مجله مهندسی زیر ساخت های حمل و نقل
سال ششم شماره 1 (پیاپی 21، بهار 1399)

In this study, cracking growth behavior of asphalt mixture was investigated by heterogeneous modeling. First, the asphalt samples are created by using generation and random distribution algorithm of the aggregates. These asphalt samples are numerically analyzed and failure parameters of the asphalt mixture are calculated. Then, the effect of aggregate distribution, elasticity modulus of aggregates, Poisson coefficient of aggregates, elasticity modulus of mastic, Poisson coefficient of mastic, and loading under combined modes on failure parameters are evaluated. Results showed that heterogeneous modeling considerably affects the mechanical responses of asphalt mixture. Position of the crack tip has significant effect on value and sign of the stress intensity factors, such that if the crack tip is located in the mastic region, the mode I of stress intensity factor in homogeneous modeling will be less than heterogeneous modeling. But if the crack tip is located in the aggregates, the stress intensity factor of heterogeneous modeling will be greater than homogeneous modeling.

Direct damage localization of bridge involves the use of a large number of vibration sensors on the structure, which is often costly and time-consuming. Through vehicle bridge interaction, dynamic response of a passing vehicle includes the bridge response which may be used for extracting bridge modal parameters. In this paper, transmissibility measurement of the vehicle response is dedicated to localize indirectly the bridge damage. As the sensor is embedded on the axle of the vehicle, recording the signal is fulfilled during the vehicle passage and there is no need to stop the vehicle. There is white noise assumption in most other techniques. But excitation characteristics are not considered in this method; which is another advantage. Since the road profile may cause modal parameter identification to be difficult, subtracting the acceleration signals from two identical axles is used here in order to remove the influence of road profile. In the numerical simulation by finite element method, the bridge model is accompanied by road profile and three vehicles are assumed to be 2DOF systems of mass-spring-damper. By solving the vehicle-bridge interaction equations simultaneously and then removing the effect of road profile, the estimation of bridge mode shape would be possible. Then, by considering bridge damage, the vehicle-bridge interaction equations are solved once more and the damage localization is fulfilled using the changes in the mode shape curvature. Results of numerical simulations indicated the capability of the proposed method in the presence of measured noise.

The type of asphalt pavement performance depends on its material properties, manufacturing process and implementation. Surface free energy is an important feature of aggregates and bitumen in predicting the performance of asphalt mixture. Surface free energy indicates the amount of bitumen and aggregate adhesion and the energy parameters related to the moisture resistance performance of bitumen and aggregate. In addition, the mixing temperature of modified bitumen, as part of the modified bitumen preparation method, may have an effective role in the final performance of the bitumen and its composition with aggregates. In this article, the effect of modified bitumens with epoxy resin and their preparation temperature on bitumen surface free energy and moisture resistance of asphalt mixtures is investigated. For this purpose, the modified bitumens containing epoxy resin additive were prepared at 2, 4, 6 and 8 percent (w/w) of bitumen at two temperatures of 90 and 130 °C and surface free energy parameters related to moisture sensitivity were calculated. Results showed different performance between various compositions of bitumen and aggregates for different percentages of additive and bitumen preparation temperatures. In bitumen and silica aggregates, modified bitumen with 6% epoxy resin at 90 °C mixing temperature, and in bitumen and limestone aggregates, modified bitumen with 4% epoxy resin, with 130 °C mixing temperature, showed optimum performance in terms of moisture resistance.

Improving bitumen with additives such as nanomaterials will be difficult in adding the materials and mixing them occasionally both in laboratory and real scale. Therefore, in this research, we tried to improve the performance of the samples by making changes in the way of preparing the samples, while simplifying production process conditions. The hypothesis of this research is based on the principle that this method firstly helps prepare the Nano-clay and increase the distance between the plates, and secondly, reduces the steps and the time duration of adding different materials to bitumen. Also, it improves the rheological properties and the way in which the materials are dispersed in bitumen. In this research, 12 samples were considered that have been prepared by pre-mixing and conventional mixing methods, and the differences in their properties were investigated under different process conditions. Using classical experiments (degree of penetration, softness and ductility point) and performance based tests such as PG and temperature sweep, tested and compared the properties of the samples improved in different methods. The results showed that the use of premixing method compared to the conventional method has a greater effect on improvement of the properties of bitumen and achievement on the similar properties with the conventional method but in less mixing speed. The reduction of mixing speed, while affecting the improvement of bitumen aging, demonstrated the superiority of using the premixing method. In general, changing the method of bitumen improvement showed its effect on reducing aging caused by the mixing process and on preparing a more homogeneous mixture having more suitable function. It should be noted that the samples made by the premixing method showed a higher "behavior change temperature" (T75 °) than the conventional method.

