Donatılı Kum Zeminlerde Düzlem Deformasyon Koşullarında Düşey Gerilme Dağılışı

Abstract

Teknolojinin gelişmesi insanoğluna daha geniş, daha ağır ve daha karmaşık yapılar yapma fırsatı vermiştir. Artan ve karmaşık hale gelen yükleri zemine aktarma problemi ile karşılaşan geoteknik mühendisleri için; zemini iyileştirmek, zeminde meydana gelecek oturmaları ve gerilme dağılışlarını tespit etmek kaçınılmaz hale gelmiştir. Son yıllarda zemini iyileştirmede kullanımı artan bir yapı malzemesi olan geotekstiller, zeminlerin taşıma gücünü etkilemektedir. Zeminde meydana gelecek oturmalar açısından gerilme dağılışı ve taşıma gücü temel tasarımının en önemli parametrelerden birkaçıdır. Bu çalışmada donatılı kum zemin yüzeyine oturan model şerit temelle düzlem deformasyon koşullarında deneyler yapılmış ve uygulanan düşey yükten dolayı zeminde belirli noktalarda meydana gelen düşey gerilme artışları tespit edilmiştir. Deneysel çalışma kapsamında, üç farklı rölatif sıkılıkta geotekstille güçlendirilmiş kum tabakalarında, önceden belirlenen noktalara yerleştirilen basınç ölçerler yardımıyla düşey gerilme artışları kaydedilmiştir. Daha sonra model deney düzeneği PLAXIS 2D programı ile modellenip Mohr-Coulomb modeli ile düşey gerilme artışları belirlenmiştir. Ayrıca donatılı zeminin, Elastisite Teorisine dayalı olarak geliştirilen analitik yöntemlerle (Poulos ve Boussinesq) düşey gerilme artışları hesaplanmıştır. Deneylerle elde edilen tüm değerler incelendiğinde, rölatif sıkılığın donatılı zemindeki gerilme dağılışında etkili bir parametre olduğu belirlenmiştir. Bununla birlikte, yaygın kullanılan Elastisite Teorisine dayalı çözümlerin düşük rölatif sıkılıktaki donatılı zeminlerde oldukça hatalı sonuçlar verdiği görülmüştür.

Keywords

• Düşey gerilme artışı,basınç ölçer,donatılı zemin,geotekstil

Vertical Stress Distribution in Reinforced Sandy Soil in Plane Strain Conditions

Abstract

Development of technology gives the opportunity to mankind to build larger, heavier and more complex structures. For geotechnical engineers, faced with transferring the loads that is more complex and increasing, stabilization of soil, and determination of stress distribution and settlement has become inevitable. Geotextiles which have been used in soil stabilization increasingly in recent years affect bearing capacity of soil. Stress distribution in terms of settlement calculation and bearing capacity are some of the most important parameters for foundation design. In this study, several tests were carried out with model strip footing in plane strain conditions in reinforced cohesionless soil and the vertical stress increments occurred in the soil medium due to applied vertical surface loads were determined at several specific locations. In scope of experimental study, the sand reinforced with geotextile sheet was placed in layers in a tank with three different relative densities and vertical stress increments were measured by pressure gauges placed at predetermined locations. Subsequently, the experimental setup was modelled with PLAXIS 2D and vertical stress increments were obtained with Mohr-Coulomb model. Additionally vertical stress distribution in soil was calculated with analytical methods (Poulos and Boussinesq) based on elasticity theory. As the findings obtained from these studies were examined, it was understood that relative density is a very effective parameter for stress distribution in soils. However, the methods based on elasticity theory give rather erroneous results in low relative density reinforced soil.

