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1、【精品文档】如有侵权，请联系网站删除，仅供学习与交流sx锤击式沉管灌注桩贯入度控制标准的探讨.精品文档.锤击式沉管灌注桩贯入度控制标准的探讨摘要：通过工程实例，介绍了锤击式沉管灌注桩贯入度设计的一般方法，指出了存在的问题，初步分析了问题存在的原因，提出了解决问题的实用方法。关键词：桩基础施工1问题的提出桩基几乎可应用于各种工程地质条件和各种类型的工程，尤其适用于软弱地基。锤击式沉管灌注桩以其诸多优点，成为多层住宅、综合楼的首选桩型。但其自身也存在一些缺陷和在设计施工中难以操作的指标，灌注桩沉管的贯入度的控制便是其中之一。本文拟通过工程实践来对此进行探讨。一般认为，桩的贯入度与其极限承载力有直接
2、的关系。贯入度通常依据现有的打桩动力公式结合当地成功经验确定。但灌注桩沉管的贯入度与桩承载力的关系是否可以用简单的经验公式确定，或者简单地套用当地成功经验，以及贯入度是否为一项控制性的设计指标，对于这些问题，笔者认为有必要作进一步的探讨。建筑桩基技术规范(JGJ9494)在灌注桩基础设计中没有贯入度设计的规定，仅提出灌注桩的贯入度“必须准确测量”，严格控制。建筑地基基础设计规范(GBJ789)也没有引入灌注桩贯入度设计概念。显然，贯入度作为灌注桩设计指标并由设计人员提出缺乏规范依据。目前，采用灌注桩的一般是九层以下的二级建筑物。由于国家规范对二级建筑物没有规定要进行现场试验确定单桩承载力，而是
3、“应根据静力触探、标准贯入、经验参数等估算，并参照地质条件相同的试桩资料，综合确定”，因此这类建筑很少在设计施工前进行桩的现场试验，设计人员依据现有的打桩动力公式结合当地成功经验确定贯入度。在施工时，对于以摩擦为主的摩擦桩，大多数情况下沉管达不到设计要求的贯入度，这时通常采用四个方法解决：(1)加深桩长；(2)复打桩；(3)扩大桩径；(4)加桩。每种方法(有时二种、三种方法同时采用)都会增大工程量，增加成本。而这些做法都属惯例，似乎没有人会怀疑贯入度要求本身的合理性。当工程验收时，单桩承载力检验合格，证明设定的贯入度“没有问题”，又可以作为经验被采用。因此，如何把握贯入度，对于工程的安全性、经
4、济性都有较大的意义。2单桩竖向承载力的计算2.1荷载传递机理桩在荷载作用下，桩身上部首先受到压缩，一部分荷载往下部桩身传递，另一部分则在桩与桩周土之间形成摩阻力。当荷载分级逐步加到桩顶时，桩身上部受到压缩而产生相对于土的向下位移，与此同时，桩周表面受到土的向上摩阻力，桩身荷载通过桩周摩阻力传递到桩周土层中去，致使桩身荷载和桩身压缩变形随深度递减。随着荷载的增加，桩身压缩量和位移量增加，桩身下部的摩阻力随之进一步发挥出来。当桩周摩阻力全部发挥达到极限状态后，若继续增加荷载，则荷载量将全部由桩端土承担。桩的这种传递理论，是符合静压试桩实际的，且已为许多桩的荷载试验所证实。2.2单桩竖向极限承载力标
5、准值单桩竖向极限承载力标准值按下式计算：sikipk（）式中单桩的竖向承载力标准值；极限端阻力标准值；桩身横截面面积；桩身周边长度；sik桩侧第i层土的极限侧阻力标准值；按土层划分的各段桩长。贯入度的设计一般依据现有的打桩动力公式，主要有格尔谢凡诺夫公式、工程新闻修正公式、海利公式和广东打沉管灌注桩公式等。上述经验公式是根据功能原理和实验推导出来的，适用对象为预制桩(包括钢管桩)；而灌注桩与预制桩在施工方法上有很大区别，如果套用上述经验公式设计灌注桩的贯入度，显然是不恰当的。在工程实践上，这种方法往往偏于安全，结果是使工程成本增加。3工程实例本例为东莞某学校的桩基实际工程。该小区位于东江形成的
6、三角洲平原，属于冲积地貌，地形平坦，场地土层分层描述如表1。设计要求采用锤击沉管灌注桩，桩端以中细砂层上部为持力层，桩长L22(从场地地坪算起)，桩径?480mm，单桩承载力标准值为600kN。沉管贯入度计算：(1)格氏公式式中打桩最后阶段平均每锤的贯入度，cm；桩及桩垫材料系数，无桩垫时，n0.5；恢复系数，无桩帽时0.25；锤重，kN；桩、桩帽、桩锤的非冲击部分重量，kN；落锤高度，cm；桩的横截面积，cm；安全系数，永久建筑为2；单桩承载力标准值，kN。根据现场设备情况和设计要求，有关参数取值为：30kN,q26kN,A1.810，100×0.880cm，600将有关数据代入格
7、氏公式后得：0.54击(2)广东打沉管灌注桩公式式中打桩最后阶段平均每锤的贯入度，cm；锤重，kN；落锤高度，m；参数，桩径?480mm,A9；参数，桩径?480mm,120；N总锤数，此时取800锤；单桩承载力标准值，kN。将有关数据代入广东打沉管灌注公式后得：0.18击由上述计算结果可知，广东公式要求较之更加严格。该地成功经验为：对于桩径?480mm、设备锤重为30kN、设定锤落距为1.0m情况，最后三阵锤击，每阵10锤，贯入度6cm。综合考虑计算结果和当地成功经验，设计规定，最后三阵锤击，要求贯入度控制在6cm10击以下。但在实际施工中，桩管打至设计标高时，大部分桩贯入度都超过了设计要求
8、，个别桩多达2250cm/10锤，距设计要求相差很大。为了减小贯入度，对于部分贯入度较大的桩采用了灌砂复打，挤密砂土的新方法。考虑到本小区桩基工程量大，基桩总数约为3000余根，为了工程安全和节省投资，并为后续施工提供依据，为此对贯入度较大的以及经灌砂复打的桩，选择了6根桩进行了静载测试，有关数据如表2、3。因为此次静载测试目的并不是做桩的破坏试验，所以最大试验荷载以满足设计要求为限。至最大试验荷载时，没有出现极限特征。从测试试验结果看出：(1)该地区的灌注桩沉管贯入度实际值是设计值的28倍(至设计标高时)，这时即使不加长桩长或复打，桩的承载力也完全能达到设计要求。可见贯入度设计值偏小。(2)
9、对于贯入度特别大的3号桩，经灌砂复打，测试结果表明，桩的承载力也能达到设计要求，且最大沉降量仍未超过规范极限值。可见，若严格控制贯入度不甚合理，分析其原因有以下几点：(1)由于构造上的原因，锤击式沉管灌注桩的预制桩靴比桩管外径大68，施工时，土对桩管的挤压力减少使桩管下沉阻力减少，因而使沉管贯入度增大。(2)成桩后灌注桩的实际桩径往往比管径大6%7%，这是因为桩靴直径较大所致。由于实际桩径扩大使得桩的承载力相应增加，因此尽管施工时的贯入度相对较大，但静载试验加载至最大荷载时沉降量仍然较小。(3)灌注桩的实际桩身表面是凹凸不平的，桩身混凝土与周围土互相咬合，致使土的摩阻力较预制桩大，且施工时桩管
10、的摩阻力小于成桩后的摩阻力。(4)沉管时由于连续锤击震动，土体内摩擦角变化很大。而在桩身灌注混凝土28天后，进行静载试验时，土体结构基本稳定，承载力有一定幅度提高。(5)灌砂复打对桩周土和桩端土进行了挤密，使桩侧摩阻力提高，桩端土的强度提高。(6)打桩公式适用于预制桩和钢管桩估算其打桩阻力，将它用于沉管贯入度的计算只是权宜之计。经过综合分析试验结果，以及其成因分析，认为可以适当加大贯入度的设计值。为了安全起见，后续桩的贯入度控制在2倍设计值范围内；个别贯入度较大的桩，采用灌砂复打的方法，将其控制在相同范围内。该项工程竣工已近6年，运行正常。这说明当时贯入度控制原则是安全合理的。4结论(1)对于
11、砂土地基，采用灌砂复打，充分利用其挤密效应，是一种经济有效地减小贯入度的方法。(2)简单套用现有的打桩动力公式设计沉管贯入度，有时与工程实际情况不符，将造成工程浪费。(3)灌注桩贯入度作为一项设计施工指标，应该加以控制，但是应该避免盲目性。在无现场试验确定单桩承载力的情况下，可以采用这样的方法：在地质钻探孔附近，土层分布和各土层的物理力学指标比较准确，宜先在此打桩，仔细做好记录，在设计标高附近一定范围内准确测量每10击的贯入度。综合分析贯入度的现场施工记录、设计值，以及当地成功经验，调整实施的贯入度值，以尽可能地使贯入度控制值趋于合理。参考文献中国建筑科学研究院建筑桩基技术规范(JGJ9494
12、）北京：中国建筑工业出版社，1995中华人民共和国城乡建设环境保护部建筑地基基础设计规范(GBJ789）北京：中国建筑工业出版社，1989陈载赋钢筋混凝土建筑结构与特种结构手册成都：四川科学技术出版社，1994JE波勒斯基础工程分析与设计北京：中国建筑工业出版社，1987（英文版 ） Two regulations promulgated for implementation is in the party in power for a long time and the rule of law conditions, the implementation of comprehensive s
