Design of Small, Hard-Shell Overflow Dams on Compressible Foundations

Considering the peculiarities of small hydropower station construction, the province of Hebei, China, has creatively built a series of hard-shell overflow dams on compressible foundations designed to meet the different geographic and geological characteristics of the sites. Structurally, locally collected stones are used as dam filter; then concrete or reinforced concrete is used to form a hard-shell overflow face slab. In upstream seepage control design, natural sealing methods are used to replace the artificial upstream blanket designs, in consideration of the river flow condition of high sediment density and high suspended sediment concentration. Based on the riverbed foundation characteristics and the hydrological properties, synthetic energy dissipation methods are used instead of the usual still plunge pool methods to simplify the dam structure and to reduce the construction cost. This is a theoretical study commissioned by the Hebei Bureau of Water Resources on the design of hard-shell overflow dams that have been constructed on compressible foundations. The major technical problems of constructing hard-shell dams on compressible foundations are (a) dam body stability and face slab structure stress analysis; (b) the influence of the settlement of the foundation and dam body on the face slab and the superstructure; (c) downstream energy dissipation and erosion control measures; and (d) seepage damage control measures of the dam body and foundation.