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1、逆作法施工技术在基坑坍塌边坡加固中的应用臧荣建 （江苏省华建建设股份有限公司深圳分公司）摘要 本文针对深圳市某工程施工过程中突发的基坑边坡坍塌险情，采用逆作法结构施工技术增强坍塌边坡稳定，避免边坡土方的二次下滑，保证上部结构顺利进行。关键词 人工挖孔桩技术 土钉墙 钢板桩技术 逆作法 深层搅拌桩随着城市地下空间利用的发展，基坑工程日益增多。确保基坑工程的安全，尤其是确保城市交通繁忙地段基坑工程的安全，减小基坑工程对周围环境的影响，是当前基坑工程的重要课题，也是对地下资源充分利用的前提。一 工程概述 深圳市某工程位于福田中心区深南路与彩田路交汇处，是深圳市中心区地产界2005年度开发的重点工程，
2、其总建筑面积为15.8万多平方米的集住宅、商业，办公为一体的综合型商住楼，设地下三层结构，地上39层，整个基坑全长218.2米，宽52.8米，基坑开挖深度为13.4716.1米，属于典型的深基坑工程，故对基坑的安全和土质要求较高。二地质情况分析和施工中出现的现象1 工程地质条件原地貌单元为低台地（剥蚀残丘）与谷地边缘，其场地北段仍保留残丘，南段经人工平整，地势较为平坦。根据地质勘察报告，垮塌口处地层从上至下：图1场地内主要含水层是含砾粘土和砾质粘性土层，渗透系数值为：0.0610.077m/d.2 原基坑支护本工程基坑采用直立开挖，北侧、东侧和南侧采用微型桩复合土钉墙支护，西侧采用桩锚支护，主
3、要支护措施有：微型桩、土钉、钻孔灌注桩、人工挖孔桩、喷砼护面等。东南侧垮塌处的原基坑支护设计如下图：（A、B、C、D、E、F为注浆土钉）图23施工过程中出现的现象本基坑工程于2005年1月基本施工结束，仅剩下东南角基坑侧壁支护未完（坑底有大量淤泥），土建单位于2005年1月受邀进场由北段向南段施工，期间南侧发生了几次小规模的坍塌，土建施工单位及时上报，积极处理，使得南部基坑暂时处于稳定状态，至2005年3月轴以北已经开始施工地下二层，2005年3月15日正在浇筑轴地下二层梁板，轴西侧也在紧张施工，就在东南侧原施工坡道出入口处底部土体清理过程中，发现该处底部土体（第四道腰梁下）喷浆支护面发生脱离
4、分层现象，底部部分淤泥状土体往基坑内滑移，此时坑底侧壁突然出现蠕动、下沉迹象，紧接着大约5分钟以后第三道腰梁下大块已喷浆支护面的土体发生滑移，往基坑内侧大块掉落，导致整个基坑由底部开始自下而上加速滑移，至9：30分左右，该处基坑东南角突然发生整体垮塌，形成的垮塌口长约20米左右，上口呈圆弧状，最大进深约6米，垮塌前该边坡高度约14.5米，坑边呈垂直状态，垮塌形状详见如下附图。图3本文就对本工程垮塌口处的结构施工和基坑稳定性的问题进行认真探讨。为满足上部结构施工的需要和当前基坑施工安全的要求。需对现有基坑边坡进行加固处理。三 边坡加固方案的选择鉴于上述施工现象的出现，立即停止该部位进一步施工的进
5、行，组织有关技术人员和专家多次会诊和观察，最后一致决定，为确保施工安全，对现有基坑进行认真加固，讨论方案归纳如下：3.1坡底堆载反压根据目前基坑现状，由于该基坑边坡因刚刚坍塌导致原土壤结构已遭到严重破坏，土体颗粒处于松散状态，且临近深基坑边缘仅2.5米的范围内埋有煤气及重要光缆等市政设施，为防止松散边坡的进一步坍塌发生，确保临时稳定，根据专家意见和现场实际情况，拟采用在坑底砂包堆载反压，预计沙包数量约350立方，同时在坡顶设置有效的沉降观测，如果其堆载量达到使基坑在连续两天内基坑变形量满足规范要求，则该基坑已处于稳定状态即能满足施工要求，然后进行土方开挖和结构施工（同时不断进行加强监测），待地
6、下结构施工完成后再将沙包撤去，该项处理预计耗用人力、财力约20万元左右，施工工期为35天时间，否则需另行处理。3.2钢板（管）桩即将在原设计结构边线外侧壁范围内施工钢板桩，以此作为边坡坍塌后的基坑护壁，然后将结构施工范围内多余的土方全部挖出外运，直至设计标高，后用C15素砼进行垫层施工，从而满足结构施工的要求，通过上述处理实际需耗费人力、财力约40万元左右，实际施工工期25天时间。3.3人工挖孔桩护壁加固即将在原设计结构边线外侧壁范围以外，先将该部位松散的土壤采用注浆处理，临时固化，再在基坑坍塌后形成的临时平台上施工共计9根直径2米的人工挖孔桩（桩深约21米），以此悬臂桩作为边坡坍塌后的基坑护
7、壁，待桩芯砼强度达到，然后将结构施工范围内多余的土方全部挖出外运，直至设计标高后用C15素砼进行垫层施工，从而满足结构施工的要求，通过上述处理实际需耗费人力、财力约30万元左右，实际施工工期50天时间。3.4 逆作法原理护壁即先将该部位松散的土壤采用注浆处理，临时固化，然后在原设计结构边柱范围内，再利用人工挖孔桩原理，在结构柱位置开挖26003000mm的人工挖孔桩施工，待人工挖孔桩护壁形成后，以此护壁作为结构柱结构施工的护壁，为防止护壁在施工过程中的位移，施工期间加强监测，同时利用型钢支架将空腔护壁支撑于已施工完成的结构上，然后在空腔护壁中进行结构柱施工及上部梁板框架体系的施工，这样满足了上
8、部结构的工期要求，最后采用逆作法工艺施工外侧墙体维护结构，最后在室内将多余的土方全部挖出外运，直至设计标高后用C15素砼进行垫层和底板的施工，从而满足结构施工的要求，通过上述处理实际需耗费人力、财力约10万元左右，实际施工工期15天时间。3.5 效果比较分析3.5.1 优缺点对比坡底堆载反压保持了原有地质的实际情况，经济实用但影响了上部结构的施工，耗时较长，若效果不佳，则更将耽误工期。钢板（管）桩方案效果很好，满足了实际施工基坑护壁的需要，但费用较高，且由于坑边存在大量的管道和通讯光缆，不能承受打桩机械的强烈振动。人工挖孔桩护壁方案可行，但风险较大，且费用较高、工期太长，由于土质无法预测，一旦
9、出现问题会严重耽误工期，影响工程的总体进度要求。而逆作法原理施工方案利用人工挖孔桩原理，工期短、费用低，可实现施工时边坡的临时加固、并可定时、定量观察基坑的变化情况。通过该种处理由于土方开挖量较小，保持了原有地质的结构情况，增强了边坡的相对稳定性，同时可以满足上部结构施工的同步进行，缩短工期，利用了人工挖孔桩空腔护壁的特殊功能，从而解决了边坡加固的实质性问题。3.5.2 结论最后经专家组讨论一致同意采用逆作法原理进行边坡加固技术。四 施工程序及要点4.1施工工艺流程桩孔定位 桩护壁施工 桩壁间支护 检查支护效果 桩孔内结构柱砼施工上部结构施工地下二层外墙施工地下三层外墙施工地下室底板施工基坑回
10、填4.2后加桩护壁施工首先在已加固的土体上方搭设施工护壁桩的操作平台，为减小操作平台对垮塌土体的影响应适当增加竖向支脚并在支脚下面放置垫块尽量增大支撑接触面，在施工中尽量减少材料的堆放做到随用随运，挖出的土体及时用塔吊运走，严禁大量材料堆放在平台上过夜。为确保结构施工操作面，挖孔护壁内径设计为26003000mm，挖孔的深度为设计承台底面以下50cm。由于土体结构不稳定，第一节人工挖孔护壁高度先做50cm左右，然后根据土体稳定情况逐步向下开挖并调整各次护壁高度，挖孔中遇到锚索、钢花管、腰梁等原支护时应保持其原状、不可进行破坏处理；施工中一旦发现有土体滑移迹象，应立即停止开挖并采取紧急加固措施，