The need for development of an urban underground transport network is increasing in modern cities. Nowadays, to excavate metro tunnels in urban areas, earth pressure balanced-tunnel boring machine (TBM-EPB) is widely employed. Nevertheless, inevitable ground movements in the surroundings of the tunnel could still be dangerous for surface structures and urban infrastructures. In this study, the effect of surface structure on tunneling-induced surface settlements was investigated. This study consisted of some sections of Madrid metro project and three hypothetical monolayer sections, and the three assumed variables were soil type, number of surface structure stories, and surface loading to tunnel diameter ratio (C/D). Three types of soil (calcareous sand, brown clay and blue plastic clay), three number of stories for surface structure (3, 5 and 10) and three C/D ratios (1, 1.5 and 2) were chosen for the parametric study. The volume loss control method and Mohr-Columb model for soil were used in the two-dimensional modeling of TBM tunneling. Results indicated that the existence of surface structures and their stiffness effect have always decreased tunneling-induced settlements. However, the intensity of this settlement reduction varied with soil type, number of surface structure stories and C/D ratio, and by changing the soil type, the effectiveness of the other two parameters varied sensibly.

Nowadays, transportation is one of the most important components of national economy. Every year, many hills and natural slopes are excavated to build transport infrastructure. The stability of trenches created by excavations is important during construction and operation. In nature, these treches are mainly unsaturated and should be analyzed with theory of unsaturated soils. One of the main causes of trench instability is rainfall and water infiltration. In this research, using theory of unsaturated soils and finite difference numerical method, rainfall infiltration trend and its effect on pore water pressure variations, saturation percent, deformations and finally its stability during rainfall event was investigated. For his purpose, in addition to field and laboratory test for estimation of geomechanical parameters of the materials, the RETC software was used to obtain soil-water characteristics parameters. Results showed that the factor of safety decreases with increasing duration of low-intensity rainfall from 1.283 to 1.221 in 5 months, but the rate of decline is not sufficient to cause complete instability. But for short-term high-intensity rainfall, due to the lack of infiltration and water flow in the slope, maximum impact occurred in the upper 2 m of the slope, and in this zone, in addition to weight increasing, suction and shear strength of the unsaturated soil have decreased. Due to conjugate effect of these two factors, within 48 hours, the factor of safety decreased to 0.981 and led to instability of trench.

Ride comfort and sight distance are two main parameters of designing roads’ vertical curves. Vertical acceleration is one of the most important criteria for measuring ride comfort in vertical curves. Vertical acceleration equations in geometric design of roads in the literature, such as Green Book of AASHTO, are based on point mass model where vehicle is assumed to be a point object with a specific mass. Considering that vehicle is a multi-body system, dynamic responses of each part of this system can be different from a point object. In this study, CarSim and TruckSim dynamic simulation softwares utilizing Multi-Body (M-B) model are used to investigate more accurately the vertical acceleration, and to compare it with the vertical acceleration of the point mass model. Dynamic responses of three types of vehicles have been investigated under different speeds and grades. Results indicated a significant difference between the results of the two models, depending on the vehicle speed and the road grade, and the point mass model suggested less acceleration such that difference of the vertical acceleration between the point mass model and the M-B model, depending on the vehicle speed and the road grade, ranged 12.6-25.9% for Sedan, 23.8-29.1% for SUV and 29-47.6% for the truck. According to the results of this study, to design vertical curves, the use of M-B dynamic model, according to more accurate simulation of the vehicle, delivers more realistic design.