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The main purpose of the present study is to investigate the role of the material parameters such as permeability, thermal diffusivity, and pore size distribution on the mechanical behavior of cementitious structures submitted to frost action, such as surface scaling. An experimental device, in which a cement paste specimen is exposed to freezing-thawing cycles under a thermal gradient, has been developed. The experimental results show that under high thermal gradient (up to 1.5°C/mm), skin damage can occur without a saline layer in contact with the frozen surface. This can be explained and quantified in the framework of poromechanics. The model is based on the coupling between liquid-ice crystal thermodynamic equilibrium, liquid water transport, thermal conduction, and elastic properties of the different phases that form the saturated porous material. It eventually predicts that a less permeable sample is more susceptible to damage by surface defacement, which explains the observed experimental result. [ABSTRACT FROM AUTHOR]

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of 460 mg L-1, with one reactor run as a control, one with 1.7 g L-1 of powdered activated carbon (PAC), and the third with 1.7 g L-1 of granular activated carbon (GAC). While COD removal was high in all reactors (>90%), in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low (<18 mg L-1), even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage. [ABSTRACT FROM AUTHOR]

Traditional deformation parameters such as drained, unjacketed, and pseudo-bulk compressibilities are developed for a saturated porous medium, assuming they can be uniquely determined by measuring the liquid pressure, confining pressure, and changes in volume. Physically, however, the liquid volume fraction (porosity for a saturated porous medium) plays an important role, yet it is not directly measurable. In this paper the compressibilities are defined in terms of the experiments used to evaluate them and then mathematically related to the compressibilities of the liquid and solid phases and the volume fraction. The results can then be used to determine the effects of the volume fraction and compressibilities of each phase on the deformation properties of the porous medium. This theory is then shown to be a generalization of previous work, and comparisons are made with previously derived relationships of Zimmerman, Biot, and Gassmann. [ABSTRACT FROM AUTHOR]

With good quality of fluidization the air flows uniformly through the bed and the particles are distributed well in the fluid stream, which may improve combustion efficiency. However, the effects of operating parameters and characteristics of waste on generation of particulate matters (fly ash) and quality of fluidization were rarely evaluated. This study investigated the relationship between the quality of fluidization and generation of particulate matters during incineration. The operating parameters included waste characteristics, operating gas velocity, and temperature. The statistical and power spectrum analyses were used to assess pressure fluctuations. The experimental results showed that when the combusion temperature was controlled at 600°C, the mean amplitude was reduced and the dominant frequency was increased, indicating that the quality of fluidization was better than for other conditions. Consequently, generation of fly ash during incineration was minimized when the combustion temperature was controlled at 600°C. The more amount of fly ash was generation with acrylonitrile–butadiene–styrene (ABS) combustion at different conditions, and combustion of wood generated the least amount of ash. It may be that the wood combustion is quite stable and the combustion behavior of ABS is the most violent among the four plastic wastes. Notably, the dominant frequency increased with temperature for wood combustion, and the quality of fluidization was improved at 800°C. For different results of U/Umf, they did not have obvious tendencies. Consequently, behavior of the bed material and quality of fluidization determined the generation of fly ash. Therefore, the combustion efficiency may be enhanced by improving the quality of fluidization. [ABSTRACT FROM AUTHOR]

Compared to geosynthetic-reinforced soil (GRS) retaining walls, GRS abutment walls are generally subjected to much greater intensity surface loads that are fairly close to the wall face. A major issue with the design of GRS abutments is the allowable bearing pressure of the bridge sill on the abutments. The allowable bearing pressure of a bridge sill over reinforced soil retaining walls has been limited to 200 kPa in the current NHI and Demo 82 design guidelines. A study was undertaken to investigate the allowable bearing pressures of bridge sills over GRS abutments with flexible facing. The study was conducted by the finite element method of analysis. The capability of the finite element computer code for analyzing the performance of GRS bridge abutments with modular block facing has been evaluated extensively prior to this study. A series of finite element analyses were carried out to examine the effect of sill type, sill width, soil stiffness/strength, reinforcement spacing, and foundation stiffness on the load-carrying capacity of GRS abutment sills. Based on the results of the analytical study, allowable bearing pressures of GRS abutments were determined based on two performance criteria: A limiting displacement criterion and a limiting shear strain criterion, as well as the writers’ experiences with GRS walls and abutments. In addition, a recommended design procedure for determining the allowable bearing pressure is provided. [ABSTRACT FROM AUTHOR]

Extremely high-suction pressures generated beneath the conical vortex flow in the roof-corner region have a devastating effect on the building roofs in high-wind events. The application of quasi-steady theory near the roof corners of low-rise buildings deserves careful investigation for the appropriate assessment of the design wind loads. A synchronized incident wind and pressure data acquisition system was set up on the full-scale experimental building at Texas Tech Univ. Experiments were conducted systematically to simultaneously collect the incident wind and roof-corner pressure data under the influence of cornering winds. By using a conditional sampling technique, a bivariate quasi-steady model was established to incorporate the influence of both horizontal and vertical wind directional variations on the roof-corner pressures. Comparison between the measured pressures and the model-predicted pressures has shown that the quasi-steady theory in the suggested form is applicable in the roof-corner separated flow region where vortices are present. This conclusion further justifies the application and codification of quasi-steady approach for wind load assessment of low-rise buildings and other structures. [ABSTRACT FROM AUTHOR]

