浅谈软土质条件下管桩施工的技术措施文献翻译.doc

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1、 浅谈软土质条件下管桩施工的技术措施摘 要：高强度预应力混凝土管桩（PHC）以其桩身混凝土强度高，适应性广，耐冲击性能好，穿透力强，具有承载力高，抗弯抗裂性能好，施工快捷、方便，质量稳定可靠，耐久性好等优点，而被广泛应用于高层建筑基础。本文探讨了管桩施工中的技术措施。 关键词：管桩施工 技术操作 桩基处理 引言：目前，高强度预应力混凝土管桩已被推广应用于房屋建筑和桥梁、码头等工程中。高强度预应力混凝土管桩（PHC）以其桩身混凝土强度高，适应性广，耐冲击性能好，穿透力强，具有承载力高，抗弯抗裂性能好，施工快捷、方便，质量稳定可靠，耐久性好等优点，而被广泛应用于高层建筑基础。管桩属挤土桩，施工速度

2、快，软土地区大量施打后，土体超孔隙水压力较大，开挖时如未进行有效控制，将会引起偏桩、断桩等的质量事故发生。因此，必须针对软土地质特点，在管桩施工、土方开挖方面采取有效技术措施，保证桩基质量和挖土进度。 一 、工艺原理 软土具有天然含水量高、天然孔隙比大、压缩性高、抗剪强度低、固结系数小、固结时间长、灵敏度高、扰动性大、透水性差、土层层状分布复杂、各层之间物理力学性质相差较大，竖向、水平方向的挤压均容易产生变形。同时，由于其含水量大，透水性差，受到挤压容易产生较大的超孔隙水压力，并且难以在短时间内消散。其固结系数小、固结时间长的特点又使其土体受到扰动后难以迅速恢复。 高强度预应力混凝土管桩为挤土

3、桩型，施工速度比较快，由此造成施工区域内的挤土效应。管桩自身抗压强度较高，但抗弯强度较低，不同土层间水平力的作用容易引起桩身断裂。因此，软土地区管桩的施工对土方开挖有着极大的影响。挖土的部署以及采取的技术措施，都应围绕“避免土体应力过快释放，避免土体施工荷载过大，合理控制土体位移与应力释放”这样的原则进行。 二 、操作要点 1挖土部署 1.1软土地区预应力管桩基础置换率一般在4左右，土方开挖前应切实了解以下情况，据此编制挖土施工方案，明确挖土部署和技术措施：a场地地质情况，b周边邻近建（构）筑物及需保护管线情况，c围护设计，d桩长、桩间距、置换率等桩基设计情况，e打桩顺序、压桩记录等桩基施工情

4、况。1.2土方开挖宜分皮进行，每皮厚度应控制在2m左右（土钉墙围护结构基坑根据土钉墙分层厚度控制），上皮挖除后再开挖下皮。坑内分级挖土留设台阶时，台阶宽度与台阶下挖土深度之比应在5以上。坑内土方坡道设置应避开塘泥等软弱区块，坡道两侧土体放坡系数在1:1.5以内应考虑喷射砼护坡，土质特别差的应加设6.5200200钢筋网片。应尽量避免工程桩位于土方坡道两侧斜坡上，如桩基较密无法避免应考虑灌芯或喷锚加固，或改用钢结构栈桥作为土方坡道。1.3禁止边压桩边开挖，开挖与桩基全部完成间隔时间应在15天以上（钻打法10天以上）。1.4承台、地梁位置如土质仍较差，宜采用人工挖土，避免挖机荷载及震动对土体的影响

5、。1.5截桩安排应提前考虑。开挖前，应对露出表面的桩先行截除；开挖过程中，应根据挖土流程分段截除。1.6挖机、车辆选择应尽量避免采用大型设备。应尽量选择小挖机，如PC100以下。坑内运土车辆避免使用10t大车。 2挖土技术措施 2.1挖土应逐层均匀进行，桩两侧土体高差不得大于1m。2.2禁止挖机碰撞桩身。机械开挖至桩顶30cm时桩两侧1m内土体采用人工开挖。2.3挖机、土方车辆行走路线及两侧工程桩应视具体情况采取喷锚、铺路基箱、填塘渣、换土等加固措施。2.4坡区及坡顶内外侧3米范围内，管桩内放入6米长614钢筋笼，箍筋为6300，钢筋笼顶标高位于桩顶以下1米处，在钢筋笼范围内灌入C20微膨胀混

