Journal of Civil Engineering
Volume:6 Issue: 3, Summer 2022

Numerical modeling of soil can be used as a complementary or alternative method for laboratory tests. Therefore, in the simulations of geotechnical problems, properly using constitutive models (such as the cap model) requires accurate calibration of the model parameters. In the present study, the draining behavior of Nevada sand at a relative density of 40% was evaluated using Mohr-Coulomb (MC), Drucker-Prager (DP), and modified Drucker-Prager/cap (MDPC) models in Abaqus and compared with laboratory data. In this context, the conventional triaxial compression (CTC) technique was used for finite element modeling of selected drained triaxial tests by keeping the radial stress constant and increasing the axial stress. Based on the results, MC and DP constitutive models, where the behavior of the materials is linear elastic-perfectly plastic, at high confining pressures, due to the inability to simulate soil hardening, showed significant differences with the experimental results. In other words, with increasing confining pressure, the behavior of sand tends to harden, and the ability of the MDPC model, which has a hardening function based on volumetric plastic strain, increased in simulating sand behavior. Proper determination of cap parameters can have a significant effect on the results. In the present study, cap hardening parameters for Nevada sand have been determined based on experimental data.

The purpose of this paper is to introduce a suitable material for Tabriz city landfill liner by using local materials. For this reason, the soil was collected from the Tabriz landfill bottom, a new under-construction site (Iran). As an additive, the nano-soil was produced from landfill local soil using the pulverization of soil samples through a high-energy milling process. Chemical and physical tests including Atomic Force Microscopy (AFM) were conducted to determine the nano-soil features and topography. To obtain the minimum requirement for landfill liner soil application, 90% of Tabriz landfill soil was mixed with 10% of Bentonite. The resulting soil was identified as clayey sand with a plasticity index of 13%. Then, the effect of nano-soil on a sand-bentonite mixture as an economical and modern additive for Tabriz city landfill liner application was investigated. This investigation was based on laboratory experiments including compaction, direct shear, and hydraulic conductivity tests. The nano-soil was used as an additive in six different contents including 0.5, 1, 1.5, 2, 2.5, and 3% of soil dry weight. According to the results, with increasing nano-soil content, the maximum dry unit weight increased and the optimum moisture content of the mixture decreased. Moreover, by increasing nano-soil content by 2%, the shear strength and hydraulic conductivity experienced the desired positive effect for a landfill bottom liner, while the excess addition of nano-soil resulted in neglectable or even negative effects.

Over the past few decades, there has been a lot of interest in short-term traffic prediction which is a crucial part of transportation systems. One of the major considerations that travelers evaluate when making travel plans is information regarding the near future. Transportation planners have investigated a number of methods to produce more reliable travel time predictions in the future. However, there have not been enough in-depth and comprehensive surveys in this area yet. In this paper, a comprehensive review of the literature has been conducted, and various traffic parameter prediction algorithms have been investigated. The methods can be divided into two main groups: parametric, and nonparametric. Parametric models are those that require the specification of some parameters before they can be used to make predictions. In contrast to nonparametric procedures, parametric approaches have a distribution with a defined number of parameters. The parametric approaches are related to statistical methods like time-series, while the nonparametric approaches are related to machine learning methods like neural networks. Predicting flow, volume, speed, density, and occupancy are the main emphasis of the majority of the literature. A detailed methodology is first presented for each of the techniques mentioned in this article, and then the outcomes of numerous articles that have used the technique are discussed.

Reusing recycled materials is one of the most important issues in the world for achieving sustainable development. Polyethylene Terephthalate, rubber, and glass particles are used instead of sand or cement in the concrete industry in recent years. In this paper, three groups of concrete mix designs with different water-to-cement ratios are investigated. Experimental specimens of each group consist of PET, rubber, and glass particles partially replacing natural fine aggregates by 5, 10, and 15 percent. These waste materials are used separately and in combination with each to study the mechanical properties of the concrete. Compressive and flexural strengths of concrete under different freezing and thawing cycles are investigated. The compressive strain of the recycled concrete was studied too. Results show that PET and rubber particles have decreasing effect on both compressive and flexural strengths of concrete and an increasing effect on compressive ultimate strains compared to those of reference specimens. But, the glass particles often have increasing and decreasing effects on strengths and strains respectively compared to those of reference specimens. The compressive strength of frozen-thawed recycled specimens is about 5 % more than that of the frozen-thawed reference specimen. Moreover, In combined PET and glass specimens, the experimental compressive and flexural strengths increased compared to only PET specimens and in combined PET-glass and PET-rubber specimens, the ultimate strain increased compared to that of glass concrete.

The liners are the principal components of solid waste landfills which have the main role in controlling the spread of pollution through the landfills. The high cost of artificial materials and their un-usability in large projects for preventing leaks is a major concern that has led to more attention to natural liner materials with low permeability and effective adsorption and stabilization condition. Clay minerals have a high capacity to adsorb heavy metals due to their high specific adsorption levels and bonding sites with numerous negative charges. Along with absorption properties, clay soils should have suitable hydraulic and geotechnical properties as landfill liners. Therefore, this study aimed to evaluate the efficiency of 5 types of soil (vermiculite clay, sepiolite clay, silty soil, silt+clay mixtures as 90% silt and 10% clay) as clay liner. The chemical, physical and mechanical properties of the study soils were evaluated to address the quality of soils as a landfill liner. The results showed that in terms of environmental quality (pollutant adsorption), soils containing sepiolite clay had a better adsorption capacity to adsorb cations rather than vermiculite clay soils. From a physical and mechanical point of view, soils containing sepiolite clay compared to vermiculite clay soil revealed a variety of landfill liner characteristics in terms of strength, permeability, and plasticity properties, respectively. Based on the technical and economic perspective, the silt and sepiolite mixtures supply good features which may justify their potential use as a liner material in solid waste landfills.

In general, the effect of load eccentricity should be considered in determining the ultimate bearing capacity of foundations. In the present study, the upper bound method of limit analysis was used to propose an equation for determining the bearing capacity of rock masses subjected to the load of a strip footing. The Hoek-Brown failure criterion was used for the rock mass and the footing load was assumed to be exerted eccentrically to the rock mass. The maximum eccentricity value was limited to 1/6 of the footing width to keep the whole footing base in contact with the underneath ground and not result in lifting the footing. Extensive parametric analyses were performed to investigate the effect of the footing width and the rock mass properties on the bearing capacity of rock masses subjected to the eccentric loads. The results show that increasing the load eccentricity from zero to 1/12 and 1/6 of the footing width results in 20% to 40% reduction in the bearing capacity of rock masses, respectively. Also, for all considered eccentricities, the effect of the rock mass unit weight and the footing width and also the Hoek-Brown parameters σci and mi on the bearing capacity were reduced by increasing GSI. Increasing the unit weight of the rock mass from 20 kN/m3 to 25 kN/m3 results in increasing the bearing capacity between zero and 15%. Also, by increasing the footing width from 1 to 5 meters, the bearing capacity increases between 13% and 46%.