原文：
                  天津经济技术开发区污水处理厂是为改善投资环境而建立的环保基础设施工程，其污水泵房建在原为被称做盐汪子的海水沉淀池上，地表下2m左右为垫填素土，再下均为多年沉积的流塑状淤泥。泵房的地下泵池埋深13m，呈凸字型，由于附近布置有变电站和脱水机房、泥饼堆放库，不可能采用明挖基坑或深基维护结构，设计为一多边形沉井结构。在流塑状淤泥中做沉井下沉，极易产生突沉、偏沉滑移，井内涌水、涌泥和超沉不止，沉井下沉的速度和方向极难控制，这是至今尚未很好解决的施工难题。承建该项工程的中铁十八局三处，根据设计意图，采用在沉井刃脚下预打粉喷桩，形成联排桩式的地下连续墙，对于沉井井壁形成具有一定强度的承拖和支撑墙体，将沉井在淤泥中下沉的过程成为一个可控的工艺，成功地解决了这一施工难题。

         1施工准备 1.1开挖填土，降低初沉标高 根据沉井部位的地质状况，隔膜泵为保证沉井初沉阶段的均衡下沉，将人工填土层挖除，把沉井预制及初沉标高设为0.48m，这样可创造两个有利条件：其一由于初沉地层为淤泥，其含水量及承载力均匀，便于初沉平稳；其二，沉井总下沉量降低2.5m，上部第三节0.5m厚沉井可不作为沉井施工，而在沉井封底后浇筑，这样既减轻了沉井自重(仍能满足下沉重量要求)，又缩短了下沉深度，一举两得。 1.2粉喷桩施工 打粉喷桩，加固沉井刃脚下软土，使沉井在连打粉喷桩形成的水泥连续墙的承托下下沉。粉喷桩施工应注意以下几点： ①位置要准确，桩外沿与井壁外边线相切，不得外露，以免沉井下沉时水泥土挤至井壁以外，失去支撑作用。 ②桩底应深入沉井刃脚设计标高以下16m。 ③外圈桩底刃脚下以及桩顶1.0m范围喷水泥量10%(按桩体重量计)，其余桩身7%。 ④内圈桩喷水泥量均为10%。 ⑤内外两排桩间距10cm，以保证开挖内侧桩体时不伤及外侧桩。

             2沉井预制 2.1预制场地平面布置 由于沉井井壁即为合建泵房泵池池壁，因此选择泵池位置为沉井预制位置。为便于施工，并考虑沉井支撑墙混凝土浇注的需要，场地软土表层用15cm、8%灰土压实，支撑墙底另做10灰土平台。 2.2预制方式 原设计沉井为三节，表层填土挖除后，地面标高正好为第二节沉井顶面标高，因此第三节沉井不再视作沉井结构，而待两节沉井下沉到位封底后再接打。为减少第一次浇注混凝土的重量，避免下沉过大及不均匀沉降造成混凝土开裂，将第一节混凝土浇注分两次完成，先浇注刃脚(高1.0m)，待混凝土强度达到设计强度70%以上时再浇注剩余部分，并依次施工第二节。两节沉井混凝土全部完成后，一次下沉就位。 2.3刃脚底模及支撑墙底模 按初步设计，刃脚下打两排粉喷桩加固软土层。 原地面为淤泥质亚粘土，容许承载力80kPa，粉喷桩桩顶水泥量10%，水泥土7d无侧限抗压强度可达600kPa，28d抗压强度可达800～1000kPa。沉井混凝土总量为444m3，按容量2.5t/m3计，总重为3610t。沉井刃脚底面积为44.88m2。因而，单以刃脚底面作支撑面时，承受荷载为804kPa。 按以上计算，并考虑粉喷桩施工的误差，则沉井刃脚置于粉喷桩顶，承载力尚不能完全满足 要求，而在沉井的预制过程中，刃脚侧面尚未承载，因此在支撑墙底增加支撑底模，以分担部分沉井的重量。

