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International Journal of Latest Research in Science and Technology Volume 6, Issue 1: Page No.41-45,January-February 2017 http://www.mnkjournals.com/ijlrst.htm ISSN (Online):2278-5299 SETTLEMENT ANALYSIS OF PILED RAFT FOUNDATION IN CLAY OF SOFT TO MEDIUM CONSISTENCY BY NONLINEAR FINITE ELEMENT METHOD 1 Dr.D.K.Maharaj, 2Dr.Sanjeev Gill 1 Director,Principal, Professsor Guru Nanak Institute of Technology (GNIT), Guru Nanak Institutions (GNI) Mullana, Ambala, Haryana, India 2 Principal, JBIT, Dehradun, India Abstract - In this paper a single pile with equivalent size of raft has been taken from an Infinite piled raft. One fourth of piled raft with equivalent area of raft has been taken from a single pile with equivalent area of raft. The soil, pile and raft have been discretized as eight nodded brick elements. The soil has been idealized as Extended Drucker-Prager yield criterion. The material behaviour of pile and raft has been considered as linear elastic medium. The load settlement curves are linear in the earlier portion of the curves and then it become nonlinear This nonlinearity is maximum at larger loading intensity and minimum at smaller loading intensity. The maximum settlement is for pile having length to diameter ratio of 10 and minimum for pile having length to diameter ratio equal to 50. The marginal difference for settlement between the curves is maximum at loading intensity equal to 50 kN/m 2 and minimum at loading intensity of 10 kN/m2. In the load settlement curves plotted for various spacing to diameter ratio the marginal difference for settlement between the curves is very very small at length to diameter equal to 10 and than it becomes better and better with increase in length to diameter ratio of pile. LITERATURE REVIEW Hongladaromp et.al (1973) studied the interaction of a rectangular pile cap with subgrade to determine the sharing of load on piles and the subgrade. Employing the finite difference technique a parametric study was carried out. They found that the resistance of the subgrade has considerable effect on settlement of footing and should be taken into consideration in the analysis. Brown and Wiegner (1975) presented results for load taken by piles, maximum displacements, differential displacements due to uniformly distributed load applied to a smooth strip footing which is supported by piles on a deep homogeneous isotropic elastic foundation. Wiesner(1980) performed laboratory tests on four model piled raft foundations having circular raft. The experimental load-settlement and load-moment curves were compared with the results of theoretical study. EI-Mossallamy (1989) presented in his paper the pile-raftsoil interaction. The analysis were carried out under the assumption of linear elastic behaviour of raft, piles and half space, unsolved bond ie. no slip between piles and half space. The load sharing between pile and raft, the effect of length of pile in reducing settlement are discussed. Clancy and Randolph (1993) describe a ‘hybrid’ approach for the analysis of piled raft foundations, based on a load transfer treatment of individual piles, together with elastic interaction between different piles and with the raft. Parametric studies are presented showing the effect of factors such as raft stiffness and pile spacing, length and stiffness. Prakoso and Kulhawy (2001). examined raft foundations enhanced with deep foundation elements (typically piles), simply known as piled rafts. Illustrative piled rafts were analyzed using simplified linear elastic plane strain finite ISSN:2278-5299 element models The results were synthesized into an updated, displacement-based, design methodology for piled rafts. Small and Zhang (2002) presents a new method of analysis of piled raft foundations in