Vertical Barrier Research Articles

Study on the performance of sealing slurry at the bottom of geomembrane composite vertical cut off walls

At the bottom of the geomembrane cut-off walls, pollutants may seep out through the bottom gap between the geosynthetic membrane and the low-permeability bedrock, contaminating the groundwater and the surrounding environment. Therefore, to address the occurrence of bottom gap seepage, this study adopts a mixture of attapulgite and cement in a certain proportion, mixed and stirred to form a sealing material. This sealing material is used to connect the bedrock and the geosynthetic membrane, thereby creating an efficient composite vertical barrier with special containment capacity. A series of laboratory experiments were conducted to investigate engineering properties of cement-attapulgite sealing slurry, including flow value tests, unconfined compressive strength (UCS) tests, improved flexible wall permeability tests, and bedrock and sealing slurry adhesion tests. The results show that the flow value of the slurry decreases with the increase of attapulgite content, and it increases with the increase of water-cement ratio. The UCS strength increases with the increase of attapulgite content, and it decreases with the increase of water-cement ratio, but the range of change is different. The hydraulic conductivity measured with hexavalent chromium solution as the penetrant is less than 50 % higher than that measured with water as the penetrant, and hexavalent chromium solution has little effect on the hydraulic conductivity of sealing slurry. The bonding performance between sealing slurry and bedrock is satisfactory, and the hydraulic conductivity of bedrock-sealing slurry is less than 1 × 10−7 cm/s (28d curing age), it is concluded that use of cement-attapulgite sealing slurry as bonding material between bedrock and geomembrane meets the engineering design requirements.

Effect of distance of vertical barrier wall and release temperature on the hydrogen jet flame width and temperature distribution induced by impingement of ignited release of cryogenic hydrogen

Cryogenic storage option is one of the important ways of storing hydrogen, but under-expanded ignited releases of cryogenic hydrogen could easily lead to jet fires, causing serious damage to people and properties. Barrier walls are important means to reduce the severity of cryogenic hydrogen jet flames, however, its effect on the cryogenic hydrogen jet flame and related temperature distribution are still unclear. In this work, the effect of the distance of barrier wall (0.20, 0.25, 0.30, 0.35 and 0.40 m) and release temperature (140, 180, 220, 260 and 300 K) on the hydrogen jet flame width and temperature distribution is investigated experimentally. It is found that the flame width in the horizontal and vertical direction and the temperature on the vertical barrier wall increase with the decrease of the distance to the nozzle and release temperature. The normalized flame width and inverse excess maximum temperature on the barrier wall increases linearly with the scaled distance considering nozzle diameter and release temperature. The temperature distribution is normalized as Gaussian distribution both in the horizontal and vertical direction, while the excess temperature is higher upward than that of downward. The results can provide a theoretical basis and data support for the blocking of jet fires formed by cryogenic hydrogen ignited releases.

Continental Scale Hydrostratigraphy: Basin-Scale Testing of Alternative Data-Driven Approaches.

Integrated hydrological modeling is an effective method for understanding interactions between parts of the hydrologic cycle, quantifying water resources, and furthering knowledge of hydrologic processes. However, these models are dependent on robust and accurate datasets that physically represent spatial characteristics as model inputs. This study evaluates multiple data-driven approaches for estimating hydraulic conductivity and subsurface properties at the continental-scale, constructed from existing subsurface dataset components. Each subsurface configuration represents upper (unconfined) hydrogeology, lower (confined) hydrogeology, and the presence of a vertical flow barrier. Configurations are tested in two large-scale U.S. watersheds using an integrated model. Model results are compared to observed streamflow and steady state water table depth (WTD). We provide model results for a range of configurations and show that both WTD and surface water partitioning are important indicators of performance. We also show that geology data source, total subsurface depth, anisotropy, and inclusion of a vertical flow barrier are the most important considerations for subsurface configurations. While a range of configurations proved viable, we provide a recommended Selected National Configuration 1 km resolution subsurface dataset for use in distributed large-and continental-scale hydrologic modeling.

