基礎(chǔ)及基礎(chǔ)工程外文翻譯

1、<p><b>　　河北建筑工程學(xué)院</b></p><p>　　畢業(yè)設(shè)計(jì)（論文）外文資料翻譯</p><p>　　系別： 土木工程 </p><p>　　專業(yè)： 土木工程 </p><p>　　班級(jí)：

2、 ********* </p><p>　　姓名： ********** </p><p>　　學(xué)號(hào)： ************** </p><p>　　外文出處： GEOLOGLCAL AND GEOTECH

3、NICAL ENGINEERING </p><p>　　附 件：1、外文原文；2、外文資料翻譯譯文。</p><p>　　注：請將該封面與附件裝訂成冊。</p><p>　　1、外文原文（復(fù)印件）</p><p>　　Foundation And Foundation Engineering</p><p>　

4、　Strucures or other constructed works are supported on the earth by foundation. The word “foundation” may mean the earth itself, something placed in or on the earth to provide support, or a combinnation of the earth and

5、the elements placed on it. The foundation for a multistory office building could be a combination for an earth-fill dam would be the natural soil or rock on which the dam is placed. Concrete footings or which or in which

6、 they are placed. The installed elements and the natural soil</p><p>　　The installed parts of the foundation system may be footings, mat foundations, slab foundations, and caissons or piles, all of which are

7、 used to transfer load from a supersteucture into the earth. These parts, which transmit load from the superstructure to the earth, are called the substructure.</p><p>　　Footing Footing or spread foundation

8、s are used to spread the loads from columns or walls to the underlying soil or rock. Normally, footings are constructed of reinfored concrete. However, under some circumstances they may be constructed of plain concrete o

9、r masonary, when each footing supports only one column, it is square. Footings supporting two coumns are called combined footings and may be either rectangular or trapezoidal. Cantilever footings are used to building lin

10、e or exterior wall. Foo</p><p>　　The sizes of footings are determined by dividing the loads to be imposed at the base of the footings by the allowable bearing pressure which can be imposed on the soil or roc

11、k of the earth. Most building codes and textbooks on foundations contain tables listing allowable bearing pressures for various types of soil and rock; however , these tables give only general classifications and descrip

12、tions of the soil or rock must be used with caution. More specific information about the soil or rock is n</p><p>　　Grade beams may be used between exterior column footings to support walls, with the beams t

13、ransferring the weight of the walls to the column footings. Beams are also used between interior column footings to act as braces or to support interior walls. Retaining walls are those walls subject to horizontal earth

14、pressures due to the retention of earth behind them. The foundation for these will not slide when subjected to the horizontal earth pressure. In addition,retaining walls must be designed so</p><p>　　Mat foun

15、dations Mat or raft foundations are large, thick, and usually heavily reinforced concrete mats which transfer loads from a number or colums and walls to the underlying soil or rock. Mats are also combined footings.,but

16、are much larger than a footing uniform pressure to the underlying soil or rock. Mats are rigid and will act as a bridge over discontinuities in the soil or rock on which they are founded. Mats founded several meters belo

17、w the ground surface, when combined with external wa</p><p>　　Slab foundations Slab foundations are used for light structures wherein the columns and walls are supportes directly on the floor slab. The floo

18、r slab is thickened and more heavily reinforced at the places where the column and wall loads are imposed.</p><p>　　Special problems Groundwater is a major problem in connection with the design and installa

19、tion of foundations where a substructure is to be placed below the groundwater level. Well points, pumping from deep wells, or pumping from sumps are methods used to dewater construction sites during foundation installat

20、ion. Other methods which are less often used are freezing of the water in the soul, removal of water by electroosmosis, and the installation of cutoff walls made of pilling or grout around </p><p>　　If a bas

21、ement is partially or totally below the groundwater level, its walls must be designed to withstand the hydrostatic pressure of the water on the outside in addition to the pressure from the soil backfill. An alternate pro

22、cedure is to install a permanent system to remove watet outside the walls. Some substructure below groundwater level may at times be subjected to hydrostaic uplift forces which are greater than the downward forces impose

23、d by the structures. In these cases, provisions must</p><p>　　Groundwater also causes problems by infiltrating though basement walls., slabs, and joints into the basement itself. This can be prevented or red

