地基分析與設(shè)計(jì)外文翻譯

1、<p>　　FOUNDATION ANALYSIS AND DESIGN FOUNDATIONSUBSOILS</p><p>　　We are concerned with placing the foundation on either soil or rock. This material may be under water as for certain bridge and marine st

2、ructures, but more commonly we will place the foundation on soil or rock near the ground surface. Soil, being a mass of irregular-shaped particles of varying sizes, will consist of the particles (or solids), voids

3、 (pores or spaces) between particles, water in some of the voids, and air taking up the remaining void space. At temperatures below freezing th</p><p>　　Soil may be described as residual or transported. Resi

4、dual soil is formed from weathering of parent rock at the present location. It usually contains angular rock fragments of varying sizes inthesoil-rock interface zone. Transported soils are those formed from rock weathe

5、red at one location and transported by wind, water, ice, or gravity to the present site. The terms residual and transported must be taken in the proper context, for many current residual soils are formed (or are being

6、formed</p><p>　　MAJOR FACTORS THAT AFFECTTHE ENGINEERING PROPERTIES OF SOILS</p><p>　　Most factors that affect the engineering properties of soils involve geological processes acting over long

7、time periods. Among the most important are the following. </p><p>　　Natural Cementation and Aging </p><p>　　All soils undergo a natural cementation at the particle contact points. The process

8、of aging seems to increase the cementing effect by a variable amount. This effect was recognized very early in cohesive soils but is now deemed of considerable importance in cohesionless deposits as well. The effect

9、of cementation and aging in sand is not nearly so pronounced as for clay but still the effect as a statistical accumulation from a very large number of grain contacts can be of significance f</p><p>　　A

10、 soil is said to be normally consolidated (nc) if the current overburden pressure(column of soil overlying the plane of consideration) is the largest to which the mass has ever been subjected. It has been found by

11、experience that prior stresses on a soil element produce an imprint or stress history that is retained by the soil structure until a new stress state exceeds the maximum previous one. The soil is said to be overconsol

12、idated (or preconsolidated) if the stress history involves </p><p>　　Overconsolidated cohesive soils have received considerable attention.Onlymore recentlyhasit been recognized that overconsolidation ma

13、y be of some importance in cohesionless soils. A part of the problem, of course, is that it is relatively easy to ascertain overconsolidation in cohesive soils but very difficult in cohesionless deposits. The behavior

14、of overconsolidated soils under new loads is different from that of normally consolidated soils, so it is important—particularly for cohesive</p><p>　　OCR = P'c / P'o </p><p>　　A n

15、ormally consolidated soil has OCR = 1 and an overconsolidated soil has OCR > 1. OCR values of 1-3 are obtained for lightly overconsolidated soils. Heavily overconsolidated soils might have OCRs > 6 to 8.

16、 An underconsolidated soil will have OCR < 1. In this case the soil is still consolidating. Overor preconsolidation may be caused by a geologically deposited depth of overburden that has since partially erod

17、ed away.Of at leastequally common occurrence are preconsoli-dation</p><p>　　Quality of the Clay </p><p>　　The term clay is commonly used to describe any cohesive soil deposit with sufficie

18、nt clay minerals present that drying produces shrinkage with the formation of cracks or fissures such that block slippage can occur. Where drying has produced shrinkage cracks in the deposit we have a fissured clay.