Evaluating the Impact of Inclined Cutoff-Wall to Control Seawater Intrusion in Heterogeneous Coastal Aquifers

Subsurface physical barriers have been effectively used to mitigate seawater intrusion (SWI). Traditionally, the primary emphasis in both numerical studies and practical implementations has been on vertical barriers. The current research aims to explore the dynamics of SWI under various cutoff-wall inclination angles and depths, as well as aquifer heterogeneity using both experimental and numerical simulations. The impact of aquifer characteristics was assessed by utilizing a low hydraulic conductivity (K) aquifer (case L), a high hydraulic conductivity aquifer (case H), and two stratified aquifers. The stratified aquifers were created by grouping different hydraulic conductivity layers into two cases: high K above low K (case H/L) and low K above high K (case L/H). The model simulations covered seven different cutoff-wall inclination angles: 45.0°, 63.4°, 76.0°, 90.0°, 104.0°, 116.6°, and 135.0°. The maximum repulsion ratio of SWI wedge length was observed at an inclination angle of 76.0° for cutoff-wall depth ratios up to 0.623. However, as the depth ratio increased to 0.811, the maximum repulsion ratio shifted to an angle of 63.4° for all aquifers studied. At an inclined cutoff depth ratio of 0.811, the cutoff-wall inclination angle of 45.0° had the most significant impact on the saltwater wedge area. This results in SWI area reductions of 74.9%, 79.8%, 74.7%, and 62.6% for case L, case H, case H/L, and case L/H, respectively. This study provides practical insights into the prevention of SWI. Nevertheless, a thorough cost–benefit analysis is necessary to assess the feasibility of constructing inclined cutoff-walls.

Water wave scattering by two vertical porous barriers over a rectangular trench

Water wave scattering by two vertical porous barriers over a rectangular trench

Research on the Effect of Sand Barriers on Highways in Desert Areas on Sand Control

Sand barriers are one of the essential measures used to prevent wind and sand disasters on expressways in desert areas. The article uses Fluent numerical simulation to consider different heights, as well as different spacing from two perspectives, and determine the ideal vertical height of sand barriers (porosity is fixed at 20%). Adding to existing wind and sand flow field research, our analysis of the wind speed and sand characteristics reveals the changing rules that affect a single group of high vertical sand barriers along the highway when considering different parameters and measuring the wind and sand performance. At the same time, we also use field research to verify the accuracy of numerical simulation. The study shows the following. (1) When the airflow passes through the single group of vertical sand barriers, it will form a deceleration zone, acceleration zone, turbulence zone and stabilization zone in different areas, and the overall distribution of the wind and sand flow field is in the shape of a “W”. (2) When the spacing is 4 H, the maximal wind speed in the transition area of the sand barriers is two to three times bigger than that when the spacing is 2 H, which is not conducive to the accumulation of sand particles. When the spacing is 1 H, the maximum wind speed of the two rows of sand barriers is two to three times bigger than that when the spacing is 2, and the two rows of sand barriers overlap in wind protection performance, reducing the overall protective capacity of the sand barriers. (3) As the height of the sand barriers continues to grow, the protective performance of the sand barriers is also enhanced. In the same position around the sand barriers, the wind speed under the 2.5 m sand barriers is lower than that under the 1.0 m sand barriers by 2–3 m/s. It is suggested that the height of the sand barriers should be controlled at 1.5–2.0 m in the actual deployment, and 2 H spacing should be used.

Oblique waves interaction with an array of perforated co-centric arc-shaped vertical barriers with a narrow gap

The purpose of this paper is to investigate the interaction between oblique waves and a circular array of perforated co-centric vertical barriers mounted at the bottom. In particular, the hydrodynamic performance of barriers is examined as a function of the width of narrow gaps. The investigation was conducted using a semi-analytical approach based on the Boundary Element Method (BEM) by taking into account linear regular waves and potential flow theory. In the solution approach, the BEM-related near singular integrals were calculated indirectly by using the mathematical relationship between Bessel functions. The model was validated by comparing the results with those obtained in previous studies. The effect of geometric parameters, permeability, gap dimension, and wavenumber on wave force and wave strength downstream has been studied. In order to demonstrate the practical application of the developed model, it was implemented on a circular arc-shaped permeable barrier with a narrow gap and a circular offshore tidal lagoon equipped with a netting entrance gate suitable for marine fish farming. It was found that barrier performance was significantly reduced in the presence of a narrow gap. The results of this research provide insight into the interaction between waves and circular permeable barriers.

