土木工程外文翻譯---壩的安全與地震

1、<p><b>　　英文文獻：</b></p><p>　　DAM SASETY AND EARTHQUAKES</p><p>　　A great tragedy was averted in the 1971 san fernando earthquake just north of Los Angeles in southern cali

2、fornia .The tower Van Norman Dam ,less than 10 kilometers from the ruptured fault,had been built 30 years before by using common method od carrying soil for fill into position by water sluices .Subsequently ,additional

3、hydraulic fill had been place in the interior portion of the dam ,leaving only a meter or so of soil on the downstream side to stop the water flowing down onto a densely</p><p>　　The incident exemplifies th

4、e importance of evaluating prospective dam sites for seismic sidk .Not only is an earth or concreat dam an expensive structure ,ut it directly affects the economy of the region ,through power generation ,flood control,an

5、d irrigation .Asthe population contiues to grow ,structural failure of a large dam will pose increasingly greater disaster for the sizsble numbers exposed to the sudden inundation of the flood plains ,Indeed ,in various

6、counstries major dams are located</p><p>　　The naturally occurring earthquakes aside ,however , we must consider also a curious connections between. Reservoirs and earthquakes .There have been at least 13 in

7、cidents countries in which swarms of earthquakes have occurred under or very near a large teservoir soon after it has been newly filed .</p><p>　　The idea that earthquakes might be triggered by impounding s

8、urface water is not new .In the 1870’s ,the U.S. corps of engineers rejected proposails for major water storage in the salton sea in suothern California on the grounds that such action might cause earthquakes .the first

9、detailed evidence of such an effcet came will the filling of Lake Mead behind hoover Dam (height 221 meters),Nevada-Arizona ,beginning in 1935 .Although there may have been local seismicity before 1935, the fact is that&

10、lt;/p><p>　　In the ensuring years ,similar case historise have been acumulated for several dozen large dams ,but only a few are well documented .Most of these dams are more than 100meters high and ,although the

11、 geological framework at the sites varies ,the most convincing examples of reservoir-induced earthquakes occur in tectonic regions with at least some history of earthquakes .Most of the thousands of large dams around th

12、e world give no sign of any onnection between reservoir filling and earthquakes;</p><p>　　Of particular interest are the following four well-studied examples of earthquakes induced by man-made reservoirs.

13、First ,Lake Kariba in Zambia began filling in 1985 behind a 128-meter high dam . Although there is some evifence for minor earthquakes in the vivinity befor the construction ,up till 1963, when the reservoir was full , m

14、ore than 2,000 local shocks, most under the reservoir ,were located with the use of nearby seismographs .The largest shock in September 1963 had a magnitude 5.8 ;sin</p><p>　　Then in Koyna,Inia an earthquake

15、(magnitude 6.5)centered close to the dam(height 103meters)caused significant damage on December 11,1967.After impounding began in </p><p>　　1962,reports of local shaking became prevalent in a prevlously almo

16、st aseismic area.Seismographs showes that focl were concentraewd at shallow depths under the lake.In 1967 a number of sizeable earthquakes occurred,leading up to the principal earthquake of magnitude 6.5 on December 11.T

17、his temblor caused significant damage to buildings nearby,killed 177 persons,and injured more than 1,500.A strong motion seismograph in the dam gallery registered a maximun acceleration of 0.63g.The series of eart</p&

18、gt;<p>　　Another series of earthquakes,which were quite conclusively reservoir induced occurred in China north of Canton.The Hsingfengkiang Dam(height 105 meters)was completed in 1959.Thereafter increasing numbers

19、 of local earthquakes were recorded,the grand total in 1972 amounting to more than 250,000.Of course,most were very small,but on March 19,1962,a strong shock of magnitude 6.1 occurred.The energu released was enough to da

20、mage the concrete dam structure,which required partial dewatering and stren</p><p>　　The data are not yet complete for the final example:the massive Nurek Dam(height 317 meters)in Tadzhikistan,USSR,the high

21、est earthfill dam in the world.Even in 1972,before its completion but after water impounding began,signs of increased local seismicity were reported.At this writing the plan is for the full load of stored water to go ont

22、o the crust in 1978;the few years following will be anxious ones as many wait to see if a large nearby earthquake shakes the facilty.</p><p>　　How does water in a large reservoir stimulate earthquakes? It is

23、 hard to belive that it is entirely the effect of the added weight on the rocks;the actual additional pressure a few kilometers below the reservoir is a small fraction of the natural tectonic stresses already presend.(Ca

