Jafar Chalabii
57219994044
Publications - 8
Urban Sustainability Through Pavement Technologies: Reducing Urban Heat Islands with Cool Pavements
Publication Name: Buildings
Publication Date: 2025-02-01
Volume: 15
Issue: 3
Page Range: Unknown
Description:
Urban development driven by population growth and technological advancements has intensified urban heat islands (UHIs), contributing to environmental damage and health risks. This study explores the potential of cool pavements as a critical strategy for mitigating UHIs, focusing on reflective, evaporative, and energy-storing technologies. Over 400 reputable scientific articles were reviewed to analyze UHI causes; measurement methods, including remote sensing and laboratory techniques; and the effectiveness of various pavement solutions. Reflective pavements demonstrated a capacity to lower surface temperatures by 5–20 °C depending on reflectivity changes, while evaporative pavements reduced temperatures by 5–35 °C based on type and design. Advanced energy-storing pavements not only achieved a 3–5 °C temperature reduction but also generated renewable energy. This research provides a comprehensive classification of pavement cooling systems and evaluates their quantitative and qualitative benefits, emphasizing the transformative role of cool pavements in enhancing urban sustainability and reducing UHI effects.
Open Access: Yes
Effect of the Particle Size Distribution of the Ballast on the Lateral Resistance of Continuously Welded Rail Tracks
Publication Name: Infrastructures
Publication Date: 2024-08-01
Volume: 9
Issue: 8
Page Range: Unknown
Description:
While the effect of ballast degradation on lateral resistance is noteworthy, limited research has delved into the specific aspect of ballast breakage in this context. This study is dedicated to assessing the influence of breakage on sleeper lateral resistance. For simplicity, it is assumed that ballast breakage has already occurred. Accordingly, nine granularity variations finer than No. 24 were chosen for simulation, with No. 24 as the assumed initial particle size distribution. Initially, a DEM model was validated for this purpose using experimental outcomes. Subsequently, employing this model, the lateral resistance of different particle size distributions was examined for a 3.5 mm displacement. The track was replaced by a reinforced concrete sleeper in the models, and no rails or rail fasteners were considered. The sleeper had a simplified model with clumps, the type of which was the so-called B70 and was applied in Western Europe. The sleeper was taken into consideration as a rigid body. The crushed stone ballast was considered as spherical grains with the addition that they were divided into fractions (sieves) in weight proportions (based on the particle distribution curve) and randomly generated in the 3D model. The complete 3D model was a 4.84 × 0.6 × 0.57 m trapezoidal prism with the sleeper at the longitudinal axis centered and at the top of the model. Compaction was performed with gravity and slope walls, with the latter being deleted before running the simulation. During the simulation, the sleeper was moved horizontally parallel to its longitudinal axis and laterally up to 3.5 mm in static load in the compacted ballast. The study successfully established a relationship between lateral resistance and ballast breakage. The current study’s findings indicate that lateral resistance decreases as ballast breakage increases. Moreover, it was observed that the rate of lateral resistance decrease becomes zero when the ballast breakage index reaches 0.6.
Open Access: Yes
Aerodynamic Behavior of Hump Slab Track in Desert Railways: A Case Study in Shuregaz, Iran
Publication Name: Buildings
Publication Date: 2024-08-01
Volume: 14
Issue: 8
Page Range: Unknown
Description:
The development of rail transport necessitates expanding environmentally friendly infrastructure. However, specific challenges arise in desert and sandy regions. One innovative solution to manage the effects of windblown sand on desert railways is the use of hump slab track superstructure. This paper develops a solid–fluid aerodynamic model based on ANSYS Fluent 2021 R2 software to simulate the hump slab track during a sandstorm. The model is validated through wind tunnel testing. A case study of a railway sandstorm in the Shuregaz region of Iran is presented, evaluating various sandstorm parameters and hump heights to determine their impact on sand concentration and particle velocity within the sand transit channels. The results indicate that increasing the sand particle diameter (from 150 to 250 µm) leads to higher sand concentration (up to 40%) and lower sand movement velocity (up to 28%). These results have been observed with a higher incremental approach concerning the sand flow rate. Conversely, increasing sandstorm velocity (from 10 to 30 m/s) decreases sand concentration and increases sand movement velocity up to 80% and 150%, respectively. Additionally, a 25 cm hump height significantly enhances sand passage by creating larger channels.
Open Access: Yes
Investigation of Shear Strength Reduction Method in Slope Stability of Reinforced Slopes by Anchor and Nail
Publication Name: Buildings
Publication Date: 2024-02-01
Volume: 14
Issue: 2
Page Range: Unknown
Description:
Since the stability of slopes in infrastructures such as road and railroad embankments, excavations, and, in general, earthwork is important, analyzing the stability of these slopes has been one of the main focuses of geotechnical engineers. Although analyzing both reinforced and unreinforced slopes is needed, reinforced slopes require special attention as the reinforcement elements significantly affect the calculations. Hence, the current study’s aim is to find out the differences between obtained safety factors using the Limit Equilibrium Method (LEM) and Shear Strength Reduction Method (SSRM). For this purpose, first, the origin differences in terms of Safety Factor (SF) are theoretically determined according to basic formulas for the aforementioned techniques. Then, to verify the formula, several numerical modelings are carried out using in situ measured geotechnical data to better understand the differences in terms of safety factors. The results indicate that for the reinforced slope with an SF value of higher than 1, the SSRM provides a higher SF in comparison with the other techniques, and the origin of this difference is the definitions of the SF in the different methods.
