Numerical modeling of the stress state around the Enguri power tunnel

The Enguri Dam in NW Georgia is one of the highest arch dams in the world. The 15 km power tunnel was initially flooded in 1978. During the rehabilitation project from January - April 2021, an 40 m long open construction-joint was observed. The construction-joints are located on both sides in the lower third of the tunnel, but only the construction-joint on the valley side showed an opening character. The research question of the paper was whether the preferential opening of this joint can be explained by rock stresses. The approach is based on the comparison of a numerical calculation of the stress-state with the observed cracks (recorded in April 2021) in the tunnel section at km 13.7, using a static, linear elastic 2D model with homogeneous material (limestone) with a variable FE-mesh. The initial stress-state is created via a lateral shortening at the valley side of the model in combination with gravitation. The results show a symmetrical distribution of tensile and compressive stresses around the power tunnel, with the axis of symmetry tilted by about 30°. This results in tangential tensile stresses on the downslope side in the region of the construction-joint, while compressive stresses are expected in the section of the upslope construction-joint. It has been shown that the initial stress-state is an important parameter for the positioning and design of the power tunnel. Furthermore, the topography can result in tilting of the stress field, which must be considered in the interpretation of observed fractures in the tunnel.