深基坑桩锚支护弹塑性有限元分析
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摘要
近年来，随着城市建设的快速发展，高层建筑的大量兴建与城市地下空间的开发利用，必将带来大规模基坑工程的开挖和支护。本文首先对国内外大量的与基坑支护相关的土压力计算基本理论和传统的支护结构设计方法进行了综合分析和评价。针对长沙市某深基坑工程，作者编制了弹塑性有限元程序进行分析。在程序中，土体采用弹塑性的Druck-Prager本构模型，护坡桩和土体都采用平面应变四结点等参单元进行网格划分，在桩和土体之间引入Goodman接触单元，对于锚杆，采用杆单元进行模拟，利用改进的“空气单元法”模拟基坑的分布开挖。对比有限元程序计算所得的位移值和实测结果，两者较吻合，验证了程序的适用性。
有限元计算结果表明，该工程的护坡桩的下部水平位移比上部水平位移大，由于桩的埋深只有1.2m，在实际工程中要特别注意“踢脚”现象；基坑坑底的隆起随着距开挖面的距离越远，隆起量也越大，最大隆起量发生在基坑的中部；基坑周围的地表沉降，在基坑顶部最大，离基坑顶部越远，沉降越小；锚杆的轴力分布为两端小，中部大；随着基坑的开挖，锚杆承受的拉力越来越大且锚杆轴力峰值有向锚杆末端偏移的趋势。最大值为197kN，小于设计抗拔力330kN。
该基坑支护综合考虑了土质条件、施工方法、周围环境等因素，方案选择安全可靠，取得了明显的社会效益和经济效益。
In the recent years, along with the high-speed development of city construction, a great number of high-rises are constructed together with the exploitation of the underground structure, which surely brings large-scale excavation and support of the foundation pit project. In this dissertation, a large quantity of the fundamental theories about the earth pressure calculation and the traditional design methods applied to the protection of the foundation pit are comprehensively analyzed and evaluated. Aiming at a deep foundation pit in Changsha, the author has written a elastic-plastic finite element program, in which a constitutive model of "Druck-Prager" is used for soil. A method employing the "Goodman" joint element to describe the frictional behavior between soil and pile which are divided into 4-noded plane strain isoparametric elements, is proposed. The anchor is divided into bar element. In this program, the modified "void element" method is adopted to simulate the excavation of the foundation pit. The
results from the comparison between calculated values and field results show that the method of elastic-plastic finite element analysis is practical.
The calculated results of the numerical model show that the horizontal displacement of the lower pile is larger than that of the upper. Because the embedded depth of the pile is only 1.2 meter, the "kick foot" phenomenon should be emphasized in the practice. The blowups of the pit bottom increases with the longer distance from the wall, reaching its maximum value in the middle of the pit. The most dramatic settlement happens in the upmost edge of the pit, decreasing with the increasing distance from the edge of the pit. The anchor tension increases with the excavation depth, and the peak value of the tension tends to move towards the end of the anchor. The allowable anchor capacity of 330 kN is larger than the maximum load of 197 kN.
The soil condition, construction method and the surrounding are considered synthetically for compare and selection of the plan. The selected plan assures the deep foundation pit is safe and reliable. Obvious social and economical benefits have been obtained.
有限元计算结果表明，该工程的护坡桩的下部水平位移比上部水平位移大，由于桩的埋深只有1.2m，在实际工程中要特别注意“踢脚”现象；基坑坑底的隆起随着距开挖面的距离越远，隆起量也越大，最大隆起量发生在基坑的中部；基坑周围的地表沉降，在基坑顶部最大，离基坑顶部越远，沉降越小；锚杆的轴力分布为两端小，中部大；随着基坑的开挖，锚杆承受的拉力越来越大且锚杆轴力峰值有向锚杆末端偏移的趋势。最大值为197kN，小于设计抗拔力330kN。
该基坑支护综合考虑了土质条件、施工方法、周围环境等因素，方案选择安全可靠，取得了明显的社会效益和经济效益。
In the recent years, along with the high-speed development of city construction, a great number of high-rises are constructed together with the exploitation of the underground structure, which surely brings large-scale excavation and support of the foundation pit project. In this dissertation, a large quantity of the fundamental theories about the earth pressure calculation and the traditional design methods applied to the protection of the foundation pit are comprehensively analyzed and evaluated. Aiming at a deep foundation pit in Changsha, the author has written a elastic-plastic finite element program, in which a constitutive model of "Druck-Prager" is used for soil. A method employing the "Goodman" joint element to describe the frictional behavior between soil and pile which are divided into 4-noded plane strain isoparametric elements, is proposed. The anchor is divided into bar element. In this program, the modified "void element" method is adopted to simulate the excavation of the foundation pit. The
results from the comparison between calculated values and field results show that the method of elastic-plastic finite element analysis is practical.