24、lculations indicate that a few kilometers down the added stress to shear the rock is only a fraction of a bar.)A more plausible explanation is the trigger mechannism that induced the Denver and Rangely earthquankes d<

25、/p><p>　　In an area where there is a likelihood of seismic activity,certain preliminary steps must be taken before constrction of a dam.First,whether the cause for concern is a natural or an induced earthquake,

26、it is essential at the design stages to estimate the intensity of ground shaking the structure will sustain during its lifetime.Also preconstruction geodetic surveys of the region are useful for purposes of detecting any

27、 changs in crustal deformations associated with reservoir loading.</p><p>　　Furthermore,in order that earthquake effects can be studied,seismographs and other instrumentation should be installed at an early

28、time.</p><p>　　Hydrographs for measuring large water waves (seiches) in the reservoir are also important.In the absence of suitable recording instruments to measure the severity of earthquake motions and of

29、the dam response,the advent of a strong earthquake nearby will pose questions that cannot be answered .If,for example,structural damage has occurred,and no such measurements has been taken,it is impossible to compare beh

30、avior with design earthquake conditions and thus to estimate performance for other and p</p><p><b>　　英文文獻翻譯：</b></p><p><b>　　壩的安全與地震</b></p><p>　　1971年,在南加利福

31、尼亞洛衫磯以北的圣非南多發(fā)生的地震中,避免了一場巨大的災難。里斷裂帶不到10公里遠的下游處是凡。諾爾曼壩.這座壩是30年前用水槽把土運到壩址出填筑起來的,這是一種常用的填筑方法。隨后在壩上又補充進行了水力充填。1971年地震期間,壩內(nèi)側出現(xiàn)了一個大的滑坡,壩的下游一側,只剩下一米左右的土墻阻止水流向人口稠密的郊區(qū)流去,幸運的是地震時水庫中的水沒有達到允許的最高水位,而且極其薄弱的壩體沒有被侵蝕。因此在水能夠排放前,一直把水擋在水庫內(nèi),當

32、時有八萬人從下游撤離。</p><p>　　這次事故可作為一個例子,說明從地震危險的角度來評價未來壩址是十分重要。土壩或混凝土壩不僅是花錢多的建筑物,而且是通過發(fā)電防洪和灌溉也是直接影響著這一地區(qū)的經(jīng)濟,由于人口不斷增長,大壩失事會給突然泛濫的洪泛平原的大量人口帶來日益增大的禍患。確實,在許多國家里,都建在過去曾發(fā)生過大地震的地區(qū)。為了確保下游居民區(qū)的安全,在壩的規(guī)劃過程中,以及竣工之后都要考慮到未來出現(xiàn)的破壞地

33、震的可能性。當然,對壩址附近的地質條件,包括滑坡和斷層,都必須仔細研究。</p><p>　　然而,撤開自然發(fā)生的地震不談,我們還必須考慮水庫和地震之間的奇妙關系。至少已有13起發(fā)生在不同國家的事故可以表明:大水庫剛蓄水后,水庫下邊或靠近水庫的地方就發(fā)生了多次地震。</p><p>　　地表蓄水可以激發(fā)地震的觀點并不新鮮。19世紀70年代,美國陸軍工程師團曾拒絕在加利福尼亞南部索爾頓湖大量

34、蓄水。其根據(jù)就是認為這種舉動可能引起地震。內(nèi)華達一亞利桑那的胡佛壩(壩高221米)上游的麥德水庫在1935年開始蓄水,隨之就首次獲得了這種作用的詳細資料,雖然1935年前,那里可能就有局部地震,但事實是1936年以后,地震頻繁的多了,1930年開始使用附近的地震儀表明,1940年的大地震(震級約為5級)后地震便減少了,檢測到幾百次的地震的震源都在麥德水庫東側急劇下陷的斷層出,而震源的深度不到八公里。</p><p&g

35、t;　　在以后的幾年里,幾十座大壩都有類似的記載,但只有幾座有完整的書面材料。這些壩中,絕大多數(shù)都高于100米。雖然壩址的構造各不相同,但水庫誘發(fā)地震的最有說服力的的例子都發(fā)生在至少都有地震史的構造地區(qū),全世界幾千座大壩中的大部分并沒有跡象可以表明水庫蓄水和地震之間有任何關系,1976年的一次民眾調(diào)查表明,美國仔細審查的500座大壩中,只有%4的離壩16公里的區(qū)域以內(nèi)發(fā)生過三級以上的地震。</p><p>　　下