11、阻止土体滑移，待处理完毕后方可继续开挖，为防止垮塌口再次发生险情必须赶在雨季到来前完成地下室抢险施工。为保证护壁的稳定，在护壁上口用型钢支撑将护壁与已浇筑的主体构件进行就近支撑，相邻护壁之间亦要进行相互支撑。在孔护壁浇筑时留置砼指导试块，待砼强度达到75%以上后再进行介入施工（如需提前施工可保留内壁筒模）。增加护壁桩位置见图4：图4 增加护壁桩示意图4.3桩孔内结构柱施工 对已形成的护壁桩孔进行清理，并将原桩头进行凿除，达到设计标高后在桩孔内进行垫层浇筑，厚度20cm，垫层砼凝固后对柱底底板承台钢筋进行绑扎、柱定位插筋，为保证承台底板的整体性，关键是要认真预留底板承台的钢筋，待后期施工时进行焊
12、接（为保证焊接长度可将预留钢筋外侧弯成90或采用双面焊接），钢筋绑扎完成经验收合格后进行砼浇筑，将柱外侧与护壁间的空隙进行构造配筋后与柱同时浇筑（同时浇筑部位详见图5），以待砼达到强度后柱与护壁能形成一个整体增加护壁的抗位移能力，砼强度达到后再对多余护壁凿除，对柱墙部位的砼界面认真的凿毛，在各个护壁桩孔内进行地下三层的柱钢筋绑扎，为增强外墙的抗压能力，在地下二层梁板下口增加设置KLa梁一道（截面为6001200，配筋同本工程同截面梁），柱墙钢筋绑扎时也要认真预留外墙的水平筋和增加的梁筋，验收合格后对柱墙内侧模板进行制安，外侧亦与墙柱进行整浇，浇筑之前在底板的柱墙部位设置防水措施。4.4桩间支护
13、由于土体内含有大量的水份，地下三层的护壁无法一次性形成。施工中在护壁外侧进行分层分段浇筑钢筋砼挡土板（图5）：以600mm高为一层、以相邻的两个挖孔护壁间距为一段进行分次浇筑直到护壁达到底板垫层下口，待上一层浇筑24小时后方可开始下一层钢筋砼挡土板的施工，上下层次的钢筋砼挡土板的钢筋要在预留的200mm高的浇筑口处进行有效的连接，同时为防止上层先浇筑的钢筋砼挡土板下滑，支撑在上层挡土板底部的钢筋（25500mm）应始终保留不动；基坑的开挖同时进行。施工过程中进行不间断的桩端和上部土体的水平位移监测（2小时/次），必须保证土体的稳定性，如有异常立即停止开挖，判断情况处理完毕后方可继续施工。图5桩
14、间支护及浇筑示意4.5检查支护效果经监测数据统计，直至土方全部挖完，护壁桩未发生明显的位移，全过程最大位移仅为6mm，完全能满足设计及施工的要求。4.6底板及地下三层外墙施工将影响施工的护壁内侧砼用小型风镐进行凿除并将预留的底板承台及外墙钢筋初略的凿出，同时浇筑底板垫层，然后人工用錾子将松动的砼块凿掉，并将预留钢筋清理干净整理顺直，并将原浇筑的承台施工缝处清理干净后进行承台底板钢筋绑扎，关键是将现绑扎的钢筋与每条预留的钢筋进行认真的焊接，少数未能凿出的钢筋进行植筋处理，再进行外墙钢筋的定位插筋认真复核验收后进行底板砼浇筑，并将外墙与钢筋砼挡土板之间的空隙进行构造配筋与承台一起浇筑，并在浇筑时于
15、板面预留吊环（用于支撑外墙模板）。砼强度达到后进行地下三层外墙钢筋绑扎，施工中注意将外墙的水平及竖向钢筋焊牢同时也要将在地下二层梁板下口增加的梁（KLa）进行连接，验收合格后在内侧进行单面封模，支撑在底板预留吊环上，最后利用塔吊进行整体浇筑。4.3.7基坑回填地下三层外墙浇筑完毕后，将外墙的支撑保留不动并将松动的支撑进行加固后立即对地下三层基坑用C10砼回填以降低基坑高度，至此地下室基坑已形成较稳定的体系从而保证了基坑和后期施工的安全。待地下室结构施工完毕后及时用级配砂石对上部基坑进行分层回填并夯实，在回填之前要预先砌筑电缆沟，保护已受损的电缆。4.3.8上部结构施工在地下三层护壁内结构柱及上
16、部梁板体系形成后，保留上述支撑体系不动的情况下，同时进行地下二层梁板及上部结构的施工和地下三层局部遗留结构（外墙及底板）的施工，由于已形成了稳定的体系，垮塌对上部施工已无影响，故上部施工已属于正常施工，只要注意处理好后来绑扎钢筋与预留的钢筋的连接问题和新旧砼之间的交接即可。4.3.9 施工注意事项施工过程中加强安全监测和边坡位移、主体沉降观测，发现异常情况应立即停止施工，及时上报处理。施工缝处的砼要认真凿毛清理并设置两条BW-7型遇水膨胀条，认真预留承台底板及地下室外墙钢筋，并保证同一平面焊接接头50%同时确保焊接长度。认真做好地下室止降水工作，防止造成砼水灰比失调，所有地下室底板及外墙砼采用
17、C30P10并掺入微膨胀剂，砼要振捣密实，切实做好砼养护工作（养护不少于28天）。五 施工体会（1）对于坍塌后的基坑施工时需特别注意坑壁地基土质的稳定性分析和观测，以免出现本工程加固前出现的问题，对工程施工造成不必要的损失。（2）对于坍塌后基坑护壁的加固应广开言路，博采众长，运用多角度方法分析和综合分析，以免误用而给工程带来不同程度的经济和工期上的损失。（3）对于发生意外情况造成的基坑坍塌后护壁的加固处理，采用本文所述的逆作法原理护壁加固技术是可行的。（4）逆作法原理护壁加固技术对保证土体稳定的优点在于利用人工挖孔桩施工的原理，依靠空腔护壁的整体性作为不稳定土体的支撑体系，从而在空腔内侧将结构
18、框架体系先行施工，然后再利用框架结构作为边坡的固定支撑，满足了上部结构施工的要求，大大的满足了工程的进度要求，因此对于护壁施工过程中监测、分析的控制是该加固技术和确保基坑安全的重点。（英文版 ） easily blame, to prevent the broken window effect. Supervise the leading cadres to play an exemplary role, take the lead in the strict implementation of the and , lead to safeguard the solemnity and aut
19、hority of the party discipline, ensure that the party discipline and the laws and regulations for implementation in place. Throughout the discipline in the daily supervision and management, strengthen supervision and inspection, from the thorough investigation of violations of discipline behavior. S
20、trengthen to key areas, key departments and key projects as well as the masses reflect the concentration of the units and departments for supervision. - strengthening supervision, discipline inspection and supervision of cadres to set an example for compliance with the and is a man must be hexyl, bl
