•The effects of cement replacement with zeolite for clay stabilization were studied.•Mechanical, durability, physicochemical and microstructural tests were conducted.•LCA analyses were performed on ...the binders and their use for road construction.•Porosity parameter was proposed for determining UCS, ALM, consumed energy, and CO2 emissions.•The durability and mechanical properties of samples having 15% zeolite were higher.
To mitigate environmental issues caused by conventional binders and gain superior geotechnical properties, pozzolanic materials can be considered for soil stabilization purposes. Herein, the effectiveness of zeolite for enhanced treatment of cement-stabilized clay was studied by measuring pH, maximum dry unit weight (MDUW), optimum moisture content (OMC), unconfined compressive strength (UCS), and accumulated loss of mass (ALM), as well as carrying out scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Then, the life cycle assessment (LCA) analyses were conducted to evaluate the potential environmental impacts of cement and zeolite production and their use as stabilizing agents in clayey soil. The soil was stabilized by 2, 4, 6, and 8% cement contents and 0, 15, 30, 45 and 60% cement replacements with zeolite. Furthermore, 56-day curing time was considered to assure accomplishment of hydration and pozzolanic reactions. Besides, samples were exposed to up to 8 wetting-drying cycles to evaluate durability-based parameters. The environmental impacts of the combination of cement, zeolite, and clay for constructing a one-kilometer pavement subgrade in terms of greenhouse gas (GHG) emissions and energy consumption in production, transportation, and execution were studied using LCA. Finally, Al2O3, SiO2, and CaO components were discussed to react with one another and to participate in the chemical reactions as the active composition (AC). UCS results indicated that up to 15% cement content replacement with zeolite, strength increased whereas it reduced thereafter. UCS and ALM were observed to decrease and increase during wetting-drying cycles, respectively. The efficacy of optimum zeolite percentage was more noticeable in higher cement percentages, both in terms of mechanical and durability tests. LCA confirmed that the efficiency of energy consumption and GHG emissions reduced with increasing zeolite. Also, for the samples containing zeolite and cement, the porosity parameter (n)/AC was nominated as a key controlling parameter for determining the UCS, ALM, consumed energy, and the produced CO2. Regarding the experimental program and LCA, the use of zeolite instead of cement is highly recommended both in terms of moisture changes, mechanical properties and environmental aspects.
Bearing capacity of shallow strip foundations placed over both unreinforced and reinforced granular soils and subjected to combined loading is calculated by implementation of upper bound finite ...element limit analysis in conjunction with second-order cone programming technique. The soil mass is considered to be a granular medium reinforced with the inclusion of horizontal single and double layers of geogrid elements. To represent the impact of tensile resistance of reinforcement elements, an axillary variable is utilized to simulate the plastic energy dissipation of reinforcing elements without the application of any stress variables. General loading conditions are considered to profile the expansion of the failure envelopes in the V-H and V-M spaces for shallow strip foundations resting on reinforced soils. Results of this study are compared and validated against three different cases including the bearing capacity of shallow strip foundations subjected to vertical loading in the case of perfectly smooth and fully rough interfaces, limit load of shallow strip foundations subjected to combined loading, and vertical bearing capacity of shallow strip footings over a soil deposit reinforced with a single-layer of geosynthetic. Consistency of the results with those reported in the literature demonstrates the efficiency of proposed extended finite element upper bound formulations. The results are reported in the form of an efficiency factor which can be multiplied by the vertical bearing capacity of the shallow strip footing over unreinforced soil to find the ultimate bearing capacity of the reinforced foundation. The results show that the load inclination angle and eccentricity have significant impacts on the limit load and the optimum embedment depths of the reinforcement layer. It is further noted that the effect of reinforcement layer(s) in the improvement of bearing capacity in the V-M space is more pronounced than in the V-H space. The efficiency of reinforcement elements inclusion in improving the expanse of safe loading domain in the V-H and V-M spaces enhances with an increase in the soil internal friction angle.
