بررسی عوامل تأثیرگذار بر نتایج آزمون‌های نفوذی ژئوتکنیک با کمک دستگاه نفوذگر ضربه‌ای دستی در خاک ماسه‌ای

نوع مقاله : مقاله پژوهشی

نویسندگان

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

موضوعات

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

[1] E. Kleyn, J. Maree, P.F. Savage, Application of a porTable.  pavement dynamic cone penetrometer to determine in situ bearing properties of road pavement layers and subgrades in South Africa, in:  Proc. 2nd European Symposium on Penetration Testing, Amsterdam, 1982, pp. 277-282.
[2] DIN., DIN 4094-3, Subsoil - Field testing - Part 3: Dynamic Probing, in, Deutsch, 2002.
[3] T. Burnham, D. Johnson, In Situ Foundation Characterization Using the Dynamic Cone Penetrometer, Minnesota Department of Transportation, 1993.
[4] A. Scala, Simple Methods of Flexible Pavement Design Using Cone Penetrometers, New Zealand Engineering, 11(2) (1956) 34.
[5] S.L. Webster, R.H. Grau, T.P. Williams, Description and Application of Dual Mass Dynamic Cone Penetrometer, US Army Corps of Engineers, Vicksburg, 1992.
[6] ASTM., ASTM D6951-03, Standard Test Method for Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications, in, ASTM International, West Conshohocken, 2003.
[7] C.R. Clayton, M.C. Matthews, N.E. Simons, Site investigation: A handbook for engineers, Blackwell Science, 1995.
[8] A. Fakher, M. Khodaparast, C. Jones, The use of the Mackintosh Probe for site investigation in soft soils, Quarterly Journal of Engineering Geology and Hydrogeology, 39(2) (2006) 189-196.
[9] M. Khodaparast, A. Rajabi, M. Mohammadi, The new empirical formula based on dynamic probing test results in fine cohesive soils, International Journal of Civil Engineering, 13(2) (2015).
[10] K. George, W. Uddin, Subgrade Characterization for Highway Pavement Design, Federal Highway Administration, Mississippi, 2000.
[11] D. Mohammadi, Development of Dynamic Cone Penetrometer (DCP) to determine engineering soil parameters in sand, Tarbiat Modarres University, 2008.
[12] E. Kianirad, Development and Testing of a PorTable.  In-Situ Near-Surface Soil Characterization System, Northeastern University, Boston, Massachusetts, 2011.
[13] F. Amini, Potential Applications of the Static and Dynamic Cone Penetrometers in MDOT Pavement Design and Construction, Ferderal Highway Administration, Jackson, Mississippi, 2003.
[14] E. Seyedi Hosseininia, Manual Dynamic Penetrometer, in: Document and Real Estate Organization (Ed.), Ferdowsi University of Mashhad, Iran, 2017. (In Persian)
[15] ASTM., ASTM D698-12 Test Methods for Moisture-Density Relations of Soils and Soil-Aggregate Mixtures, in:  Method A (Standard Proctor), Astm International., West Conshohocken, 2012.
[16] S. Mohammadi, M. Nikoudel, H. Rahimi, M. Khamehchiyan, Application of the Dynamic Cone Penetrometer (DCP) for Determination of the Engineering Parameters of Sandy Soils, Engineering Geology, 101(3-4) (2008) 195-203.
[17] S.L. Webster, R.W. Brown, J.R. Porter, Force Projection Site Evaluation Ssing the Electric Cone Penetrometer (ECP) and the Dynamic Cone Penetrometer (DCP), Army Engeener Waterways Experiment Station VICKSBURG MS Geotechnical LAB, 1994.
[18] M. Livneh, Friction Correction Equation for the Dynamic Cone Penetrometer in Subsoil Strength Testing, Transportation Research Record: Journal of the Transportation Research Board, (1714) (2000) 89-97.
[19] A. Sawangsuriya, T.B. Edil, Evaluating Stiffness and Strength of Pavement Materials, Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 158(4) (2005) 217-230.
[20] R.L. Allbright, Evaluation of the Dynamic Cone Penetrometer and its Correlations with other Field Instruments, University of Wisconsin, Madison, 2002.
[21] M. Randolph, R. Dolwin, R. Beck, Design of driven piles in sand, Géotechnique, 44(3) (1994) 427-448.
[22] G. Mayerhof, Bearing capacity and settlement of pile foundations, Journal of Geotechnical and Geoenvironmental Engineering, 102(3) (1976) 195-228.
[23] J.H. Schmertmann, A. Palacios, Energy dynamics of SPT, Journal of the Geotechnical Engineering Division, 105(8) (1979) 909-926.
[24] M. Khodaparast, Application of Dynamic Cone penetrometer in determining the relative density and undrained shear strength of fine-grained soils, Engineering Geology, 9(1) (2015) 2633-2652 (In Persian).
[25] A.B. Vesic, Bearing capacity of deep foundations in sand, 1963.
[26] R. Salgado, J. Mitchell, M. Jamiolkowski, Cavity expansion and penetration resistance in sand, Journal of Geotechnical and Geoenvironmental Engineering, 123(4) (1997) 344-354.
[27] T.R. Burnham, Application of dynamic cone penetrometer to Minnesota department of transportation pavement assessment procedures, Minnesota Department of Transportation, Office of Research Administration, Minnesota, 1997.
نشریه مهندسی عمران امیرکبیر
دوره 53، شماره 4
تیر 1400
صفحه 1295-1306

فایل ها

هم رسانی

ارجاع به این مقاله

آمار