Port construction works in the Sendai Nuclear Power Station

International Nuclear Information System (INIS)

Narahara, Akio; Minamata, Hisashi; Harada, Kensaku

1982-01-01

Sendai Nuclear Power Station is the second nuclear power station of Kyushu Electric Power Co., Inc., with two PWR plants of 890 MW each, and the operation of No.1 plant will be started in July, 1984, and that of No.2 plant in March, 1986. The civil engineering works for both plants were started in June, 1978, and March, 1981, respectively, and the rate of progress as of the end of September, 1982, was 97 % and 66 %, respectively. In the construction of this power station, the port facility was provided for the transport of construction materials and spent fuel, and for the intake of condenser cooling water. In order to make the construction by dry work, the double cofferdam structures with steel sheet piles were made offshore. The use of the wharf was started in March, 1980, though typhoons hit the area several times, and the dredging in the port was completed in May, 1982. The outline of the plan of this power station, the state of affairs before the start of construction, the outline of the port construction works, the topography, geological features and sea conditions, the design of the port such as breakwaters, unloading wharf and water intake, the manufacture and installation of caissons, dredging, and the temporary cofferdam works for water intake are described. (author)

Environmental effects of the Big Rapids dam remnant removal, Big Rapids, Michigan, 2000-02

Science.gov (United States)

Healy, Denis F.; Rheaume, Stephen J.; Simpson, J. Alan

2003-01-01

The U.S. Geological Survey (USGS), in cooperation with the city of Big Rapids, investigated the environmental effects of removal of a dam-foundation remnant and downstream cofferdam from the Muskegon River in Big Rapids, Mich. The USGS applied a multidiscipline approach, which determined the water quality, sediment character, and stream habitat before and after dam removal. Continuous water-quality data and discrete water-quality samples were collected, the movement of suspended and bed sediment were measured, changes in stream habitat were assessed, and streambed elevations were surveyed. Analyses of water upstream and downstream from the dam showed that the dam-foundation remnant did not affect water quality. Dissolved-oxygen concentrations downstream from the dam remnant were depressed for a short period (days) during the beginning of the dam removal, in part because of that removal effort. Sediment transport from July 2000 through March 2002 was 13,800 cubic yards more at the downstream site than the upstream site. This increase in sediment represents the remobilized sediment upstream from the dam, bank erosion when the impoundment was lowered, and contributions from small tributaries between the sites. Five habitat reaches were monitored before and after dam-remnant removal. The reaches consisted of a reference reach (A), upstream from the effects of the impoundment; the impoundment (B); and three sites below the impoundment where habitat changes were expected (C, D, and E, in downstream order). Stream-habitat assessment reaches varied in their responses to the dam-remnant removal. Reference reach A was not affected. In impoundment reach B, Great Lakes and Environmental Assessment Section (GLEAS) Procedure 51 ratings went from fair to excellent. For the three downstream reaches, reach C underwent slight habitat degradation, but ratings remained good; reach D underwent slight habitat degradation with ratings changing from excellent to good; and, in an area

Evaluating the Response of Biological Assemblages as Potential Indicators for Restoration Measures in an Intermittent Mediterranean River

Science.gov (United States)

Hughes, Samantha Jane; Santos, Jose; Ferreira, Teresa; Mendes, Ana

2010-08-01

Bioindicators are essential for detecting environmental degradation and for assessing the success of river restoration initiatives. River restoration projects require the identification of environmental and pressure gradients that affect the river system under study and the selection of suitable indicators to assess habitat quality before, during and after restoration. We assessed the response of benthic macroinvertebrates, fish, bird and macrophyte assemblages to environmental and pressure gradients from sites situated upstream and downstream of a cofferdam on the River Odelouca, an intermittent Mediterranean river in southwest Portugal. The Odelouca will be permanently dammed in 2010. Principal Component Analyses (PCA) of environmental and pressure variables revealed that most variance was explained by environmental factors that clearly separated sites upstream and downstream of the partially built cofferdam. The pressure gradient describing physical impacts to the banks and channel as a result of land use change was less distinct. Redundancy Analysis revealed significant levels of explained variance to species distribution patterns in relation to environmental and pressure variables for all 4 biological assemblages. Partial Redundancy analyses revealed high levels of redundancy for pH between groups and that the avifauna was best associated with pressures acting upon the system. Patterns in invertebrates and fish were associated with descriptors of habitat quality, although fish distribution patterns were affected by reduced connectivity. Procrustean and RELATE (Mantel test) analyses gave broadly similar results and supported these findings. We give suggestions on the suitability of key indicator groups such as benthic macroinvertebrates and endemic fish species to assess in stream habitat quality and appropriate restoration measures, such as the release of peak flow patterns that mimic intermittent Mediterranean systems to combat habitat fragmentation and

