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Showing 7 results for Porosity

Y. L. Luo,
Volume 11, Issue 1 (5-2013)
Abstract

The occurrence of piping failures in earth structures demonstrates the urgency and importance of studying piping. With this

intention, a new piping model was developed in the framework of continuum mixture theory. Assuming that porous media are

comprised of solid skeleton phase, fluid phase and fluidized fine particles phase, the fluidized fine particles phase is considered

to be a special solute migrating with the fluid phase. The three phases interact while being constrained by the mass conservation

equations of the three phases, and a sink term was introduced into the mass conservation equation of the solid skeleton phase to

describe the erosion of fluidized fine particles, then a new continuum fluid-particle coupled piping model was established and

validated. The validation indicates that the proposed model can predict the piping development of complicated structures under

complex boundary and flow conditions, and reflect the dynamic changes of porosity, permeability and pore pressure in the

evolution of piping.


M. Khorami, J. Sobhani,
Volume 11, Issue 4 (12-2013)
Abstract

Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2 % and 4 % of waste agricultural fibers in combination with and without 5 % replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)
Abstract

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
M. L. Li, Q. Chun-Xiang, Z. Yong-Hao,
Volume 12, Issue 2 (4-2014)
Abstract

It introduced an innovative bioengineering method of consolidating incompact sand by urea-hydrolysis producing calcite cementation under the inducement of urease producing microbe. In the paper it discussed the effects of cementation methods and time on porosity and mechanical properties of microbe-inspired cementing sand columns. Method A adopted reaction fluid gravitational permeating and external pressing and method B adopted reaction fluid gravitational permeating and outlet intermittent plugging method. 28-day sand columns prepared by method A exhibited stronger mechanical properties than those prepared by method B, considering of the compressive strengths and three-point flexural strength as well. Pore volume fractions of sand columns prepared by method A reduced with an increase in cementation time which represented the bulk densities of sand columns were improved positively with time. The compressive strengths and the flexural strengths of sand columns prepared by method A increased with time. All these improved mechanical properties were attributed to the fact that the increasing amount of microbe inspired calcite precipitation with time consolidated sand columns by filling or bridging in sand gaps.
M. Abdeen, H. Attia,
Volume 12, Issue 3 (9-2014)
Abstract

The unsteady flow in porous medium of a viscous incompressible fluid bounded by two parallel porous plates is studied with heat transfer. A uniform and constant pressure gradient is applied in the axial direction whereas a uniform suction and injection are applied in the direction normal to the plates. The two plates are kept at constant and different temperatures and the viscous dissipation is not ignored in the energy equation. The effect of the porosity of the medium and the uniform suction and injection velocity on both the velocity and temperature distributions are investigated.
S. Nwaubani,
Volume 12, Issue 3 (9-2014)
Abstract

This study assesses the kinetics of hydration of Pulverised Fuel Ash and Metakaolin cement pastes and compares how the rate of reaction affects the pore-characteristics and resistance to ionic ingress. The degrees of hydration for the different mixtures were evaluated, both as a function of the calcium hydroxide content and with respect to the chemically combined water contents. The reaction rates have been evaluated using a mathematical model (Jander model), which describes the hydration kinetics of the two materials. The results show that the reaction rate for specimens incorporating Metakaolin is several folds higher than those incorporating Pulverised fuel ash. The faster rate of reaction of the pozzolanic blends results in a faster rate of filling the pore spaces with hydration products, smaller pore volumes and reduced chloride ion diffusivity. The results from this investigation will provide engineers with a much needed uunderstanding of the kinetics of hydration and setting characteristics of these types of cement systems and help in gaining an appreciation of the early structural development, ease of placement and subsequent evolution of properties.
S.a.o. Hosseini, M. Nasiri, M. Akbarimehr,
Volume 13, Issue 3 (9-2015)
Abstract

Harvesting of timber using ground based machinery is still a common practice around the world. Track and road building, and movement of machinery during harvesting operations cause soil disturbance. Therefore the aim of this study was to investigate the change in soil properties after logging operation on skid trails (2 years and 7 years after logging) and compare disturbed soil properties with control sampling (undisturbed soil). For this purpose, soil samples were collected from the skid trail and undisturbed area. Electrical conductivity, pH, organic carbon, moisture equivalent, moisture, total porosity and bulk density were determined on the skid trail and undisturbed area. Soil characteristics were examined in two ages (2 years and 7 years skid trail). There were crucial differences in the values of electrical conductivity, organic carbon, moisture, total porosity and bulk density from skid trail and undisturbed area in 2 years skid trail (p<0.05). But on 7 years skid trail, there were no significant differences in values of mentioned factors from skid trail and undisturbed area (p>0.05) except bulk density (p=0). It has been concluded that 7 years after logging, all soil properties except bulk density were completely recovered on skid trail. These findings have important implications for assessing the impact of skidders traffic and recovery time in skid trails.

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