13、trictly strategic plan, implementation in accordance with the rules and discipline to manage the party, strengthen inner-party supervision of major initiatives. The two regulations supporting each other, the adhere to a positive advocate, focusing on morality is of Party members and Party leading ca
14、dres can see, enough to get a high standard; around the party discipline, disciplinary ruler requirements, listed as negative list, focusing on vertical gauge, draw the party organizations and Party members do not touch the bottom line . Here, the main from four square face two party rules of interp
15、retation: the first part introduces two party Revised regulations the necessity and the revision process; the second part is the interpretation of the two fundamental principles of the revision of laws and regulations in the party; the third part introduces two party regulations modified the main ch
16、anges and needs to grasp several key problems; the fourth part on how to grasp the implementation of the two regulations of the party. and revised the necessity and revised history of the CPC Central Committee the amendment to the Chinese Communist Party members and leading cadres honest politics se
17、veral guidelines and column 1 by 2015 to strengthen party laws and regulations focus. Two party regulations revision work lasted a Years, pooling the wisdom of the whole party, ideological consensus, draw historical experience, respect for the wisdom of our predecessors, which reflects the unity of
18、inheritance and innovation; follow the correct direction, grasp the limited goals, adhere to the partys leadership, to solve the masses of the people reflect a focus on the problem. The new revision of the and , reflects the partys 18 and the eighth session of the third, the spirit of the fourth ple
19、nary session, reflecting the experience of studying and implementing the General Secretary Xi Jinping series of important speech, reflects the partys eighteen years comprehensive strictly practice. (a) revised two regulations of the party need of in based on revised, the promulgation and implementat
20、ion of January 2010, to strengthen the construction of the contingent of leading cadres play an important role. But with the party to manage the party strictly administering the deepening, has not been able to fully meet the actual needs. Content is too complicated, eight prohibition, 52 are not all
21、owed to hard to remember, and also difficult to put into practice; the second is concisely positive advocated by the lack of prohibited provisions excessive, no autonomy requirements; the third is banned terms and discipline law, both with the party discipline, disciplinary regulations repeat and Cr
22、iminal law and other laws and regulations repeat; the fourth is to clean the theme is not prominent, not for the existing problems, and is narrow, only needle of county-level leading cadres above. is in 1997 based on revision, in December 2003 the promulgation and implementation, to strengthen the c
23、onstruction of the party play very important role. Along with the development of the situation, which many provisions have been unable to fully meet the comprehensive strictly administering the practice needs. One is Ji law, more than half of the provisions and criminal law and other countries laws
24、and regulations Repetition; two is the political discipline regulations is not prominent, not specific, for violation of the party constitution, damage the authority of Party Constitution of misconduct lack necessary and serious responsibility to pursue; third is the main discipline for the leading
