Spudcan fixity under combined cyclic loading

SPUDCAN FIXITY UNDER COMBINED CYCLIC LOADING YANG YU NATIONAL UNIVERSITY OF SINGAPORE 2014 SPUDCAN FIXITY UNDER COMBINED CYCLIC LOADING YANG YU (B. Eng., M. Eng., Southeast University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2014 DECLARATION I hereby declare that the thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. _________________ Yang Yu Jun 2014 i Acknowledgement First of all, I would like to express my sincere gratitude to my dear supervisors, Prof Lee Fook Hou and Asst Prof Goh Siang Huat for their great and constant guidance and useful advice for my whole PhD study. I’m indeed very thankful for their patience and immense knowledge. It would not have been possible to write this PhD thesis without them. I would like to thank Dr. Yi Jiangtao for his excellent guidance on numerical modeling. I am most grateful to my other seniors, Dr. Li Yuping, Dr. Zhang Xiying, Dr. Liu Yong and Dr. Zhao Ben for their generous help, advice and encouragement. Special thanks to Dr. Sun Jie, Dr. Wu Jer-Fang, Dr. Gu Hai, Prof Cassidy, M.J., Dr. Zhang Youhu and Dr. Purwana, O.A. for their professional advice and support during the thesis writing. I also fortunate to have the laboratory technicians Mr. Wong Chew Yuen, Mr. Tan Lye Heng, Dr. Shen Rui Fu and Madam Jamilah and other staffs for their inspiring and great help during the centrifuge tests. I also thank Mr. Martin Loh for fabricating the set-ups. Grateful acknowledgement is expressed to my dear fellow colleagues, in particular Aylee, Kok Shien, Xuguang, Zhang Lei, Hartono, Zongrui, Jiahui and Junhui for their company through this journey. ii Last, but by no means least, an honorable mention belongs to my dear family for always being there for me. For any errors or inadequacies that may remain in this thesis, of course, the responsibility is entirely my own. iii Table of Contents Acknowledgement .ii Summary .viii List of Tables . x List of Figures .xi List of Symbols xvii Abbreviations .xxii CHAPTER - INTRODUCTION . 1.1 Jack-up Rig And Spudcan 1.2 Spudcan Fixity . 1.3 Scope and Objectives . 1.4 Outline of Thesis CHAPTER - LITERATURE REVIEW 11 2.1 Introduction 11 2.2 Spudcan fixity in SNAME (2008) . 12 2.3 Yield surface under combined loadings . 16 2.4 Field Tests 22 2.4.1 Karunakaran et al. (1999) . 22 2.4.2 Temperton et al. (1999) 22 2.5 Small Scale Laboratory Tests under 1-g Condition . 23 2.5.1 Santa Maria (1988) . 23 2.5.2 Vlahos et al. (2001, 2005) . 23 2.6 Centrifuge tests 25 2.6.1 Wong et al. (1993) 25 2.6.2 Ng (1998) 26 2.6.3 Dean et al. (1998) . 26 2.7 Numerical Simulations and Theoretical Analysis 27 2.7.1 Hambly et al. (1991) . 27 2.7.2 Cassidy et al. (2004b) . 28 2.7.3 Bienen et al. (2006b) . 28 2.7.4 Wang et al. (2011) 28 2.8 Effects of Lattice Leg . 29 2.9 Current Knowledge Gaps for Current Study 30 CHAPTER – EXPERIMENTAL SET-UP IN A BEAM CENTRIFUGE 50 3.1 Centrifuge 50 3.1.1 Why centrifuge and quasi-static loading? . 50 3.1.2 Scaling laws 52 iv 3.1.3 NUS Geotechnical Centrifuge 53 3.2 Experimental Set-up . 54 3.2.1 Model spudcan and spudcan with lattice 54 3.2.2 Loading Frame 55 3.2.3 T-bar 55 3.2.4 Pore Pressure Transducers 57 3.3 Soil sample preparation 58 3.4 Undrained Condition 59 3.4.1 T-bar Penetration 59 3.4.2 Spudcan Penetration 60 3.4.3 Spudcan Rocking 60 3.5 Experimental procedures . 61 3.6 Data acquisition and servo-controlled systems 62 CHAPTER – EXPERIMENTAL RESULTS AND ANALYSIS . 70 4.1 Results on Penetration of Spudcan . 72 4.1.1 Undrained shear strength 72 4.1.2 Penetration resistance of spudcan . 74 4.1.3 Excess pore pressure during the penetration . 74 4.2 Results on Rocking of Spudcan 75 4.2.1 Introduction 75 4.2.2 Experimental results and analyses 76 4.3 Summary 97 CHAPTER – NUMERICAL SIMULATION AND VALIDATION . 143 5.1 Introduction 143 5.2 Finite Element Approach . 143 5.3 Finite Element Model of the Spudcan-Soil System . 145 5.3.1 Soil elements . 145 5.3.2 Foundation elements . 147 5.4 Results and discussions 149 5.4.1 Results on Spudcan in NC clay . 149 5.4.2 Spudcan with full circular lattice in NC clay - Short-term behavior. . 151 5.4.3 Comparison with SNN3 152 5.5 Conclusions 154 CHAPTER – NUMERICAL ANALYSIS OF YIELD ENVELOPES . 162 6.1 Introduction 162 6.2 Short-term yield envelopes 162 6.2.1 Introduction . 