نشریه مهندسی عمران
سال پنجاه و پنجم شماره 12 (اسفند 1402)

Today, soil and groundwater contamination by toxic and dangerous pollutants has been raised as a global environmental problem. Soil contamination by heavy metals, especially cadmium (Cd), is a big problem with harmful effects on human health and the earth's ecology. This heavy metal also affects the geotechnical properties of the soil, leading to irreparable effects on the soil beneath structures. One of the efficient and economical methods to rehabilitate soil contaminated with Cd is the stabilization of this toxic metal in the soil by zero-valent iron nanoparticles. The present study is conducted on the effect of heavy metal cadmium contamination on some geotechnical characteristics of soil using Etterberg limit tests (liquid limit and plastic limit), uniaxial compressive strength (UCS), and compaction. Next, this contamination is stabilized in soil by using zero-valent iron nanoparticles, and the characteristics of the modified soil are examined. For this purpose, these nanoparticles were prepared by reducing Ferric Chloride (FeCl3) with sodium borohydride (NaBH4) in a vacuum environment. The laboratory results illustrate the high efficiency of these synthesized nanoparticles in removing ionic cadmium in the sample so that the amount of absorbable Cd in the samples was significantly reduced by using them in optimal conditions. The results show a very high effect in changing the amount of kaolinite and cadmium and the presence of nanoparticles on the soil’s geotechnical parameters. Also, the results of the unconfined compression tests showed that the uniaxial stress of samples with iron nanoparticles increased by 45.6, 63, 67.1, and 67.7%, respectively,

In this paper, the mechanical properties and microstructure of cement mortar containing various recycled wastes under acidic, neutral and alkaline environmental conditions are investigated. Recycled wastes including glass powders, eggshells, iron and rubber were replaced with cement in amounts of 7, 14 and 21% by weight. After psychological examination (mini-slam), all samples at the ages of 7, 28 and 90 days underwent compressive, tensile and flexural strength tests, as well as microstructural tests including electron microscopy (SEM) and X-ray diffraction (XRD) tests. Were located. Acidic environment with pH = 2.5, alkaline environment with PH = 12.5 and neutral environment (normal water) with PH = 7 were considered for processing the samples. The results show that the highest increase in compressive, tensile and flexural strength compared to the reference sample is 33% in acidic environment, 90% in neutral and acidic environment and 67% in acidic environment of cement mortar and the presence of recycled waste, respectively. Helps improve mechanical properties under acidic processing conditions. Also, the addition of rubber powder to the cement mortar composition has reduced the compressive, tensile and flexural strength up to 6.11, 2 and 2.6 times compared to the reference sample, which is not technically recommended for use in construction projects. Using glass powders, iron and eggshell powder in amounts of 7%, the water absorption of the samples at the ages of 7, 28 and 90 days can be reduced to 7.11, 13.22 and 9.29% compared to the reference sample. Dad.

In steel structures, joints play an important role in the behavior of the structure. In this paper, using numerical modeling with Abacus finite element software, several different models of connection to steel columns, modeling and placement cases have been taken. This paper investigates the effect of beam-to-column connection with two types of t-bar and corner joints. Therefore, 20 models with different conditions of different thickness and different types of hardeners, as well as 6 models with columns have been studied. Abacus finite element software has been used for modeling. All models are modeled in this software. Used to load cyclic loads.The results show that the model with t-bar hardener has a higher and has 12 to 28% higher bending capacity in the joint than the corner hardener. With increasing the thickness of the corner or spray, the connection of the beam to the column has increased to about 12 to 25% of the capacity, in the thickness of 18 mm, the anchor capacity has increased by 12% and in the thickness of 20 mm, it has increased by 25%. Is. The model of columns with concrete is about 15 to 25% different from the similar model without concrete, and the model of columns with concrete has more bearing capacity.

