土木工程類專業(yè)英文文獻及翻譯

1、精選優(yōu)質文檔-傾情為你奉上PAVEMENT PROBLEMS CAUSEDBY COLLAPSIBLE SUBGRADESBy Sandra L. Houston,1 Associate Member, ASCE(Reviewed by the Highway Division)ABSTRACT: Problem subgrade materials consisting of collapsible soils are com-mon in arid environments, which have climatic conditions and depositional andweathe

2、ring processes favorable to their formation. Included herein is a discussionof predictive techniques that use commonly available laboratory equipment andtesting methods for obtaining reliable estimates of the volume change for theseproblem soils. A method for predicting relevant stresses and corresp

3、onding collapsestrains for typical pavement subgrades is presented. Relatively simple methods ofevaluating potential volume change, based on results of familiar laboratory tests,are used.INTRODUCTIONWhen a soil is given free access to water, it may decrease in volume,increase in volume, or do nothin

4、g. A soil that increases in volume is calleda swelling or expansive soil, and a soil that decreases in volume is called acollapsible soil. The amount of volume change that occurs depends on thesoil type and structure, the initial soil density, the imposed stress state, andthe degree and extent of we

5、tting. Subgrade materials comprised of soils thatchange volume upon wetting have caused distress to highways since the be-ginning of the professional practice and have cost many millions of dollarsin roadway repairs. The prediction of the volume changes that may occur inthe field is the first step i

6、n making an economic decision for dealing withthese problem subgrade materials.Each project will have different design considerations, economic con-straints, and risk factors that will have to be taken into account. However,with a reliable method for making volume change predictions, the best design

7、relative to the subgrade soils becomes a matter of economic comparison, anda much more rational design approach may be made. For example, typicaltechniques for dealing with expansive clays include: (1) In situ treatmentswith substances such as lime, cement, or fly-ash; (2) seepage barriers and/or dr

8、ainage systems; or (3) a computing of the serviceability loss and a mod-ification of the design to "accept" the anticipated expansion. In order to makethe most economical decision, the amount of volume change (especially non-uniform volume change) must be accurately estimated, and the degr

9、ee of roadroughness evaluated from these data. Similarly, alternative design techniquesare available for any roadway problem.The emphasis here will be placed on presenting economical and simplemethods for: (1) Determining whether the subgrade materials are collapsible;and (2) estimating the amount o

10、f volume change that is likely to occur in the'Asst. Prof., Ctr. for Advanced Res. in Transp., Arizona State Univ., Tempe, AZ85287.Note. Discussion open until April 1, 1989. To extend the closing date one month,a written request must be filed with the ASCE Manager of Journals. The manuscriptfor

11、this paper was submitted for review and possible publication on February 3, 1988.This paper is part of the Journal of Transportation.Engineering, Vol. 114, No. 6,November, 1988. ASCE, ISSN 0733-947X/88/0006-0673/$1.00 + $.15 per page.Paper No. 22902.673field for the collapsible soils. Then this info

12、rmation will place the engineerin a position to make a rational design decision. Collapsible soils are fre-quently encountered in an arid climate. The depositional process and for-mation of these soils, and methods for identification and evaluation of theamount of volume change that may occur, will

13、be discussed in the followingsections.COLLAPSIBLE SOILSFormation of Collapsible SoilsCollapsible soils have high void ratios and low densities and are typicallycohesionless or only slightly cohesive. In an arid climate, evaporation greatlyexceeds rainfall. Consequently, only the near-surface soils b

14、ecome wettedfrom normal rainfall. It is the combination of the depositional process andthe climate conditions that leads to the formation of the collapsible soil.Although collapsible soils exist in nondesert regions, the dry environment inwhich evaporation exceeds precipitation is very favorable for

15、 the formationof the collapsible structure.As the soil dries by evaporation, capillary tension causes the remainingwater to withdraw into the soil grain interfaces, bringing with it soluble salts,clay, and silt particles. As the soil continues to dry, these salts, clays, andsilts come out of solutio