Unsteady free surface flow due to a line sink at an arbitrary location with surface tension

The unsteady flow generated when a line sink is located at an arbitrary location beneath the free surface of a fluid of finite depth is considered. Interest is in the evolution to a steady state flow, splashing flows and the drawdown of the surface. The location of the sink away from, but near to, a vertical barrier leads to some interesting new surface flows due to interactions and reflection, some of which have a profound impact on the nature of the critical drawdown flow parameters. Interesting new solutions with a delayed drawdown that are initiated by a reflected wave are presented. A linearized solution and a fully nonlinear solution are presented and the results discussed. Regions of steady, unsteady and supercritical flow are identified.

Laboratory studies of the impact of non-breaking waves on a horizontal emerged deck

The horizontal elements of maritime structures are susceptible to both wave impact and resulting vibrations. These vibrations can lead to a partial or complete failure of structures and require detailed investigations. To address this issue, laboratory experiments were conducted in a wave flume. The aim of this study was to investigate the problem of standing wave impact underneath a horizontal deck. The main focus was on the effect of the wave-induced vertical forces on the global response of the structure. The physical model of the deck was installed above a still water level in front of a vertical barrier. The model was supported by a system of strings and springs. The mechanical system had one degree of freedom corresponding to a small rotational displacement around rear deck edge. Among other physical parameters, the impact pressure generated under the structure due to wave impact was measured. The high sampling frequency of the data acquisition system allowed to capture momentary slamming pressure. The systems of accelerometers and displacement gauges were installed to measure induced vibrations. Thorough analysis of the influence of wave parameters and the deck clearance on the structure response was performed based on the measurements. The rapid slamming force increase, recorded at the moment of impact is not revealed in the dynamic response of the plate.

Analytical solutions for transport of organic solutes in multi-layered porous media

In this study, analytical solutions for one-dimensional transport of organic solutes in multilayered porous media are developed using the methods of matrix transfer and variable separation, where multiple factors such as advection, diffusion, mechanical dispersion, adsorption, degradation, boundary condition type and change in concentration are systematically incorporated for the first time. Compared with the existing analytical solutions solved by the techniques of integral transformation or Laplace transformation, the approaches adopted in this paper are simpler and have a quicker convergence speed. Also, the proposed analytical solutions are more practical with clear expressions and consideration of multiple factors, which can be applied to various engineering cases such as bottom liner systems at landfills, covering systems of contaminated sediments and vertical barrier systems in contaminated sites. Furthermore, the correctness of the derived analytical solutions is effectively validated by comparison with the experimental results, as well as with the existing analytical solution and a numerical method. Following this, the effects of different factors on the transport process of a single organic solute in a five-layered medium are investigated, and some novel and vital laws are obtained. Overall, this research contributes to appropriate evaluation of the transport behaviours in multilayered porous media.

Effect of polyanionic cellulose modification on hydraulic and consolidation performance of sand-calcium bentonite slurry trench cutoff walls

Sand-bentonite slurry trench cutoff wall is one of the most common vertical barriers to retard the migration of contaminants. This study aimed to explore the hydraulic and consolidation performance of cutoff-wall materials containing polyanionic cellulose (PAC)-modified calcium bentonite (CaB) through a comprehensive laboratory investigation. First, physicochemical properties tests were conducted to demonstrate the superiority of PAC-CaB over CaB. Subsequently, modified fluid loss tests were conducted to investigate the effects of PAC modification and CaCl2 solution concentration on the chemical compatibility of CaB cake formed during slurry trench protection. Finally, slump, Atterberg limit, oedometer, and rigid/flexible-wall hydraulic conductivity tests were performed to evaluate the effect of PAC modification on the hydraulic conductivity (k) and compressibility of sand-CaB backfill. The results indicate that PAC can significantly enhance the impermeability of CaB cake when permeated with salt solutions. The 4 %PAC-CaB cake in 40 mM CaCl2 solution had the lowest k value (9.3 × 10−10 m/s), and was therefore recommended as the optimum proportion for trench protection. The addition of PAC considerably reduced the consolidation coefficient of CaB backfill and increased its compression index and swell index. Moreover, with the increase of PAC dosage from 0% to 0.2%, 0.4%, and 0.8%, the k values of CaB backfill decreased by 0.75, 0.96, and 1.29 orders of magnitude, respectively. The k values of PAC-CaB materials were lower than those of sodium bentonite materials, indicating that PAC is a promising modifier to achieve a low k value of CaB cake and sand-CaB backfill for slurry cutoff walls.

