混凝土刚性基础底模工艺在现浇箱梁施工中的应用.doc

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Antistatick opaten, jako jsou zazen, potrub, by mlo bt v souladu s technickmi pedpisy pro uzemnn design pro chemick podniky pslunch ustanoven. 7. nhl vbun petlaku nebo rychlho rozkladu vrobnch zazen nebo skladovacch zazen by mly bt vybaveny vbuchu (nevbun membrna), vvoz nonel trubice smrem k bezpenosti a aby prevence sekundrnch exploz, protiporn opaten. 8. vrobnthe principle of simplified EIA of construction projects in the region. In terms of land, linked to the implementation of urban and rural construction land increase and decrease, replacement indicators for priority areas project. Charges, into the projects of water, electricity, administrative charges and preferential policies. In the area of taxation, and settled in areas of industry and its production company, within 5 years after the completion of fiscal incentives to enterprises. In terms of financing, integration of land, tax, financial and other resources, and construct Government credit + business credit credit system, establishment of marketization, commercialization and modernization of the investment and financing platform; effective Bank-enterprise docking, encourages private capital into the Park, to raise industry development fund. 5, optimize the environment and service industries. To create policy lowlands, Highlands, integrity of service land, development land as the goal, to optimize the area under development environment. All administrative law enforcement departments to appoint a full-time personnel stationed in areas dedicated to coordinating and solving problems associated with businesses in this sector. When there are substantial issues, sector leaders arranged to personally intervene, in-person, in-person push tangible area building a green light, easy line. To further reduce and standardize administrative examination and approval items, simplify examination and approval links, improve efficiency; according to the .Since the educational practice of the mass