21、acksmith needs its own hardware. Discipline inspection organs as the executor of the party discipline, and supervisor of the defenders, for its supervision must be more strictly, discipline inspection and supervision of cadres to firmly establish the awareness of Party Constitution, sense of discipl
22、ine and rules consciousness, politics loyalty, sense obey. Action speak Ji Ordinance to set an example of the regulations of the rule of law, strengthen supervision and accept the supervision of the firmness and consciousness, do comply with and . To firmly establish the discipline must first be dis
23、ciplined, the supervisor will be subject to the supervision of concept, and consciously safeguard and implement party compasses party, take the lead in practicing three strict real strict, so loyal, clean, play. To be good at learning, the Constitution and the as morality, politics and brought to fr
24、uition; to implement , do not want to, dare not, not with disciplinary ruler to supervision; to discipline a ruler, often the control inspection, and consciously in the ideological red line to draw the row Ming Good accumulation is indeed the bottom line, so that the heart has fear, said to have qui
25、t, the line has ended. Attached: indifferent to heart, calmly to the table in our life, there are many unpredictable things will happen, some good, some bad things, we cannot control is powerless to stop, but with time, you will find in life sometimes turns out to be not good, some bad things finall
26、y turned out to be a good thing, but then we muddy however did not know, this is the life teach us things. 1, life can be complex, can also be simple. Want simple life of precipitation, to have enough time to reflect, to make Become more perfect. Life is the most important thing is not to win, but t
27、he struggle; not to have conquered, but to have fought well. 2, the plain is the background of life. Live a plain life, give up on themselves is not a coward, but the wise answers; not disillusioned after the heart, such as ashes, but experience the storm after the enlightenment; not unrewarding per
28、functorily, but calm attitude of life of unrestrained self-confidence. Plain living, there is no noise noisy, no earthly troubles, more did not fill in the discontent of desire, some just a calm, a calm. 3, memory of heart will not good things to erase the, life is a When no movie, pain is a beginni
29、ng, the struggle is a kind of process, death is a kind of ending. Give up this giving up is the helpless, do not give up the abandoned, do not give up this giving up is ignorance, do not give up should not give up is persistent. 4, a thing figured is heaven, think impassability is hell. Since the li
