Jannah Dam in Lebanon—A Remarkably Broad Range of Applied Geotechnical Works

The Jannah Dam is designed as a massive arch-gravity dam with a height of 162 m above foundation. The dam is built in a steep valley with heterogeneous ground conditions: granular soils, boulders of limestone, basalt and chert, and underlain by rock. The fresh rocks—limestone and dolostone—have compressive strengths up to 60 MPa. Between 2017 and 2021, Bauer Lebanon executed various foundation works on site, including about 9.500 m2 of plastic concrete cut-off walls (CoW), at both cofferdams, extending over a length of 128 m (U/S) and 161 m (D/S), in addition to multiple rows of overlapping diaphragm walls (d-walls), as a bulkhead. This execution concept, proposed by Bauer instead of originally considered jet grouting block, supports the deep excavation to the foundation level of the dam. The arch-shaped d-walls, with a depth of 38 m at deepest excavation axis, totaling to 3.610 m2, were constructed mostly in zones of noticeable permeability, which exacerbated the challenges imposed by the locally encountered artesian conditions. The three parallel walls, each with a wall thickness of 120 cm, are connected by a capping beam. A secant pile wall was used for subsoil improvement in the area of a geological fault. Grout curtains were constructed along the embankment foundation and in the abutments, while consolidation grouting of the rock was executed under the highly stressed parts of the foundation. The drilling depth reached about 94 m. Special rails have been installed on the slopes to allow safe and accurate drilling and grouting works on slopes fulfilling strict quality and safety requirements.