1969 04 0003.Pdf

INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. STATE OF-THE-ART REPO RT ETAT ACTUEL DES CO N AISSAN CES EARTH AN D ROCKFILL DAM S BARRAGES EN TERRE ET EN EN ROCHbM EN T by Stanley D. W ilson, Consulting Engineer Seattle, W ashington, U .S.A. and R. Squier Portland, O regon, U .S.A. INTRODUCTION This paper is a report on the state-of-the- A dam, whether it be for power production, art of the design and construction of earth flood control, pumped storage, irrigation, and rockfill dams. As such, it is intended recreation, lowstream augmentation, or multi to reflect current design and construction purpose, contains many elementa. This report practise throughout the world, but the is concerned primarily with the embankment writers are well aware that neither they nor itaelf and not with such elementa a8 power- anyone else could possibly accomplish this houaes, apillways, diversion features and solely on the basis of personal experience outlet works except insofar as they interact and knowledge. A detailed review of the with and thereby affect the embankment per published literature plus extensive conver formance. Abutments and foundation treatment sations and correspondence with colleagues are considered essential elements of the em provides tha basis for most of this report, bankment although grouting per ae ia not cov but inevitably there are errors of omission, ered in detail. particularly with regard to countries other A brief chapter on the development of earth than those in North America. and rockfill dama during the past century ia For most large dams a considerable period of presented to ahow the overall development of time elapses between preliminary design and trends in deaign and construction. This is fifat filling of the reservoir; hence profes followed by chapters on current practise with sional papers giving details of design, con respect to field explorationa, laboratory struction and performance reflect design testing, embankment design, construction, in practices which antedate by at least 3 to 5 strumentation and performance. The paper con years the publication date. For this same cludes with a brief chapter on present prob reason, however, changes in design practices lems and areas of future concern. develop slowly since engineers are reluctant The greatest emphasis is placed upon the to adopt unproven changes. Perhaps in no other developments of the past decade which have type of major construction does the engineer led to current practise in the design and rely so heavily upon experience and precedent. construction of earth and rockfill dams. 137 W ILSON and SQUIER 1. HISTORICAL Obviously group (a) is of major concern to the engineering profession, but while a failure of a minor 1.1 Failures dam a decade ago may be of little significance, a "There is probably no type of structure built by failure of the same dam a decade from now could fall man which offers so great a potential hazard to life into the category of a major disaster. The volume of and property as a large dam and reservoir upstream water impounded by the Baldwin Hills Reservoir in from a heavily populated area ." This statement was Los Angeles, for example, was small yet the property made three decades ago by Morris (1939) but Its sig damage was relatively large because of the commer nificance Is even greater today than it was on the cial and residential developments just downslope afternoon of May 31, 1889 when a dam across the which were serviced by the reservoir. Conemaugh River In Pennsylvania burst after being 1.2 Ancient Dams overtopped. In the resulting flood, many thousands of people lost their lives and about $40,000,000 Earth dams comprise some of man's oldest worth of property was destroyed (Ferris 1889) in th e works, being used initially to store or divert wate r town of Johnstown and elsewhere In the Conemaugh for irrigation. Rao (1951) describes ancient earth V alley . dams of India constructed In the period 800 A.D. to 1600 A.D. Not many details are known of these Tragic as the Johnstown Flood was, it is sig early dams, but even then certain fundamentals of nificant that the cause of the failure was overtopp in g good site selection and construction were recognize d , resulting from Insufficient spillway capacity. The including the following: dam itself, as described by Mr. H. W. Brlnkerhoff to the Engineering and Building Record was about 80 "2. A learned man In the science of feet high with upstream slopes of 2:1 and downstream Pathas and Sastras (I.e.) Hydrology. slopes of 1.5:1, apparently built In layers of "pud d le 3. A ground of hard soil. of very good quality". It was apparent early that fateful morning that overtopping was imminent, but 5. Two projected portions of hills in con shouted warnings from a man on horse back went un tact with it (the river), for the site of the heeded because of frequent prior warnings that had tank (dam) . proven uneventful. Overtopping took place at 12 . A gang of men skilled in the art of 11:00 A .M ., but final failure did not develop until tank (dam) construction. about 3:00 P.M .; this is an excellent example of the resistance of an earth dam containing cohesive It is known that these early dams were often soil to transient overtopping. breeched, primarily by overtopping because of in sufficient "waterway" capacity, but also by piping Mlddlebrooks (1953) tabulates approximately or seepage instability. The number one fault to be 200 earth dams which have failed or whose perfor avoided was stated as "water oozing from the dam". mance has been unsatisfactory. Less than 20 of thes e took place In dams that were built after 1925. Only 1.3 Nineteenth Century Dams 25 were over 100 feet in height. The most common The period 1800 to 1900 A.D. marked the causes of failure were either overtopping or piping . development of the zoned earthfill dam, the hydraulic - Babb and Mermel, (1968) have prepared a list fi 11 dam and the rockfill dam. Unfortunately, the of some 600 entries of dam disasters, failures and literature of this period is full of vague and conf lic t accidents. The authors point out, however, that the ing descriptions of the soil types used for constru c tio n . term "failure" may have rrany meanings when applied Bassell (1907) in a study of earth dams attempted to to dams and that the entries can generally be class i define and clarify some of these terms, but stated: fied Into groups described as follows: "The writer had intended to present a " (a) Major disasters . The sudden table of physical properties of different and complete failure of a dam while in materials, giving their specific gravity, service. Usually with total destruction weight, coefficient of friction, angle of and loss of the dam and of life and pro repose, percentage of imbibition, percen p e rty . tage of voids, etc. , but found it impos sible to harmonize the various classifi (b) Failures and washouts of minor cations of materials given by different dams constructed without benefit of profes authorities." sional skill and having little engineering significance. This confusion was not fully resolved until the U.S. Corps of Engineers officially adopted the (c) Failures to gates, valves, piers, Unified Soil Classification based upon the Airfield and appurtenant structures, including cracks, Classification System originally developed by leaks, and erosion where the dam as such Casagrande (1948). did not fail but received publicity associated with Its name. Schuyler (1912) describes the six ways in which earthen dams were usually constructed: (d) Accidents and failures during construction and before the dam was ready for "(1) A homogeneous embankment of earth, service. Usually corrected and not inimical in which all of the material is alike through to the satisfactory functioning of the dam out; after completion. (2) An embankment in which there is a (e) Ancient dams about which little is central core of puddle consisting either of known, and predating any modern area of dam specially selected natural materials found building which might be arbitrarily selected." on the site, or of a concrete of clay, sand, and gravel, mixed together in a pug-mill and rammed or rolled into position; 138 EARTH AN D ROCKFILL DAMS (3) An embankment In which the central or tamped, and the surface of each layei core Is a wall of masonry or concrete; should be roughened by harrowing or plow ing before the next layer is applied. Droves (4) An embankment having puddle or of cattle, sheep, or goats are often used selected material placed upon Its water- with success as tamping-machlnes for earth fa c e ; embankments. They are led or driven across (5) An embankment of earth resting against the fresh made ground, and the innumerable an embankment of loose rock: blows of their sharp hoofs pack the soil very thoroughly." (6) An embankment of earth, sand, and gravel, sluiced into position by flowing 1.4 Hydraulic Fill Dams w a t e r . " Extensive hydraulic mining on the Pacific The use of puddle, either as a central imper Coast of the United States, which followed the dis vious core or as a homogeneous dam (as in the Cone- covery of gold in California in 1849, led to the de maugh River dam) deserves clarification.

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