Analysis for design of thick granular bases under heavy aircraft loading

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Public Transport Affordability Evaluation for Addis Ababa City

The affordability of transportation services refers to the financial burden the travelers bear in purchasing such services. Key factors that affect affordability include travel demand, supply, competitiveness, quality, and cost of transport services. Surveys indicate that transport users consider affordability an important planning objective, but conventional transport planning tends to give little consideration to it. Public transport is one of the key instruments to bring sustainable mobility to cities, and its supply and quality must be maintained at acceptable levels for it to be a desirable mode of transportation. The ever-increasing demand for mass mobility resulting from rapid population growth and extended urbanization in the City of Addis Ababa calls for the provision of good quality, affordable urban public transport services. In this research, the affordability of public transport of Addis Ababa was studied. The majority of data were acquired from the City Transport Bureau. The analysis of data produced a city-wide observed affordability index (Affo) of 14.13% with the highest and lowest values of 32.11 and 3.69% for Q5 and Q1, respectively. The difference between potential and observed affordability is 28.34%. This indicates that, to reach the same motorized trip rates as the third quintile, those households in the lowest quintile need to increase their transport expenditure by 28.34% in Addis Ababa. The results of this study show that the dual affordability metric both in terms observed and potential affordability can provide an effective basis to improve the affordability of public transport in the city by adopting measures that are customized according to regional characteristics at the sub-city level

Stability Analysis of Plant-Root-Reinforced Shallow Slopes along Mountainous Road Corridors Based on Numerical Modeling

Engineering methods such as soil nails, geosynthetic reinforcement, retaining structures, gabions, and shotcrete are implemented to stabilize road cut slopes along mountainous areas. However, these structures are not environmentally friendly and, particularly in Ethiopia, it is impossible to address all road problems due to financial limitations. Nowadays, soil reinforcement with plant roots is recognized as an environmentally sustainable alternative to improve shallow slope failure along mountainous transportation corridors. The aims of this study was, therefore, to conduct slope stability analysis along a road corridor by incorporating the effect of plant roots. Five plant species were selected for the analysis based on their mechanical characteristics. Namely, Eucalyptus globules (tree), Psidium guajava (shrub), Salix subserrata (shrub), Chrysopogon zizanioides, and Pennisetum macrourum (grasses). The roots’ tensile strength and soil parameters were determined through tensile strength testing and triaxial compression tests, respectively. The factor of safety of the slope was calculated by the PLAXIS-2D software. The study showed that when the slope was reinforced with plant roots, the factor of safety (FOS) improved from 22–34%. The decreasing effect of vegetation on slope stability was observed when soil moisture increased. The sensitivity analysis also indicated that: (1) as the spacing between plants decreased, the effect of vegetation on the slope increased. (2) Slope angle modification with a combination of plant roots had a significant impact on slope stabilization. Of the five-selected plant species, Salix subserrata was the promising plant species for slope stabilization as it exhibited better root mechanical properties among selected plant species

Effect of PET Size, Content and Mixing Process on the Rheological Characteristics of Flexible Pavement

The performance of asphalt binder reinforced with waste plastic polyethylene terephthalate (PET) was investigated. Penetration, ductility, softening point, and rotational viscosity tests were conducted to check the performance of the PET-reinforced pavement. The rheological properties of the binder were determined using amplitude sweep and frequency sweep tests and performance grade (PG) measurements of aged and unaged specimens. PET size, mix mechanism, and mix temperature significantly influenced the physical properties of the AB and the penetration index (PI). The size and content of PET had pronounced effects on the PI and softening point than the blending temperature. Increasing the size of PET particles from 75 to 150 μm and the content from 0% to 10% of the bitumen resulted in the reduction of the penetration and ductility values from 96 to 85 mm and 100 to 78 cm, respectively, whereas the softening point increased from 46 to 56.6 °C. As a result, the PI value of the binder increased, which indicates that the temperature susceptibility was improved. The addition of 10% PET increased the viscosity of the baseline bitumen by threefold upto a temperature of 135 °C and dropped it by fourfold when the temperature was raised to 165 °C. Increasing the PET from 0% to 10% and the temperature from 21.1 to 54.4 °C increased the critical strain value (LVER) by 96%

The Role of Clay Swelling and Mineral Neoformation in the Stabilization of High Plasticity Soils Treated with the Fly Ash- and Metakaolin-Based Geopolymers

In the southern U.S. states, expansive soils are frequently encountered, presenting an important hazard in geotechnical engineering. This research relies on mineralogical and geochemical clues to explain the swelling behavior of smectite-rich, high-plasticity soils, documented in a series of geomechanical swelling tests that were performed on the soils stabilized with the metakaolin (MKG) and fly ash (FAG) based geopolymers. These geopolymers were mixed with the soil at several concentration levels. The lowest swelling percentage was shown to correspond to the sample stabilized with 12% FAG and was attributed to the neoformation of calcium silicate hydrates that acted as a cementitious material, preventing the soil from expanding by occupying the pore space, thus binding the clay particles together. Conversely, the 12% MKG-stabilized soil exhibited enormous expansion, which was explained by montmorillonite swelling to the point that it gradually began to lose its structural periodicity. The relatively high abundance of the newly formed feldspathoids in MKG-treated samples is believed to have greatly contributed to the overall soil expansion. Finally, the cation exchange capacity tests showed that the percentage of Na+ and Ca2+, as well as the pH value, exercised strong control on the swelling behavior of smectitic soils

Research report (Texas Tech University. Center for Multidisciplinary Research in Transportation)

This report discusses a study related to the use of emulsified asphalt (EA) as a binder for sealing roads after construction. Due to the number complex variables that affect EAs, this research is meant to help TxDOT personnel better predict which EA will be most effective and bond most quickly to allow roads to open for traffic

Further Development of Binder Quality Assurance Program [Project Summary]

The current Texas Department of Transportation (TxDOT) binder Quality Control/Quality Assurance (QC/QA) system uses two asphalt binder supplier categories: suppliers who have an approved quality control plan (QCP) on file with TxDOT and those who do not. Suppliers who maintain a current QCP can obtain approval to supply binders on either a monthly or a quantity basis, while for others, each load of asphalt must be tested for specification compliance. This binder QC/QA system has worked reasonably well until recently. A few binder supplier-grade combinations have experienced higher failure rates than in the past, and some TxDOT districts have had to resort to taking frequent field samples, as frequently as one per each transport load. Many TxDOT practitioners indicated that an approved binder source does not always provide acceptable quality binders. A more robust QC/QA system is needed to ensure a supply of binders that both meet specifications and maintain a consistent level of quality. This research project was launched to create a quality management system that utilizes the latest QC/QA principles by sharing the quality management burden between the supplier and the client TxDOT