162 v Horizontal Force (MN) e=0 e=0.3 e=0.5 e=0.7 e=0.9 e=1 0 0.5 1.5 Horizontal Displacement (m) Moment (MNm) Figure 6.15 Horizontal capacities of spudcan with lattices at 12m (1D) 50 45 40 35 30 25 20 15 10 e=0 e=0.3 e=0.5 e=0.7 e=0.9 e=1 0.03 0.06 0.09 0.12 Rotational Angle (rad) 0.15 0.18 Figure 6.16 Rotational capacities of spudcan with lattices at 12m (1D) Horizontal Force (MN) 16 14 12 10 e=0 e=0.3 e=0.5 e=0.7 e=0.9 e=1 0 0.5 1.5 Horizontal Displacement (m) Figure 6.17 Horizontal capacities of spudcan with lattices at 18m (1.5D) 189 120 Moment (MNm) 100 80 e=0 e=0.3 e=0.5 e=0.7 e=0.9 e=1 60 40 20 0 0.03 0.06 0.09 0.12 Rotational Angle (rad) 0.15 0.18 Figure 6.18 Rotational capacities of spudcan with lattices at 18m (1.5D) 190 CHAPTER – CONCLUSIONS 7.1 Summary of Findings In this study, the behaviors and fixity of spudcans with or without lattices under combined loading are studied by means of both physical and numerical modelling. A series of centrifuge tests were carried out which model the spudcan installation process and its subsequent fixity response under both short-term and long-term conditions. Both spudcans with and without lattices were studied, with different opening ratios considered in the former. Numerically, a dual-stage EulerianLagrangian approach of carrying out finite element analyses was adopted to model the spudcan installation process and its undrained fixity response in the short-term, followed by its longer term behavior under operating conditions, both during and after the dissipation of excess pore pressures. Numerical analyses were also performed to study the combined loading yield envelope characteristics for spudcans with and without lattices. The foregoing discussions on the results of centrifuge tests and numerical simulations provide a reasonably self-consistent picture on the rocking response of spudcans deeply embedded in soft clay. The findings can be summarized as follows: (a) The “full dissipation” tests showed much smaller settlements during rocking compared to the “no dissipation” tests in centrifuge tests. This is readily explained by the stiffening and strengthening of the surrounding soil following pore pressure dissipation; which is consistent with the pore pressure results. (b) The pore pressure transducer readings measured in the centrifuge tests showed 191 that excess pore pressure dissipation generated during rocking of the spudcan was not significantly affected by the lattice. (c) The presence of the lattice also caused the location of maximum bending moment to be up-shifted along the leg, towards the soil surface. This may lead to a decrease in the moment borne by the spudcan. (d) The centre of rotation was found to be above the loading reference point. However, the distance of the center of rotation from the loading reference point was only of the order of to 3m. Thus any errors arising from assuming that the loading reference point is also the centre of rotation during assessment on foundation fixity are unlikely to be significant. (e) Lattice resistance played a significant role in the rotational fixity of the spudcan-lattice system. The lattice conferred a significant lateral soil resistance, which leads to a significant increase in fixity of the spudcan. In both the “no dissipation” tests and “full dissipation” tests, a significant increase in foundation fixity, was conferred by the presence of the lattice. In addition, the lattice with smaller opening ratio did not result in significantly larger fixity. This effect was reflected in both the centrifuge models as well as numerical analyses. It can be attributed to the possible resistance from the soil that infilled the lattice during penetration. (f) Excess pore pressure dissipation also played an important role in changing the rotation stiffness during rocking. “no dissipation” tests exhibit lower rotational fixity compared to the “full dissipation” tests at the beginning of rocking. The reason might be that there was residual excess pore pressure due to the installation of foundation. This finding shows it is necessary to consider the effects of consolidation in the assessment of foundation fixity. SNAME’s 192 (2008) yield envelopes appeared to be more applicable to the short-term, rather than long-term, yield envelopes. (g) The lateral-load-moment (HM) load paths from centrifuge tests in