土建外文翻译5.docx

附录 a 1.1 桩基础桩基础是结构的一部分，它用来将上部的荷载转承给地表以下一定深度的持力层。基础的主要组成部分是柱顶和柱。桩长且细，它将荷载传给深层土或是高承载力的岩石，以弊开浅层底承载力的土。常用的桩基础材料就是木材，钢和混凝土。桩由这些材料制成后被钻入地下并与桩帽相连。根据土壤类型，桩的材料，荷载传递特征将桩相应的分类。在以下章节中我们将学习桩的分类，作用和桩的利弊。1.2 发展情况桩基础作为承载和传递力的方法已应用多年。在文明的早期，从通信，防御或战略的观点出发，村庄和城镇被建立在河湖附近。因此以某种打桩的形式来加强地表的承载力是很重要的。木材桩可手工压入地下，或是挖一个坑将桩送入后，填入沙石。1740年christoffoer polhem发明了与当今很相似的钻桩设备。钢桩在1800年开始使用，混凝土桩1900年开始使用。工业革命中，发明了蒸汽机和柴油机，这给钻桩方法带来了重大变化。最近，随着对住房和建筑需要的迫切增长，当局和一些建筑机构已开始在一些不良土壤上开拓工地。这已引起了桩及桩基方法的进步和改良。目前已有许多打桩的先进技术。1.3 桩基的作用和其它类型的基础一样，桩基础的目的是：将荷载传到坚固的地基土上，以承受垂直，水平和上顶的力。如果下部土没有足够的承载力，结构可以建立在桩上。如故调查结果显示表层土不稳定且很薄或者设计的其它方法不可取时，可以考虑桩基础。另外，与其它地基处理的方法相比，桩基础更加经济。当建筑物荷载很大时，浅层土的承载力很可能答不到要求，此时地基应建立在桩基础上。桩基础也可用于一般的地面条件来抵抗水平荷载。桩是在水上，例如码头和桥梁上应用的一种传统的基础方法。1.4 桩基础的分类1.4.1 按承载性和桩的使用功能进行分类端承桩，摩擦桩，端承桩和摩擦桩的结合。1.4.2 端承桩桩将荷载到建筑基础以下一定深度处的坚实土层之上，它的大部分承载力来自桩端（见图1.1）。桩作为一根柱子而被设立。即使在承载力较弱的土壤中，桩基础也不会因为折断而损坏，并且这种效果只能在桩无撑的情况下考虑，例如，水或空气。荷载由摩擦或桩端传递。但有时，桩周围的土黏着在桩的表面造成“消极的表层摩擦”。有时，这会对桩的承载能力造成很大的影响。消极的表层摩擦是由于地下排水和土壤加固造成的。桩的深度由调查结果和室内土工实验决定。1.4.3 摩擦桩和端承桩承载力主要来自于桩轴与土的接触与摩擦。（见图1.2）figure 1-1 end bearing piles figure 1-2 friction or cohesion pile 1.4.4 端承桩这些桩将大部分荷载通过表层摩擦传给土壤。打这种桩每组中的桩相距很近，大大减小了每组土壤的多孔性和压缩性。因此，这种桩有叫做击实桩。在将桩打入土壤的过程中，对土壤造成影响，结果土壤减小了强度。因此桩不能精确的转递一定数量的荷载而必须在打入之后才能知道。通常土壤在打桩后的三到五个月可以恢复一部分承载力。1.4.5 摩擦桩这种桩也是通过表层摩擦将荷载传递给土壤。在打这种桩的过程一点也没有使土壤压缩。这种桩通常又叫做悬浮桩基础。1.4.6 摩擦和端承的符合型桩基础当桩的承载力底时，例如黏土中，需要将桩的底部进行扩展。桩应钻入下部材料足够深以获得足够的摩擦力。底部桩承载力的进一步不同是桩扩大的支撑面积。这是通过直接向坚固地层之上的弱土层上灌入混凝土来扩大地基。一个类似的效果是在低部用一种特殊的工具将桩扩大成锥。桩是由一个具高强度的钟型提供，可用做锥型桩。（见图1-3）figure 1-3 under-reamed base enlargement to a bore-and-cast-in-situ pile 1.4.7 按桩身材料分类1) 木桩； 2) 混凝土桩； 3) 钢桩； 4) 混合材料桩。1.4.8 木桩 在一些木材丰富的地区，木桩使最早期的记录上就有使用并沿用至今。木材最适合于长的内聚力桩和堤坝之下。木材的材料应该很好，没有被虫子磕过。对于少于14米长的木材，它的直径应大于150mm。如果木材长度超过18米，直径是125mm，那是可以选择的。桩以合适的角度钻入地下是很必要的，并且它不能被钻入坚实的土地中。因为这样很容易损坏桩。使木材保持在地下水面之下，将会防止木材腐烂。为了保护和加强桩底，木材的低部应被覆盖。压力防腐剂是保护木材常用的一种方法。1.4.9 混凝土桩预制或已制混凝土桩。通常为正方形（见图1-4b），三角形，圆形或多边形，它们的长度很短，在3米到13米之间有一米的间隔。它们是预先做好的，因此能被容易的组合在一起，以达到要求的深度（见图1-4 a）。这不会减少设计承载力。桩内的加固是必要的，以帮助承受手工和机器的压力。预应力混凝土桩也被广泛应用，并比传统的桩更受欢迎，因为它需要更少的加固。图1-4 混凝土桩.b预制方型混凝土桩赫拉克勒斯类型基础连接（图1-5）能容易准确的组成桩，并能在现场很快安全的组装。它们由高级钢制成准确的尺寸。图 1-5 桩连接的种类1.4.10 混凝土桩的制作英国使用的两种主要类型是：所谓的壳桩：它被提前制作，由钢筋混凝土加固，管长大概一米，在混凝土布置在管壁上后，混凝土有钢管中心向下灌。当管壁进入一定深度时，中心管撤出，管中心再次灌人混凝土加固。管径变化范围从325到600mm。现场灌注桩：钢管被垂直竖立在它将要打入的地方，在大约一米深处石渣被填在管的末端。用重为1500到4000kg 重锤，压实土壤，然后将钢管插入土壤。当到达要求的深度时，管被轻轻提起，此时内聚力破坏。这时加入干燥的混凝土并用锤击直到形成扩大头基础。在某些地方继续加固，加入更多的混凝土并重击，直到桩的顶部到达水平地表。1.4.11 钢桩钢桩：（图1.4）钢桩适合在较大的深度。由于钢本身的强度，钢桩有相对少的接触断面，更易打入坚实的土中。它们更易切断或焊接。如果钢桩打入ph值低的土壤中，就有腐蚀的危险，但这种危险并不象人们想象的那么大。为了长期应用，可在桩表涂沥青或采用负极保护。在设计中通过简单计算钢桩断面面积，来考虑一定的腐蚀是正常的。用这种方法可将腐蚀时间延长到50年。通常腐蚀速度是0.2-0.5mm/年，在设计中，可看作1mm/年。a) x- cross-section b) h - cross-section c) steel pipe 图1-6钢桩的连接1.4.12 组合材料桩同一桩中使用不同材料的结合。如前所述，建立在地下水之上的木桩的某些部分，容易遭到虫子的破坏并易腐烂。为了避免这些，钢筋或混凝土基础在地下水位线之上，木基础放在地下水位线之下（见图1-7）1.4.13 按桩对土的作用进行分类简单的打入桩和螺旋钻孔桩经常被使用。1.4.14 打入桩打入桩又认为是位移桩。在将桩打入地下的过程中，当桩轴进入地面时，土程辐射型移走。在垂直方向也可能有土的部分运动。图 1-7 防止木基础侵蚀: a)在水位线上预制混凝土b) 在水位线下扩展桩帽 1.4.15 螺旋钻孔桩螺旋钻孔桩（位移桩）通常认为是无排水桩，空隙是在桩形成前挖掘或钻孔过程中形成。桩可以在空隙中切割混凝土形成。一些土如硬黏土用这种方法顺应桩的形成，因为打孔墙除了在地表不要求临时的支撑。在不稳定的地表，如石渣地表需要泥浆临时支撑。框架也许是可选择对象中应用很久的，但当进入洞时，打入桩更有优势。另一种不同的非位移桩也是很重要的，那就是将水泥或混凝土旋转的钻入土中，并因此形成了一个土柱。1.5 桩分类的目的为对桩的分类有快速的理解，可使用桩类型等级表示方法。不同材料桩的优缺点在1.6部分。1.6 不同材料桩的优缺点木桩：桩制作简易；木材原料充足价钱相对便宜；每部分连接在一起且很长也易搬运；桩不能在地下水位之上，承载力有一定的限制；用块巨砾按桩时容易损坏；桩很难结合且易受到盐水中钻孔虫的袭击；预制混凝土桩（加强的）提前压制的混凝土桩（打入的）受地下水影响的条件；非腐蚀性的易结合，相对便宜；在打入前混凝土的质量能被测定；紧贴地表的土，例如，软黏土，泥沙和煤泥桩的材料可在打入前被检测；如受地面冻涨影响可再次打入，这种建筑方法可不受地下水的影响；可被打入很长的距离。