振动沉管碎石桩
振动沉管挤密碎石桩施工技术
摘 要:在软土地基处理方法中,出现了一种代替振冲碎石桩的新的施工方法。就振动沉管挤密碎石桩的施工工艺、质量控制、施工时的注意事项以及该方法的可行性和优越性等方面进行论述。
关键词:公路软土地基; 地基加固; 振动沉管; 挤密碎石桩; 施工技术
1 概述
振动沉管挤密碎石桩简称碎石挤密桩,是一种新的软土地基的处理方法。加固砂土、粉土地基,可以使地基的承载力增加,沉降量减少,防止地震液化的发生,同时亦可用于增大软弱粘性土的整体稳定性。四川省达渝高速公路D4 合同段有3 段路堤,基底为低液限粘土,填筑前采用了碎石挤密桩施工处理,竣工后经监测,路基稳定。可见,碎石挤密桩能提高地基承载力,减少沉降量,防止地震液化的发生。此外,碎石挤密桩施工还可以改善施工条件,加快施工进度,降低工程造价,有着广泛的应用前景。
2 技术特点
(1) 作业规范化、程序化、标准化。
(2) 施工简单,工艺流程清晰,操作者和管理者易于掌握。
3 适用范围
本方法适用于松散砂土、粉土、低液限粘土、素填土和杂填土及其他劣质土地质条件下修筑铁路路基、公路路基、房建地基、机场、码头的基础加固。
4 基本原理
碎石挤密桩是通过成桩过程中对周围砂土、粉土层的挤密、振密作用和靠碎石的压入获得加固效果,使砂土、粉土地基的密实度增加;同时设臵的碎石挤密桩增强体,本身又是一个良好的排水通道,它的存在不仅有利于砂土、粉土地基中超孔隙水压力的消散,有效地增强土体的抗液化能力,而且在荷载的作用下,碎石挤密桩增强体又与砂土、粉土地基共同承担荷载作用,即形成碎石挤密桩复合地基。
411 对可液化砂土、粉土的加固机理碎石挤密桩加固砂土、粉土地基的主要目的是提高地基土承载力,减少变形和增强抗液化性。
(1) 挤密作用
在成桩过程中桩管对周围砂土、粉土层产生很大的横向挤压力,桩管体积的土挤向桩管周围的土层,使桩管周围的土层孔隙减小、密实度增大。
(2) 排水降压作用
碎石挤密桩加固砂土时,桩孔内充填反滤性好的粗颗粒料(碎石、砾石、卵石) ,在地基中形成渗透性能良好的人工竖向排水降压通道,可有效地消散和防止超孔隙水压力的增高,防止砂土、粉土产生液化,加快地基的排水固结。
(3) 预振效应
碎石挤密桩在成孔及成桩时,振动锤的强烈振动使填入料和地基土在挤密的同时获得强烈的预振效果,对砂土、粉土增强抗液化能力是极为有利的。
412 对粘性土的加固机理
碎石挤密桩加固粘性土地基的主要目的是提高地基土承载力、减少地基沉降量、提高土体的抗剪强度、增大土坡的抗滑稳定性。
(1) 臵换作用
对粘性土地基,由于土的粘粒含量多,粘粒间结合力强,渗透性低,在振动力或挤压力的作用下土中水不易排走,因此碎石挤密桩的作用不是地基挤密,而是acidity, mL.; M--calibration of the molar concentration of sodium hydroxide standard solution, moI/L; V--amount of the volume of sodium hydroxide standard solution, Ml; M--the weight of the sample, g. Such as poor meets the requirements, take the arithmetic mean of the second determination as a result. Results one decimal. 6, allowing differential analyst simultaneously or in quick succession for the second determination, the absolute value of the difference of the results. This value
should be no more than 1.0. 1, definitions and principles for determination of ash in starches, starch and ash: starch samples of ash the residue obtained after weight. Original sample residue weight of sample weight or weight expressed as a percentage of the dry weight of the sample. Samples of ash at 900 ? high temperature until ashing sample ... The Crucible: determination of Platinum or other conditions of the affected material, capacity of 50mL. Dryer: has effectively adequate drying agent and-perforated metal plate or porcelain. Ashing furnaces: device for controlling and regulating temperature, offers 900 incineration temperature of 25 c. Analytical balance. Electric hot plate or Bunsen. 3, crucible of analysis steps preparation: Crucible must first wash with boiling dilute hydrochloric acid, then wash with a lot of water and then rinse with distilled water. Wash the Crucible within ashing furnace, heated at 900 to 25 ? 30min, and in the desiccator to cool to room temperature and then weighing,
臵换。
(2) 排水作用
碎石挤密桩在粘土中形成一个良好的排水通道,起到了排水砂井的作用,且缩短了孔隙水的水平渗透
1 3 铁道标准设计RAILWAYSTANDARDDESIGN 2004(9)〃线路/ 路基〃路径,加速了软土的排水固结。
(3) 加筋作用
对于浅层软土层,碎石挤密桩可贯穿整个软土层至相对硬层,此时桩体在荷载作用下主要起应力集中作用,使地基承载力提高、压缩性减小。
(4) 垫层作用
软土层较厚时,碎石挤密桩可不穿过软土层,此时形成的加固复合土层起垫层作用,垫层将荷载扩散,使应力分布趋于均匀,从而达到提高地基承载力和减小沉降量的目的。
5 工艺流程
(1) 场地平整、测量放线、桩机就位,人工合龙活瓣式桩尖,对准地面上标定的桩位;
(2) 开动振动机把套管沉入土中,如遇到坚硬难沉的土层,可辅助以喷气或射水沉入,把套管沉到设计深度;
(3) 将料斗插入桩管,向管内灌入一定量的碎石;
(4) 再将套管提升到一定高度,套管内的碎石被压缩空气从管内压出;