line of the party, himself seriously in the education, practical control central eight rules and opposing the four winds and practicing three Suns, and check the spirit of Jiao Yulu, ideology, solicit opinions based on outstanding problems checked swing, careful analysis and reflection. Will now check report is as follows: first, adherence to the partys political discipline, eight in the central provision, change the style of the basic situation of 1, in compliance with the partys political disciplines. Conscientiously abide by the partys political discipline, abide by the Constitution and the rules and regulations of the party, in the political, ideological and maintain highly consistent with the CPC Central Committee on the action, there is no violation of the partys political discipline problems. 2, in the implementation of the central authorities of the eight provisions. Improving research, improving research methods, but there are less grass-roots units, primary first-hand an inadequate grasp of the problem, which is to be strengthened in the future. Second, construction, strictly in accordance with the provisions to streamline and improve the quality of meetings of the Conference. Third, streamlining file briefs, culture involves all aspects of propaganda and ideology, sometimes due to the practical needs of invention notifications, this area needs further混凝土刚性基础底模工艺在现浇箱梁施工中的应用摘要：文章所述的混凝土刚性基础底模类似于常规梁板预制工艺中的混凝土基础台座，工艺施工方便、快捷，但却因为底模的刚性对梁体混凝土的自由约束较大，相应增加了混凝土裂缝产生的风险。本文结合该工艺在xx跨江大桥南岸陆地区引桥现浇箱梁施工中的应用，介绍了一些预防裂缝出现、控制施工质量的有效措施和成功经验。关键词：刚性基础 底模 自由约束 裂缝 质量 措施0、前言嘉兴至绍兴跨江公路通道xx大桥南岸陆地区引桥为两联550m预应力混凝土连续箱梁，按双向八车道高速公路标准设计，分左右两幅布置。箱梁连续体系设计为逐跨浇筑施工，跨间纵向预应力钢束采用连接器连系。从第25#墩至27#桥台间的两跨箱梁，由于原地面标高与设计梁底高程相差不大，不具备支架搭设条件，我们采用了原地面回填处理、混凝土刚性基础充当底模的施工工艺，制订了一系列的质量控制措施，并对实施过程进行了跟踪监控、完善总结。1、工艺的提出陆地区引桥箱梁单幅采用单箱双室斜腹板断面形式，梁高3.0m，顶板宽19.8m，底板宽11.64m，翼缘悬臂长3.20m，在墩顶设1.8m厚中横梁和梁端设1.45m厚端横梁。箱梁标准断面见下图： 图1 箱梁标准横断面按照常规施工思路，我们20跨箱梁原定施工方案为支架现浇施工。但是，25#墩至27#桥台的现场地面基础情况十分不利， 具体如下：、25#-27#墩位处原为鱼塘、虾塘区，地面表层10m范围内地质为粉质沙土，基桩施工前我们对桩位处小范围内填筑宕渣进行了排淤、固结处理，原地面高程抬高约50cm。