Papers by Keyword: Permeability

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Authors: Mohamed Chikhaoui, Dashnor Hoxha, Naima Belayachi, Ammar Nechnech
Abstract: This study concerns the ground soils of the second runway of the Es-Sénia airport in Oran (Algeria). This airport was built on a very complex hydro geotechnical site when underground cavities, following the dissolution of gypsum soil, were found during the before-construction geologic studies. Several, techniques are used in laboratory (Permeability, triaxial compression tests at various confining pressure, and hydric tests in saturated and unsaturated conditions) and for in situ it’s used the results of SPT and pressure-meter tests. A comparison of parameters of two soils identified in saturated and partially saturated conditions by in situ and laboratory tests was performed in order to respond to questions of the similarity of hydro mechanical properties of two soils as well as their statistical representativeness of the in-situ reality. It is found that, in respect to the studied parameters, laboratory results are statistically significant and reconstituted soils is statistically representative of natural soil reconstitution.
Authors: Chen Song Dong, Tuong Yung Tang
Abstract: A new empirical model for predicting the permeability of fiber mats is presented in this paper. Permeability data were collected from the NIST reinforcement permeability database and categorized according to the material architecture. It is seen from the data that for each category, permeability is proportional to fiber volume fraction. In order to describe the behavior of permeability vs. fiber volume fraction, the location, scale and shape parameters were introduced for each material category. The model was validated against the experimental data and good agreement was found.
Authors: Lu Jin, Zhu Ge Yan
Abstract: Porous concrete is one of the innovative and promising concrete products, which is featured with a relatively high water permeability rate. Compared with conventional concrete products, due to the lack of fine aggregates in the mix design of porous concrete, the void spaces between the coarse aggregates remains unfilled and causes a large amount of porosity in the hardened concrete mass. On the other hand, the strength of porous concrete is usually lower than that of the conventional concrete products due to the lack of fine aggregates. For the purpose of achieving a relatively high strength of porous concrete while maintaining a good permeability of pavements, the mix design of porous concrete is modeled as a Markov Chain Monte Carlo (MCMC) system and a Gibbs Sampling method based approach is developed to approximate the optimal mix design. The simulation results show that, by using the proposed approach, the system converges to the optimal solution quickly and the derived optimal mix design achieves the tradeoff between the compressive strength and the permeability rate.
Authors: Pierpaolo Carlone, Gaetano S. Palazzo
Abstract: Liquid Composite Molding processes are characterized by the impregnation of a dry fibrous perform by means of injection or infusion of a catalyzed resin. In recent years computational flow and cure models allowed for a remarkable time and cost compression in process planning with respect to trial and error procedures. In this contest multi-scale simulative approaches are gaining considerable attention and intriguing results have been recently presented. Most of the proposed models, however, rely on deterministic hypothesis, assuming perfect fiber packing and neglecting dimensional variations between fibers, in strong contrast with experimental observations. In this paper the influence of the stochastic variability of the fiber packing on tow permeability has been investigated by means of a CFD micro scale model. The variability of the microstructure defining the Representative Volume Element has been considered introducing random perturbations of the fiber packing. The components of the permeability tensor, in each case, have then been derived applying the Darcy model to flow simulations through the representative cell.
Authors: Meng Lu, Luke D. Connell
Abstract: This short note presents a discussion on the characteristic length that appears in dualporosity models for fractured geological media, via which the empirical characteristic diffusion time is defined. The physical meaning of it is further interpreted here from a more rigorous mathematical point of view, relating the so-called characteristic length or, equivalently, the characteristic time, to a statistically averaged quantity over a local representative volume element that contains numerous matrix blocks. Each of these matrix blocks will be of distinct characteristic lengths or times unless the geometrical shapes and sizes (in an effectively volume-equivalent way) of them are identical. Theoretically, those characteristic lengths could be statistically determined through measurement of their typical distributions. Thus, the discussion presented in this article may permit one to have greater insight into the nature of these two parameters, and may also allow a laboratory approach to measure them to be developed.