19、 This material can be troublesome for field sampling because the material may be very hard, and fissures make sample recovery difficult. In laboratory strength tests the fissures can define fai</p><p>　　M

20、ode of Deposit Formation Soil deposits that have been transported, particularly via water, tend to be made up of small grain sizes and initially to be somewhat loose with large void ratios. They tend to be fairly u

21、niform in composition but may be stratified with alternating very fine material and thin sand seams, the sand being transported and deposited during high-water periods when stream velocity can support larger grain siz

22、es. These deposits tend to stabilize and may become very co</p><p>　　Soil deposits developed'where the transporting agent is a glacier tend to be more varied in composition. These deposits may contain la

23、rge sand or clay lenses. It is not unusual for glacial deposits to contain considerable amounts of gravel and even suspended boulders. Glacial deposits may have specific names as found in geology textbooks such as mo

24、raines, eskers, etc.; however, for foundation work our principal interest is in the uniformity and quality of the deposit. Dense, uniform depos</p><p>　　Soil Water </p><p>　　Soil water may

25、 be a geological phenomenon; however, it can also be as recent as the latest rainfall or broken water pipe. An increase in water content tends to decrease the shear strength of cohesive soils. An increase in the pore pre

26、ssure in any soil will reduce the shear strength. A sufficient increase can reduce the shear strength to zero—for cohesionless soils the end result is a viscous fluid. A saturated sand in a loose state can, from a sud

27、den shock, also become a viscous fluid. This p</p><p>　　In any case, the shear strength of a cohesive soil can be markedly influenced by water. Even without laboratory equipment, one has probably seen how co

28、hesive soil strength can range from a fluid to a brick-like material as a mudhole alongside a road fills during a rain and subsequently dries. Ground cracks in the hole bottom after drying are shrinkage (or tension)

29、cracks. </p><p>　　Changes in the groundwater table (GWT) may produce undesirable effects—particularly from its lowering. Since water has a buoyant effect on soil as for other materials, lower

30、ing the GWT removes this effect and effectively increases the soil weight by that amount. This can produce settlements, for all the underlying soil "sees" is a stress increase from this weight increase. Very l

31、arge settlements can be produced if the underlying soil has a large void ratio. Pumping water from wells in Mexico C</p><p><b>　　地基分析與設(shè)計(jì)</b></p><p>　　JOSEPH E.BOWLES</p><

32、;p><b>　　地基土體</b></p><p>　　人們一般關(guān)心基礎(chǔ)是坐落在“土體”或是“巖體”之上。對(duì)于某些橋梁或海上的結(jié)構(gòu)，其基礎(chǔ)可能在水面之下，但更為常見的還是將基礎(chǔ)放在地表以下較淺的土體或巖石之上。</p><p>　　土體作為形狀不規(guī)則、顆粒大小不等的土顆粒的集合，包括土顆粒（或固體）和土顆粒之間的空隙（部分空隙體積被水填充，其余孔隙體積被氣體占據(jù)

33、）。當(dāng)溫度低于冰點(diǎn)時(shí)，空隙中的水將凝結(jié)為冰，致使土顆粒分離（也就是體積膨脹），反之，當(dāng)冰融化為水時(shí)，土顆粒又相互靠緊（也就是體積縮?。Ｈ绻Ｄ瓴蝗诨?，這種冰-土混合物就被稱為“多年凍土”。顯而易見，孔隙水是一個(gè)隨機(jī)變化的東西，其狀態(tài)可以為水蒸氣、液態(tài)水或固態(tài)冰?？紫端康亩嗌偻鶗?huì)取決于氣候條件、近期的降水量或土體的位置（在地下水位之上還是以下），如圖1-1所示。</p><p>　　土體是土顆粒的集合，這些

34、土顆粒粒徑的分布范圍可能非常之廣。它屬于巖石機(jī)械風(fēng)化和化學(xué)風(fēng)化的產(chǎn)物。根據(jù)粒徑的大小可對(duì)顆粒進(jìn)行命名，如礫石、砂、粉土、黏土等，這些都將在后面進(jìn)行詳細(xì)論述。</p><p>　　土可以分為“殘積土”或“運(yùn)積土”。 殘積土由主巖在原地風(fēng)化而成的。在土層和巖層的結(jié)合處常含有不同尺寸的、大小不一的巖石碎塊。巖石在一個(gè)地方被風(fēng)化，風(fēng)化產(chǎn)生物再被風(fēng)、水、冰或搬運(yùn)至現(xiàn)在的位置所形成的土稱為運(yùn)積土?！皻埣餐痢被颉斑\(yùn)積土”這兩個(gè)