可在地下水位之上，例如，海洋结构的水；增加颗粒状土层的相对密度；相对较难切开；在打入时受到位移冻涨和土壤结构的影响；打入过程中易损坏。可采用置换桩；有时会产生噪声和振动问题；桩径很大时不能打入或受到净空高度的限制；打入或就地浇铸混凝土桩；永久性打入（地表左侧打入）；临时打入或不打入（打入检索）；在打入前可被检测，容易切割或延长到要求的深度；相对低廉；噪音小；桩可在挖掘前浇铸；桩长可随时调整；扩大基底可增加颗粒状地层的相对密度增加地层的承载力；再次加强不由手工或钻入压力的控制；以封闭的末端打入排除gw的影响；相临表层土的冻涨，它能使桩表面的不利的摩擦力增大和进一步发展；附近的护墙的位移。使提前打入的桩上升，在那里脚趾处的力可足够抵抗向上的惟一位移；对于没有加强桩的拉伸损坏或是包含绿色混凝土的桩，脚趾处的力足够抵抗向上的位移；损坏的桩包括未打入的或由于土壤的水平力作用在薄层处打入的绿混凝土在柱顶损坏。混凝土不能在桩完成后检测。当管子撤走后，如果自流水流出管子，混凝土的强度会降低；弱钢部分或预制混凝土会由于猛烈的打入而损坏；长度上的限制是由于力撤出的情况，振动和地表位移也许会损坏相临建筑；净空高度限制的地方不能打入相对昂贵耗时。不能在建筑开始时就立刻使用长度受限现场打入和浇铸（无位移桩）为适合不同的地表条件，长度可随时改变；孔中的土可被检测，如果有必要，可取样做室内实验；可安装很大的直径；黏性土中桩端可扩大到两个到三个直径大；桩的材料不由手工或打入条件决定；可打入很长的距离；可在没有噪音和振动的条件下打桩；可在很低的净空高度下打桩；无地表冻涨的风险；打入地下时可能会折断；混凝土没有放在理想的位置，不能及时检测；在自溢压力下，水会流出，冲刷水泥；没有特殊技术的非粘性材料中不能采用扩大基础；不能延伸到地下水面之上，特别是在河流和海洋条件下；钻孔的方法是挖去松散的沙和不良的土壤，在基底充填水泥很经济的达到承载力；桩下沉会导致地面内聚力的减小，导致相临建筑物倒塌；钢桩（滚动钢部分）：桩很容易处理，能容易的切割到理想的长度；能够打入密实的土层中。在打入过程中土壤的水平位移很小（钢部分h或桩部分i），能被相对容易的切割；可被用力打入很大长度；可有承受的承载力；可成功的打入倾斜的岩石中；如果有地表位移干扰，桩的小位移是很有用的；桩会受到腐蚀；在打入过程中容易偏离；相对昂贵。动力学方法：常用的估计打入桩的承载力的方法是使用能量公式或动力公式。所有这些公式都与桩的最大承载力有关（重锤落下一次时的垂向运动）并假设抵抗力与静荷载下的桩的承载力相等，它们代表桩打入最后阶段的最理想的锤击运动。通常，桩能量公式或者用于估计安全工作的承载力或者用来计算正常工作条件下的工作量。正常工作的承载力由公式计算出最大的力并由一些适当的安全因素决定。然而，动力公式在一些桩设计应用时，要求很严格。动力公式不考虑土的物理性质。这在动力公式的应用时就会导致演算结果的错误，因为它们代表的是打桩时土的情况。它们没有考虑在长时间承受荷载时土的条件，重复加固，不良的表层摩擦和成组的作用。附录 b 1.1 pile foundationspile foundations 11 are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. the main components of the foundation are the pile cap and the piles. piles are long and slender members which transfer the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity the main types of materials used for piles are wood, steel and concrete. piles made from these materials are driven, drilled or jacked into the ground and connected to pile caps. depending upon type of soil, pile material and load transmitting characteristic piles are classified accordingly. in the following chapter we learn about, classifications, functions and pros and cons of piles.1.2 historicalin the early days of civilisation2, from the communication, defence or strategic point of view villages and towns were situated near to rivers and lakes. it was therefore important to strengthen the bearing ground with some form of piling.timber piles were driven in to the ground by hand or holes were dug and filled with sand and stones.in 1740 christoffoer polhem invented pile driving equipment which resembled to days pile driving mechanism. steel piles have been used since 1800 and concrete piles since about 1900.the industrial revolution brought about important changes to pile driving system through the invention of steam and diesel driven machines.more recently, the growing need for housing and construction has forced authorities and development agencies to exploit lands with poor soil characteristics. this has led to the development and improved piles and pile driving systems. today there are many advanced techniques of pile installation.1.3 function of pilesas with other types of foundations, the purpose of a pile foundations is:to transmit a foundation load to a solid ground to resist vertical, lateral and uplift load.a structure can be founded on piles if the soil immediately beneath its base does not have adequate bearing capacity. if the results of site investigation show that the shallow soil is unstable and weak or if the magnitude of the estimated settlement is not acceptable a pile foundation