Consideration of the length limitation of earth dams on calculations of their seismic stability

Conclusions

• 1. The dam length limitation (influence of the canyon walls) has a substantial effect on its stress-strain state and dynamic characteristics — natural frequencies and modes of vibration.

• 2. The data from model and analytical investigations indicate that when the ratio L_c/ H_d⩽6 it is necessary to take into consideration in static and dynamic calculations of earth dams their length limitations.

• 3. A decrease in the ratio L_c/H_d increases the natural frequency of the system, concentrates the spectrum of their periods, and gives rise to modes of vibrations inherent to three-dimensionally working structures (arch dams).

• 4. A change in the natural modes of vibration of a structure with consideration of its length limitation leads to a different (in comparison with calculation according to the scheme of the two-dimensional problem) distribution of seismic accelerations. The maximum seismic accelerations occur not on the dam crest but lower and are localized in the central zone, occupying a limited area in the form of an ellipse with large vertical axis.

• 5. With consideration of the dam length limitation the zone of high seismic accelerations, occupies a sixfold smaller area in the dam than in the case of calculation according to the scheme of the two-dimensional problem. In this case the lower and near-wall zones of the dam are subjected to substantially smaller seismic accelerations.

• 6. Calculations of the slope stability for dams located in narrow sites (L_c/H_d⩽6) should be made by methods which permit taking into account the variable seismic accelerations over the length and height of the dam and the possibility of sliding of part of the slope along an arbitrary (not necessarily cylindrical) surface.