土木工程类专业英文文献及翻译

1、精选优质文档-倾情为你奉上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译文：湿陷性地基引起的路面问题作者：.摘要：在干旱环境中，湿陷性土壤组成的路基材料是很常见的，干旱环境中的气候条件、沉积以及风化作用都有利于湿陷性土的形成。在这方面包括了一种使

35、用常用的实验室设备和测试方法获得这些问题的土壤的体积变化的可靠估计的预测技性讨论。对典型的路面路基提供了一种方法去预测相关的应力和相应的湿陷张力。基于熟悉的实验室测试结果，使用相对简单的方法评估潜在体积的变化。引言：当土壤接触到水的时候，可能体积会减小或扩大，也可能不变化。遇到水体积增大的土叫做膨胀土，而体积减小的称为湿陷性土。土壤的类型结构、最初的土壤密度、施加应力状态以及土壤浸湿的程度范围决定了体积变化量的大小。自从专业实践开始由这些遇水体积变化的土组成的路基材料已经导致了许多公路病害，并且在维修方面已经花费了数百万美元。处理这种路基材料做出经济决策的第一步是做出可能发生的体积变化的预测。

36、每个工程项目都有不同的设计考虑、经济限制和风险因素，所有这些情况都必须考虑到。然而，最好的和最合理的设计可能会具有更大的经济优势相比于可靠的体积变化预测。例如，典型的处理膨胀黏土的技术有：(1)在现场用例如石灰、粉煤灰或者水泥等处置处理；(2)设置渗流屏障或者排水设施；(3)进行适用性散失的计算来变更设计来接受预期膨胀。为了做出最经济的决定，体积变化（特别是不均匀的体积变化）的量必须要精确计算，并且要从计算出的数据上估测出路面的平整度。同样，不寻常的设计技术可利用到任何道路问题中。 这里将重点对以下两点提供简单和经济的方法：(1)决定路基材料是否是湿陷性膨胀性或者其他;(2)估算湿陷性土在路基

37、中极有可能发生的体积变化量。这些信息将会是工程师做出合理的决定。湿陷性土在干旱地区是非常常见的。这种土的形成过程以及计算可能发生的体积变化量将在下文中介绍。美国亚利桑那州皇家经济学会高级助理教授Tempe注：讨论开放至1989年4月1日。增加截止日期一个月，必须要有ASCE期刊经理批准的书面请求。这篇文章是提交复审的初稿，可能出版的时间在1988年2月3日。本文是运输杂志收录的的一篇文章。114工程卷，6号，1988年11月。ASCE，ISSN 0733-947x / / / 88 0006-0673 1美元+每页15美元。22902号文件湿陷性土湿陷性土的结构湿陷性土有高孔隙率、低密度和较弱的黏性等特点。在干旱地区，有很高的蒸发量，而降水量较低。因此，当有降水时只有地面土壤湿润。沉积作用和气候条件共同造成了湿陷性土的形成。尽管湿陷性土存在于非沙漠地区，但干旱环境中蒸发量远超降水量这一特点非常有利于湿陷性土结构的形成。当土壤在蒸发过程中变干后，毛细张力使其余的水进入土