土建外文翻譯5

1、<p><b>　　附錄 A </b></p><p><b>　　1.1 樁基礎(chǔ)</b></p><p>　　樁基礎(chǔ)是結(jié)構(gòu)的一部分，它用來將上部的荷載轉(zhuǎn)承給地表以下一定深度的持力層。基礎(chǔ)的主要組成部分是柱頂和柱。樁長(zhǎng)且細(xì)，它將荷載傳給深層土或是高承載力的巖石，以弊開淺層底承載力的土。常用的樁基礎(chǔ)材料就是木材，鋼和混凝土。樁由這些材

2、料制成后被鉆入地下并與樁帽相連。根據(jù)土壤類型，樁的材料，荷載傳遞特征將樁相應(yīng)的分類。在以下章節(jié)中我們將學(xué)習(xí)樁的分類，作用和樁的利弊。</p><p>　　1.2 發(fā)展情況</p><p>　　樁基礎(chǔ)作為承載和傳遞力的方法已應(yīng)用多年。</p><p>　　在文明的早期，從通信，防御或戰(zhàn)略的觀點(diǎn)出發(fā)，村莊和城鎮(zhèn)被建立在河湖附近。因此以某種打樁的形式來加強(qiáng)地表的承載力

3、是很重要的。木材樁可手工壓入地下，或是挖一個(gè)坑將樁送入后，填入沙石。1740年Christoffoer Polhem發(fā)明了與當(dāng)今很相似的鉆樁設(shè)備。鋼樁在1800年開始使用，混凝土樁1900年開始使用。</p><p>　　工業(yè)革命中，發(fā)明了蒸汽機(jī)和柴油機(jī)，這給鉆樁方法帶來了重大變化。</p><p>　　最近，隨著對(duì)住房和建筑需要的迫切增長(zhǎng)，當(dāng)局和一些建筑機(jī)構(gòu)已開始在一些不良土壤上開拓工地

4、。這已引起了樁及樁基方法的進(jìn)步和改良。目前已有許多打樁的先進(jìn)技術(shù)。</p><p>　　1.3 樁基的作用</p><p>　　和其它類型的基礎(chǔ)一樣，樁基礎(chǔ)的目的是：將荷載傳到堅(jiān)固的地基土上，以承受垂直，水平和上頂?shù)牧Α?lt;/p><p>　　如果下部土沒有足夠的承載力，結(jié)構(gòu)可以建立在樁上。如故調(diào)查結(jié)果顯示表層土不穩(wěn)定且很薄或者設(shè)計(jì)的其它方法不可取時(shí)，可以考慮樁基礎(chǔ)

5、。另外，與其它地基處理的方法相比，樁基礎(chǔ)更加經(jīng)濟(jì)。</p><p>　　當(dāng)建筑物荷載很大時(shí)，淺層土的承載力很可能答不到要求，此時(shí)地基應(yīng)建立在樁基礎(chǔ)上。樁基礎(chǔ)也可用于一般的地面條件來抵抗水平荷載。樁是在水上，例如碼頭和橋梁上應(yīng)用的一種傳統(tǒng)的基礎(chǔ)方法。</p><p>　　1.4 樁基礎(chǔ)的分類</p><p>　　1.4.1 按承載性和樁的使用功能進(jìn)行分類</

6、p><p>　　端承樁，摩擦樁，端承樁和摩擦樁的結(jié)合。</p><p>　　1.4.2 端承樁</p><p>　　樁將荷載到建筑基礎(chǔ)以下一定深度處的堅(jiān)實(shí)土層之上，它的大部分承載力來自樁端（見圖1.1）。樁作為一根柱子而被設(shè)立。即使在承載力較弱的土壤中，樁基礎(chǔ)也不會(huì)因?yàn)檎蹟喽鴵p壞，并且這種效果只能在樁無撐的情況下考慮，例如，水或空氣。荷載由摩擦或樁端傳遞。但有時(shí)，樁周