          3沉井下沉

3.1准备工作 沉井必须在混凝土强度达到设计强度后才能开始下沉，下沉前作好以下准备工作： ①井壁外画观测标志，在沉井四角设水准观测点，自吸泵观测下沉量及平衡情况；在中轴线处设垂直线，观测沉井位移及平衡。 ②拆除模块。 ③挖除表层灰土 支撑墙底模拆除后，沉井稍有下沉，但刃脚侧面随即承力，沉井止沉。

 3.2下沉系数计算 下沉系数公式： K＝Q/(f·h·L)＞1(1) 式中Q——沉井自重重力 f——摩擦系数，软土取9.8～11.76kN/m2 h——最大下沉深度 L——沉井外壁周长 摩擦系数取软土的最大值，一般结构沉井自重力下沉系数尚可达到3.0，何况淤泥之中，绝无滞沉问题。存在的问题是下沉深度达到要求时仍会下沉不止，故必须采取控制措施。

 3.3粉喷桩连续墙控制下沉的机理 ①导向和防止突沉、涌土 根据初步设计构想，在井壁密度范围内、刃脚之下，预打两排粉喷桩加固地层是防止沉井突沉、沉降速度过快和涌土的综合性措施，其作用原理如下：其一，粉喷桩形成了水泥土地的连续墙，对于沉井来说是一个封闭夹在淤泥之中的承载墙体，整个沉井的下沉过程也就是这一承载墙的挖除过程，这样沉井的下沉速度和平稳程度完全可以由人工挖除粉喷桩的方法来控制。其二，在淤泥质软土中实施沉井，化工泵在挖土下沉过程中易发生涌土现象，即井壁外的流塑状淤泥因井内外土面高差较大时失稳而产生滑动，滑动弧面刃脚下挤入井内，使井内只出土但土体标高不降，而井外土体标高下沉，极易产生不均衡的土压力，致使沉井倾斜。刃脚下预先施打两圈粉喷桩，形成了1.2m厚的水泥土墙，阻止了井壁外土体形成的滑动面向井壁内滑动涌入。 ②控制沉井下沉的设计深度 沉井下沉至设计标高， 真空泵 刃脚底面之下土层仍为淤泥时，由下沉系数可知，淤泥土承载能力远远不够，将会下沉不止，现采取刃脚下预打粉喷桩地下连续墙，能够使沉井刃脚底面下沉至设计标高时，落在粉喷桩地下连续墙的桩顶面上，解决了控制沉井下沉深度问题。 当需要沉井下沉时，只需凿除桩头，沉井可凭自重克服土体的摩擦力和支撑力而下沉，一旦刃脚实至桩头即可止沉。根据以上推论，在沉井即将到达设计标高(以相差50～70cm为宜)时，预先在设计标高处将粉喷桩凿断，即可控制沉井准确就位、止沉。

 3.4开挖方法 表层灰土硬壳采用人工挖土，其余淤泥采用高压水枪冲泥，每50cm为一层，逐层冲剥下降。为防止支撑墙及地梁承受弯矩及汇水抽泥的需要，将土层冲成锅底型(中间低，四周高)。沉井刃脚下粉喷桩每暴露一层，先将内圈粉喷桩沿同标高挖断清出，外圈粉喷桩间隔挖断，以使剩余粉喷桩被沉井压碎，人工清除。

 3.5沉井纠偏 由于粉喷桩的导向作用，沉井一般不会有较大偏斜，为保证沉井就位误差在规范允许范围内，采取以下控制措施： a.随沉井下沉进行水平和中轴线监测，随时调整挖降粉喷桩的部位和高度。 b.沉井下沉接近到位时停止凿桩，挖土24h，观测沉降，若无明显沉降，可一次沉到位，不再采取其他止沉措施；若有明显沉降，则应查清原因，并增加止沉措施。 c.沉井接近就位时，若轴线位移或倾斜超过允许范围，螺杆泵可采用单侧压实填土、单侧挖土减载、配重等手段予以纠正。

