مجله مهندسی زیر ساخت های حمل و نقل
سال پنجم شماره 1 (پیاپی 17، بهار 1398)

One of the parameters affecting the underground railway vibration is the existence of a bedrock under a soil layer. The wave that propagates from the tunnel is reflected when arrives on the bedrock and affects the ground surface responses. In this paper, the influence of the bedrock on the responses of the ground surface was investigated for single and twin tunnels through the 2D finite element models. The effect of different elastic modulus of top soil layer and bedrock as well as the influence of various bedrock's depths on the ground-borne vibration were studied, as well. The results show that the soil elastic modulus is more important than the bedrock elastic modulus. When the distance from the tunnel becomes longer, the existence of a bedrock under the tunnel has a significant influence on the ground responses. Determined Insertion Gain for the existence of the bedrock above the tunnel and 30m farther from the tunnel is respectively 2dB and 7dB. The obtained results are identical for both the single and twin tunnels.

Microsurfacing is a mixture of polymer-modified emulsified asphalt, 100% manufactured well-graded fine aggregate, mineral fillers, water and chemical additives used in the preventive maintenance of pavements. One of the components that have a significant effect on the microsurfacing performance is aggregate, which comprises about 82 to 90 percent by weight of the mixture. This research presents experimental results with the aim of effecting the use of steel slag to improve microsurfacing characteristics. Therefore, in this research, 100% silica aggregate was used as a control mixture and then steel slag was replaced by 42.5%, 61% and 100% aggregate of control mixture. This study was carried out through wet cohesion test, wet track abrasion test and lateral displacement by loaded wheel test. The results of the wet cohesion test and wet track abrasion test indicated that mixtures containing steel slag aggregates compared to the control mixture due to the desired mechanical, physical and chemical properties, would improve the microsurfacing performance, including increasing the adhesion of bitumen to aggregate and increasing the abrasion resistance. Also, in the test of determining the displacement by the loaded wheel, the lowest displacement in the mixture containing 61% of the steel slag was observed and reduced the vertical and lateral displacement by 45.65% and 35%, respectively, compared to the control mixture.

Every year, Sandstorm creates many problems in the railway lines in Iran with lots of maintainace cost so it is important to provide a complete and appropriate solution for this problem. Humped slab track is a way to prevent sand accumulation on the track. In this paper simulation of sandstorm to obtain sand accumulation across the rails is done in a three-dimensional model. The railroad track section is modeled with 4 rows of humped traverses. The input flow of air and sand is simulated with homogeneous two-phase of gas-solid using Eulerain approach by STAR-CCM+ software. The sand grains with 125, 250 and 500 microns in diameter are applied based on the distribution of grains in the desert of Iran. Also, with different wind velocities, the suspention velocity of particles with different diameters is investigated. In the following, the elevation of the humps of the traverses is investigated with three heights of 10,15 and 20 centimeters. The simulation results in this paper show that the larger the diameter of the particles may lead to less particle suspention and more sands accumulation behind the humps and increase of track blockage. This study also shows that using humped slab track can be efficient at storms above 20 m/s and at the lower values, the accumulation of sand is still seen on the line.

There are different factors which play important role in cracks’ formation and propagation of asphalt layers, and also fatigue cracks are one of the most frequent damages in roads and highways. Two of these most important factors are traffic load and temperature effects. In order to introduce new eco-friendly products and reduce contaminants, and since the use of polymers is economically costly, in this paper polymer's waste are utilized as bitumen additives. Also, the decomposition or destruction of petrochemical processes’ products take many years, and their release and burial cause environmental degradation. This study, evaluates the fatigue resistance of hot-mix asphalt (HMA) modified by waste elastomeric polymers. Four-point bending (4PB) tests at constant strain mode at a temperature of 20℃ and at three strain levels were performed. In addition, indirect tensile fatigue tests (ITFT) were performed at 15 and 25 ℃ and at two stress levels. The both tests' results are compared. In addition, fatigue life analysis tests and approaches are compared based on conventional and energy approaches. According to results obtained based on 50% reduction in initial stiffness method, the Energy Ratio method and the Ratio of Dissipated Energy Change method, fatigue life of modified mixes is significantly higher than unmodified ones. Furthermore, the obtained results were analyzed for statistical comparison.

Unconfined Compressive Strength (UCS) test is commonly employed to determine the strength and quality control of the stabilized layers. This method is time consuming due to the needed time for curing of samples. Also, this method can be costly if the number of samples is increased. In this paper, the group method of data handling (GMDH) was used to develop simple models with sufficient accuracy to predict the UCS of clayey subgrade stabilized with Portland cement and lime. To this end, after stabilization of samples with different percentages of Portland cement and lime at three different moisture contents (dry, wet and optimum moisture content) and curing times of 7, 14, 21, 28 and 60 days, the UCS tests were conducted to establish a comprehensive database including 150 records. In the next step, two different UCS prediction models for clayey subgrade soil stabilized with Portland cement and lime were developed by using the GMDH method. The R2 value for training and testing sets for samples stabilized with Portland cement was 0.9294 and 0.94522, respectively, while the R2 value for training and testing sets for samples stabilized with lime was 0.8897 and 0.880, respectively. In addition, the sensitivity analysis of each model showed that the cement percentage and moisture content have the most impact on the predicted UCS, respectively.

Fast, easy, safe and low cost transportation is the base of progress and economic development. In large cities the cost of land ownership and the improvement of urban structure and environmental problems reduce the possibility of rapid development of surface transportation lines. The need for the construction of underground lines of transport seems to be the right approach. Like all the construction projects, there will be social and technical consequences; perhaps the most important technical effect is the induced surface settlement due to excavation of tunnels and the construction of underground stations on surface buildings. In this numerical study, by using finite element software "plaxis8.6", the risk classification of surface buildings with various story and width are evaluated. Because of considerable effect of tunnel geometry and surrounding soil geotechnical properties on surface settlements, the region near to S4 station of Tabriz metro line 2 adopted as a case study. In this part the tunnel has a low overburden and the width of the street that tunnel route passed under it is low. Considering operational limits, the use of in-situ concrete piles in the vicinity of the surface buildings is choose as a mitigation technique. The length of the pile and their center to center space were matters of interest. Based on obtained results the risk classification of buildings reduce from 3 to 2 category due to construction of piles, which indicates good performance of this technique. Accurate examination of interaction between structure and soil can't be completely defined. Therefore, different methods of modeling the surface structures were applied. The soil behavior was modeled by the Mohr–Coulomb and hardening soil (HS) criterions. Also, with analyses more than 220 model, the effects of tunnel contraction ratio and street width on induced surface settlements and performance of mitigation technique were studied.

Soil stabilization is an effective mechanical method for soil rehabilitation against applied loads. In recent years, synthetic fibers have been introduced as a novel technique for soil stabilization. Therefore, it is essential to assess the behavior of fiber-reinforced soils. In this study, the behavior of synthetic fiber-stabilized soil was investigated using laboratory tests. Direct shear experiments were performed on the specimens reinforced with glass and polypropylene fibers, 12 mm in length. The tested specimens were reinforced with random distribution of 0.05, 0.1, 0.2 and 0.5% of synthetic fibers. The direct shear experiments were performed under different vertical stresses. The tests results indicate that the addition of synthetic fibers improves the maximum shear strength of the tested soil samples. Reinforced samples with 0.1% fibers have the highest shear strength of tested soil. Also, the results indicate that under identical conditions, specimens reinforced with polypropylene fibers have higher shear strength than glass fiber-reinforced specimens.