30、ving, to live better. Sometimes we because of too narrow-minded, too care around the chores and penny wise and pound foolish, not worth the candle. Some things to attract trouble and worry, completely depends on how we look at and deal with it. Dont always take everything back to things, and dont ge
31、t into a blind alley, dont want to face, dont be narrow-minded. Poke to care, is a kind of open-minded, a free and easy. 5, I am not afraid of others behind me a knife, I afraid to look back and see stab me, is my intention to treat people; I am not afraid of the truth to tell the best friend, Im af
32、raid he turned to it as a joke to tell dont 6, when we are in a positive frame of mind, you will find many good things; and when we are in a negative state of mind, you will find many depressed things; life happy and worry, all is you of life attitude, optimistic, good luck; loss of sink, Eritrea co
33、mpany. When you are in adversity, may wish to change a point of view to think everything over to the good Think, because good mentality decided the fate of the! 7, people are tired, rest; heart tired, calm. Grow up, mature, this society read. Tired and sad, squat down, to their a hug. Because the wo
34、rld no one can sympathize with you, have mercy on you. You cry, tears is your own; you pain, no one can understand. Then you only tears to smile. 8, each people have youth,Each youth are a story, the life of the world never gets easier, I want what, wish the world all know, as has been the same; now
35、 want anything, for fear that others know, or like to lose the same. 9, the heart move, everything in the world is followed by birth, Rangrang, important thing is often the most difficult to open ones mouth, because words will reduce its importance; to let strangers people care about your life in th
36、e good things, the original is not easy 10, do not blame, do not laugh at who, also dont envy who. Like a person is a kind of feeling, not like a person is true. The truth is easy to explain, I feel Is unspeakable. The best travel life is that you in a strange place found a long lost touched. 11, ha
37、ppy life not in the bustling in, and in the peace of mind; no matter how many grievances, how uncomfortable, and ultimately to heal themselves or their own, others may got you to comfort, but never know your heart is how wanjianchuanxin. 12, maam, like a movie, learn to appreciate, learn to be grate
38、ful, learn tolerance, and goodness, helping others. Instead of accusing the society, as into one; and an exception is better to give than to what 13, dont envy him A sum of, dont lose your life and the life, respectively is: the former is a we experienced cannot escape in a day finally will last min
39、ute, while the latter is our persistent, we want to cherish the memory of those people and things. 14, learn to smile, learn to strong, the world you know so many people, so many people and you are, you cannot change also cant let everyone like you, so also do not want to do. Life is too short to go
