جستجوی مقالات مرتبط با کلیدواژه « پارامترهای مقاومتی » در نشریات گروه « عمران »

Therefore, the effect of the freeze-thaw process on the physical and mechanical properties of materials should be taken into account in areas with the risk of this process. In this study, the effect of freezing-thawing process on the mode I and mode II fracture toughness and the strength parameters of travertine have been investigated. For this purpose, to investigate the effect of freeze-thaw process on the mode I and mode II fracture toughness, the specimens were affected by 0, 1, 4, 8, 16, 32 and 64 freeze-thaw cycles and the fracture toughness of the specimens using cracked chevron notched Brazilian disc was determined. To investigate the effect of freeze-thaw on the strength parameters of travertine, the samples were subjected to confining pressure of 0, 2.5 and 5 MPa. Also, microscopic studies were performed to more accurately evaluate and evaluate the structural changes of the samples due to the application of freeze-thaw cycles and their texture changes. The results show that with increasing the number of freeze-thaw cycles, the mode I and mode II fracture toughness decreases exponentially and also, cohesion and internal friction angle decrease. And microscopic studies show that the microcracks in the rock have expanded due to freeze-thaw and new cracks have formed.

Geotechnical studies constitute a key part of civil engineering projects that have economic and qualitative implications for the structure and its safety during both construction and operational phases. In addition to requiring time and expenses, borehole drilling, soil sampling, and geotechnical testing can at times lead to irreparable losses and damage, such as the explosion of gas pipes or the collapse of adjacent buildings. For typical buildings, such tests can be skipped with the help of geographical information system (GIS) analysis functions. In this study, the geographical coordinates about the location of previous geotechnical studies conducted during the construction of residential structures have been determined, to create an appropriate database and with the use of GIS interpolation functions, zoning maps are prepared and presented to offer a general visualization of the geotechnical status of the area. Therefore, in this study, the geotechnical data of 170 boreholes drilled in Rasht, including soil strength parameters for individual soil layers to a depth of 12 m from ground level were collected and implemented in GIS interpolation functions. Thus, raster layers were created and after selecting the best interpolation method, zoning maps for geotechnical parameters were plotted. Results showed that overall, more than 99% of the study area has an SPT number higher than 10 and an internal friction angle lower than 28 degrees. Qualitatively, aggregate soils in the study area were generally composed of medium sandy soils while most cohesive soils in the area fall in the category of stiff.

By the expansion of the industrial zones, heavy metals enter the environment through industrial wastewater or leakage from storage tanks, which contaminates the soil and groundwater. The leakage of heavy metals such as lead, zinc, cadmium and etc. is not only an environmental crises, but also causes changes in soil shear resistance parameters. Type of soil and initial concentration of contamination are most prominent parameters that affect the behavior of contaminated soils.In this research, with Triaxial tests, the behavior of sandy soils with different percentages of kaolinite in two cases of non-contaminated and contaminated with lead is investigated. It can be seen that by increasing the lead concentration, the hydrogen bonding between kaolinite particles reduce and it decreases the resistance of contaminated soils. By increasing the concentration of heavy metals up to 20,000 ppm, the shear resistance of clayey sand with 15% and 25% kaolinite decreases by 18% and 24%, respectively. Then, to investigate the effect of clay minerals on contaminated soils, the shear resistance parameters of soil with kaolinite and soil with bentonite are compared. The results show, with variation of clay minerals in contaminated soils, resistance parameters have different behavior. Increasing the lead concentration in bentonite causes a flocculated structure, thus the shear strength increased. In soils with bentonite, shear strength parameters increase 20% to 30% with increasing the lead nitrate concentration

Soil as a substrate of land and the foundation of civil structures is of particular importance in the development of urban areas. Some soils are classified as problematic soils due to their low mechanical resistance or high sensitivity to moisture changes, such as the Chalus coastal sand. Soil stabilization with suitable materials is one of the methods of soil improvement for problematic soils. The effect of calcium carbonate (i.e., lime) and nano-calcium carbonate (i.e., nano-lime) on the mechanical properties of the Chalus coastal sand is evaluated in this study. For this purpose, after sampling the soil from the coasts of Chalus city and conducting basic geotechnical experiments, the mixtures were prepared with different percentages of lime and nano-lime and compaction and strength tests were performed on the mixtures. The results showed that lime and nano-lime improved the mechanical properties of the soil material. However, the effect of nano-lime on the mechanical properties of Chalus sand is more significant compared to lime-sand mixtures. In addition, the increase in the lime and nano-lime content in soil mixtures resulted in an increase in the internal friction angle and cohesion.