Authors: Fei Zhao, Chang Tao Sha, Gang Zhao, Ke Wang, Jin Song Kan
Abstract: A one-port waveguide method and related apparatus based on the multi-state techniques is descried in this paper. This method measures only the magnitude and phase information for the reflection coefficients of four-state before and after the samples under test being loaded. On the basis of such data, the complex permittivity and permeability of the samples can be simultaneous calculated by software programmed according to the related theories discussed herein. In addition, the error analysis is also discussed in this paper. The proposed method is applicable to measure magnetic and/or medium-to high-loss materials, hence it is suitable to characterize the properties of radar absorbing materials.
Authors: Fiorenza Quasso, Giovanni Consolati, M. Pegoraro, F. Severini
Authors: Abdulhamid Al-Abduljabbar
Abstract: Polymer-clay nanocomposites (PCNC), are characterized by the high ratio of surface area to volume of the clay nanoparticles which are in the form of clay platelets with very high aspect ratio. This feature provides superior gas barrier properties at very low volume fraction of the nanofiller. Clay platelets introduce discontinuity to flows through the bulk polymer matrix material. The extent of this improvement depends on the success of separation of clay layers during processing which would produce single-layer particles (exfoliation) or several-layer particles (intercalation) through the bulk polymer matrix. This paper discusses the common permeability models used to capture the effects of the clay nanofillers in PCNC. Since these models assume a state of full exfoliation of clay platelets; that is a single phase of the nanofiller, they fall short of representing the actual state as evidenced by experimental works, which confirm the presence of both the intercalated phase and the exfoliated phase. A model that incorporates clay inclusions with different sizes (different thicknesses) is proposed and its implications are assessed.
Authors: Jun Long Zhao, Da Zhen Tang, Hao Xu, Yan Jun Meng, Yu Min Lv
Abstract: With the analysis of key elements on the strain state of coal, a permeability dynamic prediction model which is divided by the critical desorption pressure for undersaturated coalbed methane (CBM) reservoirs was established on the basis of pore pressure and considering the matrix shrinkage effect of coal. The law between permeability and pore pressure was analyzed during production with the new model. Through case study, the rationality of the model was also verified. The research shows that the degree of permeability changes mainly depends on the relationship between the critical desorption pressure and the rebound pressure which depends on the strength of the matrix shrinkage. Under the condition of equivalent matrix shrinkage, the reservoirs permeability rebounds better with high Young's modulus and low Poisson's ratio. Adjustment factor contributes to improve the influence of matrix shrinkage on permeability and the larger the matrix shrinkage strength is, the higher the permeability rebounds. PM model and CB model are similar to the new model. PM model limits the matrix shrinkage strength, and CB model is a special case of the new model. Comparing with the well test permeability, the new model is more reasonable to characterize the matrix shrinkage effect in the development process.
Authors: Shu Ping Yi, Hai Yi Ma, Hua An Wang
Abstract: Near surface disposal of low and intermediate level radioactive waste (LILW) requires a detailed site investigation of the potential sites, in which the transport behavior of solutes in the groundwater system is one of the key processes that needed to be addressed. An investigation is undertaking for the disposal of LILW at a potential site in Southern China. In-situ test have been conducted to study the hydrogeologic characteristics of the site. Firstly, tests including pit permeability tests, injecting tests, water pressure tests, pumping tests and laboratory permeability tests have been performed according to the specific field conditions. Hydraulic conductivities for different layers of rock and soils have been calculated and their recommended values have been presented. And then in-situ dispersion tests have been performed at an area adjacent to the disposal site with non-sorbed tracers. A numerical model has been developed for the site based on data obtained during the site investigation, and has been calibrated with available measured groundwater level and measured tracer concentrations in the dispersion tests. Calibrated results indicate that the longitudinal dispersion coefficient is equal to 5.0×10-3 m2/d. Preliminary predictions have been performed for the groundwater flow and solute advection-dispersion behavior according to the design of the site, in which the center valley will be backfilled with low permeable materials. Predicted results indicate that the groundwater exhibits a lower water table and a smaller hydraulic gradient under designed site condition than under natural condition. All the tracers remain underground in the site and transport slowly mainly through advection and dispersion. Finally, conclusions for the study have been presented and the key tasks for future work have been discussed. This study provides an insight understanding of the hydrogeology characteristics of the disposal site and is useful for the assessment of environment impacts of the site under disposal of LILW.
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