Horizontal Barriers Research Articles

Analytical model for the design of in situ horizontal permeable reactive barriers (HPRBs) for the mitigation of chlorinated solvent vapors in the unsaturated zone

In this work we introduce a 1-D analytical solution that can be used for the design of horizontal permeable reactive barriers (HPRBs) as a vapor mitigation system at sites contaminated by chlorinated solvents. The developed model incorporates a transient diffusion-dominated transport with a second-order reaction rate constant. Furthermore, the model accounts for the HPRB lifetime as a function of the oxidant consumption by reaction with upward vapors and its progressive dissolution and leaching by infiltrating water. Simulation results by this new model closely replicate previous lab-scale tests carried out on trichloroethylene (TCE) using a HPRB containing a mixture of potassium permanganate, water and sand. In view of field applications, design criteria, in terms of the minimum HPRB thickness required to attenuate vapors at acceptable risk-based levels and the expected HPRB lifetime, are determined from site-specific conditions such as vapor source concentration, water infiltration rate and HPRB mixture. The results clearly show the field-scale feasibility of this alternative vapor mitigation system for the treatment of chlorinated solvents. Depending on the oxidation kinetic of the target contaminant, a 1m thick HPRB can ensure an attenuation of vapor concentrations of orders of magnitude up to 20years, even for vapor source concentrations up to 10g/m3. A demonstrative application for representative contaminated site conditions also shows the feasibility of this mitigation system from an economical point of view with capital costs potentially somewhat lower than those of other remediation options, such as soil vapor extraction systems. Overall, based on the experimental and theoretical evaluation thus far, field-scale tests are warranted to verify the potential and cost-effectiveness of HPRBs for vapor mitigation control under various conditions of application.

성능위주 소화설비 적용을 위한 표준랙크의 화재확산속도 평가

물품이 수직 집약적인 형태로 적재되는 랙크식 창고는 화재발생 시 화염의 급속한 상승으로 인해 그 피해가 매우 심각하다. 이에 ESFR 및 In-Rack 스프링클러, 수직 및 수평차단막 등, 다양한 소화설비 적용을 통해 화재확산 억제에 노력하고 있으나 랙크의 크기 및 적재밀도, 적재물품의 종류 등, 매우 다양한 구성조건으로 인해 적절한 소화설비 선정에 어려움이 있다. 이에 본 연구에서는 현장조사 및 설문조사 등을 통해 국내 랙크식 창고 실정을 반영한 표준랙크를 제작하였으며, 발화위치 조건에 따른 화재특성 확인을 위해 실규모화재시험을 수행하였다. 이를 통해 도출된 화재확산속도는 향후, 개발 및 적용 예정 소화설비들의 성능비교를 위한 기초자료로서 유용하게 활용될 것으로 기대한다. In case of fire, vertically and intensively loaded rack warehouses are faced with a severe status due to the rapid increase in fires. In this regard, there have been trials to prevent fires from spreading by applying fire extinguishing systems, such as ESFR and In-Rack Sprinklers, vertical and horizontal barriers, etc.; however, it is difficult to calculate and design proper fire extinguishing systems caused by various composition conditions, such as the size and loading density of the rack, types of loading commodities, etc. Therefore, in this study, a standard rack was manufactured, incorporating a rack warehouse in Korea by site investigations, surveys, etc. In addition, a full scale fire test was executed to check the fire characteristics depending on the conditions of the ignition points. As a result, the extracted fire spread speed is expected to be utilized as a reference for performance comparisons of the fire extinguishing systems to be developed and applied in the future.

Doğalgaz Boru Hatlarında Dalga Bariyeri olarak Yapay Ana Kayanın Dalga Yayılışına Etkisi

Earthquakes have destructive influences onto lifeline engineering and especially leading to considerable economic loss to the underground structure. Underground structures are significant unit of lifeline engineering. . Applying horizontal wave barriers is used in civil engineering as an alternative solution to reduce the soil vibrations in the wave propagation region and surrounding of the structures to be protected. In this study, discrete computer model including non-linear soil conditions as well as radiation damping is improved for testing corresponding wave propagation of earthquake vibrations in the soil under 1999 Kocaeli earthquake strong ground motion and mitigation of buried pipeline responses. Extensive parametric investigations by using the developed numerical model for isolation systems have been executed to conceive the influence of different controlling parameters on the screening efficiency. Results indicated that WIB are very promising as a cut off frequency isolators by reduction of * 70% and a promising candidate for future application in the field.

