جستجوی مقالات مرتبط با کلیدواژه « subgrade » در نشریات گروه « عمران »
تکرار جستجوی کلیدواژه «subgrade» در نشریات گروه «فنی و مهندسی»-
The fine-grained soil including the problematic ones can cause many difficulties in project accomplishment. Settlement and swelling are among the problems of the fine-grained soils. The present study compared the effects of the polypropylene waste plastic (PWP) and glass fiber reinforced polymer (GFRP) on geotechnical properties of the clayey soils for the subgrade design. To this end, the PWP and GFRP were randomly mixed with the fine soils of different plasticity indexes in similar weight percentages (i.e., 0.25, 0.50, 0.75, and 1). Further, compaction, unconfined compressive, direct shear, and California bearing ratio tests were performed in both dry and saturated conditions, followed by conducting the falling head permeability test. The results showed that PWP and GFRP materials were effective in the swelling potential of the clayey soil. In other words, the swelling potential decreased by about 32% and 33% in both CH and CL samples when the PWP content increased up to 0.75% in the specimens, respectively. In addition, this potential decreased by 60% when the GFRP (0.75%) was added to the specimens. Also, bearing capacity and elastic modulus increased mixing PWP (0.75%) or GFRP (0.5%) in the clayey soils by high and low plasticity indexes. Therefore, the improved soils can be used to make a subgrade layer for the pavement.Keywords: Subgrade, Clayey soils, Glass fiber reinforced polymer, Waste polypropylene plastic particles, Pavement}
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This paper covers using of waste glass bottles to modify the properties of poor subgrade soils. The study involved grinding of waste glass bottles into powder in two categories based on the size of particles: category S1 includes particles between 425µm and 75µm whereas category S2 includes particles finer than 75µm. For both categories, five different contents of glass powder were added to a selected soil to investigate their effects on its engineering properties. The results exhibited that increase in glass powder content increases the strength of subgrade soil and decreases its volume change susceptibility. However, using S2-powder revealed better results than those attained using S1-powder. Compared to unmodified soil, maximum dry density, resilient modulus, and CBR values of soils modified using 20% of S2-glass powder increased to 112%, 394%, and 853% respectively whereas the values of liquid limit, plasticity index, optimum moisture content, and swelling ratio decreased to 85%, 68%, 80% and 51% respectively.Keywords: Subgrade, Properties Modification, Waste Material, Glass Powder, Soil Strength, Swelling Potential}
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The subgrade soil always suffers from variation in the level of moisture due to many factors such as capillary action, precipitation, flood, and change in groundwater table. So, it''s very important for the engineer to understand clearly the nature of relationship between the subgrade strength and variation in moisture. The main objective of this study is to investigate the changing in the strength and durability of subgrade soil due to the variation in water content. The natural samples tested with three percentages of moisture contents (11.5%, 13.5%, and 15.5%).Physical and chemical tests are carried out on the natural soil samples brought from Al-Sader city. The soil classified as lean clay with accordance to Unified Soil Classification System (USCS) while classified as (A-7-6) according to (AASHTO) classification system. After (28 days) period of leaching for the natural samples with different moisture contents and under surcharge load of (10 Ibs.) the results indicate that, the samples at the dry side give higher resistance to leaching strain as compared to the other samples. With the increasing of hydraulic gradient; the strength of soil will decrease.Keywords: Subgrade, Leaching, Strength, Durability, CBR, Hydraulic gradient, Strain}
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یکی از روش های افزایش ظرفیت باربری و کنترل میزان نشست و تغییرشکل خاک در روسازی راه، استفاده از ژئوگرید ها می باشد. در این مقاله با مروری بر تحقیقات انجام شده در طول دو دهه ی اخیر در ارتباط با مکانیزم های عملکرد ژئوگرید و کاربرد های آن در راه سازی، خصوصیات مقاومتی بستر مسلح با ژئوگرید مورد بررسی قرار گرفته است. بررسی ها نشان می دهد در اثر تسلیح خاک با ژئوگرید در خاک های با ظرفیت باربری کم، خصوصیات مقاومتی خاک از قبیل CBR، چسبندگی، سختی و مدل الاستیسیته، به صورت چشمگیری افزایش می یابد ولی تغییر قابل ملاحظه ای در زاویه اصطکاک داخلی خاک ایجاد نمی کند. هرچه خاک بستر ضعیف تر باشد، تاثیر تسلیح با ژئوگرید پررنگ تر می گردد. همچنین در این مقاله مطالعات صورت گرفته در خصوص تعیین پارامتر های طراحی روسازی مسلح شده با ژئوگرید و ارزیابی عملکرد ژئوگرید برای روسازی دانه ای و روسازی انعطاف پذیر، ارائه شده است.