6、凝土。2.5在场地软硬土层交界处标高上下2m范围内，也可采取管桩内加筋灌砼的措施。2.6为减少静力压桩的挤土效应对土方开挖的影响，可选用以下措施：a设置袋装砂井或塑料排水板，以消除部分超孔隙水压力，减少挤土现象。袋装砂井直径一般为7080mm，间距l1.5m，深度1012m。塑料排水板的深度、间距与袋装砂井相同。b应力释放孔，直径400，均匀布置，深度10m左右或为桩长的0.8倍。 3桩基问题的处理 3.1开挖后如面临桩偏位、倾斜问题，可根据动测情况判定桩身质量，分别加以处理。如果桩身无断裂，可采用千斤顶推（拉）并灌芯的方法进行处理。千斤顶推（拉）力不得大于单桩水平承载力。如果桩身有裂缝，可采

7、用接桩、补锚桩的方法进行处理。如果桩身裂缝较深，且桩倾斜较大，沉井接桩也无法实施。同时，锚桩长度25m承载力不够。此时，可考虑底板相应位置留孔，待底板完成后，打设钻孔桩。 3.2管桩打入时的挤土作用会使附近已打好的桩及原有建筑物或周围其他设施产生破坏。挤土程度的大小除了与桩的截面积及某处与桩间的距离有关外，还与桩长、桩型、打桩速率及打桩顺序有较大关系。 3.3考虑到管桩施工产生的挤土效应对土方开挖情况的影响较大，为做好预控，提出几点对管桩施工技术措施建议： 3.3.1桩机自重与场地软弱土层承载力以ZYJ500液压静力压桩机为例，桩机自重506T，平面尺寸12m8.4m，平均压力约5T/m2。如

8、表层或接近表层的土质物理力学性能较差，桩机行走和施打时容易沉陷，不仅不利于施工，而且，表层的深陷导致深层土体的位移、周边土体的隆起，容易引起管桩偏移、倾斜，甚至桩身断裂。因此，在桩机选型和确定打桩路线时，应考虑到表层土地基承载力和软弱下卧层地基沉降问题。采用表层铺设塘渣、枕木、路基箱等方式加固地基，分散桩机荷载。3.3.2减小挤土效应技术措施a据工程经验，白天打桩引起的土体位移增加值会在夜晚停歇时有约25的回落，如夜晚继续打桩，挤土效应引起的土体水平、竖向位移会一直增加不回落。因此，应避免24小时不停歇的打桩安排。b桩基置换率大于4时可采用预钻孔沉桩，孔径约比桩径小50100mm，深度视桩距和

9、土的密实度、渗透性而定，深度宜为桩长的1/31/2（不超过12m），施工时应随钻随打。c工程周边、分期施工的区块周边可考虑应力释放孔、隔震沟、砂井等措施。3.3.3沉桩线路的选定 沉桩线路应尽量采取“走长线蛇形线路”，在邻近建筑物或需保护管线区域应考虑“由近及远”的施工方向。由此，可以给超孔隙水压力消散提供尽量长的时间，避免其累积叠加，减小挤土影响。3.3.4压桩速度控制沉桩速度一般控制在lm/min左右为宜，使各层土体能正确反映其抗剪能力。当地基表层中存在大块石头等障碍物时，要避免压偏。 3.4施工现场应备有应急措施的砂袋、钢管、钢筋、水泥、注浆机、发电机等施工工具。地面出现裂缝采取灌浆修补

10、，防止地表水渗入，并及时组织项目部和有关专家查明裂缝产生原因。当出现边坡水平位移超过警戒值，应立即停止相应范围内的土方开挖，必要时采取回填或设置临时支撑松木桩钢板桩加固，以控制变形发展。 综上所述，软弱土地质条件下，土方开挖过程中施工部署和技术措施的合理安排，以及管桩施工减小挤土效应的有效控制，可以有效地避免土体位移引起的管桩偏移、断桩、周边道路、建筑物沉降等问题，社会效益显著。同时，减少桩基问题的处理也减少了费用的支出。参考文献1德波尔,“岩土力学理论-建筑”英国太沙基工业出版社，pp175-1862约翰威利父子公司，“基础工程建设指南”美国工程建设出版社，1989年3马丹属，阿罗拉,“项目

11、管理：一步超越”英国土木建筑出版社，1996年10月，pp67 - 684史蒂夫伯德特“新兴角色管理inCilvil工程” 美国国际建筑出版社，1996年7月，pp69 - 73文章出处：中国学术研究2011年第五期中国学术研究协会，中国教育学会课程研究会。Soft soil conditions of the technical measures pipe constructionRalph B.PeckAbstract: The high-strength prestressed concrete pile (PHC) with its high strength concrete pil

12、e, wide adaptability and good impact resistance, penetration, with high capacity, flexural cracking performance, construction of fast, convenient stable and reliable quality, durability, etc., and is widely used in high-rise building foundation. This paper discusses the technical measures in the pip