Homogenization and concentrated capacity for the heat equation with two kinds of microstructures: uniform cases

In the present article we investigate how geometric microstructures of a domain can affect the diffusion on the macroscopic level. More precisely, we look at a domain with additional microstructures of two kinds, the first one are periodically arranged “horizontal barriers” and the second one are “vertical barriers” which are not periodically arranged, but uniform on certain intervals. Both structures are parametrized in size by a small parameter \(\varepsilon \). Starting from such a geometry combined with a diffusion(-reaction) model, we derive the homogenized limit and discuss the differences of the resulting limit problems for various particular arrangements of the microstructures.

Multicomponent gas rising through water with dissolution in stratified porous reservoirs – Application to underground storage of H2 and CO2

The exact analytical solutions have been obtained for the problem of the gravity-driven rising of gas stored in a stratified aquifer. The practical objective is to retard gas rising in order to avoid its consecutive losses, which is ensured by low permeable horizontal barriers. The problem of gas rising through water is formulated as the Riemann problem for a system of first-order hyperbolic flow equations coupled with nonlinear algebraic equations describing the dissolution of chemical components in gas and water. The interaction of the forward front of gas with a barrier represents a collision between a shock wave and a medium discontinuity, which produces reverse shock waves and significantly retards gas rising. The method of solution is a combination between the method of characteristics and the technique of geometrical diagrams for coherent waves. The exact analytical solution was constructed for two- and three-component cases. The two-dimensional flow was studied numerically.

Carbon stable isotopes as indicators of the origin and evolution of CO2 and CH4 in urban solid waste disposal sites and nearby areas

Isotopic compositions of CH4 and CO2 surface and subsurface gases and groundwater from an urban solid waste disposal site from Gualeguaychu city (Argentina) were measured to detect origin, depth distribution, migration lateral, CH4 oxidation, and dissolution in groundwater. The highest CH4 concentrations (60–88 %) with δ13C-CH4 (between −60 and −45 ‰) and δ2H-CH4 (between −350 and −260 ‰) were attributed to CH4 originated by microbial sources, v. gr. acetate fermentation. The δ13C-CO2 related to this CH4 (between −15 and −5.9 ‰) were compatible with this process. Also, the increase of DIC associated to an increase in δ13C-DIC values (−12.4, −6.4, −5.8, −1.5, +0.1 and +4 ‰) indicated the transport of dissolved gases (from methanogenesis) in the groundwater flow system. High excess deuterium in 3 piezometers suggests that there were hydrogen isotope exchange between CH4 and water too. Evidences for CH4 oxidation were decrease in CH4 concentrations, shift in C and H isotope ratios of CH4 to more enriched in the remaining CH4 (in both, δ13C-CH4 >−50 ‰ and δ2H >−260 ‰) and depletion in 13C of the associated CO2 (<−20 ‰). Since surface CH4 and CO2 concentrations over the covering layer were very low, and the major CH4 concentrations were found between 60m and 90 cm depth, it is very probable USW has been compacted with low permeability materials (e.g., clay) avoiding large emissions to the atmosphere and creating horizontal barriers within the waste that enable lateral gas migration. Horizontally, it can be seen that these gases migrated outside the disposal site following the topography and that CH4 disappeared leading to anomalous concentrations of CO2 whose values are greater than those produced by normal soil respiration. The isotopic value (δ13C) of this CO2 was also different from that of normal soil respiration (~−25 ‰) and reflected effects that generated isotopic depletion by diffusion (~−25 to −32 ‰). The analysis of C isotopes as the main tracer, together H isotopes, has allowed the effective detection of the origin and those secondary processes.