Abstract
Wastewaters discharged from different industries and hospitals may contain pharmaceuticals, especially dexamethasone (DEX). Thus, we applied the UV/H
2
O
2
photocatalytic method in the ...presence of the MgO nanoparticles to remove dexamethasone from synthetic wastewater. Moreover, the effects of parameters such as pH (3–11), hydrogen peroxide concentration (1–8 mM), initial DEX concentration (5–30 mg/L), and catalyst dosage (0.01–0.2 g/L) during the reaction times (0–30 min) were investigated. Furthermore, the efficiency of UV/H
2
O
2
in the presence and absence of catalysts was investigated. The photocatalyst is characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and Fourier-transform infrared spectroscopy (FTIR) techniques. It was found that the removal rate was enhanced by decreasing pH and the initial dexamethasone concentration. The removal rate was enhanced somewhat with concentrations of hydrogen peroxide and MgO. In the case of UV/H
2
O
2
/MgO, 87% removal efficiency was achieved, under the optimal conditions: pH 3, contact time of 30 min, dexamethasone concentration of 20 mg/L, H
2
O
2
of 0.5 mM, and UV radiation of 55 watts. The kinetic data indicated that the reaction followed the second-order kinetic model. The results showed that the UV/H
2
O
2
photochemical process can efficiently remove dexamethasone from aqueous in the presence of a MgO catalyst, and the mineralization efficiency was reached at about 98%.
Abstract
A two-dimensional (2D) finite-element limit analysis (FELA) was performed under plane strain conditions to investigate the undrained stability of tunnel launch with a rigid wall in ...anisotropic clays. The anisotropic undrained shear (AUS) failure criteria were applied to identify anisotropic soil behaviors. The average bound solutions were employed to compute the stability load factor. Different sensitivity analyses were carried out to determine the effect of cover–depth ratio (C/D), overburden factor (γD/suTC), and anisotropic strength ratio (re) on the load factor (N) of the opening in tunnel launching with a rigid wall. The failure patterns that were predicted by certain parameters were explored and investigated. To adopt a practical approach, some new design charts for the undrained stability of tunnel launching with a rigid wall in anisotropic clays were devised.
Thin granular fill layers are routinely used to aid the construction of shallow footings seated over undrained soft clay foundations and to increase their load capacity. The influence of time- and ...strain-dependent reduction in reinforcement stiffness on the bearing capacity and load-settlement response of a footing seated on a thin reinforced granular fill layer over undrained soft clay foundations is examined in this paper using finite-difference method (FDM) numerical models. The time- and strain-dependent stiffness of the reinforcement described by a two-component hyperbolic isochronous tensile load-strain model is shown to influence the bearing capacity and load-settlement response of the reinforced granular base scenario. The additional benefit of a reinforced granular layer diminishes as the time-dependent stiffness of the geosynthetic reinforcement increases. An analytical solution for the ultimate bearing capacity of strip footings seated on thin unreinforced and reinforced granular layers over undrained clay is proposed in this study. The main practical outcome from this study are tables of bearing capacity factors to be used with the analytical solution. The bearing capacity factors were back-calculated from the numerical analyses and account for the influence of rate-dependent properties of geogrid reinforcement materials and clay foundations with soft to very soft undrained shear strength.
•Load-settlement and ultimate bearing capacity of strip footing on reinforced granular layer over undrained clay is studied.•Stiffness of the reinforcement is described by a two-component hyperbolic isochronous tensile load-strain model.•Benefit of reinforced granular layer diminishes as time-dependent stiffness of the geosynthetic reinforcement increases.•Analytical solution for ultimate bearing capacity of strip footing on thin reinforced granular layer over clay is proposed.•Bearing capacity factors are back-calculated from numerical simulations using large-strain finite difference method model.
The effect of geotextile inclusion on the shear modulus and damping ratio of sands is evaluated in a wide range of shear strain amplitudes, from very small to fairly large, using the results of ...several resonant column and hollow cylinder torsional shear tests. The resonant column test results are utilized to characterize the reinforced soil behavior at the range of small to medium strains whereas the hollow cylinder torsional shear test results are exploited to assess the medium to large strain dynamic properties. The results demonstrate that the inclusion of geotextile sheets in the soil medium would increase both its shear stiffness and damping ratio in the whole range of shear strain amplitudes, thus rendering a perfect composite to resist dynamic forces applied on geo-structures in earthquake prone areas. Empirical equations are proposed to estimate the small strain and strain-dependent shear modulus and damping ratio of geotextile-reinforced sands. The effect of scaling is also accounted for by a simple analysis so that the results obtained in the current study in the element scale could be extended to the prototype scale in the field. Finally, the accuracy of the proposed scaling approach is verified against a finite element model of a geotextile-reinforced embankment.
•Effect of geotextile inclusion on shear modulus and damping ratio of sands is evaluated at various shear strain amplitudes.•Dynamic properties are assessed through several resonant column and hollow cylinder torsional shear tests.•Empirical equations are proposed to estimate the dynamic properties of geotextile-reinforced sands.•Effect of scaling is accounted for by a simple analysis to generalize the results of this study to the field scale.•Accuracy of the proposed scaling approach is verified against a finite element model of a geotextile-reinforced embankment.
