Synopsis Sysopsis The application of an electronic computer to stability analyses of earth dams with pore-water pressure is described. The analyses are based on Bishop's (1955)1adaptation of the Swedish method. The presentation of the data to the computer and its method of working are described and there is a brief discussion on the advantages of using the computer and possible future developments. On décrit l'emploi d'une calculatrice électronique pour I'analyse de stabiliti: des barrages de terre á pression d'eau interstitielle.Les analyses sont fondées sur l'adaption Bishop de la m6thode suédoise. L'on décrit ensuite l'introduction des données dans la machineet les diverses operations, et I'on discute brievement des avantages que présente I'emploi de la calculatrice, et de ses developpements éventuels.
A large industrial complex was planned to be sited at Jubail on the Gulf Coast of Saudi Arabia. The sabkha here is essentially a near sea level, fiat area of fine grained soils, partially cemented by salt (sodium chloride) and calcium sulphate. Very little carbonate was found. The rest of the site was covered by sand dunes which, further inland, reached a height of 30 m.The presence of artesian water, detected and measured at widespread locations, probably conducted through fissures in the underlying Hadrukh bedrock, was a particularly noteworthy feature of the area, having an important influence on the design of foundations and submerged structures of which examples are given. The artesian condition has been reported by a few observers for other sabkha areas. Jubail sabkha does not appear to conform in other ways with conditions at other sabkhas; for example, no traces were found of algal filaments, nor does it fit currently accepted ideas of formation or classification.At Jubail, numerous site investigation boreholes were sunk to assist the design of installations. Measurements in many of these boreholes showed artesian heads, some up to 6 m or more above ground level in sabkha areas and up to 15 m above sabkha level in dune areas. Analyses have been developed in the paper to give rates of upward flow and limits of rise of artesian water in sabkha areas.For construction reasons, sabkha was covered with 1.5 m to 3 m of compacted dune sandfill; further evidence for the underlying artesian condition was the discovery (predicted by the authors) of the rise of groundwater above the original ground surface and into sandfill. Calculations gave average rates of rise between 0.2mm/day and 1 mm/day. These artesian conditions are believed to receive a significant contribution from the sand dunes where high water tables have been recorded. Ideas have been put forward which could form a basis for a revised theory of the origin and continued existence of sabkhas at Jubail and at other similar locations.The influence of artesian water on the design of installations at the industrial complex is discussed.
In the field of embankment dams we at the Building Research Station began by studying failures, and then concentrated for some time on measuring pore pressures and total pressures, in order to check stability using effective stress analysis. We also measured settlements to see if there was correlation between the dissipation of constructional pore pressures and the compression of layers in the fill. We became interested in the deflexion of clay cores, so that we measured horizontal strains as well as settlement.57. It was clear that existing design methods were directed towards providing an adequate factor of safety against complete collapse, but were weak in predicting deformations-deformations which on occasion could be sufficient to damage the core or the upstream membrane of a dam. We have considered the possible methods of calculating strains and deformations and have developed an analytical method using a finite element technique to estimate deflexions which will occur in an embankment during construction from the results of laboratory tests on the fill material.58. This is a relatively simple method which could easily be made more complex, but the purpose of the Paper is to show that, in its first application (to Scammonden Dam) it has given estimates of movement which are quite close to the actual movements which we have measured within the body of the embankment itself. Dr J. B. BurlandIn my view, the finite element method has three distinct advantages for use in solving soil mechanics problems. The first is that it can be used to handle very complex geometry-geometries which are far too complicated for closed analytical solutions; The second is that it can cope with variations of properties across the continuumthat is, it can deal quite simply with non-homogeneity. Finally, problems in which self-weight plays a major part in determining behaviour are also fairly straightforward.60. My next point is that it is natural for engineers to attempt to relate the behaviour of real structures to that of simple, idealised models. In my view, it is not necessary for the engineer to believe the model implicitly, and I think that he is probably a wise engineer if he does not. The important thing is that the model acts as a frame of reference against which real behaviour can be checked.61. The Paper compares the observed behaviour of Scammonden Dam with a particularly simple model, deliberately so. The model material has a constant equivalent compressibility which is derived from the results of oedometer tests on the real material. In building the model on the computer, we have accurately reproduced the geometry of the dam and followed the construction sequence as accurately and closely as we can. A point which is particularly interesting is that when the downstream shoulder was raised consideraDly more rapidly than the area near the core causing reversals in the observed horizontal movements, the effects were quite accurately reproduced in the model.62. Finally, we do not wish to leave the impression that we believ...
Summary Examples are given of three dams, two rather old, water impounding dams, the other, more recently constructed, for retaining industrial waste. All three dams suffered some degree of failure and, as a result, were investigated more fully than would otherwise have been the case. At Lluest Wen, following emergency grouting and other work, a detailed examination disclosed so many imperfections in the puddle core that a new slurry trench cut off was provided. A 20 ft diameter shaft at the draw-off works was partly investigatory, partly for remedial works. The industrial waste dam developed alarming symptoms during its construction and suffered a partial failure. Following investigations, remedial works were put in hand. Even during the progress of these, there were further untoward events but finally, the dam was stabilized. Tittesworth dam suffered a downstream slide during works to raise the impounding level. The original site investigation failed to find foundation weaknesses which were not fully disclosed until excavations were made during the course of the reconstruction. A search of the owner's records showed that the slope had slipped during the original construction.
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