摘要
水泥土搅拌桩支护结构是软土地区常用的一种基坑支护型式,具有止水效果较好、无噪音、污染小等诸多优越性,且具有较好的经济效益,在开挖深度小于7m的软土基坑中得到广泛的应用。软土地区基坑中,水泥土挡墙的变形往往过大,如何有效的控制基坑变形,使基坑工程安全又经济,是人们一直研究的课题。目前主要的计算方法有极限平衡法、弹性抗力法以及有限元法,其中有限元法能从整体上分析支护结构及周围土体的应力与位移性状。本文总结了前人的研究成果,并结合工程实际,针对广东佛山某软弱土地基基坑开挖与支护工程,建立了二维有限元模型,对水泥土搅拌桩支护结构,做了较为全面的有限元分析,研究了影响基坑变形的多种因素,本文的主要研究内容和成果如下:
1.总结了目前几种常用的计算基坑受力与变形的方法,分析各种方法的特点及适用范围;随后探讨挡墙水平荷载计算的水土合算与分算问题;简要介绍格栅式水泥土挡墙的设计方法:分析了基坑变形现象和机理,并介绍基坑变形控制标准。
2.采用岩土工程分析软件Plaxis建立了二维有限元模型。在该模型中,土体和水泥土挡墙采用摩尔—库伦弹塑性模型,考虑了土的弹塑性力学性能;采用接触面单元模拟桩土之间的接触作用;较详细的介绍了该模型中各种材料参数的确定方法;讨论了基坑开挖模拟中的初始应力场,开挖荷载的处理接触面单元等问题。
3.以佛山某软弱土地基基坑开挖与支护工程为研究对象,运用该模型进行数值模拟,有限元计算结果论证了该基坑施工方案的合理性,表明有限元方法可应用于深基坑开挖与支护工程验算、指导工程设计与施工。
4.以工程实例为对象,运用该模型分析水泥土挡墙宽度、墙体嵌固深度、墙体变形模量、被动区土体加固、组合支护、地面超载等设计施工因素对基坑变形和整体稳定性的影响,并得出墙体变形、基坑坑底隆起以及墙后地表沉降的变化规律。从设计和施工两方面提出了水泥土挡墙支护基坑变形控制的具体措施,为今后类似工程的建设提出有益的建议。
Soil-cement mixing pile support structure is a kind of forms which is widely used in the soft-clay areas. With the merits of good waterproof, low noise, low pollution and low cost, it came into use broadly in soft soil foundation pit which is less than 7m in depth. In soft soil foundation pit, the large deformation of soil-cement retaining wall often occurs. How to effectively control the deformation to ensure the foundation pit security and economy is a subject of study which people having been always pursued. At present, the mainly computation methods include limit equilibrium method, elastic resistance method and the finite element method, the finite element method which can analyze the traits of stress and displacement of the support structure and the surrounding soil in all. This paper summarizes the results of previous studies, combined with engineering practice, directed to a soft soil foundation pit in Foshan, established 2-D finite-element model and analyzed the property of soil-cement mixing pile support structure roundly, and studies the impact of the design and construction of deformation factors. The main research content and results are as follows:
1. In the first part of this paper, the current calculation theory in common use of foundation pit engineering are introduced, and analyze the characteristics of various methods and the scope of application; then the method of estimating water and earth pressures on supporting structure separately and together is analyzed, and make a briefly introduction of cement-soil-type grille retaining wall design; finally, the phenomenon and mechanism of deformation is explored, and brings up the deformation control standards.
2. This paper adopts Plaxis, a geotechnical engineering analysis software, to establish a two-dimensional finite element model. In this model, the soil and cement retaining wall all use elastic-plastic Mohr-Coulomb model, taking into account of the elastic-plastic mechanical properties of soil:adopts interface element to model the contact influence between stake and soil; makes a detailed presentation of the model parameters of various materials methods; discusses a number of issues of excavation simulation, such as the initial stress field and excavation load handling.
3. Taking a supporting engineering in Foshan, makes a simulation analysis with Plaxis. Finite element calculation results demonstrates that the rationality of the construction program and the finite element method may apply to soil-cement mixing pile support structure.