largeamplitude “full dissipation” tests were shown to exceed the bounds prescribed by SNAME (2008). Furthermore, the exceedance was larger than that which could be attributed to the rocking-induced settlement. This is consistent with Martin’s (1994) observation. The contributions to the exceedance included both the contribution from the rocking-induced settlement and hardening effects under cyclic loading. This suggests that the yield surface may have to be modified to account for the influence of settlement and hardening effects. (h) For a deeply embedded spudcan under negative vertical load, the numerical results indicate that the soil around the foundation still can provide a certain level of fixity, both horizontal and rotational. Hence, it is proposed that the yield envelope should be extended to the negative vertical load region. In contrast, the yield envelopes based on SNAME (2008) not consider the application of negative vertical loads. (i) For deeply embedded spudcans, the undrained envelopes in the VH and VM planes are well fitted by second-order polynomials. While the rightmost point of the parabola is fixed at V/Vult = 1, the leftmost point is controlled by the maximum uplift resistance. Furthermore, it is interesting to note that the peak horizontal or rotational capacities not change significantly for different embedment. However, the peak horizontal capacity is related to the laterally projected area of the spudcan. (j) The undrained HM envelope is not a perfect ellipse as prescribed in SNAME (2008). The asymmetry largely depends on the directions of the horizontal 193 force and moment acting on the spudcan. The expressions of the yield envelope under the short-term condition are proposed based on the numerical results. (k) The peak normalized horizontal and rotational capacities obtained herein are slightly lower than those inferred by Wong et al. (2012) from SNAME (2008), but are significantly lower than the results reported by Zhang et al. (2011), Templeton et al. (2005) and Templeton (2009); these differences highlight the influence of installation effects, which are modeled in the present study but were not considered in the earlier works. (l) The lattice can contribute substantially to the horizontal and rotational capacities of deeply penetrated spudcans. The enhanced capacities may be due in part to soil arching effects that develop around the lattices during the imposed horizontal or rotational deformations. 7.2 Recommendations for the future research (a) There were some limitations in the present experimental setup. Firstly, as the moment on the spudcan was mainly caused by the application of the horizontal force at the timing belt elevation, the ratio between the moment and the horizontal force was approximately constant. However, this is not true under field conditions as the magnitude and direction of the environmental loads are constantly changing. Secondly, the timing belt used in this research can deform under high tensile force. This results in a series of non-constant horizontal amplitudes generated during the 1000 rocking episode. A more rigid driving system is needed to overcome this problem. Centrifuge tests with 194 different ratios between the bending moment and horizontal force applied on the spudcan should also be conducted. The ratios can be found in the paper by Vlahos (2004). The corresponding method of applying the loads with different ratio is to simulate the application of the horizontal force at different elevations along the model shaft. (b) The modified Cam-clay model used in this study is unable to model cyclic loading effects. A more advanced constitutive soil model can be adopted to further investigate the behaviors of the spudcan with lattices under cyclic loading. (c) Further exploration on the long-term yield envelopes can be conducted as much remains to be studied in this area. The long-term yield envelopes can be further examined by the centrifuge and numerical modelling. 