مجله مهندسی زیر ساخت های حمل و نقل
سال نهم شماره 2 (پیاپی 34، تابستان 1402)

Reinforcement of ballast with the help of Geogrids is one of the methods that have been studied by various researchers in the technical literature to increase the load capacity as well as reduce the deterioration of the ballast through the reduction of crushing and settlement. In this article, by introducing a new type of geogrids made with the help of waste rubber belts called Geo-scrape, their effect on the shear behavior of ballast in a large-scale shear test has been investigated. In this direction and in order to investigate the effect of the dimensions of the geo-scrap on the ballast shear behavior and by placing the geo-scrap with the dimensions of 5x5, 10x10 and 25x25 cm square in the upper layer, various tests were carried out under vertical loads of 50, 100 and 150 Kilopascal has been done and the results are presented in the form of shear stress-horizontal displacement curve, maximum shear strength, internal friction angle and dilatancy angle. The summary of the results shows that the mesh of 5x5 cm2 has provided the most favorable conditions for the ballast in terms of increasing the shear strength, increasing the internal friction angle and decreasing the dilatancy angle. So that by placing the geo-scrape with the dimensions the mesh of 5x5 cm2, the shear strength, internal friction angle and dilatancy angle are increased by 20%, 7% and 30% respectively compared to the unreinforced state.

In recent decades, population growth, increasing urban development, and polluting industries have led to an increase in the production of greenhouse gases and the phenomenon of global warming in various regions of the world. Asphalt pavements, as the main infrastructure of the road transportation system, may suffer failures with high repair costs due to their rheological properties under the influence of this phenomenon. In this study, the Prophet model was used to predict the temperature for the years 1400 to 1421 in three 7-year periods under three optimistic, intermediate, and pessimistic scenarios. The prediction accuracy of this model based on the fitting coefficient was more than R2=0.8 on average. Based on the prediction, the country's demand for bitumen with different functional classifications is then presented in comparison with the available quantities. By predicting and calculating the functional classification of bitumen in 1440 and presenting the results at two confidence levels of 50% and 98% for 34 meteorological stations in the 31 provinces of Iran, a long-term overview of the temperature situation and the required functional classification of bitumen based on the meteorological information of each station is also provided. The increase in the average temperature of the studied stations at the end of the 21-year period was 0.73 and 1.094 degrees of centigrade at a confidence level of 50% and 98%, respectively. According to these results, most of the studied areas will experience a significant temperature increase in the coming years, and this phenomenon will increase the high and low temperatures of bitumen performance, which will require the use of PG76-10 and PG82-10 bitumen. The increase in high and low performance temperatures will require the use of alternative bitumens and the use of appropriate bitumen additives for all climatic conditions.

There has always been a great desire to implement asphalt mixtures with better resistance and durability. Stone matrix asphalt (SMA) is known as one of a kind. Examining the studies done on SMA asphalt and the importance of producing and implementing more durable and economical ways has made it important to increase the knowledge of the effect of new additives in this asphalt. Due to its special gradation and more optimum bitumen consumption in comparison with other asphalt mixtures, the use of polymer additives and different fibers has drawn the attention of researchers for its modification. In this research, three different percentages of epoxy resin (10%, 15%, and 20%) were added into bitumen as a thermoset polymer modifier, also ceramic fiber was used as a mixture stabilizer. To study the modification effect, the chemical and physical properties of the modified bitumen were first investigated and then bitumen drainage, Cantabro, and freeze-thaw cycles tests were carried out on the samples. The analysis of the results shows an overall improvement in the performance of asphalts with modified bitumen and ceramic fibers compared to the control samples.