Congestion in the public transportation in Tehran is a convenient problem especially in the pick hours. Transferring in a congested transit vehicle makes passengers feel discomfort during their trips. Another important thing is the idea of time which is a subjective issue which means that passengers experience their travel times differently in a specific time interval. The literature has confirmed this issue, so the idea of “perceived travel time” has been introduced for many years. It implies that a passenger travelling by a congested public transport vehicle feels like the time is passing slower compared to those who are travelling in uncongested vehicles. The idea of perceived travel time has led some researchers to the concept of “perceived travel time reliability”. This paper is aimed at demonstrating the necessity of paying attention to these two concepts for the public transport system in Tehran. For this purpose, the first line of BRT system of Tehran has been considered as a case study. Using Automated Fare Collection (AFC) and Automatic Vehicle Location (AVL) data in a pick hour of a work day back in the autumn of 2019 and before spreading the corona virus, the perceived travel time and perceived travel time reliability are calculated. The results show that there is a significant difference between perceived and nominal. The differences show the necessity of reconsidering the analysis of public transport systems using the nominal travel time and travel time reliability. In fact, it seems that using the perceived will be more helpful

Using new and environmentally friendly materials to stabilize problematic soils is one of the challenges facing geotechnical engineers. Nanoclays are highly reactive due to their high specific surface area, low specific gravity, fine particles, and are also considered as an effective and environmentally friendly stabilizer due to their uniformity with soil materials. In the present study, the effect of Nanoclay on the behavioral properties of Kermanshah's clay fine-grained soil has been evaluated. For this purpose, after having conducted index and identification tests on the natural soil, Nanoclay was added to the studied soil with 0.5, 1, 2, and 4 percent by weight of the dry soil, and Atterberg, consolidation, unconfined compressive strength and California bearing ratio tests were conducted on these samples in curing periods 1, 14, 28 and 60 days. Also, the durability of the stabilized samples was investigated by applying wet-dry cycles, and to investigate the effect of Nanoclay on the soil microstructure, imaging was captured from unstabilized and stabilized samples by scanning electron microscopy. The results show that the stabilization performance is significantly dependent on the amount of Nanoclay and curing periods. Also, according to the results, the optimal amount of Nanoclay is 4%, and the presence of this amount of Nanoclay and increasing curing periods has increased the plastic index, compressive strength and soil bearing ratio and decreased the coefficient of consolidation, settlement, Compression, permeability, and soil swelling. It is noteworthy that soil durability against environmental conditions has also increased.

The present study, which is of an applied type, was conducted with the aim of geotechnical zoning of the soil of Ahvaz city using GIS. By collecting geotechnical information obtained from 200 drilled boreholes to a depth of 10 meters and using ArcGis, soil geotechnical parameters were zoned in Ahvaz. Factors affecting soil bearing capacity including soil adhesion, internal friction angle, and soil specific gravity were selected for zoning. The zoned interpolation map of the internal friction angle in Ahvaz city showed that with increasing soil depth, the internal friction angle has increased. With increasing depth, the internal friction angle has increased, so that at a depth of 10 meters, in most boreholes drilled in the mentioned areas, the amount of internal friction angle has increased to more than 41 degrees. The results of the adhesion zoning map based on the drilled boreholes showed that there is no statistical relationship between this geotechnical component and the depth increase. Also, the study of soil-specific gravity based on drilled boreholes and zoning interpolation map in the present study showed that with increasing soil depth, the average specific gravity increased significantly from 1.6% at 2 m depth to 47.9% at depth of 10 Meters has been reached. In general, these components, especially specific gravity, are related to determining the load-bearing capacity of the soil and can be used to assess the feasibility of choosing the best spatial option for the construction of specific projects.