13、e construction.Key words: pile construction; technical operations; pile treatmentIntroduction：Currently, high-strength prestressed concrete pipe has been applied to housing construction and bridges, piers and other projects. High-strength prestressed concrete pipe (PHC) with its high strength concre

14、te pile, wide adaptability, good impact resistance, penetration, with high capacity, flexural cracking good performance, construction speed, convenience, quality reliability, durability and good, and is widely used in high-rise building foundation. Pipe is soil compaction piles, construction speed,

15、a large number of injections in soft soil area, the soil pore water pressure, excavation without effective control, will cause partial piles, such as the quality of the broken pile accident . Therefore, we must for the quality characteristics of soft soil in the pipe construction, earth excavation t

16、echniques and adopt effective measures to guarantee the progress of pile foundation and excavation.Process Principle High water content soft soil has a natural, natural void ratio, high compressibility, low shear strength, coefficient of consolidation, consolidation for a long time, high sensitivity

17、, disturbance of the large, poor permeability, complex distribution of soil layer, the physical and mechanical properties between the layers of difference between the larger, vertical, horizontal squeeze all prone to deformation.Also, because of its large water content, poor permeability, squeezed e

18、asily have a greater excess pore water pressure, and difficult to disperse in a short time. The coefficient of consolidation, consolidation characteristics of a long time and disturbed the soil after it difficult to quickly recover.High-strength prestressed concrete pipe pile to soil compaction, con

19、struction, faster, and the resulting soil compaction within the construction area effect. Pile itself high compressive strength, flexural strength but low levels of power between the different role of soil prone to pile fracture. Therefore, the construction of soft soil on the earth excavation pipe

20、has a great impact. Excavation of the deployment and technical measures, should be around to avoid excessive soil stress release, to avoid excessive construction load of soil, reasonable control of soil displacement and stress release, such principles.Operating Points1.excavators deployed1.1The basi

21、s of soft soil prestressed concrete pipe replacement rate is generally around 4%, before excavation practical understanding of the following circumstances under which the preparation of excavation construction plan, deploy, and technical measures clearly digging: a site geological conditions, b arou

22、nd adjacent building (structure) and the need to protect the pipeline case, c enclosure design, d pile length, pile spacing, pile foundation design exchange rate situation, e piling order, piling records and other foundation construction situation. 1.2Excavation should be carried out sub-skin, skin

23、thickness should be controlled in each of about 2m (soil nailing pit envelope layer under the soil nail wall thickness control), after the excavation of excavation under the skin epithelium. Pit excavation leaving in graded steps, step width and the depth of excavation over the next steps should be

24、5 or more. Earth pit should be set to avoid the pond scum ramp so weak block, put the soil on both sides of the ramp slope coefficient of less than 1:1.5 should be considered in the sprayed concrete slope protection, soil particularly bad should be added 6.5 200 200 steel mesh. Should be avoided in

25、the earth piles on both sides of the ramp slope, such as dense pile can not be avoided should be considered or gunite reinforced grouted, or switch to steel bridge as the earthwork ramp. 1.3Edge against edge piling excavation, excavation and pile interval should be completed in 15 days or more (more

26、 than 10 days drilling play). 1.4Caps, ground beam position if the soil is still poor, the appropriate use of artificial excavation, avoid digging machine loading and vibration effects on the soil.1.5Cut pile arrangement should think ahead. Excavation before exposing the surface of the pile should b

27、e cut first; excavation process, the process should be based on sub-excavation cut off. 1.6Digging machines, vehicles should be chosen to avoid using large equipment. Should try to choose a small digging machines, such as PC100 below. Vehicles to avoid the use of earth pit 10t cart.2. Technical meas

28、ures digging2.1Excavation should be carried out layer by layer evenly, on both sides of the soil pile height shall not exceed 1m. 2.2Collision against digging machine shaft. Mechanical excavation to the top of the pile 1m 30cm on both sides of the pile with the soil excavated. 2.3Digging machines, m

29、oving vehicles, routes and both sides of the pile, as the case should be taken to spray anchor, paving the way for the base box, pond residue, such as for soil reinforcement. 2.4Top of the hill slope areas and within 3 meters inside and outside, into the 6-meter long pipe 614 within the reinforcemen

30、t cage, stirrup to 6 300, top elevation of the reinforcement cage is located at 1 m below top of the pile, the reinforcement cage within the irrigation C20 micro-expansion into the concrete. 2.5Soft and hard layer at the junction of the venue up and down elevation range of 2m, but also take concrete

31、 irrigation pipe within the reinforcement measures. 2.6To reduce static piling of the squeezing effect on the impact of excavation, the choice of the following measures: a set of sand bags or plastic drain well to remove part of the excess pore water pressure, reduce soil compaction phenomenon. Sand