195 REFERENCES ABAQUS. ABAQUS analysis user’s manual. Version 6.12. (2012). Dassault Systèmes Simulia Corp., Providence, RI, USA. Al-Tabbaa A. (1987). “Permeability and stress-strain response of speswhite kaolin”. PhD thesis, Cambridge University. Andersen, K.H. (1991). “Foundation design of offshore gravity structures”. Cyclic loading of soils: from theory to design, O'Reilly & Brown (eds), Blackie, pp. 122-173. Andersen, K.H. (2004). “Cyclic clay data for foundation design of structures subjected to wave loading”. Invited lecture, International Conf. on Cyclic Behaviour of Soils and Liquefaction Phenomena, CBS04, Bochum, Germany, pp. 371-387. Barltrop, N.D.P. & Adams, A.J. (1991). “Dynamics of Fixed Marine Structures (3rd edition)”. Butterworth Heinemann/The Marine Technology Directorate Ltd. Bell, R.W. (1991). “The analysis of offshore foundations subjected to combined loading”. M.Sc. Thesis, University of Oxford. Bienen, B., Byrne, B.W., Houlsby, G.T. & Cassidy, M.J. (2006a). “Investigating six degree of freedom loading of shallow foundations on sand”. Géotechnique 56, No 6, pp. 367-379. Bienen, B. & Cassidy, M.J. (2006b). “Advances in the three-dimensional fluidstructure-soil interaction analysis of offshore jack-up structures”. Marine Structures, 19, pp. 110-140. Bransby, M.F. & Randolph, M.F. (1998). “Combined loading of skirted foundations”. Geotechnique 48, No 5, pp. 637-655. Butterfield, R. (1978). Another look at the rigid surface footing on sand. King’s College Lecture, London. Butterfield, R. & Ticof, J. (1979). “Discussion Session 7-Design parameters for granular soils”. Proc. 7th European Conference on Soil Mechanics & Foundation Engineering, vol. 4, pp.259-262. Butterfield, R., Houlsby, G.T. & Gottardi, G. (1997). “Standardized sign conventions and notation for generally loaded foundations”. Geotechnique, Vol. 47, No. 5, pp. 1051-1054. Cassidy, M.J. (1999). “Non-linear analysis of jack-up structures subjected to random waves”. D.Phil. Thesis, University of Oxford, United Kingdom. 196 Cassidy, M.J. & Byrne, B.W. (2001). “Drum Centrifuge Model Tests Comparing the Performance of Spudcans and Caissons in Kaolin Clay”. Report No. OUEL 2248/01, University of Oxford, United Kingdom. Cassidy, M.J., Houslby, G.T., Hoyle, M. & Marcom, M.R. (2002). “Determining appropriate stiffness levels for spudcan foundations using jack-up case records”. 21st International Conference on Offshore Mechanics and Arctic Engineering, New York, USA, OMAE2005-28085. Cassidy, M.J., Martin, C.M & Houlsby, G.T. (2003). “Development and application of force resultant models describing jack-up foundation behaviour”. Proc. 9th Inter. Conf. of The Jack-up Platform: Design Construction & Operation, Eds: D’Mello, C., McKinley, B. & Boswell, L.F., City University, London. Cassidy, M.J., Byrne, B.W. & Randolph, M.F. (2004a). “A comparison of the combined load behaviour of spudcan and caisson foundations on soft normally consolidated clay”. Geotechnique, 54, 2, pp. 91-106. Cassidy, M.J., Martin, C.M. & Houlsby, G.T. (2004b). “Development and application of force resultant models for describing jack-up foundation behviour”. Marine Structures, 17, 3-4, pp. 165-193. CLAROM. (1993). “Design guides for offshore structures, stability and operation of jackups.” design guides for offshore structures, P. P. Le Tirant, Christian, ed., Paris. Dean, E.T.R., James, R.G., Schofield, A.N. & Tsukamoto, Y. (1998). “Drum centrifuge study of three-leg jackup models on clay”. Geotechnique. Vol. 48, No. 6, pp. 761-785. Dean, E.T.R. (2009). “Offshore Geotechnical Engineering”. Thomas Telford Ltd., London. Finnie, I.M.S. & Randolph, M.F. (1994). “Punch-through and liquefaction induced failure of shallow foundations on calcareous sediments”. Proc., 17th Int. Conf. on the Behavior of Offshore Structures, Boston, 1, pp. 217-230. Gan, C.T. (2010). “Centrifuge model study on spudcan-footprint interaction”. Ph. D Thesis, National University of Singapore. Gottardi, G. & Houlsby, G.T. (1995). “Model tests of circular footings on sand subjected to combined loads”. Report No. 2071/95, Oxford University Engineering Laboratory. Green, A.P. (1954). “The plastic yielding of metal junctions due to combined shear and pressure”. J. Mech. Phys. Solids, 2(3), pp. 197-211. Gourvenec, S. (2008). “Effect of embedment on the undrained capacity of shallow foundations under general loading”. Geotechnique, 58(3), pp. 177–185. 