          4沉井封底 沉井下沉完毕，其偏差应符合规范规定： ①轴线位移不大于井深1%； ②高程：+40mm，-60mm； ③倾斜度≯井深0.7%。 沉井就位2～3d后，刃脚已稳定落在粉喷桩顶，即可进行沉井封底。为避免地下水汇集形成较大浮力，顶裂封底混凝土，可在底板上均匀布置渗水井2～3个，井内埋渗水管，并以渗水管为中心向四周做辐射状碎石育沟引水，待泵池结构全部完成后封堵井口。

          5结论 在流塑状淤泥地层中实施沉井，由于地层承载能力差、摩擦系数小等特性，极易在沉井下沉过程中出现突沉、涌土，沉速过快和超沉位移及倾斜过大等现象，难以控制。本次沉井的设计和施工，充分利用了水泥土的特性，在沉井刃脚下预先打两排粉喷桩，在软土层中形成一道强度适宜的连续承载墙壁体，在沉井下沉过程中就像形成了一道可靠导轨。通过分节，分部位凿除粉喷桩桩头来调节支撑力，准确控制沉井姿态和下沉速度、深度。 通过前述施工过程可以看出，在相似土层的沉井设计和施工中，可以通过改变刃脚面积和粉喷桩长度、直径、强度(通过调整喷粉量实现)等诸多手段调整承载力，方法多样、工艺简便、成本低廉，是一种成功的施工工艺。

