بررسی آزمایشگاهی مقاومت برشی معادل در خاکهای چسبنده بهسازی شده با ستون‌های سنگی در دستگاه سه محوری

نوع مقاله : مقاله پژوهشی

نویسندگان

1 استادیار،گروه مهندسی عمران، واحد شهر قدس، دانشگاه آزاد اسلامی، تهران، ایران.

2 گروه مهندسی عمران، دانشگاه آزاد اسلامی، واحد لنجان، اصفهان، ایران

3 گروه مهندسی عمران، واحد شهرقدس، دانشگاه آزاد اسلامی، تهران، ایران

چکیده

ستفاده از ستون‌های سنگی یکی از روش‌های متداول در بهسازی خاک ضعیف است. یکی از روش‌های بررسی رفتار زمین‌های بهسازی شده با ستون سنگی روش همگن‌سازی است. در این روش مصالح ستون سنگی و خاک اطراف با یک خاک با پارامترهای معادل بهبودیافته جایگزین می‌شود. درروش همگن‌سازی پارامترهای معادل از طریق معدل‌گیری پارامترهای مصالح ستون سنگی و خاک اطراف به‌وسیله روابط خطی محاسبه می‌شود. در این تحقیق مقاومت برشی و پارامترهای مقاومت برشی معادل خاک بهسازی شده با ستون سنگی بر اساس روابط تحلیلی محاسبه و صحت روابط از طریق انجام آزمایش‌های آزمایشگاهی در دستگاه سه محوری موردبررسی قرارگرفته است. در این روش، به‌وسیله شبیه‌سازی سلول واحد در مقیاس آزمایشگاهی به بررسی رفتار ستون‌های سنگی پرداخته ‌شده است. در این تحقیق از دستگاه سه محوری باقابلیت ساخت نمونه با قطر 100 میلی‌متر و ارتفاع 200 میلی‌متر استفاده شده است. قطر ستون‌های سنگی موردبررسی برابر با 37/5 و 51 میلی‌متر و آزمایش‌های انجام شده در حالت تحکیم نیافته- زهکشی نشده در 3 فشار دورگیر 50 و 100 و 200 کیلوپاسکال انجام شده است. نتایج این تحقیق نشان می‌دهد که با به کارگیری ستون سنگی در خاک نرم، مقاومت برشی زهکشی نشده و سختی نمونه افزایش یافته و با افزایش فشار دورگیر، درصد افزایش مقاومت زهکشی نشده روند افزایشی خواهد داشت. اختالف بین پارامتر زاویه اصطکاک داخلی نتایج حاصل از رابطه تحلیلی و آزمایشگاهی با افزایش مقدار ضریب تمرکز تنش افزایش یافته و با افزایش مقاومت زهکشی نشده خاک اطراف کمتر شده است

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental study on Equivalent shear strength of cohesive soils improved with Stone columns by Triaxial Testing

نویسندگان [English]

  • Javad Nazariafshar 1
  • majid aslani 2
  • Nima Mehrannia 3
1 Assistant Professor, Department of Civil Engineering, Shahr-e-Qods Branch Islamic Azad University, Tehran, Iran
2 Department of Civil Engineering, Lenjan Branch, Islamic Azad University, Isfahan, Iran
3 Department of Civil Engineering, Shahr-e0Qods Branch, Islamic Azad University Tehran , Iran
چکیده [English]

The use of stone column is an effective method in modifying of poor soils. One of the methods of studying the behavior of soils improving with stone columns is homogenization method. In this method, the stone column and the surrounding soil are replaced with a homogenous soil. In homogenization method the equivalent parameters are calculated by means of weighted average of soil and column parameters with linear relations. In this study, equivalent shear strength and shear strength parameters of the soil improved with stone columns was calculated based on the analytical relationships and the accuracy of the relationships used was evaluated through triaxial tests. In this study with help of simulation of the unit cell in the laboratory scale and investigating the shear strength of soil improved with stone columns, behavior of stone columns was investigated. The laboratory experiment consisted of series of the triaxial tests with a diameter of 100 mm and height of 200 mm and sand column with diameter of 37.5 and 51 mm and 3 confining pressure 50,100,200 kPa. The results of this study shows that with the use of a stone columns in soft soil, the undrained shear strength and the stiffness of the sample is increased and with increased confining pressure, the percentage of undrained shear strength increased. The difference between shear strength parameters obtained from experiments and those predicted by analytical relationships with the increase in the stress concentration ratio increased and decreased with increasing undrained shear strength of the surrounding soil.