Open Access: Yes
DEM Analysis of Ballast Particle Direct Shear Tests: Exploring the Influence of Varying Particle Size Distributions on Shear Stress
Publication Name: Advances in Transdisciplinary Engineering
Publication Date: 2024-01-01
Volume: 59
Issue: Unknown
Page Range: 88-95
Description:
The dimension of particles can significantly influence the load response and the performance of uniformly graded ballast layers in railway track structures in real-world conditions. Yet, the micromechanical behavior of the unbound aggregate ballast layer assembly, particularly affected by particle size, remains largely unexplored. In this study, the distinct element model of a direct shear test was initially simulated using friction coefficients of 0.8, 0.9, and 1, and particle size distribution No.4A. The dimensions of the shear test box were 300 mm in width, 300 mm in length, and 180 mm in height. Additionally, a constant normal force of 333 kPa was applied to the sample during the simulation. Subsequently, this model was compared with experimental results, revealing a close correspondence between simulated and experimental shear stress-displacement curves, particularly for the friction coefficient of 1. Following this verification, the validated model was employed to investigate three other particle size distributions: No.4, No.5, and No.57. The results demonstrated a reduction in shear stress for particle size distributions No.4, No.5, and No.57 compared to No.4A, with quantified decreases of 11.9%, 38.2%, and 56.7%, respectively.
Open Access: Yes
DOI: 10.3233/ATDE240531
Numerical Investigation of the Effect of Longitudinal Fiberglass Dowels on Tunnel Face Support in Layered Soils
Publication Name: Infrastructures
Publication Date: 2023-10-01
Volume: 8
Issue: 10
Page Range: Unknown
Description:
Tunnel face extrusion rigidity is an important factor for solving stress–strain problems in loose ground conditions. In previous studies, the effect of horizontal and vertical soil layering on tunnel excavation face stability in the presence of longitudinal fiberglass dowels has not been studied. Therefore, in this study, the effect of fiberglass dowels on the stability of the tunnel face in layered soil has been investigated. In this matter, the best dowel arrangement for minimizing the excavation face extrusion in the case of two-layer soil (horizontal or vertical) has been focused on. For this purpose, firstly, a 3D numerical model was validated based on field data provided previously, and then a 3D numerical tunnel was developed in FLAC3D, adopting the Mohr–Coulomb failure criterion. In continuation, the effect of tunnel diameter, initial pressure ranging from 0.5 to 1.5 MPa, and different placement angles of fiberglass dowels ranging from 0 to 9 degrees, with respect to the tunnel longitudinal axes on the tunnel face extrusion, have been investigated. In the case of horizontal layering, the results showed that the maximum extrusion rate is significantly increased where the elasticity modulus of the soil is reduced. In addition, comparing the maximum extrusion in vertical and horizontal layering, it was found that its value in the horizontal mode is much higher than in the vertical. Additionally, the extrusion of the tunnel face has changed significantly due to an alteration in the initial stress. Finally, it was discovered that tunnel face extrusion is not significantly affected by altering the angle of the fiberglass dowels.
Open Access: Yes
Optimal Shape Design of Concrete Sleepers under Lateral Loading Using DEM
Publication Name: Buildings
Publication Date: 2023-07-01
Volume: 13
Issue: 7
Page Range: Unknown
Description:
Despite the significant contribution of sleepers to the lateral resistance of ballasted tracks, limited research has focused on improving the shape of sleepers in this aspect. This study aims to evaluate proposed sleeper shapes based on the B70 form, utilizing a linear optimization algorithm. First, a DEM model was verified for this purpose using the outcomes of the experiments. Then, using this model, the effect of the weight of the B70 sleeper was carried out on lateral resistance. Next, suggested shapes contacted with ballast materials were applied to lateral force while maintaining the mechanical ballast’s properties until a displacement of 3.5 mm was achieved. The current study’s results showed that the rate of lateral resistance increasing becomes lower for weights higher than 400 kg. Additionally, it was demonstrated that the sleeper’s weight will not always increase lateral resistance. The findings also indicated that although some proposal shapes had higher lateral resistance in comparison to other forms, these designs are not practical from an economic standpoint. Furthermore, despite the lower weight of some other suggested shapes in comparison with B70, the lateral resistances are 31.2% greater. As a result, it is possible to recommend employing a proposed sleeper rather than a B70 sleeper.
Open Access: Yes
Effect of Sleeper-Ballast Particle Contact on Lateral Resistance of Concrete Sleepers in Ballasted Railway Tracks
Publication Name: Materials
Publication Date: 2022-11-01
Volume: 15
Issue: 21
Page Range: Unknown
Description:
Although a sleeper makes a great contribution to the lateral resistance of ballasted tracks, in this regard, limited studies have been carried out on the effect of its contact surface with ballast aggregates. The current paper is dedicated to evaluating the effect of sleeper shape on the lateral resistance of ballasted track through discrete element modelling (DEM). For this purpose, firstly, a DEM model was validated based on the experimental results. Then, a sensitivity analysis was undertaken on the effect of the different contact areas that a standard concrete sleeper faces with the crib, shoulder and underlying ballast aggregates on lateral resistance of a single sleeper. As the main result of the current study, a high accurate regression equation for constant weight 319.2 kg and constant density 2500 kg/m3 of the sleepers was fitted between different sleeper contact areas and the maximum lateral resistance of a concrete sleeper for 3.5 mm lateral displacement in ballasted railway tracks. The obtained results showed that the effect of the sleeper’s head area compared to the underlying area of the sleeper and the head area of the sleeper compared to the sleeper’s side area in terms of lateral resistance are 8.2 times and 14.5 times more, respectively.
Open Access: Yes
DOI: 10.3390/ma15217508