contact with the soil surface. The soil is divided into multiple horizontal layers. The raft is modeled as a thin plate and the piles as elastic beams. Finite layer theory is employed to analyze the layered soil while finite element theory is used to analyze the raft and piles Comparisons show that the results from this method agree closely with those from the finite element method. Al-Mosawi et.al (2011) present experimental study to investigate the behavior of piled raft system in sandy soil. A small scale “prototype” model was tested in a sand box with load applied to the system through a compression machine. The settlement was measured at the center of the raft, strain gages were used to measure the strains and calculate the total load carried by piles. El-Garhy et.al (2013) conducted an experimental program on model piled rafts in sandy soil. The model piles beneath the rafts are closed ended displacement piles installed by driving. Three lengths of piles are used in the experiments to represent slenderness ratio, L/D, of 20, 30 and 50, respectively. The dimensions of the model rafts are 30 cm × 30 cm. The results of the tests show the effectiveness of using piles as settlement reduction measure with the rafts. As the number of settlement reducing piles increases, the load improvement ratio increases and the differential settlement ratio decreases. Raut et.al (2015) present model laboratory test on piled raft foundation to investigate load sharing ratio. Structural mild steel bars of 10 mm dia and 1 m long are used as piles. Mild steel plate of 10 mm thick and 300 mm x 300 mm 41 International Journal of Latest Research in Science and Technology. FINITE ELEMENT ANALYSIS Fig.1 shows the finite element discretization . Discretization shows one fourth of piled raft with equivalent area of raft taken from a single pile with equivalent area of raft from pile forest model The soil, pile and raft have been discretized as eight nodded brick elements. The material behaviour of pile and raft has been considered as linear elastic medium. The soil has been idealized as an Extended Drucker-Prager model. Load (kN/m2) 0 10 20 30 40 50 0 Settlement (mm) square plate is taken as raft foundation. On raft foundation (steel plate) with piles (steel bars) load is applied gradually and ultimate bearing capacity is calculated. Total load taken by piles is calculated and load sharing ratio of raft and pile is calculated. Field measurements as reported by Hooper(1973), Cooke(1981),Schwab(1991), Franke (1991), Poulos (1994) and Yamashita (1994) give very useful information for load transfer and settlement behaviour of piled raft. L/d=10, s/d=2.5 -10 L/d=20, s/d=2.5 -20 -30 L/d=30, s/d=2.5 -40 L/d=40, s/d=2.5 -50 -60 Fig.2 Load settlement curve L/d=50, s/d=2.5 Fig.3 shows the load settlement curve at spacing to diameter ratio equal to 5 for varying length to diameter ratio for different loading intensity. The load settlement curves are nonlinear. This nonlinearity is maximum at larger loading intensity and minimum at smaller loading intensity. The marginal difference of settlement between the curves is maximum at loading intensity equal to 50 kNm2 and minimum at loading intensity 10 kN/m2. With increase in spacing to diameter ratio the marginal difference of settlement between the curves decreases. Load (kN/m2) 0 10 20 30 40 50 Settlement (mm) 0 -10 L/d=10, s/d=5 -20 L/d=20, s/d=5 -30 L/d=30 ,s/d=5 -40 L/d=40, s/d=5 L/d=50, s/d=5 -50 -60 Fig.3 Load settlement curve RESULTS AND DISCUSSIONS Fig.2 shows the load settlement curve for different length to diameter ratio for varying loading intensity at spacing to diameter ratio equal to 2.5. The nature of curves are nonlinear.This nonlinearity is maximum at larger loading intensity and minimum at smaller loading intensity. The maximum settlement