(5) 继后将套管沉入到规定的深度,并加以振动,使排出的碎石振密;
(6) 再一次向套管内灌入一定量碎石;
(7) 把套管提升到规定的高度;
(8) 重复(5) ， (7) 工序,直到地面,振动沉管挤密碎石桩成桩。
在碎石桩施工前首先平整场地,局部低洼处可填土或填碎石找平,再进行初压,采用静压压路机碾压,确保桩机走行平稳,其次进行材料准备、测量放线,实地标出打桩范围与桩位,然后才开始碎石桩施工。在以上各施工程序中,关键是施工中对水、电、料的控制,即上流程的下沉挤密过程和投料与提管过程。振动挤密过程是保证成桩质量的关键,必须通过实验确定振挤次数、电机的工作电流和留振时间等参数,每次投入碎石量及挤密后提升高度是保证成桩质量的前提,为保证质量,本着“少吃多餐”的原则进行加料,每次提升高度以套管桩尖不离开碎石面为宜,以防塌孔、缩径、断桩的发生,具体参数与地质条件有关,因此必须通过实验现场确定。
6 操作要点
(1) 正式施工前应进行成桩试验,试验桩一般为7，9 根;
(2) 正式施工时,要严格按照设计的桩长、桩径、桩间距、碎石灌入量以及试验确定的桩管提升高度和速度、振密挤压次数和留振时间、电机的工作电流等施工
参数进行施工,以确保碎石挤密桩桩身的均匀性和连续性;
(3) 施工顺序从四周边开始向中心进行,相邻两桩必须跳跃间打;
(4) 应保证起重设备平稳,导向架与地面垂直,垂直偏角不应大于115 % ,成孔中心与设计桩位偏差不应大于50 mm ,桩径偏差控制在?20 mm 以内,桩长偏差不大于100 mm ;
(5) 边振动边下沉,通常每下沉015 m 留振30 s ; acidity, mL.; M--calibration of the molar concentration of sodium hydroxide standard solution, moI/L; V--amount of the volume of sodium hydroxide standard solution, Ml; M--the weight of the sample, g. Such as poor meets the requirements, take the arithmetic mean of the second determination as a result. Results one decimal. 6, allowing differential analyst simultaneously or in quick succession for the second determination, the absolute value of the difference of the results. This value should be no more than 1.0. 1, definitions and principles for determination of ash in starches, starch and ash: starch samples of ash the residue obtained after weight. Original sample residue weight of sample weight or weight expressed as a percentage of the dry weight of the sample. Samples of ash at 900 ? high temperature until ashing sample ... The Crucible: determination of Platinum or other conditions of the affected material, capacity of 50mL. Dryer: has effectively adequate drying agent and-perforated metal plate or porcelain. Ashing furnaces: device for controlling and regulating temperature, offers 900 incineration temperature of 25 c. Analytical balance. Electric hot plate or Bunsen. 3, crucible of analysis steps preparation: Crucible must first wash with boiling dilute hydrochloric acid, then wash with a lot of water and then rinse with distilled water. Wash the Crucible within ashing furnace, heated at 900 to 25 ? 30min, and in the desiccator to cool to room temperature and then weighing,
(6) 启动拔管,拔管前留振1 min ,以后边振动边拔管,拔管速度需均匀且每拔管1 m 留振1 min ;
(7) 碎石灌入量不应少于设计值的95 %(碎石灌入量按每延米不少于01224 m3 计算) ,如不能顺利下料时,可适量往管内加水;
(8) 提升和反插速度必须均匀,反插深度由深到浅,每根桩在保证桩长和碎石灌入量的前提下,总反插次数一般不得少于12 次( <377) 或9 次( <426) ;
(9) 若地表水丰富或较软弱,可先铺一层碎石垫层,有利于排水,同时提高地基强度,便于机械和施工人员行走;
(10) 振动成桩至地面时应向下复振1 m ,确保地表不产生缺碎石的凹桩。
7 机具设备
碎石桩施工的机械设备是以振动沉管桩机为核心,其他设备与桩机的生产能力相匹配,并满足质量控制和检测的需要,主要设备见表1 。
表1 机具设备
机具设备名称数量机具设备名称数量
LC 履带式沉管桩机/ 台1 T220 推土机/ 台1
110 kW发电机组/ 台2 自制手推车/ 台3
115 kW水泵1 重?型动力触探仪/ 套1
5T 自卸车6 GTS711 全站仪/ 套1
ZY16 压路机1 DSZ2 水平仪/ 套1
8 劳动力组织(表2)
9 安全措施
制定安全生产制度,落实安全生产责任制; (1) 确定安全生产目标,
(2) 加强对施工人员的安全教育,树立安全第一的思想,文明施工;
2 3 铁道标准设计RAILWAYSTANDARDDESIGN 2004(9)〃线路/ 路基〃
表2 劳动力组织
序号工种人数分工
1 调度1 现场指挥
2 技术员1 技术指导、记录
3 测试人员3 检测、质检记录
4 安全员1 安全检查及值班
5 桩机司机1 操作桩机
6 投料工4 碎石桩投料
7 机修工1 设备检修、调试
8 水电工1 供水、供电
9 机械司机8 土石方机械
10 合计21 (含材料运输)
(3) 开工前清除一切施工障碍,清理地表障碍,妥善处理地下管线及空中管线,不留隐患;
(4) 机具开工前需进行检测调试,确保安全可靠,施工中随时检查设备的完好率;
