Engineering geological behaviour of recent conglomerate deposits in dam foundation. The case of Agiokampos dam in Thessaly, Cen- tral Greece.

A typical example of dam foundation on Neogenic conglomerate deposits is presented in this paper. The case of Agiokampos dam in east Thessaly in central Greece. The level of natural compactness and the nature of the cementing material are crucial elements for the strength, the bearing capacity and the permeability of these formations. These conglomerates of medium consistency, do not allow relying on traditional sampling and tests in the boreholes. Lugeon tests are meaningless and falling head tests are recommended. Back analysis on slopes is certainly a useful tool for approaching the strength parameters of the global rock mass. Thus it is understood that the engineering geological assessment before any testing and analysis is of prime importance.Due to the fine nature of the cement, permeability is generally low and no leakages are expected. However, an impermeable grout curtain must be created due to some higher values. Conglomerates are not easily groutable and a combination of a diaphragm wall is suggested. Finally, a carpet grouting is designed since the surficial zone is susceptible to internal erosion.

Geothermal characterization of the coastal aquifer near Ravenna (Italy)

The coastal aquifer near Ravenna (Italy) contains a large volume of groundwater (2,5x109 m3) whose quality has been compromised by sea-water intrusion. Today, the phreatic groundwater is mostly brackish with some lenses of freshwater floating on top of more saline water. This water, although impossible to use as drink-water or for irrigation, is still important to guarantee the health of wetland habitats and especially of the roman historical and coastal pine forests of Ravenna. With the objective of defining the flow pattern within the aquifer and the exchange between surface and ground water, we characterized the temperature distribution in the shallow subsurface by means of a dense network of piezometers. At the same time we had the opportunity to characterize the phreatic aquifer from the geothermal point of view, so that it could eventually be considered for use as a “low enthalpy” heat source. Heat pumps are able to extract heat during the winter and dissipate it during the summer. The temperature of the groundwater in the top layer of the aquifer (surficial zone) is sensitive to the changes in atmospheric temperature throughout the year whereas the temperature of the deeper groundwater follows the geothermal gradient (geothermal zone). One of the scopes of the project is to discover at what depth is located the geothermal zone, so that the aquifer has a constant temperature throughout the year. A constant temperature is needed for storage of heat at low enthalpy. The thickness of the surficial zone and the temperature at the top of the geothermal zone are essentially related to land use, distance from the sea, sediment type, and amount of interaction between surface and groundwater. A knowledge of these factors allows to better exploit the geothermal potential of the aquifer when choosing the optimal placement of the heat pumps.