The calculated results of the numerical model show that the horizontal displacement of the lower pile is larger than that of the upper. Because the embedded depth of the pile is only 1.2 meter, the "kick foot" phenomenon should be emphasized in the practice. The blowups of the pit bottom increases with the longer distance from the wall, reaching its maximum value in the middle of the pit. The most dramatic settlement happens in the upmost edge of the pit, decreasing with the increasing distance from the edge of the pit. The anchor tension increases with the excavation depth, and the peak value of the tension tends to move towards the end of the anchor. The allowable anchor capacity of 330 kN is larger than the maximum load of 197 kN.
The soil condition, construction method and the surrounding are considered synthetically for compare and selection of the plan. The selected plan assures the deep foundation pit is safe and reliable. Obvious social and economical benefits have been obtained.
引文
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Braced Excavations. Journal of Geotechnical Engineering, 1993, 119(5): 912-929
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[40] Kar S Wong. Lateral Wall Deflections of Braced Excavations in Clay. ASCE, 1989, 115(6): 944-965
[41] Yang K Y, Lee F H, et al. Elastic-Plastic Consolidation Analysis for Strutted Excavation in Clays. Computers and Geotechnics, 1989(8): 703-729
[42] 曾国熙，潘秋元，胡一峰．软粘土地基基坑开挖性状的研究．岩土工程学报，1998，10(3)：13-22
[43] Anthony T C. Behaviour of Cantilever Retaining Walls. ASCE, Journal of Geotechnical Engineering, 1993, 119(11): 1751-1770
[44] 黄宏伟，友国华．基坑围护结构系统的性状及其状态变量．岩土力学，1997，17(4)：7-12
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[2] 国家行业标准．《建筑基坑支护技术规程》(JGJl20一99)．北京：中国建筑工业出版社，1999，1-3
[3] 陈忠汉，黄书秩，程丽萍编著．深基坑工程．北京：机械工业出版社，2002，1-7
[4] 刘金砺．我国建筑基础工程技术的现状和发展的述评．建筑技术，1997，28(7)：466-468
[5] 吴恒．深基坑工程现状及优化设计的若干问题．工程力学，1997(增刊)：45-51
[6] Rowe P W, Peaker K. Passive Earth Pressure Measurements. Geotechnique, 1965, 15(1): 879-896
[7] Terzaghi K. Theoretical Soil Mechanics. New York, Wiley, 1943, 89-92
[8] Bjerrum L, Clausen C J F, Duncan J M. Earth Pressure on Flexible Structures- A State of the Art Report. In: Fith European Conference on Soil Mechanics an Foundation Engineering, 1972, 214-232
[9] Vaziri H H. Numerical Study of Parameters Influencing the Response of Flexible Retaining Wall. Canadian Geotechnical Journal, 1996(33): 290-308
[10] 陈页开．挡土墙上土压力的试验研究与数值分析：[博士学位论文]．杭州：浙江大学，2001，2-10
[11] 谭跃虎，钱七虎．作用于支护结构的土压力测试与分析．建筑技术，1998(增刊)：250-252
[12] 何颐华，杨斌等．深基坑护坡桩土压力的工程测试及研究．土木工程学报，1997(1)：16-24
[13] 刘晓立，严驰等．柔性挡墙在砂性填土中的土压力试验研究．岩土工程学报，1999，21(4)：505-508
[14] Peck R B. Earth Pressure Measurements in Open Cuts, Chicago(Ⅲ) Subway. American Society of Civil Engineerings. Proceeding, Vol.68, 1942, No.6: 900-928
[15] White L, E A Prentis. Cofferdams. New York: Columbia University Press, 1940, 273
[16] Peck R B. Deep Excavations and Tunneling in Soft Ground. In: State-of-the-art
report, International Conference on Soil Mechanics and Foundation Engineering. Mexco, 1969, 225-290