197 Guo,W.D. (2013). “Laterally loaded rigid piles with rotational constraints”. Computers and Geotechnics, 54, pp. 72-83. Hall, J.R. (1967). “Coupled rocking and sliding oscillations of rigid circular footings”. Proc. Int. Symp. Wave Propag. Dyn. Prop. Earth Matter, University of New Mexico, Albuquerque, New Mexico, pp. 139-148 Hambly, E.C., Imm, G.R. & Stahl, B. (1990). “Jackup performance and foundation fixity under developing storm conditions”, Paper OTC 6466, Offshore Technology Conference Hambly, E.C. & Nicholson, B.A. (1991). “Jackup dynamic stability under extreme storm conditions”, Paper OTC 6590, Offshore Technology Conference. Hardin, B.O. & Black, W.L. (1968). “Vibration Modulus of Normally Consolidated Clay”. J. Soil Mech. and Found. Div., Proc. ASCE, Vol. 92, No. SM 2, March, pp. 27-42. Hossain, M.S., Randolph, M.F., Hu, Y. & White, D.J. (2006). “Cavity stability and bearing capacity of spudcan foundations on clay”. Offshore Technology Conference, Houston, OTC 17770. Hossain, M.S. (2008). “New mechanism-based design approaches for spudcan foundations on clays”. Ph. D Thesis, University of Western Australia. Hossain, M.S. & Randolph, M.F. (2009). “New mechanism-based design approach for spudcan foundations on single layer clay.” J. Geotech. Geoenviron. Eng., accepted for publication, Jan. 2009. House, A.R., Oliveira, J.R.M.S. & Randolph, M.F. (2001). “Evaluating the coefficient of consolidation using penetration tests”. International Journal of Physical Modeling in Geotechnics, 3, pp. 17-26. James, R.G. (1987). “Cambridge University Research”. Appendix B of. Foundation Fixity of Jackup Units, Report by Noble Denton to Joint Industry. James, R.G., & Shi, Q. (1988). “Centrifuge modelling of the behavior of surface footings under combined loading”. Centrifuge 88, ed.J-F.Corte, Balkema, pp. 307-311. Karunakaran, D., Bærheim, M. & Spidsøe, N. (1999). “Full-scale measurements from a large deepwater jack-up platform”. Marine Structures, vol. 12, pp. 255-275. Keaveny J. (1985). “In-Situ Determination of Drained and Undrained Soil Strength Using the Cone Penetration Test”. Dissertation presented to the University of California, Berkeley, in partial fulfillment of the requirement for the degree of Doctor of Philosophy. Khoo, E., Okumara, T. & Lee, F. H. (1994). “Side friction effects in plane strain models”, Proceeding of the International Conference Centrifuge 94, Singapore, 31st August ~2nd September, pp. 649~654. 198 Konig, D., Jessberger, H.L., Bolton, M., Phillips, R., Bagge, G., Renzi, R. & Garnier, J. (1994). “Pore Pressure Measurement during Centrifuge Model Tests: Experience of Five Laboratories”. Centrifuge 94. Eds. C.F. Leung, F.H. Lee and T.S. Tan, pp. 101108. A.A. Balkema, Rotterdam. Langen, H.V. & Hospers, B. (1993). “Theoretical model for determining rotational 199ehavior of spud cans”. Proc. 25th Offshore Technology Conference, Houston, Texas, OTC 7302. Langen, H.V., Wong, P.C. & Dean, E.T.R. (1999). “Formulation and validation of a theoretical model for jack-up foundation load–displacement assessment”. Marine Structures, vol. 12, pp. 215-230. Lee, F.H. (1985). “Centrifuge Modelling of Earthquake Effects on Sand Embankments and Islands”. Ph.D. Thesis, Cambridge University. United Kingdom. Leung, C.F., Lee, F.H. & Tan, T.S. (1991). “Principles and Application of Geotechnical Centrifuge Model Testing”. Journal of the Institution of Engineers, Singapore, vol. 31, no. 4, pp. 39-45. Li, Y. P., Lee, F. H., Goh, S. H., Yi, J. T. & Zhang, X. Y. (2012). “Centrifuge study of the effects of lattice leg on penetration resistance and bearing behavior of spudcan foundations in NC clay”. Proceedings of the ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering OMAE2012, Rio de Janeiro, Brazil. Li, Y.P. (2014) “lattice leg effects on the penetration and bearing BEHAVIOR of spudcan foundation”. Ph.D. Thesis, National University of Singapore, Singapore. Martin, C.M. (1994). “Physical and numerical modelling of offshore foundations under combined loads”. Ph.D. Thesis, University of Oxford, United Kingdom. Martin, C.M. & Houlsby, G.T. (2000). “Combined loading of spudcan foundations on clay: laboratory tests”. Géotechnique 50, No. 4, pp. 325-338. Martin, C.M. & Houlsby, G.T. (2001). “Combined loading of spudcan foundations on clay:numerical modelling”. Géotechnique 51, No. 8, pp. 687-699. Menzies, D. & Roper, R. (2008). “Comparison of Jackup rig spudcan penetration methods in clay”. Houston Texas: Proc. 40th offshore technology Conference. OTC, 2008. 