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译文：
           Technical Development Zone, Tianjin Jingji wastewater treatment plant investment climate for the Gai Shan Huan Bao Jian Li of infrastructure works, Qi Jian sewage pumping station to be called the salt in the Yuan Wang Zi's Haishui precipitation Ikegami, 2m under the surface for the pad fill Su Tu Zuo You, and then the next both years the flow of Silt deposition. Underground pumping station pumps pool depth 13m, was convex shape, as close to a substation and dehydration furnished room, mud cake stacked library, can not use cut and cover excavation or deep base to maintain the structure, designed as a polygon caisson structure. Silt in the stream to do monitoring of the sinking, apt Sudden, partial slip Shen, wells Chung, Chung more than mud and super Shen, caisson sinking is very difficult to control the speed and direction, which is not yet solved construction problems. The construction of the project in Rail 18 Board 3, according to design intent, use of pre-fight at the foot of Caisson Pile edge, forming together the piles of underground continuous wall, the wall caisson bearing strength of the formation of a certain delay and the support wall,Pneumatic and electric diaphragm pumps the caisson sinking in the mud in the process of a controlled process, to successfully solve the construction problem. A construction preparation 1.1 Excavation of fill, reduce the level of the primary sedimentation According to the geological site conditions caisson, caisson of the primary sedimentation stage to ensure the balance of sinking, the artificial fill excavation, the pre-and primary sedimentation caisson elevation Make 0.48m, this would create two advantages: its 1 As the primary settling sludge formation as its water content and bearing capacity of uniform, smooth easy to primary sedimentation; the other, sinking lower total subsidence 2.5m, 0.5m thick upper section III, from time as the caisson caisson construction, and in After sinking back pouring, so not only reduces the weight sinking (subsidence still meet weight requirements), but also shorten the sinking depth of Competition. 1.2 Pile Construction Play pile, caisson reinforced edge at the foot of soft clay, so that even the playing Caisson Pile in the formation of a continuous wall supporting the concrete under the sink. Pile Construction should note the following: ① to accurately position the pile outside the line tangent to outer edge and the wall, not exposed, so that when the caisson was sunk to the wall outside the cement soil compaction, loss of a supportive role. ② pile should reach the following Cutting Edge of Open Design Elevation 16m. ③ outer edge at the foot of pile and pile top end of range of spray cement volume 1.0m 10% (by weight of the pile) and the remaining pile of 7%. ④ inner pile of cement spray volume was 10%. ⑤ inside and outside the two rows of pile spacing 10cm, to ensure that excavation does not hurt when the inside of the pile lateral pile. 2 prefabricated caisson 2.1 The layout of the casting yard As the caisson wall shall be jointly build the pumping station pumps Pool Wall, so select the location for the sinking of prefabricated pool pump location. For ease of construction,Sweage pumps &Sludge pumps and consider pouring concrete caisson walls need support, site of soft soil surface with 15cm, 8% lime-soil compaction, do support the other end wall 10 of dirt platform. 2.2 Prefabricated way Caisson for the three original design, the surface filling excavation, the ground level just as the sinking top level II, III, therefore no longer regarded as caisson caisson structure, and two sunken well be back in place after the Afterwards hit. To reduce the weight of the first pouring of concrete to avoid sinking too much and cause uneven settlement of concrete cracking, the first section completed in two concrete pouring, pouring the first foot blade (high 1.0m), reached the design strength of concrete strength to be 70 % of time and then pouring the rest, and in turn the construction section II. 2 sinking concrete completion, a sink place. 2.3 foot blade model and support the bottom wall model According to the preliminary design, blade hit the foot of two rows of soft soil pile reinforcement. The original ground for the silt loam, allowable bearing capacity of 80kPa, DJM pile top 10% of the amount of cement, cement 7d unconfined compressive strength up to 600kPa, 28d compressive strength of up to 800 ~ 1000kPa. Caisson concrete total 444m3, by volume 2.5t/m3, the total weight of 3610t. Caisson blade foot area of 44.88m2. Thus, a single to edge the support of foot surface area, the bearing load is 804kPa. Calculated according to the above, and consider the error of Pile Construction, Pile is the top place Cutting Edge of Open, capacity can not meet the Requirements, and in the sinking of the prefabricated process, the edge of the side foot yet to carry, so additional support in the end wall supporting the end of mold, to share some of the weight of the caisson. 3 caisson sinking 3.1 preparations Caisson must meet the design strength of concrete strength can begin after the sinking, sinking the former make the following preparations: ① outside wall painted signs observed in the sinking level of observation points located corners, observing subsidence and balance; Office, located in the vertical axis, observation caisson displacement and balance. ② removed module. ③ excavation surface dust Support the bottom wall mold removal, the caisson sinking slightly, but then load-bearing foot blade side, sinking only Shen. 3.2 subsidence coefficient Subsidence factor formula: K = Q / (f · h · L)> 1 (1) Type in the  Q  - Weight gravity caisson f  - friction coefficient, the soft soil to take 9.8 ~ 11.76kN/m2 h  - the depth of maximum subsidence L  - caisson perimeter wall Friction coefficient is the maximum value of the soft soil, the general structure of self-gravity caisson sinking coefficient can still reach 3.0, not to mention among the mud, no lag Sinking. The problem is that demand will sink sinking depth of more than, control measures to be taken. 