Tekrarlı Yük Etkisinde Kil Zeminlerin Lineer Olmayan Elastik Davranışı

Yıl 2009, Cilt: 22 Sayı: 1, 169 - 185, 30.06.2009

Volkan Okur , Atilla Ansal

Öz

Zemin tabakaların dinamik yükler altındaki davranışı, tekrarlı yükleme genliğine bağlı

olarak farklılıklar göstermektedir. Bu çalışmada, İstanbul Avcılar Bölgesinden alınan

örselenmemiş kil zemin numuneler üzerinde, gerilme kontrollü dinamik üç eksenli deneyler

yapılmıştır. Normal konsolide olarak hazırlanan numuneler 0,1 Hz frekansında, farklı tekrarlı

gerilme genliklerinde yüklenmiştir. Yükleme sonucu maksimum kayma modülü, sönüm oranı

değerleri belirlenmiştir. Lineer olmayan elastik davranış sınırı kayma modülü oranının yaklaşık

% 90 değerine denk gelmektedir. Bu sınır aşıldıktan sonra malzemenin tekrarlı yük altında

davranışı, özellikle plastisite indisinden büyük oranda etkilenmektedir. Deney sonuçlarından,

maksimum kayma modülünü belirlemeye yönelik pratik amaçlar için kullanılabilecek bağıntılar

önerilmiştir. Ayrıca arazi deneylerinden elde edilen kayma dalgası hızından yola çıkarak

laboratuar ve arazi kayma modülü ve sönüm oranı arasındaki ilişki belirlenmiştir.

Anahtar Kelimeler

Başlangıç kayma modülü, sönüm oranı, dinamik üç eksenli

Non-Linear Elastic Response Of Clay Soils Under Cyclic Loadings

Öz

Response of soil deposits under dynamic loadings differs with the cyclic loading

amplitudes. In this study, stress controlled cyclic triaxial tests were conducted on the specimens

taken from the Istanbul Avcilar District. Normally consolidated specimens were cyclically

loaded under different stress amplitudes at a frequency of 0.1 Hz. Maximum shear modulus and

damping ratio values determined. Loading cycles showed that the non-linear elastic shear

modulus is approximately equal to 90% of shear modulus ratio. After this threshold it’s

observed that the material response under cyclic loading is greatly influenced from plasticity

index of the soil. From the test results empirical relationships proposed for determining the

maximum shear modulus for practical purposes. Furthermore, a correlation for field conditions

is also presented by using in situ shear wave velocities between laboratory and in-situ shear

modulus and damping ratio values.