Visual access to an outdoor range early in life, but not environmental complexity, increases meat chicken ranging behavior

Not all chickens access an outdoor range when the opportunity is provided. This may be related to the abrupt change in environments from the stable rearing conditions to the complexity of the outdoor range. We aimed to prepare chickens to range by increasing the complexity of the indoor environment early in life with the intention to encourage range use. Mixed sex Cobb500 chickens were allocated to 1 of 3 treatment groups: visual access (VA) treatment provided VA to the outdoor range from day old via transparent pop-hole covers; environmental complexity (EC) treatment provided an artificial haybale, fan with streamers and a solid vertical barrier; Control treatment was a representative conventional environment. Chickens were given access to the outdoor range at 21 d of age. Behavior in the home pen was assessed in wk 1, 2 and 5 and individual ranging behavior was monitored through radio frequency identification (RFID) technology. The VA chickens were more active compared to EC (P = 0.006) and Control (P = 0.007) chickens and spent more time foraging than control chickens (P = 0.036) during the first week of life. More VA chickens accessed the range area compared to EC chickens (P = 0.015). VA chickens accessed the range sooner after they were first provided access and spent more time on the range than EC and control chickens (P < 0.001). Mortality was lower in the VA treatment compared to EC (P = 0.024) and control group (P = 0.002). There was evidence that VA chickens weighed less than Control and EC chickens, however results were inconsistent between age and sex. Hence, providing meat chickens with VA to an outdoor range early in life increased activity in early life, decreased latency to first access the range and increased time on the range and lowered mortality. Future work should aim to understand the mechanism behind these changes in behavior to develop recommendations for producers to implement in commercial conditions.

Centrifuge modelling of ground vibrations mitigation by inclined geofoam barrier

This paper presents a centrifuge study on the performance of inclined geofoam barriers compared to a vertical geofoam barrier for the mitigation of ground vibrations induced by high-speed railways. Three different barrier inclinations (60°, 90° and 120°) are used in three centrifuge models. Each centrifuge model is tested for seven different frequencies. Therefore, the results of 21 centrifuge tests are reported in this paper. The results show that the barrier efficiency (BE) of inclined barriers is greater than the vertical BE for the points located behind the barrier. However, for a point located before the barrier, the BE reduces by using inclined barriers instead of the vertical barrier. The results also illustrate that the barrier efficiencies for the two inclined barriers used in this research, which have supplementary angles, are almost the same.

Electrical Properties of Ga2O3 Schottky Barrier Diodes with and without Mesa Structure

