Geotechnical site Investigation and Design was carried out for the investigation of the geotechnical conditions of the subsoil of the wider foundation area of the O1 & O7 (Kato Diabase) cistern and the pile wall of the O5L trench, around X. Th. 211+259 ~ 211+230, in order to determine the causes of subsidence of the road surface and widening of construction joints of the O5L pile wall on the left (in the direction of Patras) branch of the Patras Peripheral Road of the Olympia Odos.