7、圍的土黏著在樁的表面造成“消極的表層摩擦”。有時(shí)，這會(huì)對(duì)樁的承載能力造成很大的影響。消極的表層摩擦是由于地下排水和土壤加固造成的。樁的深度由調(diào)查結(jié)果和室內(nèi)土工實(shí)驗(yàn)決定。</p><p>　　1.4.3 摩擦樁和端承樁</p><p>　　承載力主要來自于樁軸與土的接觸與摩擦。（見圖1.2）</p><p>　　1.4.4 端承樁</p><p

8、>　　這些樁將大部分荷載通過表層摩擦傳給土壤。打這種樁每組中的樁相距很近，大大減小了每組土壤的多孔性和壓縮性。因此，這種樁有叫做擊實(shí)樁。在將樁打入土壤的過程中，對(duì)土壤造成影響，結(jié)果土壤減小了強(qiáng)度。因此樁不能精確的轉(zhuǎn)遞一定數(shù)量的荷載而必須在打入之后才能知道。通常土壤在打樁后的三到五個(gè)月可以恢復(fù)一部分承載力。</p><p>　　1.4.5 摩擦樁</p><p>　　這種樁也是通過表

9、層摩擦將荷載傳遞給土壤。在打這種樁的過程一點(diǎn)也沒有使土壤壓縮。這種樁通常又叫做懸浮樁基礎(chǔ)。</p><p>　　1.4.6 摩擦和端承的符合型樁基礎(chǔ)</p><p>　　當(dāng)樁的承載力底時(shí)，例如黏土中，需要將樁的底部進(jìn)行擴(kuò)展。樁應(yīng)鉆入下部材料足夠深以獲得足夠的摩擦力。底部樁承載力的進(jìn)一步不同是樁擴(kuò)大的支撐面積。這是通過直接向堅(jiān)固地層之上的弱土層上灌入混凝土來擴(kuò)大地基。一個(gè)類似的效果是在低部

10、用一種特殊的工具將樁擴(kuò)大成錐。樁是由一個(gè)具高強(qiáng)度的鐘型提供，可用做錐型樁。（見圖1-3）</p><p>　　1.4.7 按樁身材料分類</p><p><b>　　1) 木樁； </b></p><p>　　2) 混凝土樁； </p><p>　　3) 鋼樁； </p><p>

11、;<b>　　4) 混合材料樁。</b></p><p>　　1.4.8 木樁 </p><p>　　在一些木材豐富的地區(qū)，木樁使最早期的記錄上就有使用并沿用至今。木材最適合于長(zhǎng)的內(nèi)聚力樁和堤壩之下。木材的材料應(yīng)該很好，沒有被蟲子磕過。對(duì)于少于14米長(zhǎng)的木材，它的直徑應(yīng)大于150mm。如果木材長(zhǎng)度超過18米，直徑是125mm，那是可以選擇的。樁以合適的角度鉆入地下是

12、很必要的，并且它不能被鉆入堅(jiān)實(shí)的土地中。因?yàn)檫@樣很容易損壞樁。使木材保持在地下水面之下，將會(huì)防止木材腐爛。為了保護(hù)和加強(qiáng)樁底，木材的低部應(yīng)被覆蓋。壓力防腐劑是保護(hù)木材常用的一種方法。</p><p>　　1.4.9 混凝土樁</p><p>　　預(yù)制或已制混凝土樁。通常為正方形（見圖1-4b），三角形，圓形或多邊形，它們的長(zhǎng)度很短，在3米到13米之間有一米的間隔。它們是預(yù)先做好的，因此能

13、被容易的組合在一起，以達(dá)到要求的深度（見圖1-4 a）。這不會(huì)減少設(shè)計(jì)承載力。</p><p>　　樁內(nèi)的加固是必要的，以幫助承受手工和機(jī)器的壓力。預(yù)應(yīng)力混凝土樁也被廣泛應(yīng)用，并比傳統(tǒng)的樁更受歡迎，因?yàn)樗枰俚募庸獭?lt;/p><p>　　赫拉克勒斯類型基礎(chǔ)連接（圖1-5）能容易準(zhǔn)確的組成樁，并能在現(xiàn)場(chǎng)很快安全的組裝。它們由高級(jí)鋼制成準(zhǔn)確的尺寸。</p><p>