4. Using this model explores the influence of a number of factors affecting the deformation and stability of foundation pit, such as wall width, wall depth, deformation modulus of wall, soil reinforcement, combination support and ground load. The general rules of wall displacement, excavation base heave and surface settlement are obtained. Then, the detailed deformation control measures of cement-soil retaining wall are proposed at the point of design and construction, brings forward up useful recommendations for the future construction.
引文
[1]刘建航,侯学渊.基坑工程手册[M].北京.中国建筑工业出版社,1997.
[2]侯学渊,杨敏主编.软土地基变形控制设计理论和工程实践[M].上海:同济大学出版社,1996.64-217.
[3]陈忠汉,程丽萍.深基坑工程[M].北京:机械工业出版社,1999,10-54.
[4]中华人民共和国标准.岩土工程勘察规范(GB5002-2001).中国建筑工业出版社,1995
[5]建设部.软土地区工程地质勘察规范(JGJ83-91).中国建筑工业出版社,1992;
[6]交通部.公路工程名词术语(JTT002-87),人民交通出版,1987;
[7]崔江余,梁兴旺.建筑基坑工程设计计算与施工[M].北京:中国建筑工业出版社,1999.53-56.
[8]沈保汉.桩基与深基坑支护技术进展[M].北京:知识产权出版社,1999.37,44
[9]季杰.南京河西地区深层搅拌桩复合地基沉降计算[D].东南大学.硕士论文.2004
[10]Mana A I, Clough G W.Predication of movement for brace cuts in clay [J]. Journal of Geotechnical Engineering Division,ASCE,1981,107(GT6):759-778
[11]Chna D H,Morgenstern N R. Analysis of progressive deformation of the Edmonton Convention Centre Exaction[J].Canadian Geotechnical Journal,1987, 24:430-440
[12]Borja R I. Analysis of increment excavation based on critical state theory [J]. Journal of Geotechnical Engineering Division,ASCE,1981,116(6):964-985
[13]杨光华.深层搅拌桩等嵌入式重力挡土结构稳定与变形的计算[J].岩土工程学报,1996.18(4):91-94.
[14]陆瑞明,李红.水泥土挡墙的空间作用研究[J].工程勘察,1997,1:1-5
[15]熊巨华,裴健勇,杨敏.考虑桩顶冠梁效应的水泥土挡墙变形计算方法.岩土力学,1999,20(1):84-86.
[16]刘忠玉,李永振.土体非线性对水泥上挡墙水平位移的影响[J].郑州工业大学学报,2003,24(1):20-23
[17]王旭东,黄力平.基坑开挖中水泥土挡墙的变形分析[J].南京建筑工程学院学报,1994,1:25-29
[18]谭跃虎,吉同笃.软土深挖基坑中挡墙侧向变形分析与计算[J].岩土工程 学报,1995,17(4):71-76
[19]谢宁,孙钧.土体非线性流变的有限元解析及其工程应用[J].岩土工程学报,1995,17(4):95-99
[20]郑刚,史恒通,顾晓鲁.水泥搅拌桩重力式挡土墙支护技术[J].施工技术,1998,(9):16-17
[21]高文华.基于Mindlin板理论的深层搅拌桩墙体受力变形的空间效应[J].土木工程学报,1999,32(5):71-75
[22]刘润,闫澍旺,水泥搅拌桩的工作机理及有限元分析[J],中国港湾建设,2001,4,20-23
[23]周顺华,余绍锋,吴海平.水泥土—灌注桩基坑围护结构的试验与现场实测[J].岩土工程学报,1998,20(2):5-54
[24]简浩,陈晖,顾国荣.水泥土挡墙压顶在基坑变形控制中的应用及研究[J].工程技术,2003,(5):32-34
[25]李建新.水泥搅拌桩重力式挡土墙的应用研究[D].天津大学.硕士论文.2003
[26]李勇.水泥土挡墙围护结构的变形及稳定性研究[D].南京工业大学.硕士论文.2006
[27]王坤.水泥土桩复合桩墙支护结构的设计计算模式研究[D].郑州大学.硕士论文.2007
[28]吴蕾.水利工程中水泥土搅拌桩支护结构的应用研究[D].浙江大学.硕士论文.2007
[29]屈畅姿.水泥土搅拌桩支护结构性能的有限元分析[D].湘潭大学.硕士论文.2007
[30]刘成宇主编.土力学(第二版)[M].北京:中国铁道出版社,2000
[31]许锡昌.土压力问题与基坑变形分析[D].中科院武汉武汉岩土力学研究所.博士论文.2004,86-88,133-137
[32]魏汝龙.总应力法计算土压力的几个问题[J].岩土工程学报,1995,17(6),120-125.