(5) 施工人员必须戴安全帽,统一指挥,协调作业;
(6) 加强用电管理,严格执行用电安全操作规程;
(7) 执行安全施工值班制度,认真进行工前检查、工中检查、工后检查。
10 质量标准与控制
acidity, mL.; M--calibration of the molar concentration of sodium hydroxide standard solution, moI/L; V--amount of the volume of sodium hydroxide standard solution, Ml; M--the weight of the sample, g. Such as poor meets the requirements, take the arithmetic mean of the second determination as a result. Results one decimal. 6, allowing differential analyst simultaneously or in quick succession for the second determination, the absolute value of the difference of the results. This value should be no more than 1.0. 1, definitions and principles for determination of ash in starches, starch and ash: starch samples of ash the residue obtained after weight. Original sample residue weight of sample weight or weight expressed as a percentage of the dry weight of the sample. Samples of ash at 900 ? high temperature until ashing sample ... The Crucible: determination of Platinum or other conditions of the affected material, capacity of 50mL. Dryer: has effectively adequate drying agent and-perforated metal plate or porcelain. Ashing furnaces: device for controlling and regulating temperature, offers 900 incineration temperature of 25 c. Analytical balance. Electric hot plate or Bunsen. 3, crucible of analysis steps preparation: Crucible must first wash with boiling dilute hydrochloric acid, then wash with a lot of water and then rinse with distilled
water. Wash the Crucible within ashing furnace, heated at 900 to 25 ? 30min, and in the desiccator to cool to room temperature and then weighing,
执行标准:中华人民共和国行业标准《公路软土地基路堤设计与施工技术规范》(J TJ 017 —96) 、中华人民共和国行业标准《公路工程质量检验评定标准》
(J TJ 071 —98) 和中华人民共和国国家标准《建筑地基基础设计规范》( GBJ 5007 —2002) 。
(1) 材料:应由未风化的干净砾石或轧制碎石而成,粒径宜为20，50 mm ,含泥量不大于5 % ,最大粒径不应超过510 cm。
(2) 制桩试验:施工前按规定做成桩试验,严格按试桩结果控制水压,振密电流和沉管的留振时间,以及分批加入的碎石量,沉管提升高度、速度等,经验证设
计参数和施工控制的有关参数作为碎石桩施工的控制指标。
(3) 碎石桩实测项目:碎石桩实测项目见表3 。
表3 碎石桩实测项目
检查项目规定值或允许偏差检查方法和频率
桩距/ mm ?150 抽查2 %
桩径/ mm 不小于设计抽查2 %
桩长/ m 不小于设计查施工记录
竖直度/ % 115 查施工记录
灌石量不小于设计查施工记录
(4) 单桩灌石量( Q) 的计算
Q = K ×L ×πd2/ 4 (m3)
式中 d ———桩管直径,/ m ;
L ———碎石桩长度,/ m ;
———碎石桩充盈系数,一般为1115，1150 , K
视土性而定,实验确定。
(5) 碎石桩密实度检测:检测频率宜抽检5 % ,要求用重?型动力触探测试,贯入量10 cm 时,击数不小于5 次。工程实践表明,重?型动力触探不仅能作为检验和评定碎石挤密桩的连续性及其密实程度,而且作为确定碎石挤密桩单桩承载力也是十分有效的。
11 效益分析
(1) 与传统的振动冲孔碎石桩施工方法相比,因振动冲孔碎石桩是冲孔后提出冲孔器之后,直接向土孔内投碎石;而振动沉管法为向沉管中投碎石,减少了冲孔器的提升距离和频率,大大提高了施工进度,工序合理,提高工效30 %。
(2) 与传统的振动冲孔碎石桩施工方法相比,因振动沉管挤密法在沉管中完成碎石的投入,有效地防止了塌孔及断桩事故发生;且碎石在沉管中振实挤密,桩
径得到了有效控制,垂直度有保障,施工过程更简便,施工质量也更加容易控制,节约材料费20 %左右,劳动力10 %左右,约降低成本25 %。
(3) 与排水固结法相比,加固期短,可以采用快速连续加载方法施工路堤,对缩短工期十分有利,且易就地取材,经济效益明显。
(4) 充分利用天然材料,无污染,社会效益显著。
12 工程实例
达渝高速公路大竹至川渝界段D4 合同段有5 处软基,其中3 处(里程桩号: K101 + 800， K101 + 884 ;K102 + 350，K102 + 480 ; K103 + 900，K104 + 050) 采用碎石桩处理。此段软基基础为低液限粘土,一般厚度7，9 m ,地表为水田,常年积水,粘土呈可塑状,部分为软塑或流塑状,含水量大,抗剪强度低,压缩模量