35、概念須結(jié)合上下文進(jìn)行理解，因?yàn)楫?dāng)前的很多殘積土可能形成于（或正在形成于）很早歷史時(shí)期的巖石，而這些巖石又由運(yùn)積土堆結(jié)而成。后來地殼的抬升使得這些巖石暴露在外面，成為風(fēng)化作用的新對(duì)象。這些暴露的石灰?guī)r、砂巖或頁巖是很早時(shí)期地質(zhì)運(yùn)積土沉積物的典型堆積結(jié)產(chǎn)生物。這些巖石被抬升后，在近期的風(fēng)化和分解作用下再變成土，然后繼續(xù)新一輪的地質(zhì)循環(huán)。</p><p>　　比較以上的兩種土，發(fā)現(xiàn)人們更喜歡采用殘疾土形成的土層來作為支

36、撐基礎(chǔ)的地基，因?yàn)樗麄円话憔哂休^好的工程性質(zhì)。被搬運(yùn)過的土，特別是被風(fēng)或水搬運(yùn)過的土，往往性能較差。這些運(yùn)積土的典型特征為顆粒直徑較小，孔隙體積大，有可能存在大量的孔隙水，通常具有高壓縮性。然而，以上的結(jié)論并不是絕對(duì)的，一般也可能存在性能比較差的殘積土以及性能好的運(yùn)積土，總之，必須根據(jù)每個(gè)場(chǎng)地的特點(diǎn)來進(jìn)行評(píng)價(jià)。</p><p>　　影響土體工程性質(zhì)的主要因素</p><p>　　影響土體工

37、程性質(zhì)的大多數(shù)因素包括長(zhǎng)期的地質(zhì)作用，其中最重要的因素是：自然膠結(jié)與時(shí)效</p><p>　　所有土體自然的膠結(jié)過程都與土顆粒之間的接觸面有關(guān)，而時(shí)效過程似乎對(duì)膠結(jié)效果有著不同的影響。這種作用在很早以前就已經(jīng)被人們從黏性土中發(fā)現(xiàn)了。而現(xiàn)在認(rèn)為它在無黏性沉積土中也同樣起著相當(dāng)重要的作用。盡管沙土中的膠結(jié)于時(shí)效作用不如在黏性土中那么顯著，但是還會(huì)對(duì)基礎(chǔ)的設(shè)計(jì)產(chǎn)生重要影響。在準(zhǔn)確的定量確定這種作用時(shí)必須特別注意，因?yàn)樵?/p>

38、樣的變化以及室內(nèi)試樣與現(xiàn)場(chǎng)場(chǎng)地相比較缺少某些東西等因素都會(huì)對(duì)數(shù)據(jù)的測(cè)量有一定的影響，所以定量分析要比僅僅進(jìn)行估算困難的多?，F(xiàn)場(chǎng)觀測(cè)已經(jīng)充分證實(shí)膠結(jié)與時(shí)效作用的存在。特別是沉積黃土，垂直岸坡的易于開挖體現(xiàn)了膠結(jié)的有利作用。超固結(jié)如果土體現(xiàn)有上面土層覆蓋的壓力就是它曾經(jīng)經(jīng)受過的最大壓力，則稱這種土為“正常固結(jié)”的。在經(jīng)驗(yàn)中發(fā)現(xiàn)，作用于土體單元的先前應(yīng)力會(huì)留下一個(gè)記號(hào)或稱為歷史應(yīng)力，它會(huì)一直保留在土體結(jié)構(gòu)中，直到有超過先前最大應(yīng)力的新的應(yīng)力力