Keywords

• Vertical stress distribution,strain gauges,reinforced soil,geotextile

References

1. [1] Patel, M.M., Influence od Shape of Footing on The Performance of The Reinforced Sand, Proceedings of The Conference on Construction Practices and Instrumentation in Geotechnical Engineering, 265-269, 1982.
2. [2] Fragaszy, R.J. ve Lawton, E., Bearing Capacity of Reinforced Sand Subgrades, Journal of Geotechnical Engineering, ASCE, 110, 10, 1500-1507, 1984.
3. [3] Guido, V.A., Biesiadecki, G.L. ve Sullivan, M.J., Bearing Capacity of a Geotextile Reinforced Foundation, Proceedings of 11th International Conference on Soil Mechanics And Foundation Engineering, San Fransisco, 1777-1780, 1985.
4. [4] Guido, V.A., Chang, D.K. ve Sweeney, M.A., Comparison of Geogrid and Geotextile Reinforced Earth Slabs, Canadian Geotechnical Journal, 23, 435-440, 1986.
5. [5] Khing, K.H., Das, B.M., Puri, V.K., Cook, E.E. ve Yen, S.C., The Bearing Capacity of a Strip Foundation on Geogrid-reinforced Sand, Geotextiles and Geomembranes, 12, 351-361, 1993.
6. [6] Omar, M. T., Das, B. M., Puri, V. K. Yen, S. C., Ultimate bearing capacity of shallow foundations on sand with geogrid reinforcement, Geotechnical Journal, 545-549, 1993.
7. [7] Das, B. M., Shin, E. C., Omar, M. T., The bearing capacity of surface strip foundations on geogrid-reinforced sand and clay-A comparativestudy, Geotechnical and Geological Engineering, 12, 15-33, 1994.
8. [8] Tan, Ö. ve Çelik, S., Geogrid Donatılı Kumlarda Taşıma Gücünün Model Deneylerle Araştırılması, 10. Mühendislik Sempozyumu, Süleyman Demiral Üniversitesi, Bildiriler Kitabı, Isparta, 414-420, 1999.