Numerical Analysis of Horizontal Moisture Barriers in Pavements Constructed on Expansive Soils

Expansive soils experience large volume changes during the process of drying and wetting, and thus cause many problems to civil infrastructure such as roughness and cracks in pavements and uneven settlements in light-weight structures. Horizontal moisture barriers have the potential to keep the water content stable under the covered areas by increasing the length of water diffusion. The analysis and design of horizontal moisture barriers are currently based mostly on experience and empirical methods, and for instance, the influence of cracks developing outside the covered area on the performance of moisture barriers has not been investigated in detail.In this paper, the effects of parameters including unsaturated diffusion coefficient and drying times are analyzed using analytical and numerical methods. Variation of suction and settlement due to the shrinkage of the soil beneath and within the close proximity of the pavement (or covered area) are determined to evaluate the performance of moisture barriers. By comparing the changes of suction and settlement in a parametric study, the contributions of diffusion coefficient and drying times on the performance of moisture barriers are studied. An important parameter exerting critical effect on the performance of moisture barriers is the development of cracks forming outside the covered areas as a result of drying shrinkage. Outside the covered areas, shrinkage cracks can easily initiate and propagate during the drying time, and then become pathways for water infiltration and evaporation. The paper investigates the effects of outside cracks on the performance of moisture barriers.The analysis indicates that the performance of horizontal moisture barriers not only depends on the soil properties, but also depends on the climatic effects. For the same moisture barriers installed in different climatic zones whose soil properties are exactly the same, the performance of the barriers may be different because of the different drying times depending on the climate. The analysis also shows that the performance of horizontal moisture barriers is significantly degraded in the presence of the outside cracks. When the depth of outside crack reaches a specific value, the function of the horizontal moisture barriers can significantly be diminished.

A winter chlorophyll bloom analyzed using Lagrangian diagnoses in the northeastern South China Sea

The Finite Time Lyapunov Exponent technique is a highly effective way to visualize and analyze flow fields. Its ridges are referred to as Lagrangian Coherent Structures which reveal the transport barriers of fluid systems, or their hidden skeletons. This allows us to investigate the complex mesoscale and submesoscale ocean processes on a Lagrangian view. In this article, we use the Lagrangian technique to investigate one chlorophyll bloom event in the northeastern South China Sea and discuss the impact of horizontal transport on the distribution of surface chlorophyll. Our results demonstrate that horizontal transport barriers uncovered by Lagrangian Coherent Structures can shape the vortex and filament in a simple and distinct way.

Effect of horizontal wave barriers on ground vibration propagation.

The aim of this article is to introduce a method to mitigate ground surface vibration through a flexural plate coupled to the ground and acting as a horizontal wave barrier. Using the thin plate hypothesis, two flexural plates are coupled to the ground, the first plate being the excited plate and the second plate the horizontal wave barrier. For instance, the first plate may represent a slab track and be excited by the tramway wheels. A solution to the problem can be found using a spatial two-dimensional Fourier transform of the elastodynamics equation for the ground and a modal decomposition for the flexural plate vibration. The authors show that vibration is substantially mitigated by the horizontal wave barrier and depends on its thickness and width. When the top surface wavelength becomes smaller than twice the plate width, the horizontal wave barrier acts as a wave barrier in the frequency range of interest, i.e., from 20 Hz.

Evaluation of a horizontal permeable reactive barrier for preventing upward diffusion of volatile organic compounds through the unsaturated zone

Permeable reactive barriers are commonly used to treat contaminant plumes in the saturated zone. However, no known applications of horizontal permeable reactive barriers (HPRBs) exist for oxidizing volatile organic compounds (VOCs) in the unsaturated zone. In this study, laboratory column experiments were carried out to investigate the ability of a HPRB containing solid potassium permanganate, to oxidize the vapors of trichloroethylene (TCE), toluene, and ethanol migrating upward from a contaminated saturated zone. Results revealed that an increase in initial water saturation and HPRB thickness strongly affected the removal efficiency of the HPRB. Installing the HPRB relatively close to the water table was more effective due to the high background water content and enhanced diffusion of protons and/or hydroxides away from the HPRB. Inserting the HPRB far above the water table caused rapid changes in pH within the HPRB, leading to lower oxidation rates. The pH effects were included in a reactive transport model, which successfully simulated the TCE and toluene experimental observations. Simulations for ethanol were not affected by pH due to condensation of water during ethanol oxidation, which caused some dilution in the HRPB.

