Morteza Esmaeili
50161098500
Publications - 7
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
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
Slope stabilisation of railway embankments over loose subgrades using deep-mixed columns
Publication Name: Proceedings of the Institution of Civil Engineers Ground Improvement
Publication Date: 2022-12-01
Volume: 175
Issue: 4
Page Range: 247-260
Description:
An investigation was undertaken into the stability of railway embankment slopes over soft subgrades stabilised by deep-mixed columns (DMCs). Three 1:10 scale laboratory embankments were constructed over unreinforced and reinforced subgrade with DMCs in square and triangle patterns. The load-settlement responses of both embankments and columns were measured. The laboratory embankments were then mathematically modelled and the results were compared. After validation, a comprehensive parametric study was carried out to evaluate the factor of safety (FoS) of the embankment side slopes against sliding. Five embankment soil types from poor to high strength, three heights from 1.5 to 10 m and various DMC improvement area ratios from 0 to 65% were considered. The experimental outcomes indicated an increase of nearly 63% in the bearing capacity of both DMC-supported embankments compared with the unreinforced one. Regarding the parametric study, a minimum required FoS of 1.5 was observed for 1.5 m embankments of all soil types stabilised with a 60% improvement ratio. The greatest safety increase was associated with a 1.5 m height embankment with poor soil type, which showed a 36% increase.
Open Access: Yes
Ballast Stabilization with Polyurethane for Use in Desert Areas
Publication Name: Periodica Polytechnica Civil Engineering
Publication Date: 2022-06-30
Volume: 66
Issue: 3
Page Range: 853-865
Description:
Sand dune accumulation in the railways passing through desert areas leads to ballast softening and settlement, which is one of the major challenges in the ballast maintenance operation. In this regard, ballast infilling with polyurethane could be mentioned as a novel solution that has been less attentional in previous studies. In this matter, in present study using a domestic cost-effective polyurethane, the ballast stabilization has been accomplished and the relevant shear strength parameters have been investigated via a series of large-scale direct shear tests. Since the utilized polyurethane has composed of two different components, in the first stage, the best weight ratios of components have been investigated via a series of compression tests. In this matter, the ratio of 1.5 units polyol to 1 unit isocyanate has been adopted as the best composition. Then, the resulting polyurethane was injected into the ballast to perform large-scale direct shear tests. According to the measurement results, the maximum shear stress, the internal friction angle, and the cohesion coefficient increased by 109%, 9.5%, and 162.5% with respect to the non-stabilized ballast (NSB), respectively. In addition, the dilation angle decreased by 66.4% with the injection of polyurethane into the ballast. Hence, the results indicate increased shear strength and lateral track resistance in the presence of polyurethane, which can prevent lateral deflection and improve track safety. In other words, the mentioned polyurethane has improved the shear parameters of the ballast more significantly than other polyurethanes and has shown its performance in increasing the bearing capacity.
Open Access: Yes
DOI: 10.3311/PPci.19968
Investigating Slope Stability of Geocell-Reinforced Railway Embankments
Publication Name: Acta Polytechnica Hungarica
Publication Date: 2022-01-01
Volume: 19
Issue: 6
Page Range: 197-212
Description:
The current paper aims to investigate stability of side’s slops of geocell-reinforced railway embankments. For this purpose, firstly a set of six 1:20 scaled models including a reference embankment and geocell-reinforced embankments was constructed in a loading chamber and their load-settlement behaviour was assessed. In the next stage, 3D FEM models of the embankments were developed and the relevant results were verified against the laboratory test outcomes. In continue, on the basis of verified models, the scaled up railway embankments were simulated and the real train loading applied to the models. In this matter, a wide-ranging parametric study was performed on the embankment soil properties ranged from poor (ST1) to high strength (ST5) materials, geocell elasticity modulus (E), number of geocell layers (N) and their vertical location in the embankment body (U) to achieve a minimum embankment sliding safety factor (SF) of 1.5. Outcomes indicate that geocell opening size, stiffness and the placement position play an important role where the concern is to stabilize the embankments' sides slopes. It was found that middle of the embankment was the best position of geocell layers. Elasticity modulus of 1400 MPa and opening size of 245*210 mm were also determined as the optimum for geocell layers.
Open Access: Yes
Effect of Geocell, on the Mechanical Behavior of Railway Embankments, Using FE Modeling
Publication Name: Acta Polytechnica Hungarica
Publication Date: 2022-01-01
Volume: 19
Issue: 6
Page Range: 63-80
Description:
In nature, the mechanical properties of soils, vary from region to region and in some areas, high-strength soil resources lack is a serious difficulty that geotechnical engineers may face where constructing earthworks such as railway and road embankments is required. Although a wide range of soil improvement techniques exists to improve such soils, the effect of geocell, as an effective solution, has not yet been investigated for railway embankments, hence, the present study aims to develop a three-dimensional (3D) Finite Element (FE) model, to fill the gap. To do this, first, six, 1/20 scaled-down railway embankments, including an unreinforced and 5 reinforced ones, were constructed in the lab and their load-settlement behavior, was assessed. Second, a 3D FE model was validated by experimental results and then, using a parametric study, the effect of geocell opening size and geocell layers number, were investigated on bearing capacity and settlement of the embankments, for five various types of soil ranging from poor soils (ST1), to high strength soils (ST5). The outcomes indicated, although adding geocell layers up to 15 layers, results in reducing the exerted stress in railway embankments by a maximum of near 50%, the crest settlement is not efficiently affected. Moreover, it was found that geocell’s opening size has a negligible effect on decreasing the embankment’s settlement, while it affects the bearing capacity significantly, up to a maximum of 50%.
Open Access: Yes
DOI: DOI not available
Laboratory Investigation on the Effect of Microsilica Additive on the Mechanical Behavior of Deep Soil Mixing Columns in Saline Dry Sand
Publication Name: Periodica Polytechnica Civil Engineering
Publication Date: 2021-11-02
Volume: 65
Issue: 4
Page Range: 1080-1091
Description:
Since loose and salty subgrades consider as problematic barriers while constructing new transportation infrastructures such as railway tracks and roads are required, the current study aims to find a solution to stabilize these kinds of subgrades using the deep soil mixing (DSM) technique and micro silica additive. In the present study a series of experimental DSM columns were executed in a salty sand-filled chamber utilizing a laboratory scale DSM apparatuses. In the first step, by adding three salt percentages of 5, 10 and 20 into the original sand, four different sandy subgrades with a relative density of 70% were prepared. Considering three percentages of 10, 15 and 20 for micro silica additive, the water-to-cement ratio of 1, salt percentages of 0, 5, 10 and 20 totally 150 sand-cement columns were constructed in the lab environment. In continuation, unconfined compression strength (UCS) and elasticity modulus of all capped DSM columns have been determined and interpreted using scanning electron microscope (SEM) images at three ages of 7,14 and 28 days. The results indicated that increasing the salinity of subgrade soil from 0 to 20% resulted in a falling UCS and Young module by 28 and 21% for 28-days specimens. Furthermore, as a solution, adding micro silica in cement-water grout up to 15% resulted in enhancing mechanical characteristics of the DSM columns. So that adding 15% microsilica caused a 21 and 42% increase in UCS and elasticity modulus of 28-days samples respectively, executed in subgrade with 20% salt.
Open Access: Yes
DOI: 10.3311/PPci.18126
