work by the authors, coupled geomechanical and reservoir modelling of CO2 injection at KB-502 was carried out, featuring the explicit simulation of injection-induced fault reactivation and stress transfer, and the implementation of a strain-dependent permeability model to represent the fault hydrological behaviour. This approach allows a much-improved overall match to the field bottomhole pressures at KB-502 over the previous results, where fault zone reactivation and associated dynamic permeability behaviour were not considered, especially over the 4-month period of interest. Based upon the coupled modelling results, Coulomb stress changes were used to evaluate the potential for enhanced microseismicity related to CO2 injection-induced fault reactivation at KB-502. Analyses on the potential for microseismicity have shown that seismic events are likely to take place in both hydraulically connected regions and stress transfer influenced regions. The variation of computed Coulomb stress changes in near-fault areas compares favourably with the heightened field recorded seismicity during the period modelled. The integrated interpretation of microseismic monitoring and coupled geomechanics and reservoir modelling have suggested that the shear slip stress transfer mechanism was active and contributed to the occurrence of induced seismicity at In Salah.

The nuclear import of the transcription factor MyoD is reduced in mesenchymal stem cells grown in a 3D micro-engineered niche

Smart biomaterials are increasingly being used to control stem cell fate in vitro by the recapitulation of the native niche microenvironment. By integrating experimental measurements with numerical models, we show that in mesenchymal stem cells grown inside a 3D synthetic niche both nuclear transport of a myogenic factor and the passive nuclear diffusion of a smaller inert protein are reduced. Our results also suggest that cell morphology modulates nuclear proteins import through a partition of the nuclear envelope surface, which is a thin but extremely permeable annular portion in cells cultured on 2D substrates. Therefore, our results support the hypothesis that in stem cell differentiation, the nuclear import of gene-regulating transcription factors is controlled by a strain-dependent nuclear envelope permeability, probably related to the reorganization of stretch-activated nuclear pore complexes.

Compressive stress relaxation behavior of articular cartilage and its effects on fluid pressure and solid displacement due to non-Newtonian flow

In this study, we investigate the effects of the power-law index and permeability parameter on the deformation of soft tissue (articular cartilage) which is bathed in the non-Newtonian fluid under stress-relaxation in compression. Ramp displacement is imposed on the surface of hydrated soft tissue. Deformation of the tissue and the fluid pressure is examined for the fast and slow rate of compression. We have employed a linear biphasic mixture theory to develop a mathematical model for compressive stress-relaxation behavior of articular cartilage for non-Newtonian flow. Numerical results indicate that shear-thinning fluids induce less solid deformation and exhibit more fluid pressure as compared to shear-thickening fluids for fast and slow rate of compression. The results also show that linear permeability induces more deformation as compared to strain-dependent nonlinear permeability due to viscoelastic nature of articular cartilage.

Comparing mixed hybrid finite element method with standard FEM in swelling simulations involving extremely large deformations

Swelling involving (extremely) large deformations simulations have wide range of applications in biomedicine, tissue engineering and hygienic product design. Typically, standard FEM is used in which deformations and chemical potential are chosen to be the prime variables. On the other hand, mixed hybrid finite element method (MHFEM) featuring an additional independent variable field flux possesses local mass conservation property. Such a property has shown its success in Darcy’s type equations with heterogeneous permeability. In this work, we perform a full-round comparison between MHFEM and FEM in solving swelling problems involving large deformations. Specifically, based on the permeability distributions, the problems fall into three categories: constant permeability, strain-dependent permeability and permeability with a discontinuous interface. For each category, we compare the two methods in aspects like solution convergence robustness, deformation, chemical potential and flux field accuracy and computational cost. We conclude that MHFEM outperforms standard FEM in terms of solution convergence robustness and the accuracy of all three fields when a swelling problem involves discontinuous interface in permeability.

Visco-elastic behavior of articular cartilage under applied magnetic field and strain-dependent permeability

In the present article, we investigate the biomechanical response of a fiber reinforced solid matrix (soft tissue) saturated with an electrically conducting fluid. A constant magnetic field was exposed to the binary mixture of fluid and deformable porous solid. The governing mechanism of multiphasic deformation was based on the loading imposed at the rigid bony interface. The fluid flow through the cartilage network depends upon the rate of applied compression and strain-dependent permeability of the solid matrix. The components of the mixture were intrinsically incompressible; however, in the derivation of governing dynamics, the visco-elastic behavior of the solid and an interstitial fluid was developed. The continuum mixture theory was employed in modeling solid deformation and local fluid pressure. We incorporated strain-dependent permeability in the governing equations of binary mixture that was found in an early experimental study. The governing non-linear coupled system of partial differential equations was developed for the solid deformation and fluid pressure in the presence of Lorentz forces. In the case of strain-dependent permeability, a numerical solution is computed using the method of lines (MOL), whereas, the exact solution is provided when permeability is kept constant. Graphical results highlight the influence of various physical parameters on both solid displacement and fluid pressure.

