Uplift pressure of water on the bottom of concrete dams on rock foundations: Fid-Bau Portal

Uplift pressure of water on the bottom of concrete dams on rock foundations

Marchuk, A. N.

Conclusions 1. The design of the lower part of draft tubes, which necessarily includes reinforcement and anchorage of the foundation slab (sometimes with wedging and with mandatory tests of the strength of the anchorage) and construction of drain wells, ought to be simplified. 2. Calculation of uplift by the equations recommended in SN 123-60 leads to excessive safety factors both with respect to the value of the acting head and to the area of application of uplift, especially in the case where the foundation is composed of igneous rocks in which seepage occurs only along fractures. The investigations confirm the recommendations of SNiP II-54-77 concerning the value α2=0.5. However, the design value of the uplift diagrams also contains an excessive safety factor (fourfold according to our investigations), which requires a further study of this problem. 3. On plugging the drain wells the uplift pressure of water on slabs increases insignificantly (by 10–20%). We can assume that drain wells do not have a large unloading effect or that the uplift pressure of water seeping from the lower pool is not determining in the presence of the formed overall picture of seepage in the foundation from the upper to the lower pool. Of great interest in this connection would be observations of the uplift pressure of water in the bottom outlets of dams which are closed by gates but are still not sealed with concrete. 4. A relation is not always traced between the location of fractures and the local value of uplift under a slab. Thus, it is obvious for unit No. 5 of the Zeya hydrostation and practically absent for unit No. 1. An investigation of this problem requires a careful superposition of accurately executed plans of drainage and location of fractures.