Comprehensive Care of High-risk Pregnancy for Reducing Maternal Mortality - A Proposal to Establish a Korean Pregnancy and Birth Registry –

This study aims at modeling boundary layers (BLs) encountered in sparse and built environments (i.e., open, suburban and urban) at the subsonic Wind Tunnel (WT) at Ryerson University (RU). This WT has an insignificant turbulence intensity and requires a flow-conditioning system consisting of turbulence generating elements (i.e spires, roughness blocks, barriers) to achieve proper turbulent characteristics. This system was developed and validated in the current study in three phases. In phase I, several Computational Fluid Dynamic (CFD) simulations of the tunnel with generating elements were conducted to understand the effect of each element on the flow. This led to a preliminary design of the system, in which horizontal barriers (slats) are added to the spires to introduce turbulence at higher levels of the tunnel. This design was revisited in phase II, to specify slat dimensions leading to target BLs encountered by tall buildings. It was found that rougher BLs require deeper slats and, therefore, two-layer slats (one fixed and one movable) were implemented to provide the required range of slat depth to model most BLs. This system only involves slat movement to change the BL, which is very useful for automatic wind tunnel testing of tall buildings. The system was validated in phase III by conducting experimental wind tunnel testingof the system and comparing the resulting flow field with the target BL fields considering two length scales typically used for wind tunnel testing. A very good match was obtained for all wind field characteristics which confirms accuracy of the system.

The Effectiveness of Horizontal Barriers in Preventing Fire Spread on Vertical Insulation Panels Made of Polystyrene Foams

Expanded polystyrene (EPS) and extruded polystyrene (XPS) foams are both excellent exterior thermal insulation materials for buildings. However, their flammability also induces high fire hazard. Current regulation in China requires horizontal fire barriers with a minimum height of 30 cm when polystyrene foams are used as the external insulation. The present work evaluates the effectiveness of such barriers in inhibiting fire growth in insulation walls. The walls were made of B2 grade EPS and XPS foams without protective coatings but with mineral wool as horizontal barriers. Altogether six combinations of fire positions and barrier positions were tested for both EPS and XPS. The heat release rate (HRR) of the fire and the temperature distribution on the wall were recorded and analyzed. The results indicate that, without a barrier, fire starting at the middle of the wall generated higher peak HRR than that starting at the bottom, which was in turn higher than that starting at the top. When the insulation panel below the barrier was 1 m high, the upward fire spread from the bottom could be stopped by 40-cm, but not 30-cm, barriers. However, when the insulation panel below the barrier was 2 m high, even the 40-cm barriers failed. Lastly, the downward fire spread from above could not be stopped by 40-cm barrier due to dripping of burning plastics. The study highlights the limitations of horizontal fire barriers in preventing the vertical fire spread over exposed B2 grade polystyrene insulation and establishes protocols for further investigations.

Toward 5G: when explosive bursts meet soft cloud

Rapid growing demand for mobile data traffic challenges capacities and service provision in the next-generation (5G) cellular networks. Real measurement data from operating cellular networks indicates that the traffic models and scenarios disobey our traditional assumptions (i.e., expressing bursty nature). As a result, current network architectures and service management may cause experience deterioration of subscribers in future networks. In this article, we propose three approaches to alleviate the influence of various traffic bursts: baseband resource pool on a cloud platform as wireless infrastructure to enhance the capacity and flexibility of networks, cloud core networks to provide dynamic extension and service flow control abilities, and software-defined bearer networks to simplify service delivery instructed by core networks. Different from conventional stovepipe-like cloud computing network architectures, our proposed architecture interconnects and shares information between entities, breaking through horizontal device barriers and vertical layers. These cloud-based approaches not only avoid the potentially negative impact of bursts, but also provide a software-controlled end-to-end service management framework for future cellular networks. In addition, by taking advantage of open interfaces of cloud-based network elements, service control algorithms and network APIs could also be implemented to realize smart and soft 5G cellular networks.