14、　　1.4.10 混凝土樁的制作</p><p>　　英國(guó)使用的兩種主要類型是：所謂的殼樁：它被提前制作，由鋼筋混凝土加固，管長(zhǎng)大概一米，在混凝土布置在管壁上后，混凝土有鋼管中心向下灌。當(dāng)管壁進(jìn)入一定深度時(shí)，中心管撤出，管中心再次灌人混凝土加固。管徑變化范圍從325到600mm。</p><p>　　現(xiàn)場(chǎng)灌注樁：鋼管被垂直豎立在它將要打入的地方，在大約一米深處石渣被填在管的末端。用重為1

15、500到4000kg 重錘，壓實(shí)土壤，然后將鋼管插入土壤。當(dāng)?shù)竭_(dá)要求的深度時(shí)，管被輕輕提起，此時(shí)內(nèi)聚力破壞。這時(shí)加入干燥的混凝土并用錘擊直到形成擴(kuò)大頭基礎(chǔ)。在某些地方繼續(xù)加固，加入更多的混凝土并重?fù)?，直到樁的頂部到達(dá)水平地表。</p><p>　　1.4.11 鋼樁</p><p>　　鋼樁：（圖1.4）鋼樁適合在較大的深度。由于鋼本身的強(qiáng)度，鋼樁有相對(duì)少的接觸斷面，更易打入堅(jiān)實(shí)的土中。

16、它們更易切斷或焊接。如果鋼樁打入PH值低的土壤中，就有腐蝕的危險(xiǎn)，但這種危險(xiǎn)并不象人們想象的那么大。為了長(zhǎng)期應(yīng)用，可在樁表涂瀝青或采用負(fù)極保護(hù)。</p><p>　　在設(shè)計(jì)中通過簡(jiǎn)單計(jì)算鋼樁斷面面積，來考慮一定的腐蝕是正常的。用這種方法可將腐蝕時(shí)間延長(zhǎng)到50年。通常腐蝕速度是0.2-0.5mm/年，在設(shè)計(jì)中，可看作1mm/年。</p><p><b>　　圖1-6鋼樁的連接<

17、;/b></p><p>　　1.4.12 組合材料樁</p><p>　　同一樁中使用不同材料的結(jié)合。如前所述，建立在地下水之上的木樁的某些部分，容易遭到蟲子的破壞并易腐爛。為了避免這些，鋼筋或混凝土基礎(chǔ)在地下水位線之上，木基礎(chǔ)放在地下水位線之下（見圖1-7）</p><p>　　1.4.13 按樁對(duì)土的作用進(jìn)行分類</p><p&g

18、t;　　簡(jiǎn)單的打入樁和螺旋鉆孔樁經(jīng)常被使用。</p><p>　　1.4.14 打入樁</p><p>　　打入樁又認(rèn)為是位移樁。在將樁打入地下的過程中，當(dāng)樁軸進(jìn)入地面時(shí)，土程輻射型移走。在垂直方向也可能有土的部分運(yùn)動(dòng)。</p><p>　　1.4.15 螺旋鉆孔樁</p><p>　　螺旋鉆孔樁（位移樁）通常認(rèn)為是無排水樁，空隙是在樁形

19、成前挖掘或鉆孔過程中形成。樁可以在空隙中切割混凝土形成。一些土如硬黏土用這種方法順應(yīng)樁的形成，因?yàn)榇蚩讐Τ嗽诘乇聿灰笈R時(shí)的支撐。在不穩(wěn)定的地表，如石渣地表需要泥漿臨時(shí)支撐。框架也許是可選擇對(duì)象中應(yīng)用很久的，但當(dāng)進(jìn)入洞時(shí)，打入樁更有優(yōu)勢(shì)。另一種不同的非位移樁也是很重要的，那就是將水泥或混凝土旋轉(zhuǎn)的鉆入土中，并因此形成了一個(gè)土柱。</p><p>　　1.5 樁分類的目的</p><p>

