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بررسی عوامل تأثیرگذار بر نتایج آزمونهای نفوذی ژئوتکنیک با کمک دستگاه نفوذگر ضربهای دستی در خاک ماسهای | ||
| نشریه مهندسی عمران امیرکبیر | ||
| مقاله 3، دوره 53، شماره 4، تیر 1400، صفحه 1295-1306 اصل مقاله (1.62 M) | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.22060/ceej.2020.16856.6375 | ||
| نویسندگان | ||
| مهدی سردار؛ سید احسان سیدی حسینی نیا* | ||
| دانشکده مهندسی، دانشگاه فردوسی مشهد، مشهد، ایران | ||
| چکیده | ||
| آزمونهای نفوذی یکی از مهمترین آزمایشهای برجا هستند که با کمک آنها، پارامترهای ژئوتکنیکی متنوعی را میتوان تخمین زد. از ویژگیهای آزمونهای نفوذی، سرعت و سهولت انجام و تکرارپذیر بودن نتایج این آزمونها است. در این پژوهش، با استفاده از یک ابزار نفوذی به نام «دستگاه نفوذگر ضربهای دستی»، آزمایشهایی بر روی ماسه فیروزکوه با تراکم نسبیهای مختلف انجام شدهاست. اساس کار این دستگاه مشابه دستگاه های نفوذی موجود در مهندسی ژئوتکنیک بوده و تفاوت آن در ابعاد و انرژی است. هدف از این پژوهش، بررسی اثر هندسه مخروط نفوذ و انرژیهای کوبش مختلف بر نتایج آزمون بوده است. بدین منظور، از سه قطر مختلف مخروط، سه زاویه راس مختلف و سه جرم مختلف چکش استفاده شد. جهت مطالعه عملکرد دستگاه از شاخص نفوذ دینامیکی و مقدار میانگین وزنی آن نسبت به عمق نفوذ بهره گرفته شد. بررسی نتایج نشان می دهد که زاویه راس مخروط نقشی در نفوذ دستگاه نداشته، بلکه قطر مخروط است که می تواند مقدار نفوذ را تغییر دهد. همچنین، مشاهده شد رابطه ای خطی مستقیمی میان انرژی ضربات و میانگین شاخص نفوذ وجود دارد. بر اساس مشابهت مکانیزم نفوذ مخروط به زمان با شمع کوبشی، از رابطه مایرهوف جهت تخمین زاویه اصطکاک داخلی خاک استفاده شد. از مقایسه نتیجه حاصل شده با مقدار حاصل از آزمون برش مستقیم، می توان گفت که با آزمون نفوذی می توان با دقت مناسبی، این پارامتر را بدست آورد. | ||
| کلیدواژهها | ||
| انرژی کوبش؛ هندسه مخروط نفوذی؛ خاک ماسهای؛ زاویه اصطکاک داخلی خاک؛ دستگاه نفوذگرضربه ای | ||
| موضوعات | ||
| مکانیک خاک و پی | ||
| عنوان مقاله [English] | ||
| Effective Factors on the Results of Geotechnical Penetration Tests by Using Manual Dynamic Penetrometer (MDP) in Sandy Soil | ||
| نویسندگان [English] | ||
| Mahdi Sardar؛ Ehsan Seyedi Hosseininia | ||
| Civil Engineering Department, Ferdowsi University of Mashhad | ||
| چکیده [English] | ||
| Penetration tests in geotechnical engineering are field tests in order to estimate some soil parameters such as soil density, CBR (California Bearing Ratio) and internal friction angle. The advantages of these tests to other field tests are the easiness and rapidity in the application. Although the accuracy of these tests might be in question, the tests can be calibrated by other tests with accepted accuracy. In this paper, a penetration test, called Manual Dynamic Penetrometer (MDP), is introduced, which is designed and constructed at Ferdowsi University of Mashhad (FUM). The principles of the applicability of MDP are similar to other existing penetration tests (such as DCP introduced in ASTM D6591); however, the energy applied to the soil is much higher which facilitates to have more penetrated depth compared to other existing probes. In this apparatus, the probe is a solid 60-degree cone with a diameter of 18mm and the string rod diameter is 16 mm. The cone and string rod are impacted by a hammer with a mass of 10 kilograms which is manually raised and then it falls from a height of 600 mm. In this paper, MDP was applied within Firuzkuh-161 sandy soil with different soil relative densities (Dr = 55, 80, 100%). In this research, different factors influencing the penetration are investigated by using MDP. These factors are the geometry of the cone (cone apex=30o, 60o, and 90o), the cone diameter (18, 30, 40 mm), and the hammer mass (5, 8, 10 kg). The penetration results are presented in terms of penetration index (DPI) which is described as penetrated depth per each impact. By comparing the results, it is found out that cone apex has no influence on the penetration, but the cone diameter changes the rate of penetration. Furthermore, it is seen that there is a linear relationship between applied energy and the average DPI such as what is already used in SPT correlations. By considering the similitude of MDP test and pile driving, it is shown that the results of penetration tests can be used to estimate the internal friction angle of sandy soils. | ||
| کلیدواژهها [English] | ||
| Driving Energy, Cone Geometry, Sandy Soil, Internal Friction Angle, Manual Dynamic Penetrometer | ||
| مراجع | ||
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