is for pile having length to diameter ratio of 10 and minimum for pile having length to diameter ratio equal to 50. The marginal difference for settlement between the curves is maximum at loading intensity equal to 50 kN/m2 and minimum at loading intensity of 10 kN/m2. ISSN:2278-5299 Fig.4 shows load settlement curves for various length to diameter ratio and loading intensity. Each of the curve is nonlinear. The initial portion of the curves is linear. The marginal difference of settlement between the curves for spacing to diameter ratio 10 is smaller than that for spacing to diameter ratio equal to 5. This is because the raft size is greater at spacing to diameter 10 and the raft takes more load. 42 International Journal of Latest Research in Science and Technology. Load (kN/m2) 0 10 20 30 40 Load (kN/m2) 50 0 -10 L/d=10, s/d=10 -20 L/d=20, s/d=10 -30 L/d=30, s/d=10 -40 L/d=40, s/d=10 -50 L/d=50, s/d=10 -60 20 30 40 50 S/d=2.5, L/d=10 -10 -20 S/d=5, L/d=10 -30 S/d=10, L/d=10 -40 -50 S/d=15, L/d=10 -60 Fig.6 Load settlement curve Fig.4 Load settlement curve Fig.5 shows the load vs settlement curves for various length to diameter ratio at spacing to diameter ratio equal to 15. As for spacing to diameter ratio 2.5,5,10 this curve is also nonlinear.The marginal difference between the settlement of the curves is minimum i.e smaller than that with spacing to diameter ratio equal to 2.5,5 and10. This is because the raft size is greater and the raft takes more load. Fig.7 shows the load settlement curve for length to diameter ratio 20 for various spacing to diameter ratio and loading intensity. The curves are nonlinear and the marginal difference for settlement between the curves is better than in Fig.6. Load (kN/m2) 0 Load (kN/m2) 10 20 30 40 10 20 30 40 50 0 50 0 -10 -20 -30 L/d=10, s/d=15 L/d=20, s/d=15 L/d=30, s/d=15 -40 L/d=40, s/d=15 -50 L/d=50, s/d=15 Settlement (mm) 0 Settlement (mm) 10 0 Settlemenet (mm) Settlement (mm) 0 -10 -20 S/d=2.5, L/d=20 S/d=5, L/d=20 -30 -40 -50 S/d=10, L/d=20 S/d=15, L/d=20 -60 Fig.7 Load settlement curve -60 Fig.5 Load settlement curve Fig.6 shows the load settlement curve for piled raft foundation for length to diameter ratio 10 for various spacing to diameter ratio. Even in this case the load settlement curves are nonlinear. The marginal difference between the settlement curves is very very small. ISSN:2278-5299 Fig.8 shows the load settlement curve for length to diameter ratio 30 for various spacing to diameter ratio and loading intensity. The curves are nonlinear and the marginal difference for settlement between the curves is better than in Fig.6 and Fig.7. 43 International Journal of Latest Research in Science and Technology. Load (kN/m2) 0 10 20 30 40 50 Settlement (mm) 0 S/d=2.5, L/d=30 -10 -20 S/d=5, L/d=30 -30 S/d=10, L/d=30 -40 -50 S/d=15, L/d=30 -60 Fig.8 Load settlement curve Fig.9 shows the load settlement curve for length to diameter ratio 40 for various spacing to diameter ratio and loading intensity. The curves are nonlinear and the marginal difference for settlement between the curves is better than in Fig.6 ,Fig.7 and Fig.8 Fig.10 shows the load settlement curve for length to diameter ratio 50 for various spacing to diameter ratio and loading intensity. The curves are nonlinear and the marginal difference for settlement between the curves is better than in Fig.6 ,Fig.7 ,Fig.8 and Fig.9 CONCLUSIONS Based on nonlinear finite element analysis the following conclusions have been made. The load settlement curves are linear in the earlier portion of the curves and then it become nonlinear This nonlinearity is maximum at larger loading intensity and minimum at smaller loading intensity. The maximum settlement is for pile having length to diameter ratio of 10 and minimum for pile having length to diameter ratio equal to 