24、uced by providing an external permanent drainage system that carries water away from the basenment, by encasing the walls and slabs in an permeability. Combinations of the foregoing are also used. Retaining walls and abu

25、tments ofen abutments can escape. The water pressure behind the walls is relieved as the water flows though the walls into an open exte</p><p>　　Foundations placed on expansive soil are often subjected to di

26、stressing movement unless special precautions are taken. Expansive soil are those which swell and contract excessively with varying amounts of moissture. Problems can be overcome by installing foundations below the zone

27、of significant change in moisture content and backfilling with nonexpansive materials, by altering the soil with an admixture such as lime or cement so that volumn changes do not occur, or by providing flexibility in t&l

28、t;/p><p>　　Underpinning of foundation is often necessary, and it may be either remedial or precautionary. Remedial underpinning is used to correct defects in existing froundations which may have settled excessi

29、vely. If the structure is to be saved or returned to its original state, additional foundation support must be provided. Precautionary underpinning is used when new structure are to be installed adjacent to or beneath ex

30、isting structures, as in the construction of city subways. Underpinning of founda</p><p>　　Underpinning of a wall footing may be performed by excavating pits adjacent to and beneath existing foundations. The

31、 pits are small, some 0.9m wide by 1.2m long. Horizontal sheeting is placed in the pits as excavation proceeds to prevent caving of the walls and undermining of the structure being underpinned. When the new bearing strat

32、um is reached, forms are placed in the pit, and concrete is poured from the new bearing stratum up to within 76mm of the bottom of the old footing. After the new co</p><p>　　One indisputable face is this: wh

33、atever the shape of a building or structure and whatever the nature and number of its supports, the whole weight of the building must come down to, and be supported by the ground. It is therefore essential that, for any

34、propose structure, sufficient knowledge be obtained of the nature of the supporting soil and its load-bearing capacity.</p><p>　　The purpose of a foundation is to convey the weight of a building to the soil

35、in such a manner:</p><p>　　That excessive settlement will not occur;</p><p>　　That differential settlement of various sections of the building, which causes cracks in the structure, will not occ

36、ur;</p><p>　　That the soil will not fail under its load, thus causing no collapse of the building.</p><p>　　Compared with structural materials, such as steel and timber, soil is difficult to inv

37、estigate scientifically. It can vary considerably in its properties on one building site both in horizontal and vertical directions.</p><p>　　Until the 20th century, foundations were constucted mainly on the

38、 basis of experience. For important structures, deep trial pits were dug so that the soil could be examined for some distance below the surface, and sometimes loading tests on small area at the botton of the pits, were m

39、ade to estimate the safe-bearing capacity of the soil.</p><p>　　Some time about 1920 there began a more scientific approach to the behavior of soil. One of the earliest names, and a most important one, conne

40、cted with this new science, is Dr. Karl Terzaghi, who made an extensive study of the properties of soils. Since 1920 much research has been carried out in many countries; many tests (site and laboratory) have been devise

41、d, and there is now a considerable literature on the subject of soil mechanics. Modern site investigations for important structures are c</p><p>　　All the material foeming the crust of the earth likely to be

42、 affected by the pressure of strutures is dicided by engineers into two major geoups: rocks and soils. The term “rock” is reserved for hard , rigid, and strongly cemented material, while “soil” is applied to the comparat

43、ively soft and loose materials.</p><p>　　Soils without of organic deposits such as peat are broadly divided into two groups: cohesive and non-cohesive. Silts and clays are cohesive, while granular materials

44、such as sands and gravels are non-cohesive.</p><p>　　Owing to the weight of a building or other structure, there is bound to be a certain amount of settlement. It was stated previously that force cannot be a

45、pplied to any material without causing deformation. The total settlement of a building takes place in two stages:</p><p>　　Immediate settlement, as the building is being erected, due to elastic and plastic d

46、eformation of the soil.</p><p>　　Consolidation settlement caused by the sequeezing-out of water contained in the pores of the soil and thus compressing the soil to a smaller volume.</p><p>　　Fro

47、m the settlement point of view, non-cohesive soils such as sands and geavels are not very troublesome since they are only moderately compressible and are evey permeable (a permeable material is one which allows water thr