کلیدواژه‌ها [English]

  • Unit Cell
  • Equivalent shear strength
  • Homogenization
  • Triaxial Test
  • Stone Column
[1] Esmaeili, M., & Hakimpour, S. M.. Three dimensional numerical modelling of stone column to mitigate liquefaction potential of  sands.  Journal of Seismology and Earthquake Engineering, (2015),17(2), 127-140
[2] Esmaeili, M., Khajehei, H., & Astaraki, F. A.. The Effectiveness of Deep Soil Mixing on Enhanced Bearing Capacity and Reduction of Settlement on Loose Sandy Soils. International Journal of Railway Research, (2017), 4(2), 33-39.
[3] Hasheminezhad, A., & Bahadori, H.. Seismic response of shallow foundations over liquefiable soils improved by deep soil mixing columns. Computers and Geotechnics, (2019), 110, 251-273.
[4] Esmaeili, M., & Hakimpour, M.. Numerical Modeling effectiveness of Stone Column in Mitigation of Liquefaction during Earthquake. Modares Journal of Civil Engineering, (2014),14(3).
[5] Castro, J., Groups of encased stone columns: Influence of column length and arrangement, Geotextiles and Geomembranes,(2017),45(2):68-80
[6] Sivakumar, V.; McKelvey, D.; Graham, J.; Hughes, D.. “Triaxial Test on Model Sand Columns in Clay" Canadian Geotechnical Journal, 41, 299-312.
[7] Gniel, J.; Bouazza, A." Improvement of Soft Soils Using Geogrid Encased Stone Columns" Geotextiles and Geomembranes, (2004), 27(3), PP.167-175
[8] Wu, C.S. and Hong,Y.S. Laboratory tests on geosyntheticencapsulated sand columns. Geotextiles and Geomembranes, (2009), 27(2), 107-120.
[9] Hong, Y.S., Wu, C.S. and Sun, C.S. Geosynthetic-encased sand column behavior under triaxial test simulation. In Advanced Materials Research.(2012), 594,  581-584(. Trans Tech Publications.
[10] Najjar, S.S. and Skeini, H. Triaxial response of clays reinforced with granular columns. Proceedings of the Institution of Civil Engineers-Ground Improvement, (2014), 168(4), 265-281.
[11] Barksdale, R.D., Bachus, R.C. "Design and Construction of Stone Column" Vol 1 FHWA / RD, (1983).
[12] Bergrado, D.T., Lam, F.L. "Full Scale Load Test of Granular Piles with Different Densities and Different Proportions of Gravel and Sand in the Soft Bangkok Clay" Soils and Foundations, (1987), 27(1), 86-93. 
[13] Ambily, A.P; Gandhi, S.R. "Behavior of Stone Columns Based on Experimental and FEM Analysis" Journal of Geotechnical and Geoenvironmental Engineering, ASCE, (2007) ,133(4), 405-415.
[14] Schweiger, H.F."Finite Element Analysis of Stone Column Reinforced Foundations" PhD thesis, Dept. Civil Eng., Univ.Coll. Swansea, U.K, (1989).
[15] Schweiger, H.F.; Pande, G.N. "Numerical Analysis of a Road Embankment Constructed on Soft Clay Stabilized with Stone Columns" Proceedings of Numerical Methods in Geomechanic, Innsbruck, (1988), 1329-1333
[16] Schweiger, H.F.; Pande, G.N. "Modelling Stone Column Reinforced Soils- A Modified Voigt Approach." In Proceeding of Third Numerical Models in Geomechanic, Canada, (1989), 204-214.
[17] Lee, S.; Pande, G.N. "Analysis of Stone Column Reinforced Foundations" International Journal for Numerical and Analytical Methods in Geomechanics, (1998), 22(12), 1001-1020.
[18] Abdelkrim, M.; De Buhan, P."An Elastoplastic Homogenization Procedure for Predicting the Settlement of a Foundation on a Soil Reinforced by Columns" European Journal of Mechanics A/Solids, (2007) , 26,736-757.