3.3 Pile sinking continuous wall control mechanism ①-oriented and the prevention of Sudden, Chung soil According to the initial design concept, the wall density range under foot blade, two rows of pre-play formation is to prevent the caisson pile reinforcement Sudden, rapid, and Chung soil settling velocity comprehensive measures, its mechanism is as follows: First, the formation of a cement DJM land wall, the caisson is a closed trapped in the sludge into the bearing walls, the sinking of the sinking process is the bearing wall of the excavation process This sinking of the sinking speed and extent of completely smooth excavation by the artificial methods to control the DJM. Second, in the soft clay in the implementation of the sinking, sinking in the process of excavation Chung-prone soil, ie the wall outside the flow of Silt well inside and outside the soil surface elevation due to larger instability caused by sliding , slide the foot to squeeze into the wellsMulti-stage pumps arc edge, so that only the well excavated soil elevation, but did not fall, but well outside the elevation of soil subsidence, easy to produce uneven earth pressure, resulting in caisson tilted. Edge at the foot of pre-injections twice pile, forming a 1.2m thick concrete walls to prevent the outer wall of sliding for the formation of soil within the sliding wall influx. ② control the design depth of caisson sinking Caisson sinking to the design elevation, blade under the soil surface feet still mud, by the subsidence factor known, silt soil bearing capacity is not enough, it will sink more than they are now taking pre-fight edge at the foot of diaphragm wall DJM can make the caisson sinking to design edge foot elevation when the plane landed in DJM pile top underground continuous wall surface, to solve the problem of controlling sinking depth. When the need for monitoring of the sinking, just chisel except trailer coupling, coin sinking weight to overcome the friction of soil and its support for the sinking, when foot blade can only live up to the trailer coupling Shen. Based on the above reasoning, the caisson will soon reach the design elevation (to a difference of 50 ~ 70cm is appropriate), the pre-elevation in the design department will DJM chisel off, you can accurately control the caisson in place, the only Shen. 3.4 Excavation Methods Hard surface dust artificial excavation, the remaining red mud sludge using high pressure water jets, each 50cm for the layer, layer peeling red drop. To prevent the supporting wall and beam bending moment and the exchange of water pumping to withstand the needs of mud, washed into the bottom of the pot to soil type (intermediate low, around high). Caisson Pile edge at the foot of each exposed layer, first inner ring along with the elevation Waduan and clear the Pile, Pile interval Waduan outer ring, so that the remaining crushed DJM is sinking, manual removal . 3.5 Sinking correction As the guiding role of Pile, Slurry pumpsCaisson generally will not have more skewed, as the caisson in place to ensure the specification allows the error within the following control measures: a. With the caisson sinking axis horizontal and monitoring, at any time digging down to adjust the location and height of DJM. b. stop when the caisson was sunk close to the chisel in place piles, excavation 24h, observation settlement, without significant settlement, can be a Shen place, not to take other measures to stop Shen; if significant settlement, the reasons should be investigated, and increased Shen measures only. c. sunk close to the place, if the axis of displacement or exceed the allowable range of tilt, can be used side compacted fill, excavation side load shedding, weight and other means to rectify the situation. 4 sinking back Caisson sinking is completed, the bias should be consistent with specification: ① well depth axis displacement of not more than 1%; ② Height: +40 mm,-60mm; ③ ≯ well depth gradient of 0.7%. Caisson in place 2 ~ 3d, the blade foot is stable roof fell on DJM can be sunk back. To avoid the formation of a larger collection of groundwater buoyancy, the top split the back cover of concrete, water leakage at the bottom evenly arranged on 2 to 3 wells, tube wells underground seepage, and in order to seepage around the tube for the center to make radial gravel ditch water sports until the pool structure, pump sealing wellhead after completion. 5 Conclusion In the current implementation of Silt formation caisson, due to poor ground bearing capacity, friction coefficient and other characteristics, can easily arise in the course of caisson sinking Sudden, Chung soil, Shen Shen and super fast speed and tilt displacementOther pumps is too large phenomena, difficult to control. The sinking of the design and construction, full use of the characteristics of cement in the open caisson pre-fight edge at the foot of two rows of pile, in the soft soil to form a continuous bearing wall strength appropriate body, in the monitoring of the sinking process formed in as a reliable guide. By section, sub-site to adjust the chisel addition to its support for DJM pile head, accurate control of posture and caisson sinking speed, depth. Through the above construction can be seen in similar design and construction of sinking soil, you can change the blade through the area and DJM foot length, diameter, strength (achieved by adjusting the spray volume), and many other means to adjust the carrying capacity, various methods, process simple, low cost, is a successful construction process.

原文来源：http://www.1lixinbeng.com/

2010-09-03 08:10

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