48、ough it easily). Consolidation settlement due to sequeezing-out of pore water therefore occurs very quickly during and soon after the erection of the strycture, and is comparatively small. Special attention, however, mus

49、t be given to loose sands, which can show appreciable set</p><p>　　Cohesive soils such as clay have very low permeability, which means that squeezing of water from the pores due to consoildation settlement o

50、f the building is a slow process. Furthermore, the compressibility of most calys and silts is appreciable and there is a compressibility volume reduction under pressure. The final settlement of a structure founded on cla

51、y may therefore not occur until some years after erection and must be allowed for in design calculations.</p><p>　　Clay is aslo a troublesome material when encounterd in shallow foundations (for houses and o

52、ther small buildings). Cohesive soils dry out in the summer and spring; surface cracks can occur which may extend to about 0.3m in britain.</p><p>　　Precast Piles Precast piles, which are usually square or

53、octagonal in cross-section, are driven into the soil by repeated blows from a falling weighted or from a steam hammer. The piles are driven in until a certain number of blows produce only a small further penetration whic

54、h has been predetermined by zalculations in accordance with the loads , and the piles will be called upon to supports .</p><p>　　A simple illustation is that of knocking a timber stake into soil. The deeper

55、the stake is driven into the geound, the greater is the frictional resistance and the harder it is to drive the stake downwards. When a pile is driven a sufficient distance, the resultant load it has to carry is usually

56、supported partly by frictional force on the sides of the pile and partly by the bearing resistance of the soil under the foot of the pile.</p><p>　　If the strata are of such a nature that the soil can offer

57、negligible frictional resistance, the pile must be drien until it meets a hard strtum such as rock capable of supporting the full load. Alternatively the soil may be of such a nature that most of the trsistance to the do

58、wnward artion of the weight of the building is provided by frictional resistance.</p><p>　　Inspporting their loads, piles act as columns, except that the soil provides lateral restraint.</p><p>

59、　　Another method, as used by the Franki Compressed Pile Co, consists in driving a steel tube to the required depth and filling it with in-situ concrete. First, the bottom of the tube is sealed by a temporary gravel plug.

60、 The tube is then driven to the required depth by blows on this plug from a long heavy cylindrical hammer. Concrete is then placed in the tube and rammed so that a bulbous foot is produced (thus increasing bearing resist

61、ance). As the rammed concrete approaches the ground surface, t</p><p>　　Bored Piles Driven piles displace and compress the soil. Then piles are bored in situ, the soil is removed by special boring tools to

62、form cylindrial holes equal to the depths of the prepared piles. Steel reinforcenment is then inserted and concreted rammed in to form the pile, which frequently has a bulbous base due to heary ramming of the frist batch

63、 of concrete. In addition, bored piles are useful where headroom is restricted so that it is impossible to have long lengths of precast piles pro</p><p>　　Cylinder Piles Cylinder foundations, 2m or more in

64、diameter, have been employed for many years, the holes being made by excavating soil with hand or mechanically operated geabs. During the last few years new methods have developed for forming these large diameter holes.

65、In one system, first used in the United States, angles(drills), varying from 1m to 2.3m in diameter, are used for boring holes which may be as much as 25m deep or more. The bottoms of the 2.3m diameter cylinders, and 2.3

66、m for th</p><p>　　Piles Caps When small-diameter driven or bored piles are used, the number of piles required to suppore one column must be transferred to the piles by means of a foundation called a pile ca

67、p. Reinforcement is required in the cap to resist bending stresses, etc.</p><p>　　2、外文資料翻譯譯文</p><p><b>　　基礎(chǔ)及基礎(chǔ)工程</b></p><p>　　建筑物或是已建成的工程是由基礎(chǔ)下的地基土支撐著的?！盎A(chǔ)”一詞意味著土本身或在圖內(nèi)（或