The RCC construction method is one of the alternative methods in constructing concrete and earth dams. RCC is a kind of concrete which is pressed with roller, and after being compacted with roller, it is changed to a concrete like normal concrete .Primarily, using RCC in dam construction was developed to obtain the concrete structural properties and a construction method similar to earth dams. In RCC mix design, compressibility, non-segregation, maintaining the consistency of the fresh concrete, limiting the permeability, and achieving the proper bonding among the layers is required for efficiency .A qualitatively and quantitatively wide range of materials are used for constructing RCC mixtures in different dam projects. Therefore،Primarily the RCC aimed to obtain the conventional concrete properties and the construction procedure similar to earth dams. The quality and accessibility to materials to produce RCC should satisfy the structural and durability requirements. Therefore, the proper ratio of roller compacted concrete Mixture is an important step in achieving an economical and durable concrete.  This study aims to investigate the effects of various factors on the dam RCC Mixture Design (a case study of Javeh dam in the West of Iran), which optimum Mixture Design was developed as a laboratory research while observing all technical requirements and finally it was conducted as a test pad application. Javeh Reservoir Dam is located in a distance of 40 km southwest of Sanandaj, Kurdistan and 6 km from the downstream of Gaveh Roud and Qeshlaq River intersection. The dam is made of RCC. The properties of RCC in fresh and hardened conditions are of particular importance. Technical and economic advantages of RCC dams depend on the suitability of the mix design. Therefore, by an appropriate mix design, we can investigate the effect of RCC composite materials on the strength properties of RCC in terms of compressive strength, efficiency and non-separation characteristics of aggregates and their ratios in an optimal mix design. RCC must have sufficient efficiency to achieve the desired density according to the method and facilities. The efficiency of the new mix of RCC is entirely influenced by the amount of paste in the RCC mix. The paste contains the materials finer than #200 sieve including cement, pozzolan, water, filler of the aggregates and air bubbles. From the results, the total cementitious materials used in the optimum laboratory Mixture Design is 125 kg/m3. In addition, the ratio of Paste to mortar was about 5% higher than the minimum recommended in the RCC instruction given in the manual of the US Army Corps of Engineers. The compressive strength of roller concrete is affected by factors such as the amount of aggregates, the quality of fine grains, the quality of cement materials, grade density and content of mixed moisture. Considering that artificial neural networks are among the modeling methods that have shown great power to adapt to engineering problems, the models for predicting the compressive strength of this type of 180-day concrete is discussed based on the actual results from laboratory Mixture Design by neural networks modeling. The values of correlation coefficients in each of the models made in this study were close to the value of 1, which indicates the appropriate accuracy of the models.

Adsorption has been proved to be the best process of water treatment because of its significant advantages. Clays and their minerals are abundant and cheap material successfully used for decades as an adsorbent for removing toxic heavy metals from aqueous solutions (Kashif Uddin., 2017). Environmental pollutants and their toxicity cause a major problem worldwide. New pollutants keep emerging and pose severe health and scientific challenges. Water pollution is one of the biggest environmental issue causing serious problems to living beings. The removal of various toxic substances from water and wastewater has been a core interest of many scientists and researchers around the globe over the past decades. Dyeing, battery, printing, mining, metallurgical engineering, electroplating, pigment, PVC stabilizers, nuclear power operations, electric appliances manufacturing, semiconductor, cosmetics, and so on belong to industries that generate various types of pollutants in wastewater effluent [Ali et al., 2007; Gupta et al., 2009]. By construction of engineered landfills, we can prevent the groundwater pollution. In industrialized countries, the use of compacted sand-bentonite mixture (SEB) alternatives to clay Liners due to low permeability and lack of vulnerability caused shrinkage cracks (Alston et al., 1997).

This paper has investigated the affect of quicklime on engineering behaviour of contaminated soils from the Tabriz Oil Refinery. The type of contamination of studied soil was alkali hydrocarbons that had more than 14 carbon atoms (C14) and is classified in the solid phase. The laboratory tests that were undertaken are included the pH, Atterberg limits, standard compaction, uniaxial compressive strength and direct shear test. The quicklime is added to samples in 1%, 3%, 5%, and 7% of values based on weight percentages and the results of tests are investigated at curing time of 1, 3, 7, 14, 21 and 28 days. Base on the results of improvement process of contaminated soils using quicklime, the soil plasticity has been decreased. To assessment of accuracy of the affect of quicklime on contaminated soils, pH values are determined. Based on results, with addition of 5% of quicklime, the pH value was increased and then stabled that is showing the stopping of reaction between quicklime and soil. The pH values of improved contaminated clayey for 1%, 3% and 5% of added quicklime were 10.56, 11.87 and 12.52, respectively. Also, the pH values of improved silty sand for the same of added quicklime were 10.13, 11.63 and 12.17, respectively. According to the results of different researcher, the suitable pH for reaction between soil and quicklime is 12.4. Thus, adding of quicklime to the contaminated soils from Tabriz oil refinery is efficient for soil improvement. The results of compaction test indicated a decrease in maximum dry density and an increase in optimum water content for improved contamination soils. The results of compaction test are according to the results obtained by other researchers on uncontaminated soils. According to the values of UCS measured in the uniaxial compression strength tests on improved contaminated soils, there is a direct correlation between UCS and quicklime content. Base on the relationship of consistency and compression strength of soils, the CL and SM samples changes from soft consistency to hard consistency at the quicklime content of 5%. Regarding to results, the clayey soils with contamination of 66.4 mg/kg and the clayey soils with contamination more than 66.4 mg/kg, by 3% and 5% of added quicklime showed maximum strength, respectively. The optimum quicklime for contaminated silty sandy soil is not under the contamination effect and was 3% of values based on weight percentages. Comparing the uniaxial compressive strength of improved soil samples showed that the sample with low oil material contamination had high strength. Also, with increase of curing time, the uniaxial compressive strength has been increased. Direct shear test were carried out to find the effect of quicklime on strength parameters of contaminated soils from Tabriz oil refinery. The present results show a direct correlation between quicklime content and both internal friction angle and cohesion with increasing of quicklime content. The result indicate that oil material contaminated soils of Tabriz oil refinery can be stabilized satisfactory with addition of 3% and 5% quicklime.