25、cadres, does not cover all Party members. Based on the above situation, need to and the two is likely to be more relevant regulations first amendment. By revising, really put the authority of Party discipline, the seriousness in the party tree and call up the majority of Party members and cadres of
26、the party constitution of party compasses party consciousness. (II) two party regulations revision process the Central Committee of the Communist Party of China attaches great importance to two regulations revision . Xi Jinping, general books recorded in the Fifth Plenary Session of the eighth sessi
27、on of the Central Commission for Discipline Inspection, on the revised regulations made clear instructions. According to the central deployment, the Central Commission for Discipline Inspection from 2014 under six months begin study two regulations revision. The Standing Committee of the Central Com
28、mission for Discipline Inspection 4 review revised. Comrade Wang Qishan 14 times held a special meeting to study two regulations revision, amendment clarifies the direction, major issues of principle, path and target, respectively held a forum will listen to part of the province (area) secretary of
29、the Party committee, Secretary of the Discipline Inspection Commission, part of the central ministries and state organs Department The first party committee is mainly responsible for people, views of experts and scholars and grassroots party organizations and Party members. Approved by the Central C
30、ommittee of the Communist Party of China, on 7 September 2015, the general office of the Central Committee of the Party issued a notice to solicit the provinces (autonomous regions, municipalities) Party, the central ministries and commissions, state ministries and commissions of the Party (party),
31、the General Political Department of the military, every 3 people organization of Party of two regulations revision opinion. Central Commission for Discipline Inspection of extensive solicitation of opinions, careful study, attracting, formed a revised sent reviewers. In October 8 and October 12, Cen
32、tral Committee Political Bureau Standing Committee and the Political Bureau of the Central Committee After consideration of the two regulations revised draft. On October 18, the Central Committee of the Communist Party of China formally issued two regulations. Can say, two laws amendment concentrate
33、d the wisdom of the whole party, embodies the party. Second, and revision of the basic principles of two party regulations revision work and implement the partys eighteen, ten eight plenary, the spirit of the Fourth Plenary Session of the Eleventh Central Committee and General Secretary Xi Jinping i
34、mportant instructions on the revised and , highlighting the ruling party characteristics, serious discipline, the discipline quite in front of the law, based on the current, a long-term, advance as a whole, with Bu Xiuding independent and . Main principle is: first, adhere to the party constitution
35、to follow. The constitution about discipline and self-discipline required specific, awaken the party constitution of party compasses party consciousness, maintaining the authority of the constitution. General Secretary Xi Jinping pointed out that no rules, no side round. Party constitution is the fu