may become considered. further, a cost estimate may indicate that a pile foundation may be cheaper than any other compared ground improvement costs.in the cases of heavy constructions, it is likely that the bearing capacity of the shallow soil will not be satisfactory, and the construction should be built on pile foundations. piles can also be used in normal ground conditions to resist horizontal loads. piles are a convenient method of foundation for works over water, such as jetties or bridge piers.1.4 classification of piles1.4.1 classification of pile with respect to load transmission and functional behaviourend bearing piles (point bearing piles)friction piles (cohesion piles )combination of friction and cohesion piles1.4.2 end bearing pilesthese piles transfer their load on to a firm stratum located at a considerable depth below the base of the structure and they derive most of their carrying capacity from the penetration resistance of the soil at the toe of the pile (see figure 1.1). the pile behaves as an ordinary column and should be designed as such. even in weak soil a pile will not fail by buckling and this effect need only be considered if part of the pile is unsupported, i.e. if it is in either air or water. load is transmitted to the soil through friction or cohesion. but sometimes, the soil surrounding the pile may adhere to the surface of the pile and causes negative skin friction on the pile. this, sometimes have considerable effect on the capacity of the pile. negative skin friction is caused by the drainage of the ground water and consolidation of the soil. the founding depth of the pile is influenced by the results of the site investigate on and soil test.1.4.3 friction or cohesion pilescarrying capacity is derived mainly from the adhesion or friction of the soil in contact with the shaft of the pile (see fig 1.2).figure 1-1 end bearing piles figure 1-2 friction or cohesion pile 1.4.4 cohesion pilesthese piles transmit most of their load to the soil through skin friction. this process of driving such piles close to each other in groups greatly reduces the porosity and compressibility of the soil within and around the groups. therefore piles of this category are some times called compaction piles. during the process of driving the pile into the ground, the soil becomes moulded and, as a result loses some of its strength. therefore the pile is not able to transfer the exact amount of load which it is intended to immediately after it has been driven. usually, the soil regains some of its strength three to five months after it has been driven.1.4.5 friction pilesthese piles also transfer their load to the ground through skin friction. the process of driving such piles does not compact the soil appreciably. these types of pile foundations are commonly known as floating pile foundations.1.4.6 combination of friction piles and cohesion pilesan extension of the end bearing pile when the bearing stratum is not hard, such as a firm clay. the pile is driven far enough into the lower material to develop adequate frictional resistance. a farther variation of the end bearing pile is piles with enlarged bearing areas. this is achieved by forcing a bulb of concrete into the soft stratum immediately above the firm layer to give an enlarged base. a similar effect is produced with bored piles by forming a large cone or bell at the bottom with