ON D 5A 5A A 4 x 7~7~1 1 = 2 , 1 5 6~4~ 2 X 13 X 34A --A 11 X 7 X 99 X 11 X 49-4,648 Hemet = L(l +~+~a + z~ Y Y2 Y 3 +W,+. Y4 . . where y = -. y E = 4/28 .) . . . . . (7) 28 P that the hydrostatic uplift ranges from a maximum at the upstream face to zero at the B. Allowance for hydrostatic pressure, as for a pervious dam. If it be assumed downstream face, the effect is almost the same as taking the weight of the dam in water. This assumption is correct for a purely triangular dam and is a reasonable approximation in this case. Therefore it is necessary only to write ( 8 -1) instead of 8 in formula (7). which gives C = & ( l + Y + Y + -+ -+ 1/2(8 -1) 7 49.5 2 431 y3 4,648 y4. . .)
DiscussionThe Authors introduced the Paper with aid of a film. Mr C. A. Risbridger observed that the present very valuable Paper, dealing with the development of the Claerwen gathering ground, when added to the classic Paper presented in 1912 by the Mansergh brothers,l dealing with the development of the Elan gathering ground, would almost complete the thrilling story of the development of those gathering grounds. He said " almost " because the story might be rounded off in due course by information based upon the very careful records of rainfall, run-off, losses, and so on, which had been maintained on those gathering grounds during the past 50 years. Although the present Paper dealt mainly with constructional matters, it would probably not be out of place to make very brief reference to the total storage which now existed in terms of the yield expected to be obtainable from the gathering ground. The number of days was in fact slightly more than 200, on the basis of a yield of 104 million gallons per day. That figure of 200 might be compared with a figure of 180, which Mansergh had intended to provide in his original project, and with 150 days, which would be obtained by applying the old Hawksley formula of y = 500 divided by the cube root of the average annual yield of the three driest consecutive years. It was a great tribute to Mansergh that with the information provided by only one long-standing rain-gauge on the gathering ground 60 years ago, supplemented by two or three very short-term gauges, he had See footnote 1, p. 249. Downloaded by [] on [12/09/16].
so full of useful data that he felt diffident in introducing yet another topic of discussion.He proposed, however, to say a few words about some problems encountered during the construction of the Ayer ltam dam at Penang. which was now nearing completion.* 109. The area was one of high rainfall, ranging from 1 0 0 in. to more than 160 in. per annum. In last year's (1961) construction season the total rainfall was l24 in., but in spite of this they were struggling on. The local rock was granite which underwent in situ weathering under tropical conditions, giving rise to a material having not only a high angle of shearing resistance but apparently a high cohesion as well; at the same time the consolidation coefficient and permeability were rather low.110. As a result of the high rainfall, not unnaturally, the fill had been wet, and high pore pressures had occurred. The rainfall was fairly uniformly distributed during the year, except that the latter part of the year was rather wetter than the earlier part. A preliminary investigation was made of the borrow areas, and certain assumptions were made about the nature and distribution of materials in them, but unfortunately, when the contractor began his operations in them, it was found that the assumptions were not borne out in practice, and it became necessary to undertake a partial redesign of the dam. Tests which had already been done on the fill were supplemented by further tests and used in the design. 11 1. Table 5 was a summary of the results of triaxial tests on fill samples. As mentioned by the Authors of the second Paper, there had been an evolution in testing t
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