Suitable tensile strength is one of the important parameters in soils subjected to tensile stress. In recent years, biopolymer materials have been widely used to control cracking and increase the tensile strength of soil. In this laboratory study, the tensile strength of sand treated with Persian gum was investigated. For this purpose, the effect of parameters of initial relative dry density of soil, materials mixing method, temperature and humidity of curing place and curing time on the tensile strength of treated samples was evaluated by indirect tensile test. After examining the results, it was found that adding a uniform gum-water solution (including 2% gum and 16% water related to the weight of dry soil) to the dry soil was the best mixing method and the initial relative density of 50% for the soil was the optimal density to obtain the highest tensile strength. Also, there is a direct relationship between the increase in temperature and the decrease in humidity with the increase in tensile strength, so that when the temperature increases from 25 degrees in the room to 50 degrees in an oven and the relative curing humidity environment decreases from seventy to fifteen and then to zero percent, the maximum tensile strength of treated samples increases from 154 to 270 and 442 kPa respectively.

In previous researches, the properties of bitumen and asphalt mixture have been considered for investigation of thermal cracking. In these methods, the roles of different components of the asphalt mixture are not considered. The use of surface free energy and the basic characteristics of asphalt mixture can also be used in the investigation of thermal cracking. In this research, it has been tried to investigate the role of these basic properties of materials in the occurrence of these cracks along with the surface free energy parameters. For this purpose, surface free energy components have been measured for four types of aggregates and eight types of bitumen. Also, the bitumen creep stiffness and m-value were obtained from the bending beam rheometer tests. Asphalt film thickness, aggregate index and the specific surface area of the aggregates have been also determined. For thermal cracking potential, the semicircular bending test was used on 32 different combinations of asphalt mixtures at low temperature. Then, statistical methods have been used for assessing the relationship between the mentioned parameters and the semicircular bending test results. Statistical analysis shows that the basic characteristics of the materials, including the asphalt film thickness, the aggregate index, the free energy of cohesion, the free energy of adhesion, the ratio of basic to acidic components of the surface free energy and the specific surface area of the aggregate have a significant and positive effect on the cracking indices such as semicircular bending fracture energy and fracture toughness.

Conducting evaluation studies on the bridges used on the road surface is one of the most important time-consuming and costly processes, especially considering the high number of bridges in Iran, i.e., more than 35 thousand in the whole country and 8658 bridges in Zanjan province. On the other hand, the time and cost of these studies can cause delays in carrying out studies for all bridges and cause irreparable damages due to a lack of proper management of bridge repair and maintenance. Taguchi's test design method is one of the methods that predict the desired combination with the help of statistical and mathematical models, by defining its orthogonal arrays, instead of performing all possible evaluation options, by performing a limited number of evaluations. In this research, based on the Taguchi method, instead of examining 8658 bridges with 13 different criteria, only 27 combinations of the physical characteristics of bridges and atmospheric, climatic and traffic conditions affecting concrete road bridges in 5 main axes of Zanjan province were determined the deterioration indices of bridges with these combinations were calculated.It showed that the combination of bridges with 2-3 times of snow along the axis, 91-100 days of frost during the year, 26-30% of heavy vehicles passing over the bridge and a length of 7.1-12 meters has the highest structure failure index with an estimated average of 76.2725, which will lead to the highest failure risk. This means that this combination has created the highest risk of damage. Also, the most important factor in the failure of bridges is the percentage of passing heavy vehicles compared to the total traffic.

Connecting relief shelves (RS) to the retaining walls play a significant role in reducing the lateral pressure of the earth on the retaining wall of the trenches. So far, the conducted research has only evaluated the vertical state of the RS. In this article, physical modeling has been used to investigate the role of inclined RS in reducing static and active lateral pressure on the retaining wall in order to improve the stability of trenches. In this regard, by making a system including a rectangular cube box in the laboratory and performing several series of 1g tests, the changes of lateral pressure on the retaining wall during the couple of inclined RS with overheads have been evaluated. It was found that the effect of an upward-sloping RS (70 degrees) with an increase in the amount of overhead and RS width in reducing the lateral pressure on the wall was greater than that of a vertical (90 degrees) and downward sloping RS (110 degrees). This result, which was proved for the first time in the current study, shows that the changes in the angle of the RS perpendicular to the wall, either upwards or downwards, have a positive effect on reducing the lateral pressure on the wall by creating dispersion in the force level and anchor concentration. Its role will be insignificant when the width of the RS is small.