The use of finite elements and limit analysis in the stability analysis of geo-structures is not uncommon nowadays, with the assumption of associated flow rule and rigid perfectly plastic ...constitutive soil model. Nevertheless, the simplified assumption may lead to misevaluation of the objective function for the nonlinear optimisation solution, thus giving rise to uncertainty in the design of geo-structures. In this study, the influence of non-associated flow rule on the stability evaluations for obliquely- and eccentrically-loaded shallow foundations, as well as for retaining structures with cohesionless granular backfill, is examined using lower bound finite elements and second-order cone programming (SOCP). A wide range of dilation angles (ψ) is considered for the study (e.g., from zero to a maximum of soil internal friction angle φ), and it is generally observed that failing to consider the non-associated flow rule in the soil constitutive model would yield non-conservative designs of geo-structures. These inaccurate predictions and subsequent unreliable stability analysis are more pronounced in cases of large soil internal friction angles. The findings in this study would be of great importance for practical design applications.
To find the prevalence of musculoskeletal complaints and rheumatic disorders in Iran.
Tehran, with one-ninth of the population of Iran and of mixed ethnic origins, was selected as the field. Subjects ...were randomly selected from the 22 districts. Interviews were conducted once a week, on the weekend. The 3 phases of stage 1 were done on the same day, in parallel, like the fast-track Community Oriented Program for Control of Rheumatic Diseases (COPCORD).
Four thousand ninety-six houses were visited and 10,291 persons were interviewed. Musculoskeletal complaints during the past 7 days were detected in 41.9% of the interviewed subjects. The distribution was: shoulder 14.5%, wrist 10%, hands and fingers 9.4%, hip 7.1%, knee 25.5%, ankle 9.8%, toes 6.1%, cervical spine 13.4%, and dorsal and lumbar spine 21.7%. Degenerative joint diseases were detected in 16.6% of subjects: cervical spondylosis 1.8%, knee osteoarthritis (OA) 15.3%, hand OA 2.9%, and hip OA 0.32%. Low back pain was detected in 15.4% and soft tissue rheumatism in 4.6%. Inflammatory disorders were rheumatoid arthritis 0.33%, seronegative spondyloarthropathies 0.23%, ankylosing spondylitis 0.12%, systemic lupus erythematosus 0.04%, and Behçet's disease 0.08%. Fibromyalgia was detected in 0.69% and gout in 0.13% of the studied population.
The large urban COPCORD study in Iran showed a high prevalence of rheumatic complaints in the population over the age of 15 years, 41.9%. Knee OA and low back pain were the most frequent complaints.
•The use of a residual alkaline solution to enhance the clay properties is examined.•UCS, ITS, UPV and microstructural (SEM, XRD) tests are conducted.•High- and low- calcium fly ash are introduced ...into the alkaline activation process.•A microstructural analysis showed the formation of binding gels.•An environmental assessment is performed to compare the CO2 emission.
This study aims to evaluate the usability of a recycled alkaline solution, a residue from cleaning iron plates in the car manufacturing industry, to enhance the strength and stiffness of clayey soil by carrying out unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV) and microstructural (SEM, XRD) tests. High- and low- calcium fly ashes with percentages of 10% to 40% and 10% to 30%, respectively, were independently introduced into the alkaline activation process to determine the proper type and content of precursors at room temperature. Two mixtures of the residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one were also utilized to determine how efficiently binary solutions could improve the performance of the parent clay soil. These experiments revealed that all mixtures of the residual alkaline solution work better to activate high-calcium fly ash as compared to the low-calcium fly ash in terms of both mechanical strength and stiffness. The sample of high-calcium fly ash with fly ash/solid and Na/ash ratios equal to 30% and 0.037, respectively, experienced the highest improvement. A microstructural analysis showed the formation of C-(A)-S-H and N–(C)–A–S–H gels in the corresponding sample, thus providing a considerably dense structure, which in turn significantly contributed to the enhancement of the maximum strength and stiffness of the treated soil. In fact, the high-calcium precursor proved to be the best candidate for a low-range alkaline activator because it contributes more calcium to a low-alkaline environment. An environmental impact assessment was also carried out to compare the CO2 emissions of clays treated with the 4 M NaOH binary solutions tested in this study with those conventionally stabilized by cement and lime and also those treated traditionally with commercial 2, 4, and 8 M NaOH. The samples in this study treated with environmentally friendly binary solutions (residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one) performed better in terms of both CO2 emissions and strength gain compared to the samples stabilized with conventional materials.