20、;　　為對(duì)樁的分類有快速的理解，可使用樁類型等級(jí)表示方法。不同材料樁的優(yōu)缺點(diǎn)在1.6部分。</p><p>　　1.6 不同材料樁的優(yōu)缺點(diǎn)</p><p><b>　　木樁：</b></p><p><b>　　樁制作簡(jiǎn)易；</b></p><p>　　木材原料充足價(jià)錢相對(duì)便宜；</p>

21、;<p>　　每部分連接在一起且很長(zhǎng)也易搬運(yùn)；</p><p>　　樁不能在地下水位之上，承載力有一定的限制；</p><p>　　用塊巨礫按樁時(shí)容易損壞；</p><p>　　樁很難結(jié)合且易受到鹽水中鉆孔蟲的襲擊；</p><p>　　預(yù)制混凝土樁（加強(qiáng)的）提前壓制的混凝土樁（打入的）受地下水影響的條件；</p>

22、<p>　　非腐蝕性的易結(jié)合，相對(duì)便宜；</p><p>　　在打入前混凝土的質(zhì)量能被測(cè)定；</p><p>　　緊貼地表的土，例如，軟黏土，泥沙和煤泥樁的材料可在打入前被檢測(cè)；</p><p>　　如受地面凍漲影響可再次打入，這種建筑方法可不受地下水的影響；</p><p>　　可被打入很長(zhǎng)的距離?？稍诘叵滤恢?，例如，海洋結(jié)

23、構(gòu)的水；</p><p>　　增加顆粒狀土層的相對(duì)密度；</p><p><b>　　相對(duì)較難切開；</b></p><p>　　在打入時(shí)受到位移凍漲和土壤結(jié)構(gòu)的影響；</p><p>　　打入過程中易損壞?？刹捎弥脫Q樁；</p><p>　　有時(shí)會(huì)產(chǎn)生噪聲和振動(dòng)問題；</p>&l

24、t;p>　　樁徑很大時(shí)不能打入或受到凈空高度的限制；</p><p>　　打入或就地澆鑄混凝土樁；</p><p>　　永久性打入（地表左側(cè)打入）；</p><p>　　臨時(shí)打入或不打入（打入檢索）；</p><p>　　在打入前可被檢測(cè)，容易切割或延長(zhǎng)到要求的深度；</p><p><b>　　相對(duì)低

25、廉；</b></p><p><b>　　噪音??；</b></p><p><b>　　樁可在挖掘前澆鑄；</b></p><p><b>　　樁長(zhǎng)可隨時(shí)調(diào)整；</b></p><p>　　擴(kuò)大基底可增加顆粒狀地層的相對(duì)密度增加地層的承載力；</p>

26、<p>　　再次加強(qiáng)不由手工或鉆入壓力的控制；</p><p>　　以封閉的末端打入排除GW的影響；</p><p>　　相臨表層土的凍漲，它能使樁表面的不利的摩擦力增大和進(jìn)一步發(fā)展；</p><p>　　附近的護(hù)墻的位移。使提前打入的樁上升，在那里腳趾處的力可足夠抵抗向上的惟一位移；</p><p>　　對(duì)于沒有加強(qiáng)樁的拉伸損壞或

27、是包含綠色混凝土的樁，腳趾處的力足夠抵抗向上的位移；</p><p>　　損壞的樁包括未打入的或由于土壤的水平力作用在薄層處打入的綠混凝土在柱頂損壞?；炷敛荒茉跇锻瓿珊髾z測(cè)。當(dāng)管子撤走后，如果自流水流出管子，混凝土的強(qiáng)度會(huì)降低；</p><p>　　弱鋼部分或預(yù)制混凝土?xí)捎诿土业拇蛉攵鴵p壞；</p><p>　　長(zhǎng)度上的限制是由于力撤出的情況，振動(dòng)和地表位移也許

28、會(huì)損壞相臨建筑；</p><p>　　凈空高度限制的地方不能打入相對(duì)昂貴耗時(shí)。不能在建筑開始時(shí)就立刻使用長(zhǎng)度受限現(xiàn)場(chǎng)打入和澆鑄（無位移樁）為適合不同的地表?xiàng)l件，長(zhǎng)度可隨時(shí)改變；</p><p>　　孔中的土可被檢測(cè)，如果有必要，可取樣做室內(nèi)實(shí)驗(yàn)；</p><p><b>　　可安裝很大的直徑；</b></p><p>　