Convective mixing in formations with horizontal barriers

It has been shown that convective mixing in porous media flow is important for applications such as saltwater intrusion and geological storage of carbon dioxide. In the latter case, dissolution from the injected phase to the resident brine is assisted by convective mixing, which leads to enhanced storage security through reduced buoyancy. Here, we focus on the effect of horizontal barriers on the efficiency of convective mixing. Previous investigations of the effect of heterogeneity on mixing efficiency have focused on random permeability fields or barriers of small extent compared to the intrinsic finger wavelength. The effect of horizontal barriers of larger extent, such as mudstone inclusions or thin shale deposits, has not been given sufficient attention. We perform detailed numerical investigations to represent the continuous solution of this problem in semi-infinite domains with barriers arranged in a periodic manner. The results show that mass flux into the domain, which is a measure of the efficiency of redistribution of the solute, is inversely proportional to the barrier length and proportional to the horizontal and vertical aperture between the barriers, for the cases studied. The flow structure is complex, and it depends not only on the total area of barriers but also largely on the distribution of barriers. Therefore, neither simple analytical models nor simple upscaling methods that lack information about the flow paths, can be used to predict the behavior. However, we compute the effective vertical permeability by flow-based upscaling and show that it can be used to directly obtain a first-order approximation to the mass flux into the domain.

The use of a biodegradable chelator for enhanced phytoextraction of heavy metals by Festuca arundinacea from municipal solid waste compost and associated heavy metal leaching

In a column experiment with horizontal permeable barriers, the effects of a biodegradable chelator-nitrilotriacetic acid (NTA) on the uptake of heavy metals from municipal solid waste (MSW) compost by Festuca arundinacea and metal leaching were investigated. The use of NTA was effective in increasing Cu, Pb, and Zn uptakes in shoots of two crops of F. arundinacea. In columns with barriers and treated with 20mmol NTA per kg MSW compost, metal uptakes by the first and second crop of F. arundinacea were, respectively, 3.8 and 4.0times for Pb, and 1.8 and 1.7times for Zn greater with the added NTA than without it. Though NTA application mobilized metals, it caused only slight leaching of metals from MSW compost. Permeable barriers positioned between compost and soil effectively reduced metal leaching. NTA-assisted phytoextraction by turfgrass with permeable barriers to cleanup heavy metal contaminated MSW compost should be environmentally safe.

Experimental Analyses of Athabasca Bitumen Properties and Field Scale Numerical Simulation Study of Effective Parameters on SAGD Performance

Due to reduction of high quality oil resources and consequently increase of oil price around the world, new sources of energy should be find to relief the high demand of energy. Hence, countries like Venezuela, United States and particularly Canada came up with their unconventional reservoirs which contain bitumen, extra heavy oil and heavy oilas remarkable sources of energy. Exploitation of such kind of reservoirs was not beneficial in the past but in recent years due to the increase of oil price tendency to production from heavy oil reservoirs has incredibly increased. This paper introduces experimental measurement of Athabasca heavy crude oil properties and simulation study in a field conditions. The first-hand target of the performed study isto scrutinize and evaluate the performance and capability of steam-assisted gravity drainage (SAGD) process which is the greatest applicable thermal processes in tar sand reservoirs. The results show great recovery of heavy oil and reasonable amount of cumulative steam-oil ratio (CSOR). Sensitivity analyses have been done to realize the influence of different parameters on proficiencyof SAGD in the field. The significance of parameters such as permeability both in horizontal and vertical direction, horizontal and vertical shale barriers, injection rate, porosity, injector location, viscosity, preheating period, horizontal well length and steam quality were studied. Higher vertical and horizontal permeability, injection rate and steam quality have positive effect on oil production while Lower porosity, absence of preheating period and higher injection rate have adverse effects on SOR. Preheating period has impact on SOR at the start of the process. In fact without preheating period the amount of SOR at the start of process is very high. Horizontal shale barrier has more negative effect on oil production than vertical shale barriers. Locating injector close to the horizontal production well has nugatory impact. The shorter the length of horizontal wells the lower the recovery of oil. This work explains the aforementioned effects in details.