Proteoglycans exert a significant effect on human meniscal stiffness through ionic effects

BackgroundProteoglycans contribute to mechanical stiffness in articular cartilage, aiding load transmission. The magnitude of the ionic contribution of proteoglycans to the stiffness of human meniscal tissue has not been established. MethodsThirty-six discs of human meniscal tissue were placed within a custom confined compression chamber and bathed in three solutions of increasing ionic concentration. Following a 0.3 N preload, at equilibrium, a 10% ramp compressive strain was followed by a 7200 s hold phase. A nonlinear poroviscoelastic model with strain dependent permeability was fitted to resultant stress relaxation curves. All samples were assayed for proteoglycan content. Model parameters were analysed using multivariate analysis of variance whilst proteoglycan content was compared using a univariate analysis of variance model. FindingsA significant difference (p < .05) was observed in the value of the Young's modulus (E) between samples tested in deionised water compared to those tested in solutions of high ionic concentration. No differences were observed in the zero-strain permeability or the exponential strain dependent stiffening coefficient. Proteoglycan content was not found to differ with solution; but was found to be significantly increased in the middle meniscal region of both menisci. InterpretationProteoglycans make a significant ionic contribution to mechanical stiffness of the meniscus, increasing it by 58% in the physiological condition. It is therefore critical that meniscal regeneration strategies attempt to recreate the function of proteoglycans to ensure normal meniscal function.

Characterization of breast tissue permeability for detection of vascular breast tumors: An in vitro study.

The biological tissue could be considered as a porous matrix filled with the interstitial fluid. The tumoral tissue has a different permeability from the healthy tissue. With regard to this knowledge, the main objective of the present study is to study the tissue permeability as a diagnostic parameter for the detection of breast cancer. To this end, the healthy and the cancerous specimens of the breast tissue are taken from 17 female cases. All cancerous tumors are in the vascular phase of the growth. The samples undergo a uniaxial compression test by a robotic system while the strain rate is set to remain unchanged. Using the stress and the strain rate data, the strain-dependent permeability is determined, which is an exponential function of the strain level. The permeability function is identified by the initial permeability at the zero compressive strain and a material constant. Results show that the initial permeability of the healthy breast tissue is significantly different from the corresponding value for the cancerous tissue. For all cancerous samples, the permeability is less than the healthy tissue samples; as 40-70% reduction in the initial permeability is observed compared to the healthy breast tissue. The evaluation of the permeability between the healthy and the cancerous specimens is accompanied by the biopsy reports and observing structural images of the specimens using environmental scanning electron microscope. Based on the results, the permeability is suggested to have a diagnostic application for the detection of vascular breast tumors.

Preliminary study on the feasibility of co-exploitation of coal and uranium

Both coal and uranium resources are found in the Dongsheng area which is located in the northern part of Ordos Basin, China with the coal seam below the uranium deposit. In this paper, we attempt to study the feasibility of co-exploitation of the coal seam and the uranium deposit. The permeability evolution in strata around the coal seam are selected as the key parameter indexing the separate and safe concurrent recovery of two deposits and a novel strain-dependent permeability model is proposed covering the full deformation range of rock. The proposed model is first verified with experimental data with good fitting of the results. Then an upscaled numerical model is established considering the geology conditions of Dongsheng area. This is implemented using COMSOL Multiphysics; and the interface of COMSOL with MATLAB is used to study the damage to the rock mass. We show that (a) compared with the stress-dependent permeability model, the strain-dependent permeability model proposed in this work has the advantage that each strain value is associated with a unique permeability value; (b) The feasibility of co-exploitation of the coal seam and the uranium deposit depends on the relative distance between two resources. When the caved and fractured zone encroaches on the uranium deposit the coal seam should be abandoned. Conversely, when the uranium deposit lays in the constrained zone, the recovery of the coal seam would benefit recovery of the uranium deposit; (c) The feasibility of the co-recovery of the two resources can be optimized by the choice of mining approach. The top-caving mining approach and room-and-pillar mining approach can reduce the height of the caved and fractured zones and make the co-exploitation of the uranium and coal feasible. This work provides a new approach to investigate the feasibility of co-exploitation of uranium and coal.