A compression-shear fracture growing on an arch-gravity dam

In the case of a narrow valley, characterized by a strong rock mass, the excavation can be designed according to the so called convergent way. In this case, the mean value of the compression stresses at the dam-foundation joint increases as the dam moves towards down-stream under the action of the water pressure applied to the up-stream side. During this slip settlement, the stress level in both materials, concrete and rock, remains allowable. It is true that the seismic load is able to increase such a slip displacement, nevertheless, since the structure is designed for horizontal hydrostatic loads, the stress level remains allowable even in such a seismic condition. The above mentioned issue was discussed during the 14th Benchmark Workshop on the Numerical Analysis of Dams organized by the International Commission on Large Dams (Stockholm, 6–9 September 2017). The theme B of the above mentioned Workshop was the static and seismic analysis of the Janneh dam. It is an arc-gravity dam, 157 meters high, now under construction in Lebanon, a high-seismicity region. The ten participants compared their results, obtained independently from each other and through different numerical models. In this paper the contribution of the authors is presented and the mechanical hypotheses at the base of the three-dimensional evolution of the crack path, at the dam-foundation joint, are discussed.