40、 crazy to love to go to waste, to chase the dream to regret. 15, when temper, a blessing to go. A wounding elegant people, the key is to control their own emotions. With the mouth is the most stupid behavior. A control negative emotions than a can take a city more powerful water flow slow, language
41、is expensive. People spent two years of time to learn to speak, but to spend a few years time to shut up. That is a kind of ability, that is a kind of wisdom. 16, life is not perfect, sometimes, growth is not a cry, not an eyeful of tears, there is no trace of emotion, there is no gleam of hope, no
42、desire, no action, no static, there is only one kind of downward sinking feeling, sink A murky? 6? 7? 6? 7 sink? 6? 7? 6? 7 toward the bottom of the sink. 17, in some way, do not go, you will not know the other side scenery is beautiful. To you is not good, you do not mind too much, no one has an ob
43、ligation to you; you learn knowledge, is you have weapons, you can start from scratch, but not unarmed; how do you treat people, does not represent how others treat you, if cannot see through this point, only inviting worry. 18, time is like a sponge in the water, as long as you are willing to squee
44、ze, the total water is still there. Every life, after the ups and downs The best test of live, to life, survival and continuation, do not stop the struggle in the joys and sorrows of life on the road, so that different soul to bear life beat, acceptance of suffering. 19, indifferent to heart, calmly
45、 in table, elegant and comfortable life, do not take what is so important. The pursuit will be disappointed; to be alive, you will have trouble. Life is the most afraid of what all want to care about, but also what all grasp is not firm, without scenery, separated populations, such as not to desire,
46、 all docked in the fate of the end. Why is too rigid, the natural, to go stay not to live, let go of obsession, revel is 20, if the fate of the broken Hopes of sailing, please dont despair, the coast is still, if the fate of the withered petals of the beautiful, please do not sink, the spring is sti
47、ll, life will always be endless trouble, please dont helpless, because they are still alive, is still a dream, the sun still, we still. Lost, keep memories; to get, must work to; but the most important is good to cherish their own. 21, life, select the complex, is to choose the pain; choose a simple
48、, is choose to be happy. The complex world like aSignificance of pride. Hope is the ornate palace, outside people admiring the magnificent, living in the deep knowledge of living it to pay the price. Simple world as a simple log cabin outside ridiculed shabby, the heart is willing to go live to know
49、 the joy. Suffering and joy is their own choice. 22, learn how to use a single powerful heart, let the past be the past, let the future come. Life is really the end of the end of an eagle is flying wings, life is constantly pursuit. Dont miss to regret, dont wait for old just miss. Time to return, seize ev