复合加载模式作用下地基承载性能数值分析
摘要
确定竖向荷载(V)、水平荷载(H)和力矩(M)共同作用下建筑物地基的破坏模式及在荷载空间(H,V,M)中的破坏包络面是地基设计中的关键问题。为提高Swipe试验方法计算精度,提出了改进方案,进而利用有限元方法分析了复合加载模式作用下均质粘性土地基上条形基础的破坏包络面。计算表明,基于改进Swipe试验方法的数值模拟结果明显好于常规Swipe试验方法。针对海洋工程中实际复合加载模式的特点,探讨了竖向荷载分量V对地基破坏模式和H-M荷载平面上的破坏包络线的影响,结果表明竖向荷载分量显著地改变了地基的破坏模式及包络线的形状。
It is a key issue to define stability or failure envelopes and failure mechanisms of structural foundations under combined loading in the design of offshore foundation which are usually subjected to vertical component(V),horizontal component(H) and moment component(M) simultaneously.Swipe test method is effective to discover the stability/failure envelopes in the load space of H-V-M.In order to improve this method,a modification has been made in this paper by adding a transition step between the two loading steps in a conventional swipe test.As a numerical example,a homogeneous clay foundation under a strip footing subjected to combined loading is analyzed with two-dimensional finite element method based on the modified swipe test procedure.The numerical results show that the failure envelopes computed based on the modified swipe test procedure are more accurate than those based on the conventional approach.Considering the actual characteristics of combined loading in offshore engineering,the modified swipe test procedure is used to examine the effects of the vertical load component on both the failure envelopes in the load space of H-M and failure mechanisms of soil foundation.It is shown that the influence of vertical load on the behavior of the bearing capacity of foundation is somewhat noticeable and should be duly considered in the design and that the failure mechanism is closely associated with the combination of loads.
It is a key issue to define stability or failure envelopes and failure mechanisms of structural foundations under combined loading in the design of offshore foundation which are usually subjected to vertical component(V),horizontal component(H) and moment component(M) simultaneously.Swipe test method is effective to discover the stability/failure envelopes in the load space of H-V-M.In order to improve this method,a modification has been made in this paper by adding a transition step between the two loading steps in a conventional swipe test.As a numerical example,a homogeneous clay foundation under a strip footing subjected to combined loading is analyzed with two-dimensional finite element method based on the modified swipe test procedure.The numerical results show that the failure envelopes computed based on the modified swipe test procedure are more accurate than those based on the conventional approach.Considering the actual characteristics of combined loading in offshore engineering,the modified swipe test procedure is used to examine the effects of the vertical load component on both the failure envelopes in the load space of H-M and failure mechanisms of soil foundation.It is shown that the influence of vertical load on the behavior of the bearing capacity of foundation is somewhat noticeable and should be duly considered in the design and that the failure mechanism is closely associated with the combination of loads.
引文
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[2]栾茂田,王栋,郭莹,等.海床与海洋地基的动力分析理论与设计方法研究进展评述[A].土动力学与岩土地震工程[C].北京:中国建筑工业出版社,2002,28-47.
[3]Ukritchon B,Whittle A J,Sloan S W.Undrained limit analyses for combined loading of strip footings on clay[J].Journal of Geotechni-cal and Geoenvironmental Engineering,ASCE,1998,124(3):265-276.
[4]Gottardi G,Houlsby G T,Butterfield R.Plastic response of circular footings on sand under general planar loading[J].Géotechnique,1999,49(4):453-469.
[5]Gourvenec S,Randolph M.Effect of strength non-homogeneity on the shape of failure envelopes combined loading of strip and circularfoundations on clay[J].Géotechnique,2003,53(6):575-586.
[6]Taiebat H,Carter J P.Numerical studies of the bearing capacity of shallow footings on cohesive soil subjected to combined loading[J].Géotechnique,2000,50(4):409-418.
[7]Bransby M F,Randolph M F.Shallow foundations subject to combined loadings[A].Computer Methods and Advances in Geomechanics[C].Rotterdam:Balkema,1997,1947-1952.
[8]Bransby M F,Randolph M F.Combined loading of skirted foundations[J].Géotechnique,1998,48(5):637-655.
[9]Bransby M F,Randolph M F.The effect of embedment depth on the undrained response of skirted foundations to combined loading[J].Soils and Foundations,1999,39(4):19-33.
[10]Martin C M.Physical and numerical modeling of offshore foundations under combined loads[D].London:University of Oxford,1994.
[11]Martin C M,Houlsby G T.Combined loading of spudcan foundations on clay:laboratory tests[J].Géotechnique,2000,50(4):325-328.
[12]Martin C M,Houlsby G T.Combined loading of spudcan foundations on clay:numerical modeling[J].Géotechnique,2001,51(8):687-699.
[13]Tan F S.Centrifuge and theoretical modelling of conical footings on sand[D].London:Cambridge University,1990.
[14]Cassidy M J,Byrne B W,Randolph M F.A comparison of the combined load behaviour of spudcan and caisson foundations on softnormally consolidated clay[J].Géotechnique,2004,54(2):91-106.
[15]Butterfield R,Houlsby G T,Gottardi G.Standard sign conventions and notation for generally loaded foundations[J].Géotechnique,1997,47(5):1051-1054.
[16]HKS.ABAQUS users′Manual Version 6.3-1[M].Hibbit,Karlsson and Sorensen Inc,2002.
[17]Prandtl L.Uber die Eindringungsfestigkeit(Harte)plastischer Baustoffe und die Festigkeit von Schneiden[J].Journal of AppliedMathematics and Mechanics(ZAMM),1921,1(1):15-20.
[18]Hansen J B.A revised and extended formula for bearing capacity[R].Danish Geotechnical Institute Bulletin,1970,(28):5-11.
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