68、其上）布置的物體作為支撐體，或作為土和它上面布置的構(gòu)件的聯(lián)合體。多層辦公建筑的基礎(chǔ)一般是混凝土底板與土（或底板布置于其上的巖石）的聯(lián)合體。土壩的基礎(chǔ)是天然的地基土或巖石?；炷恋装寤驑都捌錁睹背１豢醋骰A(chǔ)，而不包括它們所涉及的地基土或巖石。所建立的構(gòu)件和天然的土或巖石形成了基礎(chǔ)系統(tǒng)；土和巖石為這一系統(tǒng)提供了基本支撐。已建立的基礎(chǔ)不是由基礎(chǔ)土支撐就是由巖石支撐。土和巖石對于增加給它們荷載的反應(yīng)，一般決定里基礎(chǔ)系統(tǒng)功能的好壞程度。在設(shè)計(jì)安裝

69、的基礎(chǔ)部分中，設(shè)計(jì)者必須確定安全壓力，即在土或巖石可能受到的壓力以及建筑物可能承受的總沉降或沉降差。</p><p>　　基礎(chǔ)系統(tǒng)已建的部分是底板、筏板、板基礎(chǔ)和沉箱或柱，所有這些形式把上部結(jié)構(gòu)荷載傳遞給地基土。把上部結(jié)構(gòu)荷載傳遞給地基土的部分叫下部結(jié)構(gòu)。</p><p>　　底板 底板或伸展性基礎(chǔ)是通過柱或墻把上部荷載傳給下面的土或巖石。一般來說底板由預(yù)應(yīng)力混凝土構(gòu)成。然而在一些環(huán)境下，

70、底板也可由素混凝土和磚石構(gòu)成，當(dāng)每個(gè)底板僅支撐一柱時(shí)，底板是方形。底板支撐兩個(gè)柱稱組合底板，它可能是矩形或不規(guī)則四邊形。懸臂底板承受兩根柱子的荷載，其中一根柱子和底板的末端對著建筑物輪廓線或外墻。底板支撐墻是連續(xù)底板。</p><p>　　底板的尺寸由底板地基承受的荷載除以上土或巖石允許承載壓強(qiáng)而得到。對基礎(chǔ)來說大部分規(guī)范或教科書上都有表格列出了不同類型土和巖石的允許承載力值；然而，這些表格僅給出了土和巖石一般性

71、分類和描述，使用時(shí)要謹(jǐn)慎。關(guān)于土和巖石更詳細(xì)的信息一般可通過鉆探試驗(yàn)孔、取土和巖石試件、在實(shí)驗(yàn)室測試試件得到，并做工程分析來確定適當(dāng)?shù)某休d力值。除承載力外要考慮到總的沉降以及結(jié)構(gòu)承受這樣沉降的可能性。如果沉降是一個(gè)問題，采用置換基礎(chǔ)是必要的而不是用底板或擴(kuò)大底板和減少承載力。</p><p>　　梯級(jí)梁可在外柱底板和支撐墻之間使用，用梁把墻的重量傳給柱底板。梁也在內(nèi)柱底板之間使用，起作用作為支柱（拉桿）或支撐內(nèi)墻

72、。擋土墻是承受墻后土體引起的水平土壓力的墻體。對于強(qiáng)擠出來說，當(dāng)其受水平壓力時(shí)在墻與土（或巖石）之間要有足夠的抗滑力，以至于墻不會(huì)滑動(dòng)。另外，為了防止墻傾覆也應(yīng)做擋土墻設(shè)計(jì)。在凍融敏感區(qū)，底板必須放置在凍融線以下。</p><p>　　筏板基礎(chǔ) 筏板基礎(chǔ)是大的、厚的，常常是預(yù)應(yīng)力混凝土板，通過數(shù)根柱基或柱與墻聯(lián)合體把荷載傳給下部的土或巖石。筏板也可是相連的底板，但筏板要比支撐兩個(gè)柱的底板大些。筏板可謂是連續(xù)底板，

73、它們被設(shè)計(jì)用來把相對均一的壓力傳給下面的土或巖石。筏板是剛性的，當(dāng)支撐其的土或巖石不連續(xù)時(shí)，其作用類似橋。筏板可建在地表以下幾米處，當(dāng)與外墻連接時(shí)，則稱為浮動(dòng)基礎(chǔ)。從地表到筏板底部所開挖的重量可接近于建筑物的總重量。在這一情況下，很少或沒有新的荷載施加于下部的支撐上，在建筑物建成后，建筑物沉降為最小。</p><p>　　板基礎(chǔ) 板基礎(chǔ)用于輕型建筑物，把柱和墻直接支撐在底板上。在柱和墻施加荷載的位置，底板是厚重的