Numerical and physical modeling of water flow over the ogee weir of the new Niedów barrage

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Herrera-Granados Oscar

2016-03-01

Full Text Available In this paper, two- and three-dimensional numerical modeling is applied in order to simulate water flow behavior over the new Niedów barrage in South Poland. The draining capacity of one of the flood alleviation structures (ogee weir for exploitation and catastrophic conditions was estimated. In addition, the output of the numerical models is compared with experimental data. The experiments demonstrated that the draining capacity of the barrage alleviation scheme is sufficiently designed for catastrophic scenarios if water is flowing under steady flow conditions. Nevertheless, the new cofferdam, which is part of the temporal reconstruction works, is affecting the draining capacity of the whole low-head barrage project.

Cracking control in mass concrete for three gorges dam; Sankyo damu ni okeru masu konkurito no hibiware yokusei

Energy Technology Data Exchange (ETDEWEB)

Chu, CHuanying

1999-09-10

The provisional cofferdam work of the mainstream of Three Gorges Dam project was successfully finished on November 8, 1997. Now, the work enters its second stage, and the placing of large-scale concrete was started. The total quantity of concrete used in this project reaches 15.00 million m{sup 3}. Inhibition of dam concrete cracking is an important subject. In order to manufacture concrete with good crack-resistance, cements, fly ashes, aggregates and blending agents are strictly selected; and hydration-generating heat is reduced by means of strict temperature control, precooling of aggregates, reduction of placing temperature and concrete temperature in mixers, and the like. As a consequence of maintaining the highest temperature value in concrete blocks to be lower than a predetermined value, harmful cracks can be prevented from occurring when the temperature in the dam lowers. (NEDO)

Water and sustainable land use at the ancient tropical city of Tikal, Guatemala.

Science.gov (United States)

Scarborough, Vernon L; Dunning, Nicholas P; Tankersley, Kenneth B; Carr, Christopher; Weaver, Eric; Grazioso, Liwy; Lane, Brian; Jones, John G; Buttles, Palma; Valdez, Fred; Lentz, David L

2012-07-31

The access to water and the engineered landscapes accommodating its collection and allocation are pivotal issues for assessing sustainability. Recent mapping, sediment coring, and formal excavation at Tikal, Guatemala, have markedly expanded our understanding of ancient Maya water and land use. Among the landscape and engineering feats identified are the largest ancient dam identified in the Maya area of Central America; the posited manner by which reservoir waters were released; construction of a cofferdam for dredging the largest reservoir at Tikal; the presence of ancient springs linked to the initial colonization of Tikal; the use of sand filtration to cleanse water entering reservoirs; a switching station that facilitated seasonal filling and release; and the deepest rock-cut canal segment in the Maya Lowlands. These engineering achievements were integrated into a system that sustained the urban complex through deep time, and they have implications for sustainable construction and use of water management systems in tropical forest settings worldwide.

Results of repeat bathymetric and velocimetric surveys at the Amelia Earhart Bridge on U.S. Highway 59 over the Missouri River at Atchison, Kansas, 2009-2013

Science.gov (United States)

Huizinga, Richard J.

2013-01-01

Bathymetric and velocimetric data were collected six times by the U.S. Geological Survey, in cooperation with the Kansas Department of Transportation, in the vicinity of Amelia Earhart Bridge on U.S. Highway 59 over the Missouri River at Atchison, Kansas. A multibeam echosounder mapping system and an acoustic Doppler current meter were used to obtain channel-bed elevations and depth-averaged velocities for a river reach approximately 2,300 feet long and extending across the active channel of the Missouri River. The bathymetric and velocimetric surveys provide a “snapshot” of the channel conditions at the time of each survey, and document changes to the channel-bed elevations and velocities during the course of construction of a new bridge for U.S. Highway 59 downstream from the Amelia Earhart Bridge. The baseline survey in June 2009 revealed substantial scour holes existed at the railroad bridge piers upstream from and at pier 10 of the Amelia Earhart Bridge, with mostly uniform flow and velocities throughout the study reach. After the construction of a trestle and cofferdam on the left (eastern) bank downstream from the Amelia Earhart Bridge, a survey on June 2, 2010, revealed scour holes with similar size and shape as the baseline for similar flow conditions, with slightly higher velocities and a more substantial contraction of flow near the bridges than the baseline. Subsequent surveys during flooding conditions in June 2010 and July 2011 revealed substantial scour near the bridges compared to the baseline survey caused by the contraction of flow; however, the larger flood in July 2011 resulted in less scour than in June 2010, partly because the removal of the cofferdam for pier 5 of the new bridge in March 2011 diminished the contraction near the bridges. Generally, the downstream part of the study reach exhibited varying amounts of scour in all of the surveys except the last when compared to the baseline. During the final survey, velocities throughout the