29、　黏性土中樁端可擴(kuò)大到兩個(gè)到三個(gè)直徑大；</p><p>　　樁的材料不由手工或打入條件決定；</p><p><b>　　可打入很長(zhǎng)的距離；</b></p><p>　　可在沒有噪音和振動(dòng)的條件下打樁；</p><p>　　可在很低的凈空高度下打樁；</p><p><b>　　無地表

30、凍漲的風(fēng)險(xiǎn)；</b></p><p>　　打入地下時(shí)可能會(huì)折斷；</p><p>　　混凝土沒有放在理想的位置，不能及時(shí)檢測(cè)；</p><p>　　在自溢壓力下，水會(huì)流出，沖刷水泥；</p><p>　　沒有特殊技術(shù)的非粘性材料中不能采用擴(kuò)大基礎(chǔ)；</p><p>　　不能延伸到地下水面之上，特別是在河流和

31、海洋條件下；</p><p>　　鉆孔的方法是挖去松散的沙和不良的土壤，在基底充填水泥很經(jīng)濟(jì)的達(dá)到承載力；</p><p>　　樁下沉?xí)?dǎo)致地面內(nèi)聚力的減小，導(dǎo)致相臨建筑物倒塌；</p><p>　　鋼樁（滾動(dòng)鋼部分）：</p><p>　　樁很容易處理，能容易的切割到理想的長(zhǎng)度；</p><p>　　能夠打入密實(shí)的土

32、層中。在打入過程中土壤的水平位移很小（鋼部分H或樁部分I），能被相對(duì)容易的切割；</p><p>　　可被用力打入很大長(zhǎng)度；</p><p><b>　　可有承受的承載力；</b></p><p>　　可成功的打入傾斜的巖石中；</p><p>　　如果有地表位移干擾，樁的小位移是很有用的；</p><

33、;p><b>　　樁會(huì)受到腐蝕；</b></p><p>　　在打入過程中容易偏離；</p><p><b>　　相對(duì)昂貴。</b></p><p><b>　　動(dòng)力學(xué)方法：</b></p><p>　　常用的估計(jì)打入樁的承載力的方法是使用能量公式或動(dòng)力公式。所有這些公式

34、都與樁的最大承載力有關(guān)（重錘落下一次時(shí)的垂向運(yùn)動(dòng)）并假設(shè)抵抗力與靜荷載下的樁的承載力相等，它們代表樁打入最后階段的最理想的錘擊運(yùn)動(dòng)。通常，樁能量公式或者用于估計(jì)安全工作的承載力或者用來計(jì)算正常工作條件下的工作量。</p><p>　　正常工作的承載力由公式計(jì)算出最大的力并由一些適當(dāng)?shù)陌踩蛩貨Q定。然而，動(dòng)力公式在一些樁設(shè)計(jì)應(yīng)用時(shí)，要求很嚴(yán)格。動(dòng)力公式不考慮土的物理性質(zhì)。這在動(dòng)力公式的應(yīng)用時(shí)就會(huì)導(dǎo)致演算結(jié)果的錯(cuò)誤，

35、因?yàn)樗鼈兇淼氖谴驑稌r(shí)土的情況。它們沒有考慮在長(zhǎng)時(shí)間承受荷載時(shí)土的條件，重復(fù)加固，不良的表層摩擦和成組的作用。</p><p><b>　　附錄 B </b></p><p>　　1.1 Pile foundations</p><p>　　Pile foundations [11] are the part of a structure

36、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 memb

37、ers 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 mat

38、erials are</p><p>　　1.2 Historical</p><p>　　In the early days of civilisation[2], from the communication, defence or strategic point of view villages and towns were situated near to rivers and

39、lakes. It was therefore important to strengthen the bearing ground with some form of piling.</p><p>　　Timber piles were driven in to the ground by hand or holes were dug and filled with sand and stones.</

40、p><p>　　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.</p><p>

41、;　　The industrial revolution brought about important changes to pile driving system through the invention of steam and diesel driven machines.</p><p>　　More recently, the growing need for housing and constru