74、預(yù)應(yīng)力混凝土板。</p><p>　　一些特殊問題 在設(shè)計(jì)和建設(shè)下部結(jié)構(gòu)應(yīng)布置在地下的基礎(chǔ)時(shí)，地下水是一個(gè)主要問題。在基礎(chǔ)安裝期間，從深井中抽取基坑中的水，都可用于降低地下水位。其他一些不常用的辦法是把核心部分的水加以凍結(jié)，用電滲來轉(zhuǎn)移地下水，安裝切開墻制成堆垛，或從開外內(nèi)側(cè)周圍灌漿。如果在已有建筑物周圍區(qū)域上進(jìn)行抽水，必須對建筑物注意保護(hù)，因?yàn)榈叵滤唤档涂赡軙?huì)引起建筑物下的土下沉。</p>&l

75、t;p>　　如果地下室部分或全部在地下水位以下，墻體設(shè)計(jì)除了能承受墻后的土壓力外還必須設(shè)計(jì)成能承受墻外的靜水壓力。一個(gè)可選取的方法是在墻外建立能抽取地下水永久系統(tǒng)。位于地下水位以下的一些下部結(jié)構(gòu)時(shí)?？赡苁艿綋P(yáng)壓力作用，且大于建筑物向下的自重。在這種情況下，對建筑物應(yīng)進(jìn)行錨固，以防止建筑物向上浮托。</p><p>　　地下水也會(huì)通過地下室邊墻、底板和其連接處滲透引起一些問題。這個(gè)情況可以防止或減少，通過做永

76、久排水系統(tǒng)從地下室把水排去，活用不透水的塑料膜包住壁墻和板墻做保護(hù)，也可用瀝青樹脂對外部墻體做防護(hù)以降低其滲透性。以上措施也可聯(lián)合使用。擋土墻和墩柱在其下部有排水孔，這樣在擋土墻和墩柱后面匯積的水可流走。當(dāng)水通過墻流到外部排水系統(tǒng)時(shí)，墻后水壓力可減少。</p><p>　　在沒有特殊防護(hù)條件下，建立在膨脹性土上的基礎(chǔ)會(huì)發(fā)生有壞的移動(dòng)。膨脹土在不同的含水條件下會(huì)發(fā)生過分的膨脹和收縮。把基礎(chǔ)建在含水量明顯變化帶以下并

77、填充非膨脹材料可克服這一問題，在土中加入石灰或水泥的混合物改變土的組成但體積不變，或使上部結(jié)構(gòu)更加柔性以能適應(yīng)所發(fā)生的移動(dòng)也是可行的辦法。</p><p>　　對基礎(chǔ)進(jìn)行托換常常是必要的，也可對基礎(chǔ)用修補(bǔ)或預(yù)防性辦法。修補(bǔ)性托換?？捎糜谛蘩碛腥毕莸幕A(chǔ)，這種基礎(chǔ)沉降范圍往往很大。例如建筑物要加以補(bǔ)救或恢復(fù)原貌，對基礎(chǔ)做支護(hù)加固則非常必要。當(dāng)一個(gè)新建筑物是靠近另一建筑物或在其下，采取托換基礎(chǔ)，如城市地鐵建設(shè)?；A(chǔ)托

78、換是一個(gè)專門的建設(shè)技術(shù)。這一工作一般是在有限的空間進(jìn)行，如在一個(gè)建筑物地下室或在建筑物以外開挖坑槽。建設(shè)一個(gè)新基礎(chǔ)時(shí)已存在建筑物荷載加以支護(hù)是必要的。新基礎(chǔ)可以使底板，它在地表以下深度比原來基礎(chǔ)要深，新基礎(chǔ)也可是柱或沉箱。</p><p>　　對已有基礎(chǔ)附近或在基礎(chǔ)下開挖坑槽用墻底板托換方法是可行的?？右话悴淮螅?.9m寬、1.2m長。在開挖過程的中，坑中要布置水平板以防止墻塌陷和托換基礎(chǔ)潛挖。當(dāng)?shù)竭_(dá)新的承載層時(shí)