کلید واژگان: روسازی, ژئوگرید, بستر مسلح, CBR, ظرفیت باربری}In last decade, Geosynthetics as polimerical products have been applied for various use in civil engineering such as reinforcement, separation, filtration, Drainage, Fluid barrier and Protection. Subgrade soil and its properties are very important in the design of road pavement structure and Its main function is to give acceptable base to the pavement from underneath. Since Pavements constructed over soft subgrade having poor strength parameters such as CBR leading to more thickness of the pavement, successful use of geosynthetics is ensured in a given geotechnical application. As it is well-matched and effective in improving the soil properties when appropriately used. A geogrid as a geosynthetic material containing connected parallel sets of tensile ribs with apertures of sufficient size to allow strike-through of surrounding soil, stone, or other geotechnical material is a common form of subgrade reinforcement. Geogrids used in subgrade as a part of road pavement, has primary functions of geosynthetics which are separation and reinforcement. Geogrid have been successfully used to provide a construction platform over subgrades. Due to recent studies, lateral restraint, improved bearing capacity and tensioned membrane effect are reinforcement mechanisms which have been identified the use of geogrids to reinforce pavement materials. This study investigated the behavior of reinforced subgrade with geogrid and the effect of reinforcement on soil properties. it is considered various research on geogrid use in pavement. It is shown that the composite of geogrid and soil can reduce the desired thickness of aggragate layer. It is also mentioned that the use of geogrid in pavement system will affect the cohesion of subgrade and improve the mohr-coloumb strength parameter of the soil.Keywords: Geosynthetic, Geogrid, Reinforcement, Subgrade}
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جداسازی لرزه یی به منزله ی یک رویکرد نوین کنترل غیرفعال سازه قادر است به طور چشمگیری پاسخ سازه را در حرکات قوی زمین کاهش دهد. عملکرد این سیستم ها در زلزله های حوزه ی نزدیک، که حاوی شتاب هایی با محتوای بسامدی بالا و پالس های بلند هستند، با تردید روبرو است. به کارگیری میراگرهای ویسکوز در تراز جداسازی، یکی از راهکارهای ارائه شده برای بهبود عملکرد این سیستم ها در زلزله های حوزه ی نزدیک است. در این نوشتار، تاثیر مقادیر مختلف میرایی الحاقی از 5٪ تا 40٪ در سازه های جداسازی شده تحت زلزله های مختلف در نرم افزار A B A Q U S مورد بررسی قرار گرفته است. نتایج نشان داده است که افزایش میرایی الحاقی در شتاب نگاشت های حوزه ی نزدیک، جابجایی تراز جداسازی را کاهش می دهد، اما سبب افزایش جابجایی نسبی طبقات و شتاب طبقات می شود. در حالی که افزایش میرایی الحاقی در تحلیل های تحت شتاب نگاشت های حوزه ی دور سبب کاهش جابجایی تراز جداسازی، جابجایی نسبی طبقات، و افزایش شتاب طبقات می شود.
کلید واژگان: میراگر الحاقی, جداسازی لرزه یی, تحلیل دینامیکی غیرخطی, زلزله ی حوزه ی نزدیک}Seismic isolation as a passive control method of structures and an innovative approach in resistant seismic design reduces significantly the responses of structural system induced by strong ground motions. The performance of these systems in near fault (NF) ground motions with large pulses is different from far fault (FF) ground motions. It is shown that the effects of near field earthquake with large velocity pulses can bring the seismic isolation devices to critical working conditions. To overcome this problem the application of viscous damper is represented as an approach to improve the performance of these systems in near field earthquakes. In the present paper, by modeling six base isolated structures, the seismic responses has been studied under near field and far field earthquakes. The isolators were modeled by using a mathematical model depicted by bi-linear hysteretic behavior. Nonlinear time history analyses were performed using finite element software of ABAQUS to study the influence of different values of supplemental damping (5%-40%) on the responses of base isolated structures. The variation of floor absolute acceleration, bearing displacement and storey drift for different values of supplemental damping under near field and far field earthquakes was studied. The influence of supplemental damping on the responses of isolated structures were studied under the variation of important system parameters uch s uperstructure flexibility, period of frames and number of storey of base isolated structures. The results showed that, generally, by increasing the damping ratio, responses of structures including the maximum floor acceleration and maximum floor relative displacements increased under near field earthquakes. But maximum floor elative isplacements decreased under far field earthquakes. It was observed that base displacement response decreased by increasing damping ratio under near field and far field earthquakes. This reduction under near field earthquakes is greater than far field earthquakes. Also by increasing the supplemental damping under near field and far field earthquakes, the maximum story acceleration increased.