42、ction 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

43、 of pile installation.</p><p>　　1.3 Function of piles</p><p>　　As with other types of foundations, the purpose of a pile foundations is:to transmit a foundation load to a solid ground to resist

44、 vertical, lateral and uplift load.</p><p>　　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 th

45、at 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 chea

46、per than any other compared ground improvement costs.</p><p>　　In the cases of heavy constructions, it is likely that the bearing capacity of the shallow soil will not be satisfactory, and the construction s

47、hould 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.</p&

48、gt;<p>　　1.4 Classification of piles</p><p>　　1.4.1 Classification of pile with respect to load transmission and functional behaviour</p><p>　　End bearing piles (point bearing piles)<

49、;/p><p>　　Friction piles (cohesion piles )</p><p>　　Combination of friction and cohesion piles</p><p>　　1.4.2 End bearing piles</p><p>　　These piles transfer their load o

50、n 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

51、 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 a

52、ir or water. Load is transm</p><p>　　1.4.3 Friction or cohesion piles</p><p>　　Carrying capacity is derived mainly from the adhesion or friction of the soil in contact with the shaft of the pil

53、e (see fig 1.2).</p><p>　　1.4.4 Cohesion piles</p><p>　　These piles transmit most of their load to the soil through skin friction. This process of driving such piles close to each other in grou

54、ps 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 groun

55、d, 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 wh</p><p>　　1.4.5 Friction piles</p><p>　　These pile

56、s 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.<

57、;/p><p>　　1.4.6 Combination of friction piles and cohesion piles</p><p>　　An extension of the end bearing pile when the bearing stratum is not hard, such as a firm clay. The pile is driven far eno

58、ugh 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 stratu

59、m 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 </p><p>　　1.4.7 Classification of pile with resp

60、ect to type of material</p><p><b>　　Timber </b></p><p><b>　　Concrete </b></p><p><b>　　Steel </b></p><p>　　Composite piles[12]  

61、</p><p>　　1.4.8 Timber piles</p><p>　　Used from earliest record time and still used for permanent works in regions where timber is plentiful. Timber is most suitable for long cohesion piling an

62、d 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.

63、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 dri</p><p>　　1.4.9 Concrete pile</p><p>　　Pre cast concrete Piles or Pr

64、e 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 ca

65、n 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 drivin

66、g stresses. Pre stressed concre</p><p>　　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 dimension

67、al tolerances from high grade steels.</p><p>　　1.4.10 Driven and cast in place Concrete piles</p><p>　　Two of the main types used in the UK are: West’s shell pile : Pre cast, reinforced concret

68、e 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

69、withdrawn and reinforced concrete inserted in the core. Diameters vary from 325 to 600 mm.</p><p>　　Franki Pile: A steel tube is erected vertically over the place where the pile is to be driven, and about a

70、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

71、 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 </p><p>　　1.4.11 Steel piles</

72、p><p>　　Steel 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

73、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 ta

74、r coating or cathodic protection can be employed in permanent works.</p><p>　　It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile

75、. 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</p><p>　　1.4.12 Composite piles<

76、;/p><p>　　Combination 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,

77、 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).</p><p>　　1.4.13 Classification of pile with respect to effect on th

78、e soil</p><p>　　A simplified division into driven or bored piles is often employed.</p><p>　　1.4.14 Driven piles</p><p>　　Driven piles are considered to be displacement piles. In t

79、he 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.</p><p>　　1.4.15 B

80、ored piles</p><p>　　Bored 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 co

81、ncrete 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 unsta

82、ble ground, such as gravel the ground requires temporary support from casing or bentonite slu</p><p>　　There are three non-displacement methods: bored cast- in - place piles, particularly pre-formed piles an

83、d grout or concrete intruded piles.</p><p>　　The following are replacement piles:</p><p><b>　　Augered</b></p><p>　　Cable percussion drilling</p><p>　　Large-

84、diameter under-reamed</p><p>　　Types incorporating pre caste concrete unite</p><p>　　Drilled-in tubes</p><p>　　Mini piles</p><p>　　1.5 Aide to classification of piles&