a special reaming tool. bored piles which are provided with a bell have a high tensile strength and can be used as tension piles (see fig.1-3) figure 1-3 under-reamed base enlargement to a bore-and-cast-in-situ pile 1.4.7 classification of pile with respect to type of material timber concrete steel composite piles12 1.4.8 timber pilesused from earliest record time and still used for permanent works in regions where timber is plentiful. timber is most suitable for long cohesion piling and piling beneath embankments. the timber should be in a good condition and should not have been attacked by insects. for timber piles of length less than 14 meters, the diameter of the tip should be greater than 150 mm. if the length is greater than 18 meters a tip with a diameter of 125 mm is acceptable. it is essential that the timber is driven in the right direction and should not be driven into firm ground. as this can easily damage the pile. keeping the timber below the ground water level will protect the timber against decay and putrefaction. to protect and strengthen the tip of the pile, timber piles can be provided with toe cover. pressure creosoting is the usual method of protecting timber piles.1.4.9 concrete pilepre cast concrete piles or pre fabricated concrete piles : usually of square (see fig 1-4 b), triangle, circle or octagonal section, they are produced in short length in one metre intervals between 3 and 13 meters. they are pre-caste so that they can be easily connected together in order to reach to the required length (fig 1-4 a) . this will not decrease the design load capacity. reinforcement is necessary within the pile to help withstand both handling and driving stresses. pre stressed concrete piles are also used and are becoming more popular than the ordinary pre cast as less reinforcement is required . figure 1-4 a) concrete pile connecting detail. b) squared pre-cast concert pile the hercules type of pile joint (figure 1-5) is easily and accurately cast into the pile and is quickly and safely joined on site. they are made to accurate dimensional tolerances from high grade steels.figure 1-5 hercules type of pile joint 1.4.10 driven and cast in place concrete pilestwo of the main types used in the uk are: wests shell pile : pre cast, reinforced concrete tubes, about 1 m long, are threaded on to a steel mandrel and driven into the ground after a concrete shoe has been placed at the front of the shells. once the shells have been driven to specified depth the mandrel is withdrawn and reinforced concrete inserted in the core. diameters vary from 325 to 600 mm.franki pile: a steel tube is erected vertically over the place where the pile is to be driven, and about a metre depth of gravel is placed at the end of the tube. a drop hammer, 1500 to 4000kg mass, compacts the aggregate into a solid plug which then penetrates the soil and takes the steel tube down with it. when the required depth has been achieved the tube is raised slightly and the aggregate broken out. dry concrete is now added and hammered until a bulb is formed. reinforcement is placed in position and more dry concrete is placed and rammed until the pile top comes up to ground level.1.4.11 steel pilessteel piles: (figure 1.4) steel/ iron piles are suitable for handling and driving in long lengths. their relatively small cross-sectional area combined with their high strength makes