沉井施工过程中的常见问题及处理办法

沉井施工过程中的常见问题及处理办法

摘要：沉井在施工过程中，经常会遇到难沉、突沉、沉偏、抗浮等问题，给施工带来一定的困难。在实际生产中，解决难沉的办法有增加沉井自重、采用泥浆润滑套或空气幕减小沉井外壁的摩阻力。解决突沉问题的办法有增大刃脚阻力、设横梁支撑等。解决沉偏问题的办法有在高处集中挖土，或在沉井高的一侧加重物或用高压射水冲送土层，沿沉井高的一侧井壁外面破坏土层结构，降低该侧被动土压力，再用井内偏挖土法纠偏；或井壁外侧挖土，以减小摩擦力。有条件时，还可以在沉井顶部加偏压重或水平拉力的方法来纠正。解决抗浮问题时，如验算抗浮安全系数不够时，可采取加厚井壁或增加混凝土底板厚度措施；还可以采用在封底混凝土下部设置反滤层（粗砂或碎石），并在底板上设有与反滤层相通的抽水孔或集水井。

关键词：沉井；难沉；突沉；沉偏；抗浮；挖土；侧摩阻力

Common problem and handle means in the open caisson building process/Bi kewen(Changchun Institute of Technology Changhcun,130021,China)

Abstract:The open caisson is living in the building process ,constantly be able to encountering hard lowers 、deep to dash forward 、partial to lower 、combats to float and so on the problem ,bring the specified hardship to the building .It is living in the actual manufacture ,resolving the hard deep means possess the increase open caisson to self-respect 、adopting mud to lubricate suit either the air screen decreases outside the open caisson breastwork obstruction scrapping .The means to resolve to dash forward to lower the problem possess the blade broadeing foot obstruction 、In case the crossbeam support awaits .The partial problem means resolving to lower possess altitude being living lumping to excavate earth ,either the high side of the open caisson being living is increase the weight of the matter either employs the high pressure to fire water and dashes to send the earth stratum .Tall along the open caisson side wall of an oil well wrecks the composition on earth stratum out ,cut down the passive earth load force of that side ,again in the way of excavates with prejudice inner place the well indigenous method is corrected an error. Either earth is excavate in the wall of an oil well outside ,in order to decrease friction .When possessing the term ,still may be living the ministry on open caisson peak

pluss the bias severely either level pulling power means the rectification .Resolve to combat when floating the problem .In case the checking computations are when to combat to float the fail-safe system insufficient .May take intensifies the wall of an oil well either adds the beton base plank thickness step .Still may adopt in the back cover beton lower part to put up counter filters the stratum （Wide grit either broken stone ）.Moreover be living that the base possess against counter that the filtering stratum communicates with each other on the plank to pump water well or to catchment the well.

Keywords:open caisson;hard lower;abruptly lower;lower with prejudice;stand up to come-up;excavate soil;side friction

沉井是筒状的结构物，它是以井内挖土依靠自身重量克服井壁摩擦阻力后下沉至设计标高，然后通过混凝土封底而形成的地下深基础。

沉井的优点是埋置深度可以很大、整体性强、稳定性好，能够承受较大的垂直荷载和水平荷载；沉井既是基础，又是施工中挡土及挡水的围堰结构物，施工工艺也不复杂，且占地面积较小，与大开挖相比土方量较少，能节省投资。但是沉井的缺点是施工工期较长；对细砂及粉砂类地层因井内抽水开挖，井内易发生涌砂现象，并造成沉井倾斜；沉井下沉过程中遇到大孤石、树干或井底岩层倾角过大时，都会给施工带来一定的困难。

1难沉问题

沉井下沉困难，主要是由于沉井自身重量克服不了井壁摩擦阻力，或刃脚下遇到大的障碍物所致。遇到难沉时，应根据具体情况采取适当的措施，一般依靠增加沉井自重和减小井壁摩阻力两个方面来解决，以提高下沉系数k。

1.1增加沉井自重

可提前浇注上一节沉井来增加沉井自重，或在沉井顶上压重物（如钢轨、铁块或沙袋等）迫使沉井下沉。对于不排水下沉的沉井，可以抽出井内的水已增加沉井下沉系数k，但要保证井底不产生流沙为前提。

1.2 减小沉井外壁的摩阻力

可以将沉井设计成阶梯形、鈡形，或在施工中尽量使外壁光滑。亦可在井壁内埋设高压射水管组，利用高压水流软化井壁附近的土，且水流沿井壁上升而润滑井壁。若刃脚下土层阻力过大造成难沉，则可通过挖出刃脚下的土；如遇大块石等障碍物，