85、lt;/p><p>　　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.</p

86、><p>　　1.6 Advantages and disadvantages of different pile material</p><p>　　Wood piles</p><p>　　The piles are easy to handle;</p><p>　　Relatively inexpensive where timber

87、 is plentiful;</p><p>　　Sections can be joined together and excess length easily removed;</p><p>　　The piles will rot above the ground water level. Have a limited bearing capacity;</p>&l

88、t;p>　　Can easily be damaged during driving by stones and boulders;</p><p>　　The piles are difficult to splice and are attacked by marine borers in salt water;</p><p>　　Prefabricated concrete

89、piles (reinforced) and pre stressed concrete piles. (driven) affected by the ground water conditions;</p><p>　　Do not corrode or rot;</p><p>　　Are easy to splice. Relatively inexpensive;</p&g

90、t;<p>　　The quality of the concrete can be checked before driving;</p><p>　　Stable in squeezing ground, for example, soft clays, silts and peats pile material can be inspected before piling;</p>

91、<p>　　Can be re driven if affected by ground heave. Construction procedure unaffected by ground water;</p><p>　　Can be driven in long lengths. Can be carried above ground level, for example, through w

92、ater for marine structures;</p><p>　　Can increase the relative density of a granular founding stratum;</p><p>　　Relatively difficult to cut;</p><p>　　Displacement, heave, and distur

93、bance of the soil during driving;</p><p>　　Can be damaged during driving. Replacement piles may be required;</p><p>　　Sometimes problems with noise and vibration;</p><p>　　Cannot be

94、 driven with very large diameters or in condition of limited headroom;</p><p>　　Driven and cast-in-place concrete piles;</p><p>　　Permanently cased (casing left in the ground);</p><p&

95、gt;　　Temporarily cased or uncased (casing retrieved);</p><p>　　Can be inspected before casting can easily be cut or extended to the desired length;</p><p>　　Relatively inexpensive;</p>&l

96、t;p>　　Low noise level;</p><p>　　The piles can be cast before excavation;</p><p>　　Pile lengths are readily adjustable;</p><p>　　An enlarged base can be formed which can increase

97、the relative density of a granular founding stratum leading to much higher end bearing capacity;</p><p>　　Reinforcement is not determined by the effects of handling or driving stresses;</p><p>　

98、　Can be driven with closed end so excluding the effects of GW</p><p>　　Heave of neighbouring ground surface, which could lead to re consolidation and the development of negative skin friction forces on piles

99、.</p><p>　　Displacement of nearby retaining walls. Lifting of previously driven piles, where the penetration at the toe have been sufficient to resist upward movements.</p><p>　　Tensile damage t

100、o unreinforced piles or piles consisting of green concrete, where forces at the toe have been sufficient to resist upward movements.</p><p>　　Damage piles consisting of uncased or thinly cased green concrete

101、 due to the lateral forces set up in the soil, for example, necking or waisting. Concrete cannot be inspected after completion. Concrete may be weakened if artesian flow pipes up shaft of piles when tube is withdrawn.<

102、;/p><p>　　Light steel section or Precast concrete shells may be damaged or distorted by hard driving.</p><p>　　Limitation in length owing to lifting forces required to withdraw casing, nose vibrati

103、on and ground displacement may a nuisance or may damage adjacent structures.</p><p>　　Cannot be driven where headroom is limited;</p><p>　　Relatively expensive;</p><p>　　Time consum

104、ing. Cannot be used immediately after the installation;</p><p>　　Limited length;</p><p>　　Bored and cast in -place (non -displacement piles);</p><p>　　Length can be readily varied t

105、o suit varying ground conditions;</p><p>　　Soil removed in boring can be inspected and if necessary sampled or in- situ test made;</p><p>　　Can be installed in very large diameters;</p>&

106、lt;p>　　End enlargement up to two or three diameters are possible in clays;</p><p>　　Material of piles is not dependent on handling or driving conditions;</p><p>　　Can be installed in very lon

107、g lengths;</p><p>　　Can be installed with out appreciable noise or vibrations;</p><p>　　Can be installed in conditions of very low headroom;</p><p>　　No risk of ground heave;</p&