Volume XX, Issue 2 contains the following papers:

Arch action in concrete dams with straight axis, by Chongjiang Du
In this paper an intrinsic arch, which will create an arch action in straight concrete dams, is revealed from the results of a back-analysis on a 4m thick concrete core with straight axis in a rockfill cofferdam. The concrete core has stood for two years functioning as the cofferdam to withstand upstream water and sediment pressure after all the material supporting the core was washed away during overtopping. The arch action existing in straight concrete dams challenges the traditional two-dimensional cantilever theory (gravity method) for the design of gravity dams. Results of the three-dimensional finite element back-analysis are compared with those observed on site, and agreement of the results confirms the arch effect. The conditions for forming the arch action in straight concrete dams are discussed, on the basis of which new design and construction philosophy is proposed, considering the arch action for straight concrete dams. This may result in project cost savings and/or increased dam safety.

Hydraulic design of spillway aerators, by V V Bhosekar, V Jothiprakash & P B Deolalikar
Spillways for high head dams are subject to high velocity flows. Due to the inherent surface roughness and geometrical deformities usually associated with concrete structures, spillways are susceptible to cavitation damage. Aeration is one of the most effective methods for mitigation of cavitation. Design of aerators is a subject of continuing interest. The present study describes the present state of knowledge for spillway aerators. A comparative study is presented to assess the various methods available for the estimation of jet length, sub-pressure under the nappe, and the air velocity in the ducts. The limitations of the present methodologies for the design of aerators for overflow spillways have been conveyed with the help of a sample calculation for a 125m high dam, and the need for further research investigations for high head, high discharge, intensity spillways have been identified. Special considerations for aerators of orifice spillways have also been discussed. The need for physical and mathematical modelling and limitations encountered therein are then conveyed.

Long-term behaviour of internal erosion afflicted dams comprising broadly graded soils, by Hans F Rönnqvist
Internal erosion occurs when fine-grained particles are washed out from a filling material by seepage. Sinkholes and settlements on the dam crest, sudden increased leakage, or muddy seepage, may be manifestations of progressed internal erosion. Dams with cores of glacially-formed broadly graded soils have been found to be more likely to experience internal erosion than dams composed of other materials. This paper describes and reviews case histories of thirty existing dams constructed from broadly graded soils, with a performance history of internal erosion. Understanding i) the typical signs and observations of internal erosion, ii) the timing of internal erosion incidents, iii) the possible early-warning signs, iv) the possible warning time, and v) the location of the internal erosion incident on the dam body, may provide tools for early-warning detection of internal erosion prone dams, and improve the assessment of internal erosion in existing dams.

Dam Engineering is an academic journal, published quarterly by International Water Power & Dam Construction. It contains refereed papers on subjects related to all areas of dams and hydro power. At present there is no restriction on the length of submitted papers.

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