Working in the Dry: Cofferdams, In-River Construction, and the United States Army Corps of Engineers

Science.gov (United States)

2009-01-01

and dams to manage before 1897, but within 10 years, they would have twenty. Many of the MNC engineers had gained practical experience in small lock...America’s water- ways untapped or under-exploited raw mate- rials requiring development, control, and management for human benefit.6 During the colonial...Section , ^ N 6 to sink into position ^ 5ection 5 Gr<eo.test dapth of waiter in which skeleton wa.s a.ctua.1 ly constru_cted wSig_Lfl fee

Ultrasonic-testing method

International Nuclear Information System (INIS)

Thome, Paul.

1973-01-01

Description is given of a device adapted to the detection, by means of ultrasonic waves, of all the flaws and defects included in workpieces when only one face of the latter is accessible. A beam is directed towards the rear-face of the workpiece (e.g. a plate) on which it is reflected. The image thus reflected is fed into a receiver. The latter is under the control of the displacement of that image; simultaneously a transducer checks the condition of the mirror at the places where the beam is reflected. Whenever a flow or defect comes between, a silent zone is formed. By recording the silent zones with respect to the positions of several emitters, it is possible to locates a flaw and to define the outline thereof. The apparatus comprises several ''emitter-receiver'' groups intersecting over the emitter used in order to check the good conditions of the mirror. The invention can be used for searching and identifying flaws and defects in buildings which have to be of top quality (e.g., cofferdams, nuclear devices, shipbuilding yards, aeronautics) [fr

A thermodynamic and heat transfer model for LNG ageing during ship transportation. Towards an efficient boil-off gas management

Science.gov (United States)

Krikkis, Rizos N.

2018-06-01

A non-equilibrium thermodynamic and heat transfer model for LNG ageing during ship transportation has been developed based on experimental data. The measurements reveal that the liquid temperature remains nearly constant, whereas significant variations are observed for the gas temperature. The measurement of the liquid temperature along the tank height suggests that a small scale rollover phenomenon may have taken place in one cargo tank. A time dependent heat transfer mechanism has been considered by taking into account the temperature variations of the atmospheric air, the seawater and the cofferdam environment which affect the cargo tanks. An important finding is that the evaporation rate (boil-of rate) is forced to follow the fuel flow consumption profile imposed by the vessel's propulsion system in order to match the tank pressure and volume constraints. The theoretical model is favorably compared to a comprehensive set on per hour basis of on board measurements of cargo temperatures and pressures, recorded during laden voyages, providing a better understanding of the underlying processes involved. The dominant role of the fuel consumption on the evaporation rate may be utilized in order to devise an efficient cargo management strategy during the laden voyage.

Radiation protection in exploitation of uranium ores

International Nuclear Information System (INIS)

Pavlov, I.V.; Shalaev, I.L.

1976-01-01

The results are analyzed of the study of the radiation conditions in uranium mines, design and testing of protection means, improvement of methods and equipment for the dosimetric control in different countries since 1968 to 1975. There are outlined radiation hazards and their role in the formation of the radiation situation in mines, dispersive composition of aerosols of short-living daughter products of Rn(DPR) in the mine atmosphere. Among means of the radiation protection the following are dealt with: ventilation including the calculation of air requirements, design of ventilation systems, ventilation practices in working mines; lowering of the release of radon into the mine atmosphere by isolating non-exploited pits, application of gas-proof covers to cofferdams in faces of jointing zones, intensification of mining works in dangerous zones. Methods of air cleaning to remove Rn are suggested in brief. Apparatus are described for the individual control of the level of latent energy in the zone of miners' respiration: track dosimeters, thermoluminescent crystalls (TLC), photographic films, semiconductor systems and biophysical methods of the control for uranium mines. The efficient use of existing protection means provides the normal radiation situation in mines without significant additional investments