penetration easier in firm soil. they can be easily cut off or joined by welding. if the pile is driven into a soil with low ph value, then there is a risk of corrosion, but risk of corrosion is not as great as one might think. although tar coating or cathodic protection can be employed in permanent works.it is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile. in this way the corrosion process can be prolonged up to 50 years. normally the speed of corrosion is 0.2-0.5 mm/year and, in design, this value can be taken as 1mm/year a) x- cross-section b) h - cross-section c) steel pipe figure 1-6 steel piles cross-sections 1.4.12 composite pilescombination of different materials in the same of pile. as indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. to avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level (see figure 1.7).figure 1-7 protecting timber piles from decay: a) by pre-cast concrete upper section above water level. b) by extending pile cap below water level 1.4.13 classification of pile with respect to effect on the soila simplified division into driven or bored piles is often employed.1.4.14 driven pilesdriven piles are considered to be displacement piles. in the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. there may also be a component of movement of the soil in the vertical direction.1.4.15 bored pilesbored piles(replacement piles) are generally considered to be non-displacement piles a void is formed by boring or excavation before piles is produced. piles can be produced by casting concrete in the void. some soils such as stiff clays are particularly amenable to the formation of piles in this way, since the bore hole walls do not requires temporary support except cloth to the ground surface. in unstable ground, such as gravel the ground requires temporary support from casing or bentonite slurry. alternatively the casing may be permanent, but driven into a hole which is bored as casing is advanced. a different technique, which is still essentially non-displacement, is to intrude, a grout or a concrete from an auger which is rotated into the granular soil, and hence produced a grouted column of soil.there are three non-displacement methods: bored cast- in - place piles, particularly pre-formed piles and grout or concrete intruded piles.the following are replacement piles:augeredcable percussion drillinglarge-diameter under-reamedtypes incorporating pre caste concrete unitedrilled-in tubesmini piles1.5 aide to classification of piles for a quick understanding of pile classification, a hierarchical representation of pile types can be used. also advantage and disadvantages of different pile materials is given in section 1.6.1.6 advantages and disadvantages of different pile materialwood pilesthe piles are easy to handle;relatively inexpensive where timber is plentiful;sections can be joined together and excess length easily removed;the piles will rot above the ground water level. have a limited bearing capacity;can easily be damaged during driving by stones and boulders;the piles are difficult to splice and are attacked by marine borers in salt water;prefabricated concrete piles (reinforced) and pre stressed concrete piles. (driven) affected by the ground water conditions;do not corrode or rot;are easy to splice. relatively inexpensive;the quality of the concrete can be checked before driving;stable in squeezing