[33]杨晓军,龚晓南.基坑开挖中考虑水压力的土压力计算[J].土木工程学报,1997,30(4),58-62.
[34]魏汝龙.开挖卸载与被动土压力计算[J].岩土工程学报,1997,19(6):88-92
[35]陈愈炯.对“开挖卸载与被动土压力计算”一文的讨论[J].岩土工程学 报,1998,20(3):134-135
[36]魏汝龙.对“开挖卸载与被动土压力计算”一文讨论的答复[J].岩土工程学报,1998,20(3):134-135
[37]陈愈炯,温彦锋.基坑支护结构上的水土压力[J].岩土工程学报,1999,21(2):139-143
[38]李广信.基坑支护结构上水土压力的分算与合算[J].岩土工程学报,2000,22(3),348-352.
[39]邓子胜.深基坑支护结构—土空间非线性共同作用研究[D].湖南大学.博士论文.2004,29-34.
[40]徐至钧,赵锡宏主编.地基处理技术与工程实例[M].北京:科学出版社,2008.704-709.
[41]蒋国盛,李红民等编诸.基坑工程[M].武汉:中国地质大学出版社,2000.30-61
[42]钱家欢,殷宗泽.土工数值分析[M].北京:中国铁道出版社,1991:214-218
[43]俞建霖,龚晓南.深基坑工程的空间性状分析[J].岩土工程学报,1999,21(1),21-25.
[44]周戟.高速公路软土路基应力、应变有限元分析[D].河北工业大学.硕士论文.2006,
[45]PLAXIS Version8 Manual
[46]李广信.高等土力学[M].北京:清华大学出版社,1991:214-218
[47]何敏.深基坑支护设计及稳定性数值模拟分析[M].硕士论文.贵州大学,2008,17-18
[48]谢康和,周健.岩土工程有限元分析理论与应用[M].科学出版社,2002.
[59]Chandradsekaran V.S., King G.J.Simulation of excavation using finite elements[J].Journal of Geotechnical Engineering Division,1974,100(GT9): 1086-1089
[50]Clough C.Y., Duncan J.M. Analysis of soil movement around a deep excavation[J].J. Soil Conditions,Geotechnique,1966,16(3):209-219
[51]王术江,林波,王松林,徐勇.开挖处理的虚拟单元广义初应力法及应用[J].土工基础,2005,19(5):58-60
[52]佘丽生.武汉地铁二号线江汉路和洪山广场站深基坑施工仿真分析[D].华中科技大学.硕士论文.2007,10-24
[53]Goodman R E, Taylor R L, Brekke T. A model for the mechanics of jointed rock [J].J SMFD ASCE,1968,94(3):637-660
[54]闫澍旺,杨瑞.水泥土桩基坑支护与止水围护机理研究[J].港工技术,2007,(1):40-43
[55]陈育民,徐鼎平FLAC/FLAC3D基础与工程实例[M].中国水利水电出版社,2009.139-140
[56]郑颖人,赵尚毅.有限元强度折减法在土坡与岩坡中的应用[J].岩石力学与工程学报,2004,23(19);3381-3383.
[57]Ugai K A. method of calculation of total factor of safety of slope by elasto-plastic FEM[J].Soil and Foundation,1989,29 (2):190-195.
[58]曾国熙,潘秋元,胡一峰.软粘土地基基坑开挖性状的研究[J].岩土工程学报,1988,10(3),13-22.
[59]简艳春.软土基坑变形估算及其影响因素研究[D].河海大学.硕士论文.2001
[60]尹鹏.小刚度劲性水泥土挡墙基坑支护数值分析[D].南京农业大学.硕士论文.2001