16、n, and "tack-weld" the larger grains together. Thisleads to a soil structure that has high apparent strength at its low, naturalwater content. However, collapse of the "cemented" structure may occurupon wetting because the bonding material weakens and softens, and the soilis unst

17、able at any stress level that exceeds that at which the soil had beenpreviously wetted. Thus, if the amount of water made available to the soilis increased above that which naturally exists, collapse can occur at fairlylow levels of stress, equivalent only to overburden soil pressure. Additionalload

18、s, such as traffic loading or the presence of a bridge structure, add tothe collapse, especially of shallow collapsible soil. The triggering mechanismfor collapse, however, is the addition of water.Highway Problems Resulting from Collapsible SoilsNonuniform collapse can result from either a nonhomog

19、eneous subgradedeposit in which differing degrees of collapse potential exist and/or fromnonuniform wetting of subgrade materials. When differential collapse ofsubgrade soils occurs, the result is a rough, wavy surface, and potentiallymany miles of extensively damaged highway. There have been severa

20、l re-ported cases for which differential collapse has been cited as the cause ofroadway or highway bridge distress. A few of these in the Arizona and NewMexico region include sections of 1-10 near Benson, Arizona, and sectionsof 1-25 in the vicinity of Algadonas, New Mexico (Lovelace et al. 1982;Rus

21、sman 1987). In addition to the excessive waviness of the roadway sur-face, bridge foundations failures, such as the Steins Pass Highway bridge,1-10, in Arizona, have frequently been identified with collapse of foundationsoils.Identification of Collapsible SoilsThere have been many techniques propose

22、d for identifying a collapsiblesoil problem. These methods range from qualitative index tests conducted on674disturbed samples, to response to wetting tests conducted on relatively un-disturbed samples, to in situ meausrement techniques. In all cases, the en-gineer must first know if the soils may b

23、ecome wetted to a water contentabove their natural moisture state, and if so, what the extent of the potentialwetted zone will be. Most methods for identifying collapsible soils are onlyqualitative in nature, providing no information on the magnitude of the col-lapse strain potential. These qualitat

24、ive methods are based on various func-tions of dry density, moisture content, void ratio, specific gravity, and At-terberg limits.In situ measurement methods appear promising in some cases, in that manyresearchers feel that sample disturbance is greatly reduced, and that a morenearly quantitative me

25、asure of collapse potential is obtainable. However,in situ test methods for collapsible soils typically suffer from the deficien-cy of an unknown extent and degree of wetting during the field test. Thismakes a quantitative measurement difficult because the zone of materialbeing influenced is not wel

26、l-known, and, therefore, the actual strains, in-duced by the addition of stress and water, are not well-known. In addition,the degree of saturation achieved in the field test is variable and usuallyunknown.Based on recently conducted research, it appears that the most reliablemethod for identifying

27、a collapsible soil problem is to obtain the best qualityundisturbed sample possible and to subject this sample to a response to wet-ting test in the laboratory. The results of a simple oedometer test will indicatewhether the soil is collapsible and, at the same time, give a direct measureof the amou

28、nt of collapse strain potential that may occur in the field. Potentialproblems associated with the direct sampling method include sample distur-bance and the possibility that the degree of saturation achieved in the fieldwill be less than that achieved in the laboratory test.The quality of an undist

29、urbed sample is related most strongly to the arearatio of the tube that is used for sample collection. The area ratio is a measureof the ratio of the cross-sectional area of the sample collected to the cross-sectional area of the sample tube. A thin-walled tube sampler by definitionhas an area ratio

30、 of about 10-15%. Although undisturbed samples are bestobtained through the use of thin-walled tube samplers, it frequently occursthat these stiff, cemented collapsible soils, especially those containing gravel,cannot be sampled unless a tube with a much thicker wall is used. Samplershaving an area

31、ratio as great as 56% are commonly used for Arizona col-lapsible soils. Further, it may take considerable hammering of the tube todrive the sample. The result is, of course, some degree of sample distur-bance, broken.bonds, densification, and a correspondingly reduced collapsemeasured upon laborator