19545. Murff, J.D., Hamilton, J.M., Dean, E.T.R., James, R.G., Kusakabe, O. & Schofield, A.N. (1991). “Centrifuge testing of foundation behaviour using full jackup rig models”. Proc. 23rd Offshore Technology Conference, Houston, Texas, OTC 6516. 199 Murff, J.D. (1994). “Limit analysis of multi-footing foundation systems”. Proceedings of the 8th International Conference on Computer Methods and Advances in Geomechanics, Totterdam: Balkema, pp. 233-244. Ngo-Tran, C.L. (1996). “The analysis of offshore foundations subjected to combined loading”. Ph.D. Thesis, University of Oxford. Ng, T.G. (1998). “Cyclic behavior of spudcan footing on sand”. Ph.D. Thesis, National University of Singapore, Singapore. Ng, T.G. & Lee. F.H. (2002). “Cyclic Settlement Behaviour of Spudcan Foundations”. Geotechnique. Vol 52, No. 7, pp. 469-480. Noble Denton and Associates, (1987). Joint Industry Study: “Foundation Fixity of Jackup Units”. London. Osborne, J.J., Trickey, J.C., Houlsby, G.T., James, R.G. & Kusakahe, O. (1991). “Findings from a joint industry study on foundation fixity of jack-up units”. Offshore Technology Conference 6615. Pedersen, J. (1994). “Dynamic response of rubble mound breakwater crown walls”. Proc. 2nd Project Workshop, Milan. Purwana, O.A. (2006). “Centrifuge model study on spudcan extraction in soft clay.” Ph.D. Thesis, National University of Singapore, Singapore. Purwana, O.A. Leung, C.F. Chow, Y.K. & Foo, K.S. (2005). “Influence of base suction on extraction of jack-up spudcans”. Geotechnique, 55, No. 10, pp. 741-753. Randolph, M. & Houlsby, G. (1984). “The limiting pressure on a circular pile loaded laterally in cohesive soil”. Geotechnique, 34, No. 4, pp. 613-623 Reardon, M.J. (1986). “Review of the geotechnical aspects of jack-up unit operations”. Ground Engineering, Vol. 19, No.7, pp. 21-26. Richart, F.E., Woods, R.D. & Hall, J.R. (1970). “Vibrations of soils and foundations”. Englewood Cliffs, NJ: Prentice Hall. Roscoe, K.H. & Schofield, A.N. (1956). “The stability of short pier foundations in sand”. British Welding Journal, August, pp. 343-354. Roscoe, K.H. & Burland, J.B. (1968). “On the generalized stressstrain behaviour of wet clay”. In Engineering Plasticity, eds. J. Heyman and F.A. Leckie, P 535-609. Cambridge, England:Cambridge University Press. Santa Maria, P.E.L. de (1988). “Behaviour of footings for offshore structures under combined loads”. Ph.D. Thesis, University of Oxford, United Kingdom. 200 Schotman, G.J.M. (1989). “The effects of displacements on the stability of jack-up spud-can foundations”. Proc. 21st Offshore Technology Conference, Houston, pp. 515-524, OTC 6026. Shen, R.F., Wong, C.Y. & Tan, L.H. (2011). “Geotechnical Centrifuge Users' Manual”. National University of Singapore, Singapore. Springman, S.M. & Schofield, A.N. (1998). “Monotonic lateral load transfer from a jack-up platform lattice leg to a soft clay deposit”. In T. Kimura et al. (eds), Proc. Conf. Centrifuge 98, Tokyo, pp. 563-568. Rotterdam: Balkema. Skempton, A.W. (1951). “The bearing capacity of clays”. Proceedings of Building Research Congress, 1, pp. 180-189. SNAME. (2008). “Technical & Research Bulletin 5-5, Guideline for Site Specific Assessment of Mobile Jack-Up Units”. Stewart, D.P. & Randolph, M.F. (1991). “A new site investigation tool for the centrifuge”. In Proc. of the International Conference Centrifuge 91, pp 531-538. Taiebat, H. & Carter, J.P. (2000). “Numerical studies of the bearing capacity of shallow footings on cohesive soil subjected to combined loading”. Geotechnique, 50(4), pp. 409-418. Tan, F.S.C. (1990). “Centrifuge and theoretical modeling of conical footing on sand”. Ph.D. Thesis, Cambridge University. United Kingdom. Tan, T.S., Inoue, T. & Lee, S.L., (1991). “Hyperbolic method for consolidation analysis”. Journal of geotechnical engineering 117(11), pp. 1723-1737. Taylor, R.N. (1995). “Geotechnical Centrifuge Technology”. Engineering Research Centre City University, London. Geotechnical Temperton, I., Stonor, R.W.P. & Springett, C.N. (1999). “Measured spudcan fixity: analysis of instrumentation data from three North Sea jack-up units and correlation to site assessment procedures”. Marine Structures, vol. 12, pp. 277-309. Templeton, J.S., Lewis, D.R. & Brekke J.N. (2003). “Spud Can Fixity in Clay, First Findings of a 2003 IADC Study”. 9th City University Jack-up Platform Conference, London, UK. Templeton, J.S., Brekke, J.N. & Lewis, D.R. (2005). “Spud can fixity in clay, final findings of a study for IADC”. 