Long range transport of a quasi isolated chlorophyll patch by an Agulhas ring

Using satellite retrievals of sea surface chlorophyll and geostrophic currents we study the evolution of a distinct chlorophyll patch transported by an Agulhas ring along a ˜1,500 km track. Throughout an ˜11 months period of the total 2 years eddy lifetime, the shape of the chlorophyll patch is consistently delimited by the horizontal transport barriers associated with the eddy. Analysis of Lagrangian time series of sea surface variables in and around the eddy suggests that the evolution of the chlorophyll patch is driven by two processes (i) slow lateral mixing with ambient waters mediated by horizontal stirring in filaments, and (ii) rapid events of wind induced vertical mixing. These results support the idea that mesoscale eddies shape biological production through the combination of horizontal and vertical dynamical processes, and emphasize the important role of horizontal eddy transport in sustaining biological production over the otherwise nutrient-depleted subtropical gyres.

Characterization and interpretation of discontinuity surfaces in a Jurassic ramp setting (High Atlas, Morocco)

AbstractDiscontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings. In sedimentary systems, these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record. From an applied perspective, discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization. Here, a total of 80 condensed surfaces (S1), firmgrounds (S2) and hardgrounds (S3) from a Jurassic (Middle and Upper Bajocian Assoul Formation) ramp setting of the High Atlas in Morocco are carefully documented with respect to their morphology, their secondary impregnation by Fe and Mn oxides and phosphates and their palaeoecological record. A statistical frequency distribution of two surfaces of the S1 type, 1·1 surfaces of the S2 type and 0·4 surfaces of the S3 type per 10 section metres is observed along a 220 m long carbonate succession. Based on two stratigraphically and spatially separated study windows and correlative sections, the stratigraphic frequency distribution, the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner. Specific features of the study site include the considerable stratigraphic thickness of the Assoul Formation and the conspicuous absence of subaerial‐exposure‐related features. Based on the data presented here, firmground and hardground surfaces are best interpreted as maximum‐regression‐related features. Relative sea‐level lowstand results in a lowered wave base, and wave orbitals and currents result in sea floor omission and lithification. Care must be taken to avoid overly simplistic interpretations, as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal–distal transects. The data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models.

Second-order wave diffraction by horizontal rectangular barriers

A complete second-order analytical solution for the nonlinear diffraction of waves by 2-D rectangular cylinders fixed at the free surface of finite-depth waters is presented. As a sequel to a previous linear treatment of the same problem, the present study revisits the nonlinear wave diffraction modelling in 2-D, in which a series of boundary value problems are built up by a classical perturbation expansion. Particular solution for the second-order potential is derived by means of a Fourier integral theorem, whilst the homogeneous second-order solution is obtained in a way similar to that of the linear problem. The present solution is validated by comparisons with experiments as well as with previous computational results of various researchers.

Seismic waves and seismic barriers

The basic idea of seismic barrier is to protect an area occupied by a building or a group of buildings from seismic waves. Depending on nature of seismic waves that are most probable in a specific region, different kinds of seismic barriers are suggested. For example, vertical barriers resembling a wall in a soil can protect from Rayleigh and bulk waves. The FEM simulation reveals that to be effective, such a barrier should be (i) composed of layers with contrast physical properties allowing “trapping” of the wave energy inside some of the layers, and (ii) depth of the barrier should be comparable or greater than the considered seismic wave length. Another type of seismic barrier represents a relatively thin surface layer that prevents some types of surface seismic waves from propagating. The ideas for these barriers are based on one Chadwick’s result concerning non-propagation condition for Rayleigh waves in a clamped half-space, and Love’s theorem that describes condition of non-existence for Love waves. The numerical simulations reveal that to be effective the length of the horizontal barriers should be comparable to the typical wavelength.