处理后的地面高程与设计梁底高程相比，或高、或低，相差均在1.3m范围内。具体数据见下表。、我们的支架现浇方案结合项目自有杆件材料情况、箱梁模板加工情况和支架纵横向支撑梁设计情况，对支架搭设的最小梁底净空要求为1.7m。按照该高度要求，25#墩处需下挖0.42m、26#墩处需下挖1.63m、27#墩处需下挖2.28m，平均挖深1.44m，箱梁标准横断面全幅宽41.5m、开挖断面取45m，两跨长度100m，总共要开挖土方6500m3。开挖方量较大，且施工现场附近没有弃土场可供废方。、如果采取支架现浇方案，按照1.7m的净空高度开挖后，各墩位的地面标高降低为25#墩4.33m、26#墩3.55m、27#墩2.92m，而我们施工现场的地表水常水位高程为3.97m，开挖后的基础将整体遭受地表水浸泡，无论基础顶面采取什么样的处理措施，粉质沙土基底浸泡后失稳都是一个棘手的难题。墩位原地面高程（m）设计梁底高程（m）支架基础顶面需求高程（m）地表常水位高程（m）25#4.756.0264.333.9726#5.185.2453.553.9727#5.204.6202.923.97表1 25#-27#墩基础处理高程参数对照表在上述情况下，我们放弃了原定的支架现浇方案，经过多次会议讨论、分析，提出了混凝土基础底模的施工工艺措施。2、工艺的可行性分析我们通过实地勘察、计算分析，并经多方调研、咨询和讨论，认定混凝土基础底模方案可行，施工质量、安全有充分的保障。依据如下：、原地面标高与设计梁底高程相差不大，从表1中的数据计算可得均差为-25cm，考虑到清淤、清表处理深度，填筑总体高度在100cm以内。填筑方量不大，采用挖掘机、自卸车填土，配合以压路机碾压密实，可以轻易实施。、参照施工手册，粉砂土（水上）的容许承载力为：密实情况下300KPa， 中密情况下200KPa。根据以往施工经验，填筑粉砂土，通过压路机充分碾压，密实度可以轻易达到中密以上。而我们按照箱梁设计构造尺寸对基础进行加载计算时，求得的最不利截面承载力要求为80.5 KPa，远小于粉砂土中密时的允许承载力200 KPa。经过计算求得的箱梁底板、腹板、翼缘板对应位置的地基承载力需求值见下表。承载对应部位底板腹板翼板承载力要求28.5KPa80.5KPa15.5KPa表2 箱梁底板、腹板、翼缘板对应位置的地基承载力需求值、我们考虑的基础底模，在粉砂土上层还要填筑50cm厚度的宕渣进行封层碾压，其上再浇筑15cm厚度的混凝土进行找平、补强。通过这两层的加强，基础承载力绝对有保障。3、工艺施工介绍混凝土基础底模的工艺原理类似于常规梁板预制施工中的混凝土台座。当下部结构施工结束后，对施工作业区直接进行回填处理，碾压密实后顶层浇筑15cm厚度的C20混凝土进行补强、找平，混凝土强度形成后充当底模，在其上进行常规工序施工：安装箱梁侧模，安装底板、腹板钢筋，安装内模，安装顶板钢筋，预应力管道安装与钢筋安装穿插进行，浇筑混凝土等。3.1、基础底模施工N25#墩N27#墩底模基础自上而下分为三层结构，第一层为15cm厚度的C20混凝土，从设计箱梁底向下-15cm；第二层为50cm厚度的宕渣，从设计梁底-15cm至-65cm；第三层为填筑沙土，厚度由现场清淤后的标高确定，分层填筑、层厚控制在50cm范围内。沙土回填前，先对虾塘、泥浆池进行彻底清淤处理，基础处理范围为桥中心轴线向两侧48m的宽度。回填时采用压路机进行分层碾压，每回填压实一层后采用触探仪进行承载力测试，承载力达到100KPa（砂土层取1.2倍的安全系数）以上方可进行下一层回填。沙土层回填到预定标高后，上铺50cm厚的宕渣补强，充分碾压整平后上层再铺设15cm厚C20混凝土调平。经现场检测，我们在填筑沙土时取得的地基承载力强度普遍在240 KPa左右，达到了预想的承载力目标。具体数据见下表。测点位置所测点数最大值最小值平均值腹板处60267228248底板处30252236245翼缘板处30258235242表3 25#27#墩现场碾压处理后实测地基承载力（KPa） 图2 地基承载力检测 图3 宕渣补强 图4 底模浇筑3.2、基础底模预压为了验证混凝土基础底模的实际承载力效果，我们对26#-27#墩左幅第一跨基础进行了堆载预压试验。采用堆砂袋法进行加载，荷载按梁体底板、腹板及翼板处的重量分布进行区分布置，最终加载总量为箱梁自重的130%。经测量观测，24小时内最大沉降为3mm，满足施工承载力要求。 3.3、基础底模的使用和拆除基础底模混凝土强度形成后，表面铺设一层五夹板隔离层，然后即可展开常规现浇箱梁的模板、钢筋和混凝土施工作业工序，此处不再赘述。待箱梁预应力体系张拉、压降和封锚等作业完成后，即可安排基础底模的拆除施工。考虑到机械作业不具备空间条件、易损伤箱梁成品混凝土，人工开挖工程量太大、又存在安全隐患，拆除采用“冲水抽沙”法。