50. The marginal difference for settlement between the curves is maximum at loading intensity equal to 50 kN/m2 and minimum at loading intensity of 10 kN/m2. In the load settlement curves plotted for various spacing to diameter ratio the marginal difference for settlement between the curves is very very small at length to diameter equal to 10 and than it becomes better and better with increase in length to diameter ratio of pile. REFERENCES 1. Al-Mosawi ,M.J., Y. Fattah,M. and Al-Zayadi,A.A.O (2011) Experimental Observations on the Behavior of a Piled Raft Foundation, Journal of Engineering, Volume 17, No. 4 2. Brown , P.T. and Wiesner, T.J.(1975) The behaviour of uniformly loaded piled strip footing, Soils and Foundations, 15(4),13-21 3. Clancy, P. and Randolph, M.F.(1993)An Approximate Analysis Procedure for Piled Raft Foundations, International Journal for Numerical and Analytical Methods in Geomechanics,Vol.17, No.12, pp.849–869 4. Cooke, R.W., Bryden-Smith, D.W. and Gooch(1981) Some observations of the foundation loading and settlement of a multistorey building on piled raft foundation in London clay, Proceedings, Institution of Civil Engineers,1,433-460 5. Der-Guey Lin and Zheng-Yi Feng (2006) A Numrical Study of Piled Raft Foundations, Journal of the Chinese Institute of Engineers, Vol. 29, No. 6, pp. 1091-1097 6. El-Garhy,B., Galil,A.A., Abdel-Fattah A.A.,Raia,M.A.(2013) Behavior of Raft on Settlement Reducing Piles: Experimental Model Study, Journal of Rock Mechanics and Geotechnical Engineering,Vol.5 ,pp389–399 7. EI-Mossallamy (1989) Analysis of pile-raft-soil interaction, M.Sc Thesis, faculty of engineering, Ain ShamsUniversity, Cairo, published in extracts in Proceeding First International Conference on a Structural Engineeringof Ain Shams University under the same title and names of EI-Kadi, EI-Nahhas, EI-Mossallamy. 8. Franke, E.(1991)Measurements beneath piled rafts, key note lecture to ENPC-Conference on Deep Foundations, Paris, 1-28 9. Hongladaramp, T., Chen, N. and Lee,S.(!973) Load distribution in rectangular footings on piles, Geotechnical Engineering, 4, 77-90. Load (kN/m2) Settlement (mm) 0 10 20 30 40 50 0 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50 S/d=2.5, L/d=40 S/d=5, L/d=40 S/d=10, L/d=40 S/d=15, L/d=40 Fig.9 Load settlement curve 0 Load (kN/m 2) 10 20 30 40 50 0 Settlement (mm) S/d=2.5, L/d=5 0 -10 S/d=5, L/d=50 -20 -30 S/d=10, L/d=5 0 -40 S/d=15, L/d=5 0 -50 Fig.10 Load settlement curve ISSN:2278-5299 10. Hopper, J.A.(1973)Observations on the behaviour of a piled raft foundation in London clay, Proceedings of Institution of Civil Engineers, vol.55, no.2,pp.855-877 11. Poulos,H.G.(1994) Alternative design strategies for piled raft foundations. 3rd InternationalConference on DEEP FOUNDATION PRACTICE incorporating PILETALK, Singapore. 12. Prakoso, W. and Kulhawy, F. (2001). Contribution to Piled Raft Foundation Design. Journal, Geotechnical and Geoenvironmental Engineering, ASCE Vol.127:No.17,pp.17-24. 13. Raut J.M., Khadeshwar ,S.R.and Bajad S.P.(2015)Load Sharing Ratio of Piled Raft Foundation, 50th INDIAN GEOTECHNICAL CONFERENCE 17th – 19th DECEMBER 2015, Pune, Maharashtra, India Venue: College of Engineering (Estd. 1854), Pune, India 44 International Journal of Latest Research in Science and Technology. 14. Schwab,H.H., Gundling,N. and Lutz,B.(1991)Monitoring pile raft soil interaction, Proceedings of Symposium on Field Measurements in Geotechnics, Sorum, Balkema, Rotterdam,117-127. 15. Small ,J.C. and Zhang,H.H.(2002),Behavior of Piled Raft Foundations under Lateral and Vertical Loading International Journal of Geomechanics, Vol. 2, No.1, pp.29-45 16. Wiesner, T.J.(1980) Laboratory Tests on Model Piled Raft Foundations 17. Journal of the Geotechnical Engineering Division, 1980, Vol. 106, No.7, pp. 767-783 ISSN:2278-5299 45