9. [9] Shin, E.C. ve Das, B.M., Experimental Study of Bearing Capacity of A Strip Foundation on Geogrid Reinforced Sand, Geosynthetics International, 7, 1, 59-71, 2000.
10. [10] Shin, E.C., Das, B.M., Lee, E. S. ve Atalar, C., Bearing Capacity of Strip Foundation on Geogrid-Reinforced Sand, Geotechnical and Geological Engineering, 20, 169-180, 2002.
11. [11] Patra, C.R., Das, B.M. ve Atalar, C., Bearing Capacity of Embedded Strip Foundation on Geogrid-Reinforced Sand, Geotextiles and Geomembranes, 23, 5, 454-462, 2005.
12. [12] Patra, C.R., Das, B.M., Bhoi, M. ve Shin, E.C., Eccentrically Loaded Strip Foundation on Geogrid-Reinforced Sand, Geotextiles and Geomembranes, 24, 254-259, 2006.
13. [13] Omar, M.T., Ultimate Bearing Capacity of Eccentrically Loaded Strip Foundation on Geogrid- Reinforced Sand, University of Sharjah Journal of Pure and Applied Sciences, 3, 2, 35-51, 2006.
14. [14] Sadoglu, E., Cure, E., Moroglu, B. ve Uzuner, B. A., Ultimate Loads for Eccentrically Loaded Model Shallow Strip Footings on Geotextile-Reinforced Sand, Geotextiles and Geomembranes, 27, 3, 176-182, 2009.
15. [15] Cicek,E., Guler, E., Yetimoglu, T., Effect of reinforcement length for different geosynthetic reinforcements on strip footing on sand soil, Soils and Foundations,Volume 55, Issue 4, 661-677, 2015
16. [16] Terzaghi, K., Theoretical Soil Mechanics, John Wiley and Sons Inc., New York, 510, 1943.
17. [17] Janbu, N., Settlement calculations based on the tangent modulus concept. University of Trondheim, Norwegian Institute of Technology, Geotechnical Institution, Bulletin 2, 57 p., 1967.
18. [18] Fellenius B.H., Basics of Foundation Design, 36-51, 2006.
19. [19] Binquet, J. ve Lee, K. L., Bearing Capacity Tests on Reinforced Earth Slabs, Journal of the Geotechnical Engineering Division, ASCE, 101, 12, 1241-1251, 1975.
20. [20] Adams, M.T. ve Collin J.G., Large Model Spread Footing Load Tests on Geosyntetic Reinforced Soil Foundations, Journal of Geotechnical and Geoenviromental Engineering, 123, 1, 66-72, 1997.
21. [21] Alawaji, H.A., Settlement and Bearing Capacity of Geogrid Reinforced Sand over Collapsible Soil, Geotextiles and Geomembranes, 19, 75-88, 2001.
22. [22] DeMerchant, M.R., Valsangkar, A.J. ve Schriver, A.B., Plate Load Tests on Geogrid Reinforced Expanded Shale Lightweight Aggregate, Geotextiles and Geomembranes, 20, 173-190, 2002.
23. [23] Michalowski, R.L., Limit Loads on Reinforced Foundation Soils, Journal of Geotechnical and Geoenviromental Engineering, ASCE, 130, 4, 381-390, 2004.
24. [24] Wayne, M.H., J.Han and K. Akins, The desing of geosynthetic reinforced foundation, In: Proceedings of ASCE’s Annuals Convention and Exposition, ASCE Geotechnical Special Publication, 1-8, 1998.
25. [25] Kost, A.D., Filz, G.M., Cousins, T., Brown, M.C., Full-scale investigation of differential settlements beneath a geosynthetic-reinforced soil bridge abutment, Transportation Research Record, 2462, 28-36, 2014.
26. [26] Wang, Z.-J., Ma, S.-W., Lu, L., Study of reinforced soil adjusted to differential settlement based on parabolic cable theory, Yantu Lixue/Rock and Soil Mechanics Volume 38, Issue 11, 3319-3324, 3340, 2017.
27. [27] Boussinesq, J., Application des potentiels a l'etude de l'equilibre et due mouvement des solids elastiques, Gauthiers-Villars, Paris, 1885.
28. [28] Westergaard, H.M., A problem of elasticity suggested by a problem in soil mechanics: A soft material reinforced by numerous strong horizontal sheets. In Contributions to the Mechanics of Solids, Stephen Timoshenko 60th Anniversary Volume, MacMillan, New York, 260 – 277, 1938.
29. [29] Newmark, N.M., Simplified computation of vertical stress below foundations. Univ. of Illinois Engineering Experiment Station, Circular 24, Urbana, Illinois, 19, 1935.
30. [30] Newmark, N.M., Influence chart for computation of stresses in elastic foundations. University of Illinois Engineering Experiment Station, Bulletin Series 338, Vol. 61, No. 92, Urbana, Illinois, 28, 1942.
31. [31] Taylor, D.W., Fundamentals of soil mechanics. John Wiley & Sons, New York, 700, 1948.
32. [32] Algin, H. M., Stresses from linearly distributed pressures over rectangular areas, Int. J. Numer. Anal. Methods Geomech., 24(8), 681–692, (2000).
33. [33] Poulos H. G., Stresses and displacements in an elastic layer underlain by a rough rigid base, Ge'otechnique, 17, 4, 378-410, 1967.
34. [34] Keskin, S., Laman, M., and Baran, T. Experimental determination and numerical analysis of vertical stresses under square footings resting on sand. Teknik Dergi, 19(4), 4521–4538., 2008.
35. [35] Chen, Q., An experimental study on characteristics and behavior of reinforced soil foundation., Ph.D. dissertation, Louisiana State Univ., Baton Rouge, LA., 2007.
36. [36] Çicek,E., Guler, E., Yetimoglu, T., Comparison of Measured and Theoretical Pressure Distribution below Strip Footings on Sand Soil, International Journal of Geomechanics, Volume 14, Issue 5, 2014.
37. [37] ASTM D854-14, Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer, ASTM International, West Conshohocken, PA, www.astm.org, 2014.
38. [38] ASTM D4253-16, Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table, ASTM International, West Conshohocken, PA, www.astm.org, 2016.
39. [39] ASTM D4254-16, Standard Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density, ASTM International, West Conshohocken, PA, www.astm.org, 2016.
40. [40] ASTM D3080 / D3080M-11, Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions, ASTM International, West Conshohocken, PA, www.astm.org, 2011.
41. [41] Kirkpatrick, W. M. ve Yanikian, H. A., Side Friction in Plane Strain Tests, Proceedings of the Fourth South East Conference On Soil Engineering, Kuala Lumpur, Malaysia 76-84, 1975.
42. [42] Kirkpatrick, W. M. ve Uzuner, B.A., Measurement Errors in Model Foundations Tests, Istanbul Conference on Soil Mechanics, Istanbul, 98–106, 1975.
43. [43] Plaxis 2D, Manuals. Plaxis Finite Element Code for Soil and Rock Analysis, 2D –Version 8.6. (Edited by Brinkgreve R.B.J., Broere W. And Waterman D.) Delft University of Technology & Plaxis, The Netherlands, 2004.