从每跨箱梁外侧靠近基础底模下缘纵向开挖坑槽，宽度1.0m，深度约1.0m、到达沙土层即可，然后分段采用高压水管向基础底模下横向射水，并同步布设足够数量的泥浆泵将泥沙抽运到指定地点。最终抽沙高度由设计方进行指定。 图5 底模预压4、工艺施工难点和控制要点4.1、工艺施工难点混凝土基础底模工艺施工操作起来非常方便、快捷，与支架现浇相比，相同之处是基础的碾压、处理，不同之处是用浇筑混凝土层来替代搭设支架、铺设底模。该工艺实施中需要解决三个方面的问题：1、认真做好基础处理，避免施工过程中出现基础沉降量过大和基础不均匀沉降。2、解决好箱梁底板和混凝土基础之间的脱模问题。3、与支架不同，混凝土底模是一种刚性基础，需要防止其对箱梁混凝土的约束破坏。该约束破坏主要体现在两个阶段，一是梁体混凝土强度的形成和养护期，二是箱梁预应力施加过程。4.2、工艺控制要点针对上述三个施工难题，我们采取了多方面的施工控制措施，并取得了良好的效果。具体为：1、基础回填处理前，先对原地面坑塘区进行排水、晾晒固结，然后认真做好清表、清淤工作，彻底清除松散、薄弱的下卧层。对于坑底标高接近或低于地表常水位的区域，采取抛填大块宕渣片石进行挤淤固结的措施。2、基础填筑时，严格控制层厚和压实指标，以每一层的承载力达标来保证基础整体的承载力合格。3、在靠近墩身、承台处，做好成品保护工作，机械操作不能到位的地方，采取人工作业。人工填筑沙土，采用“洒水夯实”法，层厚控制在20cm以内，填筑到预设标高后，顶部填筑两层25cm厚的小粒径宕渣封层夯实。4、做好施工场地四周和场地内的排水工作，在紧靠用地红线内侧挖设两条纵向主排水沟，场地内排水与之构连，形成通畅的排水系统，做到平时不浸泡、雨停场地干。5、底模11.64m宽混凝土分做三幅浇筑，先两侧、后中间，纵向坡度按照设计要求设置，纵向每50cm预埋一道PVC管作为侧模底口拉杆孔，做好混凝土表面收光和洒水养护工作。6、加强对基础底模的测量监控，在四周边缘易于观测的位置布设沉降观测点，在箱梁混凝土浇筑前、浇筑中、浇筑后和张拉过程中进行观测，做好记录，并对数据进行整理、分析，发现问题、及时解决。7、考虑到混凝土底模的光洁度不够，在其表面铺设一层五夹板，采用水泥钉沿四周和十字轴线施钉牢靠，做到不翘曲。五夹板表面涂刷脱模油，风干后方可进行钢筋安装。8、预防刚性底模对箱梁混凝土的不利约束，我们采取了四点主要措施：A、如上所述，在基础底模和梁底之间加设了一层五夹板隔离层，减小刚性底模对梁体混凝土的约束。B、在预应力体系张拉作业完成之前，严禁在箱梁顶板堆放任何材料、器具，避免外部荷载作用的不利影响。C、试验室加强对箱梁混凝土强度、弹性模量增长的监控，在现场多留置同步养生试件，从第三天龄期开始每天进行试件强度、弹模试验，一旦两者都达到设计要求的张拉标准，第一时间着手进行预应力施加，尽早、尽快的防止箱梁混凝土约束裂缝的产生。D、箱梁纵向预应力的施加是最为关键的一个环节，也是底板最容易出现约束裂缝的过程。在严格执行“先腹板束，再顶板、底板束；先长束、后短束；各部位钢束横向对称张拉”的原则下，我们把整个张拉过程划分成“起拱前、起拱中、起拱后”三个阶段进行区分控制，采用全站仪、水准仪进行全程观测监控；同时把各部位的钢束进行分批，如腹板束N1-N6分成N1和N2、N3和N4、N5和N6三批，每批钢束张拉完成后间隔等待30分钟。起拱前、起拱中，每束钢绞线张拉时，采取“五步骤”张拉，即“0.1k0.2k0.5k0.7k1.0k”，并尽量放缓每个行程的节奏、适当延长持荷时间；起拱后，钢绞线可恢复常规的“三步骤”张拉，并取消分批间的间隔时间。三个阶段的判别，我们采取了两个标准：标准一，仪器观测到箱梁上拱值达到1mm，肉眼观察到箱梁底板和底模交接处的混凝土有轻微挣脱、掉渣迹象；标准二，仪器观测到箱梁上拱值达到3mm，肉眼明显观察到箱梁底板和底模交接处的混凝土出现脱缝；标准一之前为起拱前阶段，标准一、二之间为起拱中阶段，标准二之后为起拱后阶段。通过上述措施，我们达到了对箱梁施工质量的有效控制：刚性基础底模承载力满足要求，没有出现不利沉降；箱梁混凝土底板、腹板自始至终没有出现裂缝；箱梁底板与刚性基础间脱模情况总体较好，局部出现粘接脱皮现象，需要进一步对隔离层进行优化、调整。5、结束语混凝土刚性基础底模工艺在本项目的尝试应用，取得了既定的成效，积累了一定的经验，对今后类似工况下的类似工艺施工有着积极的指导意义。参考文献1、公路桥涵施工技术规范（JTJ041-2000） 人民交通出版社20002、交通部第一公路工程总公司 公路施工手册-桥涵 人民交通出版社1999.113、路桥施工计算手册 人民交通出版社2001.5to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, 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