فصلنامه جاده
سال نوزدهم شماره 1 (پیاپی 67، تابستان 1390)

In recent years, there has been much greater attention given to planning and development in Iran, due to increasing environmental, financial and social factors. In particular, a very important subject area within this field is that of aviation and more specifically; passenger transport by air. There has been a considerable research effort that has resulted in the collection of a large amount of data on this topic. However, despite this massive information-gathering exercise, the required statistical analyses and the matter of mathematical modeling have been neglected, meaning that conclusions and improvements in future practice have not been drawn from the extensive data. This paper intends to rectify this, by presenting a mathematical model that can predict the demand for aerial trips in Iran. The model is based on a process according to which the determined social and economic transportation system variables are connected to the demand for transport by air. To calibrate the model, the regression method has been used, based on data that was collected from several Iranian cities.

In this paper a closed-form stress plasticity solution is presented for gravitational and earthquake-induced earth pressures on retaining walls. The proposed solution is essentially an approximate yield-line approach, based on the theory of discontinuous stress fields, which takes into account the following parameters: (I) weight and friction angle of the soil material, (2) wall inclination, (3) backfill inclination, (4) wall roughness, (5) surcharge at soil surface, and (6) horizontal and vertical seismic acceleration. Both active and passive conditions are considered by means of different inclinations of the stress characteristics in the backfill. Results are presented in the form of dimensionless graphs and charts that elucidate the salient features of the problem. Comparisons with established numerical solutions, such as those of Chen and Sokolovskii, show satisfactory agreement (with a maximum error for active pressures of around 10%). It is shown that the solution does not perfectly satisfy equilibrium at certain points in the medium, and hence cannot be classified in the context of limit analysis theorems. Nevertheless, extensive comparisons with rigorous numerical results indicate that the solution consistently overestimates active pressures and under-predicts the passive. Accordingly, it can be viewed as an approximate lower-bound solution, rather than a mere predictor of soil thrust. Compared to the Coulomb and Mononobe-Okabe equations, the proposed solution is simpler, more accurate (especial1y for passive pressures) and safer, as it overestimates active pressures and underestimates the passive. Contrary to the aforementioned solutions, the proposed solution is symmetric, as it can be expressed by a single equation describing both active and passive pressures, by using appropriate signs for friction angle and wall roughness.

Basal heave instability is one of the deep excavation failures in soft clay. This type of instability usually occurs immediately after excavation and should be controlled according to a short term analysis (undrained). In order to evaluate the base stability of excavations, numerous equations have been developed by various researchers based on the limit equilibrium theory. The differences among these methods are in terms of the failure mechanisms and simplified assumptions. Despite extensive academic and practical use of these equations, some uncertainties can yield results with doubtful levels of accuracy. In this paper, the basal heave stability is evaluated using the finite element method, and the results are compared with the safety factor obtained from equations based on limit equilibrium analyses such as the Terzaghi equation (which considers wall embedded depth), the Eide et al. equation and the Japan Code method (resisting moment). Using a sensitivity analysis, the effect of various parameters on the results from these methods is then investigated. The results indicate that the safety factors from the numerical analyses are in good agreement with those obtained from the resisting moment method. Moreover, using the Terzaghi equation in basal heave stability analyses yields underestimated results.

This paper presents the fundamental principles and practice of four commonly used asphalt mixture design procedures in the United States. The methods covered include the Marshall, Hveem, Superpave and GTM mix design methods. Emphasis is placed on comparing them with regards to the three main elements of mix design procedures, namely: 1) Method for preparation and compaction of the asphalt mixtures2) The properties of the compacted specimens to be measured3) Criteria used for selecting acceptable and optimum mix designs

With regards to transportation vehicles, the substantial improvement in technology and the numerical increase of them in the transportation system; means that improvements in the quality and quantity development of roads has became a vital issue. One method of improvement and promotion of safety of roads and their performance is the use of higher quality and more appropriate materials, which will allow an increase in durability and bearing capacity. Slag is a material, which in regards to its engineering and performance characteristics could be used to replace some of the natural aggregates in asphalt used to manufacture the layers of a pavement. In this research study, the potential of using slag to replace aggregates in the base and sub base pavement layers is reviewed in accordance with the standard of ASTM5108. The recommended tests in this standard that were carried out are: Chemical analysis, specific gravity, absorption, abrasion and soundness. The results of the tests on the addition of slag indicate that due to its characteristics it is a suitable aggregate material for use in the base and sub base layers of pavements.

Two main of mechanisms of damage in rails and wheel contacts are wear and Rolling Contact Fatigue (RCF).The material selection for the wheel and rails is based on wheel wear, where the wear rate of wheels is greater than that of the rails. It can be seen that the wear of wheel surfaces results in the removal of the initiated micro cracks that would be subject to propagation and failure with rolling contact fatigue. However, despite this advantage, the micro cracks initiated on the rail surfaces gradually propagate and cause sudden fracture or detachment of a piece of the rail surface material. This could cause derailments, which is a vitally important issue in rail transportation. This paper investigates the mechanisms of RCF failure, which is a primary phenomenon in rails. Recently, due to the introduction of high velocity trains and increased axel loads, this issue has drawn greater attention, especially with regards to failure mechanisms, prediction of failures, effective parameters and predictive methods.

Shrinkage cracking occurs in cement-treated bases due to desiccation and cement hydration. Eventually these cracks propagate through the pavement surface. These cracks render the pavement susceptible to water infiltration and increase the likelihood of accelerated pavement distress. Numerous options exist for minimizing the incidence of these reflective cracks. This paper focuses on the effects of microcracking on the performance and behavior characteristics of cement-stabilized bases. The microcracking concept can be defined as the application of several vibratory roller passes to the cement-treated base during a short curing stage typically after one to three days, in order to create a fine network of cracks. Based on the investigations carried out immediately after the microcracking, the stiffness and compressive strength of the stabilized layer will be diminished. Furthermore, as this is performed only a few days after placement, in the long term the microcracking will not impact the pavement’s overall structural capacity. Additionally, the research study has shown that microcracking is quite effective at reducing shrinkage cracking problems in the stabilized base. Thus microcracking should be considered as a viable and inexpensive option to incorporate shrinkage crack control into the construction of cement-stabilized bases.