Nitrogen and phosphorus budget of a polyculture system of sea cucumber ( Apostichopus japonicus), jellyfish ( Rhopilema esculenta) and shrimp ( Fenneropenaeus chinensis)

Science.gov (United States)

Li, Junwei; Dong, Shuanglin; Gao, Qinfeng; Zhu, Changbo

2014-06-01

The nitrogen (N) and phosphorus (P) budget and the ecological efficiency of a polyculture system of sea cucumber ( Apostichopus japonicus), jellyfish ( Rhopilema esculenta) and shrimp ( Fenneropenaeus chinensis) were studied in a cofferdam, 120.2 ha in size. The nutrients were supplied by spring tide inflow. In total, 139600 kg N yr-1 and 9730 kg P yr-1 input to the system; while 118900 kg N yr-1 and 2840 kg P yr-1 outflowed from the system concurrently, thus the outflow was 85.7% (N) and 29.2% (P) of inflow. The production of N and P was 889.5 kg yr-1 and 49.28 kg yr-1 (sea cucumber) and 204 kg yr-1 and 18.03 kg yr-1 (jellyfish and shrimp), respectively. The utilization rate of N and P by polycultured animals was 7.8‰ and 6.9‰, respectively, 21.9% and 38% higher than that of monocultured sea cucumber. Our results indicated that the polyculture system was an efficient culture system of animals and a remediation system of coastal environment as well; it scavenged 14.3% and 70.8% of N and P, respectively. Such an ecological efficiency may be improved further by increasing either the stocking density or the size of sea cucumber or both.

A natural ice boom

Energy Technology Data Exchange (ETDEWEB)

Hopper, H.R. [Manitoba Hydro, Winnipeg, MB (Canada)

1998-10-01

Planning for ice jams and ice movements are critical on the Nelson River in northern Manitoba in designing cofferdams. Experience on the St. Lawrence River demonstrated the possibility of exercising some control over ice action by judicious placement of log booms or ice control structures. The success of experiments with man-made controls led to field tests in which an ice sheet of sufficient magnitude and competence was introduced into the open water stream of the Nelson River. The ice sheet was subsequently jammed in a narrow channel, thereby creating a natural ice bridge or boom upstream of a proposed hydro development. Under favourable conditions, this boom would initiate the progression of the ice cover from its location upstream, cutting off the downstream reach from the ice producing potential of the upstream reach. Although ice would still be generated downstream, the length of the reach between the ice boom and the development site would be short enough that ice jamming at the development site would never occur. Although problems in blasting prevented the introduction of a competent ice sheet into the main stream of the river at the location chosen, sufficient confidence in the theory was gained to warrant further consideration. 4 refs., 1 tab., 10 figs.

Abandonment of the low level outlet structure at the McGregor South Dam

Energy Technology Data Exchange (ETDEWEB)

Mack, D.L; Murray, T.K. [Klohn-Crippen Consultants Ltd., Calgary, AB (Canada); Soutar, B.M. [Alberta Transportation, Edmonton, AB (Canada)

2008-07-01

The Carseland-Bow River Headworks (CBRH) is a major multi-purpose water delivery system, situated in southern Alberta. It supplies water to 87,000 hectares of agricultural land and several municipalities. The system was originally built starting in 1909. It consists of diversion works on the Bow River, 65 kilometres of canal, and the McGregor and Little Bow reservoirs. In the 1950s, the system was rehabilitated by the Prairie Farm Rehabilitation Administration (PFRA), and Travers Reservoir was added in 1954. In 1973, ownership and operation of the CBRH system was turned over to Alberta Environment. In 2001, Alberta Transportation implemented a major program to rehabilitate and upgrade the CBRH system. This program included increasing the capacity of the canals and structures, and upgrading the dams to meet current dam safety guidelines. The project involved raising the north and south dams, providing an auxiliary spillway to accommodate the probable maximum flood (PMF), and rehabilitating the existing reservoir inlet and low level outlet structures. This paper discussed the abandonment of the existing low level outlet structure located within the south dam. The paper discussed the existing dams and outlet structure as well as the south dam and outlet structure. The abandonment of the existing low level outlet structure was discussed in terms of general construction; demolition; upstream conduits and gatewell; and downstream conduit. Several illustrations and photographs of the dam and the demolition were presented. It was concluded that the in-place abandonment of the existing low level outlet structure at the McGregor South Dam provides significant advantages, including eliminating the need to construct and remove an extensive cofferdam within the reservoir. 6 refs., 2 tabs., 4 figs.