36、ndamental law, the party must follow the general rules. In early 2015 held the eighth session of the Central Commission for Discipline Inspection Fifth Plenary Session of the 16th Central Committee, Xi Jinping again pointed out that constitution is the party must follow the general rules, but also t
37、he general rules. the revision of the and is Method in adhere to the regulations established for the purpose of combining rule of virtue is to adhere to the party constitution as a fundamental to follow, the constitution authority set up, wake up the party constitution and party rules the sense of d
38、iscipline, the party constitution about discipline and self-discipline specific requirements. 4 second is to adhere to in accordance with the regulations governing the party and the party. The Party of rule of virtue de, mainly refers to the partys ideals and beliefs, excellent traditional style. Th
39、e revised the closely linked to the self-discipline, insisting on the positive initiative, for all members, highlight the vital few, emphasized self-discipline, focusing on the morality, and the majority of Party members and the ideological and moral standards. The revised Ji method separately, Ji,
40、Ji Yan to Method, as a negative list, emphasizing the heteronomy, focusing on vertical gauge. Is this one high and one low, a positive reaction, the strict party discipline and practice results transformation for the integration of the whole party to observe moral and discipline requirements, for th
41、e majority of Party members and cadres provides benchmarking and ruler. Third, insist on to. In view of the problems existing in the party at the present stage, the main problems of Party members and cadres in the aspect of self-discipline and abide by the discipline to make clearly defined, especia
42、lly the partys eighteen years strict political discipline and political rules, organization and discipline and to implement the central eight provisions of the spirit against the four winds and other requirements into Disciplinary provisions. Not one pace reachs the designated position, focusing on
43、in line with reality, pragmatic and effective. After the revision of major changes, major changes in the and modified and needs to grasp several key problems (a) adhere to according to regulations governing the party and party with morals in combination, for at the present stage, the leadership of t
44、he party members and cadres and Party members in existing main problems of self-discipline, put forward principles, requirements and specifications, showing Communists noble moral pursuit, reflected at all times and in all over the world ethics from high from low 5 common requirements. One is closel
45、y linked to the self-discipline, removal and no direct relation to the provisions of . the second is adhere to a positive advocate, eight prohibition 52 are not allowed to about the content of the negative list moved into synchronization amendment . Three is for all the party members, will apply obj
46、ect from the leadership of the party members and cadres to expand to all Party members, fully embodies the comprehensive strictly required. The fourth is prominent key minority, seize the leadership of the party members and cadres is the key, and put forward higher requirements than the ordinary Par
47、ty members. Five is to simplify, and strive to achieve concise, easy to understand, easy to remember. The revised is the ruling Party since the first insists on a positive advocate forAll Party members and the self-discipline norms, moral declaration issued to all members of the party and the National Peoples solemn commitment. criterion of a clean and honest administration consists of