Geophysical Investigations of Seepage and Settlement Effects at Mornos Dam

A combined application of the Multichannel Analysis of Surface Waves (MASW), electrical resistivity tomography (ERT) and crosshole seismic tomography between crest and tunnels successfully provided crucial information about seepage and differential settlement effects in the Mornos dam, central Greece. The Mornos dam is an 816 m long and 139 m high earthen dam. The dam is exclusively used for the water supply of the capital city of Athens. The seepage through the dam foundation was found to be related with the efficiency of the grout curtain. The weak zones were mainly detected at places, where the jet-grouting has not been absolutely effective due to problematic geological setting, sliding zones, faults etc. In the interior of the core, MASW detected a weak zone along the crest, probably originated by a differential settlement. At its deepest part (at the centre of the dam) this zone had also been detected in the past by the monitoring instruments of the dam. The geophysical survey and particularly the methods of MASW and refraction tomography also revealed the existence of tensional zones at the two edges of the crest.