10th City University Jack-up Platform Conference, London, UK. Templeton, J.S. (2009). “Spudcan fixity in clay, further results from a study for IADC”. 12th City University Jack-up Platform Conference, London, UK. Tho, K.K., Leung, C.F., Chow, Y.K., & Swaddiwudhipong, S. (2011). “Important considerations in the application of Eulerian technique for spudcan penetration 201 analysis”. London: Proc. 13th Int Conf on the jack-up platform design, Construction & Operation. Tromans PS, Anaturk AR, Hagemeijer P. (1991). “A new model for the kinematics of large ocean waves—applications as a design wave”. Proceedings of the 1st international offshore and polar engineering conference, vol. 3. Edinburgh. pp. 64–71. Vesic, A.S. (1975). “Bearing capacity of shallow foundations”. Foundation Engineering Handbook (ed. Winterkorn H F and Fang H Y), Van Nostrand, New York, pp. 121-147. Vlahos, G., Martin, C.M. & Cassidy, M.J. (2001). “Experimental investigation of a model jack-up unit on clay”. Proc. 11th Int. Offshore and Polar Engineering Conf., Stavanger, Vol. 1, pp. 97-105. Vlahos G. (2004). “Physical and numerical modelling of a three-legged jack-up structure on clay soil”. Ph.D. Thesis, The University of Western Australia. Vlahos, G., Martin, C.M., Prior, M. & Cassidy, M.J. (2005). “Development of a model jack-up unit for the study of soil-structure interaction on clay”. International Journal of Physical Modelling in Geotechnics, Vol. 5, No. 2, pp. 31-48. Watson, P. G., Newson, T. A. & Randolph, M.F. (1998). “Strength profiling in soft offshore soils”. Proc. 1st Int. Conf. on Site Characterisation - ISC ’98, Atlanta, 2, pp. 1389-1394. Wang, L.Z., Shu, H., Li L.L. & Guo, Z. (2011). “Undrained bearing capacity of spudcan under combined loading”. China Ocean Engineering, Vol. 25, Issue 1, pp.1530. Williams, M.S., Thompson, R.S.G & Houlsby, G.T. (1998). Non-linear dynamic analysis of offshore jack-up units. Computers and Structures, Vol. 69, pp. 171-180. Wong, P.C., Chao, J.C., Murff, J.D., Dean, E.T.R., James, R.G., Schofield, A.N. & Tsukamoto, Y.K. (1993). “Jackup rig foundation modelling II”. Proc. 25th Offshore Technology Conference, Houston, Texas, OTC 7303. Wong, P.C., Templeton, J.S., Purwana, O.A., Hofstede, H., Cassidy, M.J., Hossain, M.S. & Martin, C.M. (2012). “Foundation modeling and assessment in the new ISO standard 19905-1”. Offshore Technology Conference, Houston. Wroth, C. P. (1984), “Interpretation of in situ soil tests”. Geotechnique, 34(4), pp. 449-489. Yang, Y., Lee, F.H., Goh, S.H., Wu, J.F. & Zhang, X.Y. (2013). “Pore Pressure Generation and Dissipation Effects on Spudcan Fixity in Normally Consolidated Clay”, ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering, Nantes, France. 202 Yi, J.T., Goh, S.H., Lee, F.H., Zhang, X.Y., & Wu, J.F. (2012). “Eulerian finite element analysis of excess pore pressure generated by spudcan installation into soft clay”. Computers and Geotechnics, 42: pp. 157-170. Yi, J.T., Zhao, B., Li, Y.P., Yang, Y., Lee, F.H., Goh, S.H., Zhang, X.Y., & Wu, J.F. (2014). “Post-Installation Pore-Pressure Changes around Spudcan and Long-term Spudcan Behaviour in Soft Clay,” Journal of Computers and Geotechnics, No. 56, pp. 133-147. Zhang, F., Kimura, M., Nakai, T. & Hoshikawa, T. (2000). “Mechanical behavior of pile foundations subjected to cyclic lateral loading up to the ultimate state”, Soils and Foundations, vol. 40, No. 5, pp. 1-17. Zhang, Y.H., Bienen, B., Cassidy, M.J. & Gourvenec, S. (2011). “The undrained bearing capacity of a spudcan foundation under combined loading in soft clay”. Marine Structures, vol. 24, pp. 459-477. Zhang, Y.H., Cassidy, M.J. & Bienen, B. (2013). “Development of a combined VHM loading apparatus for a geotechnical drum centrifuge”. International Journal of Physical Modelling in Geotechnics, 13 (1), pp. 13-30. Zhou, X.X., Chow, Y.K. & Leung, C.F. (2009). “Numerical modelling of extraction of spudcans,” Geotechnique, 59, No. 1, pp. 29–39. 203 Appendix A 204 [...]