[19] Hassen, G.; Buhan, P.; Abdelkrim, M. "Finite Element Implementation of a Homogenized Constitutive Law for Stone Column-Reinforced Foundation Soils, with Application to the Design of Structures" Computers and Geotechnics, (2010), 37 (1-2),40-49.
[20] Najjar, S.; Sadek, S.; and Maakaroun, T.."Effect of Sand Columns on the Undained Load Response of Soft Clay" Journal of Geotechnical and Geoenvironmental Engineering, ASCE, (2010), 136(9), 1263-1277.
[21] Miranda, M. and Da Costa, A., Laboratory analysis of encased stone columns. Geotextiles and Geomembranes, (2016), 44(3),269-277.
[22] Aboshi, H., E. Ichimoto, M. Enoki, and Harada. K, "The Compozer -A Method to Improve Characteristics of Soft Clays by Inclusion of Large Diameter Sand Columns," proceeding A, International Conference on Soil Reinforcement: Reinforced Earth and other Techniques. (1979), Paris, 211-216.
[23] Cooper, M. and Rose, A.N., Stone column support for an embankment on deep alluvial soils”, ICE Proceedings Geotechnical Engineering, (1999), 137(1):15-25.
[24] Abusharar, S.W. and Han, J. Two-dimensional deepseated slope stability analysis of embankments over stone column-improved soft clay”, Engineering Geology, (2011), 120(1-4):103-110.
[25] Christoulas, S.T., Giannaros, C.H., Tsiambaos, G. Stabilization of embankment foundations by using stone columns, Geotechnical and Geological Engineering, (1997), 15(3):247-258.
[26] Mestar P, R.Y."Validation des modeles numerigues de sol ameliore par colonnes". Proceedings international symposium on ground improvement, (2004), 229-243.
[27] Priebe H. Abschatzung des Scherwiderstandes eines durgh Stopfverdichtung verbesserten Baugrundes”, Die Bautechnik, (1978), 55(9):281-284.
[28] Standard, ASTM. D2850-03a,"Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils" ASTM International, United States.
[29] Ranjan, G., "Ground treated with granular piles and its response under load”. Indian Geotechnics, (1989), 31:1-22.
[30] Hasan, M., Samadhiya, N.K. "Experimental and Numerical Analysis of Geosynthetic-Reinforced Floating Granular Piles in Soft Clays". Int. J. of Geosynthetic. And Ground Eng., (2016).
[31] Institution, I.S., "Indian standard code of practice for design and construction for ground improvementguidelines. New Delhi, (2003).
[32] Fox, Z., "Critical State, Dilatancy and Particle Breakage of Mine Waste Rock". Colorado state university: Fort Collins, USA. (2011).
[33] Stoeber, J.N., "Effects of Maximum Particle Size and Sample Scaling on the Mechanical Behavior of Mine Waste Rock; a Critical State Approach". )2012(, Colorado state university: Fort Collins, USA.
[34] Standard, ASTM. D4767-04, "Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soils". ASTM International, United States.
[35] Nayak, N.V. "Recent Advances in Ground Improvements by Stone Column". In: Proceedings of Indian Geotechnical Conference, Madras (1983). India.
[36] Nazariafshar, J. Mehrannia, N, Kalantary, F. Ganjian, N.” Bearing Capacity of Group of Stone Columns with Granular Blankets” International Journal of Civil Engineering, (2019), 17:253-263.
[37] Mehrannia, N. NazariAfshar, J. and Kalantary, F. “Experimental Investigation on the Bearing Capacity of Stone Columns with Granular Blankets" Geotechnical and Geological Engineering, (2018), 36:209-222.
[38] Aslani, M. Nazariafshar, J. and Ganjian, N. “Experimental Study on Shear Strength of Cohesive Soils Reinforced with Stone Columns", Geotechnical and Geological Engineering, (2019), 37(3):2165-2188 https://doi. org/10.1007/s10706-018-0752-z