PERMEABILITY OF SAVCIBEY DAM (BİLECİK AXIS LOCATION AND DESIGN OF GROUT CURTAIN

Directory of Open Access Journals (Sweden)

Mustafa Can Canoğlu

2016-12-01

Full Text Available This study comprise the design of the planned grout curtain in Savcıbey Dam (Söğüt/Bilecik in order to provide impermeability along the dam axis. Within the context of field studies, engineering geology map was generated, ground investigation drilling was realized and permeability tests were performed. Within the field studies, the joint conditions of the geological units (Triassic aged Bozuyük Metamorphic schists under the dam axis and its effect on permeability was observed considering the positions of the discontinuities with regard to the dam axis location. Orientation of discontinuities generally have strikes changing between N – S and NNE – SSW. 5 boreholes on dam axis, 2 boreholes on cofferdam, 3 boreholes on diversion tunnel and 2 boreholes on spillway total 245 m ground investigation borehole were drilled. In order to determine the permeability profile of dam axis and design the grout curtain, Lugeon tests in Bozuyük Metamorphic units observed in dam axis, falling head permeability tests in alluviums observed in thalveg and slope debris observed in right abutment were performed. Lugeon tests realized in Bozuyük Metamorphic units show that the unit is generally permeable and partly low permeable. Alluvium and slope debris are highly permeable. In addition, drilling works realized in dam axis shows that the augmentation of the weathering degree cause an increase of permeability in Triassic aged Bozüyük Metamorphic schists. As a result of these studies information about the permeability of Savcıbey Dam was collected and the grout curtain hole was designed. Accordingly, it is predicted that approximately 40 m depth of grout curtain from the stripping excavation with the depth of 1.50 m would prevent the possible leakages.

Evaluation of Terrestrial Laser Scanner Accuracy in the Control of Hydrotechnical Structures

Science.gov (United States)

Muszyński, Zbigniew; Rybak, Jarosław

2017-12-01

In many cases of monitoring or load testing of hydrotechnical structures, the measurement results obtained from dial gauges may be affected by random or systematic errors resulting from the instability of the reference beam. For example, the measurement of wall displacement or pile settlement may be increased (or decreased) by displacements of the reference beam due to ground movement. The application of surveying methods such as high-precision levelling, motorized tacheometry or even terrestrial laser scanning makes it possible to provide an independent reference measurement free from systematic errors. It is very important in the case of walls and piles embedded in the rivers, where the construction of reference structure is even more difficult than usually. Construction of an independent reference system is also complicated when horizontal testing of sheet piles or diaphragm walls are considered. In this case, any underestimation of the horizontal displacement of an anchored or strutted construction leads to an understated value of the strut's load. These measurements are even more important during modernization works and repairs of the hydrotechnical structures. The purpose of this paper is to discuss the possibilities of using modern measurement methods for monitoring of horizontal displacements of an excavation wall. The methods under scrutiny (motorized tacheometry and terrestrial laser scanning) have been compared to classical techniques and described in the context of their practical use on the example hydrotechnical structure. This structure was a temporary cofferdam made from sheet pile wall. The research continuously conducted at Wroclaw University of Science and Technology made it possible to collect and summarize measurement results and practical experience. This paper identifies advantages and disadvantages of both analysed methods and presents a comparison of obtained measurement results of horizontal displacements. In conclusion, some

Geomorphic response of the Sandy River, Oregon, to removal of Marmot Dam

Science.gov (United States)

Major, Jon J.; O'Connor, Jim E.; Podolak, Charles J.; Keith, Mackenzie K.; Grant, Gordon E.; Spicer, Kurt R.; Pittman, Smokey; Bragg, Heather M.; Wallick, J. Rose; Tanner, Dwight Q.; Rhode, Abagail; Wilcock, Peter R.