39、狀態(tài)出現(xiàn)。如果土體在應(yīng)力歷史上曾經(jīng)承受過比現(xiàn)有上面土層覆蓋壓力更大的壓力時(shí)，則稱這種土體為“超固結(jié)”。人們對(duì)超固結(jié)狀態(tài)的黏性土已經(jīng)相當(dāng)?shù)闹匾暳?。但才在最近人們才認(rèn)識(shí)到超固結(jié)對(duì)黏性土也具有一定的重要性。當(dāng)然，造成此種情況的部分原因在于確定黏</p><p>　　OCR= Pc’/ Po’ </p><p>　　對(duì)于正常固結(jié)狀態(tài)放入土

40、體有OCR=1，而對(duì)于超固結(jié)狀態(tài)的土體有OCR>1。OCR值在1~3范圍內(nèi)的為弱超固結(jié)狀態(tài)。強(qiáng)超固結(jié)狀態(tài)的土體其OCR可能在6~8之間.處于欠固結(jié)狀態(tài)的土體有OCR<1.在這種狀態(tài)下土體仍處于固結(jié)狀態(tài)。超固結(jié)可能是由于原先沉積的一定厚度的上面覆蓋土層被部分侵蝕掉所引起的，也可以由干-濕的循環(huán)產(chǎn)生的收縮應(yīng)力形成的先期固結(jié)作用。上述作用易于在干旱和半干旱的地區(qū)發(fā)生，但是在較為溫和的氣候地區(qū)也可能發(fā)生。若超固結(jié)是由收縮引起的，那么

41、一般僅表層1~3層的土體處于超固結(jié)狀態(tài)，而其下面的土體則處于正常固結(jié)狀態(tài)。OCR值從接近地面較高值逐漸減小至與正常土層交界面處的1.黏土的性質(zhì)“黏土”一詞通常用于描述那些含有足夠黏土礦物的黏性沉積土。這種土在干燥時(shí)會(huì)收縮并形成裂縫，因此會(huì)導(dǎo)致發(fā)生塊體滑移。當(dāng)沉積土?xí)蚋稍锒a(chǎn)生收縮裂縫，就稱這種土為“裂縫黏土”。這種土的現(xiàn)場(chǎng)取樣較為麻煩，因?yàn)樗赡芊浅?jiān)硬，而且列裂隙的存在會(huì)使的試樣難于制備。于原位測(cè)試（尺寸效應(yīng)可使得由裂隙造成的不連續(xù)

42、性受到側(cè)向限制或?yàn)榧雍砂逅茉剑┫啾容^，在室內(nèi)強(qiáng)度試驗(yàn)中，裂隙面可成為潛在的破壞面，從而得到不真實(shí)的過低強(qiáng)度預(yù)</p><p>　　相應(yīng)的，稱沒有裂隙的土為“原狀黏土”。原狀黏土一般為正常固結(jié)的或至少?zèng)]有因?yàn)槭湛s應(yīng)力而產(chǎn)生超固結(jié)。盡管這種黏土也會(huì)因上覆土層丟份兒開挖而回彈，但隨后的自由水對(duì)其的潛在危害并不像對(duì)裂隙黏土那樣大，因?yàn)樗畬?duì)原狀黏土的作用幾乎僅限于土體表面而沒有深入到其內(nèi)部。</p><

43、;p><b>　　沉積土層的構(gòu)造</b></p><p>　　運(yùn)積土層（尤其是經(jīng)過水力搬運(yùn)的）一般由細(xì)小的土顆粒組成，且最初的結(jié)構(gòu)較為松散，具有較大的孔隙比。土的成分相當(dāng)均勻但是也可能存在顆粒很細(xì)的土層于薄砂夾層的戶層，這些砂是在高水位期被搬運(yùn)并沉積下來的，由于水的流速較大，故可能搬運(yùn)較大尺寸的顆粒。這些沉積物會(huì)在之后的地質(zhì)時(shí)期里隨著上覆土層壓力的增大以及膠結(jié)于時(shí)效的過程而逐漸趨于穩(wěn)定