The forces applied to cutting discs are among the most important design parameters for tunnel boring machines (TBMs) used in rock excavation. These forces include normal and rolling forces, which are influenced by factors such as penetration depth, spacing, linear and rotational speed of the disc. Therefore, it is necessary to carefully examine these forces for the design of TBMs. Linear cutting tests are time-consuming and expensive, so high-accuracy numerical simulations can be a suitable alternative. In this article, LS-DYNA software was used to conduct simulations for the validation of two behavioral models of concrete, Johnson Halmquist (JHC) and RHT. The effect of variables such as penetration depth, linear and rotational speed of the disc on the forces was investigated. The results indicate that penetration depth has a significant effect on both normal and rolling forces. Increasing the penetration depth from 2.5 to 7.6 mm results in an increase in normal force from 96 to 159 kN and an increase in rolling force from 6.1 to 22.5 kN. As the linear and rotational speed of the discs increase, the forces decrease slightly. However, increasing the linear speed from 0.33 to 1.65 mm only causes a 13% decrease in normal force (from 155 to 175 kN) and a 5% decrease in rolling force (from 20.6 to 19.5 kN), according to the obtained results.

In recent years, the issue of identifying polluting sources in rivers has been one of the most important topics in scientific researches in the field of water. In the main researches, the pollutant sources have been considered as the point sources and in order to recover pollutant concentration, it is necessary to have an observation point for each source. In this study, the places where groundwater enters to river are considered as several distributed sources with known location and length and goal is to recover the intensity of sources, using only one observation point. The sources which considered in this research are distributed sources with constant loading and significant distance from each other. The existence of significant distance among sources prevents the complete mixing of concentration at observation point. This matter and also the constant intensity of loading, makes it possible to recover several distributed sources using only one observation point. For this purpose, the inverse solution of the advection-dispersion equation is done using the simulation-optimization approach. To design the backward model, MIKE11, linked with genetic algorithm in MATLAB. Considering one observation point for recovering the salinity intensity of several distributed sources and providing a general framework to recovery of distributed sources are advantages of the present study. The performance of the developed approach is evaluated under different examples and measurement error conditions. The computational results indicated the backward model can recover the salinity intensity of several distributed sources with high accuracy using only one observation point, even with noise.

The present study was conducted with the aim of investigating the water quality characteristics and nutritional status of Miankaleh wetland using Carlson Trophy Index (TSI) and TRIX. Measurement of parameters has been done during 6 seasons and 8 sampling periods in 6 stations of Dahane-ye-chopoghli, Bandar-e-Gaz, Gharehsu, Galogah, Ismaeilsay and Miyan ghaleh. Based on the presented results, Dahane-ye-chopoghli, and Gharehsu stations respectively have the highest amounts of phosphate (0.12 mg/l), nitrate (11.04 mg/l), the lowest DO (87 mg/l) and the highest BOD (mg/l 14/77) which indicates the unfavorable condition of the wetland in terms of quality. Calculation of index (TSI) based on (TP) shows that Miankale wetland is in hypertrophic condition (70-80) in four stations and in eutrophic condition (60-70) in Bandar-e-Gaz and Ismaeilsay stations. On the other hand, based on (TN), except for Galogah station,, the rest of the stations are in acute hypertrophic condition (80-100). In general, based on the total TSI index (29.62), the status of the wetland is in the eutrophic range (60-70). The main cause of these conditions is the discharge of sewage and drains from different units on the edge of the lagoon, which contain large amounts of nitrate and phosphate compounds. Therefore, emphasizing the correct and balanced use of chemical fertilizers in accordance with soil needs in order to reduce the load of micronutrient elements should be planned.

In the current study, the performance of helical soil-nailed walls (HSNWs) was evaluated under footing loading using reduced-scale model tests. For this purpose, sixteen soil-nailed wall models were constructed with different lengths, patterns and inclinations of the helical nails and then were loaded to failure using the strip footing. The quantitative and qualitative responses of the models to footing loading were identified in terms of the wall displacements, the deformation modes and the bearing capacity of footing. Particle Image Velocimetry (PIV) technique was also used to trace shear bands and identify the failure mechanism. PIV results showed that increasing the nail length, as well as using a square pattern and a 15° angle to install the nails, could be three effective solutions to reduce the penetration depth of the slip surface and, consequently, to limit wedge failure dimensions. Findings also indicated that 15° can be introduced as the optimal inclination for installing helical nails in walls under strip footings to achieve the maximum bearing capacity and minimum lateral wall displacements.