2012-01-01

The October 2007 breaching of a temporary cofferdam constructed during removal of the 15-meter (m)-tall Marmot Dam on the Sandy River, Oregon, triggered a rapid sequence of fluvial responses as ~730,000 cubic meters (m3) of sand and gravel filling the former reservoir became available to a high-gradient river. Using direct measurements of sediment transport, photogrammetry, airborne light detection and ranging (lidar) surveys, and, between transport events, repeat ground surveys of the reservoir reach and channel downstream, we monitored the erosion, transport, and deposition of this sediment in the hours, days, and months following breaching of the cofferdam. Rapid erosion of reservoir sediment led to exceptional suspended-sediment and bedload-sediment transport rates near the dam site, as well as to elevated transport rates at downstream measurement sites in the weeks and months after breaching. Measurements of sediment transport 0.4 kilometers (km) downstream of the dam site during and following breaching show a spike in the transport of fine suspended sediment within minutes after breaching, followed by high rates of suspended-load and bedload transport of sand. Significant transport of gravel bedload past the measurement site did not begin until 18 to 20 hours after breaching. For at least 7 months after breaching, bedload transport rates just below the dam site during high flows remained as much as 10 times above rates measured upstream of the dam site and farther downstream. The elevated sediment load was derived from eroded reservoir sediment, which began eroding when a meters-tall knickpoint migrated about 200 m upstream in the first hour after breaching. Rapid knickpoint migration triggered vertical incision and bank collapse in unconsolidated sand and gravel, leading to rapid channel widening. Over the following days and months, the knickpoint migrated upstream more slowly, simultaneously decreasing in height and becoming less distinct. Within 7 months

Puente de hormigón pretensado sobre el río Caroni

Directory of Open Access Journals (Sweden)

Fernández, Álvaro

1964-06-01

Full Text Available This bridge consists of a. series of portal frames, of 96 m span each, making up a total length of about 500 m. The piles over the river have caused certain difficulties, and it became necessary to build a number cofferdams with sheetpiling, which became permanent formwork for the concrete foundations. The deck is a box section beam, of prestressed concrete. The most notable aspect of this structure is the constructive method. The total length of the deck was divided into 50 sections, each of them prefabricated at a nearby workshop. Each section was aligned along the deck axis: the deck already built serving as sliding ramp for each successive section. To carry out this difficult operation, neoprene was employed, which has a very low friction coefficient, on sliding over steel. To push the heavy table sections to their final position use has been made of hydraulic jacks. After these initial operations were completed, the groups of prestressed cables were correctly aligned: these cables had been provisionally stretched, during the process of putting the deck sections together. These groups of cables are attached to the inner surface of the side walls of the box sections of the deck.Este puente consta de una serie de tramos porticados de luces máximas (96 m , con longitud total de unos 500 metros. Las pilas o soportes han presentado cierta dificultad en los tramos correspondientes al río, pues han sido necesarias ataguías formadas por células de tablestacas que han servido de encofrados perdidos para hormigonar los cimientos. El conjunto del tablero está constituido por una viga-cajón, de hormigón pretensado. La particularidad más notable de esta estructura radica en los métodos constructivos llevados a cabo en su realización. La longitud total del tablero se ha subdividido en 50 trozos prefabricados en un taller próximo al puente y alineado con el eje del mismo, que ha servido de rampa para el traslado y corrimiento a su posici

El puente Woodrow Wilson Memorial

Directory of Open Access Journals (Sweden)

Editorial, Equipo

1964-06-01

Full Text Available The project for the new bridge over the Potomac river, which is 1,800 m long, and will be situated within the metropolitan zone of Washington had to be approved by the Arts Commission of the local council, which is responsible for the aesthetic quality of all new urban developments. This important bridge consists of multiple short span arches and a drawbridge span, over the navigable canal. The wide deck, carrying altogether six lanes of traffic, is supported on groups of four cylindrical posts, of reinforced concrete. Each of these posts rests on a number of fairly deeply driven prestressed concrete piles. The position of each of these was fixed by means of a timber guide, which mutually related the position of the various piles. After driving in all the piles, a concrete slab was constructed on top of them, which in turn supports the palissade of four posts. The whole operation was carried out within cofferdams built with sheetpiling. The construction of the deck was a straightforward operation, and only the drawbridge, supported on four hinges, involved certain difficulties owing to the need that these hinges be perfectly aligned at all times.El proyecto de ejecución del nuevo puente sobre el río Potomac, de 1.800 m de longitud total, en la zona metropolitana de Washington (Estados Unidos, ha necesitado la aprobación de la Comisión de Bellas Artes, encargada de velar por la armonía general del paisaje circundante. Esta importante obra, de tramos múltiples, de reducidas luces, presenta la particularidad de un tramo levadizo, que salva el canal navegable y rompe la continuidad entre los otros tramos adyacentes. Las pilas que soportan la amplia calzada —de seis bandas agrupadas en dos direcciones únicas de circulación—, son del tipo de cuatro montantes cilíndricos, de hormigón, y en forma de palizada. Cada una de las pilas descansa sobre una serie de pilotes, bastante profundos, de hormigón pretensado. La hinca de pilotes se