[17] Terzaghi K, Peck R B. Soil Mechanics in Engineering Practice. New York, Wiley, 1967, 729
[18] Tschebotarioff G P, J D Welch. Effect of Boundary Conditions on Lateral Earth Pressures. In: International Conference on Soil Mechanics and Foundation Engineering. Rotterdam, 1948, 308-313
[19] Vaziri H, Simpson B, Pappin J W and Simpson L. Integrated Forms of Mindlins Equations. Geotechnique, 1982, 32(3): 275-278
[20] 徐日庆，龚晓南，杨林德．土的非线性抗剪强度及土压力计算．浙江大学学报，1997(3)：22-29
[21] Kennedy T C, Lindberg H E. Tunnel Closure for nonlinear Mohr-Coulomb Functions. Journal of the Engineering Mechanics Division, ASCE, 1978, 104(6): 1313-1326
[22] Wang Y L. The Effect of a Nonlinear Mohr-Coulomb Criterion on Borehole Stresses and Damage-zone Estimate. Canadian Geotechnical Journal, 1994(31): 104-109
[23] 魏汝龙．开挖卸载与被动土压力计算．岩土工程学报，1997，19(6)：88-92
[24] 陈书申．经典土压力理论的局限与小变位土压力计算的建议．土工基础，1999，11(2)：15-21
[25] 吴铭炳．软土地基深基坑支护中的土压力．工程勘察，1999(2)：15-17
[26] 孙淑贤．基坑开挖伴随应力状态改变对土压力的影响．工程勘察，1998(3)：5-8
[27] 周瑞忠，邱高翔，苏友聪．Rankine土压力理论现代改进方法．福州大学学报，1999，27(3)：89-92
[28] 徐日庆，龚晓南等．基坑开挖中土压力计算方法探讨．见：中国土木工程学会第八届土力学及岩土工程学术会议论文集．北京：万国学术出版社，1999，667-670
[29] Haliburton T A. Numerical Analysis of Flexible Retaining Structures. Journal of Soil Mechanics & Foundation Div. ASCE, 1968, 94(6): 1233-1251
[30] 王建林，顾晓鲁．基坑开挖中的土压力探讨．建筑技术，1998(增刊)：258-261
[31] Clough G W, Duncan J M. Finite Element Analyses of Retaining Wall Behavior. ASCE, 1971, 97(12): 165-167
[32] Andrew J W, Youssef M A. Analysis of Deep Excavation in Boston. Journal of Geotechnical Engineering, 1993, 119(1): 69-89
[33] Sunil S Kishnai, Ronaldo I. Seepage and Soil-structure Interface Effects in
Braced Excavations. Journal of Geotechnical Engineering, 1993, 119(5): 912-929
[34] Charles W Ng, Martin Lings. Effects of Modeling Moil Nonlinearity and Wall Installation on Back-Analysis of Deep Excavation in Stiff Clay. Journal of Geotechnical Engineering, 1995, 121(10): 687-695
[35] 侯学渊，夏明耀等．软土深基坑工程的稳定与隆起研究．见：深基坑施工技术会议论文集，上海：同济大学出版社，1991，123-128
[36] Tsui Y, Cheng Y M. A Fundamental Study of Braced Excavation Construction, Computers and Geotechnics, 1998(8), 632-657
[37] Lambe T W. Braced Excavation Lateral Stress in the Ground and Design of Earth-Retaining Structures, ASCE, 1981, 107(9): 1362-1380
[38] 孙钧，侯学渊．地下结构(上、下册)．北京：科学出版社，1988，352-431
[39] Clough, Hansen. Clay Anisotropy and Braced Wall Behavior. ASCE, 1981, 107(6): 893-913
[40] Kar S Wong. Lateral Wall Deflections of Braced Excavations in Clay. ASCE, 1989, 115(6): 944-965
[41] Yang K Y, Lee F H, et al. Elastic-Plastic Consolidation Analysis for Strutted Excavation in Clays. Computers and Geotechnics, 1989(8): 703-729
[42] 曾国熙，潘秋元，胡一峰．软粘土地基基坑开挖性状的研究．岩土工程学报，1998，10(3)：13-22
[43] Anthony T C. Behaviour of Cantilever Retaining Walls. ASCE, Journal of Geotechnical Engineering, 1993, 119(11): 1751-1770
[44] 黄宏伟，友国华．基坑围护结构系统的性状及其状态变量．岩土力学，1997，17(4)：7-12
[45] 侯学渊，夏明耀，李桂花．软土深基坑工程的稳定与隆起研究．见：软土地基理论与实践，北京：中国建筑工业出版社，1992，54-59
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