44、寧排列緊密.</p><p>　　進(jìn)過冰川搬運(yùn)，則形成的沉積土的成分就比較復(fù)雜一些。沉積土中可能含有大的沙?；蝠ね镣哥R體。冰積土中含有相當(dāng)數(shù)量的礫石甚至懸浮的漂石也不足為奇。冰積土在地質(zhì)學(xué)科教科書中有專用名稱，如冰河沙堆等，而對(duì)于基礎(chǔ)工程來說，考慮的重點(diǎn)應(yīng)在于沉積土的均勻性及工程特性。密實(shí)均勻的沉積土一般不處理。成分無規(guī)律的沉積土可以滿足使用要求，但土性參數(shù)卻很難獲得。性質(zhì)變化大的漂石或透鏡體可能會(huì)對(duì)施工造成困難

45、。</p><p>　　對(duì)于殘積土，考慮的重點(diǎn)在于 應(yīng)在迄今為止所發(fā)生過的降水量。大量的地表水可將較淺區(qū)域的礦物淋溶至較深區(qū)域。在一定深度存在的由細(xì)顆粒組成的土層可對(duì)整個(gè)場(chǎng)地地基的承載力的沉降特性產(chǎn)生影響。</p><p><b>　　土中水</b></p><p>　　土中水的存在可能是由早期的地質(zhì)現(xiàn)象多造成的，但也有可能是由近期的降水或水管

46、破裂所引起的、含水率的增大可降低黏性土的抗剪強(qiáng)度。在任何種類的土體中，孔隙水壓力的增大都能造成土體抗剪強(qiáng)度的降低。當(dāng)孔隙水壓力增大到一定程度時(shí)，抗剪強(qiáng)度可能降低為零————對(duì)于無粘性土來說，最終的結(jié)果就是形成粘滯流體。處于比較疏松的飽和狀態(tài)的沙，當(dāng)受到瞬時(shí)震動(dòng)時(shí)也會(huì)變?yōu)檎硿黧w。這種現(xiàn)象稱為“液化”，在易震區(qū)建造重要建筑（比如發(fā)電廠）時(shí)，防止液化就是一個(gè)相當(dāng)重要的話題。</p><p>　　當(dāng)土中水的含量恰好只能

47、使砂濕潤(rùn)時(shí)，水所產(chǎn)生的表面張力可以允許實(shí)施淺部的垂直開挖。土中水的蒸發(fā)將會(huì)引起坑壁的坍塌。然而，在土中水還未完全蒸發(fā)前，施工過程中的振搗就可能導(dǎo)致坑壁的坍塌。在粘性土中垂直開挖的基坑坑壁有可能在降水對(duì)黏土的軟化作用以及流入地表張裂縫的過量地表水所產(chǎn)生的凈水壓力的聯(lián)合作用下發(fā)生坍塌。</p><p>　　總之，水可對(duì)黏性土的抗剪強(qiáng)度產(chǎn)生顯著影響。即使不用試驗(yàn)設(shè)備，人們或許也曾經(jīng)看到過道路路堤旁的排泥孔中的黏性土是如

48、何從降雨時(shí)的流體變成干燥后堅(jiān)硬的像磚一樣的材料的。土體干燥后在孔的末端形成的地表裂縫為收縮（或張拉）裂縫。</p><p>　　地下水位的變化會(huì)產(chǎn)生不利的后果，特別是在地下水位下降時(shí)。水對(duì)土體像對(duì)其他物體一樣都會(huì)產(chǎn)生浮力，水位的降低可消除浮力，并使土體的重量得到有效增加，重量的增加量就等于浮力的消除量。這樣會(huì)導(dǎo)致產(chǎn)生沉降，因?yàn)閺乃械南路翆觼砜矗细餐翆又亓康脑黾蛹礊閼?yīng)力的增加。如果下伏層具有較大的孔隙比，則會(huì)