Devices based on wide bandgap (WBG) semiconductors like silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) are ideal for high-power electronics in harsh environments. Among the WBG semiconductors, ultrawide bandgap (UWBG) β-phase gallium oxide (Ga2O3), EG ≈ 4.8 eV, is emerging as a replacement for the current commercially available wide bandgap (WBG) power electronics due to its generational improvements in performance and manufacturing cost [1]. Ga2O3 has a high theoretical breakdown electrical field of 8 MV/cm which in turn gives its Baliga’s figure of merit for power devices that is larger than other WBG materials. The availability of high-quality Ga2O3 substrates produced from melt-grown bulk single crystals also facilitates the development of vertical power devices.In the current stage, the vertical Schottky barrier diode (SBD) with Ga2O3 can have an improved current spreading effect when compared to power diode devices from Si, SiC, and GaN. Especially, the Ga2O3 is expected to surpass the trade-off relationship between breakdown voltage (BV) and on resistance (Ron,sp) that other materials have [2]. Nevertheless, the Ga2O3 vertical SBD still cannot achieve the theoretical breakdown electric field. One of the key topics for WBG semiconductors application is a structure for improved electrical management such as field rings, junction termination extension, and field plates to reduce the leakage current in the reverse bias state.Here, we investigate the characteristics of Ga2O3 SBDs with and without mesa structure in extreme environments at high and low temperature. Conventional and mesa Ga2O3 SBDs were fabricated on the halide vapor phase epitaxy (HVPE) grown β-Ga2O3 (001). A Sn-doped substrate with 61016 cm-3 was used for the HVPE growth. In the SBD with mesa structure, the circular mesa with a diameter of 162 μm and a depth of 500 nm was formed around anode electrodes. The Ti/Au metal stack on the back side of the substrate acted as a cathode and the anode electrode deposited Ni/Au/Pt layers. After the fabrication process, current-voltage (I-V) measurements were performed on the SBDs between -5 V and 1 V. From the results, the values of Ron,sp at 0.7 V are 46.4 Ω•cm2 and 46.2 Ω•cm2 in conventional and mesa SBDs, respectively. And additionally, the leakage current at -5 V is reduced by approximately 44.3% in the mesa structure. To obtain the Schottky barrier height (SBH) from I-V and capacitance-voltage (C-V) measurements, the C-V was observed in the range of -5 V to 0.5 V at 100 kHz. The SBH values from I-V and C-V measurements, the mesa SBDs have 1% - 5% larger SBH compared to the conventional structure, and it could be related to lower leakage current. Moreover, the depletion depths of conventional and mesa SBDs were 52.2 nm and 57.8 nm, respectively, from C-V measurements. For considering the electrical characteristics in extreme temperatures, the I-V measurements of both SBDs structure will be measured between 75 K to 525 K. From an initial low temperature measurement series, we determine a Richardson constant of 49 A/cm2 comparable to what has been reported by other groups. Furthermore, we will extend the study by performing deep-level transient spectroscopy (DLTS) to understand the defect information in Ga2O3.

Effect of Bentonite Admixture Content on Effective Porosity and Hydraulic Conductivity of Clay-based Barrier Backfill Materials

Clay-based barrier wall has been diffusely employed as vertical barriers. Nevertheless, there were few project practices of these walls in China. And few research have been performed to study the impact on the permeability of the addition of domestic bentonites. To solve this problem, the influences of bentonite level on hydraulic conductivity, porosity and clay-bound water of soil-bentonite admixtures have been assessed employing a flexible-wall test and water centrifugal dewatering experiment with various bentonites. The outcomes revealed that as barrier walls are constructed by blending bentonite and Fujian standard sandy soil, there is a critical bentonite level of the smallest porosity. If the bentonite level is less than the critical bentonite content, hydraulic conductivity is reduced quickly, while if the bentonite level is greater than the critical bentonite content, hydraulic conductivity is reduced gently. Additionally, as the bentonite level grew, the clay-bound water centage of the admixtures continually improved. Supposing that the clay-bound water enclosed the clay grains, a near computation approach of the effective porosity is put forward and showed that the effective porosity decreased with bentonite content. Additionally, an exponential relationship was found between the effective porosity and the permeability.

Oxygen Plasma Treatment to Enable Indium Oxide MESFET Devices

AbstractMetal‐semiconductor field‐effect transistor (MESFET) devices based on pulsed laser deposition (PLD) grown In2O3 thin films with on–off ratios exceeding 6 orders of magnitude and low sub‐threshold swing values close to the thermodynamic limit are reported. Oxygen plasma treatment and compensation doping with Mg are utilized to suppress the accumulation of electrons at the surface of In2O3, which is a major obstacle for its use as an active material in electronic devices. The influence of both methods is investigated on the electrical properties of thin films as determined by Hall effect measurements on samples of varying film thickness. Using the performance of vertical Schottky barrier diodes as a benchmark, fundamental plasma parameters such as input power and background gas pressure are optimized.