Keywords: Seismic Isolation, Near Field, Damping, Subgrade, Abaqus} -
In this study, the performance of shred tire mixed with railway subgrade is evaluated to reduce environmental vibrations caused by trains’ passage. Since incorporating the Shred Tire seeds in soil affects on its shear strength and deformability parameters so, the first stage of the study was allocated to conducting a series of laboratory tests such as the unconfined compression test, and CBR and cyclic plate loading tests on the base material of GW-GC in combination of tire derived aggregates with particle size ranged from 0.475 to aggregation 2.5 cm in four various percentage of 0,5,10 and 15. Moreover, the cyclic plate loading tests were accomplished to determine the mixture elasticity modulus in the second loading cycle as Ev2.By using the obtained values of shear strength as well as deformability parameters obtained in the lab, a 2D numerical model of ballasted track was established under step loads corresponding to a passenger bogie. The numerical results showed that due to increase in shred tire percentage from 5 to 15 percent, the vertical vibration velocity at the ballast shoulder decrease up to 44.56 percent while this value reach to 44 percent for a point with 5 m distance from track shoulder. As a practical result an equation was proposed to show the relation between shred tire percentage and value of environmental vibration.Keywords: mix of shred tire, Subgrade, plate loading test, vibration caused by trains}
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مدول بستر ریل یکی از پارامتر های مهم در طراحی بهینه خط است که با توجه به اجزای تشکیل دهنده خط بالاستی تعیین می شود.
شناخت رفتار بستر خط راه آهن تحت شرایط مختلف و بر روی زیرسازی با مشخصات پیچیده امری لازم و مفید است. مشخصات فنی و هندسی زیرسازی خط می تواند بر مدول بستر ریل نقش بسزایی را ایفا کند. مروری بر تحقیقات اخیر در راه آهن های کشورهای مختلف دلالت بر اهمیت شرایط سیستم حائل ریل برنتایج تحلیل ریل دارد. در این تحقیق اهمیت تاثیر تغییر مشخصات اجزای زیرسازی ریل بر تعیین مدول بستر ریل به عنوان یکی از پارامتر ها در تحلیل و طراحی سیستم راه آهن در دو قسمت تحلیل عددی و تست میدانی مورد بررسی قرار می گیرد، برای این مهم ابتدا خطوط بالاستی راه آهن در محدوده مشخصات هندسی و فنی مدلسازی می گردد سپس برای کنترل صحت مدل سازی به کمک تست میدانی انجام شده قبلی مدل کالیبره می شود و براساس طبقه بندی اجزای سیستم خطوط مختلف، مدل به روش المان محدود تحلیل می گردد، در پایان نمودا رها و جدول هایی برحسب ضخامت لایه بالاست و نوع بستر جهت تعیین و کنترل مقدار مدول بستر ریل و نیز تخمین نشست ریل برای انواع شرایط خطوط راه آهن ارایه می شود که با توجه به آن در طی سیکل عملیات زیرکوبی و پایدارسازی در دوره بهره داری، رفتار خط در محدوده رفتار تیر بر روی بستر الاستیک حفظ و از زوال خط جلوگیری می گردد و همچنین ضمن بهره برداری بهینه، ایمنی و عمر خط افزایش می یابد.
کلید واژگان: مدول بستر ریل, بستر, بالاست, خط راه آهن, خیز ریل}Rail bed modulus is one of the main parameters in optimal track design which is determined based on components of ballasted railway tracks. Perception of track bed behavior in different conditionsand on substructure with complex characteristic has an important role in the rail system analyses. Technical and geometric characteristics of track may have a significant impact on rail bed modulus. Review of recent researches on railways in different countries indicates the importance of rail supporting system in rail analysis results. This paper studies the importance of change in rail bed components characteristics in determining track modulus as one of the parameters of rail system analysis and design. This study is divided into two parts including field tests and numerical analysis. To achieve this goal, ballasted railway tracks are modeled according to technical and geometrical characteristics. Then, model is calibrated using field test in order to confirm the validity of model, and it is analyzed by employing finite element method based on tracks components classification. Finally, some diagrams and tables are presented for different conditions of rail roads according to ballast layer thickness and the type of the subgrade in order to determine track modulus and control rail vertical deflection.Keywords: Rail Bed Modulus, railway track, Rail Deflection, Ballast, Subgrade}
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