نشریه مهندسی عمران فردوسی
سال سی و دوم شماره 1 (بهار 1398)

This study aimed at investigating air travellers’ behaviour with regard to choices for ground access to Imam Khomeini International Airport. The choices included subway, bus, carpooling, taxi, private car (parking) and private car (car drop-off). Data collection for this study was done during three days in summer, 2014, and Multinomial logit modelling was employed for this purpose. The survey was administered as a face to face interview in Imam Khomeini International Airport, which is located in Tehran, Iran. A total number of 257 questionnaires were collected, with the degree of validation being 34%. The most important results of this research indicate that the majority of imam Khomeini passengers have a high income(%90of them have 1.5 million tomans per month or higher) and car ownership(%92 of them have at least one car in their household). Considering that these passengers don’t have intention for using metro, with increasing the travel time, public transportation costs (e.g. parking cost) and improving metro service qulity (e.g. increasing the reliability and decreasing the travel time) , it may be possible to absorb them to use metro.

In this research, effects of pine tree sawdust on geotechnical properties of two types of kaolinite clayey soil was evaluated. So that, sawdust in 3, 6 and 9 percent (by weight) in dry condition randomly mixed with two kaolinite clayey soil with different plasticity index. Compaction, uniaxial, permeability (falling head) and consolidation tests were performed on specimen. Results showed while 3% sawdust mixed to samples, 24% minimum void ratio (emin) decreased in kaolinite clay with high plasticity index. Also, in this condition, increasing of bearing capacity and strength, ductility and decreasing in water absorbing have been happened

Marls are problematic soils, which easily erode if they are exposed to water flow and problems in the stability of the bedding of construction projects can be occurred. One of the methods for soil chemical modification is the use of additives such as lime, cement and nanoparticles. The effect of adding nano-SiO2 on the lime performance on the enhancement of the improvement process of the marl soil engineering properties and the formation of new compounds due to the stabilization process has been investigated in the present study. In this regard, after determining the geotechnical properties of Marl soil, improvement of engineering properties of samples stabilized with various percentages of lime and nano-SiO2 after the end of the curing period was analyzed by performing large-scale experiments (Atterberg limits, aggregation, deposition and unconstrained compressive strength (UCS), and microstructure ((pH) and X-ray diffraction (XRD)). According to the results of this study, the presence of nano-SiO2 in the marl-lime soils system has led to increased pozzolanic activities and growth of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) nanostructures and uniform distribution of these nanostructures. The compressive strength of the modified samples with the combination of nanosilica and lime proportional to the increased nano-silica additive has a quite ascending trend. Based on the results of the present study, the development rate of improvement of marl soil engineering properties in a modified specimen with 6% lime and 1% nano-SiO2 increased the compressive strength in the first 7 days by 18.45 kg/cm2 and the compressive strength increased by 18 times compared to the reference specimen.

The aim of this research is to experimentally investigation of ordinary stone column and reinforced stone column using horizontally laminated geotextile disks in stabilizing sandy slopes. The sand slope model saturated through precipitation and reinforced by installing ordinary stone column and horizontal layers of geotextile within the stone column, and then slope crest undergo loading. Accuracy of experimental results confirmed using 3-D finite difference method (FLAC3D). Both experimental and numerical results show that geotextile reinforced stone column in the middle of sandy slope have an impressive impact on increasing stability of reinforced slope. In such way that reinforced stone column, increase shear strength of sandy slope up to 1.5 times more than ordinary stone column.

Two effective modifications were introduced for Pastor-Zienkiewicz (PZ) model to improve the prediction of dynamic behavior of granular soils. The first modification was implementation of degradation effect for dense granular soils under cyclic loading, and the second was improvement of ratcheting effect for granular soils under cyclic loading. Three cyclic triaxial tests and three cyclic plane strain test were used to validate the introduced modifications. Predictions of stress versus strain for both of modifications were satisfactory. However, predictions of volumetric strain for the second modification were better than those of the first modification.

In this paper, the mechanical properties of special concrete with magnetic heavy weight aggregates and steel fibres, from 24 different mixed designs with 0, 50, 100% of heavy weight aggregates replacing with regular aggregates, 0.52 and 0.4 water-cement ratios and 0, 1, 1.5 and 2% of steel fibers, totally 300 specimens including cubic, cylindrical, and beam was investigated. The results showed that the compressive, tensile and shear strenghts were improved with using special aggreagate and fibres particularly with 50% high weight aggreagate and 2% steel fibres.

In this paper epistemic uncertainty of random variables in the reliability analysis of Adjusted Stability Transformation Method has been modeled and fuzzy structural reliability index has been determined using GA. In the reliability analysis process, a dynamic adaptive approach based on stability transformation method has been applied which the control coefficient is self-adapted at each iteration. Moreover in order to investigate the importance of epistemic uncertainty in the fuzzy structural reliability index, sensitivity analysis using Entropy-Shannon has been done. Survey results of three structural examples indicate that the proposed reliability method provides stable results with suitable computational efficiency. The sensitivity of failure probability to epistemic uncertainty has shown a considerable effect on the structural reliability in some problems.

Increasing construction industry and the need to build structures on lands that do not have sufficient load-bearing capacity resulted in the development of soil improvement techniques to enhance site capability. The use of stone columns for the ground improvement for reasons such as environmental compatibility, cost effective, minimizing the liquefaction potential of the ground, settlement reduction, increase of the load-bearing capacity and significant reduction in the period of consolidation is considered as one of the most effective soft soil reinforcement methods. Stone columns can be designed to bear on the hard stratum or as a floating system where the toe is embedded in the soft layer. What in recent years were as the basis for designing of groups of stone columns were based on the theories developed for single stone columns ignoring the group interaction. Most of the existing design methods for stone columns adopt unit cell idealization which is not applicable to spread footing. To assess the influence of various parameters on the performance of a group of stone columns, in this paper which is based on the finite element method, the effect of hardness and resistance parameters affecting the load bearing capacity was discussed. More than 140 analyses of different parameters of soil and stone columns were carried out and were discussed in the form of graphs to compare the effects of these parameters. Results showed that using stone columns had a significant impact on increasing the bearing capacity of the soft grounds. The rate of growing enhances with increase of replacement ratio of stone columns into the soft soil due to group interaction. Increase of elasticity and internal friction angle of column materials as well as soil Poisson's ratio have a significant impact on increasing load-bearing capacity on the other hand when Poisson's ratio of stone columns increases any substantial change isn’t see. In addition of bearing capacity increase, growth of replacement ratio enhances the impact of strength and stiffness parameters of soil and columns on bearing capacity increase which shows the influence of the group interaction. End bearing columns were observed as a factor influencing the increase of bearing capacity and intensifying the effect of stiffness and strength parameters on column bearing capacity.

In this research an attempt has been made to model flow field in compound channel with skewed floodplains for two skew angles of 5.1o and 9.2o and relative depths of 0.15, 0.24, 0.41 and 0.50. For numerical modelling the k- turbulence model and the ANSYS-CFX software were used. The results of numerical modelling of the velocity and boundary shear stress distributions at two selected sections were then compared to the Flood Channel Facility Experimental Data. The study shows that more or less there are good between the experimental data and the results of numerical modelling. Using the momentum equations for the control volumes on the floodplains, the interaction between flow in the main channel and on the floodplains for different skew angles and relative depths has been investigated. The study indicates that in general by increasing the skew angle and water depth due to mass exchange between the subsections, the apparent shear forces at the vertical interface between the main channel and floodplains increases.