79、，把模子放入坑中，澆混凝土從新承載層至原有底板向上76mm范圍內(nèi)。在新的混凝土變硬后，用砂、水泥和少量水混合物對76mm空隙進(jìn)行人工封堵。所謂灌漿是把新底板的頂部和原底板下面之間的空間用混凝土緊密的加以封堵?；拥耐袚Q基礎(chǔ)過程是在整個(gè)墻底板長度上重復(fù)進(jìn)行的。新的托換基礎(chǔ)可以是連續(xù)墻，也可以是間隔墩。</p><p>　　一個(gè)無可爭辯的事實(shí)是：不管建筑物或結(jié)構(gòu)物的形狀怎樣，也不管支撐物的性質(zhì)和數(shù)量，建筑物的整個(gè)重量

80、必然向下傳遞并由地基支撐。因此，對任何建筑物來說，對支撐土的性質(zhì)和它的承載能力進(jìn)行充分了解是一個(gè)基本的問題。</p><p>　　修建基礎(chǔ)的目的是承載建筑物的重量，對土來說應(yīng)是這樣：</p><p>　　（1）廣泛的沉降不會(huì)發(fā)生；</p><p>　　（2）建筑物種不同部分差異性沉降在建筑物中不會(huì)發(fā)生裂縫；</p><p>　?。?）土在本身

81、荷載作用下不發(fā)生破壞，建筑物不會(huì)發(fā)生坍塌。</p><p>　　以建筑材料如鋼、木材等與土比較，土調(diào)查起來頗為困難。在同一建筑現(xiàn)場，土在水平方向和垂直方向其性質(zhì)會(huì)有相當(dāng)大的變化。</p><p>　　直到20世紀(jì)，基礎(chǔ)建設(shè)主要靠經(jīng)驗(yàn)。對一些重要建筑物，要挖一些深坑來檢驗(yàn)地表下一定深度處的情況，有時(shí)在試坑底部做荷載試驗(yàn)，以估算土的安全承載力。</p><p>　　大約

82、在1920年前后，在圖的特性上開始了更科學(xué)的研究。在這一領(lǐng)域最早最為重要的一個(gè)人就是Karl Terzaghi博士，他對土的特性作了廣泛研究。從1920年起許多國家進(jìn)行了這方面的研究；設(shè)計(jì)了許多實(shí)驗(yàn)（室內(nèi)和現(xiàn)場），目前在土力學(xué)方面文獻(xiàn)頗多。對一些重要建筑物的現(xiàn)場調(diào)查由一些專家公司完成，他們有經(jīng)驗(yàn)過專業(yè)培訓(xùn)的人員，取土樣和鉆探設(shè)備以及室內(nèi)實(shí)驗(yàn)設(shè)備。</p><p>　　受建筑物壓力作用的地殼材料被工程人員分成兩組基

83、巖石和土。巖石一詞表示堅(jiān)硬、剛性和很強(qiáng)的膠結(jié)材料，土則表示相對較軟和疏松的材料。</p><p>　　沒有有機(jī)質(zhì)的土如泥炭土，被廣泛的分成兩組：有凝聚力和無凝聚力。砂性土和黏土是有凝聚力的，礫狀材料如砂和礫石無凝聚力。</p><p>　　建筑物和其結(jié)構(gòu)物在自重作用下，一定會(huì)發(fā)生一定量的沉降。過去曾說過，有力就有變形。建筑物總的沉降分為兩個(gè)階段：</p><p>　

84、　（1）瞬時(shí)沉降是在建筑物中引起的，即土?xí)l(fā)生彈性和塑形變形；</p><p>　?。?）固結(jié)沉降是由土中孔隙水被排出，使土的體積減少。</p><p>　　從沉降的觀點(diǎn)考慮，非黏性土如砂和礫石不存在這一問題，因?yàn)樗鼈冇幸欢▔嚎s性和很大的滲透性（滲透材料是指水很容易通過的材料）。固結(jié)沉降是由水?dāng)D出引起的，因而在建筑物建設(shè)及建成以后很快會(huì)發(fā)生，沉降相對不大。然而。要特別注意的是松砂，當(dāng)松砂受