32、 Wick diameter is generally 70 80mm, spacing l 1.5m, the depth of 10 12m. Plastic drain depth, spacing and the same Sand Wick. b stress release holes, diameter of 400, uniformly arranged around the depth of 10m or 0.8 times the pile length.3.Handling of pile3.1Pile after excavation, such as face dev

33、iation, skew problems, according to pile dynamic testing conditions to determine the quality of, respectively, to be addressed. If the pile without breaking, jack can be used to push (pull) and the core of the method of irrigation treatment. Jack push (pull) force shall not be greater than the horiz

34、ontal bearing capacity of single pile. If there are cracks in the pile, can be connected piles, anchor piles make way for processing. If deep cracks in the pile, and pile inclination larger caisson pile can not be implemented then. Meanwhile, the length of 25m anchor pile bearing capacity is not eno

35、ugh. At this point, consider the corresponding bottom hole location to stay until the floor is completed, set to play bored piles.3.2Pile into the soil compaction when the role will have to play well near the original building or the surrounding piles and other facilities have destroyed. In addition

36、 to the size of soil compaction and the degree of cross-sectional area and somewhere in the pile and the distance between piles, but also with the pile length, pile, piling rate and more related to the piling sequence.3.3Taking into account the pipe construction squeezing effect generated by the sit

37、uation on the impact of large earth excavation, in order to make pre-control, to make a few suggestions on technical measures pipe construction:3.3.1Pile weight bearing capacity of soft soil with the site to ZYJ-500 as an example of hydraulic static pile driver, pile driver weight 506T, plane size 1

38、2m 8.4m, the average pressure of about 5T/m2. Surface or near the surface, such as physical and mechanical properties of soil is poor, when the pile driver is easy walking and injections of settlement, is not conducive to construction, and that led to the deep surface of the deep soil displacement,

39、uplift of the surrounding soil, easily lead pipe pile offset, tilt, or pile fracture. Therefore, in the pile driver, route selection and determine the piling should take into account the land surface of the base load capacity and weak underlying layer of foundation settlement problems. Pond by layin

40、g the surface residue, ties, roadbed foundation reinforcement boxes, etc., scattered pile driver load. 3.3.2Effect of technical measures to reduce soil compaction, according to engineering experience a day and piling soil displacement caused by the added value will stop at night when about 25% of th

41、e decline, such as the night continued piling, compacting effect of soil caused by the level of vertical will always increase in displacement does not come down. Therefore, we should avoid the 24-hour non-stop piling arrangements. b pile replacement rate of more than 4% can be pre-bored piling, pile

42、 diameter smaller than the pore size of about 50 100mm, depth of soil as the pile spacing and density, permeability, depending on the depth of the pile length of 1 should be / 3 to 1 / 2 (less than 12m), construction should be drilling with the fight. c projects around, stage construction of the blo

43、cks around the hole could be considered stress release, isolation trenches, sand wells and other measures.3.3.3Pile pile selected line route should be taken to take the long snake-like lines in the adjacent building or area should consider the need to protect the pipeline, from near and far, the con

44、struction of direction. As a result, can dissipate excess pore water pressure to provide as long as possible, to avoid the accumulation of superimposed, reducing the squeezing effect. 3.3.4Pile piling speed control speed control in general lm / min is appropriate, to properly reflect the physical la

45、yers of soil shear strength. Exist in the local base surface obstructions such as large stones, it is necessary to avoid the pressure side.3.4The construction site should be equipped with emergency measures of sand bags, steel, steel, cement, grouting machines, generators and other construction tool

46、s. Grouting to repair cracks in the ground to prevent surface water infiltration, and promptly organize the project department and experts to identify cause of the cracks. When the horizontal displacement of the slope above the warning value, should immediately stop the appropriate range of earth ex

47、cavation, backfill, or, when necessary, temporary steel sheet piles of pine pile support to control the deformation development. In summary, weak geological condition, the process of construction of earth excavation and technical measures to deploy a reasonable arrangement, and the pipe construction

48、 reduces the effective control of squeezing effect, can effectively avoid the pile soil displacement caused by partial shift, broken pile, the surrounding roads, building settlement and other issues, social benefits. At the same time, reduce the piles handling also reduces expenses.References1De Boer,The Orijins of the Theory of Consolidation:the Terzaghi-Fillunger dispute,Geotechnique 46,No2,pp175-1862John Wiley&Sons,Inc.,Encyclopedia of architecuure,Design,Engineering&Construction,19893Madan L.Arora,“Project Management:One Step Beyond”,Civil Engineering,October 1996,pp67-684Steve Burdett