36、面仔細研究的人工水庫誘發(fā)地震的四個例子尤為有趣。第一個例子是贊比亞的卡里巴湖,壩高128米,1958年開始蓄水.雖然在建壩前就有證據(jù)表明附近有小地震,但直到1963年水庫蓄滿水時,附近的地震儀測到過2000多次局部地震,大部分發(fā)生在水庫下面。1963年9月發(fā)生的最大的一次地震,震級為5.8級,從那以后,地震的活動性就減小了。</p><p>　　第二個例子發(fā)生在印度的庫依納。1967年12月11日，震中靠近大壩（

37、壩高103米）的一次6.5級地震造成了嚴重破壞。1962年水庫開始蓄水以后，在這個先前幾乎無地震的地區(qū)里，局部地震的報告頻繁了。地震儀顯示出震源都在水庫下面很求淺的地方，1967年發(fā)生了一連串相當大的地震，導致了12月11日的6.5級的主震。這次地震造成附近餓建筑物嚴重破壞，177人死亡，1500多人受傷。大壩廊道里的一臺強動地震儀記錄的最大加速度為0.63g。庫依納的一連串地震記錄圖形似乎與降雨規(guī)律一致。對比地震次數(shù)和水庫水位至少可以

38、表明每年雨季之后的幾個月中，水庫水位最高時，地震的次數(shù)也增加了。在現(xiàn)在已知的其他例子中，這種相關關系并不那么明顯。</p><p>　　完全可以肯定是由水庫誘發(fā)的另外一連串地震則發(fā)生在中國廣州的北部。新豐江壩（壩高105米）于1959年完工。此后，實測到的局部地震次數(shù)越來越多。1972年總數(shù)已達25萬多次。當然，大多數(shù)地震都是很小的。但是1962年3月19日發(fā)生了6.1級的強烈地震，釋放出來的能量足夠破壞這座混凝

39、土壩的結構。需要部分地放水和加固大壩。多數(shù)震源在水庫最深處附近，位于地下不到十公里的深處。有些震源與附近的主要斷層的交叉重合。</p><p>　　最后一例的數(shù)據(jù)目前還不完全，是蘇聯(lián)塔吉克的巨大的努列克壩（壩高317米）——世界上最高的土壩。早在1972年，壩還未完工只是開始蓄水的時候，據(jù)報告，局部地震就有了增加的跡象。在撰寫本文時，計劃在1978年達到設計蓄水位的全部荷載就要作用在地殼上。以后的幾年將是令人憂慮

40、的幾年，因為很多人都在等著瞧附近發(fā)生的大地震是否會動搖這個大壩。</p><p>　　大型水庫里的水是怎樣誘發(fā)地震的呢？很難相信這完全是附加重量對巖層作用的結果。在水庫下面幾公里處實際增加的壓力只相當于原有構造應力的很小一部分。（計算表明，在幾公里下面，所增加的巖石剪力只有零點幾吧）一種似乎更合理的解釋是觸發(fā)機理誘發(fā)了本章前面所討論的丹佛和蘭奇麗地震。這種機理簡述如下：水庫加載產(chǎn)生的額外的水壓力以壓力波或脈沖傳入

41、地殼。它的傳播速度緩慢，可能要用幾個月或幾年的時間才能傳播5公里的距離，這取決于巖石的滲透性和破碎程度。但是，如果壓力脈沖最終達到達微裂隙區(qū)，就可能使水進入這些微小的裂隙縫，從而減少了對已經(jīng)存在的構造并行的抵抗力，構造變形會促使巖層斷層滑動和回彈。</p><p>　　在可能有地震活動的地區(qū)，建壩前必須采取一些預防措施。首先，不管關心的原因還是自然地震，或者是誘發(fā)地震，在設計階段必須估計建筑物在使用期間能經(jīng)受得住

42、地震強度。施工前該地區(qū)的大地測量對于檢測與水庫加載有關的地殼變形也是有用的。</p><p>　　此外，為了研究地震的影響，應該盡早安裝地震儀和其他的儀器。安裝測量水庫里大的水面波動的自記水位儀也是很重要的。沒有適當?shù)挠涗泝x器來測量地震活動和壩的反映強度，附近強烈的地震出現(xiàn)時就會產(chǎn)生一些無法回答的問題。例如，地震出現(xiàn)結構破壞而又沒有進行這樣的觀測，要想對該次地震的特點和所設計的地震情況進行比較，從而估計其他的以及