85、到震動(dòng)會(huì)有感知的沉降。</p><p>　　有黏性的土如黏土滲透性很低，這意味著有建筑物所引起的固結(jié)沉降使孔隙水被排出是一個(gè)很漫長的過程。因此，大部分黏土和砂土的壓縮性是明顯的，在壓力下可壓縮的體積會(huì)減少不小。在黏土上所建建筑物最終沉降在建成以后若干年并沒完成，在設(shè)計(jì)計(jì)算中必須考慮到這一點(diǎn)。</p><p>　　在淺基礎(chǔ)中黏土仍是麻煩的材料（如房子和一些小型建筑物）。在夏天和春天黏性土?xí)?/p>

86、燥，并產(chǎn)生收縮裂縫，在英國這樣的裂縫達(dá)0.3m。</p><p>　　預(yù)制樁 預(yù)制樁在斷面上通常是方形或八角形的它由落體重物或氣錘重復(fù)打擊而進(jìn)入土中。每次錘擊樁，導(dǎo)入的深度會(huì)越來越小，一直到按荷載計(jì)算得到的預(yù)定的深度，這時(shí)樁被用來作為支撐物。</p><p>　　以打入土中的木樁為例做一簡單的說明。木樁打入土中越深，摩擦阻力越大，向下大的時(shí)候越困難。當(dāng)樁導(dǎo)入足夠深度后，總的力由以下兩部分承

87、擔(dān)，一為樁周圍的摩擦力，二為樁底端土的抗阻力。</p><p>　　例如地層為摩阻力可忽略不計(jì)的天然狀態(tài)土，樁應(yīng)打到具有能支撐全部荷載的堅(jiān)硬巖石。而所選土也可能有如此的特性，即建筑物重量向下作用的大部分力由摩擦力來承擔(dān)。</p><p>　　在支撐上部荷載時(shí)，樁的作用被看做支撐柱，當(dāng)然土提供了側(cè)向約束。</p><p>　　另外一種方法像Franki壓樁公司所提出的

88、那樣，吧一個(gè)鋼管打到要求深度并在管內(nèi)填混凝土。首先，管低端用一個(gè)暫時(shí)礫狀插頭封起來。然后，利用一個(gè)重而長的圓柱形錘頭來沖擊樁頭，把管子打到要求深度。再把混凝土放入管中并加振搗，以便形成球形樁腳（增加承載阻力）。當(dāng)振搗的混凝土達(dá)到地表，管子被逐漸的抽出來。</p><p>　　鉆孔樁 用樁來置換和擠壓土體。在現(xiàn)場用樁打孔，并用專門的鉆具把土移除形成一個(gè)圓柱孔，其深度等于設(shè)計(jì)樁深。再把鋼筋插入，澆混凝土振搗構(gòu)成樁，該

89、樁通常會(huì)有球形底板，這是由第一批混凝土受到重型振搗形成的。另外，鉆孔樁應(yīng)用條件是頂部空間受到限制以致預(yù)制樁長度在地面以上不可能伸展太長才采用這種辦法。</p><p>　　圓柱樁 直徑是2m或更大的圓柱基礎(chǔ)，多年來一直得到應(yīng)用，鉆孔用人工或機(jī)械抓斗來形成。在最近幾年為了形成這樣一個(gè)大直徑鉆孔提出了一些新的方法。這一情況首先在美國得到應(yīng)用，用一個(gè)直徑1~2.3m的鉆孔機(jī)鉆25m或更深。當(dāng)孔底鉆孔直徑是2.3m時(shí)用專

90、門鉆具把它擴(kuò)成5m，當(dāng)直徑是1m時(shí)擴(kuò)成2.3m。一個(gè)大的承載面積在底部形成；這一方法在倫敦黏土中得到應(yīng)用，設(shè)計(jì)支撐荷載為2000t。這種大直徑的圓柱優(yōu)點(diǎn)在于上部重量大，如果需要幾個(gè)小直徑支撐時(shí)，可由一個(gè)柱承擔(dān)，這樣上部樁帽就可省下，使費(fèi)用減少。</p><p>　　柱帽問題 當(dāng)使用小直徑的圓柱樁或鉆孔柱時(shí)，幾個(gè)小直徑樁來支撐上部一個(gè)立柱，這樣把立柱荷載分到每個(gè)樁的安全荷載范圍內(nèi)。立柱荷載用柱帽來傳遞給柱。在樁帽中