A fluid-filled cylindrical cavern of circular cross section in a homogeneous infinite fluid-saturated polycristalline (salt) formation subjected to isotropic stress is set under internal pressure that differs from the confining pressure. The fluid in the cavern and in the mixture is treated as ideal and the solid as elastic. The state of stress that is established as a consequence of an outside pressure and a cavern pressure serves as the reference state. Perturbing the cavern pressure induces small changes in the solid and fluid densities and in the solid displacements. We compute these and other fields as functions of the radial distance from the cavern center and show that, depending on the relative stress levels, the (salt) formation experiences either a dilatation or a compaction that is highly concentrated in a thin boundary layer near the cavern wall and tapers off as one moves away from it. The amount of dilatation/compaction of the cylindrical wall and the thickness of the boundary layer grow with an increase in the difference between the referential confining pressure and the pressure in the cavern. [ABSTRACT FROM AUTHOR]

A mathematical model capable of simulating tropical cyclone tracks and central pressure histories over the Coral Sea, Australia, is described. The modeling approach assumes that each cyclone is an independent realization of the same underlying stochastic process. Relatively simple autoregressive models are used for the time series of latitude, longitude, and central pressure. The model is used to generate a large database of synthetic storms whose statistical characteristics are shown to simulate those of the population of real storms. Each synthetic storm can be used, in conjunction with a separately developed wind field model, to drive numerical models for computing wave heights and water levels (including storm surges) throughout the Great Barrier Reef Marine Park. In this way, the sample size available for estimating extreme wave heights and water levels is greatly increased [ABSTRACT FROM AUTHOR]

The theory for a fluid saturated linearly isotropic elastic matrix is still the basis for many geophysical applications, and commonly adopts Biot’s symmetric stress–strain laws for the matrix stress and fluid pressure. These involve a shear modulus and three elastic moduli governing the mixture and constituent compressions, in contrast to four compression moduli if Biot’s invalid potential energy argument is not applied. We now show that an energy argument applied to undrained loading also leads to three compression moduli, but distinct from those derived by Biot (Biot symmetry). However, there are two distinct solutions of this energy balance, corresponding to the Voigt and Reuss limits of the analogous theory of a linear two-phase elastic composite, whereas a unique undrained modulus not at either limit would be expected. It is proposed that an energy contribution is lost due to the idealised assumptions made for undrained loading, which therefore does not determine a further restriction, so that there are four independent compression moduli. The general and restricted combinations of the total pressure and fluid pressure (effective stress) governing the matrix compression are then presented, together with the alternative forms of the partial differential equations governing the deformation and flow. [ABSTRACT FROM AUTHOR]

A numerical analysis has been conducted to evaluate the effect of confining pressure on the damage evolution and the fracture process of brittle rock materials by using the rock failure process analysis code (RFPA2D). A fractal dimension D associated with material damage and a damage variable ω are defined to describe the damage process of the specimen subjected to tensile or compressive load. We find that the spatial distribution of microfractures is fractal and has very good statistical self-similarity in the specimen under different confined conditions. The fractal dimension D increases progressively with loading. Meanwhile, the damage variable ω develops from 0 to 1, and the specimen failure is characterized by the critical damage variable ωc with 0.4 ≥ωc ≥ 0.8. The initial damage is delayed by the confining pressure. The confining pressure plays an important role in the mode of rock failure in numerical simulations. The tensile microfractures dominate near the brittle splitting of the specimens under no and low confining pressure. Conversely, a few tensile microfractures appear in the ductile shear failures of the specimens under immediate or high confining pressures. The tensile microfractures run through all failure processes in the specimen under uniaxial tensile loading. The stress-strain curves are also obtained in numerical simulation. The results show that the specimen is strengthed by the confinement and fails according to Mohr-Coulomb failure criterion. [ABSTRACT FROM AUTHOR]

In this study, a pilot-scale pulse-jet baghouse is utilized to control the particulate emission of an oil-fired boiler. The operating and design parameters, such as filtration velocity, initial tank pressure, and nozzle diameter, were varied to evaluate the cleaning effect of the pulse-jet baghouse. Two different cleaning types, (1) high initial tank pressure and one bag cleaning; and (2) low initial tank pressure and two consecutive bag cleanings, are used to compare the bag-cleaning performance in this study. It is found that the cleaning effect increases with the initial tank pressure. However, the cleaning intensity (overpressure) does not increase with the nozzle diameter. There exists an optimum nozzle diameter to achieve higher cleaning intensity and a better cleaning effect. This phenomenon results from the small volume of the baghouse compartment in this study. If an industrial size baghouse was used, it suggests that a nozzle diameter larger than 13 mm and initial tank pressure greater than 2.5 kg/cm2 should be adopted to achieve a higher cleaning effect. Between the two cleaning types, type 2 is found to be more effective to clean the bag and the energy consumption for compressed air is reduced significantly from type 1. Therefore, type 2 bag cleaning is suggested to be a better method to clean the baghouse. [ABSTRACT FROM AUTHOR]