小,沉降量大,孔隙比大,承载力小,且填土高度在10，20 m ,历时12 d 完成acidity, mL.; M--calibration of the molar concentration of sodium hydroxide standard solution, moI/L; V--amount of the volume of sodium hydroxide standard solution, Ml; M--the weight of the sample, g. Such as poor meets the requirements, take the arithmetic mean of the second determination as a result. Results one decimal. 6, allowing differential analyst simultaneously or in quick succession for the second determination, the absolute value of the difference of the results. This value should be no more than 1.0. 1, definitions and principles for determination of ash in starches, starch and ash: starch samples of ash the residue obtained after weight. Original sample residue weight of sample weight or weight expressed as a percentage of the dry weight of the sample. Samples of ash at 900 ? high temperature until ashing sample ... The Crucible: determination of Platinum or other conditions of the affected material, capacity of 50mL. Dryer: has effectively adequate drying agent and-perforated metal plate or porcelain. Ashing furnaces: device for controlling and regulating temperature, offers 900 incineration temperature of 25 c. Analytical balance. Electric hot plate or Bunsen. 3, crucible of analysis steps preparation: Crucible must first wash with boiling dilute hydrochloric acid, then wash with a lot of water and then rinse with distilled water. Wash the Crucible within ashing furnace, heated at 900 to 25 ? 30min, and in the desiccator to cool to room temperature and then weighing,
1 315 根合10 526 延米碎石桩。经南充市交通局公路工程试验检测中心检测,完
全符合规范及设计标准。经监测工后地基沉降量满足规范及设计要求,并于2003 年3 月通过竣工验收。采用本方法施工,分项工程质量优良,受到了监理、
业主的一致好评,取得了良好的经济效益和社会效益。
参考文献:
[ 1 ] 雷向阳,唐国萍,陈大华. 对粒料桩处理软粘土地基的检测评价分
析[J ] . 铁道标准设计,2002 (9) .3 3 铁道标准设计RAILWAYSTANDARDDESIGN 2004(9)〃线路/ 路基〃
__
acidity, mL.; M--calibration of the molar concentration of sodium hydroxide standard solution, moI/L; V--amount of the volume of sodium hydroxide standard solution, Ml; M--the weight of the sample, g. Such as poor meets the requirements, take the arithmetic mean of the second determination as a result. Results one decimal. 6, allowing differential analyst simultaneously or in quick succession for the second determination, the absolute value of the difference of the results. This value should be no more than 1.0. 1, definitions and principles for determination of ash in starches, starch and ash: starch samples of ash the residue obtained after weight. Original sample residue weight of sample weight or weight expressed as a percentage of the dry weight of the sample. Samples of
ash at 900 ? high temperature until ashing sample ... The Crucible: determination of Platinum or other conditions of the affected material, capacity of 50mL. Dryer: has effectively adequate drying agent and-perforated metal plate or porcelain. Ashing furnaces: device for controlling and regulating temperature, offers 900 incineration temperature of 25 c. Analytical balance. Electric hot plate or Bunsen. 3, crucible of analysis steps preparation: Crucible must first wash with boiling dilute hydrochloric acid, then wash with a lot of water and then rinse with distilled water. Wash the Crucible within ashing furnace, heated at 900 to 25 ? 30min, and in the desiccator to cool to room temperature and then weighing,
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