32、y testing. However, for collapsible soils, which arecompressive by definition, the insertion of the sample tube leads to localshear failure at the base of the cutting edge, and, therefore, there is lesssample disturbance than would be expected for soils that exhibit general shearfailure (i.e., satur

33、ated clays or dilative soils). Results of an ongoing studyof sample disturbance for collapsible soils indicate that block samples some-times exhibit somewhat higher collapse strains compared to thick-walled tubesamples. Block samples are usually assumed to be the very best obtainableundisturbed samp

34、les, although they are frequently difficult-to-impossible toobtain, especially at substantial depths. The overall effect of sample distur-bance is a slight underestimate of the collapse potential for the soil.675譯文：濕陷性地基引起的路面問題作者：.摘要：在干旱環(huán)境中，濕陷性土壤組成的路基材料是很常見的，干旱環(huán)境中的氣候條件、沉積以及風化作用都有利于濕陷性土的形成。在這方面包括了一種使

35、用常用的實驗室設備和測試方法獲得這些問題的土壤的體積變化的可靠估計的預測技性討論。對典型的路面路基提供了一種方法去預測相關的應力和相應的濕陷張力?；谑煜さ膶嶒炇覝y試結果，使用相對簡單的方法評估潛在體積的變化。引言：當土壤接觸到水的時候，可能體積會減小或擴大，也可能不變化。遇到水體積增大的土叫做膨脹土，而體積減小的稱為濕陷性土。土壤的類型結構、最初的土壤密度、施加應力狀態(tài)以及土壤浸濕的程度范圍決定了體積變化量的大小。自從專業(yè)實踐開始由這些遇水體積變化的土組成的路基材料已經導致了許多公路病害，并且在維修方面已經花費了數(shù)百萬美元。處理這種路基材料做出經濟決策的第一步是做出可能發(fā)生的體積變化的預測。

36、每個工程項目都有不同的設計考慮、經濟限制和風險因素，所有這些情況都必須考慮到。然而，最好的和最合理的設計可能會具有更大的經濟優(yōu)勢相比于可靠的體積變化預測。例如，典型的處理膨脹黏土的技術有：(1)在現(xiàn)場用例如石灰、粉煤灰或者水泥等處置處理；(2)設置滲流屏障或者排水設施；(3)進行適用性散失的計算來變更設計來接受預期膨脹。為了做出最經濟的決定，體積變化（特別是不均勻的體積變化）的量必須要精確計算，并且要從計算出的數(shù)據(jù)上估測出路面的平整度。同樣，不尋常的設計技術可利用到任何道路問題中。 這里將重點對以下兩點提供簡單和經濟的方法：(1)決定路基材料是否是濕陷性膨脹性或者其他;(2)估算濕陷性土在路基

37、中極有可能發(fā)生的體積變化量。這些信息將會是工程師做出合理的決定。濕陷性土在干旱地區(qū)是非常常見的。這種土的形成過程以及計算可能發(fā)生的體積變化量將在下文中介紹。美國亞利桑那州皇家經濟學會高級助理教授Tempe注：討論開放至1989年4月1日。增加截止日期一個月，必須要有ASCE期刊經理批準的書面請求。這篇文章是提交復審的初稿，可能出版的時間在1988年2月3日。本文是運輸雜志收錄的的一篇文章。114工程卷，6號，1988年11月。ASCE，ISSN 0733-947x / / / 88 0006-0673 1美元+每頁15美元。22902號文件濕陷性土濕陷性土的結構濕陷性土有高孔隙率、低密度和較弱的黏性等特點。在干旱地區(qū)，有很高的蒸發(fā)量，而降水量較低。因此，當有降水時只有地面土壤濕潤。沉積作用和氣候條件共同造成了濕陷性土的形成。盡管濕陷性土存在于非沙漠地區(qū)，但干旱環(huán)境中蒸發(fā)量遠超降水量這一特點非常有利于濕陷性土結構的形成。當土壤在蒸發(fā)過程中變干后，毛細張力使其余的水進入土