Anahtar Kelimeler

Initial shear modulus, damping ratio, dynamic triaxial

Kaynakça

• [1] K. Ishihara, “Soil Behavior in Earthquake Geotechnics”, Clarendon Press, 1996, Oxford.
• [2] B.O. Hardin, W.L. Black, “Vibration Modulus of Normally Consolidated Clay, Journal of the Soil Mechanics and Foundations”, ASCE, Vol. 94, pp. 353-369, 1968.
• [3] T. Kagawa, “Moduli and damping factors of soft marine clays”, Journal of Geotechnical Engineering, Vol. 118, pp. 1360-1375, 1992.
• [4] W.F. Marcuson, H.E. Wahls, “Time Effects on Dynamic Shear Modulus of Clays”, Journal of the Soil Mechanics and Foundations, ASCE, Vol. 98, pp. 1359-1379, 1972.
• [5] K. Zen, Y. Umehara, K. Hamada, “Laboratory tests and in-situ seismic survey on vibration shear modulus of clayey soils with various plasticities”, Proceedings of the 5th Japanase Earthquake Engineering Symposium, Japan, pp. 721-728, June 1978.
• [6] T. Kokusho, Y. Yoshida, Y. Esashi, “Dynamic properties of soft clay for wide strain range, Soils and Foundations”, Vol. 22, pp. 1-18, 1982.
• [7] A.M. Ansal, H. Yıldırım, “Killerin tekrarlı yükler altında kayma mukavemeti”, II. Ulusal Kil Sempozyomu, Haccettepe Üniversitesi, Ankara, 24-27 Eylül 1985 , s. 329-341.
• [8] G. Viggiani, J.H. Atkinson, "Stiffness of fine-grained soil at very small strains”, Geotechnique, Vol. 45, pp. 249-265, 1995.
• [9] H.B. Seed, I.M. Idriss, “Soil moduli and damping factors for dynamic response analyses”, College of Engineering, University of California Technical Report, EERC 70-10, Berkeley, California, 1970.
• [10] F. Tatsuoka, S. Shibuya, “Deformation characteristics of soils and rocks from field and laboratory tests”, Proceedings of the 9th Asian Regional Conference on Soil Mechanics, Bangkok, 9-13 December, Thailand pp.101-170, 1992.
• [11] M. Jamiolkowski, R. Lancellotta, D.C.F. Presti, “Remarks on the stiffness at small strains of six Italian clays”, Proceedings of the International Symposium on Pre-Failure Deformation Characteristics of Geomaterials, Sapparo, 12-14 September, Japan, pp. 135-144, 1994.
• [12] D.W. Hight, V.N. Georgiannou, “Effects of sampling on the undrained behavior of clayey sands”, Geotechnique, Vol. 45, pp. 237-247, 1995.
• [13] S. Guha, V.P. Drenevich, J.D. Bray, “Dynamic characteristics of Old Bay Clay”, Geotechnical Testing Journal, ASTM, Vol. 20, pp. 383-393, 1997.
• [14] R.W. Cunny, Z.B. Fry, “Vibratory in-situ and laboratory soil moduli compared”, Journal of the Geotechnical Engineering Division, ASCE, Vol. 99, pp. 1022-1076, 1973.
• [15] J.D. Bray, M.E. Riemer, W.B. Gookin, “On the dynamic characterization of soils”, Proceedings of 2nd International Conference on Earthquake Geotechnical Engineering, Lisbon, 21-25 June, Portugal, pp. 847-856, 1999.
• [16] K. Ishihara, “Approximate forms of wave equations for water-saturated porous materials and related dynamic modulus”, Soils and Foundations, Vol. 10, pp. 10-38, 1970.
• [17] C.C. Ladd, R. Foott, “New design procedure for stability of soft clays”, Journal of the Geotechnical Engineering Division, ASCE, GT7, pp.763-786, 1974.
• [18] P. Kallioglou, T.H. Tika, K. Pitilakis, Dynamic characteristics of natural cohesive soils, Earthquake Geotechnical Engineering, Vol. 17, pp. 113-117, 1999.
• [19] T.J. Larkin, P.W. Taylor, “Comparison of down hole and laboratory shear wave velocities”, Canadian Geotechnical Journal, Vol. 16, pp. 152-162, 1979.
• [20] K.H. Stokoe, F.E. Richart, “In-situ and laboratory shear wave velocities”, Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering, Moscow, June 1973, Russia, pp. 403-409, 1973.
• [21] Y. Ohta, N. Goto, “Empirical shear wave velocity equations in terms of characteristic soil indexes”, Earthquake Engineering and Structural Dynamics, Vol. 6, pp. 123-135, 1978.
• [22] K. Yokota, M. Konno, “Comparison of soil constants obtained from laboratory tests and insitu tests”, Proceedings of Symposium on Evaluation of Deformation and Strength of Sandy Grounds, Special Publication of Japanese Society of Soil Mechanics and Foundation Engineering, pp. 145-162, 1985.
• [23] R. İyisan, “Geoteknik özelliklerin belirlenmesinde sismik ve penetrasyon deneylerin karşılaştırılması”, Doktora Tezi, İ.T.Ü. Fen Bilimleri Enstitüsü, İstanbul, 1994.