Hydro-mechanical behavior and microstructure evolution of red clay-bentonite backfills

Soil-bentonite (SB) cutoff walls have been extensively used as vertical engineering barriers to control groundwater flow and subsurface contaminant migration. As the pollution containment capability of the SB backfills is intimately related to the hydro-mechanical behavior, consolidation tests and hydraulic conductivity tests were carried out to investigate the effects of bentonite content on the hydro-mechanical behavior of red clay-bentonite backfills, and the microstructure evolution of backfills under vertical loading was evaluated based on mercury intrusion porosimetry (MIP) tests and field emission scanning electron microscope (FESEM) observations. The results of microstructure analysis also evaluated the influence of bentonite on the clay fabric which changed the relationship between hydraulic conductivity and void ratio. The results indicated that the void ratio and hydraulic conductivity decreased linearly with the increase of the effective consolidation stresses, and the compression index decreased with the increase of bentonite content. Meanwhile, the pore size distribution (PSD) curve of the backfill specimen almost turned into unimodal characteristics with only micropores distributed after consolidation. Additionally, the flow paths became more tortuous under compression which decreased the hydraulic conductivity. The montmorillonite aggregates in red clay-bentonite backfill formed into tortuous network structure which bound the clay aggregates together and effectively increased the tortuosity of flow paths.

Cork barriers for the remediation of soils polluted with lindane

The in-situ removal of lindane from spiked soil was studied using cork barriers combined with electrokinetic and ohmic heating soil remediation processes. Both vertical and horizontal cork barriers have been evaluated to retain pollutants mobilized by electro-osmotic flow or volatilized by ohmic heating. Moreover, the addition of surfactant solutions in electrolyte wells has been evaluated to promote the dragging of lindane by electrokinetic fluxes. Results indicated that the drag of lindane by liquid flows is not as important as expected, opposite to what happened with the dragging by gaseous flows. The retention of gaseous lindane was also confirmed in adsorption tests carried out in a column packed with cork granules. The addition of surfactant had a very limited effect on the mobility of lindane, and dragging of this species to the electrode wells or to a permeable reactive barrier. On the contrary, the reactivity of lindane during the electrochemical treatments is relevant due to the electrokinetic basic front promoting the in-situ conversion of lindane into less chlorinated pollutants.

Pandemic lockdown as policy window for street-level innovation of health and substitution treatment services for people who use drugs

PurposeThis paper aims to examine policy innovation among street-level bureaucrats at low-threshold services to people who use drugs during the COVID-19 pandemic in Denmark.Design/methodology/approachThis paper builds on two research projects conducted during the first pandemic lockdown in Denmark. The first is a case study of how COVID-19 impacted on people who use drugs (PWUD) and services for PWUD at the open drug scene in the neighborhood of Vesterbro in Copenhagen. The second is an ethnographic study of how users of services at the intersection of drug use and homelessness were impacted by lockdown.FindingsDrawing on Kingdon’s “multiple policy streams” approach, this study shows how lockdown opened a “policy window” for innovating services to people who use drugs. This paper further shows how the pandemic crisis afforded street-level bureaucrats new possibilities for acting as “policy entrepreneurs” in a context where vertical bureaucratic barriers and horizontal cross-sectoral silos temporarily collapsed. Finally, the authors show how this had more lasting effects through the initiation of outreach opioid substitution treatment.Social implicationsIn Denmark, the emergence of a “policy window” for street-level bureaucrats to act as street-level “entrepreneurs” occurred in a context of rapid government response to the pandemic. For crises to act as “policy windows” for innovation depends on strong, preexisting institutional landscapes.Originality/valueThis paper adds to existing literature on policy innovation during COVID-19 in two ways: methodologically by contributing an ethnographically grounded approach to studying policy innovation and theoretically by examining the conditions that allowed policy innovation to occur.

Parametric Study on the Aerodynamic Characteristics of Wind Guide Barriers for a Train–Bridge System

This paper presents a new type of wind guide barrier (WGB). Through wind tunnel experiments, the key parameters of three types of WGB were studied, as well as their effects on the aerodynamic characteristics of a high-speed train and blunt body box girder system, while the bridge deck wind field was investigated. The results show that the shielding effect is the main factor affecting the windproof performance of the WGB. When the WGB is installed, the mean wind pressure distribution on the train is comparable to that of using a vertical wind barrier while reducing barrier resistance and the resistance of the bridge–barrier system. At the same time, the WGB can guide the oncoming flow, resulting in an increase in the streamwise and vertical wind velocity ratios on the bridge deck, as well as an increase in the maximum aerodynamic coefficient on the train.