... approach The soil surrounding the spudcan will provide some rotational stiffness, so that the spudcan is more likely to behave as a partially fixed connection This study is conducted to examine the mechanism of spudcan fixity response under cyclic combined loading Through an improved understanding of the spudcan fixity phenomenon, it is possible to gain deeper insights and a better appreciation of the... the spudcan on leg 1 Figure 2.29 Spudcan fixity – seabed stiffnesses Figure 2.30 Yield surfaces for spudcan fixity on clay and sand seabeds Figure 2.31 Load paths followed by footings using multiple surface model Figure 2.32 Moment rotation response of the upwave spudcan using multi-surface model Figure 2.33 (a) Hull plan and loading direction (b) spudcan with model sign convention Figure 2.34 Spudcan. .. all other foundation structures, the spudcan is vulnerable to foundation stability problems during its operations To conduct an accurate analysis of spudcan behaviour and its effect on the overall structural response, a better understanding of spudcan fixity is required Spudcan fixity is a growing field of interest in offshore engineering SNAME (2008) defines spudcan fixity as the rotational restraint... the spudcan performance The results from finite element analysis were also used to study the yield surface characteristics associated with spudcan fixity The influence of different forms of lattice on the yield surface response was also considered 1.3 Scope and Objectives In this research programme, the behaviour of spudcan with and without lattices and its fixity characteristics under cyclic combined. .. (1) To study the fundamental mechanism of spudcan fixity, with and without lattices, so as to obtain a better understanding of the fixity response and how it may be incorporated into the design process, (2) To study the effect of lattice legs on spudcan fixity The role of the lattice legs is examined to better understand their role in enhancing the foundation fixity, which can in turn reduce the lower... associated with the current practice of assuming a pinned connection A special loading frame was designed for this study, which can apply both vertical and cyclic combined loading to the spudcan The tests were carried out in the NUS geotechnical centrifuge facility under a 100-g acceleration field During the tests, the spudcan with and without lattice was first pushed inflight from the surface of the... of spudcan behaviour and its effect on the overall structural response, a better understanding of spudcan fixity is required In this study, centrifuge experiments were carried out which considered the various parameters that may affect spudcan fixity behaviour with/without lattices The results were analyzed to examine if the assumption of a pinned condition introduces undue conservatism to the spudcan. .. restraint offered by the soil supporting the spudcan foundation The degree of fixity is affected by the soil type, the maximum vertical footing load during installation, the foundation stress history, the structural stiffness of the unit, the geometry of the footings and the combination of vertical and horizontal loading under consideration The significance of spudcan fixity has been discussed in many studies,... rotation Figure 4.82 Foundation fixity in NC clay Figure 4.83 Relationship between opening ratio and Spudcan fixity/ Foudnation fixity Figure 4.84 Foundation fixity in OC clay Figure 4.85 Lattice effect to horizontal force on timing belt in “no dissipation” tests Figure 4.86 Lattice effect to horizontal force on timing belt in “full dissipation” tests Figure 5.1 Numerical model for spudcan with shaft (for SNN4)... well as increase the natural frequency of the spudcan (as discussed in Section 1.2) This could potentially result in a more economic design of the foundation (3) To study soil consolidation effects on the fixity of spudcans Since oil-drilling operations are typically carried out over a period of many years, a better 4 understanding of the long-term spudcan fixity response is crucial for evaluating the . SPUDCAN FIXITY UNDER COMBINED CYCLIC LOADING YANG YU NATIONAL UNIVERSITY OF SINGAPORE 2014 SPUDCAN FIXITY UNDER COMBINED CYCLIC LOADING YANG YU (B. Eng., M. Eng.,. stiffness, so that the spudcan is more likely to behave as a partially fixed connection. This study is conducted to examine the mechanism of spudcan fixity response under cyclic combined loading. Through. special loading frame was designed for this study, which can apply both vertical and cyclic combined loading to the spudcan. The tests were carried out in the NUS geotechnical centrifuge facility under